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 γ denotes actual stress due to bending under symmetrical loading over the stress computed by elementary beam theory, a compound parameter Nyθ/ωL is a measure of the shear‐lag effect in this particular example, where Ny is effective prestress force, θ is the inclined angle of tendon at support, ω is the intensity of uniformly distributed load, and L is the span length of bridge. On the Nyθ/ωL and γ diagram, an asymptote exists. Usually in engineering practice Nyθ/ωL is equal to or greater than unity. Based on this approach, some preliminary conclusions are presented for this study.