Base Isolation of Structures - Essay Example

OF EAST LONDON Department of Civil Engineering BASE ISOLATION OF STRUCTURES AND PRESENTATION OF BEng FINAL YEAR PROJECTS 2009 BASE ISOLATION OF STRUCTURES ABSTRACT This paper illustrates and examines the use of base isolation with reference to its merits and demerits. A special attention is paid to the architectural shapes and structural configurations so that the effectiveness of the seismic protection can be attained through the base isolation approach. A rational methodology to evaluate behaviour factors for base isolated structures (BIS) code design is presented here. Along with this the influence of several parameters on the ultimate behaviour of BIS has been analysed. ACKNOWLEDGEMENT In the outset I must express my heartfelt thanks to my learned Guide who helped me a lot with timely directions and advice to complete this assignment well in time. And I do extend my thanks to the lecturers and professors of University of East London, who supported me with their revered wisdom and guidance throughout so as to enable me to fulfil my assignment. I take this opportunity to thank my friends and parents who have imparted their knowledge in a friendly and loving manner, and the librarian of the University, without whom this project would not have been materialised. My gratitude also goes to http://www.ecs.csun.edu/shustov/Topic4.htm, and http://www.architectjaved.com/earthquake_resistant_structures/base_isolation_techniques_for_earthquake_resistance.html, from where I took the required data for reference during the course of my work. CONTENTS CHAPTER 1: BASE ISOLATION AND ITS WORKING 1.1 Introduction 1 1.2 What is Base Isolation 1 1.3 History of Base Isolation 2 CHAPTER 2: MODERN PRINCIPLES OF BASE ISOLATION 2.1 Principles 4 2.2 Types of Isolation Systems 5 CHAPTER 3: WORKING PRINCIPLE 3.1 Working Principle 7 3.2 Reaction of Base Isolated Buildings 8 3.3 How Base Isolation Works 9 3.4 The First Base Isolated Structures in the United states 10 3.5 Cases that Use Base Isolation - Results after Earthquake 11 CHAPTER 4: COSTS FOR INCORPORATING BASE ISOLATION 4.1 Costs 12 4.2 Limitations of Euro code 8 12 4.3 Limitation of Interstorey Drift from Euro codes 8 15 4.4 SAP 2000 software and the Numerical Analysis of Base Isolation Buildings 16 4.5 Reasons Why SAP2000 17 Conclusion 19 References 21 Appendices (Nil) List of Symbols (Nil) List of Tables 22 List of Figures 22 List of Formulae 22 1. BASE ISOLATION OF STRUCTURES 1.1 INTRODUCTION Base isolation which is also known as seismic or base isolation system is nothing but an accumulation of structural constituents which considerably dissociates the main structure from the damaging components of the earthquake. This prevents the main structure from absorbing the earthquake energy. The total superstructure must be defended on separate isolators whose vibrant characteristics are selected to separate the ground motion. Some isolators are also intended to add considerable damping. Dislocation and compliant are determined at the point of the isolation devices, and the superstructure. Base isolation for earthquake protection was first used in Pasargadae which is a city in antediluvian Persia and dates back to the VI century BC. 1.2 WHAT IS BASE ISOLATION Base isolation is the most powerful tool of earthquake engineering when it comes to the aspect of controlling the shakiness of a structure and the technology used for it. It is intended to enable a building or non-building structure to come through a potential crushing seismic impact by way of accurate initial design or following alterations. Sometimes the application of base isolation helps in raising both the structure's seismic performance and also its seismic sustainability to a great extend. Base isolation is thus the method by which the complete structure is cut loose and physically alienated from the foundation system that is cast into the underneath soil structure. In a restoration this requires cutting of all the perpendicular load columns in the structural system to render around 18 inch gap between the base of the column and the groundwork system below. Isolation pads or bearings are then positioned in this gap. The perimeter wall system which is occupied with the groundwork must also be cut loose. This can engage key building changes in open structures that have perimeter load bearing 1 walls. The isolated structure and the main structure must then be made over to rest linearly elastic under the utmost possible event. This is typically done by adding up a large number of stimulated frames or by adding up a large number of real shear walls. (7) 1.3 HISTORY OF BASE ISOLATION The Earthquake Engineering Research Centre (EERC), now known as the Pacific Engineering Research Centre (PEER), of the University of California at Berkeley, was the first institution in the United States to perform research on the viability of natural rubber bearings as base isolators to protect buildings from earthquakes in the year 1976. The research program was a joint effort between the EERC and the Malaysian Rubber Producers Research Association (MRPRA) from the United Kingdom. Initially, this research program was wholly funded by the MRPRA which set aside multiple grants for it over a number of years, and later, it was funded by the National Science Foundation and the Electric Power Research Institute. The research at EERC was under the guidance of Professor James M. Kelly and several graduate students added their theoretical and experimental contributions to it. (7) Though the concept of base isolation had been around for quite a while at that point of time, with some concepts of isolation using rollers or sliders having been proposed, most professionals in the field of structural engineering considered the practice to be completely impractical and not worthy of consideration. A simple three storey, 20 ton model on which were used hand made bearings, made from very low modulus rubber, marked the beginning of the research project. Shaking table tests conducted on the model proved that the use of isolation bearings was capable of bringing about a decrease in the acceleration by a factor of up to ten in comparison with conventional designs. Confirming predictions, the study showed that the model responded as a rigid body and all the deformation happened only in the isolation system. This initial research pointed out the need for a certain degree of damping in the proposed system; owing to the small scale of the model, the usage of 2 more practical compound of rubber was ruled out. In the year 1978, a more realistic model, a five-storied, three bay, forty ton model was used to demonstrate the concept of base isolation, this time with the help of commercially produced bearings that were damping enhanced. An extensive battery of tests on this five storey model led to the establishment of the finding that isolation achieved through rubber bearings, was capable of substantially reducing the acceleration experienced by the structure itself, and also led to even more substantial reductions in the acceleration experienced by the internal equipment, which was a key area of interest in the research of the EERC. The very same research also established that the use of additional elements such as lead plugs in the bearings or energy absorbing devices constructed from steel in the isolation system to increase the amount of damping decreased the ability of the isolation system in reducing the acceleration experienced by the internal equipment. So, this turned the research towards the direction of finding an efficient way to incorporate the damping within the rubber bearing and not as a separate element added to the isolation system. Why the rubber bearings found to be such effective isolators These bearings are relatively easy to manufacture, can withstand the test of time, have no moving parts and are excellent resistors of environmental degradation. Rubber bearings used in isolation systems are manufactured by bonding sheets of vulcanized rubber to thin reinforcing plates made of steel. The resultant bearings tended to be flexible horizontally, while being extremely stiff in the vertical direction, and so, during seismic activity, the layer of bearing isolated the structure from the horizontal factors of ground movement while the vertical factors are transferred to the building, relatively intact. (7) Vertical acceleration is not known to affect most structures, but the bearings were also capable of isolating the building from unwanted high frequency vertical vibration produced by sources such as traffic and underground railways. 3 2. MODERN PRINCIPLES OF BASE ISOLATION 2.1 PRINCIPLES In modern days base isolation is being increasingly applied to different structural design methods for buildings and bridges which are situated in extreme seismic areas. Many structures have been constructed using this technique, and still many others are in the design stage or under construction phase. Nearly all the completed buildings and also those which are under construction use rubber isolation bearings in the isolation system. (5). "From the very beginning, the theory of seismic (or base) isolation engineering rested on two pillars: heavy damping and frequency separation. Unfortunately, nobody paid any attention that heavy damping is a sort of a strong connection between a substructure and superstructure, and that the idea of decoupling them with the help of such connections is no good. As a result, the only problem left seemed to be development of proper design provisions for seismic-isolated structures" (Shustov, 1994). Diagram (Courtesy:http://www.ecs.csun.edu/shustov/Topic4.htm) Regular building Base-isolated building FIGURE-2.1(1) Base isolation system comprises of isolation units with or without isolation elements, where: 4 1. Isolation units are the fundamental components of base isolation system. These components are intended to provide decoupling effect to a building or a non-building structure. 2. Isolation elements are the links between isolation units and their parts which do not have any dissociating consequences of their own. Isolation units are normally divided into two and their division depends on the response they have to an earthquake impact. The basic categories are: 1. Shear Units 2. Sliding Units. 