عنوان مقاله [English]
During the recent decade, there have been many studies undertaken regarding progressive collapse in steel frame structures.Progressive collapse is a phenomenon wherein the local damage or failure of an element spreads through other adjacent elements, leading to the eventual failure of the structure.Past studies have mainly focused on progressive collapse in frame structures by removing specific columns located in the first story.In this aper, rogressive collapse of a steel tube in the tube structures under seismic loads has been evaluated. For this purpose, three types of steel tube in the tube structures have been modeled, with 2, 2.67, and 3.2 meter distances between the columns, and 30, 45, and 60 stories in height. The structures have been analyzed using time-history dynamic analysis.Because of the formation of plastic hinges under seismic loads at the height of this type of structure, the elements removed were modeled with hinges that had not been placed in the first story but had spread to the other stories.The plastic hinges formed under increased seismic loads in the elements have been modeled by elements with hinges that can resist a portion of the bending moment.Results show that by increasing the distance between columns in the 30 and 45-story tube in the tube structure, the chance of progressive collapse increases. It is due to the formation of a plastic hinge in the lower story, and development of a negative shear lag in the upper stories.In ontrast to 30 and 45-story tubes, increasing the distances between columns in the 60-story tube in the tube structure results in a reduction of the chance of progressive collapse. It occurs because of the distribution of plastic hinges at the height of the structure, and also lack of negative shear lag in this type of structure.The results indicate that the tubes in tube systems are efficient in the very high structures.