We have developed the large sized coned disk springs for the vertical seismic isolation system with the common deck supporting the important main equipment in FBR plants, assuming that the horizontal base isolation system for the entire building would be provided. The outer diameter of disk spring in actual size is 1000mm. We have established the fabricability of such a large-sized coned disk spring, and have grasped the vertical / horizontal load-deflection relationship and the design constant such as the coefficient of friction due to experimental tests by the actual size. So the applicability of the large coned disk springs for the vertical isolation system and the design method were confirmed.
The procedure for design and selection of rational damper structural parameters includes searching the optimal parameters of viscous damping for linear dynamic model on the basis of construction of spectral density of seismic input power and selection of force characteristic for the damper, ensuring damping, equivalent to optimal viscous damping. Purpose-oriented function of optimization is the minimum of dispersion of seismic isolated object accelerations. This experiment had confirmed the correctness of damper structure choice procedure for provision of the required dissipation level.
The new approach proposed by the authors in this paper consists of implementing friction pendulums having the sliding surface profile based on a polynomial function of superior order. This seismic isolation system permits, for each surface, a greater flexibility in controlling the oscillations of the upper structure, in terms of displacements or dissipated energy, by using three parameters to control the force-displacement relation. Namely, these parameters are the friction coefficient µ, and two characteristic values of the curve on which the sliding surface is constructed.
Developing Lead Rubber Bearing for Seismic Isolation of Nuclear Power Plants: H. P. Lee & M. S. Cho, J. Y. Park; Republic of Korea; World conference on Earthquake Engineering; 2012: In the cases of seismic isolation at nuclear power plant facilities oversees and preliminary design methods of seismic isolation systems in order to secure seismic performance of nuclear power plant facilities at the time of an earthquake, and then performed preliminary design of a seismic isolation system for APR1400, a domestically-developed, new PWR with the capacity of 1,400MWe. For preliminary design of a seismic isolation system for nuclear power reactor structures, the weight of APR1400 was applied, and the natural seismic isolation period, horizontal effective stiffness, design displacement and equivalent damping ratio, etc. were established in accordance with the ASCE7-10 design process. Lead rubber bearings (LRBs), which are a kind of seismic isolators using laminated rubber bearings with material characteristics often used in seismic isolation systems for general structures, were applied to this study’s preliminary design, and based on this, the specifications and quantity of the seismic isolation system required for nuclear power plant structures were calculated with sufficient applicability. To be fully adopted to the seismic isolation system for actual nuclear power plant structures, vigorous research is going on in Korea to develop the standards, analysis models and procedures for seismic isolation of domestic nuclear power plant structures, and the researchers of this study will develop an improved seismic isolator to satisfy new standards to be established in the future as a result of such research endeavours, while also demonstrating the seismic isolation design for nuclear power reactors and its performance, as well as its effect.
In order to understand the tendency of the responses due to the seismic isolation system applied to the two-story steel structure, the comparison was performed as in Fig 9. with the response of the non-isolated structure. Fig. 9 a) to c) are artificial seismic waves, Fig. 9 d) to f) are graphs of response acceleration results for measured seismic waves. It was confirmed that the response acceleration of the isolated structure compared to the response acceleration of the non-isolated structure was greatly reduced in both the artificial and the measured seismic waves. Table 3 summarizes the results of stratified response acceleration for the non-isolated and isolated structures for each seismic wave. The response acceleration of the one-story slab of the isolated structure compared to the non-isolated structure was 30% or more, 70% or more in the two-story slab, and 80% or more in the three-story slab. This shows that the risk of non-isolated structures due to input seismic waves can be reduced and the response of structures can be reduced and the damage of structures can be minimized from the application of seismic isolation systems. Fig. 10 shows the results of the layer response spectrum of the seismic and non-isolated structures, Fig. 10 a) to c) are the results of artificial seismic waves, Fig. 10 d) to f) are the measured seismic waves. The maximum response point of the non-isolated structure is seen in the natural frequency band of the structure, but the maximum response occurs in the frequency band other than the natural frequency band. It is considered that the short-period component of the structure is long-circuited by the application of the seismic isolation system, and the response generated in the structure is reduced by avoiding the resonance of the structure. Also, the response of the non-isolated structure was amplified by artificial and seismic waves, but it was confirmed that the response of the seismic structure was greatly reduced. This means the degree of damage of the structure, and it seems that the damage caused by seismic waves can be greatly reduced when the seismic isolator is applied.
