BEHAVIOR OF STANDARD HOOK ANCHORAGE MADE WITH CORROSION RESISTANT REINFORCEMENT

By

GIANNI T. CIANCONE

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA

2007

1

© 2007 Gianni T. Ciancone

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This thesis is dedicated to my loving wife Hilda and my daughter Alessandra for their support and caring throughout my academic endeavors

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ACKNOWLEDGMENTS

The author would like to thank my graduate advisor, committee chairman, Dr. H.R.

Hamilton III, for his patience, advice, and support throughout this research. Also, I would to

acknowledge the rest of the committee, Dr. Ronald A. Cook, and Dr. John M. Lybas. Their

extensive knowledge, and experience in the Department of Civil and Coastal Engineering is

greatly respected.

The author would like to thank Florida Department of Transportation (FDOT) State

Materials Office and Structural Lab for their support testing materials, and bending the bars.

Special thanks go to the University of Florida-Structural Laboratory personnel, and to all the

members of the Dr. Hamilton Group for their support constructing the specimens.

The author would also like to thank VALBRUNA stainless steel, MMFX Technologies

Corp, FLORIDA ROCK Industries, and BARSPLICE Products Inc. for their contributions to this

research.

Finally, I would like to thank my wife, daughter and close friends who have supported me

during this research.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS ...............................................................................................................4

LIST OF TABLES...........................................................................................................................7

LIST OF FIGURES .........................................................................................................................9

ABSTRACT...................................................................................................................................12

CHAPTER

1 INTRODUCTION ..................................................................................................................14

2 LITERATURE REVIEW .......................................................................................................15

Hook Behavior and Geometry ................................................................................................15 Current Hook Design Practice ................................................................................................16 High-Strength Steel Reinforcement........................................................................................21 Strut and Tie Evaluation of Anchorage ..................................................................................21

3 EXPERIMENTAL PROGRAM.............................................................................................29

Specimen Design ....................................................................................................................29 Concrete Mixture Designs ......................................................................................................32 Specimen Construction...........................................................................................................33

Formwork ........................................................................................................................33 Casting.............................................................................................................................34 Test Setup ........................................................................................................................34 Data Acquisition Setup....................................................................................................35

4 RESULTS AND DISCUSSION.............................................................................................47

Materials Properties ................................................................................................................47 Concrete...........................................................................................................................47 Steel .................................................................................................................................47

Grade 60 Steel ..........................................................................................................48 Stainless Steel...........................................................................................................48 MMFX Steel.............................................................................................................49

Specimens Test Results ..........................................................................................................49 Behavior and Failure Modes ...........................................................................................49 Mild Steel Specimens ......................................................................................................51 Stainless Steel Specimens................................................................................................55 MMFX Specimens...........................................................................................................56

5 ANALYSIS OF RESULTS ....................................................................................................72

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Anchorage Capacity ........................................................................................................72 Bond Stress......................................................................................................................73 Ductility...........................................................................................................................75 K-Factor...........................................................................................................................75

6 CONCLUSIONS ....................................................................................................................86

APPENDIX

A CONCRETE COMPRESSIVE STRENGTH AND TENSILE RESULTS............................88

B CRACKS PATTERNS, LOAD-SLIP, AND LOAD-DISPLACEMENT..............................90

LIST OF REFERENCES.............................................................................................................114

BIOGRAPHICAL SKETCH .......................................................................................................116

LIST OF TABLES

Table page 2-1 Minimum hook dimensions. .............................................................................................24

3-1 Specimen design details for series 1. ................................................................................37

3-2 Specimen design details for series 2 through 5.................................................................38

3-3 Concrete mixture proportions (quantities are per cubic yard). .........................................39

4-1 Compressive concrete strengths........................................................................................59

4-2 Tension test results for ASTM A615 reinforcement.........................................................59

4-3 Tension test result for stainless steel (316LN)..................................................................59

4-4 Tension test results for MMFX steel. ...............................................................................59

4-5 Test results for mild steel #5 and #7 specimens. ..............................................................60

4-6 Test results for stainless steel 16 mm and 20 mm specimens...........................................61

4-7 Test results for MMFX steel #5 and #7 specimens...........................................................62

5-1 Anchorage capacity ratio for mild steel. ...........................................................................77

5-2 Anchorage capacity ratio stainless steel. ..........................................................................77

5-3 Anchorage capacity ratio for MMFX steel. ......................................................................78

5-4 Bond stress normalized for mild steel...............................................................................78

5-5. Bond stress normalized for stainless steel. .......................................................................79

5-6 Bond stress normalized for MMFX steel..........................................................................79

5-7 Ductility ratio for mild steel..............................................................................................80

5-8 Ductility ratio for stainless steel. ......................................................................................80

5-9 Ductility ratio for MMFX steel.........................................................................................81

5-10 K-factor for #5 and #7 mild steel bars. .............................................................................81

5-11 K-factor for 16 mm and 20 mm stainless steel bars..........................................................82

5-12 K-factor for #5 and #7 MMFX bars..................................................................................82

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A-1 Compressive concrete strength results –age (days) ..........................................................88

A-2 Tensile test results.............................................................................................................88

LIST OF FIGURES

Figure page 2-1 Cantilever beam .................................................................................................................25

2-2 Normal bar stresses #7 – 90 deg standard hook.................................................................25

2-3 Standard hook details.........................................................................................................25

2-4 Points where slip was measured. .......................................................................................26

2-5 Recommended ϕ factor. .....................................................................................................26

2-6 Comparison of proposed and ACI 318-77 hook provisions. .............................................27

2-7 Typical uses of a standard hook anchorage and F.B.D......................................................27

2-8 Extended nodal zone for standard hook anchorage. ..........................................................28

2-9 Strut and tie model of specimen used in Marques and Jirsa research................................28

3-1 Specimen design with idealized boundary conditions. ......................................................40

3-2 Specimen design for series 1..............................................................................................40

3-3 Specimen design for series 2 through 5. ............................................................................41

3-4 Formwork schematics. .......................................................................................................41

3-5 Formwork details. ..............................................................................................................42

3-6 Ready-mixed concrete being discharged into the container for transporting. ...................42

3-7 Slump of ready-mixed concrete. ........................................................................................43

3-8 Casting and compaction of the specimen...........................................................................43

3-9 Curing of the specimens.....................................................................................................43

3-10 Load test setup ...................................................................................................................44

3-11 Coupler system...................................................................................................................45

3-12 Specimen schematic reactions. ..........................................................................................45

3-13 Slip wire position in hooked bar. .......................................................................................45

3-14 Bond slip instrumentation ..................................................................................................46

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3-15 Linear potentiometer placed at the top face of the specimen.............................................46

3-16 Data acquisition system. ....................................................................................................46

4-1 Stress-strain curve..............................................................................................................63

4-2 Stress-strain comparison. ...................................................................................................63

4-3 Cracks. ...............................................................................................................................63

4-4 Crack pattern for concrete splitting failure. .......................................................................64

4-5 Concrete crushed inside of bend radius .............................................................................64

4-6 Load-displacement for mild steel.......................................................................................65

4-7 Mild steel results in terms of hook capacity. .....................................................................65

4-8 Load-slip for specimens.....................................................................................................65

4-9 Locations where relative slip was measured......................................................................66

4-10 Load-slip for specimen. .....................................................................................................66

4-11 Typical load-slip behavior for #5 mild steel specimens with 180-degree hook (60_5_180_35_2 shown). ..................................................................................................66

4-12 Relative slip at locations D1 and D2 for unconfined specimens with debonded length..................................................................................................................................67

4-13 Typical load-slip behavior for #7 mild steel specimens with 180-degree hook (60_7_180_35_4 shown). ..................................................................................................67

4-14 Load - displacement for stainless steel. .............................................................................68

4-15 Stainless steel results in terms of hook capacity. ...............................................................68

4-16 Load-slip for specimens . ...................................................................................................68

4-17 Typical load-slip behavior for 16mm stainless steel specimens with both 90 and 180-degree hooks (SS_16_180_35_4 show).............................................................................69

4-18 Typical load-slip behavior for 20mm stainless steel specimens with both 90 and 180-degree hooks (SS_20_90_35_2 shown).............................................................................69

4-19 Load-displacement for MMFX steel..................................................................................70

4-20 MMFX results in terms of hook capacity. .........................................................................70

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4-21 Typical load-slip behavior for #5 MMFX specimens with both 90 and 180-degree hooks (MM_5_90_25_2 shown)........................................................................................70

4-22 Typical load-slip behavior for #7 MMFX specimens with both 90 and 180-degree hooks (MM_7_180_35_4 shown)......................................................................................71

5-1 Anchorage capacity ratios..................................................................................................83

5-2 Comparison of normalized bond stress at capacity............................................................84

5-3 Comparison of ductility ratios ...........................................................................................85

B-1 Crack patterns, load-slip, and stress-strain curves for mild steel hooked bars. .................90

B-2 Crack patterns, load-slip, and stress-strain curves for stainless steel hooked bars. ...........97

B-3 Crack patterns, load-slip, and stress-strain curves for MMFX hooked bars....................106

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering

BEHAVIOR OF STANDARD HOOK ANCHORAGE MADE WITH CORROSION RESISTANT REINFORCEMENT

By

Gianni T. Ciancone

December 2007

Chair: H. R. Hamilton Major: Civil Engineering

The objective of this study was to evaluate the behavior of standard hooks that are made

using high strength reinforcing bars and tested in tension. The bars evaluated were ASTM A615,

316LN Stainless Steel and MMFX microcomposite steel. The impetus is that the current

ACI/AASHTO equations for the development length of standard hooks do not address the use of

high-strength and corrosion resistant steel bars. The development length of standard hooks was

evaluated in terms of concrete strength, bar size, hook geometry, concrete covers, debonded

length, and lateral reinforcement.

Forty-eight specimens with different development length of standard hooks were

constructed in accordance with ACI 318 and AASHTO Bridge Design Specifications. Four

specimen design configurations were used as unconfined, confined with stirrups, unconfined

with debonded length for 90 degree hooked bar and unconfined with debonded length for 180

degree hooked bar.

Compressive cylinders tests were conducted in order to determine the target of average

concrete strength of 5500 psi. Also, rebar samples were tested in tension to obtain the yield, and

tensile strength.

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A test frame was constructed in the University of Florida-Structures Lab to test

specimens in tension by means of a center hole hydraulic jack. During the test, cracks pattern

were observed, and load-displacement were recorded.

Test results were compared in function of anchorage capacity, bond stress, ductility, and

K-factor. Also, test results indicated that mild steel was consistent and agreeable with ACI and

AASHTO requirements for development lengths. For #7 MMFX hooked bars, however, further

investigation need to be conducted to evaluate the proper development length.

Based on the results obtained from this research the test setup and the procedures using the strut

and tie approach appear to provide an adequate basis to evaluate the unconfined anchorage

capacities of grade 60 hooked bars.

CHAPTER 1 INTRODUCTION

Mild steel reinforcing bars have been used for decades in buildings, bridges, highways,

and other construction projects. One weakness of reinforcement is its lack of corrosion resistance

if the concrete cover is breached or penetrated by corrosive elements such as chlorides. This

issue can drastically reduce the service life of the structure requiring costly repairs or even

replacement early in the life of the structure. One potential solution that has been explored is the

use of corrosion resistant steels such as stainless steel, and MMFX. These materials typically

have higher strengths than that of mild steel. However, the use of high-strength and corrosion

resistant bars has been presented as a substitute for coated and uncoated Grade 60 bars. On the

other hand, high-strength reinforcing steel bar reduces not only the use of steel in structural

elements but also the labor costs.

The main objective of this research was to evaluate the behavior of standard hook

anchorages made with high-strength bars as Stainless Steel and MMFX microcomposite steel

relative to Grade 60 steel. Since the current ACI/AASHTO Code specifications do not address

the use of these kinds of materials, equations for the development length of standard hooks made

with high-strength and corrosion resistant steel bars need to be evaluated. The development

length of standard hook was evaluated in terms of concrete strength, bar size, hook geometry,

concrete covers, slip, anchorage capacity, ductility, bond stress, and K-factor. Also, cracks

pattern were evaluated with respect to the failure modes.

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CHAPTER 2 LITERATURE REVIEW

The structural performance and flexural behavior of high-strength steel reinforcement has

been evaluated as a substitute for Grade 60 bars. Limited research, however, has been conducted

dealing with the behavior of standard hook anchorages made with high-strength reinforcement.

Hook Behavior and Geometry

The structural concrete codes are designed so that, wherever possible, the reinforcement

will yield before the concrete crushes when the nominal strength of a reinforced concrete

element is reached. Development of the yield strength of a reinforcing bar requires that a

sufficient length of bond is available on either side of the critical section where capacity is

expected to occur. In locations where space is limited, insufficient space may be available to

allow a reinforcing bar to develop. In these cases, it is common to bend the bar to form either a

90-degree or 180-degree hook. Figure 2-1 gives an example of one possible situation where a

concentrated load is located near the end of a cantilever beam. The critical section for flexural

strength is located at the face of the support. If the required straight development length is

longer than the cantilever, then the bar would protrude from the concrete. The typical method to

deal with this situation is to turn the bar down into the section, creating a 90-degree hook.

The required length to develop the hook is shorter due to the mechanical advantage

provided by the concrete located at the inside radius of the bend. Figure 2-2 shows the normal

bar stresses in a #7 90-degree hook as reported by Marques and Jirsa (1975). The stresses in the

bar increase dramatically around the bend of the hook (from 13 ksi to 57 ksi), indicating that the

bearing of the inside of the hook against the concrete provides a significant portion of the

anchorage. These bearing stresses cause significant lateral tensile stresses, which can result in a

splitting failure when confinement reinforcement is not present.

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Because the strength of hooked anchorages is determined empirically, it was necessary to

create a standard geometry for hooks. Figure 2-3 shows the dimensions for “standard hooks”

that are the same in both ACI and AASHTO design specifications. The development length

approach was first proposed by Pinc, Watkins, and Jirsa (1977). Table 2-1 shows the minimum

hook dimensions proposed in this research.

Current Hook Design Practice

Standard hook anchorages are currently designed using either the provisions of AASHTO

Bridge Design Specifications (2004) for bridges or ACI Building Code and Commentary (2005)

for buildings. The ACI Equation is

f 'c

yf

bλd02.0

dhl

eψ= (2-1)

and AASHTO LRFD Specifications equation is:

60y

f

f c

bd38

l 'dh= (2-2)

where ldh is the hook development length in in., ψe is the coating factor, λ is the lightweight

aggregate concrete factor, db is the bar diameter in in., f’c is the specified concrete strength in psi,

and fy is the specified yield strength of the bar in psi.

These provisions were developed in the early 1970s and were finally implemented into

the code in their present form in 1979.

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Minor and Jirsa (1975) studied the factors that affect the anchorage capacity of bent

deformed bars. Specimen geometry was varied to determine the effect of bond length, bar

diameter, inside radius of bend, and angle included in the bend. Slip between the bar and the

concrete was measured at several points along the bar as load was applied. Load-slip curves were

used to compare different bar geometries. The results indicated that most of the slip occurred in

the straight and curve portion of the hook.

Marques and Jirsa (1975) investigated the anchorage capacity of hooked bars in beam-

column joints and the effect of the confinement at the joint. The variables considered were size

of anchored bars, hook geometry, embedment length, confinement, and column axial load. Full

scale beam-columns specimens were designed in order to allow the use of large diameter hooked

bars in accordance with ACI 318-71 code hook geometry standards. The test used #7 and #11

mild steel bars anchored in the columns. ACI 318-71 specifications were used for 90 or 180

degree standard hooks. Also, for 90 and 180 degree standard hooks, slip of the bar relative to the

surrounding concrete was measured at five points along the anchored bar (Figure 2-4).

As results, the slip measured on the tail extension of the hook was very small in

comparison with slip measured at the point (1H) and the point (2H). The slip measured at the

lead was greatest in most of the cases. Also, the slip at point (2H) was similar to the slip at point

(1H) when the lead straight embedment was short. In addition, the strength of the bars was

evaluated using the ACI 318-71 design provisions for hooked bar. The strength was determined

by calculating the stress developed by the hook (fh) plus an additional straight lead embedment

(ll). It was found that the straight lead embedment calculated using the basic equation for

development length was not enough to develop the yield stress in the hooked bar. On the other

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hand, the use of shorter straight embedment did not improve the stress transferring from the bar

to the concrete.

Marques and Jirsa (1975) found that the equations from ACI 318-71 underestimated the

anchorage capacity of the hooks. They found that for their test specimens the tensile stress in the

bar when the bond capacity was reached was:

'f)d3.01(700f cbh ψ−= (2-3)

where fh can not be greater than fy in psi, db is the diameter of the bar in in., f’c is the average

concrete strength in psi, and ψ is a coefficient factor which depends on the size of the bar, the

lead straight embedment, side concrete cover and cover extension of the tail.

