# Earthquake-Induced Pounding of Medium-to-High-Rise Base-Isolated Buildings
## 4 Concluding Remarks  
The influence of earthquake-induced structural bounding on the response of medium-to-high-rise base-isolated buildings has been investigated in this paper. The analysis has been focused on collisions between two insufficiently separated five-story and eight-story base-isolated and fixed base buildings aligned in three different configurations. The results of the study clearly indicate that structural collisions may significantly increase the response of medium-to-high-rise isolated buildings during ground motions. They show that the  
Figure 11: Hysteresis curves for isolators of the base-isolated building for bounding and no bounding cases during the Northridge earthquake (stations: Buena-Park, Saturn Street School, and Century CCC). structural behavior depends very much on the gap size between structures. The results indicate that with the increase in the gap size, the response of the base-isolated building becomes smaller, and this trend is observed up to the gap size large enough to prevent rounding. The significant influence of the gap size on the bounding-involved structural response underlines the importance of this parameter for all possible structural configurations under different earthquake excitations. Moreover, it has also been observed from the analysis that the increase in the structural response is larger when the heights of both colliding buildings are close to each other, as compared to the case when the isolated building is smaller than the adjacent fixed base structure. It should be underlined, however, that the effects of bounding can be even more pronounced when the base-isolated building has more stories. That makes the analysis concerning closely-spaced medium-to-high-rise structures quite difficult, especially that the number of stories in buildings is designed based on the needs of the owner, and should rather not be restricted by requirements of earthquake-induced structural bounding. The results of study also indicate that the response amplification factors due to bounding are much different for different stories of the isolated building. Larger amplifications of accelerations can be expected due to collisions in the case of the upper stories which undergo bounding, while they are substantially smaller for the stories above bounding level. On the other hand, the amplifications of the story shears have not shown any specific trend, and they can be either increased or decreased for different stories of the analyzed isolated structure. Finally, the obtained hysteresis curves have confirmed that structural bounding during earthquakes has significant influence on displacement responses of the base-isolated medium-to-high-rise building, as well as on the shapes of the hysteresis curves themselves. This conclusion is very important from the point of view of choosing appropriate types of isolation devices with particular characteristics which should be applied in the case of different structural configurations. It should be underlined that the results of the study described in the paper can be useful for the design of base-isolated buildings adjacent to other medium-to-high-rise structures with the same or different heights. In particular, they can be applied when a new base-isolated building is planned to be constructed close to the existing fixed-base structure and the construction site is very limited (i.e., due to high land prices in highly populated cities). The decision concerning the new structure can be made with relation to its dynamic parameters, number of stories, characteristics of isolation devices, etc. Another example might concern the situation when the seismic retrofitting (by applying base isolation) of one of the existing closely-spaced buildings is planned to be carried out and no change in the in-between gap size can be considered. In any case, the analysis described in the paper can be successfully used to assess the minimum gap size so as to prevent structural bounding between both buildings during an earthquake.