Damping evaluation of an eight-story steel building with nonlinear oil damper under strong earthquakes

Abstract

Fluid viscous damper has been applied widely for energy dissipation and shock absorption in dynamic structural systems, specifically the oil damper. Nevertheless, there's an issue of precisely incorporating shaft bearings and pressure sealings for oil dampers, which restricts its wide application in new or existing structures. A type of nonlinear oil damper with viscoelastic polymer packing soft links is posed and investigated to allow for easy production. To explore the effectivity and actual performance of the nonlinear oil dampers, vibration monitoring system has been instrumented both on the dampers and the building since it was built in 2003, which accumulated huge amount of precious data. A Bayesian based order selection of auto-regressive exogenous model is exploited to the recorded earthquake responses to extract dynamic properties of the passively-controlled 8-story steel building. Thus, damping characteristics of the whole structure can be identified and analyzed. Besides, an analytical model for the nonlinear oil damper is investigated and estimated by particle filter improved with Metropolis-Hastings algorithm, which can be incorporated into the whole structure model for model updating, reliability as well as response prediction. Furthermore, the calculation formulas of the additional effective damping ratio provided by oil damper are deduced based on above analysis using modal strain energy, and damping ratio of the main steel frame structure are also estimated. Taking a set of actual ground motion monitoring data as an example, the proposed method is then exploited to estimate the effective damping ratio of oil damper for each floor.