They also determined the straight lead embedment length (ll) between the critical section

and the hook could be expressed as follows:

''

chybl l]f/)ff(A04.0[l +−= (2-4)

where l’ is 4db or 4 in., whichever is greater, Ab is the bar area in sq. in., fy the yield strength of

the bar in psi, fh the tensile stress of the bar in psi, and f’c is the average concrete strength in psi.

Pinc, Watkins, and Jirsa (1977) also studied beam-column joints to determine the effect

of lead embedment and lightweight aggregate concrete on the anchorage capacity of the hook.

The first approach consisted in examining the hook and lead embedment separately. Variables as

fl/f’c0.5 and ll/db were correlated to obtain the straight embedment strength (fl). The total strength

of the anchored bar (fu) resulted by adding the straight embedment strength (fl) and the hook

strength (fh) equation:

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'cblbu f)d/l8.0d4.01(550f ψ+−= (2-5)

Also, the variables fu/f’c

0.5 and ldh/db were plotted to obtain the following equation:

bdh d/fl50f 'cu ψ= (2-6)

As results, it was found that Equation 2-5 and Equation 2-6 were practically the same

except for the number of terms in each equation. Equation 2-6 can be rearranged into a form that

gives the development length, a parameter that is more useful in design:

'

c

ybdh f

fd02.0l

ψ= (2-7)

where ldh represents the development length for a hooked bar in in., db is the diameter of the bar

in in., fy is the yield strength of the bar, f’c is the average concrete strength in psi, and ψ is a

coefficient factor which depends on the size of the bar.

The ACI 408.1R-79 presented recommendations for standard hook provisions for

deformed bars in tension based on the study reported by Pinc, Watkins, and Jirsa (1977), and

those recommendations were discussed and explained by Jirsa, Lutz, and Gergely (1979). The

development length (ldh) for standard hook proposed for the ACI 408 committee was the result of

the product of the basic development length (lhb) and the applicable factors. The basic

development length was computed as:

'

c

bhb f

d960l

φ= (2-8)

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where lhb represents the basic development length for a hooked bar in in., db is the diameter of

the bar in in., f’c is the average concrete strength in psi, and ϕ represents the factor for anchorage

which was incorporated in the design equation.

The applicable factors included in ACI 408 committee were fy/60,000 for reinforcement

having yield strength over 60,000 psi, 0.7 for side cover, 0.8 for use of stirrups, 1.25 for use of

lightweight aggregate, and Asr/Asp for reinforcement in flexural members in excess. Figure 2-5

shows the recommended ϕ factor not only for splices but also for hooked bar, and it compares

the test/calculated values for ACI 318-77 with proposed ϕ factor of 0.8.

Figure 2-6 shows a comparison between the development length proposed and ACI 318-

77. The proposed development length was computed as a lineal function of the diameter of the

bar (Figure 2-6), the greater the diameter of the bar the greater the development length. For ACI

318-77, the development length was underestimated from #3 until #8 bars and overestimated for

bars greater than #8 in comparison with the proposed.

Basically, the ACI 318 for basic development length for hooked bar has not changed

since 1979. Also, most of the applicable factors have not changed except for the inclusion of the

epoxy-coated factor of 1.2 which was proposed by Hamad, Jirsa, and D’Abreu de Paulo (1993)

and included in the ACI 318-95.

For ACI 318-02, the basic development length equation changed in the way as the terms

were arranged. Applicable factors as epoxy-coated (β), lightweight concrete (λ) and the yield

strength of the bar (fy) were included in the equation rather than being multiplier factors.

Additionally, in this code was included a factor of 0.8 for 180 degree hook enclosed within ties

or stirrups.

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Finally, the development length and the factors included in the current ACI 318 code are

the same as ACI 318-02.

High-Strength Steel Reinforcement

High strength steel reinforcement has been introduced as a material which is more

durable than steel reinforcing bars. The use of high strength reinforcing bars is increasingly

rapidly due to the advantages that can offer over conventional reinforcing steel such as fatigue

resistance, corrosion resistant, toughness, and ductility. Also, high strength reinforcing bars can

be used in bridges and other structures where the high seismic activity is prevalent. Stainless

Steel and MMFX are one of the materials categorized as high strength steel due to they do not

have well-defined yield points and do not exhibit a yield plateau. Stainless Steel reinforcing bars

can be used in reinforced concrete structures where very high durability is required and the life

cost analysis is justified. Also, stainless rebar has been used thoroughly in North America and

Europe. Stainless rebar might be considered to be used in marine structures where chloride ion is

present. As Stainless Steel, MMFX reinforcement is a corrosion-resistant material and stronger

than conventional steel. MMFX reinforcing bars have been also used in structures across North

America including bridges, highways, parking garage, and residential and commercial projects.

Several researches using stainless steel and MMFX reinforcing bars have been conducted and

published by universities throughout the United States and sponsored for the Federal Highway

Administration (FHWA), and State Departments of Transportation (DOTs). These third parties

have conducted studies investigating bond stress behavior, corrosion evaluation, tensile tests, and

bending behavior in concrete structures.

Strut and Tie Evaluation of Anchorage

The strut-and-tie method was proposed by Schlaich, Schäfer, and Jennewein (1987). This

method was incorporated in AASHTO LRFD Specifications in 1994 and in ACI 318 - Appendix

21

A in 2002. The design basis of the strut-and-tie method is based on a truss model. The truss

model has been used in beams loaded in bending, shear and torsion. However, this model just

takes into account certain parts of the structure. The strut-and-tie method consists of struts and

ties connected by means of nodes as a real truss. The struts represent the compressive member

(concrete) and they serve either as the compression chord in the truss or as the diagonal struts.

Diagonal struts use to be oriented parallel to the expected axis of cracking. The ties represent the

tension member (stirrups and longitudinal reinforcement) where the anchorage of the ties is

crucial to avoid anchorage failure.

In order to apply correctly the strut-and-tie model, the structure is classified in B and D

regions. The B-regions (B for Bernoulli or beam) are based on the Bernoulli hypothesis which

facilitates the flexural design of reinforced concrete structures by allowing a linear strain

distribution for any loading stages (bending, shear, axial forces and torsional moments). On the

other hand, D-regions (D for discontinuity, or disturbance) are portions of a structure where the

strain distribution is nonlinear. D-regions are characterized for changes in geometry of a

structural portion (geometrical discontinuities) or concentrated forces (statical discontinuities).

For most types of D-regions as retaining walls, pier cap, and deep beam, the use of standard

hooks are common as anchorage (Figure 2-7).

Additionally, the strut-and-tie model is based on the lower bound theorem of plasticity

which allows yielding the bar (ties or stirrups) before crushing of concrete (struts and nodes).

The nodes can be classified according with the sign of the forces. At least three forces

should act on the node for equilibrium. A C-C-C node represents three compressive forces, a C-

C-T node represents two compressive forces and one tensile force, a C-T-T node represents two

tensile forces and one compressive force, and a T-T-T node represents three tensile forces. A C-

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C-T node (Figure 2-8) show the nodal zone and extended nodal zone which serve to transfer

strut-and-tie forces. The extended nodal zone is defined as the portion limited by the intersection

of the strut width (ws) and the tie width (wt). The anchorage length (lanchorage) as shown in Figure

2-8 represents the development length of the hooked bar which is anchored in the nodal and

extended nodal zone.

Figure 2-9a shows the beam-column specimen used for Marques and Jirsa (1975) and

Figure 2-9b shows the strut-and-tie behavior of the hooked bar.

Table 2-1. Minimum hook dimensions. 180 degree 90 degree

Bar No. db (in) Diameter (in.) 6db

Head (in.) 4db

Extension (in.) 4db

Tail (in.) 12db

Ratio (in.) 3db

5 0.625 3.75 2.50 2.50 7.50 1.88 7 0.875 5.25 3.50 3.50 10.50 2.625 16 mm 0.629 3.77 2.52 2.52 7.55 1.89 20 mm 0.787 4.72 3.15 3.15 9.44 2.36

24

Critical Sectionfor Flexure

Figure 2-1. Cantilever beam.

57 ksi

13 ksi

75 ksi

45 kips

Figure 2-2. Normal bar stresses #7 – 90 deg. standard hook.

Figure 2-3. Standard hook details.

25

columnface

1H2H3H

4H

4V

3V

Slip Vert.Horiz.{

Figure 2-4. Points where slip was measured.

Figure 2-5. Recommended ϕ factor.

26

Figure 2-6. Comparison of proposed and ACI 318-77 hook provisions.

A

B

STRUT

C

Figure 2-7. Typical uses of a standard hook anchorage and F.B.D. A) Pier cap, B) Deep beam, and C) Retaining wall.

27

28

Extended nodal zone

Nodal zone

C

C

T

lanchorage

wt

ws

Figure 2-8. Extended nodal zone for standard hook anchorage.

Figure 2-9. Strut and tie model of specimen used in Marques and Jirsa research.

CHAPTER 3 EXPERIMENTAL PROGRAM

Specimen Design

Figure 3-1 illustrates the typical hooked bar anchorage uses that were targeted with this

research. The specimen and load configuration were designed to simulate the development

conditions indicated in the figure. Reinforcing bars fabricated with steel that did not have a well-

defined yield point were used to investigate the behavior of hooked bar anchorage designed

using ACI/AASHTO equations. The effects of concrete strength, bar size, concrete cover,

debonded length, and lateral reinforcement were considered. The bars evaluated were ASTM

A615, 316LN Stainless Steel and MMFX microcomposite steel.

Initial testing was conducted with the design shown in Figure 3-1a and b, which are

denoted as unconfined and confined, respectively. The specimen configuration incorporated a

single bar centered in a concrete block. The focus of this initial testing was to validate the test

setup, specimen design, and loading configuration. Consequently, only ASTM A615

reinforcement was tested. Because the design complied with both design specifications, the

expectation was that the specimens would be capable of reaching at least the yield strength of the

mild steel reinforcement in both the confined and unconfined specimens. The test results,

however, indicated that the confined specimens could reach yield, but that the unconfined

specimens were well below yield when the concrete failed. Furthermore, the failure was

generally spalling of a corner section of concrete under the reaction at the outside of the hook,

which was not the targeted splitting of the specimen in the plane of the hook.

In general, the mechanics of hooked bar anchorage can be defined using a strut and tie

approach as indicated in the free body diagrams shown for each of the common hook uses. This

approach is followed by ACI 318-05 Appendix A and AASHTO LRFD (Sec. 5.6.3.5-2004). In

29

fact, as indicated in Figure 8, the available development length for the anchorage is defined by

the intersection of the reacting compression strut with straight portion of the hooked bar

(Schlaich, Schäfer, and Jennewein, 1987).

Adjustment to the specimen configuration to simulate the strut and tie behavior of the

actual hook is shown in Figure 3-1c and d. The bearing over the hook was lengthened to ensure

complete engagement of the bar over the design development length. Although the figure shows

the bearing as uniform, it is likely that the actual bearing distribution varied along the length of

the specimen. This was not expected to affect the results significantly. The embedded portion of

the bar beyond the design development length was debonded to create strut angles between 25

and 47 degrees. The remainder of the testing was conducted with these two configurations using

unconfined specimens.

Forty eight specimens were cast and tested in five series, with each series representing the

specimens cast with a single batch of concrete. The specimen details and testing configuration

for the first series are given in Figure 3-2 and Table 3-1.

Table 3-1 complied with both AASHTO and ACI design specifications for clear cover and

spacing. A factor of 0.7 was applied because the specimen side cover and cover on bar extension

beyond hook were not less than 2-1/2 in and 2 in., respectively. In addition, a factor 0.8 was

applied to the confined specimens to account for the hooks being enclosed by ties or stirrups.

Confined specimens used #3 stirrups spaced at 1.88 or 2.63 in. along the development length of

the hook.

The remaining four series are detailed in Figure 3-3 and and also complied with both

AASHTO and ACI design specifications for clear cover and spacing. The specimen naming

convention is as follows. The first term represents the type of steel where (60) indicates ASTM

30

A615, (SS) stainless steel, and (MM) microcomposite steel. The second term represents the bar

size, #5, #7, 16 mm or 20 mm. The third term represents the hook bend angle of 90 or 180

degrees. The fourth term represents the strut angle 25, 35 or 47 degrees, and the last term

represents the specimen number or the presence of # 3 stirrups in the hook region.

The metric designation of the stainless steel bars was retained because they were

manufactured in Italy under “hard” metric sizes. The 16 mm diameter and area are very near that

of a U.S. Customary #5, the 20 mm has slightly smaller diameter and respective area than that of

a #7.

In Table 3-1 and Table 3-2 fy is the yield strength used to calculate the development length

of the bars and does not necessarily represent the actual yield strength of the material. In the

ASTM A615 specimens the specified yield strength was used to provide a basis of comparison

for the subsequent high-strength steel bars. The values used for fy in determining the

development lengths of the SS and MM specimens were taken from tests conducted on bars from

the same heat as those used in the pullout tests. The yield strength for these bars was determined

using the 0.2% offset method. Detailed results of these tests are in Chapter 4.

The target concrete strength (f’c) used to calculate the development length is shown in

these tables. Actual concrete strengths for each of the series varied somewhat from these target

values. Actual concrete strengths are provided in Chapter 4.

The remainder of the variables in the tables describe the specimen geometry including the

development length of the hooked bar as measured from the back edge of the hook. The strut

angles shown in the tables are a function of the specimen geometry and were varied to determine

the effect of the strut angle on the hook capacity.

31

In series of specimens two and three, there were found that slips from specimens with 35

degree strut were greater than slips obtained for specimens with 25 degree strut. Therefore, the

strut angle used in series four and five was 35 degree. Also, different development lengths were

evaluated for the same kind of rebar. Specimens number 1 and 2 were tested in accordance with

ACI 318-05 Section 12.5 (development of standard hooks in tension), whereas specimens

number 3 and 4 were tested with larger development lengths already used in series three (Figure

3-3 and Table 3-2).

Concrete Mixture Designs

Five batches were used during the research, which correspond to each series detailed in the

previous section. The batch for the first series was prepared at Florida Department of

Transportation State Materials Office (SMO) in Gainesville, and the last four batches were

prepared by Florida Rocks Industries, a local ready-mix concrete supplier.

The concrete mixture proportions per cubic yard are shown in Table 3-3. All mixtures used

a maximum aggregate size of 3/8-in. (#89 crushed limestones) and silica sand as coarse and fine

aggregates respectively. The first batch had a water to cement ratio of 0.44, and a slump of 5 in.

The cement, fine and coarse proportion was 1:2.4:1.99.

The second batch had a water to cement ratio of 0.28, and a slump of 7.5 in. The cement,

fine and coarse proportion was 1:2.45:2.05. The last three batches had an average water to

cement ratio of 0.19, and a slump of 7.5 in. The cement, fine, and coarse proportion for those

three batches were 1:1.82:1.62. The size of the concrete batch for the first batch was nine cubic

feet (0.25 cubic meters), and for the last four batches was 81 cubic feet (2.29 cubic meter) per

batch. Air-entrained admixture and high-range water reducer were included in the mixture

proportions. The water to cement ratio was reduced in the last four batches by means of the

inclusion of high-range water reducer (superplasticizer) in order to obtain high concrete strengths

32

at early age (14 days). Air-entraining admixture was also used to improve the workability of the

concrete. The volume of concrete used in each batch included the specimens, extra examples and

concrete for quality control testing. As quality control testing was used the Standard Test

Method for Slump of Hydraulic Cement Concrete (ASTM C 143).

About twenty standard cylinders 6 x 12-in (152 x 305-mm) were cast at the same time, and

vibrated in two layers by means of a vibrating table which was used to assure the compaction.

Also, the cylinders were cured at room temperature and under the same condition as the

specimens for each concrete batch. Compressive tests were performed in accordance with the

Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens (ASTM

C39–01). All cylinders were loaded at a load rate of 35 pound square inch per second, and also

they were loaded to failure. The maximum load obtained from the universal testing machine was

used to calculate the maximum compressive strength.

Specimen Construction

Formwork

The formwork design, shown in Figure 3-4, consisted of a base, two side forms, one front

form, one back form, and two 2 x 4 pieces. The front and back forms were kept between the side

forms to allow adjustment in the specimen length. This flexibility in the specimen length allowed

the formwork to be reused for differing specimen configurations. The front form was built in two

pieces to ease bar placement. Three pieces of 2 x 4 were attached below the base to allow forms

to be moved either with the crane or the forklift. The long pieces of plywood were clamped

together with two 2 x 4 and two threaded rods. The 2 x 4 braces maintained the shape of the

forms and dimensions of the specimen. The forms were sealed with a water-based adhesive

caulk.

33

Casting

Four specimens were cast in series one and two, twelve specimens in series three and four,

and sixteen specimens in series five. All specimens were cast with the bar placed in the bottom

of the forms with the tail of the bend pointed upward (Figure 3-4b and Figure 3-5). A thin wire

was attached to the side forms and to the tail of the hook to hold the bar level, and to maintain

the side cover required. The debonded part of the bar was composed of a plastic tube which was

sealed with electric tape to prevent cement paste from entering the tube.

