Analysis and Design Of Multi Cell Box Girder Type Bridge Super Structures

Abstract

Bridge construction today has achieved a world – wide level of importance. The numbers and sizes of bridges have continuously increased in the last fifteen years in India. Man’s increasing mobility through railway and motorized transport has caused such complex forms of bridges to be built. To cope-up with this demand, tremendous efforts in India in the form of construction of bridges are continuing. Due to this heavy traffic existing single lane bridges are transferred to multilane bridges. Increase the construction of long span bridges. In recent years, single or multi – cell reinforced concrete box girder bridges have been widely used as economic and aesthetic solution for today’s highway systems. The main advantage of this type of bridge lies in the high rigidity in torsion. This is due to the closed box–section and convenience in varying the depth along the span. High torsion stiffness gives them better stability and load distribution characteristics and also makes this form particularly suitable for Grade separations. This hollow section also can be used to accommodate services and has added advantage of less weight. This work was carried for study the concept & mechanisms of multi cell box girder bridges. The study includes methods available for analysis of multi cell box girders. The grillage analogy method used for analysis of all multi cell box section. The dead and live load combination used for analysis, live load consider as per IRC- 6, 2000. The section analysed for three live load cases Class 70-R, Class AA and Class A vehicles. In multi cell section the moving load generated in both the direction i.e. longitudinally and transversally for getting maximum response in each web. From the analysis transverse live load distribution coefficients obtained for multi cell sections span varies from 20m to 50m. In bridge section normally two types of diaphragms provided as intermediate and end diaphragms. The study is performed on with and without intermediate diaphragms model on three cell, 30m box section. The analysis shows that intermediate diaphragms providing better stability to the structure by reducing III deflection. But considering construction aspect and increasing in the cost, effectiveness of intermediate diaphragms is less. So intermediate diaphragms is not provided in multi cell box sections. The five condition of cell i.e. single to five are considered for analysis and to found economical alternatives the parametric studies performed. The parametric study performed with three alternatives, 1. Cell variation – single, two, three, four and five cell consider. 2. Span variation – 20 to 50m. 3. Depth variation. This parametric study obtained the economical span/depth ratio for particular span. Also obtained the economical multi cell section for particular span.