of Anchor Wedge Parameters on Post Strand...

Effects of Anchor Wedge Dimensional Parameters on Post‐Tensioning Strand Performance

Kevin Q. Walsh, Randy L. Draginis, Richard M. Estes, and Yahya C. Kurama

PTI ConventionNorfolk, VirginiaMay 6, 2014

2002 – 2007Brad Weldon PhD Research at ND

2007 – 2009Kevin Walsh MS Research at ND

• Questions:

– How is PT strand/anchor performance affected by changes in anchorage configuration?

– How is PT strand/anchor performance affected by changes in loading parameters?


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0 2 4 6 8 10 12Time (min.)

Stre

ss (p

si)

0.85fpu

0.40fpu

144”


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0 0.01 0.02 0.03 0.04 0.05Fracture Strain (in./in.)

Frac

ture

Str

ess

(psi

)

ICC (0.5") CYC (0.5")ICC (0.6") CYC (0.6")

Component PublicationRequired Strength (ksi)

Required Strain at

Ultimate Load

Strand/Anchor System

ACI 318‐08 Section 18.21.1 0.95fnominal 2.0%


ACI 423.7‐07 Section 2.6 0.95factual 2.0%


ACI 423.3R‐05 Section 4.1 0.95factual 2.0%


PTI‐2000Section 2.2.1 0.95factual 2.0%

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0 0.01 0.02 0.03 0.04 0.05Fracture Strain (in./in.)

Frac

ture

Str

ess

(psi

)

Without Ring (0.5") With Ring (0.5")Without Ring (0.6") With Ring (0.6")


• Additional question:

– How can strand/anchor performance be reliably improved?


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0.061.1

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2.0

Ultimate strand

strain

(in./in.)

Wedge height, Hw (in.)

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6.75

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7.25

Ultimate strand

strain

(in./in.)

Anchor taper angle, ATA (degrees)

2010 ‐ 2013Hayes Research at ND

Wedge taper angle differential Wedge crown thickness

Wedge Taper Angle Differential

Wedge Thickness Measured at Crown

Wedges Tested

6.87.07.27.47.67.88.08.28.48.68.8

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Wed

ge ta

per a

ngle, W

A(degrees)

Wedge crown thickness, WT (in.)0.5‐in. strand samples 0.6‐in. strand samples

Strand Tested

Component PublicationRequired Strength (ksi)

Required Strain at Ultimate Load

Strand ASTM A416‐06 Section 6

1.00fnominal,factual > fnominal

3.5%


ACI 318‐08 Section 18.21.1 0.95fnominal 2.0%


ACI 423.7‐07 Section 2.6 0.95factual 2.0%


ACI 423.3R‐05 Section 4.1 0.95factual 2.0%


PTI‐2000Section 2.2.1 0.95factual 2.0%

Strand Tested

• VIDEO

Strand Tested for Free‐Length Failure

Strand spool as (in2)fpm,free-length

(ksi)εpf,free-length E (ksi)

0.5A 0.149 286.7 0.0736 28,028

0.5F 0.151 285.5 0.0726 28,767

0.5G 0.151 287.6 0.0680 29,874

0.6A 0.219 280.9 0.0752 27,872

0.6F 0.218 282.5 0.0677 28,811

0.6G 0.220 285.2 0.0675 28,985

Test Program

Dimensional Parameters versus Performance

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Ultimate strand

strain (in./in.)

Wedge thickness, WT (in.)

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Ultimate strand

strain (in./in.)

Wedge taper angle, WA (degrees)

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Ultimate strand

strain (in./in.)

Wedge thickness,WT (in.)

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0.066.8

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Ultimate strand

strain (in./in.)


0.5‐in strand (optimal 8.00±0.25 degrees)

0.5‐in strand (optimal 0.484±0.010 in.) 0.6‐in strand (optimal 0.548±0.010 in.)


