Diaphragm Effectiveness in Prestressed-Concrete Girder Bridges

Each year many prestressed-concrete (P/C) girder bridges are damaged by overheight vehicles or vehicles transporting overheight loads. The effects of this type of loading on P/C bridge behavior was investigated for various types and locations of intermediate diaphragms. The research included a comprehensive literature review; a survey of design agencies; the testing of a full-scale, simple-span, P/C girder-bridge model with eight intermediate diaphragm configurations, as well as a model without diaphragms; and the finite-element analyses of the bridge model assuming both pinned- and fixed-end conditions. The vertical load distribution was determined to be essentially independent of the type and location of the intermediate diaphragms, while the horizontal load distribution was a function of the intermediate diaphragm type and location. Construction details at the girder supports produced significant rotational-end restraint for both vertical and horizontal loading. Both the vertical and horizontal load distributions were found to be affected by the girder-end restraint. A fabricated intermediate structural steel diaphragm was determined to provide essentially the same type of response to lateral and vertical loads that was provided by the reinforced-concrete intermediate diaphragms presently used by the Iowa Department of Transportation.