INCREASED LOAD CAPACITY OF ARCH BRIDGES USING SLAB REINFORCED CONCRETE

This paper reports the results of a series of small-scale centrifuge model tests undertaken to investigate the service and ultimate load capacity of un-strengthened and repaired/strengthened masonry arch bridges. Un-strengthened two dimensional 1:12 scale models of a 6-m single span arch bridge were initially tested using appropriate service loads and were subsequently line loaded up to the observation of the first sign of failure. Two types of arch geometry were tested, one shallow arch with span/rise ratio of 4 and one deep semicircular arch. The ultimate strip load was applied over the whole width of the arch barrel on top of the backfill at the quarter point of the arch span for both arch geometries. Following the initial tests the arches were repaired/strengthened by laying a reinforced concrete slab on top of the backfill. The arches were subsequently re-tested, initially with a service loading, and then up to full failure. Deflection of the arches and the backfill/arch interface pressures were recorded during the application of all loads. The strengthened arch results are compared to both the un-strengthened results and to previous tests undertaken using a similar concrete slabs saddled immediately above the extrados and sprayed onto the intrados. The present results indicate a significant improvement in the ultimate load capacity of the repaired arch over the un-strengthened arch. The load at failure of the shallow strengthened model was 3.4 times of that of the un-strengthened model and 2.7 of average benchmark failure load with of the same shape. The results for the strengthened deep arch were, respectively, 3.7 and 3.2 times as strong as the un-strengthened arch. The application of the slab to the surface appears to be at least equivalent to application directly to the arch intrados and extrados.