Reduction of safety factor for cables in design of long-span suspension bridges based on simple reliability optimization of structural system

摘要

Employing a long-span suspension bridge as a structural system example, the optimal allocation of the safety factors for different components is studied from an economical viewpoint. The effect of uncertainties due to unknown factors and/or gross errors on structural reliability is also taken into account in this study. The results show that the numerically higher safety factor for the components subject to larger variable load effects is optimal. In other words, the higher safety factors for stiffening girder and tower and the lower for the cables are optimal. It should be noted that the reliability level of cables is still higher than those of stiffening girder and towers even if this allocation of safety factors is adopted. Concretely speaking, the value of safety factor of 2.0 for cables adopted in the current design specification for long-span suspension bridges may be reduced to the value of about 1.8.