2.2 TYPES OF ISOLATION SYSTEMS There are 2 fundamental types of isolation systems; one that makes use of elastomeric bearings and the other, which makes use of the sliding system. The elastomer is made of either raw rubber or neoprene. This technique makes use of the approach in which the building or structure is uncoupled from the horizontal components of the earthquake ground motion by interjecting a level with low horizontal stiffness. This is placed between the structure and the foundation. This sheet gives the structure a basic rate of recurrence which is much lesser than its rigid-base frequency. It is also much lesser than the predominant frequencies of the ground motion. The first vibrant form of the isolated structure is bent only in the isolation system where as the structure above intents rigidity. The elevated mode which produces distortion in the structure is orthogonal to the first mode and as a result also to the ground motion. These higher modes do not partake in the motion thereby preventing the high energy in the ground motion at these higher frequencies not to be transmitted into the structure. The isolation system will not take in the earthquake energy, but rather fends it off through the moral force of the system. This kind of isolation is useful to a system which is linear and even when un-damped; however, some damp is helpful to hold back any potential reverberation at the isolation frequency. (2) 5 The 2nd fundamental type of isolation system is the sliding system. This exploits by restricting the shift of shear across the isolation interface. Many sliding systems have been projected and some have been utilized already. In China there are at least 3 buildings on sliding systems which makes use of particularly chosen sand at the sliding interface. A type of isolation comprising a lead-bronze plate slipping on stainless steel with an elastomeric bearing has been expended for a nuclear power plant in South Africa. The friction-pendulum scheme is a sliding system which uses a particular kind of interfacial material which slides on stainless steel. This has been utilised for quite a lot of plans in the United States, both for new and retrofit constructions. FIGURE-2.2(2) Designing Technique of Base Isolation Buildings (Courtesy: http://www.architectjaved.com/earthquake_resistant_structures/base_isolation_techniques_for_earthquake_resistance.html) Because of the suppleness in the structure, a healthy medium-rise building material or non-breakable solid building turns extremely flexible. The isolators are often intended to suck up energy and add damping to the system. This aids in additional reduction in the seismic response of the building. Many of the base isolators appear like large rubber pads, even though there are other cases which are based on sliding of one 6 part of the building in relation to the other. Also, base isolation is not appropriate for all buildings. More often than not low to average rise buildings perched on hard soil underneath; high-rise buildings or buildings perched on soft soil are not appropriate for base isolation. Lead-rubber bearings are the regularly-used cases of base isolation bearings. A layer of rubber sandwiched together with layers of steel, is a lead rubber bearing. The middle part is made of solid lead "plug". The top and the bottom of the bearing are fixed with steel plates which are utilised to bind the bearing to the building and foundation. The bearing is very rigid and sturdy in the vertical direction, but supple in the horizontal direction. 3. WORKING PRINCIPLE 3.1 WORKING The figure above displays an earthquake working on base isolated building and a conservative, fixed-base building. Due to an earthquake, the ground underneath each building starts to move. Each building reacts with motion which inclines towards the right. The buildings shift in the direction opposite the ground motion is in fact due to inertia. The inertia forces which act on a building is the most crucial of all those brought forth during an earthquake. Apart from displacing towards right, the un-isolated building also changes its shape from a rectangle to a parallelogram and this is a case of deformation. The key cause of earthquake harm to buildings is the twist which the building undergoes as a result of the inertial forces acting on the building.(3) 3.2 REACTION OF BASE ISOLATED BUILDINGS: The base-isolated building holds back its master, rectangular shape. The base 7 isolated building itself gets away from the distortion and damage. This shows that the inertial forces acting on the base isolated building has been decreased. Experiments and observations of base-isolated buildings in earthquakes shows that as little as of the acceleration of the corresponding fixed-base buildings.