DIAPHRAGM EFFECTIVENESS IN PRESTRESSED-CONCRETE GIRDER BRIDGES

Each year many prestressed-concrete (P/C) girder bridges are damaged b y overheight vehicles or vehicles transporting overheight loads. The e ffects of this type of loading on P/C bridge behavior was investigated for various types and locations of intermediate diaphragms. The resea rch included a comprehensive literature review; a survey of design age ncies; the testing of a full-scale, simple-span, P/C girder-bridge mod el with eight intermediate diaphragm configurations, as well as a mode l without diaphragms; and the finite-element analyses of the bridge mo del 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 lo cation. Construction details at the girder supports produced significa nt rotational-end restraint for both vertical and horizontal loading. Both the vertical and horizontal load distributions were found to be a ffected by the girder-end restraint. A fabricated intermediate structu ral steel diaphragm was determined to provide essentially the same typ e of response to lateral and vertical loads that was provided by the r einforced-concrete intermediate diaphragms presently used by the Iowa Department of Transportation.