United States Department of Transportation
i
Field verification for the effectiveness of continuity diaphragms for skewed continuous P/C P/S concrete girder bridges : tech summary.
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2009-10-01
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Abstract:The majority of highway bridges are built as cast-in-place reinforced concrete slabs and prestressed concrete
girders. The simple-span precast, prestressed concrete girders made continuous through cast-in-place decks
and diaphragms have been widely used in the United States since 1960’s. Shear connectors on the top of the
girders assure composite action between the slabs and girders. The design guidelines for bridges in AASHTO
Standard Design Specifi cations Section 8.12 indicate that diaphragms should be installed for T-girder spans
and may be omitted where structural analysis shows adequate strength. Similar discussions are presented
in Load Resistance Factor Design (LRFD) Bridge Design Code (AASHTO 2004). The advantages of continuity
diaphragms are the reduced expansion joint installation and maintenance costs, the improved riding quality,
and the enhanced structural redundancy. Furthermore, the eff ects of diaphragms are not accounted for in the
proportioning of the girders. Therefore, the use of diaphragms should be investigated.
In 2004, the Louisiana Transportation Research Center (LTRC) sponsored the
theoretical investigation on the eff ects of continuity diaphragms for skewed
continuous span precast prestressed concrete girder bridges. The results of the
research were published in LTRC Report 383. The research team, Saber et al.,
reported that continuity diaphragms used in the prestressed girder bridges on
skewed bents cause diffi culties in detailing and construction. Details for small
skewed bridges (> 30° from perpendicular) have not been a problem for the
Louisiana Department of Transportation and Development (LADOTD), but as
the skew angle increases or the girder spacing decreases, the connection and the
construction become more diffi cult. Also, results of the research indicated that
the continuity diaphragms could be eliminated without any signifi cant eff ects
on the stresses or defl ections in the bridge girders. One of the objectives of this
research was to conduct fi eld verifi cation for the analytical results reported in
LTRC Report 383.
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