(5) Acceleration is reduced as the base isolation system increases a buildings period of tremor the time taken for a building to rock back and forth and then back again to its original position. And in common structures with longer periods of trembling incline to cut down acceleration, while those with lesser periods incline to increment or expand acceleration. FIGURE-3.2(3) Second type of base isolation (Courtesy: http://www.architectjaved.com/earthquake_resistant_structures/base_isolation_techniques_for_earthquake_resistance.html) Orbicular slipping isolation systems are the other type of base isolation. The building is backed by bearing pads that have a crooked surface and low friction. At the time of an earthquake the building is unloose to slide on the bearings. As the bearings have a bent surface, the building slips both horizontally and vertically. The forces required to move the building in an upwardly direction prevents the horizontal or 8 sidelong forces which would or else cause building distortions. Also by correcting the radius of the bearings kinked surface, this property can be utilised to design bearings that also elongate the buildings phase of vibration. FIGURE-3.2.(4) Two platforms move freely against each other in one orthogonal plane (courtesy of AS Inc., Japan) 3.3 HOW BASE ISOLATION WORKS: Two horizontal platforms as shown in the figure above which can shift freely against each other in one orthogonal direction only are set up beneath existing or new showcases. By tweaking the dynamic characteristics of the base isolation system its motion in the presence of a seismic episode cancels the movement of the sustaining structure, a considerable reduction of the seismic reaction can be attained. Method and Codes (Courtesy: Multidisciplinary Center for Earthquake Engineering Research). The design steps for base isolation ultimately shift the frame's period. Acceleration is significantly reduced, smaller lateral forces are developed which means that smaller lateral forces are developed. 3.4 THE FIRST BASE ISOLATED STRUCTURES IN THE UNITED STATES The honour of being the very first base isolated building in the United States goes 9 to the Foothill Communities Law and Justice Centre, situated in Rancho Cucamongo San Bernardino County, located 60 miles east of downtown Los Angeles. This building is situated 12 miles from the San Andreas Fault, and so, the County, which was the first in the country to adopt a thorough earthquake preparedness program, requested for the structure to be designed to be capable of withstanding an earthquake of Richter magnitude 8.3, considered being the maximum plausible quake for that area. The building was completed in 1985, and it stood four stories tall with a full basement plus a secondary basement to host the isolation system which comprised of 98 isolators which featured multi-layered natural rubber bearings that had steel plate reinforcements. Additionally, the superstructure of the building had a structural steel frame that was stiffened with the help of braced frames in some of the bays. The maximum horizontal displacement demand that the isolation system of this building was designed to meet was 380mm or 15 in. with respect to the isolators at the corners of the structure. Full scale samples of these bearings were tested to verify the said capacity and proved successful. The isolators were made from highly filled natural rubber, which was developed as part of the research program at the EERC. The mechanical properties of this rubber, such as its high shear stiffness for small strains, which then tended to decease by a factor of four or five with increase in the strain, achieving its lowest value at a 50 percent shear strain, and then increasing again for shear strains of more than 100 percent, made it a very suitable candidate for use in a base isolation system. When it came to damping, this rubber followed a similar pattern at a less dramatic level, initially decreasing from 20 percent to a minimum of ten percent and then rising again. Basically, the system is designed assuming minimum values for stiffness and damping and a linear response. The high stiffness at the initial stage is brought in to play only for wind load design while the high strain response is only for fail-safe action. The Fire Department Command and Control Facility (FCCF), was a structure on which the same high damping rubber isolation system was implemented. This building is 10 located in the Los Angeles County and was completed in the year 1990. It houses the computer systems that control the emergency systems of the Los Angeles County, requiring it to stay functional even during and after extreme events such as earthquakes. It is interesting to note that the exact same isolation system using high damping rubber bearings was adopted for the telephone company S.I.P's building in Ancona, Italy. This building holds the distinction of being the first modern base isolated structure in all of Europe.