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تعداد صفحات این فایل: ۲۵ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Tuned mass damper effects on the response of multi-storied structures observed in geotechnical centrifuge tests~~en~~

Abstract

Tuned mass dampers (TMDs) are widely used to reduce vibrations in structures. However, very little research is available on the experimental investigation of TMDs and their performance in soil-structure systems. In this paper, a series of geotechnical centrifuge tests was conducted to investigate the effects of TMDs on the response of a multiple-storey sway frame structure undergoing dynamic soil-structure interaction (SSI). Structural responses were recorded for a wide range of input motion characteristics, damper configurations and soil profiles. The practicality associated with the use of TMDs in the damping of resonant structures in light of unexpected earthquake characteristics different from design earthquakes was experimentally demonstrated. Tuning a TMD to soil-structure system properties rather than fixed-base structural properties was found to double the improvement in damping and reduce the original peak response by nearly half. The potential effectiveness of a de-tuned mass damper in light of significant SSI was also demonstrated.

۱ Introduction

A popular method of mitigating risks from earthquakes to structures is the use of vibration resisting devices. A tuned mass damper (TMD) is one of the simplest and most reliable vibration control devices in existence today and has been widely installed in many structures around the world [1]. It operates through the dissipation of vibrational energy induced in a structure, which is achieved through the combined action of inertial dissipation and material damping [2].

The overwhelming majority of TMDs in use today are linear and passive in nature, the latter meaning that they are not externally driven but that they react solely in response to the motion of the floor in which they are installed. Passive linear TMDs are well understood and have been shown to be very effective and reliable in practice [3]. In the case of fixed-base structures, tuning of the natural frequency of the TMD to the pre-dominant modal frequency of the structure is desired to ensure the damper’s optimum operational efficiency [4]. In reality however, inclusion of soil flexibility is expected to result in an overall decrease in stiffness and a different natural frequency of the soil-structure system in comparison to the fixed-base structure [5]. By means of shaking table testing under 1 g conditions Jabary and Madabhushi [6] experimentally demonstrated that TMD performance is optimum when the natural frequency of the TMD is tuned to the predominant modal frequency of the soil-structure system.

With the aim of reducing one or more structural response parameters, past studies into TMDs have focused on the development of analytical expressions for the optimisation of the TMD parameters mass, stiffness and damping. Occasional parametric verifications of such analytical expressions have made reference to very specific model structures with a limited number of defined variables in structural and soil properties. Studies into the response of structures considering their interaction with the foundation soil and the TMD have been performed by several authors [2,7,8]. However, prior to Ghosh and Basu [9] very few authors had looked into the effects of altered structural properties as a result of soil-structure interaction (SSI) on the performance of TMDs in seismic vibration control. Ghosh and Basu [9] investigated SSI effects on the TMD performance in a single-degree-of-freedom structure. Nevertheless, their numerical study was based on many simplifications, most notably their assumption of linearity of the soil’s stress–strain behaviour. Furthermore, the efficiency with which TMDs operate in practice is often reduced considerably compared to theoretically developed responses [10]. In addition to these general drawbacks associated with theoretical studies that have been conducted on TMD performance, the bulk of such studies considered the long-established use of TMDs in windexcited structures, with the use of TMDs in seismically-excited structures being a relatively new concept that has not been as extensively explored [11,12].

The aim of this paper is to overcome limitations of theoretical analyses of TMD performance through the experimental investigation of TMD effects on the response of a multiple-storey sway frame structure undergoing dynamic SSI. No such studies have been performed to date using geotechnical centrifuge testing. For the purpose of this study a series of centrifuge tests was conducted on a range of structure–damper configurations. Two different soil profiles and multiple earthquake scenarios were recreated by subjecting various soil-structure models to an extensive range of input motion characteristics.

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