Performance Evaluation of Stone Masonry Arch Railway Bridge Under Increased Axle Loads
Many of the masonry arch bridges in the network of railway bridge stock belong to the civil engineering heritage of the railways. Therefore, their maintenance and management require careful consideration. Effective procedure for performance evaluation should promote solutions that are directed towards preservation and restoration of arch bridges by evaluating their existing structural capacity. Full scale experimental investigations have been carried out on a stone masonry arch bridge using a test train formation, for evaluating its performance under increased axle loads. Instrumentation of the interior span of the 3-span arch bridge is carried out to measure the displacement of the arch, stresses, tilt and strain of pier under increased axle loads. Dynamic tests have been carried out to evaluate the longitudinal force in the rail and longitudinal stress in arch due to tractive effort, braking and uniform speed cases to obtain the time-histories of deflection. Detailed analyses of the data acquired from field investigations are carried out. The numerical model is validated by comparing the deflections obtained from finite element analysis with that of the experimental static test results. It is found that the measured deflections for different static test cases are in good correlation with the results obtained from the analytical results. The maximum deflection measured under dynamic test conditions is found to be 0.465mm and this is found to be within the permissible limit. Longitudinal stresses in arch due to tractive effort and braking have been arrived based on the data collected from the tests. Based on the experimental results, it is found that the maximum longitudinal force (per rail) at rail level is 12.31T in instrumented span. The maximum longitudinal force per track is 24.62T. The maximum longitudinal stress in the arch due to tractive effort is 0.312MPa which is in close agreement with the numerical analysis. The responses (deflection at crown, arch spread, live load stresses and pier strain) obtained from the present study show that these are in permissible limit for the bridge considered. The study has provided a technique for measuring strain in piers which are generally very low and cannot be measured using conventional strain gage instrumentation. It is opined that the flatjack technique as described in the study would pave the way for measuring the live load stresses in masonry arch bridges under dynamic load conditions which will facilitate the engineers for planning appropriate maintenance strategies.
