Dividing Building Structure Into Four Interactive Parts With Tubular System and Rocking Motion To Make It Repairable After Major Earthquakes

Abstract eng:
Most of seismic design codes for building systems allow heavy damages to buildings, in case of major earthquakes, provided that the buildings are prevented against collapse or to keep the buildings' performance in LS or at least CP level. However, amount of the allowed damage can be so high that requires demolishing of the buildings, and this, in turn, results in some unacceptable consequences in large populated cities, such as thousands of homeless and/or jobless people for a very long time, very time consuming, difficult, and costly demolishing and debris removal, and finally very massive, and therefore, costly and time consuming required reconstruction works. Regarding these facts, any idea which can lead to creation of repairable buildings is greatly acknowledgeable. One such idea is ‘Directed-Damage Design’ (DDD) idea, which means guiding the damage to some pre-decided parts of the structural system, so that other parts do not experience any major plastic deformation, and therefore, making the building easily repairable only by replacing the damaged elements. Design of repairable buildings, based on the DDD idea, have been paid great attention by some researchers in recent decade and rocking as well as seesaw motions have been employed for this purpose. Rocking motion can be easily triggered in buildings with aspect ratio higher than 2 (relatively tall buildings), however, for midrise buildings, which usually have lower aspect ratios, creation of rocking potential is not easy. In this study to create repairable regular midrise steel multistory buildings, the capability of rocking motion has been given to the system by dividing the buildings’ skeleton into four similar narrower structures with a 4-cell configuration, each cell having a plan area of almost ¼ of the original structure. Each cell of the 4-cell structure has a tubular frame structural system and is capable to do rocking motion during earthquake, in which the closely-spaced columns at each side can bear the whole weight of the cell. At the base of each of the circumferential closely-spaced columns a yielding plate energy dissipator is used, which works when the column’s bottom end moves upward and downward above the foundation level during the rocking motion of the cell. To create more potential of energy dissipation, some dampers can be also used between each pair of the four cells. To show the efficiency of the proposed structural system, a set of 5- and 8-story buildings with similar plans were considered and a series of nonlinear time history analysis (NLTHA) were performed by using a set of 3-component scaled accelerograms of some selected earthquakes, including both far- and near-field events. Numerical results of NLTHA show that the proposed rocking structures can efficiently decrease the seismic damage in the building, so that plastic deformation happens basically in the energy dissipators, and the main structural elements remain elastic, and therefore, the buildings designed and constructed by the proposed technique can be easily repaired even after major earthquakes, and the building can basically keep the IO performance level.

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