Seismic evaluation of existing reinforced concrete bridges in Karachi (Pakistan) with lightweight concrete in deck slab

Bridges are lifeline structures and vulnerable to significant damage particularly in earthquake prone region like Karachi. The paper evaluated the seismic response of existing prototype reinforced concrete (RC) bridges in Karachi as a function of their economic and commercial importance. Three case study bridges with different configurations in sub and super-structures were identified from authorized stakeholders and evaluated for overall response with and without lightweight concrete (LWC) in deck slab. A detailed nonlinear finite element model of each case-study bridge has been developed and analyzed through nonlinear static pushover analysis. The behavioral changes were investigated in terms of engineering demand parameters including base shear and displacement in bridge pier along with fragility functions for both the cases. Results showed that seismic demand in terms of base shear and displacement in bridge pier curtailed in case of LWC as compared to normal weight concrete (NWC). The average reduction in base shear is 7% and in displacement it is around 6%. Furthermore, damage capacities obtained from fragility functions for different limit states increased from minor to collapse limit states in LWC as compared to counterpart. This increment 2-7% in Bridge-I, 6-12% in Bridge-II and 3-6% in Bridge-III were observed from minor to collapse damage states.