Three-Mass Structural-Isolating-Damping Model Subjected to Near- and Far-Fault Earthquakes

Seismic base isolators and dampers are commonly used as control tools in building frames to mitigate earthquake damage. This study proposes and investigates a structural system consisting of a central fixed core and an isolated section, the two parts of which are connected to each other by a damper. In new structures, called partially isolated (PI) structures, the interaction between conventional frames with fixed bases and frames equipped with control tools including isolators and dampers is measured using a three-mass model by three simplified differential equations of motion. Validating the proposed model provided good results. The model with various modes of partial isolation and certain mass ratios was subjected to seven near-fault and seven far-fault earthquakes to be evaluated. The mean displacement, acceleration, and shear responses of the structural-isolating-damping model were compared with those of fully isolated (FI) and fully fixed (FF) structures. The results showed that by connecting the two parts, responses of the fixed part to FF structure and those of the isolated part to FI structure significantly improved. Under near-fault earthquakes, the displacement response reduction of the fixed part to FF model was estimated to be about ۲۰% and the response of the isolated part to FI model was about ۵۰%. Due to the functional weaknesses observed in FI structures including large displacement of the structure base, poor performance of the isolator in near-fault earthquakes, and high costs of preparing and installing the isolation system, these points were significantly resolved in PI structures.

Keywords:

Partially isolated (PI) structure , Seismic isolator , Damper , Near-fault earthquake , Far-fault earthquake