This chapter presented an instrument designed for the study of the mechanical up-con- version phenomenon in metals. Two key points make the approach presented here differ- ent from previous studies. First of all, given the authors’ involvement in the gravitational wave observatory Advanced LIGO, this system will study the behavior of metals in the elastic regime, far from the yield stress that would introduce plastic deformations. As already pointed out, to the best of our knowledge there has been no experimental inves- tigations of this kind in this regime. Secondly, since we expect the up-conversion events, if present, to be of very small amplitude, our intended measurement is not the detection of the single events, but rather the statistical properties of the up-conversion noise that arise as the incoherent sum of all the events. In particular, we are interested in the dependence of the noise power on the low frequency external disturbance the metal is subjected to. At the time of writing, the experimental apparatus has been constructed and commis- sioned. Although it has not yet reached the design sensitivity, characterization of the background noise was successful. With a measured sensitivity level of ≈ 10 − 14 m / √ Hz at 50–100 Hz, the experiment has already reached a sensitivity level which is significantly better than the first prototype of the instrument. However, several limitations of the present setup have been already identified and are being tackled with small scale, short term modifications of the seismic isolation system and of the control electronics. This will allow meaningful upper limits to be set for the contribution of up-conversion noise to the Advanced LIGO detectors’ sensitivities, and may possibly yield a direct detection of up-conversion noise in metals still operating within the elastic regime.
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Three dimensional (3D) seismic isolation devices have been developed to use for the base isolation system of the heavy building like a nuclear reactor building. The developed seismic isolation system is composed of rolling seal type air springs and the hydraulic type springs with rocking suppression system for vertical base isolation device. In horizontal direction, the same laminated rubber bearings are used as horizontal isolation device for these systems.
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Seismic isolation is intended to prevent earthquake damage to structures, buildings and building contents. One type of seismic isolation system employs load bearing pads, called Isolators. Since the isolators carry large vertical loads and deform to significant lateral displacement, the components of the structure above and below the isolator need to be designed properly. Specifically, to make isolation system work in proper manner, the structure should be free to move in any direction up to the maximum specified displacement. Base isolation is achieved by inventing several isolation devices to meet the desired requirements of an earthquake resistant structure.
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Thirty-eight lead rubber (LR) bearings are used to isolate the GNF. The target isolation period is approximately 2 seconds for design basis shaking (DBE), with the same system being used at both sites. (The isolated period at the LANL site is greater than at the INL site because the seismic hazard is greater at LANL thus producing greater DBE horizontal displacements and corresponding axial forces, and a smaller effective horizontal stiffness.) The isolators are located beneath the shear walls; their spacing is limited to 25 ft. The seismic isolation system was designed for design basis earthquake (DBE) shaking (see next section) per the provisions of ASCE/SEI Standard 4-16 (ASCE 2016). The product of the analysis was one size of isolator for both the INL and LANL sites: 33 inches in diameter, central lead plug of 6 inches in diameter, twenty-five layers of 0.42-inch thick rubber, twenty-four 0.2-inch thick shim plates, two 1.25-inch diameter end plates, and two 1.25-inch thick flange plates, for a total bearing height of 20 inches. The locations of the isolators and their design were not optimized.
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Base isolation is a well-known and considerably mature technology to protect structures from strong earthquakes. A number of base isolation systems have been developed all over the world since 1970s. Some of them, for example rubber bearings and friction systems, have been adopted widely for buildings and civil structures such as bridges in several countries of a high seismicity, and their effectiveness has been demonstrated through surviving real strong earthquakes. The basic concept of a base isolation is to decouple a structure from the horizontal components of an earthquake ground motion by interposing a soft layer with a low horizontal stiffness between the structure and the foundation. This soft layer gives the structure a much lower fundamental frequency than its fundamental frequency for a fixed base and also much lower than the predominant frequencies of the ground motion. When a destructive earthquake occurs, since most of the deformation behavior is concentrated on the soft layer, the remainder of the structure will remain nearly elastic. Thus, a floor acceleration and interstory drift of the structure will be significantly reduced and also damage to the structural elements will be dramatically reduced. Also, the elastic behavior of the isolated structure will give a more reliable response than conventional structures.
The variation of RMS velocity of top floor with damping ratio of the structure for different earthquake load is shown in Figs.17-19, respectively. It is observed that the RMS velocity gradually decreases with increase in the damping ratio of the structure. Also the reduction in RMS velocity is more in case of structures with BI and VED system installed together compared to that with only VED system installed.
A column is supposed to be a vertical member starting from foundation level and transferring the load to the ground. The term floating column is also a vertical element which at its lower level rests on a beam which is a horizontal member. Buildings with columns that hang or float on beams at an intermediate storey and do not go all the way to the foundation and have discontinuities in the load transfer path. The beams in turn transfer the load to other columns below it. Such columns the load was considered as a point load. The previous Earthquake data provides enough evidence for behaviour of different types of structures under different seismic conditions and foundation aspects has become stuff for Engineers and Scientists. This has given various types of innovative techniques to save structures from seismic effects. Among those, Base Isolation is one of the recent techniques. The main aim of base isolation is to provide flexibility and dissipation of energy by incorporating the isolated devices so called isolators, which is provided between the foundation and the super structure. Thus, base isolation essentially dissociates the building from the ground during seismic excitation. The use of flexible layer by base isolation systems at the base of the structure will allow relative displacements between the foundation and the superstructure. Addition of isolation layer elongates the fundamental time period of the structure.
