Optimum Dimensions of Suspension Bridges Considering Natural Period

Abstract

Suspension bridge is an efficient structural system particularly for large spans. Many difficulties related to design and construction feasibility arises due to its long central span. There are many suspension bridges around the world and dynamic behavior has been found to be the primary concern for those bridges. Natural period of a suspension bridge mainly dependent on the span and other structural dimensions related to the stiffness. In the present study, the effects of structural parameters like deck depth and tower height on natural period of suspension bridges having different central spans are conducted. Natural periods are analyzed by modal analysis for central span lengths ranges from 600m to 1400m. The modal analysis is performed by finite element software package SAP2000. For each central span, tower heights and deck depth are varied and the consequences of these variations on the natural periods of various types of vibration modes are investigated and dominant mode for each span is recognized. Obtained values from the analysis were utilized to plot three dimensional surfaces representing correlation among natural period, deck depth, tower height, and span, using MATLAB functions. A relationship among tentative optimum deck depth, optimum tower height and central span of suspension bridge is developed for obtaining minimum natural period. This relationship can be used to obtain the tentative optimum dimensions of a suspension bridge with central span between 600m to 1400m.