COST OPTIMIZATION ASPECTS OF RCC BOX GIRDER BRIDGE

Abstract

The importance of transportation for the prosperity of any country cannot be disregarded. The transportation system is the major guiding wheel for the development of any country. Bridge engineering is one of the most important part of the transportation industry and an utmost fascinating field in civil engineering. In today’s world, bridge construction and engineering has achieved a worldwide level of significance, due to its ability to disseminate congested traffic, economic contemplations and visual appearances. The behaviour of a structure depends upon the span arrangement and its stiffness. Apart from the structural significance, the economy plays a vital role. The criterion of finding the best and cost-efficient results with maximum possible advantage is called optimization. As a result of past and present advancements in structural engineering field it is easier to adopt a safe design but it is certainly difficult to find the economical design, hence optimization technique is necessary to get most cost-efficient design. There are a lot of parameters which controls the design of a bridge structure, such as the span to depth ratio of the bridge, span length, cross section, material properties etc. The major components that affect the cost of the bridge were selected on the basis of parametric study performed on all variables. The major variables were selected for their effect on cost and the performance of reinforced concrete box girder bridges. The slenderness ratio is generally being selected by the designers by the past experiences or from the construction projects executed in the past, but there is a need to identify the most optimum values so as to control the economy of the structure. This thesis considers the important aspects related to cost optimization of box girder bridge structure. In this study, a Box girder section of different spans such as 30m,40m and 50m for the both cases of single cell and double cell is considered. It is then iterated with the span/depth ratios of 15,20 and 25. Total 18 no. of cases are formulated and a thorough design and analysis is carried out. The dead load and the live load effects have been taken into the consideration according to latest IRC 6:2016 recommendation. The analysis is taken out on the software Staad.Pro to get the maximum deflection, and the maximum bending moment and shear stresses. The deflection which is obtained from the analysis is compared with the permissible deflection and the percentage variation in each case is attained. The detailed design of the Box girder

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section for each span is carried out on the spreadsheet. The cost optimization is carried out by calculating cost for each configuration by calculating the material quantities in each case and then by applying rates as per Government of India Schedule. The results are taken out in the form of graphs and the most optimum values for each case of span depth ratio is iterated. From the study it is found that with increase in the span depth ratio the deflection increases, but the unit cost of RCC box girder decreases. The trend is similar for the increase in span lengths with constant depth. It is contemplated that the decrease in cost with respect to material quantity is significant only up to a specific ratio of span-depth. It is pragmatic that after a certain span-depth ratio considered in this study, the deflection increases beyond permissible limit. It is also observed that the number of cells plays a significant role in the structural behaviour and the economy of the structure.