Mechanical devices to control, limit and attenuate shocks, vibrations and seismic movements in buildings, equipment and piping networks

Seismic Control Systems 47 Mechanical devices to control, limit and attenuate shocks, vibrations and seismic movements in buildings, equipment and piping networks V. Serban, M. Androne, A. G. Ciocan & A. M. Zamfir Subsidiary of Technology and Engineering for Nuclear Projects, Bucharest-Magurele, Romania Abstract The paper presents new types of mechanical devices developed by SITON and SIGMA SS companies in cooperation with other units in Romania, by means of which to control, limit and damp shocks, vibrations and seismic movements in buildings, equipment and pipe networks. The new devices, called SERBdevices can sustain large static loads to which dynamic loads may be superimposed and be damped. The devices allow cutting-off the dynamic action in-coming from the environment to the protected systems (building, equipment, pipe network, etc) and the sustaining of shocks and vibrations generated by the systems to protect the environment. The devices may have high relative displacements, with or without restoring force, allowing thus the performance of a good isolation of the components against the dynamic action, also sustaining the displacements due to thermal expansions or support yielding. The hysteretic force has the form with consolidation for effective control and limits the degradation of the structure. The devices are made of materials that are practically not affected by the aging phenomenon and relative large temperature variations and may be guaranteed throughout the service-life of each unit, without maintenance or repair. The devices are small in size if compared with the existing ones for similar performances. The radiation resistance capacity is very good and therefore allows their use in nuclear-power plants. Keywords: shocks, vibrations and seismic movement, control, limitation, damping, base isolation systems. doi:10.495/978-1-84564-67-1/ 05

48 Seismic Control Systems 1 Introduction Buildings, equipment and pipe networks are generally affected by shocks and vibrations generated by the operation of equipment or fluid flow through pipe networks. Additionally, on sites with average or high seismic activity, seismic movements need to be considered in the design of equipment, pipe networks and buildings. Such shocks and vibrations affect the proper operation of the technological equipment and components, damage the buildings structure where they are installed in and generate waves and noises that propagate to the environment, affecting the foundations of sensitive equipment and components, and also generate a discomfort for the operation personnel and for the occupants of buildings. Depending on their generating source, shocks and vibrations evidence strong different dynamic characteristics and the elimination or reduction of their effects may be obtained only by special solutions applicable to each individual case, after having analyzed excitation kinetic characteristics. This paper is a presentation of SERB-SITON solution application to enhance the safety level of components against shocks, vibrations and seismic movements. The new SERB supports and devices for components are developed on basis of the Romanian Invention Patent no. 119845 (Serban [1]) and Patent request nr. A/01093/31.10.011 (device to protect a structure to overload [8]), now in the process of being internationally protected. The first industrial application related to shock and vibration reduction was in 003. It was aimed to isolate a 150 kgf forging hammer located in the Forging Workshop (IUS Brasov, Romania) and the inlets and outlets of a pressurized air pipe []. Subsequent applications, among others, were: another 150 kgf forging hammer from IUS-Brasov; the strengthening of a ground floor and 5-stories building with reinforced concrete frame structure (NAVROM Galati-Romania) and the isolation of 5 electrical cabinets from Heavy Water Production Plant in Drobeta-Turnu Severin, Romania. One of the high quality isolation from noises, shocks, vibrations and seismic movement is the new solution applied to CETAL (Integrated Center for Laser Advanced Technologies [9]). The isolation assures the reduction of the amplitude vibration to values smaller than 3x10-6 m/s [9]. SERB supports and devices are certified in Romania by TECHNICAL AGREMENT 016-03/144-005 [3]. The systems response to dynamic actions The effect of shocks, vibrations and seismic movements on buildings, equipment, pipe networks, etc. herein called systems, is dependent on both the intensity of the dynamic action and the response of the systems at dynamic actions. The excitation may transfer to the system a quantity of energy per oscillation cycle equal or smaller than the energy corresponding to one

