Bond and Development of Deformed Square Reinforcing Bars
-
Upload
wahyuniarsih-sutrisno -
Category
Documents
-
view
11 -
download
0
description
Transcript of Bond and Development of Deformed Square Reinforcing Bars
ACI Structural Journal/May-June 2007 333
ACI Structural Journal, V. 104, No. 3, May-June 2007.MS No. S-2006-182.R1 received May 5, 2006, and reviewed under Institute publication
policies. Copyright © 2007, American Concrete Institute. All rights reserved, includingthe making of copies unless permission is obtained from the copyright proprietors. Pertinentdiscussion including author’s closure, if any, will be published in the March-April2008 ACI Structural Journal if the discussion is received by November 1, 2007.
ACI STRUCTURAL JOURNAL TECHNICAL PAPER
Square deformed reinforcing bars were widely used prior to andduring the transition to circular deformed reinforcing steel uponadoption of ASTM A 305-50, which standardized geometry, weight,deformation height, and spacing requirements. Bond stress anddevelopment lengths for deformed square bars have traditionallybeen computed as equivalent round bars of equal cross-sectionalarea and weight, although this approach has not been validated.Data is presented from archival research on deformed square andcircular reinforcing bars both prior and subsequent to adoptionand implementation of ASTM A 305-50 that provides informationfor assessment of bond and development of deformed squarereinforcing bars in vintage and historic structures. Pullout testresults show that deformed square bars exhibited average bondstress similar to those of round deformed bars. Based on the archivaltest results and the comparisons presented, treatment of deformedsquare bars as equivalent round bars for calculation of developmentlength appears reasonable and conservative.
Keywords: bond stress; development length; reinforcement.
INTRODUCTIONSquare deformed reinforcing bars were widely used in
concrete building and bridge construction throughout thefirst half of the twentieth century. As these structures age,begin to deteriorate, or undergo use changes, the questions ofremaining capacity and available service life become importantfor making rehabilitation and retrofit decisions. The currentAASHTO’s “Manual for Conditional Evaluation of Bridges”1
and ASCE’s “Guideline for Structural Condition Assessment ofExisting Buildings”2 provide general guidelines for assessmentof concrete bridges and buildings, respectively, in terms ofconcrete compressive strength and reinforcement yieldstrength, but neither guide addresses treatment of differentreinforcing bar geometries, critical for assessment of bothflexural and shear capacity, given the move toward sectionalanalysis methods.
A focus of the archival literature was on service performancedriven by the allowable stress design philosophy used bydesigners of the day. As a result, little of the historic data areavailable to specifically characterize the development lengthnecessary to achieve yielding of the reinforcing. However,sufficient data are available to support recommendations forassessing bond of deformed square reinforcing bars incomparison with deformed round reinforcing bars.
Standardization of deformed reinforcing barsConcrete reinforcing bars evolved during the early part of
the twentieth century to the standardized round bars that areused today. Prior to standardization of geometries anddeformations, however, a wide array of different bar typeswere used. Many were patented systems and employedunique cross-sectional shapes and deformations to enhancebond between the concrete and steel, examples of which canbe seen in Fig. 1 from Abrams’3 early work. Of the manydifferent bar types available, round and square bars were
predominant and square bars were broadly used, particularly fordesigns requiring large bar sizes. While smooth (undeformed)bars were also used, deformed bars were recognized early onto provide superior bond. Due to wide variations in deforma-tion height and geometric patterns used throughout the early1900s, however, consistent bond stresses were not assured.In 1946, Clark4 developed a method of rating many differentpatterns of reinforcing bars based on their average bond stress atseveral predetermined slip values. His investigation led toASTM A 305-47T,5 later adopted as ASTM A 305-49.6 Thespecification provided standard deformation heights andspacing for round bars and also included deformationpatterns for three square bars that corresponded to equivalentround areas (1-1/4 in. square = No. 11; 1-1/8 in. square = No. 10;1 in. square = No. 9). The specification was modified thefollowing year as ASTM A 305-507 and excluded square
Title no. 104-S33
Bond and Development of Deformed Square Reinforcing Barsby Daniel A. Howell and Christopher Higgins
Fig. 1—Reinforcing bars used in Abrams’3 tests.
334 ACI Structural Journal/May-June 2007
bars entirely. Nonetheless, square bars continued to be usedwell into the late 1950s and were still referenced to theASTM A 305 specification on construction documents. It isof interest to note that the current ASTM A 6158 specificationfor deformed reinforcing bars remains identical to the ASTMA 305-507 specification as it pertains to the bar size anddeformation geometry, as seen in Table 1.
Current development length requirementsThe current ACI equation for development length9 is
based on several factors, but the most relevant term for thisinvestigation relates to the bar size and the relevance of thebar cross section on bond efficiency. The simplifieddevelopment length formulas from ACI 318-05 for round
bars with clear spacing not less than 2db and clear cover notless than db are
for No. 6 reinforcing bar and smaller (1a)
for No. 7 reinforcing bar and larger (1b)
If the previous clear spacing and cover requirements arenot met, the simplified development length formulas are
for No. 6 reinforcing bar and smaller (2a)
ldfyψtψeλ
25 fc′-------------------⎝ ⎠⎜ ⎟⎛ ⎞
db=
ldfyψtψeλ
20 fc′-------------------⎝ ⎠⎜ ⎟⎛ ⎞
db=
ld3fyψtψeλ
50 fc′-----------------------⎝ ⎠⎜ ⎟⎛ ⎞
db=
ACI member Daniel A. Howell is a Graduate Research Assistant in the Department ofCivil Engineering at Oregon State University, Corvallis, Oreg.
ACI member Christopher Higgins is an Associate Professor in the Department ofCivil Engineering at Oregon State University. His research interests include evaluationand rehabilitation of aging and deteriorated concrete bridges.