Since most of the formwork as placed inside of University of Florida-Structural

Laboratory, the concrete from the ready mix truck was poured directly to a galvanized steel

container (Figure 3-6). Afterward, the container was moved to be near to the formworks, and a

slump test was performed as stated in ASTM C143-00 (Figure 3-7).

To ensure that the instrumentation and bar position were not disturbed, concrete was

delivered to the forms from the container by hand (Figure 3-8A). Each specimen was cast in two

lifts, which were compacted using mechanical vibrators. As concrete was placed in the forms,

standard 6x12-in (152 x 305-mm) cylinders were cast, and also vibrated in two layers. Once

finished with the casting procedure, the top surfaces of the specimens were smoothed with a

finishing trowel (Figure 3-8B). Finally, a plastic sheet was placed over the specimens to

minimize the evaporation of the water (Figure 3-9). The specimens and cylinders were left to

cure in the same environment until they were tested.

Test Setup

A test frame was constructed with back-to-back structural channels. Each two structural

channels were connected and stiffened by 0.5-in. thick plates. A double C15x40, and C15x40

were welded together to form a 90 degree frame. Each end of the frame was then welded to

C12x30 shapes, which were attached to the strong floor and wall. Stiffeners were added to stiffen

34

the frame against the heavy concentrated loads from the specimen (see Figure 3-10A, and Figure

3-10C).

After fabrication, the test frame was connected to the strong wall and floor by means of

eight 5/8” bolts, and eight 1-1/4” bolts respectively (Figure 3-10B). The specimen was seated in

a 22 x 22-in. steel base. Tension was applied to the bar extension by means of a center hole

hydraulic jack. The threaded rod passed through the 2C15x40 beam, and the center hole

hydraulic jack (Figure 3-10B). A coupler system was used to connect the anchored bar to a

threaded rod (Figure 3-11). This load was reacted with a strut placed between the specimen and

the horizontal member of the reaction frame. The moment generated by the couple was reacted

horizontally with the vertical member of the reaction frame. The reaction on the left face of the

specimen shown in Figure 3-12 was distributed over the development length of the hook. The

remaining portion above the bar was debonded to ensure that only the portion of the hook under

the reaction contributed to the bar development.

Data Acquisition Setup

Slip between the hooked bar and the concrete was measured by a procedure developed and

used by Minor and Jirsa (1975). Figure 3-13 shows the locations along the hook where relative

slip was measured. Location 1 was at the loaded end and location 2 was at the beginning of the

bend. A 0.0625 in. diameter hole was drilled in the hooked bar. A 0.016 in. diameter wire was

attached to the anchored bar at points 1 and 2 by inserting part of the wire to the ¼-in deep holes

and securing with a small brass screw. The wire was placed inside of a thin plastic conduit of

0.042 in. diameter along the entire length in order to prevent bonding and to allow free

movement of the wire relative to the surrounding concrete (Figure 3-14).

The conduit containing the wire was extended from the bar attachment point through the

concrete and exited the specimen on the side opposite to the straight portion of the bar. The

35

36

exposed conduit and wire was then connected to a linear pot placed in a 1 x 1-in. frame (Figure

3-14B). The linear pots were used to measure the relative movement between the wire and the

conduit, which is nearly a direct measure of the relative movement of the bar and concrete at

attachment point of the wire. Bar displacement was also measured relative to the top side of the

specimen using a linear pot clamped to the bar (Figure 3-14A, Figure 3-15). The purpose of this

linear pot was to measure the strain of the debonded portion of the bar and any slip that might

occur before failure.

The data acquisition system consisted in a LabView virtual instrument which was

programmed to read and record data points from linear pots, and a load cell (Figure 3-16).

Table 3-1. Specimen design details for series 1.

Specimen fy (ksi) f'c (psi)

W (in)

H (in)

B (in)

Strut Angle

ldh tested (in)

dL (in)

60_5_90_S 60 5700 14.5 8.5 10 - 6 - 60_5_90_1 60 5700 14.5 10.5 10 - 8 - 60_7_90_S 60 5700 18.5 11.5 10 - 9 - 60_7_90_1 60 5700 18.5 13.5 10 - 11 -

37

Table 3-2. Specimen design details for series 2 through 5. Series Number Specimen fy

(ksi) f'c (psi)

W (in)

H (in)

B (in)

Strut Angle

ldh tested (in)

dL (in)

60_5_90_25_1 60 5490 14.5 12.1 10 25 7 2.6060_5_90_25_2 60 5490 14.5 12.1 10 25 7 2.6060_7_90_47_1 60 5490 18.5 22.8 10 47 10 10.30Two

60_7_90_47_2 60 5490 18.5 22.8 10 47 10 10.30SS_16_90_25_1 103 6350 14.5 17.1 10 25 12 2.60SS_16_90_25_2 103 6350 14.5 17.1 10 25 12 2.60SS_16_90_35_1 103 6350 14.5 18.4 10 35 12 3.90SS_16_90_35_2 103 6350 14.5 18.4 10 35 12 3.90MM_5_90_25_1 114 6450 14.5 19.1 10 25 14 2.60MM_5_90_25_2 114 6450 14.5 19.1 10 25 14 2.60MM_5_90_35_1 114 6450 14.5 20.4 10 35 14 3.90MM_5_90_35_2 114 6450 14.5 20.4 10 35 14 3.90MM_7_90_25_1 114 6600 18.5 27 10 25 20 4.50MM_7_90_25_2 114 6600 18.5 27 10 25 20 4.50MM_7_90_35_1 114 6600 18.5 29.1 10 35 20 6.60

Three

MM_7_90_35_2 114 6600 18.5 29.1 10 35 20 6.60SS_16_180_35_1 103 6100 14.5 17.4 10 35 11 3.90SS_16_180_35_2 103 6100 14.5 17.4 10 35 11 3.90SS_16_180_35_3 103 6100 14.5 18.4 10 35 12 3.90SS_16_180_35_4 103 6100 14.5 18.4 10 35 12 3.90MM_5_180_35_1 114 6320 14.5 18.4 10 35 12 3.90MM_5_180_35_2 114 6320 14.5 18.4 10 35 12 3.90MM_5_180_35_3 114 6320 14.5 20.4 10 35 14 3.90MM_5_180_35_4 114 6320 14.5 20.4 10 35 14 3.90MM_7_180_35_1 114 6170 18.5 26.1 10 35 17 6.60MM_7_180_35_2 114 6170 18.5 26.1 10 35 17 6.60MM_7_180_35_3 114 6170 18.5 29.1 10 35 20 6.60

Four

MM_7_180_35_4 114 6170 18.5 29.1 10 35 20 6.6060_5_180_35_1 60 6330 14.5 13.4 10 35 7 3.9060_5_180_35_2 60 6330 14.5 13.4 10 35 7 3.9060_7_180_35_1 60 6330 18.5 18.0 10 35 9 6.6060_7_180_35_2 60 6330 18.5 18.0 10 35 9 6.6060_7_180_35_3 60 6330 18.5 19.0 10 35 10 6.6060_7_180_35_4 60 6330 18.5 19.0 10 35 10 6.60SS_20_90_35_1 97.2 6150 17.0 21.1 10 35 13 5.60SS_20_90_35_2 97.2 6150 17.0 21.1 10 35 13 5.60SS_20_90_35_3 97.2 6150 17.0 22.1 10 35 14 5.60SS_20_90_35_4 97.2 6150 17.0 22.1 10 35 14 5.60SS_20_180_35_1 97.2 6150 17.0 21.1 10 35 13 5.60SS_20_180_35_2 97.2 6150 17.0 21.1 10 35 13 5.60SS_20_180_35_3 97.2 6150 17.0 22.1 10 35 14 5.60SS_20_180_35_4 97.2 6150 17.0 22.1 10 35 14 5.60MM_7_90_35_3 114 6150 18.5 29.1 10 35 20 6.60

Five

MM_7_90_35_4 114 6150 18.5 29.1 10 35 20 6.60

38

39

Table 3-3. Concrete mixture proportions (quantities are per cubic yard). Series and Mixing Dates 1 2 3 4 5

Materials 2/1/2007 3/9/2007 4/9/2007 5/9/2007 6/8/2007 W/C 0.44 0.28 0.22 0.23 0.22 Cement (lb) 513 512 702 668 680 Fly Ash (lb) 145 145 145 152 150 Water (lb) 290 184 184 189 185 Fine Aggregate (lb) 1557 1607 1527 1527 1527 Coarse Aggregate (lb) 1309 1347 1360 1360 1360 Air-entrained (oz) 6.6 4.33 1 1.33 1 Admixture (oz) 39.5 100 156 155 155 Slump (in.) 5 7.5 7.5 8 7.25

ldh

A

ldh

B

STRU

T

Debonded

ldh

C

STRU

T

Debonded

ldh

D Figure 3-1. Specimen design with idealized boundary conditions. A) Unconfined, B) Confined

with stirrups, C) 90 deg. hook, unconfined with debonded length, and D) 180 deg. hook, unconfined with debonded length.

B

H

Ctail

Ct

Cb

W

Cs

A A

Section A - A

A

A A

Section A - AW B

Cs

Ct

Cb

W No. 3 stirrup

H

Se

Cb

Ct

Ctail

Ss

B Figure 3-2. Specimen design for series 1: A) Unconfined specimen details and B) Confined

specimen details.

40

A A

Section A - A

B

W

Cb

dL

W

Hldh

a

Ctail

Cb

Ct

A Section A - A

B

W

Cb

A A

dL

W

H

a

ldhCtail

Ct

B Figure 3-3. Specimen design for series 2 through 5: A) Unconfined specimen details for 90

degree bend and B) Unconfined specimen details for 180 degree bend.

A A

2 x 4 Lumber5/8" Thread Rod 1 x 1 Lumber

Coupler

A

2.5"Plywood 3/4"

Coupler

2 x 4 Lumber

Section A - A

2 pieces of 3/4"of Plywood placedabove and below thebar

B Figure 3-4. Formwork schematics A) Plan view, and B) Section.

41

Figure 3-5. Formwork details.

Figure 3-6. Ready-mixed concrete being discharged into the container for transporting.

42

Figure 3-7. Slump of ready-mixed concrete.

A B Figure 3-8. Casting and compaction of the specimen A), and B) Finishing of specimens.

Figure 3-9. Curing of the specimens.

43

2C15x40

2C15x40

StrongWall

C12x30

C12x30

4' - 2"

4'

5' - 3"

Load CellHydraulic

Jack

StrongFloor

A

A HSS4x3x1/4

A

58

" BoltsOpen holes

17"14" 12"

78

"

14"

Section A-A

22" x 22" Base

2C6x13

ThreadRod Coupler

B

C Figure 3-10. Load test setup A) Plan view schematic, B) Section schematic, and C) Photo.

44

Figure 3-11. Coupler system.

T

2C6x13

Shims 6x10x1/4Neoprene 6x8x1/4

Neoprene6x8x1/4

HSS4x3x1/4

Shims 6x12x1/4

Neoprene6x12x1/4

Plate12x30x1

Bearing lengthvaried as neededto create targetdevelopment length

STRU

T

ldh

Figure 3-12. Specimen schematic reactions.

1 2

Figure 3-13. Slip wire position in hooked bar.

45

1

2

Bond Slip

Bond Slip

Displacement

Load Cell

A B Figure 3-14. Bond slip instrumentation A) Displacement and slip position, B) Linear

potentiometers.

Figure 3-15. Linear potentiometer placed at the top face of the specimen.

Figure 3-16. Data acquisition system.

46

CHAPTER 4 RESULTS AND DISCUSSION

Materials Properties

Concrete

About twenty standard cylinders 6 x 12-in (152 x 305-mm) per batch were tested in

accordance with the Standard Test Method for Compressive Strength of Cylindrical Concrete

Specimens (ASTM C39–01). Compressive strengths of each batch are shown in Table 4-1. The

first batch was mixed at Florida Department of Transportation State Materials Office (SMO) in

Gainesville, and the last four batches were delivered by Florida Rocks Industries, a local ready-

mix concrete supplier. Compressive strengths were tested after 7, 14, 21, and 28 days of

continuous lab cured for all the concrete mixes (APPENDIX A).

Steel

ACI indicates that for bars exceeding a specified yield strength of 60 ksi (413 MPa), the

yield strength is to be determined using the stress corresponding to a 0.35% strain. The 0.2%

offset method (ASTM A370-07), however, is more generally applicable to high strength steel

that have no well-defined yield point.

Consequently, for the stainless steel and MMFX bars that do not have well-defined yield

points and do not exhibit a yield plateau, the 0.2% offset method was used in lieu of the 0.35%

strain method. All the tension tests were conducted at Florida Department of Transportation

State Materials Office (SMO) in Gainesville. Four coupons were tested for each Grade 60,

Stainless Steel, and MMFX bars. The load rate used was 0.20 inches per minute per in. of

distance between the grips (in/min/in) until the yield point was determined. After yielding, the

rate used was 3.5 in/min/in until bar rupture occurred.

47

Stainless steel and MMFX bars do not have a well-defined yield point and do not exhibit a

yielding plateau; therefore, the 0.2% offset method (ASTM A370-07) was used to determine the

yield strength of the bar. This method is illustrated in Figure 4-1 where the intersection of the

stress-strain curve with a line parallel to the slope equal to the initial tangent modulus and which

intercept at 0.002 strain defines the yield point.

Data gathered during tension tests included strain at 0.2% offset, load at 0.2% offset, and

ultimate strength. Complete tension test results are given in APPENDIX A.

Grade 60 Steel

All mild steel bars came from the same heat and were purchased locally at a building

supply center. The #5 bar had yield strength measured at 0.35% (0.0035 in/in) strain of 63 ksi,

and a tensile strength of 105 ksi. The #7 bar had yield strength measured at 0.35% (0.0035 in/in)

strain of 64 ksi, and a tensile strength of 106 ksi (Table 4-2). The two samples of each size

exceeded and complied with the ASTM A615 (Grade 60) standard which established the

minimum yield strength, and tensile strength of 60 ksi, and 90 ksi, respectively.

Stainless Steel

The stainless steel 316LN bars were made in Italy and were provided by Valbruna

Stainless Steel. Valbruna Stainless Steel is a company specialized in supplying and producing

stainless steel and special metal alloys. The company has several braches in United States and

Canada. Their stainless steel bars have been used worldwide in different applications as bridges,

highway and roads, viaducts, and ports. After testing, the 16 mm bar had a yield strength

measured at 0.2% (0.002 in/in) strain offset of 106 ksi, and a tensile strength of 124 ksi. The 20

mm bar had a yield strength measured at 0.2% (0.002 in/in) strain offset of 96 ksi, and tensile

strength of 120 ksi (Table 4-3). The yield and tensile strengths measured in the two samples of

48

each size exceeded and complied with the minimum yield strength of 75 ksi and minimum

tensile strength of 100 ksi required for ASTM A955 and Valbruna product specifications.

MMFX Steel

The MMFX bars were provided for MMFX Steel Corporation of America. MMFX Steel

Corporation of America is a subsidiary of MMFX Technologies, a company that has invented the

MMFX 2 steel bar which has a microstructure different to the conventional steel. The MMFX 2

steel rebar is a corrosion resistant and a high grade steel which has been used nationwide in

different construction applications as bridge decks, bridge structures, and residential. After

testing, the #5 and #7 bars had yield strengths measured at 0.2% (0.002 in/in) strain offset of 122

ksi, and 128 ksi, respectively (Table 4-4). The yield strength measured in the two samples of

each size exceeded and complied with the minimum yield strength of 120 ksi required for ASTM

A1035 and MMFX product specifications.

Specimens Test Results

Behavior and Failure Modes

Figure 4-2 shows the stress-strain plot of three pullout specimens to illustrate the typical

behavior of each type of steel. Load-slip and stress-strain curves for all specimens are shown in

APPENDIX B. The stress was obtained by dividing the measured load by the nominal area of the

reinforcing bar. The strain was obtained by dividing the measured bar displacement by the

debonded length.

In general, as load was applied the specimen remained uncracked and linear elastic until

the yield point was reached. In some of the specimens cracking occurred, this caused a loss of

bond and a premature failure. This failure mode was deemed concrete splitting which occurred

suddenly when the peak load was reached. This type of failure was characterized by cracks that

split the specimen from the front to the right face (Figure 4-3A). Also, diagonal cracks formed on

49

the right and left side of the specimen confirming the strut behavior of the specimens (Figure

4-3B). The front face of the specimen presented the typical Y – crack which is seen in bond test

using beam end specimens (Ahlborn and DenHartigh, 2002). The rear face exhibited an inverted

Y – crack which split the specimen in three parts (Figure 4-3C and D).

Crack pattern of this kind of failure was seen in specimen MM_7_180_35_3 as it is shown

in Figure 4-4.

After testing, a larger portion of the side cover was easy to remove. During the specimen

examination, it was found crushing of the concrete inside radius of the hook. This kind of

behavior was seen not only in 90 degree but also in 180 degree hooks (Figure 4-5). Moreover,

crushing of the concrete near to the radius of the bend was because of the higher tensile force

applied to the bar producing mini cracks between the bar and the concrete and resulting in loss of

bond.

