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The lately proposed mega sub-controlled structure (MSCSS) remarkably improved the seismic resistance ability and reduced vibration effects much more than the mega substructure (MSS). However, the controlling effectiveness and its optimization remain a significant concern. In this paper, a new configuration of MSCSS is analyzed in which viscous dampers are optimally arranged between mega-frame and substructural frame and optimal damper parameters are investigated. Also, rubber bearings are designed and introduced at the top of the additional column to ease the horizontal constraints between the additional column and mega-floor beam and improve the structural design of MSCSS, so that the structure has a larger span and further reduces the structural response. The result showed that optimal parameters of the damper and its optimal arrangement have a significant influence in the control effectiveness of MSCSS. Furthermore, the addition of a rubber bearing at the top of the additional column improves the mechanical behavior of the column and further reduces the acceleration response of both the mega-frame structure and the substructure. This paper also shows that the percentage reduction of the acceleration is more within the substructure than at the mega-frame structure. The seismic response of this structure under El Centro is less than the Taft (NE) wave and the percentage reduction is more under the Taft wave than under the El Centro wave.

It is still a serious challenge for structural engineers to effectively reduce the seismic responses of tall and super tall buildings to further improve these structural safeties. In order to solve this problem, in this article a new kind of structural configuration, named passive mega-sub controlled structure (PMSCS), is presented, which is constructed by applying the structural control principle into structural configuration itself, to form a new structure with obvious response self-control ability, instead of employing the conventional method. In the analysis of PMSCS the equations of motion of the seismically excited system are developed, based on a realistic analytical model of the complete mega-structural system. Expressions of the displacement and acceleration response of the structure, resulting from simulated earthquake ground motions represented by stationary and nonstationary random processes, are derived. These responses are then determined for both the PMSCS and its conventional mega-sub structure (MSS) counterpart, whose configuration was modeled after the traditional mega-frame that was used in the construction of the Tokyo City Hall. A parametric study of the structural characteristics that influence the response control effectiveness of the PMSCS is presented and discussed. The region over which these structural characteristics yield the optimum seismic response control of the PMSCS is identified and serves as a very useful design tool for practitioners. The study illustrates that the proposed PMSCS offers an effective means of controlling the seismic displacement and acceleration response of tall/super-tall mega-systems. It also overcomes shortcomings exhibited in earlier proposed mega-sub controlled structural configurations.

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The improved mega sub-controlled structure system (MSCSS) significantly reduced the building responses and improved the control effectiveness as compared to conventional mega substructure (MSS). However, since the MSCSS is designed to resist future earthquakes, the seismic risk assessment of the structure remains a significant concern. In this study, the seismic risk analysis of MSCSS is performed to probabilistically compare the building performance and its resistance to future earthquake damage at certain categories of limit states (LSs), which include category one (slight damage, moderate damage, and collapse damage LS) and category two (damage control and collapse prevention). The comparison is realized with the result of the traditional MSS. The probability of exceedance of the above damage LS for a particular ground motion (GM) intensity (i.e. Sa (T1,5%)) is evaluated to assess and compare the vulnerability of these buildings. The evaluation is done through developing fragility curves and relationships for MSCSS and MSS. The result showed that the improved MSCSS has strong seismic resistance ability and provides a better response from a nonlinear analysis result. Furthermore, the fragility curve of moderate and collapse damage LSs indicated that MSCSS requires higher GM intensity to reach a moderate and collapse damage LS than MSS. That means MSCSS is the most stable with a significant difference as compared to its counterpart. This is also true for the second category of LS, that is, damage control and collapse prevention. While at the slight damage LS, both the MSCSS and MSS require approximately the same GM intensity to reach a slight damage LS, as the difference is not significant.