Table 1—ASTM A 3056 and ASTM A 6158 reinforcing bar geometry and deformation requirements
ASTM A 305-496
Nominal size, in. (mm)Diameter, in. (mm)
Cross-sectional area, in.2 (mm2)
Perimeter,in. (mm)
Spacing and height of deformations
Maximum gap (chord of 12-1/2% of nominal perimeter), in. (mm)
Maximum average spacing,
in. (mm)Minimum height,
in. (mm)
Rounds
3/8 (9.525) 0.375 (9.525) 0.11 (70.967) 1.178 (29.921) 0.262 (6.655) 0.015 (0.381) 0.143 (3.632)
1/2 (12.7) 0.500 (12.7) 0.20 (129.032) 1.571 (39.903) 0.350 (8.890) 0.020 (0.508) 0.191 (4.851)
5/8 (15.875) 0.625 (15.875) 0.31 (200.000) 1.963 (49.860) 0.437 (11.100) 0.028 (0.711) 0.239 (6.071)
3/4 (19.05) 0.750 (19.05) 0.44 (283.870) 2.356 (59.842) 0.525 (13.335) 0.038 (0.965) 0.286 (7.264)
7/8 (22.225) 0.875 (22.225) 0.60 (387.096) 2.749 (69.825) 0.612 (15.545) 0.044 (1.118) 0.334 (8.484)
1.00 (25.4) 1.000 (25.4) 0.79 (509.676) 3.142 (79.807) 0.700 (17.780) 0.050 (1.27) 0.383 (9.728)
Squares
1.00 (5.400) 1.000 (25.400) 1.00 (645.160) 4.000 (101.600) 0.700 (17.780) 0.050 (1.270) 0.500 (12.700)
1 1/8 (28.575) 1.125 (28.575) 1.27 (819.353) 4.500 (114.300) 0.787 (20.000) 0.056 (1.422) 0.562 (14.275)
1 1/4 (31.750) 1.250 (31.750) 1.56 (1006.450) 5.000 (127.000) 0.875 (22.225) 0.063 (1.600) 0.625 (15.875)
Rounds having sections equivalent to sections of following squares
1.00 (25.400) 1.128 (28.651) 1.00 (645.160) 3.544 (90.018) 0.790 (20.066) 0.056 (1.422) 0.431 (10.947)
1 1/8 (28.575) 1.270 (32.258) 1.27 (819.353) 3.990 (101.346) 0.889 (22.581) 0.064 (1.626) 0.487 (12.370)
1 1/4 (31.750) 1.410 (35.814) 1.56 (1006.450) 4.430 (112.522) 0.987 (25.070) 0.071 (1.803) 0.540 (13.716)
Note: Certain rounds are rolled to sections equivalent to section of squares. Nominal size shall be taken as diameter of plain rounds having same area as corresponding squares.
ASTM A 6158
Bar no.Nominal weight,
lb/ft (N/m)Diameter, in. (mm)
Cross-sectional area, in.2 (mm2)
Perimeter, in. (mm)
Spacing and height of deformations
Maximum gap (chord of 12-1/2% of nominal perimeter), in. (mm)
Maximum average spacing,
in. (mm)Minimum height,
in. (mm)
3 0.376 (5.487) 0.375 (9.525) 0.11 (70.968) 1.178 (29.921) 0.262 (6.655) 0.015 (0.381) 0.143 (3.632)
4 0.668 (9.749) 0.500 (12.700) 0.20 (129.032) 1.571 (39.903) 0.350 (8.890) 0.020 (0.508) 0.191 (4.851)
5 1.043 (15.221) 0.625 (15.875) 0.31 (200.000) 1.963 (49.860) 0.437 (11.100) 0.028 (0.711) 0.239 (6.071)
6 1.502 (21.920) 0.750 (19.050) 0.44 (283.870) 2.356 (59.842) 0.525 (13.335) 0.038 (0.965) 0.286 (7.264)
7 2.044 (29.830) 0.875 (22.225) 0.60 (387.096) 2.749 (69.825) 0.612 (15.545) 0.044 (1.118) 0.334 (8.484)
8 2.670 (38.966) 1.000 (25.400) 0.79 (509.676) 3.142 (79.807) 0.700 (17.780) 0.050 (1.270) 0.383 (9.728)
9 3.400 (49.619) 1.128 (28.651) 1.00 (645.160) 3.544 (90.018) 0.790 (20.066) 0.056 (1.422) 0.431 (10.947)
10 4.303 (62.798) 1.270 (32.258) 1.27 (819.353) 3.990 (101.346) 0.889 (22.581) 0.064 (1.626) 0.487 (12.370)
11 5.313 (77.537) 1.410 (35.814) 1.56 (1006.450) 4.430 (112.522) 0.987 (25.070) 0.071 (1.803) 0.540 (13.716)
14 7.650 (111.643) 1.693 (43.002) 2.25 (1451.610) 5.320 (135.128) 1.185 (30.099) 0.085 (2.159) 0.648 (16.459)
18 13.600 (198.477) 2.257 (57.328) 4.00 (2580.640) 7.090 (180.086) 1.580 (40.132) 0.102 (2.591) 0.864 (21.946)
Note: 1 in. = 25.4 mm.
ACI Structural Journal/May-June 2007 335
for No. 7 reinforcing bar and larger (2b)
where fy equals the yield strength of steel (psi); ψt equals thereinforcement location factor, for bars with more than 12 in.of concrete below them, ψt = 1.3, otherwise ψt = 1.0; ψeequals the coating factor used for epoxy coated bars, foruncoated reinforcement, ψe = 1.0, for epoxy coated bars withcover less than 3db or clear spacing less than 6db, ψe = 1.5,for all other epoxy coated bars, ψe = 1.2; λ equals the light-weight aggregate factor, for lightweight concrete, λ = 1.3,otherwise λ = 1.0; fc′ equals the compressive strength ofconcrete (psi); and db equals the diameter of bar under consider-ation (in.). For uncoated, bottom, round bars in normalweightconcrete, the required development length depends on thebar yield stress, concrete compressive strength, and the bardiameter. The diameter dimension describes the availablebar perimeter by which bond stresses can be developed. Bycomparison, square bars have approximately an 11% largerperimeter than round bars of equivalent area. However, it isnot clear if the square cross-sectional shape can developbond stress as efficiently as round bars.
Experimental methods used forbond stress research
Review of the early literature on bond and anchorage ofreinforcing steel indicated that different researchersemployed a wide array of different specimens, loadingprotocols, material properties, measurement devices, andreference measures. Early investigators such as Abrams3
used pullout tests to analyze bond stress. The specimenconsisted of a bar embedded longitudinally in a concretecylinder or prism with the free or unloaded end of the barprotruding a short distance beyond one end and the loadedend extending a longer fixed distance beyond the concretespecimen. The specimen was placed on a bearing block andtested to failure by either splitting of the concrete or pulloutof the bar. A small number of researchers used lateralrestraints placed along the perimeter of the pullout specimens toprevent splitting of the samples, thus increasing the bondstrength at failure due to the increased constraint.
Alternative test methods were developed because it wasrecognized that the pullout test placed the concretesurrounding the bar in compression and the bar in tension,whereas in practice, both the bar and the concrete are intension. Also, the boundary conditions of the concrete on thebearing plate affected the bond stress. As pointed out byLeonhardt,10 a specimen mounted on a plate or bearing blockinduces friction and produces lateral stresses on the concrete,thereby artificially increasing the measured bond stress.
