Fundamental study on a drift-controlled stiffening and supplemental damping system for seismic protection of buildings

Abstract

Seismic protection systems are typically designed to limit loss of life in the event of a high-magnitude seismic event. This objective is achieved by preventing collapse of the structure. The objective of some other seismic protection systems is to limit the damage to buildings; however, they often do not adequately prevent collapse of buildings. This research develops a seismic protection system that achieves the collapse prevention objective or the damage prevention objective, depending on the magnitude of the applied loading. The seismic protection system developed consists of three distinct components. The first component developed is referred to as drift-controlled stiffening. This component supplements the lateral stiffness of a building when high-intensity loads are applied to the building, thereby preventing collapse of the building and when subjected to low-intensity loads the lateral stiffness of the building is not supplemented. The next components are vehicle shock absorbers that supplement the damping in a building to prevent damage to the building. The last component is a mast damper connection, which provides an efficient method for transferring inter-story motion to motion across supplemental damping devices. Combining these components resulted in a seismic protection system that achieves collapse prevention under high-magnitude loads, and damage prevention under low-magnitude loads. Investigations of the effect of drift-controlled stiffening and a mast damper connection on simple systems showed the ability for drift-controlled stiffening to prevent collapse of buildings and a mast damper connection to effectively transfer inter-story motion to motion across a damper. A preliminary investigation of vehicle shock absorbers suggested similarities between shock absorbers and viscous fluid dampers currently used in seismic protection systems, however research has not determined the behavior of vehicle shock absorbers subjected to motion that is commonly seen in structures. The aforementioned investigations motivated experimental testing of vehicle shock absorbers and a scale building model. The experimental testing of vehicle shock absorbers confirmed that their force output can be predicted using a generalized viscous dashpot model. The experimental testing of a scale building model shows that the seismic protection system has the ability to meet different objectives dependent on the intensity of the applied seismic ground motions. The scale building model was constructed with drift-controlled stiffening and vehicle shock absorbers installed using a mast damper connection. The addition of vehicle shock absorbers was shown to increase the damping of the scale building model by a factor of twenty five, and the mast damper connection was shown to transfer eighty percent of roof displacement to displacement across the vehicle shock absorbers. Drift-controlled stiffening was shown to have a minimal effect on the response of the scale building model to low intensity seismic loads. Meanwhile, when subjected to high intensity seismic loads, drift-controlled stiffening reduced the displacement of the roof of the scale building model by over twelve percent.