JSCE specifications on stainless steel bars and new...

JSCE specifications on stainless JSCE specifications on stainless steel bars and newsteel bars and newanchorage/splice technologiesanchorage/splice technologies

Takumi ShimomuraNagaoka University of Technology

JAPAN SOCIETY OF CIVIL ENGINEERSJAPAN SOCIETY OF CIVIL ENGINEERS

Standard Specifications for Standard Specifications for Concrete StructuresConcrete Structures

2007 editionDesignMaterials and ConstructionMaintenanceDam ConcreteTest Methods and Specifications for Concrete


Recommendations and Recommendations and GuidelinesGuidelines

Recent publications:Recommendations on Environmental Performance Verification for Concrete Structures (Draft)Recommendations for Mix Design of Fresh Concrete and Construction Placement related Performance EvaluationRecommendations for Design and Construction of High Performance FiberReinforced Cement Composite with Multiple Fine Cracks (HPFRCC)Ancient Roman Concrete


Publications in EnglishPublications in EnglishMost JSCE Standard Specifications for Concrete Structures, Recommendations and Guidelines have been translated into English.You can purchase them from our web site. http://www.jsce.or.jp/

JSCE Standards on Test Method for Diffusion Coefficient of Chloride Ion in Concrete

RECOMMENDATIONS FOR SHOTCRETING (DRAFT)

STANDARD SPECIFICATIONS FOR CONCRETE STRUCTURES-2002 "Structural Performance Verification"

STANDARD SPECIFICATIONS FOR CONCRETE STRUCTURES -2002 "Seismic Performance Verification"


Topics todayTopics today

Recommendations for Design, Fabrication and Evaluation of Anchorages and Joints in Reinforcing Bars [2007] (August 2007)Recommendations for Design and Construction of Concrete Structures Using Stainless Steel Bars –Draft- (August 2008)


Anchorages and Joints in Reinforcing Bars

Anchorages and Joints in Anchorages and Joints in Reinforcing BarsReinforcing Bars


Background of revision of the Background of revision of the guidelineguideline


Previous guideline on joints in reinforcing bars was published in 1982.Reinforcing bar arrangement has become denser due to highly required seismic performance.A lot of technologies of anchorages and joints have been developed.The design methods of concrete structures have been shifted to the performance-based design, recently.



Characteristics of new editionCharacteristics of new edition

Anchorages in reinforcing bars are included as well as joints.Joints are evaluated not only by their performance but also considering the reliability of construction and inspection, which are practically significant.


Anchoring methodsAnchoring methods

Mechanical anchoring methods involving the installation of anchorage elements at the ends of reinforcing bars,Methods using the bond strength between concrete and reinforcing bars



mechanical anchorage

bonding

bearing

conventional anchorage

Development of mechanical Development of mechanical anchorageanchorage


Mechanical anchorage was developed to reduce complexity in arrangement of reinforcement.Benefit:

improvement of constructabilityshorten construction periodcost downimprovement of reliability in compaction of concrete


Variation in mechanical Variation in mechanical anchorageanchorage

Flash-welded anchorage

Threaded deformed bar anchorage

Friction-welded anchorage

Enlarged-ended bar anchorage



Verification method for Verification method for anchorageanchorage


If the anchorage under consideration follows the performance requirements for the performance items, which is necessary at the design stage such as strength and pullout resistance, high-stress cyclic loading capacity, and fatigue strength, the mechanical anchorage may be needed for design purposes to be equivalent to a standard hook.