In spite of the drawbacks, pullout tests remained popularand were used extensively by researchers because the testswere relatively inexpensive and easy to perform, in contrastto alternatives that could produce more realistic stressconditions. Alternative approaches for the pullout testincluded use of a concrete specimen with a bar extendinglongitudinally past the concrete at both ends (double pulloutor tensile specimen), as well as the modified cantileverbeam, beam-end specimen, and full-scale beam tests. Datafrom all of these types of test specimens were used in thesubsequent analyses and the specimen type used in thevarious archival research is reported in Table 2.
ld3fyψtψeλ
40 fc′-----------------------⎝ ⎠⎜ ⎟⎛ ⎞
db=RESEARCH SIGNIFICANCE
The current state of the practice is to treat square bars asequivalent round bars for determining anchorage anddevelopment, although this approach has not been validated.This paper reviews archival technical literature on bond andanchorage of vintage reinforcing bars from the turn of thelast century to the late 1960s to establish recommendationsfor treatment of deformed square reinforcing bars to aid inevaluation of older and historic concrete structures, many ofwhich contain square bars.
ARCHIVAL RESEARCH USED IN STUDYThe specimen details, sorted by researcher, are shown in
Table 2. As seen in this table, many of the tests were on pullouttype specimens without special reinforcing to prevent splittingof the concrete, but several beam tests were also included inthe sample space.
Abrams’3 research in 1913 was the most comprehensivework at the time, involving several hundred pullout tests, butthe concrete strength was low by modern standards (1750 psi[12.07 MPa]). In 1917, Howard11 tested pullout and beamspecimens, but again the concrete strength was relativelylow (1357 psi [9.36 MPa]). Howard’s work included 3/4 in.(19.05 mm) diameter round and 3/4 in. (19.05 mm) squarebars cast vertically and horizontally. His work indicated thatsquare bars developed higher bond stresses than the roundsin both casting positions. Howard also reported that higherbond stress was obtained for bars cast in the vertical position.
In 1920, Slater et al.12 investigated bond stress for barswith anti-corrosive coatings, and used uncoated bars ascontrol specimens. The uncoated bars are used in the currentstudy. In 1936, Gilkey and Ernst13 investigated pullout testsof similar bars in three different strengths of concrete. In1937, Gilkey et al.14 investigated bond strength based on theresults of both traditional pullout tests as well as half beamtests in which specimen strain values were reported using aseries of mirrors projected onto a large grid. In 1937,Wernisch15 investigated both pullout and beam specimens of13 types of round bars with normal- and high-strengthconcrete. Menzel16,28 produced papers in 1939 and 1952 thatincluded round and square pullout specimens. The 1939specimens were cast in prisms with a 1-15/16 in. (49.2 mm)minimum cover based on the contemporary ACI guidelines.The 1952 paper indicated that bars held rigidly in the horizontalposition during casting exhibited reduced bond strengthcompared with horizontal bars permitted to settle a givendistance when cast. The rigidly held bars are included in thecurrent study.
In 1940, Johnston and Cox17 investigated the effect oflocalized surface rust on the bond strength of round andsquare deformed bars using unrusted bars as control specimens.Only the unrusted bars are included in the current study.Watstein18,21 produced papers in 1941 and 1947 thatinvestigated the distribution of bond stress over the embedmentlength in pullout specimens and not simply the maximumaverage bond stress over a given length. In 1945, Watsteinand Seese20 investigated bond efficiency of several bar typesbased on crack width at the outer surface of the concrete,with crack gauges that were mounted at seven locationsalong the length of the specimen. The specimens weremounted into a tensile testing machine that placed both thesteel and concrete in tension. Also in 1945, Kluge and Tuma19
investigated lapped bar splices in beams with two continuousbars placed adjacent to one lapped bar with a clear spacing of
336 ACI Structural Journal/May-June 2007
Table 2—Bond and anchorage tests: 1913-1969
Investigator YearTest type
Spiral reinforced
Boundary conditions
Slip at free or loaded
endConcrete
dimensions Specimen type
No. of tests per data
pointfy,ksi
fy,nominal or
actualfc′ ,psi
Embedment length, in.
Reported stress
Casting position
Abrams3 1913 Pullout Yes Spherical bearing block Free end
8 in.diameter cylinder
1/2 in. square
5 40 Nominal 1750 8.0 0.01 in. slip and at failure Vertical
1/2 in. square
9/16 in. diameter round
1 in. square
1 in. square
1-1/8 in. diameter round
Howard11 1917 Pullout No Spherical bearing block Free end
6.75 in.diameter cylinder
12 x 8 x 8 in.
3/4 in. square 1Varied 38.0 to
40.0
Nominal and actual 1357 12.0 or 8.0 0.01 in. slip
and at failure
Vertical and
horizontal
Slater et al.12 1920 Pullout No Spherical bearing block Free end 6 in. diameter
cylinder 1/2 in. square 2 61.3 Nominal and actual 5500 6.0 0.01 in. slip
and at failure Vertical
Gilkey and Ernst13 1936 Pullout No Spherical
bearing block Free end3 in.
diametercylinder
1/4 in. diameter round
1 65.0 NominalVaried 2360 to
6525
Varied 6.0 to 12.0
0.01 in. slip and at failure Vertical
3/8 in. diameter round
Gilkey et al.14 1937
Pullout NoPlaster of
paris bearing block
Mirrors and dial
gauges at both ends
4 x 4 x 12 in. in length
3/8 in. diameter round
5/8 in. diameter round
3/4 in. diameter round
1Varied 50.0 to
70.6
Nominal and actual
Varied 3040 to
5438
12.0
At failure only Vertical
Beams NoHalf and full simple span
beams
Mirrors and dial
gauges at both ends
Varied 4 x 6 x 42 to 78 in.
in length
12.0 nominal
Wernisch15 1937
Pullout No Spherical bearing block Free end 6 in. diameter
cylinder3/4 in. diameter
round
4Varied 50.0 to
59.0Nominal
Varied 2830 to
76506.0 At failure
only Vertical
Beams 8 stirrups/ beam
Simple span beam Free end 6 x 12 x 36 in.
in lengthVaried 2 to 3
Varied 3310 to
76506.0 nominal At failure
onlyBottom
horizontal
Menzel16 1939 Pullout No Spherical bearing block Free end 4-7/8 x 6 in.
cube
1 in. diameter round 1 40.0 Nominal
Varied 3600 to
6000
Varied 8.25 to 22.0
At failure only
Vertical and
horizontal1 in. square
Johnston and Cox17 1940 Pullout No Spherical
bearing block Free end6 and 10 in.
diameter cylinder
3/8 in. diameter round
6
50.0
Nominal and actual
Varied 2320 to
2580
3.0
At failure only Vertical
1/2 in. diameter round
52.3 4.0
3/4 in. diameter round
46.0 6.0
1 in. square 44.8 8.0
1-1/4 in. square 40.0 10.0
Watstein18 1941 Pullout No Spherical bearing block Free end
6 in. diameter cylinder
3/4 in. diameter round
3Varied 43.3 to
50.1
Nominal and actual
4310 18.0 At failure only
Vertical
Kluge and Tuma19 1945 Beams
Stirrups in outer thirds
Simple span lapped bars NA
7 x 7-1/4 x 96 in. and 13 x 14 x 144 in.
