GRILLAGE ANALYSIS OF BOX GIRDER BRIDGES FOR VERTICAL LOADS

Abstract

A box girder bridge deck consists of top and bottom slabs connected by vertical or inclined webs. The area enclosed by the webs and slabs imparts very high torsional stiffness to the box section, so box sections are most suitable for highway bridges which are curved in plan and subjected to heavy eccentric loads. An analytical solution of box girder bridge under load is rather complicated due to the development of distortional stresses which depend on,many factors. The present dissertation work consists of the development of analysis program for concrete box girder bridges for I.R.C. live loads. The program is data based and incorporats complete details of all classes of I.R.C. loadings. The input for loading is selection of class of I.R.C. loading and coordinates of one load only. For discretization of the structure, grillage analysis has been used. The structure has been discretized into the longitudinal members in two mutually perpendicular directions. For analysis of discretized grid, stiffness approach has been adopted using matrix notations. The analysis program calculates member forces such as torsional moment, bending moment and shear force at various sections of box girder bridge. The program also calculates maximum value of each force with corresponding other forces values to determine critical placing of loading for various sections of bridge deck. The program has been written in 'FORTRAN-77 and can run on a 'PC-XT'. For drawing various graphs, 'GRAPHER' software has been used