Lateral Load Distribution on Transverse Floor Beams in Steel Plate Girder Bridges

Many twin plate girder bridges have been recently rated inadequate for their current design loads. The controlling members that determine the bridge rating is often the transverse floor beams. The current provisions assume no lateral load distribution on the floor beams. This research focused on determining how the load is actually distributed. Using the SAP2000 finite element program, different floor system models were studied. The floor beam moments found by finite element modeling were 5-20% lower than the moments predicted by the current provisions due to load distribution and the moment carried by the concrete slab. An experimental test was also run on a similar floor system and the moments on the floor beam for this test were even lower than the moments predicted using finite element modeling showing that the finite element results are conservative as well. Recommended load distribution methods for the design and rating of floor beams are presented.