Effect of retrofit type on the blast performance and failure mode of HSC beams retrofitted with UHPFRC

Abstract

This paper presents a strategy to prevent shear failure and improve the structural performance of existing high-strength concrete (HSC) beams under blast loading. The strategy involves retrofitting with ultra-high performance fiber reinforced concrete (UHPFRC), a novel material which is well-adapted for the blast hardening of concrete structures. Shock-tube air-blast tests are conducted on seven HSC beams which are retrofitted with UHPFRC. The objective was to characterize the effectiveness of various retrofit types on the blast behaviour of both shear-deficient and flexural-dominant HSC members. Three retrofit types were considered: U-jacketing (UJ), full-jacketing (FJ) and a tension-sided (T) overlay. Other parameters included the effects of the concrete substrate roughening method, as well as the tension steel ratio (1.6% or 2.4%) and presence of stirrups in the beams. Both the UJ and FJ retrofits were found to be effective in preventing shear failure in shear-deficient HSC beams having varying shear demands. In addition, both retrofits increased member strength and stiffness, thereby reducing blast-induced displacements and increasing overall blast resistance. Comparing the two retrofits, optimal performance was obtained with full-jacketing due its ability to delay concrete crushing. In HSC beams with sufficient stirrups, both the T-sided and FJ retrofits reduced blast-induced displacements; however, the use of full-jacketing was better able to control damage and increase blast capacity. The roughening method had no substantial effect on the FJ retrofit performance or failure mode, with no debonding observed in the tests.