ANALYSIS OF BOX GIRDER BRIDGES USING 3-D CURVED SHELL ELEMENTS

Abstract

Advent of reinforced and prestressed concrete box girder bridges unicellular and multicellular, in the present bridge industry can be attributed to their better stability, serviceability, economy, aesthetic appearance and structural efficiency. Because of its potential rigidity against torsion under unsymmetrical loads, usually encountered in bridges, box girder section is the optimum solution for all bridges, especially those curved in plan or elevation. Hence use of box girder bridges, for bridging small to large spans, are gaining popularity. The analysis and design of box girder bridges are quite involved due to its complex three dimensional behaviour consisting of bending in longitudinal and transverse directions, torsion and distortion. Effect of shear lag, warping of cross section and associated influences on transverse load distribution increases the above complexity. The purpose of this work is to develop a software using finite element method to analyse the complex behaviour of the box girder bridges. Three dimensional curved shell element has been used to this effect. The element developed on the basis of degeneration concept coupled with reduced integration technique performs well. The finite element program `BOXFEM' computes deflection, stress resultants like membrane forces, transverse shear, moments due to-selfweight of the structure, IRC recommended live loads and temperature induced forces. The program is successfully tested by analysing few standard problem having known solutions. A few cases of box girder bridges have been analysed under above type of loads using the program. It is observed from the results that certain aspects like shear lag effect, effect of number of cells of the box girder are prominently manifested. The software can be conveniently used for practical design purposes.