۱- Introduction

۲- Modularized suspended structure, calculation model and mean square responses

۳- Single-objective optimization analysis

۴- Multi-objective optimization analysis

۵- Time history performances

۶- Discussion

۷- Conclusion

References

Abstract

Suspended building systems with vibration control features dissipate seismic energy by the interaction between their main parts and the suspended parts; they are also architecturally appealing. A modularized suspended structure has been previously proposed to overcome the fragility of its secondary structure and to enhance overall attenuation. However, the full potential of modularization is yet to be achieved via the previous configuration, especially in terms of multi-mode control. In this study, the protection effect of prefabricated modules is further harnessed in such a way that drastic vertical-irregularities of inter-story stiffness and dampers within the suspended segment are allowed. Vertical distribution vectors of structural parameters were set as the variables in genetic-algorithm optimizations, with the maximum mean square moment of the primary structure being the main objective. The results show considerably improved attenuation of responses in multiple modes instead of only the fundamental mode. In the optimized distributions, peaks of damping coefficient occur at the troughs of inter-story stiffness, but without a highly concentrated pattern. Models with different irregularity levels have well-separated Pareto fronts; this indicates that comprehensive improvement can be obtained at compromised choices. The main mechanism is that, with the well-designed irregularities, the secondary structure provides satisfactory dissipation and tuning to the primary structure in the major modes. The analysis with non-stationary excitations reveals that optimized vertical distributions further quicken the vibration decay. The time-history performance verifications and the structural uncertainty analysis are also carried out.

Introduction

Mega-substructure systems [1–۱۴] consist of two structural parts, namely, the main part (the primary structure) and the suspended or base-isolated part (the secondary structure) which is architecturally functioning. Various forms of mega-substructure systems exist: coretube with suspended floors [1,2,7,8,14], mega-frame with suspended floors [5] or isolated floors [3,6,12], frame structure with suspended floors [10] or isolated floors [11], isolated roof [4] and inter-story isolations [9,13]. While the secondary structure delivers loads to the primary structure, the relative motion between the two parts can be harnessed to dissipate energy and reduce vibration. Mega-substructure systems possess high robustness [3,15] against parameter deviation and wide-band excitations in terms of passive vibration control and can be applied to scenarios in which regular dampers cannot perform with the highest efficiency [3]; these scenarios include systems with dominant flexural-type deformation such as core-tubes. In this kind of systems, the secondary structures interact with the primary structure over a wide frequency range, with the secondary structures being large-scale tuning masses, energy absorbers as well as spaces with attenuated accelerations. A majority of suspended building structures [1,2,5,7,8,14] belong to the category of mega-substructure systems and are architecturally appealing as the vertical members are tensioned instead of compressed, leading to reduced cross sections and, consequently, increased transparency along with reduced weights [1,8]. Additionally, a large column-free space can be easily formed in the first story [16].