Behaviour of composite beam-column joint with fin plate connection subjected to impact loads

Abstract

Falling-debris impact on a remaining building is detrimental and may lead to propagation of initial damage by abnormal loadings (gas, explosion, etc.), if the structure is not able to resist the impact. This in turn will lead to progressive collapse of the whole structure. For a frame structure, fin plate (or shear tab) connections ideal for gravity-dominant design is normally weaker than seismic connection. Therefore, its integrity under dynamic loading is of great importance for anti-progressive collapse performance. A series of tests on composite joints with fin plate connections subjected to impact loads was conducted to investigate the dynamic behaviour, which served as an unfavourable loading scenario for falling-debris impact which occurred close to the beam-to-column connection. Three middle joints and one side joint were designed and tested in the experimental programme. The test parameters included impact load, joint type and composite slab thickness. Structural response, failure mode and development of strains were investigated. A comparison of test results and design predictions of ultimate strength was conducted. The comparison was also extended to composite joints subjected to quasi-static loads. It was found that an intermediate level of strain rate in the order of 1 s−1 was recorded for the impact tests and it would lead to maximum increases of 28 % in concrete strength and 16 % in steel reinforcement strength, respectively. Compared to quasi-static tests, strain rate effect in the impact tests could increase compressive arch, catenary and flexural resistance of composite FP joints. Moreover, composite slab effect was beneficial to flexural resistance and detrimental to tying resistance, since deformation capacity of fin plate connection was consumed for flexural resistance at small deformation stage.