Relative Strength of Repaired Arch Bridges

This paper reports on two sets of experimental data on the strength of repaired arch bridges which had been previously loaded to failure. The repair was carried out by applying sprayed concrete to the intrados of arch, increasing the total arch barrel thickness by 33%. This data is compared with parametric studies conducted using a finite element program developed for the assessment of masonry arch bridges. The finite element study indicates that the most significant factor affecting performance is the condition of the interface between concrete and masonry; if perfect bond is assumed, the load capacity of masonry arches may be increased by up to 1000% when the original thickness of the arch barrel is doubled with a concrete saddle. For a 33% increase in arch barrel thickness, the numerical studies showed that, depending on the bond condition, up to double the load carrying capacity may be expected. The two test arches gave consistent results with an average 83% increase in load carrying capacity. Equations are also given which provide upper and lower bound guidance on the strengthening effect of concrete saddles.