Analysis and Design Of Steel-Concrete Composite Road Bridge Superstructure

Abstract

The bridging activity is as old as human civilization. Innumerable bridges of various kinds and of various materials have been built from times immemorial. In design of any kind of structure the economy is very essential criteria. Design of short and medium span highway bridge system requires careful selection of structural elements in a preliminary stage. The motive behind present study is to prepare some useful interface for preliminary design of composite road bridge system as per IS 800:1984 and IS 800:2007 provisions and then to find an economical section for the system. The primary aim of structural economy is to determine the most suitable combination of design variables, so as to achieve satisfactory performance of the structure, subjected to the behavioral and geometrical constraints, for specified loading. To achieve this aim, trials start from the initially assumed structural combination. There is no unique form of design which would be economical. The economical design can be found by comparing the costing of composite bridge in a given set of conditions. Economy mainly depends on various factors like span and superstructure cross sectional dimensions. The present study includes parametric study on steel-concrete composite four lane road bridge. In that various alternatives are taken for analysis and design. These alternatives consist of variation in span and span to depth ratio and designs as per IS 800:1984 and combination of IS 800:2007 and IS 11384:1985 by which superstructure design is mainly affected. For these total 25 alternatives were taken considering spans from 15m, 20m and 25m with various span to depth ratio. The analysis of the composite bridge is done by using professionally available ‘MIDAS Civil software’ for dead load, superimposed load and moving load as a class A and class 70R IRC loading. The finite element model is used to generate composite bridge superstructure model in MIDAS Civil. The Excel sheet is prepared for design of deck slab, composite longitudinal girders, cross girders, stiffeners, web splice, flange, shear connectors and weld connections. IV Parametric study was done for calculation of most economical L/D ratio for 15m, 20m and 25m spans as per IS 800-1984. For this all 25 alternative’s costing was done with quantity analysis and rate analysis as per current market rates. From these most economical L/D ratios with minimum cost was found 9.9, 13.08 and 13.34 respectively for span 15m, 20m and 25m. Study was also done to find out the weight difference between composite section design and non-composite section design. It was found that composite section design was economical and cost was about 33 to 37% less as compared to noncomposite section design. Cost comparison was also done between IS 800-1984(working stress method) and IS 800-2007(limit state method). It was found that the limit state method design sections were 7 to 10 percent costlier than working stress method design section. The section design aids were also prepared for 15m, 20m and 25m span as per the IS 800:2007 and IS 11384:1985 with their section properties. The sections selected for design aids are safe in bending and shear. The complete project provides a direct and simple method for optimal economic design of steel-concrete composite road bridge superstructure.