Abstract
When eccentric live loads are applied on the deck overhang of steel-box girder bridges, torsional moments, comprising pure torsional and distortional moments are generated on the box sections. The torsional moment on the bridge girders distorts the box girder cross-sections, inducing additional normal stress components and causing instability of the box girder sections in severe cases. Hence, it is essential to install intermediate diaphragms in the box sections to minimize distortional behaviors. Although the applied live loads are critical parameters that influence intermediate diaphragm spacings, the effects of live load combinations have rarely been addressed in the design of intermediate diaphragm spacings. Thus, load combinations should be evaluated to design the intermediate diaphragm spacing of the box girder bridges more thoroughly. In this study, the load combination effects on the distortional behavior and adequate intermediate diaphragm spacing were evaluated through a finite element analysis (FEA). Composite rectangular box girder bridges with different cross-sectional aspect ratios (H/B) and spans (L) were analyzed in the parametric study. It was found that the truck load, which represents the concentrated load, significantly influences the distortional warping normal stress, normal stress ratio, and intermediate diaphragm spacing. In addition, the FEA results showed that the controlling load combinations could be varied with the span.
Highlights
Steel-box girders exhibit higher torsional rigidity than plate-type girders and have been widely applied in bridge engineering, in the interchanges of urban infrastructures
Distortional Warping Normal Stress Based on finite element analysis (FEA) Results
The maximum distortional warping normal stress existed at the midspan where the concentrated loads were applied, but the maximum stress under distributed loads existed near the diaphragm locations
Summary
Steel-box girders exhibit higher torsional rigidity than plate-type girders and have been widely applied in bridge engineering, in the interchanges of urban infrastructures. When eccentric live loads are applied to the deck overhang of a steel-box girder, they generate torsional moments, consisting of pure torsional and distortional moments, on the box sections (Figure 1). Since the distortion may generate unstable cross-section states, resulting in the instability of the box girders, bridge design codes specify the installation of intermediate diaphragms to prevent distortion and excessive distortional stresses in the box section. Conventional provisions of the design code require installed intermediate diaphragms to control distortional stresses to values lower than 5% or 10% of the bending stress. Since Dabrowski [1] theoretically analyzed the distortion behavior of a box girder, several researchers have contributed to distortional analysis and intermediate diaphragm design techniques to minimize the distortional behavior of box sections.
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