(4) 3.5 CASES THAT USE BASE ISOLATION - RESULTS AFTER EARTHQUAKE The University of Southern California Teaching Hospital is an eight story building situated in eastern Los Angeles. The isolation system designed for this building has 68 lead rubber isolators and 81 elastomeric isolators supporting the concentrically braced steel frame structure. Due to the location of the building, the foundation system included spread footing and grade beams on rock. Multiple setbacks over the height had to be incorporated into the building plan as well as the elevation, which made them highly irregular, a feature that had to be incorporated due to functional requirements. The structure also incorporated two wings on either side, which were connected through the necked down part of the building. The irregular configuration of the structure led to coupling of the lateral and torsional vibration modes and extreme demands of shear force in the area between the two rings. These were the two main reasons why seismic isolation was considered important for this building. (1) This hospital happened to be just 23 miles away from the epicentre of the 6.8 Mw Northridge earthquakes of 1994. While the area around the structure experienced a maximum ground acceleration of 0.49 g, the insides of the structure registered only around 0.10 - 0.13 g. While the ground motion was powerful enough to wreak significant damage on many other buildings in the medical centre, the isolation system incorporated 11 in this structure was successful at isolating it from the same powerful ground motions. To date, this event represents the severest test that an isolated building has had to face. (1) 4. COSTS FOR INCORPORATING BASE ISOLATION 4.1 COSTS Costs for integrating base isolation technology into structures differ, but normally this technology adds between 5 percent and 20 percent to the cost of a new conservative structure. This is a comparatively modest investment by the owner equated to downtime and probable business losses. For a structure housing indispensable functions, the building owner will find this cost worth the effort. Base isolation is the best obtainable high-performance alternative for a building that must endure "The Big One." (10) 4.2 LIMITATIONS OF EURO CODE 8 (Courtesy: http://www.cidect.org/de/Downloads/DG9update1.pdf) Euro code 8 (CEN 2003a) recommends the following two design concepts: Concept a) Low dissipative structural behaviour Concept b) Dissipative structural behaviour In concept (a) the action effects may be calculated on the basis of an elastic global analysis without taking into account a significant non-linear material behaviour. In concept (b) the capability of parts of the structure (dissipative zone) to resist earthquake actions through inelastic behaviour is taken into account. The design concepts, structural ductility classes and upper limit reference values of the behaviour factors recommended by Euro code 8 are summarized in the table below. 12 Design concept Structural ductility classes Range of the reference values of the behaviour factor q Concept a) Low dissipative structural behaviour DCL(Low) 1.5 - 2 DCM(Medium) 4 also limited by the values of Table 6.2 DCH(High) only limited by the values of Table 6.2 Table -4.2(1) showing values of q in Euro code 8 for different combinations of the Structural type and ductility class. TABLE-4.2(1) As can be seen from the above table, Euro code 8 assorts building structures into 3 ductility classes. The structure which belongs to the low ductility class (DCL) can be used only for the low seism city zone. This zone is considered as areas in which the design ground speed is not more than 0.1g. The resistor of the members and links should be measured in accordance with Euro code 3 (CEN 2003) without any additional requirements. The 1994 version of Euro code 8 included a design concept of non-dissipative structural behaviour. This concept is applicable to very low seism city areas in which design ground acceleration is less than 0.05g. Such areas were excluded from the scope of the 2003 version of Euro code 8. Structures designed to concept b) should belong to ductility classes DCM or DCH. These classes correspond to the increased ability to dissipate energy in plastic mechanisms and hysteretic behaviour. Depending on the ductility classes the behaviour factor q is linked to the ductility demands on members and connections, hence to the 13 class of steel sections, detailing rules, rotational capacity and so forth. Joints in Dissipative Zones (Courtesy: http://www.cidect.org/de/Downloads/DG9update1.pdf) Euro code 8 defines the following criteria for seismic design. 1. Structural parts of dissipative zones should have adequate ductility and resistance until the structure sustains sufficient deformation without failing due to overall instability. 2. Non-dissipative parts of dissipative structures and the connections of the dissipative parts to the rest of the structure should have sufficient over strength to allow cyclic yielding or local buckling of the dissipative parts. To ensure the sufficient over strength of connections Euro code 8 specifies the following detailing rules. 1. The actual maximum yield strength fy,max of the steel of dissipative zones satisfies the following expression, fy,max 1.1ovfy where ov The over strength factor. The recommended value is equal to 1.25. When actual yield strength fy,act of the steel of each dissipative zone is determined from measurements, the over strength factor is computed for each dissipative zone as ov= fy,act/fy fy The nominal yield strength of the steel of dissipative zones 2. Connections of dissipative parts made by means of complete joint penetration (CJP) groove welds (full-penetration butt welds) are considered to satisfy the over strength criterion. 