GIRDER BRIDGE ANALYSIS USING MOMENT DESIGN COEFFICIENT

Abstract

A girder bridge consists of two structural systems -transverse and longitudinal. The transverse system by way of slab and crossbeam/diaphragm transfer the imposed load on the deck to the main girders which in turn transmit them to the supports. Various methods of analysis aim at finding the distribution of imposed load amongst the girders, commonly referred to as Load Distribution Theories. Harmonics method is one such theory which possesses certain unique features in terms of the structural indentification of the bridge systems. It lends a powerful tool to the bridge designer from viewpoint of quickly assessing the structural behaviour of the girders irrespective of whether the bridge is skew or right. Harmonics method is applicable when loads are directly acting on girders. Thus, the laod on the deck lying in-between girders are replaced by an equivalent system of loading acting on the girders. The equivalent load system is obtained as per assumptions and suggestions made in chapter 5 of this dissertation. These equivalent loads acting now on the girders are distributed amongst all the girders of the bridge in accordance with the load distribution theory of Harmonics method. As stated earlier, harmonics method lends itself to develop bending moment coefficients for girders based (iv) on certain structural parameters of a bridge. Taking advantage of this feature, the equivalent loads as computed above have been suitably combined with the girder moment coefficients already available to obtain moment values at various locations of the girders. In the present dissertation work, efforts have been made to develop an efficient computation procedure to quickly obtain the equivalent loads for any transverse position of the IRC bridge load systems. These computation procedure have been extensively used to obtain girder moments for the following types of bridge and class of IRC loadings: (1) Right bridge ()-=-0°): (a) IRC: class A vehicle (b) IRC: class AA tracked vehicle (c) IRC: 70 R wheeled vehicle (2) Skew bridge (A=30°): IRC: claSS AA wheeled vehicle Based on the relevant discussions logical conclusions have been arrived at. The main burden of efforts has been to demonstrate the accuracy and efficiency of hand computation techniques for analysis of girder bridges (right or skew) using harmonic bending moment coefficients.