1 in. diameter round
1Varied 45.0 to
61.8
Nominal and actual 4700
Varied 7.75 to 43.0
At failure only
Bottom horizontal1/2 in. diameter
round
Watstein and Seese20 1945 Pullout No Concrete in
tension NA6 in.
diameter cylinder
7/8 in. diameter round 3
Varied 47.0 to
57.0
Nominal and actual 3950 12.0 NA Unknown
Watstein21 1947 Pullout No Spherical bearing block
1/4 point from
Tuckerman gauges
6 in.diameter cylinder
3/4 in. diameter round 5
Varied 43.0 to
48.0
Nominal and actual 4080 8.0 and 12.0 0.01 in. slip
and at failure Vertical
Collier22 1947 Pullout No Spherical bearing block Loaded end
6 in. square cubes and 6 in. diameter
cylinder
7/8 in. diameter round 5 42.0 Nominal 5350 10.5 0.01 in. slip
and at failureBottom
horizontal
Clark23 1949 Pullout Yes Spherical bearing block Free end 8 x 9 x 10 in.
No. 10 round3 40.0 Nominal 3750 10.0 0.01 in. slip Bottom
horizontal1-1/8 in. square
Walker24 1949 Pullout No Spherical bearing block Free end
8 in. diameter cylinder
3/4 in. diameter round 5
Varied 42.4 to
46.8
Nominal and actual
Varied 5730 to
66508.0 0.01 in. slip Vertical
1 in. square
Mains25 1951
Pullout 8 stirrups/ test
Spherical bearing block NA 8 x 12 x
21 in.7/8 in. diameter
round 1 71.5 Nominal
Varied 3460 to
398021.0
At failure only
Bottom horizontal
Beams 10 stirrups/beam Simple span NA 8 x 12.5 x
78 in.
Varied 3760 to
4180
21.0 nominal
Bottom horizontal
Note: 1 in. = 25.4 mm; 1 in.2 = 645 mm2; 1 psi = 6.895 KPa.
ACI Structural Journal/May-June 2007 337
Table 2—Bond and anchorage tests: 1913-1969 (cont.)
Investigator YearTest type
Spiral reinforced
Boundary conditions
Slip at free or loaded
endConcrete
dimensions Specimen type
No. of tests per data
pointfy,ksi
fy, nominal or actual
fc′ , psi
Embedment length, in.
Reported stress
Casting position
Walker26 1951 Pullout No Spherical bearing block Free end
8 in. diameter cylinder
3/4 in.diameter round
10
42.4
Nominal and actual
3410
8.00.01 in. slip
and at failure
Vertical3/4 in. diameter round 46.8 3610
1 in. square 46.5 3950
Chamberlin27 1952 Pullout Yes Spherical bearing block Free end
6 in. square and 9 in. square cubes
1/2 in. diameter round
6 50.0 Nominal 31706.0 0.01 in. slip
and at failure
Vertical3/4 in. diameter
round 9.0
Menzel28 1952 Pullout No Spherical bearing block Loaded end 4-7/8 x 6 in.
cubes
1 in. diameter round 1 45.0 Nominal 3600 22.0 At failure
onlyBottom
horizontal1 in. square
Chinn et al.29 1955 Beams Stirrups in outer third
Simple span lapped bars NA
3.62 to 9 in. x 6 to
7 in. x 87 in.
3/4 in. diameter round 1
Varied 57.0 to
79.0Nominal
Varied 3160 to
7480
Varied 5.5 to 24.0
At failure only
Tophorizontal
Chamberlin30 1956 Beams Wire mesh Simple span beam Free end Varied No. 4 round and
No. 6 round 3Varied 46.0 to
50.0Nominal
Varied 3700 to
5870
Varied 3.0 to 16.0
At failure only
Bottom horizontal
Chamberlin31 1958 Beams None Simple span beam Free end 6 x 6 x
36 in. No. 4 round 1 50.0 Nominal 4500 Varied 6.0 to 12.0
At failure only Horizontal
Mathey and Watstein32 1961
Beams Stirrups in outer third
Overhang simple span NA 8 x 18 x
88 in.No. 4 and No. 8
bars
1No. 4 Bar
114.7 and
No. 8 Bar 97.0
Actual
Varied 3495 to
4485
Varied 7.0 to 18.0
At failure only
Bottom horizontal
Pullout Yes Spherical bearing block Free end
10 in. x 10 in. x varied
1Varied 3235 to
4865
Varied 7.0 to 34.0 Bottom
Ferguson and Thompson33 1962 Beams No Simple span
lapped bars NA
12 to 18.34 in. x 9 to 13 in. x varied
No. 7 bar 1 87.5 NominalVaried 2380 to
5950
Varied 15.75 to 28.0
At failure only NA
Ferguson and Breen34 1965 Beams No Simple span
lapped bars NA VariedNo. 8 bar
2 75.0 Nominal 3000 Varied 18.0 to 84.0
At failure only
Bottom horizontalNo. 11 bar
Untrauer and Henry35 1965 Pullout No Spherical
bearing block Loaded end 6 in. cubeNo. 6 bar
1 92.0 NominalVaried 4480 to
69206.0 At failure
only HorizontalNo. 9 bar
Perry and Thompson36 1966 Eccentric
pullout No Bearing block NA Varied No. 7 bar 1 50.0 NominalVaried 2500 to
50009.0 At failure
only On side
Lababidi37 1967 Eccentric pullout No Bearing block NA Varied No. 6 bar 1 75.0 Nominal
Varied 2600 to
51009.0 At failure
only Vertical
Ferguson and Briceno38 1969 Beams No Simple span
lapped bars NA VariedNo. 8 bar Varied 2 to
4 per beam
Varied 65.0 to
70.0Nominal
Varied 2450 to
4350
Varied 32.0 to 85.0
At failure only On side
No. 11 bar
Perry and Jundi39 1969 Eccentric
pullout No Bearing block NA Varied No. 6 bar 1 75.0 NominalVaried 2200 to
50609.0 At failure
only Vertical
Warren40 1969 Beams Stirrups Simple span overhang NA Varied No. 9 bar Varied 2 to
7 per beam
Varied 74.4 to
90.0
Nominal and actual
Varied 3090 to
4360
Varied 35.0 to 76.0
At failure only Vertical
Note: 1 in. = 25.4 mm; 1 in.2 = 645 mm2; 1 psi = 6.895 KPa.