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0.560

Coefficient of variatio

n, CV, of

ultim

ate strand

strains

Average wedge thickness, WT (in.)

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Coefficient of variatio

n, CV, of

ultim

ate strand

strains

Average wedge thickness, WT (in.)

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8.8Coefficient of variatio

n, CV, of

ultim

ate strand

strains

Average wedge taper angle, WA (degrees)

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0.76.8

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8.8Coefficient of variatio

n, CV, of

ultim

ate strand

strains

Average wedge taper angle, WA (degrees)

Dimensional Parameters versus Variation in Performance


0.5‐in strand (optimal 0.484±0.010 in.) 0.6‐in strand (optimal 0.548±0.010 in.)


Statistical Validation of ResultsStrand spool

Anchor Wedge # of testsWedge taper

angle WA(degrees)

Wedge thicknessWT (in.)

Average ultimate strain (in./in.)

p-valuep-value <

0.05

0.5A BarrelStd. 15 6.98 - 7.03 0.468 - 0.469 0.0218

3.17E-06 YesOpt. 15 8.03 - 8.04 0.487 - 0.489 0.0357

0.5A CastStd. 9 7.00 - 7.02 0.467 - 0.469 0.0122

3.26E-04 YesOpt. 9 8.03 - 8.06 0.487 - 0.489 0.0291

0.5G BarrelStd. 10 6.99 - 7.02 0.466 - 0.470 0.0182

1.60E-08 YesOpt. 10 8.03 - 8.05 0.487 - 0.489 0.0511

0.5G CastStd. 10 6.99 - 7.02 0.466 - 0.470 0.0126

3.20E-05 YesOpt. 10 8.03 - 8.05 0.487 - 0.489 0.0399

0.6A BarrelStd. 20* 6.99 - 7.03 0.528 - 0.531 0.0292

6.14E-04 YesOpt. 20 8.03 - 8.05 0.549 - 0.551 0.0400

0.6A CastStd. 9 7.00 - 7.01 0.529 - 0.531 0.0138

9.62E-04 YesOpt. 9 8.03 - 8.04 0.549 - 0.550 0.0298

0.6G BarrelStd. 10 6.99 - 7.01 0.528 - 0.531 0.0217

3.94E-02 YesOpt. 10 8.03 - 8.05 0.549 - 0.551 0.0297

0.6G CastStd. 10 6.99 - 7.01 0.528 - 0.531 0.0104

1.66E-03 YesOpt. 10 8.03 - 8.05 0.549 - 0.551 0.0246

Statistical Validation of Results

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0.000

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0.055Ultimate strand

stress (p

si)

Ultimate strand strain (in./in.)0.5A Cast Std. 0.5A Cast Opt.0.6A Cast Std. 0.6A Cast Opt.

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stress (p

si)

Ultimate strand strain (in./in.)0.5G Barrel Std. 0.5G Barrel Opt.0.6G Barrel Std. 0.6G Barrel Opt.

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stress (p

si)

Ultimate strand strain (in./in.)0.5G Cast Std. 0.5G Cast Opt.0.6G Cast Std. 0.6G Cast Opt.

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0.050


stress (p

si)

Ultimate strand strain (in./in.)0.5A Barrel Std. 0.5A Barrel Opt.0.6A Barrel Std. 0.6A Barrel Opt.

Statistical Validation of ResultsStrand spool

Anchor Wedge # of testsWedge taper

angle WA(degrees)

Wedge thicknessWT (in.)

