Preliminary Analysis of Short-Span Suspension Bridges

The Elastic Theory developed by Prakash can be used to analyze suspension bridges with short spans for preliminary analysis and design of bridges. In this paper, this theory has been used to study single span suspension bridges with two hinged support condition for the stiffening girders and influence line diagrams for hanger forces, bending moments, shear forces and deflections have been developed. The basic assumption used in this theory is that the hanger forces are uniform and their magnitude is such as to minimize the flexural strain energy of the stiffening girder. This assumption is likely to be valid for suspension bridges of relatively small spans, less than about 600m, wherein the geometric stiffness effects may not be very significant. This study shows that for the most common case of suspension bridge with two-hinged stiffening girders, the maximum bending moments and live load deflections occur near the quarter-span points. The theory developed gives a more economical design compared to Rankine's theory, as per which the critical section for bending moment is at mid-span with about twice the value. This study is limited to the static behavior of the single span suspension bridge with no dynamic and wind analysis.