Experimental study on the residual seismic resistance of ultra high performance cementitious composite filled steel tube (UHPCC-FST) after contact explosion

This paper aims to ex perimentally study the residual seismic resistance (RSR) of Ultra high performance cementitious composite filled steel tube (UHPCC-FST) specimen after contact explosion. Firstly, six 1/4 scaled circular UHPCC-FST were fabricated with the column height, outer diameter and core concrete compressive strength being 2000 mm, 203 mm and 131.5 MPa, respectively. Then, four of which were tested under contact explosion, in which the TNT charge weights were 1-3 kg and the height of bursts are all 250 mm. Furthermore, the RSR of both four post-blast UHPCC-FST columns and two intact control specimens were examined through the low-frequency horizontal cyclic loading test, in which two perpendicular loading directions were considered. It indicates that: (i) UHPCC-FST column suffered the localized cratering damage beneath the explosive, and the damage level became more severe with increasing the TNT charge weight; (ii) all the specimens endured the bending failure under the cyclic loadings, which occurred near the column bottom and cratering position for intact and post-blast specimens, respectively; (iii) RSR of the post-blast column deteriorated more obviously for the cyclic loading direction being perpendicular to the cratering face compared to that being parallel to the cratering face. Finally, based on the quantitative degradation of the seismic resistance, stiffness and energy consumption of the present UHPCC-FST specimens, a composite damage index was proposed to evaluate the RSR of the post-blast column after contact explosion. The present work could provide helpful references in the damage assessment and retrofitting of the post-blast column under potential contact explosions in the seismic zone.