Performance evaluation criteria Performance evaluation criteria for anchorages for anchorages

steel rod or invar wire

transducer

reference hook anchorage specimen

mechanical anchorage specimen



Examples of test results of Examples of test results of static strength (D16)static strength (D16)

0.25 0.50 0.75 1.00 1.25

100

200

300

400

500

0

pullout (mm)

stre

ss(N

/mm

2 )

Mechanical anchorage reference hook



(2)<(3)

(1) difference in pullout under upper limit stress during thirtieth loading cycle between mechanical anchorage and reference hook

(2) difference in pullout of mechanically anchored reinforcing bar between thirties and first loading cycles

(3) difference in pullout of reinforcing bar anchored by reference hook between thirtieth and first loading cycles

pullout

(2)(3)

stre

ss

0.95fyn

0.02fyn

mechanical anchorage

reference hook anchorage

(1)


Examples of results of Examples of results of highhigh--stress stress cyclic loading testcyclic loading test

Jointing methodsJointing methodsPressure-welded jointingWelded jointingMechanical jointingLap jointing (conventional)



Pressure-welded jointing

Welded jointing

Lap jointing (conventional)

concrete

Mechanical jointing

General (for joints)General (for joints)


(1) It must be verified that all joint zones meet the performance requirements.

(2) The steel joints to be used must be selected appropriately according to such factors as the type of steel to be used as base metal, bar diameter, the state of stress, joint location and joint performance requirements.

(3) For all materials to be used for steel joints, it must be verified in advance that those materials conform to relevant quality standards such as JIS.

(4) When steel joints are used, their reliability resulting fromconstruction and inspection must be taken into consideration.

(5) Steel joints should not be located as much as possible in cross sections in which large stresses occur.

(6) Steel joints should be spaced apart and should not be concentrated in a cross section as much as possible.


Examples of construction of jointExamples of construction of joint



Examples of inspection of jointExamples of inspection of jointAnchorages and Joints in Reinforcing Bars


Reliability resulting from Reliability resulting from construction and inspection construction and inspection


The reliability of reinforcing bar joints resulting from construction and inspection is classified in three classes: I, II and III.

Reliability determined by the reject rate of joints

Reliability of jointReject rate of joints considering reliability of construction and inspection

reject rate of joints

Level I The reject rate of joints is extremely low. 0.3% or less

Level II The reject rate of joints is low. 5% or less

Level III The reject rate of joints is at or below a certain level.

15% or less


Reliability of joint affected by Reliability of joint affected by construction and inspection construction and inspection

Reliability of jointReliability of joint

Attentiveness of construction workers

Qualification Response to evaluation result

Human action

Accuracy Human error

Sampling ratio

Reliability of constructionReliability of construction

Reliability of inspectionReliability of inspection

Skills of construction workers



Construction level and Construction level and inspection levelinspection level


(i) Construction levels1: The probability of occurrence of a defective joint is extremely low,

and few defective joints are produced unintentionally.2: The probability of occurrence of a defective joint is sufficiently low.3: The probability of occurrence of a defective joint is low.

(ii) Inspection levels1: The probability of judging a defective joint to be acceptable is

extremely low, and, as a general rule, a supervisor inspects all joints and few defective joints are overlooked.

2: The probability of judging a defective joint to be acceptable is sufficiently low.

3: The probability of judging a defective joint to be acceptable is low.



Reliability of joints determined by Reliability of joints determined by construction and inspection levelsconstruction and inspection levels

Inspection levelConstruction level

1 2 3

1 Level I Level I Level II

2 Level I Level II Level III

3 Level II Level III Level III


Stainless Steel Bars

Stainless Steel BarsStainless Steel Bars


Background of stainless steel Background of stainless steel barsbars

Reinforcement corrosion in concrete due to chloride ingress or carbonation is most serious problem to reduce durability of concrete structures in Japan.Countermeasure to reinforcement corrosion:

low W/C concreteconcrete admixturesthick concrete coversurface protectionepoxy-coated barsFRP reinforcementelectrochemical corrosion control method

JIS for Stainless steel bars for concrete reinforcement was established in 2008.



epoxy-coated bars

reinforcement corrosion

Type of stainless steelType of stainless steelStainless Steel Bars

SUS304 (18%Cr-8%Ni, ASTM:A276 304)Basic steel alloy most widely used as stainless steel.

