The bi-tuned semi-active TMD for tall buildings under multi-hazard loads

Tall buildings are often built in areas prone to significant winds and earthquakes. Both hazards may damage building components in these areas, reducing the buildings' profitability. Therefore, multi-hazard design methodologies are necessary, especially for appropriate energy dissipation devices like tuned mass dampers (TMDs). However, winds and earthquakes are remarkably different in intensity, occurrence rate, dynamic properties, and critical structural responses. Thus, tackling these hazards while designing a protective system represents a serious challenge. An innovative solution to overcome this obstacle and improve tall buildings' performance in multi-hazard environments is presented in this work: the bi-tuned semi-active TMDs (BSTMDs). Depending on the instantaneous active hazard, a BSTMD may be tuned to two distinct frequencies and damping ratios. Hence, a BSTMD has two tuning options: a wind-related option and a seismic-related option. Every tuning option consists of a particular frequency and a specific damping ratio. Then, while a passive TMD design requires three parameters (mass, tuning frequency, and damping ratio), a BSTMD design requires five. An optimization-based methodology is employed to design a system of multiple BSTMDs, by minimizing the total BSTMDs added mass. The BSTMD's parameters previously mentioned are taken as design variables. The building life-cycle cost (LCC), the sum of the expected restoration costs connected to extreme wind and seismic events along the building lifespan, is adopted as a performance measure and used as a constraint. Finally, examples of applications are solved for a benchmark building using an efficient gradient-based algorithm. In the case studies, different locations are assumed, thus emphasizing the design differences that emerge from distinct local hazard parameters. The results are also compared to corresponding passive TMDs solutions, highlighting the superior performance of BSTMDs with respect to TMDs under multi-hazard loads.