Base Isolation

An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. The earthquake generated vertical inertial forces are to be considered in design unless checked and proven by specimen calculations to be not very significant. Special attention should be taken to the effect of such vertical component of ground motions. It is the responsibility of the structural engineer to protect the building against such vibrational forces. In practice no building can be earthquake resistant. In other words, it is impossible to make a building which can resist the earthquake completely. But, efforts can be made to reduce the damage caused by it. Many researches and studies have been done to develop such concepts that can help to minimize the structural damages to the building and thereby reducing the casualties caused during an earthquake. Base isolation is one such concept which can be employed in the buildings so as to reduce the damages caused due to earthquakes and at the same time strengthening the structure.

— For seismic response of base isolated building under recorded earthquake ground motion, the analytical studies are presented. In comparison with base isolation system, superstructure is relatively rigid. This can lead to idealization of the superstructure as a rigid body, modelling the base-isolated structure as a single-degree-of-freedom system. Such analysis significantly reduces the computational efforts required to design the base-isolated structure under seismic loading. A comparison is made of the seismic response of Building with and without base isolators to investigate the seismic response of isolated building and compare it with corresponding response of non isolated building, to identify the effectiveness of isolation system, in this study. Various types of bearings is considered as base isolation systems. I. INTRODUCTION To improve the seismic performance of strategically important buildings such as commercial buildings, industrial structures, elevated water tanks, residential houses etc. in addition to places where sensitive equipments are intended to protect from the hazardous effects during earthquake, base –isolation is recognized as a mature and efficient technology can be adopted. The choice of the isolation system varies according to the extent of control to be achieved over the seismic response and there upon its design is done to suite the requirement of use of the structure. In the seismic design of base-isolated structures, the superstructure is decoupled from earthquake ground motion by introducing flexible interface between the foundation and the base of the structure. Due to these isolation systems shift the fundamental time-period of the structure to a large value and dissipate the energy in damping, limiting the amount of force that can be transferred to the superstructure such that inter-story drift and floor accelerations are reduced drastically. In the range of 0.1 – 1.0 sec is the dominant time-period of typical earthquake accelerations and maximum acceleration usefully occurs in the range of 0.2 – 0.6 sec. Therefore, when the vibration time-period of the structure is increased beyond these limits the matching of fundamental frequencies of base-isolated structures and the predominant frequency contents of earthquake is avoided thereby the preventing the near-resonance response, resulting in dramatic reduction in structural response. The superstructure is decoupled from the earthquake ground motion in seismically base-isolated systems by introducing a flexible interface between the foundation and the base of structure. Thereby, the isolation system shifts the fundamental time period of the structure to a large value and/or dissipates the energy in damping, limiting the amount of force that can be transferred to the superstructure such that inter-story drift and floor accelerations are reduced drastically. The matching of fundamental frequencies of base-isolated structures and the predominant frequency contents of earthquakes is also consequently

2018

Hospital buildings are of great importance after any natural calamity such as earthquake. The structural and non-structural components should remain operational and safe after earthquake. So to mitigate the effect of earthquake on the structure the base isolation technique is the best alternative as a seismic protective system. The basic idea of base isolation system is to reduce the earthquake induced inertia forces by increasing the fundamental period of the structure. The aim of this study is the use of High Damping Rubber Bearing (HDRB), Lead Rubber Bearing (LRB) and Friction Pendulum System (FPS) as an isolation device and then to compare various parameters between fixed base condition and base isolated condition by using ETAB software. In this study the (G+5) storey hospital building is used as a test model. Analytical result obtained natural period, horizontal by acceleration and total lateral forces or seismic base shear for fixed base building using IS 1893:2002 (Part-I).

2012

Base isolation (BI) system for buildings is introduced to decouple the building structure from potentially damaging induced by earthquake motion, preventing the building superstructures from absorbing the earthquake energy. The mechanism of the base isolator increases the natural period of the overall structure, and decreases its acceleration response to earthquake / seismic motion. A steel building with structural rubber bearing is introduced throughout this study. The study analysis performed to check for the adequacy of the base isolation against building lateral drift and inter-story drift as per allowance in National Building Code of Canada 2010. Two buildings were analyzed using the nonlinear time history response analysis using the dynamic MODAL analysis for fixed base (FB) building, and Isolated base (IB) building with rubber bearing. The analysis represents a case study for symmetric steel building to show the ultimate capacity of the selected structural bearing, and to make a comparison for the difference between the isolated base and the fixed base buildings. Initial results show that the presence of the structural rubber bearing reduces significantly the vertical displacement, moment and shear generated for the same mode.

The effectiveness of base-isolated system is investigated. The base-isolated system is modelled as a shear type structure with one lateral degree-of-freedom. From equations of motion for the fixed-base and base-isolated system, modal expansion of effective earthquake forces and modal static responses for base shear are calculated. In base-isolated system, pseudo acceleration and base shear reduces drastically compared to fixed-base system. The effective response comes from first mode of vibration only. The natural vibration period of first mode is much longer than the fixed-base time period of structure. It causes the isolation effective for first or isolation mode only.

Base isolation (BI) system for buildings is introduced to decouple the building structure from potentially damaging induced by earthquake motion, preventing the building superstructures from absorbing the earthquake energy. The mechanism of the base isolator increases the natural period of the overall structure, and decreases its acceleration response to earthquake / seismic motion. A steel building with structural rubber bearing is introduced throughout this study. The study analysis performed to check for the adequacy of the base isolation against building lateral drift and inter-story drift as per allowance in National Building Code of Canada 2010. Two buildings were analyzed using the nonlinear time history response analysis using the dynamic MODAL analysis for fixed base (FB) building, and Isolated base (IB) building with rubber bearing. The analysis represents a case study for symmetric steel building to show the ultimate capacity of the selected structural bearing, and to make a comparison for the difference between the isolated base and the fixed base buildings. Initial results show that the presence of the structural rubber bearing reduces significantly the vertical displacement, moment and shear generated for the same mode.

Base isolation is a mechanism that provides earthquake resistance to the new structure. The base isolation n system decouples the building from the horizontal ground motion induced by earthquake, and offers very stiff vertical components to the base level of the superstructure in connection to substructure (foundation). It shifts the fundamental lateral period, dissipates the energy in damping , and reduces the amount of the lateral forces that transferred to the building, inter story drift, and the floor acceleration. The work deals with modeling and finite element analysis of a high damping rubber bearing displacement controlled transient analysis was done to analyses the behavior of the isolator during earthquakes

SCITECH Nepal, 2020

Currently she is an Associate Professor at Nepal Engineering College and is engaged in teaching for last 14 years. She has experienced in different building projects and Middle Marsyangdi hydroelectric project of Nepal. She has published articles in national and international journals. Sanyog kumar Upadhay is studying Bachelor in Civil engineering in Nepal Engineering College under the affi liation of Pokhara University. He had participated in different research program, in and out the country such as Hultprize regional in Mumbai. He had conducted different college and national level research programs before.

Proceedings of the Institution of Civil Engineers - Structures and Buildings, 1995

Wtitten discussion closes ISJuly 1995 seismic excitation is presented. The An updated state-of-the-art review of the behaviour of base-isolated buildings to review includes the literature on theoretical aspects of seismic isolation, parabuildings and experimental studies to metric behaviour of base-isolated verify some of the theoretical findings. A brief review of the earlier and c u r r e n t base-isolation devices-proposed or implemented-is given, and aspects for f u t u r e research in the area of base islation are included.