SUS316 (16%Cr-10%Ni-2%Mo, ASTM:A276 316)

More corrosion-resistant steel alloy obtained by adding molybdenum to SUS304.

SUS410L (12%Cr-LowC, ASTM:A276 410L)Chromium stainless steel with a controlled alloy content.

Corrosion-resistance: SUS316 > SUS304 > SUS410


Tests on corrosionTests on corrosion--resistance resistance of stainless steel barsof stainless steel bars


Bare steel in solutionEmbedded in mortarEmbedded in concreteExposed to actual corrosive environmentTouching with different kind of metaletc.


Corrosion test in solutionCorrosion test in solutionStainless Steel Bars

Potentiostat Solution

Reference Electrode

Thermostatic Tank (40deg)

Counter electrode

Specimen

3 types of solutionsNo.1: pH9.1-9.7 No.2: pH11.9-12.6 No.3: pH13.2-13.4

Duration of test：48hourscorrosion criterion ：0.5mA/cm2


Results of corrosion test in solutionResults of corrosion test in solution

corroded not corrodedin 0.5% Cl- in 0%

conventional carbon steel

corroded not corrodedin 0.5% Cl- in 0% Cl-

stainless steel: SUS410L


pH 12.6

corroded not corrodedin 4.0% Cl- in 3.0% Cl-

stainless steel: SUS304

corroded not corrodedin 8.5% Cl- in 8.0% Cl-

stainless steel: SUS316

Corrosion criterion of chloride Corrosion criterion of chloride concentration in solutionconcentration in solution

0

2

4

6

8

10

12

14

16

8 9 10 11 12 13 14 15pH

corr

osi

on c

rite

ria(

%)

Carbon steel

SUS410L

SUS304

SUS316



conventional carbon steel

stainless steel

Accelerated corrosion test in concrete

40deg, 10％ NaCl solution, 18.5monthsstainless steel bars: SUS304-SD, SUS316-SD, SUS410-SDconventional carbon steel: SD295Abar diameter: D13cover: 20mmconcrete (W/C 50%)

10％ NaCl溶液

40℃

20mm

crack

10% NaCl solution 10% NaCl solution


specimen without crack specimen with crack


Results of accelerated Results of accelerated corrosion test in concretecorrosion test in concrete

stainless steel: SUS304-SD18.5months, crack width 0.18mm


not corroded not corroded


not corrodedcorroded


conventional carbon steel3months, crack width 0.20mm

0

5

10

15

20

25

0 5 10 15 20

duration time(months)

Concentr

atio

ns

of chlo

ride

ion

(kg/

m3)

SUS410L SUS316 SUS304

seawater

Chloride concentration in Chloride concentration in concrete during the testconcrete during the test



Proposed durability design of Proposed durability design of RC using stainless steel barsRC using stainless steel bars


Verification of corrosion resistance of RC structures by JSCEw < wa

w: crack widthwa: limit value of crack width

Cd < ClimCd: design value of chloride concentration at location of reinforcementClim: threshold value of chloride concentration for onset of corrosion


wCl-

reinforcement

chloride ingress

Chloride concentrationC(x,t)

xCd

x

))2

1.0(1(0

tDc

erfCCd

dcld

⋅

⋅−⋅= γ

Limit value of crack width (Limit value of crack width (wwaa) ) For conventional carbon steel reinforcement

For stainless steel reinforcement


Type of reinforcement

Environmental conditions for reinforcement corrosion

Normal Corrosive Severely corrosive

Deformed bar

Prestressing steel

0.005c 0.004c 0.0035c

0.004c

c: cover < 100mm

Type of stainless steel Limit value of crack width

SUS304-SD

SUS316-SD

0.5mm

0.5mm

min (0.5mm, 0.005c)SUS410-SD

c: cover < 100mmJAPAN SOCIETY OF CIVIL ENGINEERSJAPAN SOCIETY OF CIVIL ENGINEERS


Threshold value of chloride concentration Threshold value of chloride concentration for onset of corrosion (for onset of corrosion (CClimlim) )

