Determining Tensions in Suspension Bridge Anchor Span Strands at Their Erection Stage: An Analytical Method

Abstract

During suspension bridge erection, tensions in its anchor span strands undergo continuous changes until the completed bridge state is attained. Calculating the precise tension values in the anchor span strands is critical to ensure the structural safety of the entire bridge under construction. To this end, an analytical method is proposed to determine the actual tensions in anchor span strands at the strand erection and tensioning stage, during which a temporary constraint on the splay saddle is removed as appropriate, and the resulting coupling relationship between strand tensioning and splay saddle rotation is considered. Then, based on the condition for moment equilibrium acting on the splay saddle, we determine the timing for letting the splay saddle stand on its own and the deflection angle of the splay saddle between the position with temporary constraint and that in the free-cable state. Further, the actual tensions in the anchor span strands are estimated during bridge erection. The proposed method ensures that the values of strand tensions and splay saddle position with all strands tensioned coincide with those required for the free-cable state. The innovation of this study is that it permits one to avoid the strand tension adjustment after tensioning the strands according to the values calculated by the proposed method. The performed calculations prove that strand tensions on the left and right sides are symmetrical before the temporary constraint of the splay saddle is removed and asymmetrical after this event. However, for the same layer of strands, the tensions on the two sides still tend to be symmetrical. The proposed analytical method is user-friendly and reliable, which was verified by a case study.