PARAMETRIC STUDY OF CONCRETE BOX GIRDER BRIDGE by Nupur Singla
With more and more infrastructure projects coming up in India and all around the world the economics of bridges have also received a lot of attention in last few decades. Bridges are an essential part of transportation infrastructure of any country. It is becoming increasingly essential for a designer to find out the most efficient solution which could be both safe and economical. Structural behavior and economy of a bridge largely depends upon its span arrangement and geometry. Major geometrical parameters chosen for superstructure is span length, span/depth ratio and number of cells in Box Girder Bridge. Designers use these parameters based on the past experiences and same typical values are used repetitively considering their satisfactory performance. With the advancement of construction technology and invention of high performance concrete it is necessary to revise the conventional values and make the structure more economical. Span-to-depth ratio, also known as slenderness ratio (L/h), is an important bridge design parameter that relates a bridge’s span length to its girder depth. Similarly number of cells in Box Girder Bridge also plays a vital role in structural behavior of a bridge. Hence, all these parameters are considered together to study the effect of their effect on the structural behavior as well as cost of a box girder bridge. In the present work, the effect of Span to depth ratio, span length and number of cells is studied by analyzing and designing Reinforced Concrete Box Girder Bridge by considering different values of these parameters. Span to depth ratios 15, 20 and 25, Span length 30m, 40m and 50m is considered each for single and double cell Box Girders. Thus, total 18 cases are considered in this study. Detailed analysis is carried out to find out the design bending moment, shear force and deflection values. The analysis of bridge superstructure is carried out in STAAD Pro. Software. From the detailed analysis & design of each configuration, the influence of given parameters is studied on the deflection of Box Girder Bridge. The design as per Indian Standard Codes for each configuration is done. Following that, the drawings are prepared from which the material quantity i.e. Concrete and steel are calculated. Then the rate as per state government schedule is applied to these quantities to obtain the total unit cost of a Concrete Box Girder Bridge superstructure. From the study it is observed that with increase in span to depth ratio, deflection of the structure increases. With increase in ratio, depth decreases which ultimately decrease the quantity of material. This eventually lowers the cost of superstructure. It has been observed from the present study that with change in span length there is significant change in overall steel and concrete quantity for the bridge which leads to huge variation in raw material costs and also the variation in deflection of bridge deck. Similarly number of cells in Box Girder Bridge also plays a vital role in structural behavior and economy of a bridge.