Analysis and Design of "T" Beam Slab Type Bridge Superstructure and Comparision of Economy

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 element in preliminary stage.

The motive behind present study is to prepare some useful interface for preliminary design of bridge 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 or environmental conditions. To achieve this aim, designer must begin with proper initial structural combination.

This initial combination can be selected from the interface developed from this study. There is no unique form of design which would be always most economical. It is only by comparing a few designs that the economic design can be found in a particular set of conditions. Economy can be achieved by separately or simultaneously considering one or more of the following factors: Span, Superstructure Cross Section, Cost of Prestressing Steel and Concrete Consumption. The present study includes parametric study on prestressed concrete girder bridge superstructure. In that the various alternatives are taken for analysis & design. The alternatives are variation in span, number of girder, span to depth ratio and skew angle, by which superstructure design is mainly affected. Total 72 different alternative cases were studied.

The analysis was done by using professionally available software ‘SAP2000 software’. The finite element model is used to generate bridge superstructure in SAP2000. For modeling all alternatives in SAP2000 one general spreadsheet was prepared which can be directly imported in SAP2000. All geometry and loadings can be easily modeled in SAP2000 by prepared worksheet. The spreadsheet was prepared for design and estimation of cost.

Parametric study was done for calculation of most economical span to depth ratio, L/D ratio of 18 was found most economical in present study. Therefore L/D ratio was taken as 18 and all alternative cases were studied and the cost comparison was done.

The variation in various forces and resulting changes in design with respect to increase in span and skew angle is also discussed. The effect of change in span and skew angle on cost for various components of designed bridge is also covered. It is found that the 4 girder system up to 30 m span with L/D ratio of 18 is more stable and preferable.

The complete project provides a direct and simple method for optimal economic design of prestressed T beam slab type bridge superstructure.