This type of behavior was also observed and reported by Marques and Jirsa (1975) and

Hamad, Jirsa, and D’Abreu de Paulo (1993). The main objective of those studies was to evaluate

bond characteristics and anchorage capacity of uncoated (mild steel) and epoxy-coated hooked

bars for 90 and 180-degree bend angle.

If the specimen was able to sustain load beyond yield, one of two possible failure modes

occurred. The bar yield with concrete splitting, occurred after the bar had yielded indicating that

the anchorage was able to hold load at least to the yield point. Cracks pattern are similar to the

concrete splitting failure.

Bar yield was characterized by continued deformation of the bar without concrete splitting

or bar rupture. This typically occurred on the stainless steel specimens when the hydraulic jack

stroke limit was reached. Specimens SS_16_90_25_1, SS_16_90_25_2, SS_16_90_35_1,

50

SS_16_90_35_2, SS_16_180_35_1, and SS_16_180_35_4 were loaded until the stroke of the

hydraulic jack reached its limit, however; the bar reached the yielding point before the test was

terminated. After testing, cracks were not seen on the faces of the specimen.

Finally, several specimens failed due to bar yield and rupture. This occurred when the full

rupture strength of the bar was reached before the concrete failed. The bar yield and rupture

failure was mainly observed in MMFX specimens.

Mild Steel Specimens

In this section the detailed results of the mild steel specimens are presented and discussed.

Failure modes for each specimen are documented as well as the load displacement and load slip

behavior.

Figure 4-6 shows the load displacement behavior for all of the #5 and #7 mild steel

specimens. Also, Figure 4-6 show the coupon yield load (Pyt) for #5 and #7 which confirms that

the bars reached yield. The plots for each are shown with different scales to accentuate the

differences in behavior among the specimens with the same size bar. The 25-degree strut

specimens appear to have a larger initial stiffness than that of the 35-degree strut specimens

when comparing the results for the #5 bar. This is likely due to the manner in which the

displacements were measured. The linear potentiometer was attached to the bar at the point

where it exits the concrete and measured the relative movement between the bar and concrete.

The 25-degree strut specimens had shorter debonded lengths than that of the 35-degree strut

specimens resulting in larger elastic deformations under the same load.

The sudden change in slope of the load displacement plots indicate yielding of the bars and

generally agreed well with the measured yield strength of the bare bars. The anchorage strength

of #5 specimens with 180-degree hook improved about 23% with respect to #5 specimens with

90-degree hooked bar as the concrete strength and the strut angle increased (Figure 4-6a).

51

Post-yield slopes are not likely to provide useful information because the measurement of

bar displacement is made relative to the concrete surface around the bar. Microcracking is likely

to occur near yield, which will result in movement of the concrete along with the bar as ultimate

strength is approached. This behavior is described more fully when the slip data are presented.

Figure 4-7 summarizes the results of the tests in terms of the hook capacity.

The complete test results for mild steel specimens are shown in the Table 4-5. f’c shows

the average concrete strength of the specimen concrete as tested on the day of the pullout test. Pu

is the peak measured load applied to the bar. To allow comparison of the peak measured loads

among the specimens that contained varying concrete strength, Pu was normalized to the square

root of the ratio of the design strength (5500 psi) to the measured strength. Pye is the load at

which the bar yielded using the 0.35% strain. Δu is the displacement corresponding to Pu and Δy

is the displacement corresponding to Pye. The bar stress based on the peak measured load is also

given (Pu /Ab). D1 and D2 represent the total measured slip of the bar when the load in the bar is

Pu.

The load slip data gathered during the testing provides interesting insight into the behavior

of the hooked bar anchorages.

Figure 4-8 show two graphs that compare the confined and unconfined #5 bar specimens

from the first series of testing. Recall that this testing was conducted with the original test

configuration. It is readily apparent that the unconfined specimen (which did not reach yield)

has a shallower load-slip slope than that of the confined specimen with stirrups, indicating that

the lack of stirrups allowed greater bar movement prior to reaching ultimate capacity. This

confirms observations by Hamad, Jirsa, and D’Abreu de Paulo (1993). Hamad, Jirsa, and

D’Abreu de Paulo evaluated beam-column joints with mild steel and epoxy-coated hooked bars.

52

Their results concluded that for #7 uncoated specimens with 90 degree hooked bar, the

anchorage strength increased about 51% with the inclusion of stirrups. However, for #7

specimens tested in this research with 90 degree hooked bar, the anchorage strength increased

about 69% with the inclusion of stirrups. The differences between the results of comparative

tests are based on the test setup, the use of high concrete strength, strut-and-tie approach, and

stirrups spacing.

Further examination of the plots indicates that the slip at D1 is greater than that of D2 until

higher loads are reached where the plots cross. This occurs in both the confined and unconfined

specimens. D1 was expected to remain greater than D2 up to failure since the bar exits the

specimen near where D1 is measured. The cross-over of the plots is likely due to cracking late in

the loading process and is a function of the slip measurement technique and not an indication of

peculiar behavior. Figure 4-9 shows the idealized location of cracks in unconfined and confined

specimens, which are similar to those observed during and after the testing. As load is applied,

the slip at D1 is greater than that of D2. As additional load is applied, diagonal cracks form

perhaps along line 2-3. When these cracks occur, a spall in the shape of 1-2-3 forms and moves

with the bar as further load is applied resulting in zero bond stress in this area. Because the slip

measurement device measures relative movement between the concrete and steel, less (or zero)

slip will register after the spall occurs. These cracks likely form when the specimen is near

capacity, which confirms the crossing locations in the plots.

For unconfined specimens, initial slip located at D1 was greater than slip located at D2

until diagonal cracks formed as shown in Figure 4-9a. For confined specimens, the use of

transverse reinforcement not only improved the anchorage capacity of the hooked bar but also

53

controlled crack propagation. The inclusion of transverse reinforcement was sufficient to yield

the bar and to achieve the bar rupture failure.

Figure 4-10 shows the relative behavior of the confined and unconfined #7 tests. The

unconfined test is similar to that of the #5 with failure occurring before bar yield and with a

crossing of the slip plots near the specimen ultimate capacity. In contrast, however, the confined

specimen never exhibits the cross-over of the slip plots. This is probably due to the confinement

restricting the formation of the spall in the region of D1.

Slip behavior of the series 2 through 5 tests was similar to that of the unconfined specimen

from series 1 except that most of the specimens tested with the revised setup reached yield before

failure. Figure 4-11 provides an example of the load slip behavior for a #5 bar with a 180-deg.

hook. As expected, D1 remained greater than D2 for the entire test, and never crossed D2 as the

load approached capacity. Recall that the slip D1 was measured at the end of the debonded

length (dL), which placed it closer to the bend than in the previous test setup (Figure 4-12).

Figure 4-12 shows two possible locations where diagonal cracks formed at the edge of the strut.

Crack 2-3 is shown above D1 and Crack 4-5 is shown below. It is believed that the reason there

was no cross-over is that the cracking occurred primarily along line 2-3, which formed spall 1-2-

3 and allowed the relative slip D1 to continue to be measured up to failure. Furthermore, the D2

plot shows a plateau forming while D1 remains linear up until failure of the concrete indicating

that the bar was well beyond its yield point at D1.

Typical behavior of a #7 mild steel bar with a 180-degree hook is shown in Figure 4-13.

The behavior illustrated is similar to that of the #5 specimen in that D1 remains larger than D2

until failure.

54

Stainless Steel Specimens

Detailed results of the stainless steel specimens are presented and discussed. Failure

modes for each specimen are documented as well as the load displacement and load slip

behavior.

Figure 4-14 shows the load displacement behavior for all of the 16 and 20-mm stainless

steel specimens. Also, Figure 4-14 show the coupon yield load (Pyt) for 16mm and 20mm, which

confirms that the bars reached yield. The plots for each are shown with different scales to

accentuate the differences in behavior among the specimens with the same size bar. All of the

specimens with 16 mm bars reached their yield point with no bar rupture. In many cases, the test

was terminated when the stroke of the hydraulic jack reached its limit. In contrast, most

specimens with 20 mm bars reached their yield point but then failed by splitting of the concrete.

During this portion of the testing program it was discovered that stainless steel bars from two

different heats had used (Pyt1 and Pyt2), which explains the difference in the yield loads exhibited

in Figure 4-14a for the 16 mm bars.

For 16 mm and 20 mm specimens, the bond between the bar and the concrete made the

tangent modulus slopes steeper (Figure 4-14). For 20 mm specimens, load-displacement curves

were quite similar despite of different development lengths, strut angles, and hook geometries

(Figure 4-14b).

Figure 4-15 summarizes the results of the tests in terms of the hook capacity.

The test results for stainless steel specimens are shown in the Table 4-3. f’c shows the

average concrete strength of the specimen concrete as tested on the day of the pullout test. Pu is

the peak measured load applied to the bar. To allow comparison of the peak measured loads

among the specimens that contained varying concrete strength, Pu was normalized to the square

root of the ratio of the design strength (5500 psi) to the measured strength. Pye is the load at

55

which the bar yielded using the 0.2% offset strain. Δu is the displacement corresponding to Pu

and Δy is the displacement corresponding to Pye. The bar stress based on the peak measured load

is also given (Pu /Ab). D1 and D2 represent the total measured slip of the bar when the load in

the bar is Pu.

Because of the 25-degree strut specimens had shorter debonded lengths than that of the 35-

degree strut specimens resulting in larger elastic deformations under the same load (Figure 4-16).

As a result, it was found that the maximum slip for specimen SS_16_90_35_2 increased about

56% as the strut angle increased in comparison with the specimen SS_16_90_25_2 ( Table

4-6).

Typical load-slip behavior is illustrated in Figure 4-17 for 16 mm stainless steel specimens.

Initial slip is larger for D1 than for D2. As the load nears yield, however, the plots cross,

indicating that the diagonal crack formed the 1-4-5 spall (Figure 4-12) in the debonded region of

the bar.

Figure 4-18 indicates that the 20 mm stainless steel specimens behave more like the #7

mild steel specimens than that of the 16 stainless steel specimens. This may be due to the

difference in the failure mode. Recall that the 16 mm stainless steel specimens did not split

while both the #7 mild steel and 20 mm stainless steel specimens yielded and then split.

MMFX Specimens

In this section the detailed results of the MMFX specimens are presented and discussed.

Failure modes for each specimen are documented as well as the load displacement and load slip

behavior.

Figure 4-19 shows the load displacement behavior for all of the #5 and #7 MMFX

specimens. Also, Figure 4-19 show the coupon yield load (Pyt) for #5 and #7 which confirms that

the bars reached yield. The plots for each are shown with different scales to accentuate the

56

differences in behavior among the specimens with the same size bar. All of the specimens with

#5 bars reached yield, which appears to be at approximately the same load. In contrast, just a

few specimens with #7 bars reached their yield point before failure by concrete splitting

occurred, indicating that the bond strength was not sufficient to develop the #7 bars as fully as

the #5 bars.

It was found that the anchorage strength at failure of #5 specimens with 180-degree hook

improved about 9% as the development length increased ( Table 4-7).

Figure 4-20 summarizes the results of the tests in terms of the hook capacity. Also, in

Figure 4-20, it was not noticed any difference between the average strength of 90 and 180-degree

hook for #5 and #7 specimens.

The test results for MMFX specimens are shown in the Table 4-7. f’c shows the

average concrete strength of the specimen concrete as tested on the day of the pullout test. Pu is

the peak measured load applied to the bar. To allow comparison of the peak measured loads

among the specimens that contained varying concrete strength, Pu was normalized to the square

root of the ratio of the design strength (5500 psi) to the measured strength. Pye is the load at

which the bar yielded using the 0.2% offset strain. Δu is the displacement corresponding to Pu

and Δy is the displacement corresponding to Pye. The bar stress based on the peak measured load

is also given (Pu /Ab). D1 and D2 represent the total measured slip of the bar when the load in

the bar is Pu.

Typical behavior of a #5 and #7 mild steel bar with a 90 and 180-degree hooks is shown in

Figure 4-21, and Figure 4-22. The behavior illustrated is similar to that of the #5 and #7 mild

steel specimens with 180 degree hook in that D1 remains larger than D2 until failure. The

maximum slip for specimen MM_5_90_35_2 increased about 114% as the strut angle increased

57

58

in comparison with the specimen MM_5_90_25_2. Also, it was found that the maximum slip for

specimen MM_5_180_35_2 increased about 116% as the development length increased in

comparison with the specimen MM_5_180_35_4.

Table 4-1. Compressive concrete strengths. Series 1 2 3 4 5

Average Concrete Strength 5700 5520 6500 6180 6070 Coefficient of Variation (%) 4.84 3.84 3.34 3.41 3.74 Table 4-2. Tension test results for ASTM A615 reinforcement. Grade 60

Yield Strength at 0.35% strain (ksi)

Strain at 0.35% yield (in/in)

Load at 0.35% (kip)

Ultimate Strength (ksi)

#5 Average 62.8 0.00350 19.5 104.7COV (%) < 1 0.00 < 1 0.11 #7 Average 63.7 0.00350 38.2 105.9COV (%) < 1 0.00 < 1 < 1 Table 4-3. Tension test result for stainless steel (316LN). Stainless Steel

Yield Strength at 0.2% offset (ksi)

Strain at 0.2% offset yield (in/in)

Load at 0.2% offset (kip)

Ultimate Strength (ksi)

16 mm (0.625 in) Average 106.2 0.00615 32.9 123.8COV (%) < 1 1.15 < 1 < 1 20 mm (0.787 in) Average 95.7 0.00575 46.5 120.1COV (%) 6.09 1.23 6.09 < 1 Table 4-4. Tension test results for MMFX steel. MMFX

Yield Strength at 0.2% offset (ksi)

Strain at 0.2% offset yield (in/in)

Load at 0.2% offset (kip)

Ultimate Strength (ksi)

#5 Average 122.4 0.00649 37.9 158.1COV (%) < 1 < 1 < 1 < 1#7 Average 128.0 0.00670 76.8 162.9COV (%) < 1 2.11 < 1 < 1

59

Table 4-5. Test results for mild steel #5 and #7 specimens.

Specimen notation f'c (psi) Pu (kips)

Pye (kips) Δu (in) Δy (in)

D1u (in)

D2u (in)

Pu/Ab (ksi)

cu f

P'

5500

(kips) Failure Modes 60_5_90_1 5700 20.2 N.A 0.085 NA 0.162 0.152 63.8 19.8 Bar yield with concrete splitting 60_5_90_S 5700 25.5 N.A 0.289 NA 0.117 0.074 80.8 25.0 Bar yield and rupture 60_5_90_25_1 5490 26.5 18.7 0.151 0.009 NA NA 85.6 26.5 Bar yield with concrete splitting 60_5_90_25_2 5490 27.0 19.1 0.150 0.009 0.167 0.132 87.1 27.0 Bar yield with concrete splitting 60_5_180_35_1 6330 34.6 18.9 0.274 0.017 0.178 0.081 106.0 32.9 Bar yield and rupture 60_5_180_35_2 6330 34.8 18.9 0.275 0.016 0.157 0.074 106.5 33.0 Bar yield and rupture 60_7_90_1 5700 27.8 N.A 0.037 N.A 0.102 0.097 45.4 27.3 Concrete splitting 60_7_90_S 5700 47.0 N.A 0.089 N.A 0.099 0.019 77.0 46.2 Bar yield with concrete splitting 60_7_90_47_1 5490 58.1 38.9 0.497 0.036 N.A N.A 97.0 58.2 Bar yield 60_7_90_47_2 5490 54.1 39.5 0.358 0.036 0.249 0.164 90.2 54.1 Bar yield 60_7_180_35_1 6330 54.4 40.8 0.172 0.023 0.166 0.158 84.6 50.7 Bar yield with concrete splitting 60_7_180_35_2 6330 52.4 31.2 0.163 0.023 0.251 0.226 81.5 48.9 Bar yield with concrete splitting 60_7_180_35_3 6330 58.9 36.5 0.238 0.023 0.174 0.085 91.5 54.9 Bar yield with concrete splitting

60

60_7_180_35_4 6330 59.1 36.9 0.285 0.023 0.401 0.263 91.8 55.1 Bar yield with concrete splitting

Table 4-6. Test results for stainless steel 16 mm and 20 mm specimens.

