Distribution of Girder Loads in a Composite Highway Bridge

Background material on refined and simplified methods for the analysis of bridge superstructures was presented. Seven methods were briefly described: five refined methods and two simplified methods. Using the full-scale experimental specimen of Project 350, subjected to vertical loads at 4 points on the deck surface, the variation of bending moments along the length of center girder was determined, both before and after deck cracking. These experimentally determined girder moments were compared with the moments obtained from the AASHTO Specifications, from the Ontario Highway Bridge Design Code, and from a finite element model of the bridge.

The experimentally determined values were approximated fairly closely by those of the Ontario Code and the finite element analysis. The peak moment predicted using the AASHTO procedure exceeded the corresponding experimental value by about 80 percent.

In assessing the proper role of these methods for estimating girder moments, it is important to recognize that each method has its place. An AASHTO-type method (or perhaps a simplification of the Ontario procedure) is necessary for preliminary design. After preliminary deck and girder sizes have been picked, an Ontario-type procedure can be used to produce a more efficient revised design. The finite element method appears advantageous primarily for checking local behavior.