3. For fillet welded or bolted connections the following requirements should be met. These are also applicable to connections at the ends of bracings. 14 a) (Resistance of the connection according to Part 1-8 of Euro code 3) 1.1ov x (plastic resistance of the connected part according to Part 1-1 of Euro code 3) b) For bolted shear connections bearing failure should precede bolt shear failure. 4. During construction it should be ensured that the yield stress of actual steel used does not exceed fy,max noted on drawings for dissipative zones by more than 10 per cent. 4.3 LIMITATION OF INTERSTOREY DRIFT FROM EOROCODES 8 Maximum interstorey drift demands of Frames 3 and B (bare frames) for the Vrancea record. Maximum interstorey drift demands of all the frames for the Vrancea record are given in Table 1. The Vrancea record gives the largest seismic demands among the three records. According to EC8 (2004) Part 1 Clause 4.4.3 ("damage limitation requirement") the demand interstorey drift of the structure shall not exceed 1.25%dr= assuming a reduction factor (see Clause 4.4.3.2(1) a). This has been taken as the target performance index for the upgraded structure. 4.0=v. As can clearly be seen in Table 1, the maximum interstorey drift demands of all the frames for the Vrancea record are significantly larger than the allowable value. 15 Storey Number Frame 1 3 4 5 6 7 A B D E F 8 0.66 0.70 0.69 0.66 7 1.35 1.24 1.16 1.15 1.21 2.18 1.61 1.19 1.15 1.15 6 2.09 1.98 1.92 1.98 2.16 3.36 2.53 1.87 1.81 1.83 5 1.38 1.44 1.55 1.71 1.89 2.11 3.03 2.40 1.69 1.45 1.29 4 1.44 1.50 1.62 1.79 1.99 2.21 3.15 2.51 1.80 1.56 1.40 3 1.39 1.45 1.58 1.76 1.95 2.20 2.92 2.35 1.75 1.57 1.46 2 1.29 1.31 1.37 1.48 1.60 1.82 2.31 1.86 1.43 1.35 1.31 1 0.64 0.63 0.65 0.68 0.72 0.82 0.99 0.80 0.64 0.62 0.62 TABLE-4.3(2) Table 4.3.(2) Showing Maximum interstorey drift demands (%) of all the frames for Vrancea record (bare frames) 4.4 SAP 2000 SOFTWARE AND THE NUMERICAL ANALYSIS OF BASE ISOLATION BUILDINGS: (Courtesy: http://comp-engineering.com/products/SAP2000/sap2000.html) SAP2000 features a very sophisticated, spontaneous and resourceful user border motorized by a matchless analysis engine and design tools for engineers who work on industrial, transportation, sports, public works, and other facilities. From its 3D object founded graphical designing background, to the extensive range of analysis and design choices totally incorporated across one powerful user interface, SAP2000 has proven to be the most integrated, productive and practical general purpose structural program on the market today. 16 Bridge Templates FIGURE-4.4(5) This spontaneous interface allows for creation of structural models quickly and spontaneously without long learning curve delays. The power of SAP2000 can be used for analysis and design tasks, including small day-to-day problems. Complex Models can be generated and meshed with powerful Templates built into the interface. Bridge Designers can use SAP2000 Bridge Templates for bringing forth Bridge Models, Automated Bridge Live Load Analysis and Design, Bridge Base Isolation, Bridge Construction Sequence Analysis, Large Deformation Cable Supported Bridge Analysis and Pushover Analysis. 4.5 REASONS WHY SAP2000 (Courtesy: http://comp-engineering.com/products/SAP2000/sap2000.html) For bridge design, SAP2000 automatises moving load scrutiny like no other software. Lanes are effortlessly offset from beam centerline to think about torque and other reactions, even with curved and inclined systems. Built-in AASHTO vehicles with user defined options for truck and train loads. Auto generation of influence lines and 17 min/max force & moments for all possible permutations of traffic loads. Several built-in design codes, including AASHTO, for steel and concrete design. Steel member sizes can be optimised depending on power per design code with consumer determined auto select lists of sections. SAP2000 shell elements render single element expressions which keep off the 'shear locking' problems found with classical finite elements. The ability of SAP2000 to output shell forces and moments at each shell joint which are integrated over the shell thickness, and then sum them provides several advantages. First of all, forces & moments from shell joints can be selected and summed using SAP2000's group joint force sum option in order to obtain useful results such as base shear and moments, or section cuts for strength design. SAP2000 stress resultants are reported by joint per unit of in-plane length. SAP2000 constraint options provide unique capabilities to rigidly 'link' joints which are offset from one another. Advanced analysis options are also available for nonlinear base isolators, dampers, gaps, large deflection, and plastic hinges for pushover analysis. Modal, response spectrum, linear or nonlinear time history dynamic analysis and there is no limit on use of springs, dampers, and other elements in dynamic analysis. 