Optimal Depth-to-Span Ratio for Composite Rigid-Frame Bridges

Abstract

The depth-to-span ratio is not only an important part of steel-concrete composite rigid-frame bridges (CRFBs) but is also one of the important parameters in designing CRFBs, determining the appearance of the bridge, volume of work for the whole bridge, arrangement of the prestressed reinforcements, clearance of the bridge, mechanical performance, and so on. However, there is little research about the effects of depth-to-span ratio with the steel section length on the structural mechanical behavior. This study examined the influence of depth-to-span ratio on the structural behavior of a rigid-frame bridge (e.g., bending moment and stress) and conducted the optimization of the depth-to-span ratio using the bending strain energy as the objective function. Taking a CRFB with a span combination of (84 + 200 + 84 m) as an example, the structural optimization yielded an optimal center-span depth-to-span ratio of 1:32 and support depth-to-span ratio of 1:16, which had the least bending strain energy and acceptable magnitudes of bending moment, bending stress, and structural deformation. The sensitivity study via parametric analysis indicated that the depth-to-span ratio had a significant influence on the mechanical responses of the CRFB, including the bending moment and bending stress at the critical locations. The outcome of this study provides guidance for the structural design of CRFBs regarding the steel section length.