Influence of Lateral Load Resisting System on Collapse Performance of Reinforced Concrete Structures Exposed to Blasts

Abstract

The objective of this study is to examine the influence of the type of lateral load resisting system on the progressive collapse behavior of reinforced concrete structures exposed to extreme blast loads. In this study, three 10-story hypothetical reinforced concrete structures were modeled with shear wall systems and corresponding moment resisting frame systems. The structures consisted of 3, 4, and 5-bay plans, and designed according to American Concrete Institute (ACI 318- 11) Code Standards to resist gravity and wind loads. The structures were exposed to a charge at the ground floor level and close to the middle exterior columns. The blast was of sufficient magnitude to severely damage at least one of the exterior columns in all of the structures. The collapse behavior was modeled with the Applied Element Method, which captured the nonlinear, transient dynamic response of the structures. In this approach, elements are initially connected with spring elements between element surfaces, and once material failure occurs, elements may separate and collide to replicate material disintegration and debris propagation. Concrete failure behavior is simulated with a Maekawa compression model, where cracking initiates when principal stress equals the material tensile strength. Reinforcement is modeled with spring elements, and the steel nonlinear stress-strain curve is described by Ristic’s model. Models ranged in size from approximately 75,000-117,000 elements and were solved with a time step increment of 0.0001 s to capture realistic blast response. It was found that the reinforced concrete frames that contained shear wall systems generally resisted a progressive collapse more successfully than moment resisting frames, where the collapse progression was halted once it reached the shear walls. On the other hand, moment-resisting frame buildings usually resulted in a complete progressive collapse.