Simplified analysis of mid‐story seismically isolated buildings

Abstract

The mid-story isolation design method is recently gaining popularity for the seismic protective design of buildings located in the areas of high population. In a mid-story isolated building, the isolation system is incorporated into the mid-story rather than the base of the building. In this paper, the dynamic characteristics and seismic responses of mid-story isolated buildings are investigated using a simplified three-lumpedmass structural model for which equivalent linear properties are formulated. From the parametric study, it is found that the nominal frequencies of the superstructure and the substructure, respectively, above and below the isolation system have significant influences on the isolation frequency and equivalent damping ratio of a mid-story isolated building. Moreover, the mass and stiffness of the substructure are of greater significance than the superstructure in affecting the dynamic characteristics of the isolated building. Besides, based on the response spectrum analysis, it is noted that the higher mode responses may contribute significantly to the story shear force of the substructure. Consequently, the equivalent lateral force procedure of design codes should carefully include the effects of higher modes.S.-J. WANG ET AL.(r sub , r sup )=(1, 5) (r sub , r sup )=(2, 5)

Model reduction and optimal parameters of mid-story isolation systems

“…Tsuneki et al [1], Tasaka et al [2] and Murakami et al [3] discuss some building designs that incorporate the midstory isolation systems in Japan and its impact on structural response. Several numerical as well as experimental studies [3][4][5][6][7][8]16,17] analyzing the effectiveness and limitations of such isolation systems have also appeared. The effect of nonlinearity of the system (Shirayama, et al [4]; Hu et al [5]), the impact of the placement of isolators at different story levels and other isolator parameters on the isolation effectiveness (Huang, et al., [6]; Zhou et al [7]) and the effect of modal coupling on response amplification of isolated upper structure (Kobayashi and Koh 8) have been reported.…”

“…In a mid-story isolation system, this flexible representation of the upper part leads to a three-lumped mass model. Such three-lumped mass models have been used by Kobayashi and Koh [8] and Wang et al [17], to study the impact of modal interaction on the lower substructure and isolated superstructure response. In fact Wang et al [17] have used such a model to identify the range of sub and super structure frequencies where modal interaction can adversely affect the performance of the isolation system.…”

“…To examine the impact of some of these parameters, reduced but representative two-and three-lumped mass models have been commonly used in the literature on the subject of the base isolation [15], roof isolation [11,12] and mid-story isolation [7,16,17] to demonstrate the effectiveness and impact of the proposed schemes. The two-lumped mass models of mid-story isolation system are often based on the premise that the isolated part of the building above the level at which a soft isolator is inserted behaves as a rigid body under earthquake excitations.…”

Optimal stiffness distribution of mid-storeyisolated buildings considering storey drift and floor acceleration response

“…In addition, a mid-storey-isolation system [1][2][3][4][5][6][7][8][9] has been devised, and there exist practical examples. However, a design scheme which considers both structural deformation and acceleration response has not been proposed so far.…”

Seismic Performance of Midstory Isolated Structures under Near-Field Pulse-Like Ground Motion and Limiting Deformation of Isolation Layers

“…More importantly, it can enhance the construction feasibility in highly populated areas where installing an isolation system beneath the base of a building can be extremely difficult if the building separation and property line are particular concerns. The effectiveness has been proven regarding midstory isolation's role in reducing seismic demand on the superstructure above the isolation system subject to far-field ground motion [4][5][6][7].…”