Specimen notation f'c (psi) Pu (kips)

Pye (kips) Δu (in) Δy (in) D1u (in) D2u (in)

Pu/Ab (ksi)

cu f

P'

5500

(kips) Failure Modes SS_16_90_25_1 6350 35.4 32.15 0.497 0.036 0.287 0.186 105.7 33.0 Bar yield SS_16_90_25_2 6350 33.3 27.44 0.497 0.015 0.265 0.126 99.2 31.0 Bar yield SS_16_90_35_1 6350 36.7 32.84 0.658 0.024 0.446 0.235 109.6 34.2 Bar yield SS_16_90_35_2 6350 33.6 28.98 0.729 0.022 0.413 0.148 100.2 31.3 Bar yield SS_16_180_35_1 6100 36.3 22.62 0.882 0.022 0.400 0.882 110.4 34.5 Bar yield SS_16_180_35_2 6100 37.3 34.89 0.204 0.024 0.207 0.108 113.5 35.4 Bar yield with concrete splitting SS_16_180_35_3 6100 35.1 32.43 0.177 0.024 0.109 0.102 106.8 33.3 Bar yield and rupture SS_16_180_35_4 6100 37.4 28.64 0.758 0.032 0.334 0.051 113.8 35.5 Bar yield SS_20_90_35_1 6150 59.5 39.83 0.263 0.033 0.239 0.188 114.9 56.3 Bar yield with concrete splitting SS_20_90_35_2 6150 59.1 39.75 0.099 0.032 0.193 0.146 114.0 55.9 Bar yield with concrete splitting SS_20_90_35_3 6150 58.5 N.A 0.011 N.A 0.166 0.158 113.0 55.4 Bar yield with concrete splitting SS_20_90_35_4 6150 60.4 39.38 0.150 0.032 0.077 0.041 116.5 57.1 Bar yield with concrete splitting SS_20_180_35_1 6150 62.4 40.94 0.364 0.032 0.222 0.061 120.4 59.0 Bar yield with concrete splitting SS_20_180_35_2 6150 62.5 35.15 0.358 0.031 0.146 0.043 120.6 59.1 Bar yield with concrete splitting SS_20_180_35_3 6150 52.5 41.74 0.056 0.032 0.167 0.132 101.3 49.6 Bar yield with concrete splitting

61

SS_20_180_35_4 6150 55.6 38.03 0.066 0.032 0.152 0.079 107.2 52.5 Bar yield with concrete splitting

Table 4-7. Test results for MMFX steel #5 and #7 specimens.

Specimen notation f'c (psi) Pu (kips)

Pye (kips) Δu (in) Δy (in) D1u (in) D2u (in)

Pu/Ab (ksi)

cu f

P'

5500

(kips) Failure Modes MM_5_90_25_1 6450 49.5 27.6 0.115 0.017 0.071 0.067 159.7 45.7 Bar rupture MM_5_90_25_2 6450 48.6 28.2 0.155 0.017 0.114 0.077 156.7 44.8 Bar rupture MM_5_90_35_1 6450 44.9 33.3 0.064 0.025 0.145 0.057 144.9 41.5 Bar yield with concrete splitting MM_5_90_35_2 6450 49.4 34.6 0.162 0.025 0.244 0.233 159.3 45.6 Bar yield with concrete splitting MM_5_180_35_1 6320 41.0 23.1 0.057 0.025 0.019 0.014 132.3 38.2 Bar yield with concrete splitting MM_5_180_35_2 6320 51.0 32.7 0.096 0.025 0.087 0.037 164.4 47.5 Bar yield with concrete splitting MM_5_180_35_3 6320 47.4 44.8 0.051 0.025 0.199 0.197 153.0 44.3 Bar yield with concrete splitting MM_5_180_35_4 6320 52.9 31.4 0.145 0.026 0.187 0.154 170.5 49.3 Bar rupture MM_7_90_25_1 6600 69.9 N.A 0.021 N.A 0.379 0.291 116.5 63.8 Concrete splitting MM_7_90_25_2 6600 71.7 N.A 0.029 N.A 0.044 0.018 119.4 65.4 Bar cast out of position MM_7_90_35_1 6600 58.3 N.A 0.010 N.A 0.003 0.000 97.1 53.2 Bar cast out of position MM_7_90_35_2 6600 65.8 N.A 0.029 N.A 0.284 0.150 109.6 60.0 Bar cast out of position MM_7_90_35_3 6330 58.9 N.A 0.044 N.A 0.237 0.234 98.2 54.9 Concrete splitting MM_7_90_35_4 6330 77.2 67.5 0.059 0.044 0.088 0.086 128.6 71.9 Bar yield with concrete splitting MM_7_180_35_1 6170 59.3 N.A 0.035 N.A 0.171 0.126 98.8 56.0 Concrete splitting MM_7_180_35_2 6170 71.4 65.3 0.051 0.044 0.077 0.052 119.1 67.5 Bar yield with concrete splitting MM_7_180_35_3 6170 67.6 N.A 0.014 N.A 0.106 0.096 112.7 63.9 Concrete splitting

62

MM_7_180_35_4 6170 70.4 59.6 0.068 0.044 0.309 0.252 117.3 66.5 Bar yield with concrete splitting

f

fy

ε εy 0.2 %

Figure 4-1. Stress-strain curve.

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-Strain Comparison

-0.01 0.04 0.09 0.14 0.19 0.240

40

80

120

160

0

300

600

900

1200

-0.01 0.04 0.09 0.14 0.19 0.240

40

80

120

160

0

300

600

900

1200

60_5_90_25_1MM_5_90_25_1SS_16_90_25_1

Figure 4-2. Stress-strain comparison.

A

STRUT

B Figure 4-3. Cracks A) on the Top, B) on the side faces, C) on the rear and D) on the front faces.

63

C D Figure 4-3. Continued.

Top Front Rear Bottom

Right Left Figure 4-4. Crack pattern for concrete splitting failure.

A B Figure 4-5. Concrete crushed inside of bend radius A) 90 deg. hook and B) 180 deg. hook.

64

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement#5 - Grade 60

-0.01 0.09 0.19 0.29 0.390

6

12

18

24

30

36

0

25

50

75

100

125

150

-0.01 0.09 0.19 0.29 0.390

6

12

18

24

30

36

0

25

50

75

100

125

150

Pyt

60_5_90_25_160_5_90_25_260_5_90_160_5_90_S60_5_180_35_160_5_180_35_2

A Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement#7 - Grade 60

0 0.14 0.28 0.42 0.56 0.70

10

20

30

40

50

60

70

0

40

80

120

160

200

240

280

Pyt

60_7_90_47_160_7_90_47_260_7_90_160_7_90_S60_7_180_35_160_7_180_35_260_7_180_35_360_7_180_35_4

B Figure 4-6. Load-displacement for mild steel A) #5, and B) #7.

P u/A

b (k

si)

0

30

60

90

120

90 180 90 180

85

112

94 94

Bend Angle:Bar Size: #5 #7

Figure 4-7. Mild steel results in terms of hook capacity.

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.05 0.1 0.15 0.20

5

10

15

20

25

30

0

15

30

45

60

75

90

Pucrossing

D1D2

A Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.05 0.1 0.15 0.20

5

10

15

20

25

30

0

15

30

45

60

75

90

Py

Pucrossing

D1D2

B Figure 4-8. Load-slip for specimens A) 60_5_90_1 and B) 60_5_90_S.

65

D1

D2

loss in stiffnessfrom cracking

1

3

2Spall

A

loss in stiffnessfrom cracking

D1

D2

Spall

1 2

3

B Figure 4-9. Locations where relative slip was measured for A) Unconfined, and B) Confined

with stirrup.

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.04 0.08 0.12 0.160

10

20

30

40

50

60

0

15

30

45

60

75

90

Pu

D1D2

A Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.04 0.08 0.12 0.160

10

20

30

40

50

60

0

15

30

45

60

75

90Pu

Py

D1D2

B Figure 4-10. Load-slip for specimen. A) 60_7_90_1 and B) 60_7_90_S.

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.05 0.1 0.15 0.20

10

20

30

40

0

30

60

90

120Pu

Py

D1D2

Figure 4-11. Typical load-slip behavior for #5 mild steel specimens with 180-degree hook

(60_5_180_35_2 shown).

66

D1

D2

loss in stiffnessfrom cracking

dL

Potential cracklocations

1 2

3

4

5 STRUT

Figure 4-12. Relative slip at locations D1 and D2 for unconfined specimens with debonded

length.

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.1 0.2 0.3 0.4 0.50

10

20

30

40

50

60

70

0

15

30

45

60

75

90

105Pu

Py

D1D2

Figure 4-13. Typical load-slip behavior for #7 mild steel specimens with 180-degree hook

(60_7_180_35_4 shown).

67

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement16 mm - Stainless Steel

0 0.1 0.2 0.3 0.40

8

16

24

32

40

0

30

60

90

120

150

180

Pyt1

Pyt2

SS_16_90_25_1SS_16_90_25_2SS_16_90_35_1SS_16_90_35_2SS_16_180_35_1SS_16_180_35_2SS_16_180_35_3SS_16_180_35_4

A Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement20 mm - Stainless Steel

0 0.14 0.28 0.42 0.56 0.70

15

30

45

60

75

0

60

120

180

240

300

Pyt

SS_20_90_35_1 SS_20_90_35_2

SS_20_90_35_4SS_20_180_35_1SS_20_180_35_2SS_20_180_35_3SS_20_180_35_4

B Figure 4-14. Load - displacement for stainless steel A) 16 mm, and B) 20 mm.

P u/A

b (k

si)

0

30

60

90

120

90 180 90 180

104111 115 112

Bend Angle:Bar Size: 16mm 20mm

Figure 4-15. Stainless steel results in terms of hook capacity.

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.1 0.2 0.3 0.4 0.50

8

16

24

32

40

0

25

50

75

100

125

Pu

Py

D1D2

A Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.1 0.2 0.3 0.4 0.50

8

16

24

32

40

0

25

50

75

100

125Pu

Py

crossing

D1D2

B Figure 4-16. Load-slip for specimens A) SS_16_90_25_2 and B) SS_16_90_35_2.

68

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.1 0.2 0.3 0.40

10

20

30

40

50

0

30

60

90

120

150

Pu

Py

D1D2

Figure 4-17. Typical load-slip behavior for 16mm stainless steel specimens with both 90 and

180-degree hooks (SS_16_180_35_4 show).

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.05 0.1 0.15 0.2 0.250

10

20

30

40

50

60

70

0

20

40

60

80

100

120

140Pu

Py

D1D2

Figure 4-18. Typical load-slip behavior for 20mm stainless steel specimens with both 90 and

180-degree hooks (SS_20_90_35_2 shown).

69

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement#5 - MMFX

0 0.1 0.2 0.3 0.40

10

20

30

40

50

60

0

40

80

120

160

200

240Pyt

MM_5_90_25_1MM_5_90_25_2MM_5_90_35_1MM_5_90_35_2MM_5_180_35_1MM_5_180_35_2MM_5_180_35_4

A Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement#7 - MMFX

0 0.14 0.28 0.42 0.56 0.70

20

40

60

80

0

80

160

240

320Pyt

MM_7_90_25_1MM_7_90_25_2MM_7_90_35_4MM_7_180_35_1MM_7_180_35_2MM_7_180_35_3MM_7_180_35_4

B Figure 4-19. Load-displacement for MMFX steel A) #5, and B) #7.

P u/A

b (k

si)

0

40

80

120

160

90 180 90 180

143 144

103 106

Bend Angle:Bar Size: #5 #7

Figure 4-20. MMFX results in terms of hook capacity.

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.05 0.1 0.15 0.20

10

20

30

40

50

60

0

30

60

90

120

150

180Pu

Py

D1D2

Figure 4-21. Typical load-slip behavior for #5 MMFX specimens with both 90 and 180-degree

hooks (MM_5_90_25_2 shown).

70

71

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

0 0.1 0.2 0.3 0.40

20

40

60

80

0

30

60

90

120Pu

Py

D1D2

Figure 4-22. Typical load-slip behavior for #7 MMFX specimens with both 90 and 180-degree

hooks (MM_7_180_35_4 shown).

CHAPTER 5 ANALYSIS OF RESULTS

The results presented in the previous chapter can be qualitatively summarized as follows:

1. The mild steel specimens generally behaved as would be expected, indicating that the test specimen design and test set-up provide an effective method of testing hook bar anchorages.

2. ACI/AASHTO equations appear to ensure that both the 16 and 20-mm bars develop their

yield strength.

3. ACI/AASHTO equations appear to ensure that the #5 MMFX hooked anchorage can

develop well beyond its yield strength, but that the #7 MMFX hooked anchorage was unable to develop significant additional force or deformation beyond yield.

This chapter presents the results of several analyses that are intended to quantitatively

analyze results of the hooked anchorage tests and determine the suitability of the current design

equations.

Anchorage Capacity

One method that can be used to compare the results of tests on high strength bars is the

excess force capacity available beyond the yield point. Mechanical couplers are required to reach

least 1.25 times the yield strength (fy) of the bar when splicing reinforcement (ACI 318-05

Section 12.14.3.2). The rationale for this approach is not clear but it has also been used by

Marques and Jirsa (1975) and by Ueda, Lin, and Hawkins (1986) in evaluating the capacity and

ductility of hooked bar anchorages that used mild steel. The disadvantage of this approach,

however, is that the current research is comparing steels that have different yield strengths and

post-yield mechanical properties than that of mild steel. Consequently, the bars already vary in

how much post-yield strength is available, both in the absolute and relative sense.

Figure 5-1 shows the calculated anchorage capacity ratios compared to the limit of 1.25.

The anchorage capacity ratio was calculated by dividing the peak measured load (anchorage

72

capacity) by bar yield strength (Pu/Py), which was taken from the results of the bar tests using the

0.2% offset method.

For mild steel specimens the anchorage capacity ratio exceeded the coupler requirement

of 1.25 by about 12% and 40% for #5 with bend angle of 90 and 180 degrees. For #7 bars the

anchorage capacity ratio was exceeded by 14% and 16%, respectively (see Figure 5-1 and Table

5-1).

For 16mm stainless steel specimens with bend angle of 90-degree, the anchorage capacity

ratio was sufficient to yield the bar but less than the limit of 1.25. However, the anchorage

capacity ratio was exceeded by about 22% and 34% for 16 mm specimens with 180-degree as the

development length increased. For 20 mm stainless steel specimens with bend angles of 90 and

180 degrees, the anchorage capacity ratios increased about 14% (Figure 5-1 and Table 5-2).

The anchorage capacity ratio was exceeded by 43% for #5 MMFX specimens with bend

angle of 90-degree, and with strut angles of 25 degree. For #5 MMFX specimens with bend

angle of 180-degree, the anchorage capacity ratio increased about 25%. For three #7 MMFX

specimens, however, the anchorage capacity ratio was less than the limit of 1.25 but it was

sufficient to yield the bar (Figure 5-1 and Table 5-3). The remainders of the specimens were at

anchorage capacity ratio of less than 1.0, a clear indication that the anchorage capacity was

insufficient.

Criteria for judging the anchorage capacity of high strength bars in concrete is not clearly

defined. It is rational to judge the results of this tests not only based on anchorage capacity ratio

but also on the bond capacity, ductility and K-factor.

Bond Stress

Another method that can be used to compare the relative performance of the different

steel types is to examine the bond stress. Figure 5-2 shows the bond stress normalized by the

73

square root of the measured concrete strength. The bond stress was calculated by dividing the

peak measured load by the nominal surface area of the straight, bonded portion of the hook.

The straight portion of the in unconfined specimens is lesser than in confined specimens

with stirrups, and unconfined specimens with debonded length. Also, it was found that the bond

stress for #5 mild steel specimens was greater than #7 specimens (Figure 5-2A). The bond stress

for #5 mild steel unconfined specimens with debonded length improved as the concrete strength

and the strut angle increased from 43.19 ksi to 53.30 ksi respectively. Bond stresses were similar

for #7 mild steel specimens with stirrups and without stirrups with debonded length, and with 90

and 180-degree bend angle (Figure 5-2A and Table 5-4).

The bond stress for 20 mm stainless steel specimens was greater than for 16 mm

specimens (Figure 5-2B and Table 5-5). For 16 mm stainless steel specimens with 90-degree

hooked bar, the bond stress was similar about 22 ksi. Also, the bond stresses were similar for 20

mm specimens with bend angle of 90 and 180-degree, and with same development length

(Figure 5-2B).

The bond stress for #5 MMFX specimens was greater than for #7 specimens (Figure 5-2C

and Table 5-6). For #5 specimens with 90-degree hooked bar, the bond stress was similar about

24 ksi. The bond stresses were similar for #7 specimens with bend angle of 90 degree (Figure

5-2C and Table 5-6).

Bond stress for mild steel, stainless steel, and MMFX are shown in Table 5-4, Table 5-5,

and Table 5-6. Pu represents the maximum peak load, ls represents the straight length of the

hooked bar and db represents the diameter of the bar. umax represents the maximum bond stress,

and umax/f'c1/2 represents the bond stress normalized by the square root of the measured concrete

strength.

74

Ductility

Yet another option is to compare hook behavior based on the displacement capacity of

the specimen beyond the yield point. A ductility ratio was then calculated as the ratio of the

strain at peak measured stress (Su) to the strain at yield corresponding with the 0.2% offset

method (Sy).

Ductility ratios for bend angle, 90 to 180 degrees, varied from 12.25 at 5490 psi to 14.80

at 6100 psi for #5 mild steel specimens. Also, for #7 mild steel specimens, ductility ratios for

bend angle, 90 to 180 degrees, varied from 7.72 at 5490 psi to 8.80 at 6330 psi. However, the

ductility ratio varied from 5.65 at 6330 psi to 8.83 at 6330 psi for #7 specimens with 180-degree

as the development length increased (Figure 5-3A and Table 5-7).

