Behaviors of Post-Tensioning and Anchorage Systems

REU student: Geoff Madrazo

PI’s: Dr. Richard Sause and Dr. James Ricles

Graduate Mentor: David Roke

ATLSS Center, Lehigh University

Overview

• Introduction

• Purpose

• Objectives

• Methods and Materials

• Results

• Conclusion

Introduction

• What is post-tensioning?– Used as reinforcement for structural

components.– Prestressing structural elements increases

their tensile strength.

Figure 1Concrete slab under loadingSource: Post-Tensioning Institute

Introduction

Structural elements that use post-tensioning:

• Many types of bridges

• Elevated slabs

• Foundations

• Walls and columnsFigure 2Post-tensioned highway overpassSource: Charlie

Purpose

• Acquire helpful data on the strength and behaviors of post-tensioning and anchor systems

• Produce a useful reference for future works which implement post-tensioning

Objectives

• Test and analyze the PT strand and anchor system

• Observe and understand behaviors of the anchorage system as documented by Dr. Maria Garlock

• Find practical scope of use for the strand and anchor in future projects

Methods and Materials

wedgesPT strand

anchor plate

Figure 3Anchorage componentsSource: DSI

Figure 4Cross-section of anchorageSource: Williams Form Engineering Corp

Methods and Materials

• PT strand - ASTM A416– 7-wire treated carbon steel

– Min. TY (yield) = 52.74 kips

– Min. TU (breaking) = 58.60 kips

• Anchors - ACI code– Guaranteed up to 95% of

the breaking strength TU

Figures 5 and 6Wedges and strandSource: Williams Form Engineering Corp

Methods and Materials

• Static loading tests– 2 part wedge vs. 3 part

wedge– Stress testing

• Tensile tests– Wirelock– Copper plates

Figure 7Wirelock compoundSource: Millfield Group

Results – So far• Static loading tests -

test # of wedges Texp (kips) Texp/T,m ,est (%)

1 3 57.50

2 2 53.85

3 3 53.85

4 3 56.55 .9371 1.341

5 3 55.70 .9230 1.040

6 3 57.80 .9578 2.443

7 3 57.30 .9495 2.002

8 3 57.87 .9589 2.504

9 3 57.68 .9558 2.339

10 3 56.65 .9387 1.428

11 3 56.81 .9414 1.569

12 3 56.52 .9366 1.315

13 3 57.08 .9459 1.810Table 1Test data

Results.600" 270 7W Low Relaxation

0

9

18

27

36

45

54

63

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

Strain, %

Load, kips

Low TU

High TU

Min. TY - 52.74 kipsAvg. TU

Figure 8Stress-strain curve

ResultsTwo- vs. Three-Wedge

0.9689

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1 2 3 4

Number of Wedges

Texp/Tu,n (%)

SATEC Tests

Fritz Tests

Fritz Tests (old strand)

Avg. Value

Figure 9Two-wedge vs. three-wedge plot

Conclusions

• The anchorage system can not be relied upon to the 95% TU (breaking strength)

• The PT strand and anchors consistently exceed the yield strength of the strand

• Three-part wedges perform better under higher loads than two-part wedges

Conclusions

• There doesn’t appear to be any correlation between the elongation rate (or load rate) and the breaking strength

• For the Self-Centering Damage-Free Seismic-Resistant Steel Frame Systems project, it is reasonable to design past the yielding of the strands

Acknowledgements

David RokeDr. SauseDr. Ricles

John HoffnerGene Matlock

Dr. Eric KauffmanChad Kusko

ATLSSNEESNSF