Year

2012

Degree Name

Doctor of Philosophy

Department

School of Civil, Mining and Environmental Engineering

Abstract

Building structures are often built close to each other because of lack of available land in metropolitan cities. To reduce the response of a structure to earthquake excitation, various types of control system devices have been proposed for adjacent buildings. One of the methods to mitigate structural seismic response is installing supplemental damping devices between adjacent buildings. The aim of this study is to develop a method for analysing the random seismic response of a structural system consisting of two adjacent buildings interconnected by fluid viscous damping and rubber bearing devices. An investigation is carried out to analyse the earthquake induced pounding between two insufficiently separated buildings considering the inelastic behaviour of the structures’ responses. The seismic response history analysis of multi-storey inelastic adjacent buildings of different sizes with soil-structure interaction (SSI) during impact is investigated based on the reduction of displacement, acceleration and shear force responses of adjacent buildings.

The El-Centro 1940, Kobe 1995, Sakarya 1999, Loma Prieta 1989 and Duzce 1999 earthquake records are used to examine the seismic response of two buildings under the different ground motions in this study. The resulting systems of second order constant coefficient equations are reformulated as a system of first order ordinary differential equations and solved using the ordinary differential equation solver of MATLAB. The pounding behaviour of the buildings has considerable influence on the behaviour of the lighter building causing substantial amplification of the response and leading to considerable permanent deformations due to yield strengths. The parametric investigation has led to the conclusion that the peak displacement of the lighter and more flexible building is very sensitive to the structural parameters by varying gap size, storey mass, the friction coefficient for sliding, and structural stiffness. The lateral torsion response of the couple buildings is affected when impact takes place with the adjacent buildings. The modal response histories of the lighter and heavier buildings are significantly reduced due to the effect of the small SSI. Further, it is also observed that the roof twist of the lighter building which is assumed to be inelastic is decreased for the large SSI effect compared to the small SSI effect.

This study investigates the efficacy of optimal semi-active dampers for achieving the best results in seismic response mitigation of adjacent buildings connected to each other by magnetorheological (MR) dampers under earthquakes. The modified Bouc-Wen models are used for MR dampers. One of the challenges in the application of this study is to develop an effective optimal control strategy that can fully utilize the capabilities of the MR dampers. Hence, a significant task based on genetic algorithms (GA) is improved in order to obtain input voltages and number of dampers to understand the desired control forces at each floor level. Linear quadratic regulator (LQR) controller is used for obtaining the desired control forces, while the desired voltage is calculated based on clipped voltage law (CVL). The control objective is to minimize both the maximum displacement and acceleration responses of the structure. The multi objectives are first converted to a fitness function that is used in standard genetic operations, i.e. selection, crossover, and mutation. In fact, increasing the number of dampers can exacerbate for the dynamic response of the system. As a result, decreasing the number of dampers necessarily increase the efficiency of the system.

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