Ductility ratios for bend angle, 90 to 180 degrees, varied from 32.34 at 6350 psi to 37.80

at 6100 psi for 16 mm stainless steel specimens. Also, for 20 mm specimens, ductility ratios for

bend angle, 90 to 180 degrees, varied from 8.10 at 6100 psi to 11.13 at 6100 psi (Figure 5-3B

and Table 5-8).

Ductility ratios for bend angle, 90 to 180 degrees, varied from 6.20 at 6450 psi to 3.92 at

6450 psi for #5 MMFX specimens. Also, ductility ratios for #7 MMFX specimens was less than

1 because of most of them did not reach yield point. Only three #7 MMFX specimens reached

yield point (Figure 5-3C and Table 5-9).

K-Factor

Another way to compare the hook behavior was by means of the K-factor. The

development length for standard hooks proposed by the ACI 318-07 can be expressed as:

f 'c

yf

bKd

dhl = (5-1)

75

76

where the K-factor represent the constant value of 0.02, the coating and lightweight concrete

factors equal to 1.0, and an applicable modification factor of 0.7.

The side cover and cover on bar extension beyond hook were not less than 2-1/2 in. and 2

in. for all hooked specimens. The K-factor used to calculate the development length for all the

specimens was 0.014.

After testing, an experimental K-factor was computed as shown in Equation 5-2, and it was

compared with the K-factor used in the Equation 5-1.

'cfsf

bdlK testeddh−= (5-2)

where ldh-tested represents the development length tested, db represents the diameter of the bar, fs

represents the peak stress at failure, and f’c represents the average concrete strength.

Table 5-10, Table 5-11, and Table 5-12 show the experimental K-factor obtained for each

specimen.

For Grade 60, stainless steel, and #5 MMFX bars, the average experimental K-factor were

0.009, 0.012, and 0.0104, respectively. Also, these average K-factors were less than the K-factor

of 0.014 used in the Equation 5-1. Therefore, for all the specimens as Grade 60, Stainless Steel,

and #5 MMFX, the development length calculated was enough either to yield the hooked bar or

in most cases to exceed the anchorage capacity of 1.25 times the yield strength.

In contrast, for #7 MMFX bars, the average experimental K-factor was similar or in some

cases greater than the K-factor of 0.014 (Table 5-12) resulting in insufficient development length

to yield the bar.

Table 5-1. Anchorage capacity ratio for mild steel.

Specimen notation

Pu (kips)

cu f

P'

5500

(kips)

Yield load at 0.35% Pyt (kips)

Anchorage Ratio – test (Pu/Pyt)

Exp. yield load Pye (kips)

Anchorage Ratio -experimental (Pu/Pye)

60_5_90_1 20.2 19.8 19.5 1.02 N.A NA60_5_90_S 25.5 25.0 19.5 1.29 N.A NA60_5_90_25_1 26.5 26.5 19.5 1.36 18.7 1.4260_5_90_25_2 27.0 27.0 19.5 1.39 19.1 1.4160_5_180_35_1 34.6 32.9 19.5 1.69 18.9 1.7460_5_180_35_2 34.8 33.0 19.5 1.70 18.9 1.7560_7_90_1 27.8 27.3 38.2 0.71 N.A NA60_7_90_S 47.0 46.2 38.2 1.21 N.A NA60_7_90_47_1 58.1 58.2 38.2 1.52 38.9 1.5060_7_90_47_2 54.1 54.1 38.2 1.42 39.5 1.3760_7_180_35_1 54.4 50.7 38.2 1.33 40.8 1.2460_7_180_35_2 52.4 48.9 38.2 1.28 31.2 1.5760_7_180_35_3 58.9 54.9 38.2 1.44 36.5 1.5060_7_180_35_4 59.1 55.1 38.2 1.44 36.9 1.49

Table 5-2. Anchorage capacity ratio stainless steel.

Specimen notation

Pu (kips)

cu f

P'

5500

(kips)

Yield load at 0.2% offset Pyt (kips)

Anchorage Ratio – test (Pu/Pyt)

Exp. yield load Pye (kips)

Anchorage Ratio -experimental (Pu/Pye)

SS_16_90_25_1 35.4 33.0 32.93 1.00 32.15 1.03SS_16_90_25_2 33.3 31.0 28.22 1.10 27.44 1.13SS_16_90_35_1 36.7 34.2 32.93 1.04 32.84 1.04SS_16_90_35_2 33.6 31.3 28.22 1.11 28.98 1.08SS_16_180_35_1 36.3 34.5 28.22 1.22 22.62 1.52SS_16_180_35_4 37.4 35.5 28.22 1.26 21.09 1.68SS_20_90_35_1 59.5 56.5 46.53 1.21 39.83 1.42SS_20_90_35_2 59.1 56.1 46.53 1.21 39.75 1.41SS_20_90_35_4 60.4 57.3 46.53 1.23 39.38 1.46SS_20_180_35_1 62.4 59.2 46.53 1.27 40.94 1.45SS_20_180_35_2 62.5 59.4 46.53 1.28 35.15 1.69SS_20_180_35_3 52.5 49.8 46.53 1.07 41.74 1.19SS_20_180_35_4 55.6 52.8 46.53 1.13 38.03 1.39

77

Table 5-3. Anchorage capacity ratio for MMFX steel.

Specimen notation

Pu (kips)

cu f

P'

5500

(kips)

Yield load at 0.2% offset Pyt (kips)

Anchorage Ratio – test (Pu/Pyt)

Exp. yield load Pye (kips)

Anchorage Ratio -experimental (Pu/Pye)

MM_5_90_25_1 49.5 45.7 37.96 1.20 27.6 1.66MM_5_90_25_2 48.6 44.8 37.96 1.18 28.2 1.59MM_5_90_35_1 44.9 41.5 37.96 1.09 33.3 1.25MM_5_90_35_2 49.4 45.6 37.96 1.20 34.6 1.32MM_5_180_35_1 41.0 38.2 37.96 1.01 23.1 1.65MM_5_180_35_2 51.0 47.5 37.96 1.25 32.7 1.45MM_5_180_35_4 52.9 49.3 37.96 1.30 31.4 1.57MM_7_90_35_4 77.2 71.9 76.85 0.94 67.5 1.07MM_7_180_35_2 71.4 67.5 76.85 0.88 65.3 1.03MM_7_180_35_4 70.4 66.5 76.85 0.87 59.6 1.11 Table 5-4. Bond stress normalized for mild steel.

Specimen notation Pu (kips)

cu f

P'

5500

(kips) ls (in) db (in) umax (ksi) umax/f'c1/2

60_5_90_1 20.2 19.8 5.48 0.625 1.8 24.4 60_5_90_S 25.5 25.0 3.48 0.625 3.7 48.5 60_5_90_25_1 26.5 26.5 4.54 0.625 3.0 40.2 60_5_90_25_2 27.0 27.0 4.54 0.625 3.0 40.9 60_5_180_35_1 34.6 32.9 4.03 0.625 4.2 53.2 60_5_180_35_2 34.8 33.0 4.03 0.625 4.2 53.4 60_7_90_1 27.8 27.3 7.53 0.875 1.3 17.4 60_7_90_S 47.0 46.2 5.53 0.875 3.0 40.2 60_7_90_47_1 58.1 58.2 6.5 0.875 3.3 43.9 60_7_90_47_2 54.1 54.1 6.5 0.875 3.0 40.9 60_7_180_35_1 54.4 50.7 5.5 0.875 3.4 42.2 60_7_180_35_2 52.4 48.9 5.5 0.875 3.2 40.6 60_7_180_35_3 58.9 54.9 6.5 0.875 3.1 38.6 60_7_180_35_4 59.1 55.1 6.5 0.875 3.1 38.7

78

Table 5-5. Bond stress normalized for stainless steel.

Specimen notation Pu (kips)

cu f

P'

5500

(kips) ls (in) db (in) umax (ksi) umax/f'c1/2

SS_16_90_25_1 35.4 33.0 9.53 0.625 1.8 22.1 SS_16_90_25_2 33.3 31.0 9.53 0.625 1.7 20.8 SS_16_90_35_1 36.7 34.2 9.53 0.625 1.8 22.9 SS_16_90_35_2 34.2 31.3 9.53 0.625 1.7 21.0 SS_16_180_35_1 36.3 34.5 8.53 0.625 2.1 26.3 SS_16_180_35_2 37.3 35.4 8.53 0.625 2.1 27.1 SS_16_180_35_3 35.1 33.3 9.53 0.625 1.8 22.8 SS_16_180_35_4 37.4 35.5 9.53 0.625 1.9 24.3 SS_20_90_35_1 59.5 56.5 9.86 0.787 2.3 29.7 SS_20_90_35_2 59.1 56.1 9.86 0.787 2.3 29.5 SS_20_90_35_3 58.5 55.6 10.86 0.787 2.1 26.5 SS_20_90_35_4 60.4 57.3 10.86 0.787 2.1 27.3 SS_20_180_35_1 62.4 59.2 9.86 0.787 2.4 31.1 SS_20_180_35_2 62.5 59.4 9.86 0.787 2.4 31.2 SS_20_180_35_3 52.5 49.8 10.86 0.787 1.9 23.8 SS_20_180_35_4 55.6 52.8 10.86 0.787 2.0 25.2 Table 5-6. Bond stress normalized for MMFX steel.

Specimen notation Pu (kips)

cu f

P'

5500

(kips) ls (in) db (in) umax (ksi) umax/f'c1/2

MM_5_90_25_1 49.5 45.7 11.54 0.625 2.0 25.1 MM_5_90_25_2 48.6 44.8 11.54 0.625 2.0 24.6 MM_5_90_35_1 44.9 41.5 11.54 0.625 1.8 22.8 MM_5_90_35_2 49.4 45.6 11.54 0.625 2.0 25.1 MM_5_180_35_1 41.0 38.2 9.50 0.625 2.1 25.8 MM_5_180_35_2 51.0 47.5 9.50 0.625 2.5 32.1 MM_5_180_35_3 47.4 44.3 11.54 0.625 2.0 24.6 MM_5_180_35_4 52.9 49.3 11.54 0.625 2.2 27.4 MM_7_90_25_1 69.9 63.8 15.50 0.875 1.5 18.4 MM_7_90_25_2 71.7 65.4 15.50 0.875 1.5 18.9 MM_7_90_35_1 58.3 53.2 15.50 0.875 1.2 15.4 MM_7_90_35_2 65.8 60.0 15.50 0.875 1.4 17.3 MM_7_90_35_3 58.9 54.9 15.50 0.875 1.3 16.2 MM_7_90_35_4 77.2 71.9 15.50 0.875 1.7 21.2 MM_7_180_35_1 59.3 56.0 11.54 0.875 1.8 22.5 MM_7_180_35_2 71.4 67.5 11.54 0.875 2.1 27.1 MM_7_180_35_3 67.6 63.9 15.50 0.875 1.5 19.1 MM_7_180_35_4 70.4 66.5 15.50 0.875 1.6 19.9

79

Table 5-7. Ductility ratio for mild steel.

Specimen notation

Pu (kips)

cu f

P'

5500

(kips)

Strain at Pu (Su) (in/in)

Strain at 0.35% yield (Sy) (in/in)

Ductility Ratio (Su/Sy)

60_5_90_25_1 26.5 26.5 0.0580 0.0035 16.6 60_5_90_25_2 27.0 27.0 0.0579 0.0035 16.6 60_5_180_35_1 34.6 32.9 0.0699 0.0035 20.0 60_5_180_35_2 34.8 33.0 0.0701 0.0035 20.0 60_7_90_47_2 54.1 54.0 0.0347 0.0035 9.9 60_7_180_35_1 54.4 50.7 0.0261 0.0035 7.5 60_7_180_35_2 52.4 48.9 0.0248 0.0035 7.1 60_7_180_35_3 58.9 54.9 0.0361 0.0035 10.3 60_7_180_35_4 59.1 55.1 0.0433 0.0035 12.4 Table 5-8. Ductility ratio for stainless steel.

Specimen notation

Pu (kips)

cu f

P'

5500

(kips)

Strain at Pu (Su) (in/in)

Strain at 0.2% offset yield (Sy) (in/in)

Ductility Ratio (Su/Sy)

SS_16_90_25_1 35.4 33.0 0.1856 0.0062 30.2 SS_16_90_25_2 33.3 31.0 0.1896 0.0056 34.2 SS_16_90_35_1 36.7 34.2 0.1682 0.0062 27.4 SS_16_90_35_2 33.6 31.3 0.2090 0.0056 37.7 SS_16_180_35_1 36.3 34.5 0.2256 0.0056 40.6 SS_16_180_35_4 37.4 35.5 0.1939 0.0056 34.9 SS_20_90_35_1 59.5 56.5 0.0466 0.0058 8.1 SS_20_90_35_2 59.1 56.1 0.0175 0.0058 3.0 SS_20_90_35_4 60.4 57.3 0.0266 0.0058 4.6 SS_20_180_35_1 62.4 59.2 0.0645 0.0058 11.2 SS_20_180_35_2 62.5 59.4 0.0635 0.0058 11.0 SS_20_180_35_3 52.5 49.8 0.0099 0.0058 1.7 SS_20_180_35_4 55.6 52.8 0.0116 0.0058 2.0

80

Table 5-9. Ductility ratio for MMFX steel.

Specimen notation

Pu (kips)

cu f

P'

5500

(kips)

Strain at Pu (Su) (in/in)

Strain at 0.2% offset yield (Sy) (in/in)

Ductility Ratio (Su/Sy)

MM_5_90_25_1 49.5 45.7 0.0440 0.0065 6.8 MM_5_90_25_2 48.6 44.8 0.0590 0.0065 9.1 MM_5_90_35_1 44.9 41.5 0.0165 0.0065 2.5 MM_5_90_35_2 49.4 45.6 0.0414 0.0065 6.4 MM_5_180_35_1 41.0 38.2 0.0147 0.0065 2.3 MM_5_180_35_2 51.0 47.5 0.0247 0.0065 3.8 MM_5_180_35_4 47.4 44.3 0.0130 0.0065 2.0 MM_7_90_25_1 52.9 49.3 0.0370 0.0065 5.7 MM_7_90_25_2 71.7 65.4 0.0052 0.0067 0.8 MM_7_90_35_1 58.3 53.2 0.0013 0.0067 0.2 MM_7_90_35_2 65.8 60.0 0.0038 0.0067 0.6 MM_7_90_35_3 58.9 54.9 0.0066 0.0067 1.0 MM_7_90_35_4 77.2 71.9 0.0089 0.0067 1.3 MM_7_180_35_1 59.3 56.0 0.0053 0.0067 0.8 MM_7_180_35_2 71.4 67.5 0.0077 0.0067 1.2 MM_7_180_35_3 67.6 63.9 0.0021 0.0067 0.3 MM_7_180_35_4 70.4 66.5 0.0103 0.0067 1.5 Table 5-10. K-factor for #5 and #7 mild steel bars.

Specimen notation

f'c (psi)

fs (peak) (psi)

ldh tested (in) db (in) ldh / db fs / f'c0.5 K

60_5_90_S 5700 82226 6 0.625 9.60 1089.11 0.008860_5_90_25_1 5490 85514 7 0.625 11.20 1154.12 0.009760_5_90_25_2 5490 86986 7 0.625 11.20 1173.99 0.009560_5_180_35_1 6100 111600 7 0.625 11.20 1428.89 0.007860_5_180_35_2 6100 112201 7 0.625 11.20 1436.59 0.007860_7_90_S 5700 78350 9 0.875 10.29 1037.77 0.009960_7_90_47_1 5490 96865 10 0.875 11.43 1307.32 0.008760_7_90_47_2 5490 90110 10 0.875 11.43 1216.15 0.009460_7_180_35_1 6330 90706 9 0.875 10.29 1140.08 0.009060_7_180_35_2 6330 87406 9 0.875 10.29 1098.60 0.009460_7_180_35_3 6330 98150 10 0.875 11.43 1233.64 0.009360_7_180_35_4 6330 98450 10 0.875 11.43 1237.41 0.0092

81

Table 5-11. K-factor for 16 mm and 20 mm stainless steel bars.

