An Investigation on Transversely Prestressed Concrete Bridge Decks

1
An Investigation on Transversely Prestressed
Concrete Bridge Decks

• J. Paul Smith

2
Objective

• Study of transverse post-tensioning of concrete
  bridge decks as an alternative to improve
  durability.

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Types of Bridges in Indiana
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Scope

• Develop design specifications applicable to
• Slab bridges
• Slab-on-Girder bridges

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Problem Statement

q F/L
s?
Assumption Linear behavior
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Specimen for Experimental Phase of Texas Study
Location of strain gages
1.2ksi
0.6ksi
1.2ksi
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(No Transcript)
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Comparison of Analytical (SAP2000) Experimental
(Texas Study) Results
Modeling Type
Top Stresses
3D(III)
3D(II)
3D(I)
2D
14
14
14
16
m
42
38
38
40
Max
m mean(ss/sexp)-1x100
Max Max(ss/sexp)-1x100
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Analysis using ANSYS 5.7

• Alternative modeling
• Use brick and shell elements

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SAP2000 vs. ANSYS 5.7(Texas Model)

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Variables of Interest

• Girders (spacing, stiffness)
• Diaphragms (spacing, stiffness, location)
• Boundary conditions
• Post-tensioning spacing
• Slab thickness

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Base Case
22 in.
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Preliminary Evaluation of Variables (2D Modeling)

• Base Case

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Preliminary Evaluation of Variables (2D Modeling)

• Effect of Girder Spacing

a) Half Spacing
b) Quarter Spacing
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Preliminary Evaluation of Variables (2D Modeling)

• Effect of Girder (No diaphragms)

a) Concrete girders
b) Steel girders
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Preliminary Evaluation of Variables (2D Modeling)

• Effect of Diaphragms

Top half diaphragms present
Bottom half diaphragms no present
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Preliminary Evaluation of Variables (2D Modeling)

• Effect of boundary conditions

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Preliminary Evaluation of Variables (2D Modeling)

• Effect of Post-tensioning Spacing

a) Forces at every other node
b) Forces every four nodes
_at_ 4
_at_ 8
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Preliminary Evaluation of Variables (2D Modeling)

• Effect of Slab Thickness

8 slab
6 slab
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Preliminary Identification of Relevant Variables
(2D Modeling)

• Diaphragms (stiffness, location, spacing)
• Boundary conditions
• Post-tensioning spacing

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Effect of Diaphragms

• Distribution of transverse stresses is mainly
  affected by diaphragm size and location.

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Notation
Normalized stress ss/q
y
x
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Effect of Diaphragm Size
y
y
Stripe 1
Stripe 2
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Effect of Diaphragm Location(Exterior Diaphragms
Only)
y
y
Stripe 2
Stripe 1
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Minimum Stress vs. Diaphragm Position
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Effective Width of T Beam vs. Top Stress
Beff
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Diaphragm Location vs. Effective Width
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Conclusions at this Stage

• Distribution of transverse stresses mainly
  influenced by
• Diaphragm axial stiffness and position
• Boundary conditions
• Influence of diaphragm position Rationalized
  using T-beam analogy