Effect of intermediate diaphragm on lateral load distribution factor of multicell box-girder bridges

Abstract

The current American bridge design codes state that intermediate diaphragms should be used to preserve section geometry against accidental overturning of girders and during construction of a bridge. There is inconsistency in practice for the design of intermediate diaphragms, such that most specifications either ignore or underestimate the contribution of these members to the lateral distribution of live load. Current studies indicate that neglecting the effect of intermediate diaphragms might lead to highly conservative values for bending moment distribution factors and result in non-economic designs for skew bridges. This paper reports on a parametric study performed on 160 prototypes of straight and skew concrete multicell box-girder bridges. The obtained results were used to develop practical expressions to account for the diaphragm effects on American Association of State Highway and Transportation Officialsformulas for live load distribution factors. It was observed that decks with internal transverse diaphragms perpendicular to the longitudinal webs are the best arrangement for load distribution in skew bridges. Thus, a sufficient number of diaphragms should be provided between span lengths and over the supports of bridge decks.