18 CONCLUSION In this age of technological mutiny, the world of seismic engineering is in requirement of creative thinking and superior technology beyond conservative solutions. Seismic isolation is an appropriate technology for the security of an array of buildings which has the essential energetic characteristics. Base isolation technology has developed in recent years to highly trustworthy and reliable level. Academic research on the subject is sophisticated, and its practical appliance is becoming well-known throughout the world. In recent times semi-active control techniques have been projected and got much notice. In semi-active base isolation, the coefficient of viscous damping or the spring constant is altered efficiently based on the state of the control object. The system utilising a semi-active damper is assorted as a bilinear system which belongs to non-linear systems. Base Isolation also defends non-structural constituents and equipment by decreasing the complete structure's speed during an earthquake, as contradicted to strengthening alone. There are a variety of isolation methods and plans accessible. The Code does not favor a type, but it demands that the system should have the following 3 properties: 1. Stable for the requisite displacement 2. Supply rising resistance with rising displacement 3. Does not corrupt under cyclic loading Base isolation renders the uppermost stage of fortification - "operational" - after a major earthquake. Base isolation has important welfares for the earthquake protection of historic structures. Base isolated buildings are competent of protesting GSA blast loads and their capability to move decreases the overall affect of the blast force on the building. Rolling type base isolation systems have proved to be very successful in amending the seismic functioning of operational and functional elements attached to the principal structural system. Lately, a rolling type of base isolation arrangement called 19 Tuned Configuration Rail (TCR) has been fruitfully practical in the last few years in seismic base isolation of private housing, computer servers and more extensively in museum showcases. It is a condensed isolator that considerably reduces the speed response and can without difficulty be installed beneath new or existing showcases, shelves, statues and preservation racks. 20 REFERENCES 1. Paz, Mario. International Handbook of Earthquake Engineering: Codes, Programs and Examples. October, 1994; Chapman and Hall. London, England. 2. McCormack, Jack. Design of Reinforced Concrete. 2001; John Wiley & sons, Inc. New York, New York. 3. Kelly, James M.; Naeim, Farzad. Design of Seismic Isolated Structures: From Theory to Practice. 1999; John Wiley & sons, Inc. New York, New York. 4. Clark, Peter W., Masahiko Higashino, and James M. Kelly. 1996. "Performance of Seismically Isolated Structures in the January 17, 1994 Northridge Earthquake." Proceedings of the Sixth U.S.-Japan Workshop on the Improvement of Building Structural Design and Construction Practices in the United States and Japan. Victoria, B.C., Canada: Applied Technology Council and Japan Structural Consultants Association. ATC-15-5. 5. Kelly, James. M. 1997. Earthquake-Resistant Design with Rubber. 2nd ed. Berlin and New York: Springer-Verlag. 6. Taniwangsa, Wendy, and James M. Kelly. 1996. Experimental and analytical studies of base isolation applications for low-cost housing. Berkeley, Calif.: Earthquake Engineering Research Center, University of California. UCB/EERC-96/04. 7. Naeim, F. and Kelly, J. M., Design of Seismic Isolated Structures, John Wiley, New York, 1999. 8. Park, Y. J., Wen, Y. K. and Ang, A. H. S., Random vibration of hysteretic systems under bi-directional ground motions.Earthquake Eng. Struct. Dyn, 1986, 14, 543-557. 9. Deb, S. K., Paul, D. K. and Thakkar, S. K., Simplified nonlinear analysis of base isolated buildings subjected to general plane motion. Eng. omput., 997, 14, 542-557. 21 10. Ryan, K. L. and Chopra, A. K., Estimation of seismic demands on isolators based on nonlinear analysis. J. Struct. Eng., ASCE, 2004, 130, 392-402. 11. International Code Council, International Building Code, 2000. 12. Aiken, I. D., Kelly, J. M. and Tajrican, F. F., Mechanics of low shape factor elastomeric seismic isolation bearings. Report No.UCB/EERC- 89/13, University of California at Berkeley, 1989. 13. Kelly, J. M., Shake table tests of long period isolation system for nuclear facilities at soft soil sites. Report No.UCB/EERC-91/03, University of California at Berkeley, 1991. LIST OF TABLES 1. Table -4.2(1) Values of q in Euro code 8 Page No.13 2. Table -4.3(2) Maximum Interstorey Drift Demands Page No.16 LIST OF FIGURES 1. Figure -2.1(1) Regular building-Base-isolated building Page No. 4 2. Figure -2.2(2) Designing Technique of Base Isolation Page No. 6 3. Figure -3.2(3) Second type of base isolation Page No. 8 4. Figure -3.2(4) Platforms Page No. 9 5. Figure - 4.4(5) Bridge Templates Page No.17 LIST OF FORMULAE 1. Formulae ov= fy,act/fy Page No.14 22 Read More