Evaluation of continuity detail for precast prestressed girders.
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2011-08-01
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Edition:Final report; March 2008-Dec. 2010.
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Abstract:The construction of highway bridges using precast prestressed concrete (PSC) girders is considered one of the most
economical construction alternatives because of the advantages they offer (e.g. reducing formwork and rapid construction).
Constructing multi-simple span bridges is an easy alternative for precast PSC girder bridges. However, the existence of
expansion joints often leads to a host of problems in their vicinity due to drainage leaks and debris accumulation. The
maintenance of expansion joints is, therefore, an activity that bridge owners would rather avoid by eliminating these joints by
building connections between precast elements that are capable of resisting the forces resulting from establishing continuity.
Several continuity details have been used over the years for slab-on-girder bridges with the goal of avoiding the
aforementioned maintenance issues and reaping the benefits of continuity without the drawbacks of introducing it in large
structures such as bridges (e.g. thermal movements). A new continuity detail is adopted in the John James Audubon Bridge
that differs from the current standard detail in Louisiana. The new detail is based on the recommendation of the National
Cooperative Highway Research Program (NCHRP) Report 519 [1].
A 96-channel monitoring system was installed to provide information that can be used to assess the performance of the
continuity detail. Embedded and surface-mounted sensors of different types were installed to measure strains, temperatures,
rotations, and gap openings in critical locations in the monitored segment. Data from about 24 months of monitoring was
collected. The data, its processing, and interpretation are presented in this report. Analyses based on NCHRP Report 519
model and finite element models were also conducted to further understand the behavior of the new detail. Results from the
analyses were also used to recommend girder age at continuity to meet prespecified design criteria. A live load test was also
conducted to assess the performance of the new detail.
Recommendations based on the findings of the project are drawn. It can be said that the continuity detail is capable of
transferring forces between girder ends. However, girder ends may be subjected to high localized strains, especially due to
thermal variation, which can cause cracking. Such cracks are detrimental to the shear strength of PSC girders. Therefore,
thermal gradients need to be considered in the design of this detail.
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