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Under a disproportionate collapse, the sudden loss of a support causes a dynamic response that can amplify the internal forces in the surrounding members and lead to significant global damage. This study considered a two-dimensional, quarter scale, two bay, two story reinforced concrete frame with discontinuous reinforcement. In order to simulate an interior bay condition, the frame was axially restrained at the adjacent-bay beam locations. Dead weights were applied to simulate the dead and live loads expected to be present during a collapse event. To initiate the test, and to simulate the sudden loss of a load-bearing column, a kickstand was implemented. The results presented herein are from four dynamic tests under various levels of applied load. The fourth drop, with a load corresponding to 42 percent of the 1.2*DL + 0.5*LL typically specified in disproportionate collapse guidelines, resulted in a catenary action. The results show that there is a very fine tipping point at which the structure is pushed past the compressive arch and flexural range of resistance into the catenary action range (hereafter referred to as the snap-through effect). Furthermore, the results show that due to this snap-through effect, the dynamic increase factor can be as great as 2.4, significantly higher than the value specified by the aforementioned guidelines.	

Dynamic increase factor in reinforced concrete frames under disproportionate collapse