Comparative study on simply supported pre-stressed box girders and double T beams for Two lane highway bridges

Abstract

There are about 3800 bridges on National Road Network with length varying from 3.0 m to 300.0m.These bridges have varying widths about 3.0m to 20.0m and some of these have been constructed more than 50 to 100 years back. Most of the bridges span 30m and above. They were constructed using steel concrete composite or steel. Steel is a very costly material, even though it has some very good structural advantages./ Few bridges have been constructed in the recent past using T,M,Y,I beams in the span around 30m by launching side by side. And this was a very tedious procedure. Aesthetic view of a bridge has been neglected during the past 50 years or more due to the design complexity. Time for completion of a bridge has become an uphill task these days due to the price fluctuation and other constrains such as traffic and utility services./ This study is concentrated on the design of a simply supported 30m pre-stressed post tensioned box girder and comparing the properties and other advantages mainly with the Double T beams. Mainly the geometry of the box girder was selected with the help of past research papers and the geometry of the double T beam was selected where the cross sectional area is approximately equal to the cross sectional area of the box girder. Design of the box girder is done using three dimensional finite element method and the spine beam method. Although the Finite Element method is very versatile and powerful manual, calculations is also done as box girders designs are very rare. As the history of the double T beams arc also very rare, it is also designed using SAP 2000, spine beam, and three dimensional Finite Element methods./ Both beams are analyzed for HA,HB moving loads. Load combinations are considered, dead plus HA live load as load combination 2 and dead plus HB as load combination 3 Shear force, bending moment, tortional moment, support reactions, stresses, amount of tendons were compared. In spite of that, the launching method, capability for utility services were also compared. Conclusions and the recommendations of the study will be laid down based on the results in the study