Constitutive Models of Prestressed Steel-Fiber Concrete Christopher - - PowerPoint PPT Presentation

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Constitutive Models of Prestressed Steel-Fiber Concrete Christopher P. Caruso Dept. of Civil & Environmental Engineering University of Houston NSF REU Program August 2007 Outline of Presentation Introduction Experimental Program

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SLIDE 1

Constitutive Models of Prestressed Steel-Fiber Concrete

Christopher P. Caruso

  • Dept. of Civil & Environmental Engineering

University of Houston NSF REU Program August 2007

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SLIDE 2

Outline of Presentation

  • Introduction
  • Experimental Program
  • Results
  • Discussion
  • Conclusions
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SLIDE 3

Introduction

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SLIDE 4

Purpose

  • Investigate the behavior of prestressed steel-

fiber concrete (PSFC) under shear.

– Can steel fibers replace traditional shear stirrups?

  • Is this a practical and economical

improvement?

TXDOT sponsored project

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SLIDE 5

Prestressed Concrete

  • High transverse load-bearing capacity

– Initial compressive stress

  • Used commonly in highway bridge girders.

−

+

−

+

−

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SLIDE 6

Steel Fiber Concrete

  • Concrete with short steel wires mixed in.
  • Known to reduce crack propagation

– Absorb energy released when a crack opens

Crack

  • Fig. 3. Cracked Concrete

Panel under a tensile load P. P P Without Steel Fibers

Energy

With Steel Fibers

Energy

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SLIDE 7

Constitutive Models

  • Relate Stress and Strain in a material.

– Eg. Prestressed Concrete

  • Must be determined experimentally.
  • Can be used to analyze indeterminate

structures

– Consider with force equilibrium and strain compatibility

Sometimes referred to as “Stress-Strain Curve”

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SLIDE 8

Research Significance

  • Earthquake load simulation
  • Hollow Bridge Piers subjected to reverse

cyclic loading (Yeh and Mo 1999)

– Full-scale shake-table test

Actuator Oil jack Column Reaction Wall Strong Floor RC Foundation Load Cell Dial gauge Cross beam Hinge

Cross beam Universal joint

Load Cell Universal joint

1500 1500 900 900 64-#7

#3@200

66 168 132 168 132 168 132 168 132 168 66

300

i j b a

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SLIDE 9

Research Significance

  • Constitutive Models

are used to accurately predict structure behavior.

  • Construct a Finite

Element Model

Nonlinear BeamColumn Elements Rigid Beam

A A

(a) Elevation view

N 3 N 3 N 3 P 3 P 3 P 3

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SLIDE 10

Objective

  • Investigate Behavior of Prestressed Steel-Fiber

Concrete (PSFC).

– Construct PSFC panels. – Test panels in sequential loading.

  • Tension  Compression
  • Record applied loads and panel deformations.

– Analyze data.

  • Determine stress strain curves for concrete and

prestressing tendons.

– Compare to prestressed concrete panel data.

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SLIDE 11

Experimental Program

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SLIDE 12

Experiment Plan

  • Fabricate two PSFC panels for testing

– TEF1: 0.5 % Steel Fibers by volume. – TEF2: 1.0 % Steel Fibers by volume.

  • Test panels in Universal Element Tester

– Tension – Compression

  • Collect load & deformation data

– Jack Load Sensors – Linear Variable Differential Transformers (LVDT)

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SLIDE 13

Panel Design

  • Concrete

– Type 1 Portland Cement – 6 ksi Compressive Strength – 7 in. Slump

  • Reinforcement

– 10 steel prestressing tendons. – 10 steel compression bars. – Dramix short hook-end steel fibers

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SLIDE 14

Unit: mm

t l

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SLIDE 15
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SLIDE 16

t l

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SLIDE 17

Empty UET Loaded UET

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SLIDE 18

Test Procedure

  • Tensile load to 40 kips
  • Tensile strain to 1%
  • Tensile strain to 1.5%
  • Tensile strain to 2%
  • Compressive load to 30 kips
  • Compressive strain to crushing failure
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SLIDE 19

Results

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SLIDE 20

Test Results

  • TEF1 experienced premature tendon failure

– Most tension data was recoverable

  • TEF2 was not tested due to malfunctioning

servo control box

– Will be tested once box is repaired

  • TEF1 data compared to prestressed panel data

– Jung Wang, Ph.D student

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SLIDE 21

Experimental Stress vs. Strain

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SLIDE 22

Concrete Stress vs. Strain

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SLIDE 23

Prestressing Tendon Stress vs. Strain

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Discussion

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Questions

  • Why did TEF1 experience premature

tendon failure?

  • What do the stress strain curves indicate

about the panel’s behavior?

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SLIDE 26

TEF1 Failure

  • Severe cracks formed at panel boundaries

– Disproportionately higher tendon loads during test.

  • Tendon conduits not fully grouted

– Short lengths near panel boundaries experienced unacceptably high strain.

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SLIDE 27

t l

Severe Crack Severe Crack Tendon Chuck Severe Crack Tendon Bracket Flexible Metal Conduit Prestressing tendon Chuck Ungrouted Region

Concrete

Friction Plate Tendon U- Bracket

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SLIDE 28
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SLIDE 29

Conclusions

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SLIDE 30

Conclusions

  • TEF1 stress-strain curves appear well

predicted by prestressed constitutive models.

  • Despite premature tendon failure, results are

promising for success of future tests.

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SLIDE 31

Future Work

  • Apply maximum compressive load

through friction plates

  • Apply high-strength grout between

friction plates and panel

  • Use tubes to pre-form bolt holes for

friction plates