1.2 kg/m3 is recommended for conventional carbon steel reinforcementFollowing values are recommended for stainless steel reinforcement


Type of stainless steelThreshold value of chloride concentration for onset of corrosion (kg/m3)

SUS304-SD 15

SUS316-SD 24

SUS410-SD 9

Mechanical properties of Mechanical properties of stainless steel reinforcementstainless steel reinforcement


strengthfatigue strengthstress-strain curveYoung's modulusthermal expansion coefficient


StressStress--strain curvesstrain curves

0

100

200

300

400

500

0 5000 10000 15000 20000

ひずみ(×10-6)

応力

(N/m

m2)

D19

D25

SD345（D19）

0

100

200

300

400

500

0 5000 10000 15000 20000

ひずみ(×10-6)

応力

(N/m

m2)

D19

D25

SD345（D19）

0

100

200

300

400

500

0 5000 10000 15000 20000

ひずみ(×10-6)

応力

(N/m

m2)

D25

D19

SD345(D19）

0

100

200

300

400

500

0 5000 10000 15000 20000

ひずみ(×10-6)

応力

(N/m

m2)

D25

D19

SD345(D19)

similar with conventional

strain hardening

strain (x10-6) strain (x10-6)

strain (x10-6)strain (x10-6)

stre

ss (

N/m

m2 )

stre

ss (

N/m

m2 )

stre

ss (

N/m

m2 )

stre

ss (

N/m

m2 )

SUS340 -SD SUS316 -SD

SUS410 –SD295 SUS410 –SD345JAPAN SOCIETY OF CIVIL ENGINEERSJAPAN SOCIETY OF CIVIL ENGINEERS


Strength and stressStrength and stress--strain strain model for designmodel for designStress-strain model for stainless steel reinforcement

Definition of strength of stainless steel reinforcement

ε

σ

0

f yd

σ=E s・ ε

σ=f yd +E u ・ (ε-ε y )

ε y ε

σ

0

f yd

σ = E s・ ε

σ= f yd

SUS410-SD295 except SUS410-SD295

ε

σ

0

f yk

0.2%

E s




Fatigue propertiesFatigue propertiesSUS304-SD, SUS316-SD: higher fatigue strengthSUS410-SD: fatigue strength is close to estimated by JSCE conventional design equation

100

150

200

250

300

350

400

0 500 1,000 1,500 2,000

破断繰返し数N(×103)

応力

振幅

σ0(N

/m

m2)

示方書式

SUS304-SD

SUS316-SD

SUS410-SD

100

150

200

250

300

350

0 500 1,000 1,500 2,000

破断繰返し数N(×103)

応力

振幅

σ0(N

/m

m2)

示方書式

SUS304-SD


number of loading at fracture N (x103)

stre

ss a

mpl

itude

(N

/mm

2 )

JSCE eq.JSCE eq.

stre

ss a

mpl

itude

(N

/mm

2 )

JSCE equation can be used as well as conventional reinforcement.

sud

spk

a

srd fNf γ

σ⎟⎟⎠

⎞⎜⎜⎝

⎛−= 110190s

ud

spk

a

srd fNf γ

σ⎟⎟⎠

⎞⎜⎜⎝

⎛−= 110190

number of loading at fracture N (x103)D19 D35

Test on seismic performance of RC member using stainless steel

reversed cyclic loading test of RC column specimen

-200

-150

-100

-50

0

50

100

150

200

-150 -100 -50 0 50 100 150

変位(mm)

荷重

（ｋ

N)

displacement (mm)

load

(kN

)

lateralreinforcement (SUS304, D13)

longitudinal reinforcement (SUS304, D25)

loading point




LCC assessment of RC LCC assessment of RC structure using stainless barsstructure using stainless bars