Specimen notation f'c (psi)

fs (peak) (psi)

ldh tested (in) db (in) ldh / db fs / f'c0.5 K

SS_16_90_25_1 6350 113546 12 0.625 19.20 1424.90 0.0135SS_16_90_25_2 6350 106613 12 0.625 19.20 1337.90 0.0144SS_16_90_35_1 6350 117785 12 0.625 19.20 1478.10 0.0130SS_16_90_35_2 6350 109561 12 0.625 19.20 1374.89 0.0140SS_16_180_35_1 6100 116314 11 0.625 17.60 1489.25 0.0118SS_16_180_35_2 6100 119583 11 0.625 17.60 1531.11 0.0115SS_16_180_35_3 6100 112436 12 0.625 19.20 1439.59 0.0133SS_16_180_35_4 6100 119836 12 0.625 19.20 1534.35 0.0125SS_20_90_35_1 6150 128962 13 0.787 16.52 1651.19 0.0100SS_20_90_35_2 6150 128001 13 0.787 16.52 1638.89 0.0101SS_20_90_35_3 6150 126845 14 0.787 17.79 1624.08 0.0110SS_20_90_35_4 6150 130792 14 0.787 17.79 1674.62 0.0106SS_20_180_35_1 6150 135149 13 0.787 16.52 1730.40 0.0095SS_20_180_35_2 6150 135456 13 0.787 16.52 1734.33 0.0095SS_20_180_35_3 6150 113708 14 0.787 17.79 1455.88 0.0122SS_20_180_35_4 6150 120405 14 0.787 17.79 1541.62 0.0115 Table 5-12. K-factor for #5 and #7 MMFX bars.

Specimen notation f'c (psi)

fs (peak) (psi)

ldh tested (in) db (in) ldh / db fs / f'c0.5 K

MM_5_90_25_1 6450 172919 14 0.625 22.40 2153.09 0.0104MM_5_90_25_2 6450 169641 14 0.625 22.40 2112.28 0.0106MM_5_90_35_1 6450 156954 14 0.625 22.40 1954.31 0.0115MM_5_90_35_2 6450 172534 14 0.625 22.40 2148.31 0.0104MM_5_180_35_1 6320 141781 12 0.625 19.20 1783.45 0.0108MM_5_180_35_2 6320 176188 12 0.625 19.20 2216.24 0.0087MM_5_180_35_3 6320 164023 14 0.625 22.40 2063.23 0.0109MM_5_180_35_4 6320 182788 14 0.625 22.40 2299.27 0.0097MM_7_90_25_1 6600 127619 20 0.875 22.86 1570.89 0.0146MM_7_90_25_2 6600 130814 20 0.875 22.86 1610.21 0.0142MM_7_90_35_1 6600 106386 20 0.875 22.86 1309.52 0.0175MM_7_90_35_2 6600 120097 20 0.875 22.86 1478.30 0.0155MM_7_90_35_3 6330 105349 20 0.875 22.86 1324.13 0.0173MM_7_90_35_4 6330 137982 20 0.875 22.86 1734.28 0.0132MM_7_180_35_1 6170 104625 17 0.875 19.43 1331.97 0.0146MM_7_180_35_2 6170 126112 17 0.875 19.43 1605.51 0.0121MM_7_180_35_3 6170 119386 20 0.875 22.86 1519.89 0.0150MM_7_180_35_4 6170 124289 20 0.875 22.86 1582.31 0.0144

82

83

Anc

hora

ge C

apac

ity R

atio

0

0.4

0.8

1.2

1.6

2

2.4

60_5

_90_

25

60_5

_180

_35

60_7

_90_

47

60_7

_180

_35_

1&2

60_7

_180

_35_

3&4

Limit Value = 1.25

A

Anc

hora

ge C

apac

ity R

atio

0

0.4

0.8

1.2

1.6

2

2.4

SS_16_

90_2

5

SS_16_

90_3

5

SS_16_

180_

35_1

SS_16_

180_

35_4

SS_20_

90_3

5

SS_20_

90_3

5_4

SS_20_

180_

35_1

&2

SS_20_

180_

35_3

&4

Limit Value = 1.25

B

Anc

hora

ge C

apac

ity R

atio

0

0.4

0.8

1.2

1.6

2

2.4

MM_5_9

0_25

MM_5_9

0_35

MM_5_1

80_3

5_1&

2

MM_5_1

80_3

5_4

MM_7_9

0_35

_4

MM_7_1

80_3

5_2&

4

MM_7_9

0_25

_1&2

MM_7_9

0_35

_1&2

MM_7_1

80_3

5_1&

3

Limit Value = 1.25

• < 1.0 Specimen did not yield

C

igure 5-1. Anchorage capacity ratios A) Mild steel, B) Stainless steel, and C) MMFX steel.

F

Bon

d St

ress

, um

ax/f'

c1/2

0

20

40

60

80

60_5

_90_

1

60_7

_90_

1

60_5

_90_

S

60_7

_90_

S

60_5

_90_

25_1

&2

60_7

_90_

47_1

&2

60_5

_180

_35_

1&2

60_7

_180

_35_

1&2 -

60_7

_180

_35_

1&2

24.37

48.5443.19

53.30

0

17.45

40.24 41.68 41.41 38.67

A

Bon

d St

ress

, um

ax/f'

c1/2

0

10

20

30

40

50

SS_16_

90_2

5

SS_20_

90_3

5_1&

2

SS_16_

90_3

5

SS_20_

90_3

5_3&

4

SS_16_

90_3

5_1

SS_20_

180_

35_1

&2

SS_16_

180_

35_4

SS_20_

190_

35_3

&4

21.4* 22*

26.7*

23.5*

29.626.9

31.1

24.5

* Bar yield no rupture stroke limit reached

B

Bon

d St

ress

, um

ax/f'

c1/2

0

10

20

30

40

50

MM_5_9

0_25

MM_7_9

0_25

MM_5_9

0_35

MM_7_9

0_35

MM_5_1

80_3

5_1&

2

MM_7_1

80_3

5_1&

2

MM_5_1

80_3

5_3&

4

MM_7_1

80_3

5_3&

4

24.9 23.9

28.926.0

18.7 17.5

24.8

19.5

C Figure 5-2. Comparison of normalized bond stress at capacity A) Mild steel, B) Stainless steel,

and C) MMFX steel.

84

85

Duc

tility

Rat

io

0

5

10

15

20

25

60_5

_90_

25_1

60_5

_90_

25_2

60_5

_180

_35_

1

60_5

_180

_35_

2

60_7

_90_

47

60_7

_180

_35_

1

60_7

_180

_35_

2

60_7

_180

_35_

3

60_7

_180

_35_

4

A

Duc

tility

Rat

io

0

15

30

45

SS_16_

90_2

5_1

SS_16_

90_2

5_2

SS_16_

90_3

5_1

SS_16_

90_3

5_2

SS_16_

180_

35_1

SS_16_

180_

35_4

SS_20_

90_3

5_1

SS_20_

90_3

5_2

SS_20_

90_3

5_4

SS_20_

180_

35_1

SS_20_

180_

35_2

SS_20_

180_

35_3

SS_20_

180_

35_4

B

Duc

tility

Rat

io

0

2

4

6

8

10

MM_5_9

0_25

_1

MM_5_9

0_25

_2

MM_5_9

0_35

_1

MM_5_9

0_35

_2

MM_5_1

80_3

5_1

MM_5_1

80_3

5_2

MM_5_1

80_3

5_4

MM_7_9

0_35

_4

MM_7_1

80_3

5_2

MM_7_1

80_3

5_4

MM_7_9

0_25

_1&2

MM_7_9

0_35

_1&2

MM_7_1

80_3

5_1&

3

• • •

• < 1.0 no yield

C Figure 5-3. Comparison of ductility ratios A) Mild steel, B) Stainless steel, and C) MMFX steel.

CHAPTER 6 CONCLUSIONS

Based on experimental observations, the following conclusions are made:

1. The test setup and the procedures using the strut and tie approach appear to

provide an adequate basis to evaluate the unconfined anchorage capacities of grade 60 hooked

bars. The predominant failure mode generated using this test setup was splitting of the concrete

in the plane of the hook. Mild steel gave results consistent and agreeable with ACI and

AASHTO requirements for development lengths.

2. The anchorage capacity was improved in specimen configurations using the strut

and tie approach in comparison with confined specimens using stirrups.

3. Anchorage capacities obtained in grade 60, stainless steel, and #5 MMFX bars

were above the limit value of 1.25 times the yield strength of the bar.

4. The anchorage capacity ratio was greater for grade 60 specimens with 180-degree

than specimens with 90-degree bend angle. Also, the anchorage capacity increased as the

development length increased for #7 mild steel specimens with 180-degree.

5. For all mild steel specimens was noted that the displacement at yield point

increased by an average of 53% as the strut angle and the development length increased.

6. For 90 degree hooked bars, the average ductility ratio for 16 mm stainless steel

was greater than #5 grade 60, and #5 MMFX about 164% and 420% respectively. Also, for 180

degree hooked bars, the average ductility ratio for 16 mm stainless steel was greater than #5

grade 60, and #5 MMFX about 155% and 864% respectively.

7. Average bond stress for #5 grade 60 was greater than 16 mm stainless steel, and

#5 MMFX specimens about 88% and 66% respectively. Also, for # 7 grade 60, the average bond

stress was greater than 20 mm stainless steel and #7 MMFX specimens about 43% and 96%

86

87

respectively. On the other hand, the bond stress for #5 grade 60, and #5 MMFX specimens were

greater than #7 grade 60, and #7 MMFX specimens about 12% and 33% respectively.

Based on the results obtained from this study, most of the #7 MMFX hooked bar did not

develop the minimum anchorage capacity proposed in the existing provisions of both AASHTO

and ACI 318.

Further investigation need to be conducted to evaluate the proper development length for

#7 MMFX hooked bars.

APPENDIX A CONCRETE COMPRESSIVE STRENGTH AND TENSILE RESULTS

Table A-1. Compressive concrete strength results –age (days). Concrete Strength (psi) - Age (days)

Batches 7 14 21 28 1 4670 5850 6320 -2 3490 4420 5050 58903 6350 6690 - 80604 5170 6320 6670 71605 4170 5330 6150 6880 Table A-2. Tensile test results.

#5 Grade 60

Samples Yield Strength at 0.35% strain (ksi)

Strain at 0.35% yield (in/in)

Load at 0.35% strain (kip)

Ultimate Strength (ksi)

1 62.777 0.0035 19.461 104.642 62.744 0.0035 19.451 104.81Avg. 62.761 0.0035 19.456 104.73COV (%) 0.037 0.00 0.04 0.115

#7 Grade 60

Samples Yield Strength at 0.35% strain (ksi)

Strain at 0.35% yield (in/in)

Load at 0.35% strain (kip)

Ultimate Strength (ksi)

1 63.506 0.0035 38.103 105.902 63.955 0.0035 38.373 105.93Avg. 63.73 0.0035 38.238 105.92COV (%) 0.498 0.00 0.499 0.020

16 mm Stainless Steel

Samples Yield Strength at 0.2% offset (ksi)

Strain at 0.2% offset yield (in/in)

Load at 0.2% offset (kip)

Ultimate Strength (ksi)

1 106.213 0.0061 32.926 123.872 106.205 0.0062 32.924 123.75Avg. 106.209 0.00615 32.925 123.81COV (%) 6.09 1.23 6.09 0.182

20 mm Stainless Steel

Samples Yield Strength at 0.2% offset (ksi)

Strain at 0.2% offset yield (in/in)

Load at 0.2% offset (kip)

Ultimate Strength (ksi)

1 99.865 0.0058 48.534 120.312 91.615 0.0057 44.525 120Avg. 95.74 0.00575 46.530 120.155COV (%) 0.953 0.19 0.95 0.317

88

Table A-2. Continued. #5 MMFX

Samples Yield Strength at 0.2% offset (ksi)

Strain at 0.2% offset yield (in/in)

Load at 0.2% offset (kip)

Ultimate Strength (ksi)

1 123.273 0.00648 38.215 157.792 121.622 0.00650 37.703 158.50Avg. 122.448 0.00649 37.959 158.14COV (%) 0.009 2.11 0.01 0.135

#7 MMFX

Samples Yield Strength at 0.2% offset (ksi)

Strain at 0.2% offset yield (in/in)

Load at 0.2% offset (kip)

Ultimate Strength (ksi)

1 128.089 0.0066 76.854 163.122 128.073 0.0068 76.844 162.81Avg. 128.081 0.0067 76.849 162.97COV (%) 0.009 2.11 0.01 0.135

89

APPENDIX B CRACKS PATTERNS, LOAD-SLIP, AND LOAD-DISPLACEMENT

Top Front Rear Bottom

Right Left

60_5_90_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

60_5_90_S

Bar Rupture

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_5_90_1

0 0.05 0.1 0.15 0.20

5

10

15

20

25

30

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_5_90_S

0 0.05 0.1 0.15 0.20

5

10

15

20

25

30

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_5_90_1 vs. 60_5_90_S

0 0.08 0.16 0.24 0.320

4

8

12

16

20

24

28

0

20

40

60

80

100

120

60_5_90_160_5_90_S

Figure B-1. Crack patterns, load-slip, and stress-strain curves for mild steel hooked bars.

90

Top Front Rear Bottom

Right Left

60_5_90_25_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

60_5_90_25_2

Bar yield followed by concrete splitting

Right Left

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_5_90_25_2

0 0.05 0.1 0.15 0.20

5

10

15

20

25

30

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_5_90_25_1 vs. 60_5_90_25_2

-0.01 0.04 0.09 0.14 0.190

5

10

15

20

25

30

0

20

40

60

80

100

120

-0.01 0.04 0.09 0.14 0.190

5

10

15

20

25

30

0

20

40

60

80

100

120

60_5_90_25_160_5_90_25_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-Strain60_5_90_25_1 vs. 60_5_90_25_2

-0.01 0.01 0.03 0.050

20

40

60

80

100

0

150

300

450

600

60_5_90_25_160_5_90_25_2

Figure B-1. Continued.

91

60_5_180_35_1

Bar Rupture

Top Front Rear Bottom

Right Left

60_5_180_35_2

Bar Rupture

Top Front Rear Bottom

Right Left

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_5_180_35_1

0 0.05 0.1 0.15 0.20

6

12

18

24

30

36

0

20

40

60

80

100

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_5_180_35_2

0 0.05 0.1 0.15 0.20

6

12

18

24

30

36

0

20

40

60

80

100

0 0.05 0.1 0.15 0.20

6

12

18

24

30

36

0

20

40

60

80

100

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_5_180_35_1 vs. 60_5_180_35_2

0 0.06 0.12 0.18 0.24 0.30

6

12

18

24

30

36

0

25

50

75

100

125

150

60_5_180_35_160_5_180_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-Strain60_5_180_35_1 vs. 60_5_180_35_2

0 0.02 0.04 0.06 0.080

20

40

60

80

100

120

0

150

300

450

600

750

60_5_180_35_160_5_180_35_2

Figure B-1. Continued.

92

Top Front Rear Bottom

Right Left

60_7_90_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

60_7_90_S

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_7_90_1

0 0.04 0.08 0.12 0.160

10

20

30

40

50

60

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_7_90_S

0 0.04 0.08 0.12 0.160

10

20

30

40

50

60

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_7_90_1 vs. 60_7_90_S

0 0.025 0.05 0.075 0.10

10

20

30

40

50

60

0

40

80

120

160

200

240

60_7_90_160_7_90_S

Figure B-1. Continued.

93

Top Front Rear Bottom

Right Left

60_7_90_47_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

60_7_90_47_2

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load_Slip for Linear Pots60_7_90_47_2

0 0.08 0.16 0.24 0.320 0

10 17

20 33

30 50

40 67

50 83

60 100

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_7_90_47_1 vs. 60_7_90_47_2

0 0.15 0.3 0.45 0.60

10

20

30

40

50

60

0

40

80

120

160

200

240

60_7_90_47_160_7_90_47_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-Strain60_7_90_47_1 vs. 60_7_90_47_2

-0.01 0.01 0.03 0.050

20

40

60

80

100

0

150

300

450

600

60_7_90_47_160_7_90_47_2

Figure B-1. Continued.

94

Top Front Rear Bottom

Right Left

60_7_180_35_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

60_7_180_35_2

Bar yield followed by concrete splitting

Right Left

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_7_180_35_1

0 0.08 0.16 0.24 0.320

10

20

30

40

50

60

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_7_180_35_2

0 0.08 0.16 0.24 0.320

10

20

30

40

50

60

0

15

30

45

60

75

90

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_7_180_35_1 vs. 60_7_180_35_2

0 0.05 0.1 0.15 0.20

10

20

30

40

50

60

0

40

80

120

160

200

240

0 0.05 0.1 0.15 0.20

10

20

30

40

50

60

0

40

80

120

160

200

240

60_7_180_35_160_7_180_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-Strain60_7_180_35_1 vs. 60_7_180_35_2

0 0.008 0.016 0.024 0.0320

20

40

60

80

100

0

150

300

450

600

0 0.008 0.016 0.024 0.0320

20

40

60

80

100

0

150

300

450

600

60_7_180_35_160_7_180_35_2

Figure B-1. Continued.

