Effect of initial blast response on RC beams failure modes

In this study the dynamic response of Reinforced Concrete (RC) beams was experimentally evaluated under blast loading. Eighteen beams were field tested using 40 to 250kg charges of ANFO explosive detonated at a ground standoff distance of 10 to 30m. Other test parameters included variation of transverse and longitudinal reinforcements. Blast wave characteristics, displacement and strain histories were measured, and the post-blast damage and mode of failure of the test specimens were observed. Results showed change in failure mechanism with variation of blast load scaled distance, and/or longitudinal reinforcement. To simulate the observed responses of the test beams and investigate the relationship between the initial forces and deformations developed in RC beams due to blast loading and the associated failure modes, beams were modeled using the Timoshenko beam theory. It was determined that beam deformations in the initial phase of a blast induced response cycle were dominated by shear. The ratio of shear demand to shear capacity, the latter computed based on the Canadian Standard CAN/CSA A23.3, was deemed to be the most influential parameter that governed the failure mechanism. In addition, assuming a deformed shape based on static loading resulted in underestimating the shear demand, which, in turn, could lead to inaccurate predictions of the failure mechanism.