PRELIMINARY ANALYSIS OF A SUSPENSION BRIDGE WITH MULTIPLE MAIN CABLE PROFILES

Abstract

Suspension bridges characteristics and influence of different key parameter in analysis have been studied for conventional bridge. Analysis results using classical theories have compared with modern finite element based SAP2000 software analysis for single cable bridge for validation purpose. Controlling live load deflection is the central objective in design of suspension bridge. Deflections can be controlled by increasing the flexural stiffness (El) of the deck or by increasing the geometric/gravity/ P — A stiffness/Horizontal component of cable force in main cable. Designer often have to increase flexural stiffness of deck i.e. high stiffening deck section or geometric stiffness of cable by increasing dead load to limit deflections. Use of multiple main cable profiles allows designer to produce large axial force (P) in cables with small deflection (d). This study explores about suspension bridge with multiple main cable profile and its analysis using SAP2000, 2 to 10 main cable cases is considered with and without reduced moment of inertia. Concept of reverse cable is presented in this work. Pre-tensioned reverse cable produces downward pull on deck which increases the geometric stiffness of cable. Also reverse cable produces it own geometric stiffness due to P — 0 effects. Deflection theoryll] considering geometric nonlinearity is modified for analyzing suspension bridge with reverse cable. Analytical solution is performed using MATLAB and compared with SAP-2000 analysis. Finally advantage of reverse cable is illustrated by taking case study of 504 m long suspension bridge. Two different cases are taken with reverse cable sag of 14 m and 40 m. It is found that effect of reduced deck flexural stiffness on deflection is negligible, whereas bending moment is reduced almost in proportion with reduction in flexural stiffness. Finally there is need to compare all above theory and models to ascertain the economy that can be achieved via use of multiple main cable and reverse cable. Economic study is performed for a common design data of 504 m bridge with common deflection limits. Comparison is made based on total cable area required and area of chord members of stiffening truss of deck. It is found that considerable economy can be achieved with these profiles.