Residual seismic resistance of CFDST columns after a close-in explosion: Experimental study

This paper examines the residual seismic resistance of a concrete filled double-skin steel tube (CFDST) column after a close-in explosion experimentally. First, six 1/4 scaled CFDST columns were fabricated and tested under a close-in explosion with scaled distances ranging from 0.116 m/kg1/3 to 0.232 m/kg1/3. After that, the failure mode and seismic behaviours of the CFDST columns, including one intact specimen, three postblast specimens, and three postblast specimens with retrofitting, were investigated via the cyclic loading test. Additionally, a modified composite damage index was proposed. The results showed that: (i) The CFDST column exhibited a combined localized crater and overall deformation under a close-in explosion, which became more severe as the scaled distance decreased. (ii) As the initial damage degree of the specimen increased, the likelihood of a plastic hinge developing in the blast-induced crater region to consume the hysteretic energy increased. (iii) A weak hinge formed at the crater caused by slight blast damage can assist the plastic hinge induced by the repeated lateral loading to enhance the energy dissipation capacity of the specimen. (iv) In the cyclic loading test, the lateral loading capacity, initial stiffness and energy dissipation of the specimens decreased with the increase in the initial degree of the blast-induced damage. (v) The deformation of the inner steel tube had an unfavourable influence on the stiffness and energy dissipation capacity of the postblast specimen with and without retrofitting. (vi) Among all the specimens, the retrofitted columns exhibited the worst lateral loading capacity, ductility, and energy dissipation capacity due to weld joint failure at the column foot. (vii) When the damage index is less than 0.5, the postblast CFDST column should be retrofitted for further use. In particular, the inner steel tube should be repaired. When the damage index exceeds 0.5, demolishing the postblast CFDST column is suggested.