A Novel Base Isolation System for Asymmetric Buildings in Seismic Active Zones: Damping Supplied by Tuned Liquid Column-
The vulnerability of civil engineering structures with fundamental frequency, say roughly above 1 Hz, (or buildings with less than 10 stories), when exposed to the strong motion phase of an earthquake is considerably reduced by means of base isolation. Th
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Abstract The vulnerability of civil engineering structures with fundamental frequency, say roughly above 1 Hz, (or buildings with less than 10 stories), when exposed to the strong motion phase of an earthquake is considerably reduced by means of base isolation. The low pass filter for isolating horizontal vibrations is redesigned where the classical elastomeric bearings are substituted by a number of prestressed helical steel springs with pivoted columns along vertical axes carrying part of the dead weight and guiding the horizontal motion. The base isolated building in its fundamental modes is considered to be rigid. Low cost Tuned Liquid Column Gas Dampers, in optimal arrangement in the plan of the basement of the building, supply the effective damping of the remaining horizontal vibrations. The action of the passive damping device is commonly considered to be sufficient. Since the gas spring effect counter acts changes in fluid mass, the absorber can be used as a water reservoir. However, early peaks in the response may require active control for their proper reduction. Consequently, such a hybrid absorber is discussed with gas injection from a standby high-pressure vessel, making it independent from any public energy transmission line.
1 Introduction It is the horizontal component of the strong motion phase of an earthquake that shakes and possibly endangers regular buildings. To reduce the vulnerability of buildings with fundamental frequency higher than about 1 Hz (or buildings with
F. Ziegler () Vienna University of Technology, Vienna A-1040/E2063, Austria e-mail: [email protected] B. Khalid Directorate of Civil Engineering and Design, Islamabad, Pakistan e-mail: [email protected] H. Irschik et al. (eds.), Advanced Dynamics and Model-Based Control of Structures and Machines, DOI 10.1007/978-3-7091-0797-3 26, © Springer-Verlag/Wien 2012
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less than 10 stories), base isolation is best suited. Currently, a low pass filter is put between the building and its foundation mainly in the form of a shear spring consisting of rubber sheets reinforced by placing them between steel plates. The resulting fundamental mode should have a frequency below about 0.5 Hz. In that case the required damping of the resulting nearly rigid body mode of the base isolated building is supplied by the plastic deformation of a lead core placed in the center of the isolation element. This element has a rather large ratio of the vertical to the horizontal stiffness; the latter in a rough approximation is given in terms of the rubber shear modulus by k1h D GA=ns1 , where A and s1 are respectively, the cross-sectional area and the thickness of the n-times repeated rubber sheets. There are lifetime problems encountered, mainly caused by the increase of temperature due to plastic deformation of the lead core within the first occurrence of the earthquake or during the aftershocks. Consequently and avoiding any such lifetime problems, in this paper we describe a novel base isolation element con
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