behaviors of post-tensioning and anchorage systems reu student: geoff madrazo pi’s: dr. richard...
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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