Special detailing techniques to improve structural resistance against progressive collapse

Previous research work has found that catenary action can significantly increase structural resistance in addition to flexural capacity under column removal scenarios. However, whether reinforcements in beams can effectively function as ties to develop catenary action against progressive collapse is a big concern in current engineering practice because of the limited rotational capacity of RC beam-column connections. Therefore, four RC frame specimens were designed and tested to investigate their structural behavior under a column removal scenario. In addition to a specimen designed with conventional detailing in accordance with ACI 318-05, the other three specimens were designed with special detailing techniques at little or no additional cost, endeavoring to improve catenary action capacity at large deformations without reducing the structural resistance at small deformations. The special detailing included placing an additional reinforcement layer at the midheight of beam sections, partially debonding bottom reinforcing bars in the joint region, and setting partial hinges at one beam depth away from the adjacent joint interfaces. Furthermore, the nonlinear static responses obtained from the tests were used to evaluate the progressive collapse resistances of the four specimens with the consideration of dynamic effect. With systematic instrumentation, the effects of detailing techniques on structural behavior are demonstrated in this paper at different levels. In particular, the mechanism of each special detailing to affect beam-column connection rotations is illustrated and discussed in detail. Finally, suggestions on structural design against progressive collapse via catenary action are provided.