1-1/2 bar diameters. In 1947, Collier22 investigated the bondstrength of reinforcing bars with several deformation patternsusing pullout tests.
In 1949, Clark23 continued the rating technique from his1946 work based on bar stress at given slip values for severaldifferent bar types. His data provides a large sample space,but is limited because the reported bond stress versus slipcurves were determined from an average of two differentembedment lengths. Despite these drawbacks, Clark showedthat, while deformation area per square inch was an importantfactor in bond strength, the spacing of the deformations andthe area between the lugs—the shearing area—was anequally important factor. He suggested a ratio of 5 to 6 forthe shearing area to bearing area. The current inverse ratio,referred to as the relative rib area by ACI 408.3,24 is similarto those recommended in Clark’s report.
In 1949 and in 1951, Walker24,26 investigated spaced andtied reinforcement using pullout specimens. Spacing of thebars varied from 1-1/8 to 1-7/8 in. (28.6 to 47.6 mm) for the
1949 and 1951 tests, respectively. In 1951, Mains25 lookedinto the distribution of bond stress on embedded bars usingstrain gauges mounted longitudinally inside the bars along aprecut channel in both beams and pullout specimens. Helooked at both hooked and straight plain and deformed barsin both series of tests.
Chamberlin27,30,31 undertook several investigations dealingwith bond strength, publishing three journal articles from1952 through 1958. The 1952 article investigated spacing ofspliced bars in pullout specimens. The specimens werespirally reinforced against bursting and lapped bars werespaced at 1-1/2 in. (38.1 mm). In 1956, Chamberlin continuedto look at the spacing of reinforcement in concrete, this timewith a modified concrete beam. While the previous researchinvolved splicing of bars in pullout specimens, the focus ofthe 1956 work dealt with minimum cover for single parallelreinforcing bars placed in concrete beams. Chamberlin useda beam subjected to two-point loads producing a constantmoment region in the center of the beam. Between the point
338 ACI Structural Journal/May-June 2007
loads, the reinforcing bar was exposed relative to the adjacentconcrete. To account for varying cover requirements, thewidth of the beam at the location of the reinforcing bar variedwith respect to the fixed width of the aforementioned beam.Chamberlin used the modified beam with cover variationsfrom 1/2 to 5-1/2 in. (12.7 to 139.7 mm) including both plainand deformed reinforcement to investigate average bondstrength. The final series of tests in 1958 investigated thespacing of lapped bars as well as the lap length for beamspecimens. The work involved only one type of deformedbar with no lateral reinforcement against bursting.
In 1955, Chinn et al.29 investigated the bond strength of3/4 in. (19.1 mm) diameter round bars in tension lap splicesin beams. The beams failed due to splitting (no stirrups wereincluded in the specimens) of the side or bottom cover.
In 1961, Mathey and Watstein32 investigated the bondstrength of pullout and beam specimens constructed withhigh yield strength (100 ksi [689.8 MPa]) deformed steelbars based on seven development lengths that varied from7 to 34 in. (177.8 to 863.6 mm). Both types of specimenswere reinforced to prevent lateral bursting with the use ofwelded wire fabric and No. 4 stirrups in the outer third of themember for the pullout and beam specimens, respectively.The beam specimens contained single longitudinal reinforcingbars with eccentric bearings to offset any added compressionat the supports, while the pullout specimens were of thetraditional type.
In 1962, Ferguson and Thompson33 investigated thedevelopment length of high strength reinforcing bars (75 ksi[517.4 MPa]) in beams. The bulk of the work concentratedon No. 7 bars without stirrups. A continuation of the initialinvestigation with larger bars by Ferguson and Breen34 in1965 and Ferguson and Briceno38 in 1969 included No. 8and No. 11 bars in a constant width beam with and withoutstirrups simulating the forces in a retaining wall stem.
In 1965, Untrauer and Henry35 looked into the effect ofnormal pressure on bond strength based on pullout tests of highstrength (92 ksi [634.6 MPa]) round deformed reinforcementbars. Specimens with no applied normal stress were used ascontrol specimens and are included in this study. In 1966,Perry and Thompson36 investigated the maximum bondstress with eccentric pullout specimens with instrumentationsimilar to Mains using strain gauges placed inside thereinforcing bars within a center voided area.
Laboratory tests based on static and dynamic repeatedloadings of pullout specimens were performed by Lababidi37 in1967 as part of a thesis work, which was later published byPerry and Jundi39 in 1969. Both these sources used differentdata for static loading of eccentric pullout specimens based onvarying concrete strength and fixed embedment length.
In 1969, Warren40 reported bond strengths for No. 9 barsin beams with stirrups to guard against splitting. Specimenscontained varying beam width, bar spacing, number of barsper beam, and varying embedment length.
PRESENTATION OF RESULTSThe relevant archival test data were used to assess bond
and development of vintage square bars. Round deformedbar data were used for relative comparisons with the squarebar results. Several investigators reported the concretecompressive strength, reinforcement yield strength, andmaximum average bond stress based on the mean value fromseveral tests with no other accompanying statistical data. Inaddition, some investigators reported actual reinforcement
yield stress while others reported only the nominal yieldstress. Test results were reported at failure or at certain slipvalues (the most common being 0.01 in. [0.25 mm]) and ateither the free or loaded end (for pullout specimens), or forsome cases both ends were reported. Consequently, consideringthe wide ranging variability in the available archival data,some limits were required and not all data could becompared across all of the variables. For consistency, thefollowing conventions were used:• All bars were deformed; no plain bars were included in
the sample space.• Bars that were permitted to settle with the surrounding
concrete were not included in the data.• All of the bars were assumed to be adequately encased
by the surrounding concrete.• Concrete cover was based on the dimensions reported
by the authors and the appropriate simplified ACIdevelopment length equations (Eq. (1) or (2)) were used.
• For square bars, an equivalent diameter (to produce equalround and square steel area) was used in the ACI equations.
• Where the average bond stress was reported, thereinforcing bar stress was determined as the bondstress times the bar embedded surface area divided bythe bar cross-sectional area.
• Where the maximum reinforcing bar tensile stress wasreported, the bond stress was determined as the reinforcingbar stress times the cross-sectional area divided by theembedment surface area, with an upper limit on theembedment length of the ACI development length(Eq. (1) or (2)).
• Reinforcing bar stress or bond stress was evaluated attwo reference points: slip of 0.01 in. (0.25 mm) and/orat maximum applied load where reported.
• Evaluations were made with the nominal yield stress and/or the actual yield stress (where reported) for the reinforcingbar material used in the different research studies.
