International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 04 | Apr -2017
p-ISSN: 2395-0072
www.irjet.net
SEISMIC PERFORMANCE AND ECONOMIC FEASIBILITY OF STRUCTURES BY OPTIMAL POSITIONING OF COMBINED BASE ISOLATION SYSTEMS Susan Paul 1, Dr. T. Sundararajan 2, Prof. Basil Sabu 3 1M.Tech 2
in Structural Engineering, Mar Athanasius College of Engineering, Kothamangalam
Head, SMSD, Vikram Sarabhai Space Centre, Indian Space Research Organisation, Thiruvananthapuram
3Professor,
Department of Civil Engineering, Mar Athanasius College of Engineering, Kothamangalam ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract -
Seismic base isolation is an earthquake resistant design method that is based on decreasing the seismic demand instead of increasing the seismic capacity. Earthquake ground motions can cause significant or severe structural damages. Recorded accelerograms for bidirectional ground motions compatible with the reference elastic response spectrum have been used for the evaluation of the seismic response of the structure. Modeling and analysis is done using the finite element software SAP2000 version 18 for El-Centro earthquake ground motion records. Maximum vertical reaction is obtained from analysis in SAP2000 software and this vertical reaction and the total mass of structure are used for designing the lead rubber bearings and friction pendulum systems manually. The seismic responses of 14 storied reinforced concrete structure base isolated with different types of isolators such as Lead Rubber bearing and Friction Pendulum System are determined by performing dynamic nonlinear analysis. Time-history analysis is carried out in order to evaluate floor response, accelerations and displacements during a ground motion. This paper intends to demonstrate how an isolation system can be efficient, evaluating its effectiveness for the building in terms of, base shear, storey drift and storey displacement and storey acceleration reductions. Combinations of base isolation systems are placed optimally at the base of the structure to achieve the most efficient and economically feasible earthquake resistant structure.
transmitted to the structure relatively unchanged. Base isolators deflect and absorb the seismic input energy horizontally transmitted to the structures. The principle of seismic isolation is to introduce flexibility in the basic structure in the horizontal plane, while at the same time adding damping elements to restrict the resulting motion and the basic concept of base isolation is to increase the natural period of the building to take it away from resonance with the forcing motions of earthquake and thereby reducing the design base shear. The successful seismic isolation of a particular structure is strongly dependant on the appropriate choice of the isolator devices, or systems, used to provide adequate horizontal flexibility with minimal centering forces and appropriate damping. It is also necessary to provide an adequate seismic gap which can accommodate all intended isolator displacements. A reasonable design displacement should be of the order of 50 to 400 mm, and possibly up to twice this amount if ‘extreme’ earthquake motions are considered. The primary function of an isolation system is to support a structure while providing a high degree of horizontal flexibility. This gives the overall structure a long effective period and hence low maxima for its earthquake generated accelerations and inertia forces. The expected life of an isolated structure will typically range from 30 to 80 years and its maintenance problems should preferably be no greater than those of the associated structure.
Key Words: Base isolation, lead-rubber bearing, friction pendulum system, non- linear time-history analysis, storey acceleration, floor displacement, storey drift, base shear.
1.1 Review of Literature
1. INTRODUCTION Base isolation is most effective methods to reduce vibrations transmitted from ground to the structure and one of the most widely accepted seismic protection systems in earthquake prone areas. It mitigates the effect of an earthquake by essentially isolating the structure from potentially dangerous ground motions, especially in frequency range where building is mostly affected. When the seismic isolation system is located under the structure, it is referred as “base isolation”. The role of the base isolator under seismic loading is to isolate the structure from the horizontal components of the earthquake ground movement, whereas the vertical components are © 2017, IRJET
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Impact Factor value: 5.181
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Pradeep Kumar T. V et al. [1] have shown forcedeformation behavior of isolation bearings. The isolation system is determined to increase the natural period of the structure away from the high-energy periods of the earthquake and a damper to absorb energy in order to reduce the seismic force. The most common isolation bearing used was the lead rubber bearing. It has been observed that lead rubber bearings have little strain-rate dependence for a wide frequency range which contains typical earthquake frequencies. The isolation bearings are modeled by a bilinear model based on the three parameters: initial stiffness, lower stiffness, and characteristic strength. It provides relationship to find out the yield displacement and yield force for an equivalent bilinear isolation bearing system. Compared to the ISO 9001:2008 Certified Journal
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