Prestress Influence on Shear‐Lag Effect in Continuous Box‐Girder Bridge

Abstract

The shear-lag effect in a thin-walled box girder has been recognized and introduced in the technical literature. In contrast however, a discussion of shear-lag effect caused by the combination of prestress force and self-weight of a box girder is limited. In this paper, the shear-lag effect is treated by the principle of superposition by considering that the configuration of a prestressed tendon takes the form of a broken straight line. Two equal spans of a continuous box girder of constant depth with a shear-lag effect are used as an illustrative example. If λ\N denotes actual stress due to bending under symmetrical loading over the stress computed by elementary beam theory, a compound parameter \IN\N\I\dy\Nθ\N/ω\N\IL\N is a measure of the shear-lag effect in this particular example, where \IN\N\I\dy\N is effective prestress force, θ\N is the inclined angle of tendon at support, ω\N is the intensity of uniformly distributed load, and \IL\N is the span length of bridge. On the \IN\N\I\dy\Nθ\N/ω\N\IL\N and λ\N diagram, an asymptote exists. Usually in engineering practice \IN\N\I\dy\Nθ\N/ω\N\IL\N is equal to or greater than unity. Based on this approach, some preliminary conclusions are presented for this study.