For each archival test result, and using the constraintsdescribed previously, results were categorized according tothe maximum applied force at failure and the applied force ata measured slip of 0.01 in. (0.25 mm). The reported embedmentlength was normalized by the ACI computed requireddevelopment length (Eq. (1) or (2)) and the reinforcing barstress achieved in the test was normalized by the reportednominal or actual yield stress of reinforcement. Bond stresseswere also computed. None of the square bars in the samplespace were reported to explicitly meet the ASTM A 305-496
requirements. As a result, a direct comparison of equivalentround and square bars meeting the ASTM designation wasnot feasible. However, comparisons between round bars thatdid meet the ASTM A 3057 designation (and thus themodern ASTM A 6158 designation) and square bars undersimilar test conditions were made to identify possibledifferences in bond and development between the differentbar types. The dark solid line in Fig. 2 through 9 representsthe ACI required embedment length.
ANALYSIS AND DISCUSSIONAll of the applicable archival test data are shown in Fig. 2
and 3 with the reported maximum applied force and with theapplied force at a measured end slip of 0.01 in. (0.254 mm).These figures include all specimen types and both deformedround and square bars considering both reported nominaland actual yield stress values. Square bar results are isolatedin Fig. 4 and 5 and consisted of pullout specimens only.
ACI Structural Journal/May-June 2007 339
Round bar results are isolated in Fig. 6 and 7 and included alltest specimen types (pullout, eccentric pullouts, and beams).The sample space for bars meeting ASTM A 305-496 isshown in Fig. 8 and 9 according to reinforcing bar size. Thisdata set is representative of reinforcing bar manufacturedfrom the 1950s to the late 1960s. Much of the data in Fig. 8and 9 are from eccentric pullout and beam specimens (defined
herein as alternative specimens) due to changes in the testingmethodology that moved away from direct pullout tests aswell as improvements in metrology. As seen in all thesefigures, there were more test results available with nominalyield stresses for the maximum applied force cases.
Figures 2 and 3 indicate that, regardless of bar type, defor-mation pattern, shape, or spacing, the deformed bars tended
Fig. 2—All test results at maximum force with: (a) reportedactual yield; and (b) reported nominal reinforcing baryield stress (legend at end of paper).
Fig. 3—All test results at slip of 0.01 in. with: (a) reportedactual reinforcing bar yield; and (b) reported nominalreinforcing bar yield stress (legend at end of paper).
Fig. 4—Square bar test results at maximum applied forcewith: (a) reported actual reinforcing bar yield; and (b)reported nominal reinforcing bar yield stress (legend atend of paper).
Fig. 5—Square reinforcing bar test results at slip of 0.01 in.with: (a) reported reinforcing bar yield; and (b) reportednominal reinforcing bar yield stress (legend at end of paper).
340 ACI Structural Journal/May-June 2007
to perform at or above the simplified ACI developmentrequirements (and implied ASTM A 6158/ASTM A 3057
deformations), with only a few exceptions. The bars tendedto develop stress in some proportion to the embedded lengthand the ACI requirements provide a reasonable lower bound.Only a few of the tests were conducted with embedments
beyond the specified ACI development length, but even so,many of the bars were able to achieve bar stresses above theyield stress (nominal or actual). For several of the specimenswhere the actual yield strength was reported, the bars wereable to achieve stresses well into the theoretical strain-hardening range. The idealized upper limit on development
Fig. 6—All pullout test results for round reinforcing bar atmaximum applied force with: (a) reported actual bar yield;and (b) reported nominal reinforcing bar yield stress (legend atend of paper).
Fig. 7—Pullout test results for round reinforcing bar meetingASTM A 305 at maximum applied force with: (a) reportedactual reinforcing bar yield; and (b) reported nominalreinforcing bar yield stress (legend at end of paper).
Fig. 8—All alternative test results for round reinforcing barat maximum applied force with: (a) reported actual reinforcingbar yield; and (b) reported nominal reinforcing bar yield stress(legend at end of paper).
Fig. 9—Alternative test results for round reinforcing barmeeting ASTM A 305 at maximum applied force with: (a)reported actual reinforcing bar yield; and (b) reported nominalreinforcing bar yield stress (legend at end of paper).
ACI Structural Journal/May-June 2007 341
behavior of the bars, denoted by the dark horizontal line,originally illustrated by Kluge and Tuma,19 demonstratesthat after a reinforcing bar is embedded beyond the lengthrequired to develop the yield strength of the bar, no additionalstrength is possible (until the onset of strain hardening,which is commonly disregarded for design/analysis).
Comparison of average bond stresses for the different bartypes was performed to quantitatively identify differences inbond behavior between round and square bars. Averagebond stresses were calculated for the test results withmaximum applied force, where adequate data were available.The average bond stress was taken as that reported or as theapplied force divided by the embedded surface area (with thelength dimension limited to an upper bound of the ACIdevelopment length). The bond stresses developed in thearchival data for both round and square deformed bars areshown in Fig. 10 as a function of the reported concretestrength. The current ACI implied average bond stress forreinforcing bar No. 6 and smaller and reinforcing bar No. 7and larger, as well as the AASHO allowable bond stressesfrom 1949 and 1953 for unanchored bars are shown in thisfigure for reference. The 1949 AASHO allowable bondstress is the most stringent as these were based onnonstandard deformation requirements prior to adoption ofASTM A 305.5 The bond stresses show scatter with nostrong correlation associated with the compressive strengthfor the pullout specimens. There was also scatter from thealternative specimens. The distribution of average bondstress was normalized with respect to fc′ , and normalizedhistograms for the different reinforcing bar and test types areshown in Fig. 11. The pullout tests for both round and square
bars exhibited a normal distribution while the alternative testtypes exhibited log-normal distributions. The statistics forthese results are reported in Table 3 and the idealizeddistributions are shown in Fig. 12. Cumulative distributionfunctions for the normalized average bond stress of thedifferent reinforcing bar and specimen types are shown inFig. 13. As seen in this figure, the square and round pulloutbars have similar normal distributions with reasonably goodfit over the range of values. The square and round pulloutbars have similar mean and the square pullout bars have aslightly smaller coefficient of variation (COV). As a result,no significant differences were observed for the two rein-forcing bar cross-sectional types in similar test conditions.The alternative specimens do not fit well with the normaldistribution, particularly at the upper and lower tails. Thebetter fit was the log-normal distribution, as this adequatelycaptured both the upper and lower tails. Thus, the more realisticstress conditions produced by the alternative test methodsresulted in lower average bond stresses and different distributionof results. The current ACI approach is based on these moremodern findings for round bars with ASTM A 3055 and A 6158
standardized deformations. Without additional data, it is notpossible to tell precisely how square bars might performunder similar alternative test conditions. Based on thesimilarities between round and square deformed bars in thedirect pullout tests (over a range of concrete strength, reinforcingbar material, and different researchers), however, it is anticipatedthat square bars will also show reduced average bondstresses in the more realistic stress conditions. It is furtherassumed, based on the pullout test similarities, that deformedsquare bar bond stresses in alternative test conditions would
Fig. 12—Statistical distributions of normalized averagebond stress for different reinforcing bar and test types.
