Experimental study on dynamic responses of reinforced concrete frames under sudden column removal applying concentrated loading

Abstract

This paper focuses on structural behaviour of storeys above the targeted column that is suddenly lost due to accidental/terrorist events. The pertinent question is whether these storeys will remain stable, or the ensuing dynamic motion will cause them to fail during the free-fall stage. It is assumed that the two-dimensional frame structure above the targeted column is in pristine state. Previous quasi-static studies on reinforced concrete beam-column structures under missing column scenario have highlighted the potential of catenary action on providing alternate load paths to prevent catastrophic collapse. However, corresponding dynamic tests, either did not share the same loading configuration with the static tests, or did not have sufficient headroom and the specimen hit the ground before catenary action could be fully mobilised. On this paper, a series of dynamic tests was carried out for two-dimensional reinforced concrete beam-column frames simulating the sudden removal of a supporting column via a quick-release device. The specimens were loaded and hung by a mechanism which could be released to effect free vibration. Development of catenary action, which has not yet been confirmed in any previous dynamic tests, was well captured. The study also showed the influence of inertial and strain rate effects on structural response. Most importantly, the dynamic tests applied the same method of concentrated loading at the middle joint as the previous quasi-static tests conducted on similar specimens. As a result, comparisons could be made on damage patterns and failure modes between the dynamic tests and the static tests. Compared to static environment, the dynamic tests only took a few seconds and their behaviours are closer to the actual behaviour of the storeys that undergo free-fall acceleration.