Effective Core Placement and Optimal Outrigger Location in Irregular Tilted-Midsection Buildings

The inclined façades of irregular tilted-midsection buildings, which midsections are intentionally designed to be inclined, generate eccentric loads on each floor. In addition, lateral loads, such as earthquakes, and self-weight induce overturning moments, causing lateral displacement in the inclined direction of the structure. To compensate for this structural instability and disperse the overturning moment, the lateral displacement needs to be controlled by applying multiple cores, or by adding a lateral force-resisting system, such as an outrigger system. In this study, the lateral force resistance performance of an irregularly shaped 60-story building with the midsection tilted by approximately 12.1° was investigated according to the change in core placement. The analysis modeling was classified into single–core and dual–core models, and consisted of six models where the core position was shifted horizontally along the tilted direction (X–axis). Eigenvalue and seismic response analyses were performed, and the structural characteristics were analyzed by comparison with the regular analysis model. The analysis results showed that as the core was placed in the inclined direction of the structure, the structural responses of the irregular tilted building under the load combination of vertical load seismic loads decreased. In addition, an analysis model with the best seismic resistance was evaluated for each core placement, and the location of the outrigger system that could effectively reduce the story drift ratio and maximum lateral displacement was investigated through static and time history analyses. This study can be used as a guideline for core placement and the number and location of outrigger systems installed in the planning and initial design stages of irregular tilted-midsection structures.