Crack damage of multi-story CFT frame under strong ground motion

The damage ratio equation of H-section beam under strong repeated load is obtained on the basis of the very low-cycle fatigue of it. By introducing not only the steel tube crack of CFT column but also the very low-cycle fatigue of H-section beam, the seismic response and collapse of multi-story CFT frames under extremely strong ground motion have been calculated. From the results it is shown that the fracture of H-section beam does not affect the collapse of CFT frame directly. The damage ratios of CFT frame under strong ground motion have been also investigated in relation with the column-over-design factor (r(c)) of it. From the results it is shown that the damage ratios of CFT frame are closely related with the value of r(c) and r(c) = 2.5 is proposed as the lower limit value in the earthquake resistant design of multi-story CFT frame.