95

Top Front Rear Bottom

60_7_180_35_3

Bar yield followed by concrete splitting

Right Left

Top Front Rear Bottom

60_7_180_35_4

Bar yield followed by concrete splitting

Right Left

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_7_180_35_3

0 0.1 0.2 0.3 0.4 0.50

10

20

30

40

50

60

70

0

15

30

45

60

75

90

105

Linear Pot 1Linear Pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear Pots60_7_180_35_4

0 0.1 0.2 0.3 0.4 0.50

10

20

30

40

50

60

70

0

15

30

45

60

75

90

105

Linear Pot 1Linear Pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-Displacement60_7_180_35_3 vs. 60_7_180_35_4

0 0.08 0.16 0.24 0.320

10

20

30

40

50

60

70

0

40

80

120

160

200

240

280

60_7_180_35_360_7_180_35_4

Strain (in./in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-Strain60_7_180_35_3 vs. 60_7_180_35_4

0 0.01 0.02 0.03 0.04 0.050

15

30

45

60

75

90

105

0

100

200

300

400

500

600

700

60_7_180_35_360_7_180_35_4

Figure B-1. Continued.

96

Top Front Rear Bottom

Right Left

SS_16_90_25_1

Bar yield no rupture stroke limit reached

Top Front Rear Bottom

Right Left

SS_16_90_25_2

Bar yield no rupture stroke limit reached

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_90_25_1

0 0.08 0.16 0.24 0.320

8

16

24

32

40

0

25

50

75

100

125

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_90_25_2

0 0.08 0.16 0.24 0.320

8

16

24

32

40

0

25

50

75

100

125

Linear pot 1Linear pot 2

Displacment (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacmentSS_16_90_25_1 vs. SS_16_90_25_2

0 0.15 0.3 0.45 0.60

8

16

24

32

40

0

30

60

90

120

150

180

SS_16_90_25_1SS_16_90_25_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainSS_16_90_25_1 vs. SS_16_90_25_2

0 0.06 0.12 0.18 0.240

20

40

60

80

100

120

0

150

300

450

600

750

SS_16_90_25_1SS_16_90_25_2

Figure B-2. Crack patterns, load-slip, and stress-strain curves for stainless steel hooked bars.

97

Top Front Rear Bottom

Right Left

SS_16_90_35_1

Bar yield no rupture stroke limit reached

Top Front Rear Bottom

Right Left

SS_16_90_35_2

Bar yield no rupture stroke limit reached

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_90_35_1

0 0.1 0.2 0.3 0.4 0.50

8

16

24

32

40

0

25

50

75

100

125

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_90_35_2

0 0.1 0.2 0.3 0.4 0.50

8

16

24

32

40

0

25

50

75

100

125

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_16_90_35_1 vs. SS_16_90_35_2

0 0.25 0.5 0.75 10

8

16

24

32

40

0

30

60

90

120

150

180

SS_16_90_35_1SS_16_90_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress_StrainSS_16_90_35_1 vs. SS_16_90_35_2

0 0.06 0.12 0.18 0.240

20

40

60

80

100

120

0

150

300

450

600

750

SS_16_90_35_1SS_16_90_35_2

Figure B-2. Continued.

98

Top Front Rear Bottom

Right Left

SS_16_180_35_1

Bar yield no rupture stroke limit reached

Top Front Rear Bottom

Right Left

SS_16_180_35_2

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_180_35_1

0 0.1 0.2 0.3 0.4 0.50

10

20

30

40

0

30

60

90

120

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_180_35_2

0 0.1 0.2 0.3 0.4 0.50

10

20

30

40

0

30

60

90

120

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_16_180_35_1 vs. SS_16_180_35_2

0 0.25 0.5 0.75 10

8

16

24

32

40

0

30

60

90

120

150

180

SS_16_180_35_1SS_16_180_35_2

Strain (in/in.)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainSS_16_180_35_1 vs. SS_16_180_35_2

0 0.06 0.12 0.18 0.240

20

40

60

80

100

120

140

0

150

300

450

600

750

900

SS_16_180_35_1SS_16_180_35_2

Figure B-2. Continued.

99

Top Front Rear Bottom

Right Left

SS_16_180_35_3

Bar Rupture

Top Front Rear Bottom

Right Left

SS_16_180_35_4

Bar yield no rupture stroke limit reached

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_180_35_3

0 0.1 0.2 0.3 0.40

10

20

30

40

0

30

60

90

120

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_16_180_35_4

0 0.1 0.2 0.3 0.40

10

20

30

40

0

30

60

90

120

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_16_180_35_3 vs. SS_16_180_35_4

0 0.2 0.4 0.6 0.80

10

20

30

40

0

40

80

120

160

SS_16_180_35_3SS_16_180_35_4

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainSS_16_180_35_3 vs. SS_16_180_35_4

0 0.06 0.12 0.18 0.240

20

40

60

80

100

120

140

0

150

300

450

600

750

900

SS_16_180_35_3SS_16_180_35_4

Figure B-2. Continued.

100

Top Front Rear Bottom

Right Left

SS_20_90_35_1

Bar yield followed by concrete splitting

SS_20_90_35_2

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_90_35_1

0 0.06 0.12 0.18 0.24 0.30

10

20

30

40

50

60

70

0

20

40

60

80

100

120

140

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_90_35_2

0 0.06 0.12 0.18 0.24 0.30

10

20

30

40

50

60

70

0

20

40

60

80

100

120

140

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_20_90_35_1 vs. SS_20_90_35_2

0 0.06 0.12 0.18 0.24 0.30

15

30

45

60

75

0

60

120

180

240

300

SS_20_90_35_1 SS_20_90_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainSS_20_90_35_1 vs. SS_20_90_35_2

0 0.01 0.02 0.03 0.04 0.050

20

40

60

80

100

120

140

0

150

300

450

600

750

900

SS_20_90_35_1SS_20_90_35_2

Figure B-2. Continued.

101

Top Front Rear Bottom

Right Left

SS_20_90_35_3

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

SS_20_90_35_4

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_90_35_3

0 0.06 0.12 0.18 0.24 0.30

10

20

30

40

50

60

70

0

20

40

60

80

100

120

140

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_90_35_4

0 0.06 0.12 0.18 0.24 0.30

10

20

30

40

50

60

70

0

20

40

60

80

100

120

140

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_20_90_35_3 vs. SS_20_90_35_4

-0.02 0.02 0.06 0.1 0.140

20

40

60

80

0

80

160

240

320

SS_20_90_35_3SS_20_90_35_4

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainSS_20_90_35_3 vs. SS_20_90_35_4

-0.005 0.005 0.015 0.0250

20

40

60

80

100

120

140

0

150

300

450

600

750

900

SS_20_90_35_3SS_20_90_35_4

Figure B-2. Continued.

102

SS_20_180_35_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

SS_20_180_35_2

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_180_35_1

0 0.05 0.1 0.15 0.2 0.250

20

40

60

80

0

40

80

120

160

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_180_35_2

0 0.05 0.1 0.15 0.2 0.250

20

40

60

80

0

40

80

120

160

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_20_180_35_1 vs. SS_20_180_35_2

0 0.1 0.2 0.3 0.40

20

40

60

80

0

80

160

240

320

SS_20_180_35_1SS_20_180_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (K

N)

Stress-StrainSS_20_180_35_1 vs. SS_20_180_35_2

0 0.02 0.04 0.06 0.080

20

40

60

80

100

120

140

0

150

300

450

600

750

900

SS_20_180_35_1SS_20_180_35_2

Figure B-2. Continued.

103

Top Front Rear Bottom

Right Left

SS_20_180_35_3

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

SS_20_180_35_4

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_180_35_3

0 0.04 0.08 0.12 0.16 0.20

10

20

30

40

50

60

0

20

40

60

80

100

120

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsSS_20_180_35_4

0 0.04 0.08 0.12 0.16 0.20

10

20

30

40

50

60

0

20

40

60

80

100

120

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementSS_20_180_35_3 vs. SS_20_180_35_4

0 0.02 0.04 0.06 0.080

10

20

30

40

50

60

0

50

100

150

200

250

SS_20_180_35_3SS_20_180_35_4

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainSS_20_180_35_3 vs. SS_20_180_35_4

0 0.003 0.006 0.009 0.0120

25

50

75

100

125

0

150

300

450

600

750

SS_20_180_35_3SS_20_180_35_4

Figure B-2. Continued.

104

Top Front Rear Bottom

Right Left

MM_5_90_25_1

Bar rupture

Top Front Rear Bottom

Right Left

MM_5_90_25_2

Bar rupture

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_90_25_1

0 0.03 0.06 0.09 0.120

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_90_25_2

0 0.03 0.06 0.09 0.120

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_5_90_25_1 vs. MM_5_90_25_2

0 0.04 0.08 0.12 0.160

10

20

30

40

50

60

0

40

80

120

160

200

240

MM_5_90_25_1MM_5_90_25_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_5_90_25_1 vs. MM_5_90_25_2

0 0.02 0.04 0.06 0.080

30

60

90

120

150

180

0

200

400

600

800

1000

1200

MM_5_90_25_1MM_5_90_25_2

Figure B-2. Continued.

105

Top Front Rear Bottom

Right Left

MM_5_90_35_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

MM_5_90_35_2

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_90_35_1

0 0.08 0.16 0.24 0.320

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_90_35_2

0 0.08 0.16 0.24 0.320

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_5_90_35_1 vs. MM_5_90_35_2

0 0.04 0.08 0.12 0.16 0.20

10

20

30

40

50

60

0

40

80

120

160

200

240

MM_5_90_35_1MM_5_90_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_5_90_35_1 vs. MM_5_90_35_2

0 0.01 0.02 0.03 0.04 0.050

30

60

90

120

150

180

0

200

400

600

800

1000

1200

MM_5_90_35_1MM_5_90_35_2

Figure B-3. Crack patterns, load-slip, and stress-strain curves for MMFX hooked bars.

106

Top Front Rear Bottom

Right Left

MM_5_180_35_1

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

MM_5_180_35_2

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_180_35_1

0 0.02 0.04 0.06 0.08 0.10

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_180_35_2

0 0.02 0.04 0.06 0.08 0.10

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_5_180_35_1 vs. MM_5_180_35_2

0 0.025 0.05 0.075 0.10

10

20

30

40

50

60

0

40

80

120

160

200

240

MM_5_180_35_1MM_5_180_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_5_180_35_1 vs. MM_5_180_35_2

0 0.007 0.014 0.021 0.0280

30

60

90

120

150

180

0

200

400

600

800

1000

1200

MM_5_180_35_1MM_5_180_35_2

Figure B-3. Continued.

107

Top Front Rear Bottom

Right Left

MM_5_180_35_3

Bar yield followed by concrete splitting

Top Front Rear Bottom

Right Left

MM_5_180_35_4

Bar rupture

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_180_35_3

0 0.06 0.12 0.18 0.240

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_5_180_35_4

0 0.06 0.12 0.18 0.240

10

20

30

40

50

60

0

30

60

90

120

150

180

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_5_180_35_3 vs. MM_5_180_35_4

0 0.04 0.08 0.12 0.160

10

20

30

40

50

60

0

40

80

120

160

200

240

MM_5_180_35_3MM_5_180_35_4

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_5_180_35_3 vs. MM_5_180_35_4

0 0.01 0.02 0.03 0.040

30

60

90

120

150

180

0

200

400

600

800

1000

1200

MM_5_180_35_3MM_5_180_35_4

Figure B-3. Continued.

108

Top Front Rear Bottom

Right Left

MM_7_90_25_1

Concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_90_25_1

0 0.1 0.2 0.3 0.40

20

40

60

80

0

60

120

180

240

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_90_25_2

0 0.1 0.2 0.3 0.40

20

40

60

80

0

60

120

180

240

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_7_90_25_1 vs. MM_7_90_25_2

0 0.008 0.016 0.024 0.0320

20

40

60

80

0

80

160

240

320

MM_7_90_25_1MM_7_90_25_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress_StrainMM_7_90_25_1 vs. MM_7_90_25_2

0 0.0015 0.003 0.0045 0.0060

25

50

75

100

125

0

150

300

450

600

750

MM_7_90_25_1MM_7_90_25_2

Figure B-3. Continued.

109

Top Front Rear Bottom

Right Left

MM_7_90_35_1

Bar cast out of position

Top Front Rear Bottom

Right Left

MM_7_90_35_2

Bar cast out of position

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_90_35_1

0 0.08 0.16 0.24 0.320

20

40

60

80

0

30

60

90

120

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip ComparisonMM_7_90_35_2

0 0.08 0.16 0.24 0.320

20

40

60

80

0

30

60

90

120

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_7_90_35_1 vs. MM_7_90_35_2

0 0.008 0.016 0.024 0.0320

20

40

60

80

0

80

160

240

320

MM_7_90_35_1MM_7_90_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_7_90_35_1 vs. MM_7_90_35_2

0 0.001 0.002 0.003 0.0040

20

40

60

80

100

120

0

150

300

450

600

750

MM_7_90_35_1MM_7_90_35_2

Figure B-3. Continued.

110

Top Front Rear Bottom

Right Left

MM_7_90_35_3

Concrete splitting

Top Front Rear Bottom

Right Left

MM_7_90_35_4

Bar yield followed by concrete splitting

Displacement (in)

Loa

d (k

ip)

Loa

d (K

N)

Load_DisplecementMM_7_90_35_3 vs. MM_7_90_35_4

0 0.02 0.04 0.06 0.080

20

40

60

80

0

80

160

240

320

MM_7_90_35_3MM_7_90_35_4

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_7_90_35_3 vs. MM_7_90_35_4

0 0.002 0.004 0.006 0.008 0.010

40

80

120

160

0

300

600

900

MM_7_90_35_3MM_7_90_35_4

Figure B-3. Continued.

111

Top Front Rear Bottom

Right Left

MM_7_180_35_1

Concrete Splitting

Top Front Rear Bottom

Right Left

MM_7_180_35_2

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_180_35_1

0 0.05 0.1 0.15 0.20

20

40

60

80

0

30

60

90

120

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_180_35_2

0 0.05 0.1 0.15 0.20

20

40

60

80

0

30

60

90

120

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_7_180_35_1 vs. MM_7_180_35_2

0 0.015 0.03 0.045 0.060

20

40

60

80

0

80

160

240

320

MM_7_180_35_1MM_7_180_35_2

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_7_180_35_1 vs. MM_7_180_35_2

0 0.002 0.004 0.006 0.0080 0

32 224

64 448

96 672

128 896

MM_7_180_35_1MM_7_180_35_2

Figure B-3. Continued.

112

113

Top Front Rear Bottom

Right Left

MM_7_180_35_3

Concrete Splitting

Top Front Rear Bottom

Right Left

MM_7_180_35_4

Bar yield followed by concrete splitting

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_180_35_3

0 0.1 0.2 0.3 0.40

20

40

60

80

0

30

60

90

120

Linear pot 1Linear pot 2

Slip (in.)

Loa

d (k

ip)

Stre

ss (k

si)

Load-Slip for Linear PotsMM_7_180_35_4

0 0.1 0.2 0.3 0.40

20

40

60

80

0

30

60

90

120

Linear pot 1Linear pot 2

Displacement (in.)

Loa

d (k

ip)

Loa

d (K

N)

Load-DisplacementMM_7_180_35_3 vs. MM_7_180_35_4

0 0.02 0.04 0.06 0.080

20

40

60

80

0

80

160

240

320

MM_7_180_35_3MM_7_180_35_4

Strain (in/in)

Stre

ss (k

si)

Stre

ss (M

Pa)

Stress-StrainMM_7_180_35_3 vs. MM_7_180_35_4

0 0.003 0.006 0.009 0.0120

25

50

75

100

125

0

150

300

450

600

750

MM_7_180_35_3MM_7_180_35_4

Figure B-3. Continued.

LIST OF REFERENCES

AASHTO (2001). “ Standard Specifications for Highway Bridges.” American Association of States Highway and Transportation Officials.

ACI 408.1R-79 (1979). “Suggested Development, Splice, and Standard Hook Provisions for Deformed Bars in Tension.” American Concrete Institute.

ACI Committee 318 (1977). “Building Code Requirements for Reinforced Concrete (ACI 318-77).” American Concrete Institute.

ACI Committee 318 (1995). “Building Code Requirements for Reinforced Concrete (ACI 318-95).” American Concrete Institute.

ACI Committee 318 (2002). “Building Code Requirements for Reinforced Concrete (ACI 318-02).” American Concrete Institute.

ASTM A 370 (2007). “Standard Test Methods and Definitions for Mechanical Testing of Steel Products.” American Society for Testing and Materials.

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Pinc, R.L., Watkins, M.D. and Jirsa, J.O (1977). “Strength of Hooked Bar Anchorages in Beam-Column Joints.” CESRL Report No. 77-3, Department of Civil Engineering, The University of Texas, Austin, Texas.

BIOGRAPHICAL SKETCH

Gianni T. Ciancone was born in Caracas, Venezuela, to Maria Teresa and Raffaele

Ciancone. He received his Bachelor of Science in Civil Engineering in Summer of 1993 from the

University of Santa Maria, Venezuela. Gianni worked in a Power Company for 14 years in

several positions not only in the Design and Construction field but also in the Business field.

Gianni continued his education by entering graduate school to pursue a Master of

Engineering in the Structural Group of the Civil and Coastal Engineering Department at the

University of Florida in Fall 2005. During his stay at the University of Florida, Gianni worked as

graduated research assistant for Dr. H.R. Hamilton III. Gianni plans to pursue a career in the

field of structural engineering.

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