STIFF vertical seismic absorbers

Abstract

Seismic isolation is proven to be an effective technology for seismic protection of building structures, equipment, and industrial facilities. The majority of the existing isolation systems and techniques are related to horizontal ground motions, whereas there are only a few vertical isolation systems. The main reason is because of the conflict concerning the demand for isolation stiffness. More specifically, a vertical isolated system must have sufficient vertical rigidity to sustain the weight of the isolated object/system and retain the static vertical deflection in reasonable limits. On the other hand, the isolated system must also have enough flexibility to isolate the accelerations. In order to overcome this difficulty, a novel vertical seismic absorber system is proposed, that combines negative stiffness-driven absorbers with inerters. The inerter manages to reduce the frequency of the system, without weakening the structure or increasing the seismic load. At the same time, the effective damping is significantly increased with the KDamper. This way, the dynamic behavior of the system is improved, in terms of absolute accelerations, and simultaneously, the static settlements are retained at any desired level. The design of the vertical seismic absorber is based on engineering criteria, and the excitation input is selected according to the seismic design codes. The dynamic performance of the vertical seismic absorber is also evaluated with real earthquake records, using a realistic displacement-dependent configuration for the realization of the negative stiffness element. Finally, the detuning phenomena are observed and discussed via sensitivity analysis.