Evaluation of Progressive Collapse Effects in Modular Bundled Tube Frames under Near-Field Earthquakes imposed through Incidence Angles

In this study, the nonlinear behavior of a studied 20story steel bundled tube frame structure is evaluated under applying the assumed incidence angles to the imposed directions of near-field records. Additionally, the related effects on the stability of the studied structure subjected to the probable forming of progressive collapse, have been studied too. The results of this research were obtained based on conducting nonlinear dynamic time history analyses. Four assumed incidence angle case studies were considered to an ensemble of three-component earthquake records. Moreover, three-member removal situations were also assumed for the selective column elements of the studied structure subjected to all chosen ground motions.The results of this study show that the structural response parameters have a relatively larger amplitude under removing of the corner column at the first story, than the other two cases of column removal which to be assumed at 10th story and also for the middle column of the outer frame. Furthermore, the structural responses did not change significantly with the increase of the incidence angle from 0° to 45°. The obtained results show that the formation of plastic hinges and inelastic zones in the structure would indicate high deformation demands at the middle stories and also the induced demand variation decreases along upward of the height. Additionally, removing of the corner column would result in the formation of more plastic hinges, which cause relatively greater structural damages and gradually reduces the stability of the studied structure. It is worth noting that the structural response parameters under each element removal and subjected to strong near-field records, remains in a relatively stable domain. Furthermore, the variation of response parameters did not exceed the life safety limit.