Resilience Evaluation of Seismically Detailed Reinforced Concrete-Block Shear Walls for Blast-Risk Assessment

The increased demand for resilient infrastructure under accidental or deliberate explosions has resulted in the urgent need to quantify the performance of both existing and new building components under such extreme loading events. The current study focuses on evaluating the resilience of reinforced masonry (RM) shear wall systems under blast, which is accomplished by quantifying the walls’ blast response in the out-of-plane direction and the resulting damage levels. In seismic zones, such RM walls are detailed to resist in-plane loads in a ductile manner, and thus minimal damage is usually expected. Given that blast resistant design of civilian buildings only recently has been formally introduced in North American design standards, quantifying the out-of-plane response and ductility capacities of RM shear walls has not been common practice in mainstream building design. In this paper, a nonlinear single-degree-of-freedom (SDOF) model is developed to predict the out-of-plane response of RM wall components under blast loading. The SDOF model is first validated by using live explosive (free-field) test results. Subsequently, the model is used to perform a numerical investigation beyond the range of experimental parameters adopted in the test program, by considering a number of wall design characteristics such as wall reinforcement ratio, concrete block size and strength, wall height, and reinforcement arrangements; a wider range of design basis threat levels––identified by charge-mass and standoff-distance combinations––is also considered. In general, the study indicates that RM walls are capable of withstanding substantial explosions, which would result in different damage intensities depending on the wall vulnerability and blast hazard levels. The study also shows that significant reduction in the wall out-of-plane response can be achieved by using two layers of reinforcement instead of the typical single layer in RM walls, even in the case of reduced reinforcement ratio. The SDOF model is also used to develop RM wall performance charts that can be further refined to serve as design guidelines for the purpose of blast risk mitigation in future editions of the North American blast design standards. Finally, the findings from this study indicate that RM walls that are detailed to respond in a ductile manner under in-plane seismic loads might not necessarily exhibit a ductile response when subjected to out-of-plane blast loads. The latter observation highlights the importance of adopting a holistic multihazard design approach when evaluating the vulnerability and resilience of building systems under extreme events.