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Multi-span suspension bridges show greater vertical deflection of the girders and greater longitudinal displacement of the towers, as compared to typical three-span suspension bridges with the same center span length. These characteristics are affected by the sag ratio of the main cable, live load conditions, the strength of the main cable and the boundary conditions between the tower and girder. Therefore, to demonstrate the structural characteristics of the entire system, we analyzed the ultimate behavior of multi-span suspension bridges by considering these parameters.

<p>This paper presents an improved deflection theory considering extensible hangers for the static analysis of a suspension bridge. The coupled differential equations for the deflections of the main cable and girder are presented and numerically solved by ATLAB. For verification, the two- dimensional finite-element method, the conventional deflection theory, and the improved deflection theory are used to obtain the static responses of an example model of a three-span suspension bridge. The results show that the improved theory can demonstrate accurate static behaviors of suspension bridges.</p>

System buckling analysis is usually used to determine the critical buckling load in the buckling design of cable-stayed bridges. However, system buckling analysis may yield unexpectedly large effective lengths of the members subjected to a relatively small axial force. This paper proposes a new method to determine reasonable effective lengths of girder and tower members in steel cable-stayed bridges using fictitious axial forces. An improved inelastic buckling analysis with modified tangent modulus is also presented. The effective lengths of members in example bridges calculated using the proposed method are compared with those obtained using the conventional buckling analysis method. The proposed method provides much more resonable effective lengths of the members. When girder and tower members are built with HSB800 steel instead of conventional steel, the effective lengths of the members under a small axial force slightly decreases in the inelastic buckling analysis without fictitious axial forces, while the proposed method that considers fictitious axial forces provides almost no changes in such lengths.