Retrofitting existing buildings by coupling method using passive devices

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Retrofitting existing buildings by coupling method using passive devices

 

Author: Yang, Zhidong
Title: Retrofitting existing buildings by coupling method using passive devices
Degree: Ph.D.
Year: 2015
Subject: Buildings -- Repair and reconstruction.
Structural analysis (Engineering)
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Environmental Engineering
Pages: xxx, 259 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2827238
URI: http://theses.lib.polyu.edu.hk/handle/200/8284
Abstract: The objective of this study is to investigate the feasibility of retrofitting existing buildings by coupling method using passive devices. The study begins with experimentally testing of a shear type fluid damper. It is found that the fractional derivative model can accurately represent the fluid damper. The equations of motion of buildings coupled by fluid dampers are then derived. Parametric studies show that when buildings with a substantial difference in the number of stories (or in the period of vibration) are linked by fluid dampers, significant seismic mitigation can be achieved. The response reduction is limited when the buildings have the same or similar number of stories. The effect of the soil-structure interaction (SSI) on the response of buildings connected by fluid dampers is investigated. The soil-structure interaction or structure-soil-structure interaction (SSSI) has little effect on the response of coupled buildings on moderately soft or moderately stiff soil or rock site. For coupled buildings on soft soil, the response considering SSI is less than that without SSI. When buildings on soft soil are retrofitted by the coupling method, the analysis of coupled buildings without SSI or SSSI provides conservative examination. Thus subsequent analyses are conducted without SSI and SSSI. An optimization procedure has been developed to optimize the position and size of fluid dampers in the frequency domain. It is found that the top floor of the building with lesser number of stories is the best location for the installation of fluid dampers. When there is a large difference in the number of stories (or in natural frequencies) between two buildings, the maximum standard deviation of drift can be substantially reduced. Vice versa, response reduction diminishes when the natural frequencies of the buildings are close to each other. Representing a nine and an eight-story building, two 1/15 scale models have been built and tested. When a fluid damper is installed between the two models in fixed-base conditions, the fundamental frequencies and damping ratios are slightly increased. There is a limited reduction in the maximum response. When one model in fixed-base condition is connected to the other model in base-isolated configuration by a visco-elastic damper, the response of both models is significantly reduced. Theoretical studies on the response of a fixed-base building connected to a base-isolated building indicate that the properties of visco-elastic dampers are the dominant factor that influences the response of the fixed building. Analysis results show that the fundamental frequencies of both buildings are considerably reduced. The response of the coupled buildings is significantly decreased. Supplementary studies have been conducted to retrofit a core-frame system. Base isolators are applied to protect the buildings from ground motion. Story isolators are employed to connect the cores and buildings. The retrofitting strategy can effectively reduce the maximum drift response of the cores and the frames. To conclude, it is feasible to retrofit adjacent buildings by the coupling method using passive devices. For buildings with a different number of stories, it is recommended to connect them together using fluid dampers. Adjacent buildings with the same or similar number of stories can be strengthened by coupling them together with visco-elastic dampers with one of the buildings being base isolated.

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