Fig. 13—Fit of normalized average bond stress distributionsfor different reinforcing bar and test types.
Fig. 10—Average bond stress versus concrete compressivestrength. (Note: 1 psi = 6.89 KPa.)
Fig. 11—Normalized histograms of average bond stressnormalized with respect to √fc′ .
342 ACI Structural Journal/May-June 2007
be of similar magnitude and distribution to those observedfor the deformed round bars.
For the deformed square bars in this study, the normalizedaverage bond stresses were similar to those reported forround bars meeting ASTM A 3055 when using the sidedimension to determine the embedment perimeter. Thus, itappears reasonable to use this value as the reinforcing bargeometry parameter in the ACI development length equations.Using an equivalent round diameter for square bars results indevelopment lengths that are 13% longer then when the sidedimension is used. The difference is relatively small and useof the equivalent diameter is conservative and thusrecommended for analysis purposes.
The round and square bars were also sorted based oncross-sectional area to establish trends associated withreduced bond efficiency for larger bars. Only pullout testresults were used for these comparisons. The normalizedaverage bond stress was shown to decrease as the reinforcingbar cross-sectional area increased, as seen in Fig. 14.Comparison of round and square pullout test results showedthat square bars had slightly higher normalized average bondstress than round bars meeting ASTM A 305,5 except at barssizes above 1.3 in.2 (838.7 mm2), where little data wasavailable. In general, the trends were similar indicating thattransition to longer development lengths for bigger sizedbars is also warranted for square bars, with greater uncertaintyfor square bars above 1 in. (25.4 mm) due to lack of data.
CONCLUSIONSA review of bond and development tests on vintage
deformed square and round reinforcing bars has beenconducted. Experimental results from the available archivalliterature were used to compare the bond performance of
square and round deformed reinforcing bar. The studyincluded bars from the earliest tests of Abrams3 in 1913 tomodern bars up to 1969. The square bars that were reportedin the literature were based on early designs, in which theactual deformation information was not reported, or weremore modern square bars that did not meet the ASTM A 305-496
criteria. Based on review and analysis of the test results, thefollowing conclusions are presented:• Application of the simplified ACI development length
equations to characterize the reinforcing bar stressprovided a reasonable lower bound for both square andround bars across all test types. Similar results werefound for round and square results.
• The ACI approach was similarly conservative for partialreinforcing bar embedments of round and square resultsand indicates that linear interpolation of availablereinforcing bar stress for embedment lengths less thanthe computed development length also appears reasonablefor square reinforcing bar.
• Comparison of average bond stresses for pullout testresults showed that round and square reinforcing bar(computed using the actual perimeter and embedmentlength) have similar normal distributions and squarebars have slightly smaller variability (coefficient ofvariation for square bars was 26.5% compared with32.8 and 34.9% for all round bars and for round barsmeeting ASTM A 305,6 respectively).
• Alternative test types (tensile specimen, modified canti-lever beam, beam-end specimen, and full-scale beamtests) produced lower average bond stresses than pull-out tests for round reinforcing bar and further exhibitedlog-normal distributions. No data from alternative testtypes were available for square reinforcing bar. Giventhe similarities in results between round and squarebars in pullout tests, however, it is anticipated thatsquare reinforcing bar would also exhibit reduced averagebond stress in alternative test conditions.
• Computation of development length using the ACIformula with an equivalent round diameter for squarereinforcing bar results in lengths 13% larger than whenthe side dimension is used. This is conservative andrecommended for practice given the lack of test dataavailable for large square reinforcing bar sizes andalternative test configurations.
FUTURE WORKThe reported investigation was based on bond test results
from previous research conducted in the early 1900s through1969. No square bars meeting ASTM A 305-496 were availablein the archival literature. Therefore, additional tests usingcurrently accepted bond and development evaluation methodsof square bars meeting the deformation requirements of ASTMA 305-507 would be of interest to supplement the database.
ACKNOWLEDGMENTSThe authors wish to thank the Oregon Department of Transportation for
financial support of this research, although the findings and conclusions arethose of the authors and may not represent those acknowledged.
REFERENCES1. AASHTO, Manual for Condition Evaluation of Bridges, American
Association of State Highway and Transportation Officials, Washington,D.C., 2000, pp. 49-72.
2. SEI/ASCE 11-99, “Guideline for Structural Condition Assessment ofExisting Buildings,” American Society of Civil Engineers, 2000, 160 pp.
3. Abrams, D. A., “Tests of Bond between Concrete and Steel,” Bulletin
Table 3—Statistical measures for different reinforcing bar and test types
Reinforcing bar type
Specimen type
Test measure
No. of samples
Mean fb /(f ′c
0.5) COV, %
Square Pullout Maximum force 33 15.4 26.5
All round Pullout Maximum force 115 15.0 32.8
ASTM A 305 round Pullout Maximum
force 29 15.3 34.9
All round Alternative Maximum force 222 8.7 17.1
ASTM A 305 round Alternative Maximum
force 177 8.5 17.3
Fig. 14—Normalized average bond stress for pullout tests ofreinforcing bar with different cross-sectional areas.(Note: 1 in.2 = 645 mm2.)
ACI Structural Journal/May-June 2007 343
No. 71, University of Illinois Engineering Experiment Station, 1913, 239 pp.4. Clark, A. P., “Comparative Bond Efficiency of Deformed Concrete
Reinforcing Bars,” ACI JOURNAL, Proceedings V. 43, No. 11, Nov. 1946,pp. 381-400.
5. ASTM A 305-47, “Minimum Requirements for the Deformations ofDeformed Steel Bars for Concrete Reinforcement,” ASTM International,West Conshohocken, Pa., 1947.
6. ASTM A 305-49, “Minimum Requirements for the Deformations ofDeformed Steel Bars for Concrete Reinforcement,” ASTM International,West Conshohocken, Pa., 1949, 3 pp.
7. ASTM A 305-50, “Minimum Requirements for the Deformations ofDeformed Steel Bars for Concrete Reinforcement,” ASTM International,West Conshohocken, Pa., 1950, 3 pp.
8. ASTM A 615/A 615M-05a, “Standard Specification for Deformedand Plain Carbon-Steel Bars for Concrete Reinforcement,” ASTMInternational, West Conshohocken, Pa., 2005, 6 pp.
9. ACI Committee 318, “Building Code Requirements for StructuralConcrete (ACI 318-05) and Commentary (318R-05),” American ConcreteInstitute, Farmington Hills, Mich., 2005, pp. 194-196.
