Connection of Simple-Span Precast Concrete Girders for Continuity (2004) / Chapter Skim
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Appendix C - Proposed Revisions to the AASHTO LRFD Bridge Design Specifications
Appendix C - Proposed Revisions to the AASHTO LRFD Bridge Design Specifications
Pages 69-82
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From page 69... ...
C-1 APPENDIX C PROPOSED REVISIONS TO THE AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS INTRODUCTION A major goal for this research project was to develop proposed revisions to the AASHTO LRFD Bridge Design Specifications addressing the design of simple-span precast girders made continuous. Existing Article 5.14.1.2.7 specifically addresses this type of construction.
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From page 70... ...
(C5.14.1.2.7c) Atr = area of concrete deck slab with transformed longitudinal deck reinforcement (IN2)
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From page 71... ...
Multi-span bridges composed of precast girders with continuity diaphragms at interior supports that are designed as a series of simple spans are not required to satisfy the requirements of Article 5.14.1.2.7. If a negative moment connection is provided between precast girders and the continuity diaphragm is installed prior to placement of the deck slab, the girders may be considered to be continuous for the dead load of the deck slab and for any other applied loads placed on the noncomposite girder after continuity is established.
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From page 72... ...
Analysis also predicts that precast girder bridges with composite deck slabs that are made continuous will develop negative restraint moments because of differential shrinkage between the girders and the deck. The older the girders are at the time the deck is cast, the more severe the predicted negative moment development.
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From page 73... ...
Ac = gross area of concrete deck slab (IN2) Atr = area of concrete deck slab with transformed longitudinal deck reinforcement (IN2)
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From page 74... ...
If no age is specified, the girders shall be assumed to be 7 days old at the time continuity is established. The following simplification may be applied if the owner will permit this simplification to be used and if the contract documents require a minimum girder age of at least 90 days when continuity is established: • Positive restraint moments caused by girder creep and shrinkage and deck slab shrinkage may be taken to be as 0.
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From page 75... ...
If the connection between precast girders at a continuity diaphragm does not satisfy these requirements, the joint shall be considered partially effective. Superstructures with fully effective connections at interior supports may be designed as fully continuous structures at all limit states for loads applied after continuity is established.
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From page 76... ...
5.14.1.2.7g Strength Limit State The connections between precast girders and a continuity diaphragm shall be designed for the strength limit state. The reinforcement in the deck slab shall be proportioned to resist negative design moments at the strength limit state.
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From page 77... ...
All longitudinal reinforcement in the deck slab may be used for the negative moment connection. Negative moment connections between precast girders into or across the continuity diaphragm shall satisfy the requirements of Article 5.11.5.
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From page 78... ...
The requirements of Article 5.7.3.4 shall apply to the reinforcement at positive moment connections at continuity diaphragms. • Positive Moment Connection Using Mild Reinforcement The anchorage of mild reinforcement used for positive moment connections shall satisfy the requirements of Article 5.11 and the additional requirements of this article.
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From page 79... ...
5.14.1.2.7j Continuity Diaphragms The design of continuity diaphragms at interior supports may be based on the strength of the concrete in the precast girders. C-11 Strands that are debonded or shielded at the end of a member may not be used as reinforcement for the positive moment connection.
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From page 80... ...
Precast girders may be embedded into continuity diaphragms. If horizontal diaphragm reinforcement is passed through holes in the precast beam or is attached to the precast element using mechanical connectors, the end precast element shall be designed to resist positive moments caused by superimposed dead loads, live loads, creep and shrinkage of the girders, shrinkage of the deck slab, and temperature effects.
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From page 81... ...
Ma, Z., Huo, X., Tadros, M.K. and Baishya, M., "Restraint Moments in Precast/Prestressed Concrete Continuous Bridges," PCI Journal, Vol.
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From page 82... ...
and McCrate, T.E., Bond of Untensioned Prestress Strand, Interim Report 73-5A, Missouri Cooperative Highway Research Program, Missouri State Highway Department, Aug.
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