The long-spanning of Hanok can be considered by two types, that is, beam direction and dori direction. Beam direction which is shown in Fig. 2(a) is related to depth, and dori direction shown in Fig. 2(b) is related to width of Hanok. In Hanok, beam is subjected to concentrated load and the deflection is proportional to the third times of its length and flexural stress is proportional to just its length. On the other hand, dori is subjected to distributed load and the deflection is proportional to the fourth times of its length and flexural stress is proportional to the second times of its length. Due to the structural characteristics of Hanok the actual deflection and flexural stress is more in beam direction than dori direction, so that, beam direction is more sensitive to long-spanning than dori direction. If the span of beam or dori is more than about 10m, the section size needed becomes so large that lumber is no longer feasible to be used but glue-laminated wood is more feasible and the use of hybrid system must be considered to accommodate the long span.
NECS was commissioned by EDF to perform the numerical dynamic analyses (Task n°6 of Table 2). Results from previous tasks, such as type and number of bearings, are used as input data. An optimization procedure was used for the establishment of the bearings layout. The objective of the procedure is to minimize the dispersion of the compression value for each device under static loads, while minimizing the rotation effects under seismic loads. This is achieved with an iterative procedure that minimizes the distance between the center of rigidity of bearings and the vertical projection of the center of gravity of the EPR Nuclear Island, and provide a uniform load distribution on bearings.
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The adoption of seismic isolators, by decoupling the seismic input perceived by the IRIS NSSS and the seismic excitation actually perceived by the IRIS reactor vessel and ESF Structures Systems and Components (SSCs), is effectively shifting all fragilities towards the right end side, thus significantly reducing the conditional probability of seismic induced failures. The combination with the hazard curves is now non-trivial only in those portions of the hazard curve (i.e., with extremely high accelerations), which are associated with extremely long return periods. Obviously, the treatment of such portions of the hazard curve represents a critical point, due to the high uncertainties associated to the lack of statistical data.
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Seismic isolation also known as base isolation is one of the best earthquake resistant design concept in which a building is decoupled from the earthquake ground motion or seismic waves. In base isolation the base of the structure is isolated using isolators (normally bearing isolators) which help in decoupling (it should be notice that the structures are generally failed due to couple formation during seismic action). When a building is decoupled from ground motion it significantly reduces response in the structure which would have affected building if it is fixed base. Base isolation decouples the building from ground motion by decreasing the fundamental frequency when compared to fix based building. This concept of base isolation also makes to remaining building behave elastic during an earthquake. Base isolation concept is also useful in other infrastructures like bridges, nuclear power plants and liquid storage tanks etc.
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Story shear is the shear generated at each storey during seismic action while the base shear is the required amount of reactive shear force to make the structure fully stable during seismic action. It can be seen in base isolated building story shear in x-x direction were reduced significantly at each storey when compared to fixed base building. This means after the use of Lead rubber bearing as base isolator the storey shear, base shear, Lateral load at each floor etc in x-x and other direction are reduced. The base isolated building story shears in x-x direction at top story reduced by 92.844% when compared with fixed base building. The overall base shear reduced upto 43.484%. Other results are also reduced but due to lack of space we are not able to show all the comparisons.
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LRB was first invented in 1975 in New-Zealand. The components of the LRB are lead plug, endplates, steel shims and rubber layers. The steel shims provide vertical stiffness to the LRB and layers of rubber provide lateral flexibility or horizontal stiffness. Lead core of the LRB gives extra stiffness to the isolators and it also provides damping to the system. The LRB has four functions listed below:-
Base isolation of structures is one of the most desired means to protect it against earthquake forces. The term base isolation have two word first is ‘base’ its meaning is a part that supports from underneath or perform as a foundation of a structure, and second is ‘isolation’ its meaning of the state of being disparate. The effective reduction of inter storey drift in the floor of base isolation system can ensure the lowest damage to facilities and also human safety.
• The five isolated buildings of the TELECOM Italia (former SIP) Telephone Company at Ancona (Marche Region), owned by SEAT and designed by Dr. G.C. Giuliani, the first Italian application of base SI (beginning of years ‘90s), which were equipped with High Damping Rubber Bearings (HDRBs) manufactured by ALGA and were provided by ENEL with a seismic monitoring system that recorded the March 1998 aftershock of Marche and Umbria earthquake (in the films use has also been made of some pictures shot in 1990 during impressive forced- and free-vibration tests, the latter to 110 mm base displacement );