10. Leonhardt, F., “On the Need to Consider the Influence of LateralStresses on Bond,” Proceedings of the Symposium on Bond and CrackFormation in Reinforced Concrete, V. 1, Stockholm, Sweden, 1958, pp. 29-35.
11. Howard, G. C., “Tests of Bond Between Concrete and Steel,” PhDthesis, Lehigh University, South Bethlehem, Pa., 1917, 70 pp.
12. Slater, W. A.; Richart, F. E.; and Scofield, G. G., “Tests of BondResistance Between Concrete and Steel,” Department of Commerce—Technologic Papers of the Bureau of Standards, No. 173, 1920, 68 pp.
13. Gilkey, H. J., and Ernst, G. C., “Pullout Tests for Bond Resistance ofHigh Elastic Limit Steel Bars,” Proceedings of the Highway ResearchBoard, V. 16, 1936, pp. 82-95.
14. Gilkey, H. J.; Chamberlin, S. J.; and Beal, R. W., “Bond Resistanceof High Elastic Steel Bars, Series of 1937,” Proceedings of the HighwayResearch Board, V. 17, 1937, pp. 150-186.
15. Wernisch, G. R., “Bond Studies of Different Types of ReinforcingBars,” ACI JOURNAL, Proceedings V. 34, No. 11, Nov. 1937, pp. 145-164.
16. Menzel, C. A., “Some Factors Influencing Results of Pull-Out BondTests,” ACI JOURNAL, Proceedings V. 35, No. 6, June 1939, pp. 517-542.
17. Johnston, B., and Cox, K. C., “The Bond Strength of Rusted DeformedBars,” ACI JOURNAL, Proceedings V. 37, No. 9, Sept. 1940, pp. 57-72.
18. Watstein, D., “Bond Stress in Concrete Pull-Out Specimens,” ACIJOURNAL, Proceedings V. 38, No. 9, Sept. 1941, pp. 37-52.
19. Kluge, R. W., and Tuma, E. C., “Lapped Bar Splices in ConcreteBeams,” ACI JOURNAL, Proceedings V. 42, No. 9, Sept. 1945, pp. 13-34.
20. Watstein, D., and Seese, N. A., “Effect of Type of Bar on Width ofCracks in Reinforced Concrete Subjected to Tension,” ACI JOURNAL,Proceedings V. 41, No. 2, Feb. 1945, pp. 293-304.
21. Watstein, D., “Distribution of Bond Stress in Concrete Pull-OutSpecimens,” ACI JOURNAL, Proceedings V. 43, No. 5, May 1947, pp. 1041-1052.
22. Collier, S. T., “Bond Characteristics of Commercial and PreparedReinforcing Bars,” ACI JOURNAL, Proceedings V. 43, No. 6, June 1947,pp. 1125-1134.
23. Clark, A. P., “Bond of Concrete Reinforcing Bars,” ACI JOURNAL,Proceedings V. 46, No. 11, Nov. 1949, pp. 161-184.
24. Walker, W. T., “Spaced and Tied Reinforcing Bar Splices,” LaboratoryReport No. SP-20, Research and Geology Division, U.S. Bureau ofReclamation, 1949, pp. 1-11.
25. Mains, R. M., “Measurement of the Distribution of Tensile and BondStresses Along Reinforcing Bars,” ACI JOURNAL, Proceedings V. 48, No. 11,Nov. 1951, pp. 225-252.
26. Walker, W. T., “Laboratory Tests of Spaced and Tied ReinforcingBars,” ACI JOURNAL, Proceedings V. 47, No. 1, Jan. 1951, pp. 365-372.
27. Chamberlin, S. J., “Spacing of Spliced Bars in Tension Pull-OutSpecimens,” ACI JOURNAL, Proceedings V. 49, No. 12, Dec. 1952, pp. 261-274.
28. Menzel, C. A., “An Investigation of Bond, Anchorage and RelatedFactors in Reinforced Concrete Beams,” Research Department Bulletin 42,Portland Cement Association, Nov. 1952, 114 pp.
29. Chinn, J.; Ferguson, P. M.; and Thompson, J. N., “Lapped Splices inReinforced Concrete Beams,” ACI JOURNAL, Proceedings V. 52, No. 10,Oct. 1955, pp. 201-213.
30. Chamberlin, S. J., “Spacing of Reinforcement in Beams,” ACI JOURNAL,Proceedings V. 53, No. 7, July 1956, pp. 113-134.
31. Chamberlin, S. J., “Spacing of Spliced Bars in Beams,” ACI JOURNAL,Proceedings V. 54, No. 2, Feb. 1958, pp. 689-697.
32. Mathey, R. G., and Watstein, D., “Investigation of Bond in Beam andPull-Out Specimens with High-Yield-Strength Deformed Bars,” ACI JOURNAL,Proceedings V. 57, No. 3, Mar. 1961, pp. 1071-1090.
33. Ferguson, P. M., and Thompson, J. N., “Development Length of HighStrength Reinforcing Bars in Bond,” ACI JOURNAL, Proceedings V. 59, No. 7,July 1962, pp. 887-922.
34. Ferguson, P. M., and Breen, J. E., “Lapped Splices for HighStrength Reinforcing Bars,” ACI JOURNAL, Proceedings V. 62, No. 9,Sept. 1965, pp. 1063-1078.
35. Untrauer, R. E., and Henry, R. L., “Influence of Normal Pressure on BondStrength,” ACI JOURNAL, Proceedings V. 62, No. 5, May 1965, pp. 577-586.
36. Perry, E. S., and Thompson, J. N., “Bond Stress Distribution onReinforcing Steel in Beams and Pullout Specimens,” ACI JOURNAL,Proceedings V. 63, No. 8, Aug. 1966, pp. 865-876.
37. Lababidi, M. F., “Bond Stress Distribution Along Reinforcing BarsSubjected to Repeated Dynamic Loadings,” MS Thesis, the University ofTexas at Austin, Austin, Tex., 1967, 68 pp.
38. Ferguson, P. M., and Briceno, E. A., “Tensile Lap Splices—Part 1:Retaining Wall Type, Varying Moment Zone,” Research Report No. 113-2,Center for Highway Research, the University of Texas at Austin, Austin,Tex. 1969, 31 pp.
39. Perry, E. S., and Jundi, N., “Pullout Bond Stress Distribution UnderStatic and Dynamic Repeated Loadings,” ACI JOURNAL, Proceedings V. 66,No. 5, May 1969, pp. 377-380.
40. Warren, G. E., “Anchorage Strength of Tensile Steel in ReinforcedConcrete Beams,” PhD thesis, Iowa State University, Ames, Iowa, 1969,104 pp.
41. ACI Committee 408, “Bond and Development of Straight ReinforcingBars in Tension (ACI 408R-03),” American Concrete Institute, FarmingtonHills, Mich., 2003, 49 pp.