LOAD DISTRIBUTION ON A TIMBER-DECK AND STEEL-GIRDER BRIDGE (ABRIDGMENT)

Strain gauges were applied to 8 of the 14 girders at midspan on this in-service bridge. The structure was then loaded with a truck that simulated the type 3 loading designated by AASHTO. The study determined the stresses in the steel girders that resulted from various loading sequences. Load distribution characteristics of the structure were determined under varying conditions with loosened floor fasteners. It was found that the live load stresses were both laterally distributed in a reasonably consistent manner and also reasonably low (at most only 31 percent of the maximum allowable for A36 steel, and generally only 25-30 percent) with loosening of the deck plank having no very significant effect on either magnitude or lateral distribution of the stresses. It is concluded that the Virginia Department of Highways and Transportation's current practice of distributing the live load moments to the interior girders of all timberdeck bridges by using a factor of S/4, where S is the spacing in feet between adjacent girders specified by AASHTO, is conservative; and that a distribution factor for the interior girders of S/5 would be adequate for legal limits. This factor of S/5 is also felt to be more realistic than current procedure for exterior girders as well.