Average ultimate strain (in./in.)

p-valuep-value <

0.05

0.5A BarrelStd. 15 6.98 - 7.03 0.468 - 0.469 0.0218

3.17E-06 YesOpt. 15 8.03 - 8.04 0.487 - 0.489 0.0357

0.5A CastStd. 9 7.00 - 7.02 0.467 - 0.469 0.0122

3.26E-04 YesOpt. 9 8.03 - 8.06 0.487 - 0.489 0.0291

0.5G BarrelStd. 10 6.99 - 7.02 0.466 - 0.470 0.0182

1.60E-08 YesOpt. 10 8.03 - 8.05 0.487 - 0.489 0.0511

0.5G CastStd. 10 6.99 - 7.02 0.466 - 0.470 0.0126

3.20E-05 YesOpt. 10 8.03 - 8.05 0.487 - 0.489 0.0399

0.6A BarrelStd. 20* 6.99 - 7.03 0.528 - 0.531 0.0292

6.14E-04 YesOpt. 20 8.03 - 8.05 0.549 - 0.551 0.0400

0.6A CastStd. 9 7.00 - 7.01 0.529 - 0.531 0.0138

9.62E-04 YesOpt. 9 8.03 - 8.04 0.549 - 0.550 0.0298

0.6G BarrelStd. 10 6.99 - 7.01 0.528 - 0.531 0.0217

3.94E-02 YesOpt. 10 8.03 - 8.05 0.549 - 0.551 0.0297

0.6G CastStd. 10 6.99 - 7.01 0.528 - 0.531 0.0104

1.66E-03 YesOpt. 10 8.03 - 8.05 0.549 - 0.551 0.0246

Conclusions and Recommendations• Increasing the wedge taper angle and

crown thickness can improve the ultimatestrand strain and potentially reduce thevariance

• Wedge taper angles with about a +1deg angle differential, 7 deg + 1 deg =8 deg (placed within an anchorhousing of about 7 degrees)

• Wedge crown thickness of about0.488 in. for the 0.5‐in. strandconfigurations and 0.549 in. for the0.6‐in. strand configurations

• For specimens tested in this program

Conclusions and Recommendations

• Visual evidence shows that there is animproved (i.e., more uniform)distribution of stress transfer within theanchor

• Two different failure modes limit thestrain capacity of the PT strands – outerwire slippage through the anchor andwire fracture within the anchor

• Increasing the wedge taper angle orcrown thickness too far outside theeffective ranges results in exterior wireslips and reduced performance

Conclusions and Recommendations

• No three‐piece wedgeswere tested in thecurrent study

• Two‐piece wedges maybe more desirable thanthree‐piece wedges

Future and Ongoing Work• Slightly longer wedges with

increased crown thickness andtaper angle may be investigated

• FEM analysis of stressdistribution within anchor maybe investigated

• Wedge seating depth and itsrelationship to strand/anchorperformance is currently beinginvestigated at ND

Acknowledgements• Norris Hayes and co‐author Randy Draginis of Hayes Industries Ltd.

in Sugar Land, Texas

• Steven Walsh, Eric Herbert, and co‐author Richard Estes atUniversity of Notre Dame

• Wiss, Janney, Elstner Associates Inc. in Northbrook, Illinois & Dr.Neil Hawkins, Professor Emeritus at University of Illinois at Urbana‐Champaign

• Kevin’s employers: Auckland Council and Professor Jason Ingham atthe University of Auckland, New Zealand

• The opinions, findings, and conclusions expressed in thepresentation are those of the authors and do not necessarily reflectthe views of those acknowledged.

Additional slides

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0 1 2 3 4 5 6 7Ultimate strand

strain (in./in.)

Number of wire fractures

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0 1 2 3 4 5 6 7

Ultimate strand

strain (in./in.)

Number of wire fractures

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0 1 2 3 4 5 6

Ultimate strand

strain (in./in.)

Number of exterior wire slips

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0 1 2 3 4 5 6

Ultimate strand

strain (in./in.)

Number of exterior wire slips

Failure Mode versus Performance

0.5‐in strand

0.5‐in strand 0.6‐in strand

0.6‐in strand

Dimensional Parameters versus Failure Mode

0.5‐in strand

0.5‐in strand

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6.8

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Num

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fractures


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Wedge thickness, WT (in.)

of Anchor Wedge Parameters on Post Strand...

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