BRIDGE DECK BEHAVIOUR VIS-A-VIS LONGITUDINAL GIRDERS

Abstract

Girder bridges are structurally efficient and economical for short and medium spans. A good deal of thinking goes into deciding about the sizes and arrangement of various structural elements of a bridge deck suiting a particular site. Safety end economy consideration govern the number of girders, diaphragms, cross-beams and thickness of deck slab. This necessitates the knowledge of comparative merits and demerits of different sets of combinations of deck elements. Herein,a study is made with different number of girders for a particular bridge, keeping the volume of material of the deck as constant and without varying the slab thickness so that the influence of girders alone may precipitate in the result.. This has been carried out, with - different skew angle keeping the span constant. Stiffness matrix method has been adopted for the deck analysis. To make the bridge deck amenable to stiffness matrix method, it is suitably discretized into proper grid work comprising longitudinal and cross structural elements. The bridge deck is loaded with IRC class AA tracked vehicle in a manner to have the maximum effect on the girders. Two possible modes of application of loads have been studied. Based on practice as well belief that the imposed load dispersion is solely a function of the transverse medium, it is common practice to manipulate the structural elements of the transverse medium in an effort to effectively distribute the deck loads amongst the girders. However, it is quite apparant that the overall deck behaviour will depend upon the relative stiffness of the transverse medium to that of longitudinal member. With a view to studying this aspect of deck system behaviour, eighteen girder bridge systems have been analysed by appropriately varying the longitudinal system while keepihg the transverse system constant,. Theresults are depicted in terms of bending moment, shear, deflection and support reactions with a view to deciding about the number of longitudinals and their corss