Analysis and Design of Simply Supported RCC Bridge for Vehicle Loads

Reinforced concrete T-beam bridges are among the most common superstructures used for highway spans of 12 m to 25 m in India. The deck slab and the longitudinal girders act together as flanged beams, which gives an efficient section for resisting the large bending moments produced by heavy vehicles. This study presents the analysis and design of a simply supported RCC T-beam bridge with an effective span of 20 m for a two-lane national highway, with particular emphasis on the effect of the vehicle loads specified in IRC 6:2017 on the deck slab, longitudinal girders and cross girders. The superstructure consists of three longitudinal girders spaced at 2.5 m, cross girders at the supports and at mid-span, and a 250 mm thick deck slab with cantilever overhangs carrying crash barriers. The carriageway width is 7.5 m. The main live loads considered are IRC Class A loading in two lanes and Class 70R wheeled and tracked loading, with the impact factors specified in IRC 6. Because the distribution of vehicle load among the girders strongly influences the design, the transverse distribution is studied using both the classical Courbon method and a grillage model in STAAD.Pro. The deck slab panels between the girders are analysed for concentrated wheel loads using Pigeaud's method, which accounts for the two-way action of slabs supported on four sides. The longitudinal girders are analysed for the absolute maximum bending moment and maximum shear force under moving loads, and influence lines are used to identify the critical positions of the Class A train and the Class 70R vehicle. The grillage model, consisting of longitudinal members representing the girders and transverse members representing the slab and cross girders, is loaded with the IRC vehicles through the moving load generator of STAAD.Pro. The girders are designed as T-beams for the ultimate limit state of flexure and shear according to IRC 112:2011, and they are checked for the serviceability limit states of stress, crack width and deflection. The deck slab and cross girders are also designed, and the reactions at the supports are used for the selection of elastomeric bearings. The results from the Courbon method and the grillage analysis are compared to assess the accuracy of the simplified method for the adopted girder spacing and cross girder arrangement. The study finds that the Class 70R tracked vehicle governs the bending moment in the outer girder when placed eccentrically, while two lanes of Class A loading govern the moment in the central girder. The Courbon method gives outer girder moments about 9 percent higher than the grillage analysis, which shows that it is conservative for this configuration. The design results in girders of 1.6 m overall depth with a web thickness of 300 mm. The work provides a clear procedure for the design of T-beam bridges under IRC loading and can be extended to continuous and prestressed girder bridges.