Objective structure: piled pierObjective structure: piled pier

HWL+2.36

LWL+0.00

20.0

(unit: m)

super structure



Calculation conditionCalculation condition

Service life t (year) 50 or 100

Concrete cover c (mm) 70

cement Ordinary Portland Cementconcrete

W/C 0.45

Reinforcement Conventional SUS410-SD SUS304-SD SUS316-SD

Clim（kg/m3） 1.2 9 15 24

Dd（cm2/year） 1.46

Surface chloride C0（kg/m3） 9 or 13


Results: chloride concentration in Results: chloride concentration in concreteconcrete


In case that C0=13kg/m3:conventional steel bars: corroded in 10yearsSUS410-SD: corroded at 43yearsother stainless bars: not corroded

In case that C0=9kg/m3:conventional steel bars: corroded in 10yearsstainless bars: not corroded

year

Chlo

ride

conc

entr

atio

n (k

g/m

3 )

SUS410

conventional steel


Estimation of initial costEstimation of initial cost

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

N S-4 S-7 S-10

初期

建設

費用

の比

Conventional

Assumed material cost of stainless steel

SUS304-SD: 7 times of conventional steel



Calculated initial cost of structure

SUS304-SD: 1.3 times of conventional structure



SUS410-SD SUS304-SD SUS316-SD

Nor

mal

ized

initi

al c

ost



structures using stainless steel

Results of LCC assessmentResults of LCC assessment（（CC00=9kg/m=9kg/m33 ））

0

1

2

3

4

0 10 20 30 40 50 60

LCC

比

時間(年）

B-1(表面被覆）

B-2(電気防食)

S-4(SUS410相当)

S-7(SUS304相当)

S-10(SUS316相当)

100

B-1

B-2

C0=9kg/m3 S-4

year

Nor

mal

ized

LCC

conventional steel + surface coating

conventional steel + electrochemical corrosion protection

LCC of structures using stainless steel

SUS410-SD

LCC of structures using SUS304-SD, SUS316-SD, SUS410-SD are just equal to their Initial Cost because of no corrosion.Due to the maintenance cost, LCC of conventional structures are higher than that of structures using stainless steel.


Results of LCC assessmentResults of LCC assessment（（CC00=13kg/m=13kg/m33 ））

0

1

2

3

4

0 10 20 30 40 50 60

LC

C比

時間(年）

B-1(表面被覆）

B-2(電気防食)

S-4(SUS410相当)

S-7(SUS304相当)

S-10(SUS316相当)

100

B-1

B-2

S-4

C0=13kg/m3

比year

Nor

mal

ized

LCC

conventional steel + surface coating

conventional steel + electrochemical corrosion protection

LCC of structures using stainless steel

SUS410-SD

LCC of structures using SUS304-SD, SUS316-SD are just equal to their Initial Cost because of no corrosion.Structure using SUS410-SD need to be repaired before 43 year due to reinforcement corrosion, which will affect its LCC.



Examples of concrete structures Examples of concrete structures using stainless steel using stainless steel reinforcementreinforcement


LeveeLeveeStainless Steel Bars


Aomori Prefecture MuseumAomori Prefecture Museum



Stone cutters bridge (Hong Kong)Stone cutters bridge (Hong Kong)Stainless Steel Bars

main tower (height: 298m)

cable-stayed bridge (span: 1018m)

2882 ton of stainless steel reinforcements were used.

Design service life: 120years!


KouriKouri ohashiohashi bridge (Okinawa, Japan)bridge (Okinawa, Japan)



PC continuous box girder + PC rigid frame bridge (length: 1960m), constructed in 2004

Stainless steel reinforcementswere adopted in wheel guard portion considering UV ray attack during construction.

severely corrosive environment, severe UV rays

Epoxy-coated reinforcements were mainly adopted.

box girder segment

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