Effects of UHPFRC jacketing and axial loading on the blast behaviour of reinforced concrete beams and columns

The objective of this study was to characterize the effects of axial loading and UHPFRC (ultra-high performance fiber-reinforced concrete) jacketing on the blast performance of reinforced concrete beams and columns. The test group included two as-built and strengthened columns with UHPFRC jacketing applied over the full span (FJ). The companion group included three as-built and UHPFRC-strengthened beams, with jacketing applied either over the full span (FJ) or in the middle hinge region (FJ-Mid). With the exception of axial load, the specimens in both groups had the same dimensions, reinforcement properties and boundary conditions. In both groups, the UHPFRC jacketing improved control of blast-induced displacements and damage when compared to the as-built specimens. Under equivalent blasts, axial loading was also confirmed to reduce the magnitude of the displacements in both the as-built and retrofit specimens. In addition, applying UHPFRC jacketing increased the blast capacity of the columns, but ultimately led to rupture of the tension steel bars. As part of the numerical study, finite element (FE) modelling was used to predict the blast behaviour of the test specimens, and to study the effects of parameters not considered in the experiments, including the effects of axial load ratio, boundary conditions, longitudinal steel ratio and jacket design on blast performance and failure mode.