Seismic Control Systems 49 oscillation cycle, depending on the harmonization or dis-harmonization of the system eigen-motion with the dynamic action. In order to see how the total dynamic loading (action + response) acting to a system may be reduced, the authors analyzed the behavior of the dynamic response of a SDOF oscillating system in the frequency domain, subjected to a harmonic dynamic action, (Serban et al. [4]). Consider a simple SDOF oscillating system with a mass m, damping c (proportional to the vibration velocity), and stiffness k (proportional to the relative displacement). The oscillating system is subjected to an oscillating movement of the support, represented by u s (t), which, in the analysis, is approximated with a harmonic, T s -period movement, in the form: u s t Asin t, (1) The equations of motion of the oscillating system, written in terms of relative displacement x(t), and the total displacement y(t), respectively, are: x t x t x t a sin t (a) y t y t y t Asin t A cos t (b) with the initial conditions: x 0 0, x 0 v ; 0 y 0 0, y 0 0 (3) where v 0 is the relative initial velocity that is equal with and in opposite direction to the support velocity at t = 0, the critical damping ratio and ω the angular frequency. The amplitudes of the kinetic and elastic energies specific to the mass of the oscillating system versus the source energy amplitude E s (Serban et al. [5]) are: r r E ( 4 ) c E, r s W ( r 1) 4 r p E (4) s ( r 1) 4 r For an oscillating system to respond to dynamic loads with smaller or equal amplifications than the static loads of the same intensity (without amplification), it is necessary that the amplitude of the kinetic and elastic energy built-up in the oscillating system be smaller than or equal to the excitation energy: E c E s and W p E s. For the kinetic energy the relation is: 1 or r T, T s irrespective of the oscillating system damping. The condition that the maximum elastic energy amplitude of the oscillating system is smaller than or equal to the maximum energy amplitude of the source per oscillating cycle which is dependent on the oscillating system damping and it corresponds to an oscillating system vibration period greater than 1.41T s. Figs. 1 and illustrate the variation of the kinetic and elastic energy amplitude of an oscillating system for = 5% and = 0%, respectively. Analyzing the diagrams, it becomes clear that the most efficient solution to reduce the total energy of a system subjected to dynamic actions is to make an elastic connection with optimum damping (30% recommended) at the level of the anchoring point. T s

50 Seismic Control Systems Ekin Wpot 1000 Kinetic and Potential energy 100 10 1 0.1 0.01 0.001 0.1 1 10 ratio = T/Ts Figure 1: The kinetic and elastic energy amplitudes related to excitation ones; critical damping ratio = 5%. Ekin Wpot 1000 Kinetic / potential energy 100 10 1 0.1 0.01 0.001 0.1 1 10 ratio = T/Ts Figure : Kinetic and elastic energy amplitudes related to excitation ones; critical damping ratio = 0%. a) For an oscillating system with 5% damping, the kinetic and elastic energy built-up in the system is 100 times greater than the energy of the excitation for resonance T = T s and only about 10 times greater at the system vibration period which is different from the excitation oscillation period by 0%. For T/T S =, E C is 4 times smaller than W P of the system. b) For a 0% damping of the oscillating system, the kinetic and elastic energy built-up in the system from the source is about 8 times greater than the energy of the excitation for resonance T = T s and only about 5 times greater than the system vibration periods which are different from the excitation oscillation periods by 0%. For T/T S =, the amplitude of the kinetic energy of the system is 10% of the amplitude of the source energy for 5% damping and about 15% for 0% damping; this demonstrates that an increase of the damping capacity of the

Seismic Control Systems 51 oscillating system leads to the increase of energy accumulated in the system, including his response in this area. For better understanding the phenomenon of energy transfer from the excitation to the oscillating system, an analysis of this power transfer is given below. The amplitude of the power transferred from the excitation to the oscillating system and that of the dissipated power of oscillating system for the system unit mass, is: 3 4 Pe P s, ( ) 4 P d P (5) s 4 Figs. 3 and 4 show the amplitude variation of the power transferred from the excitation to the oscillating system and the amplitude of the power dissipated by the oscillating system for a mass unit of the oscillating system as functions of the ratio between the oscillating system period and the period of the excitation for 5% and 0% of the critical damping, respectively. Pd Pe 100 Damping and Seismic ground power 10 1 0.1 0.01 0.001 0.01 0.1 1 10 100 ratio = T/Ts Figure 3: Power amplitude transferred from the excitation to the oscillating system and dissipated power amplitude in the oscillating system; critical damping ratio = 5%. Pd Pe 100 Damping and Seismic ground power 10 1 0.1 0.01 0.001 0.01 0.1 1 10 100 ratio = T/Ts Figure 4: Power amplitude transferred from the excitation to the oscillating system and dissipated power amplitude in the oscillating system; critical damping ratio = 0%.

5 Seismic Control Systems The amplitude elastic, damping and total seismic force becomes: F e u - elastic force; (6) ( ) 4 F d u - damping force; (7) ( ) 4 F s 4 u - total force. (8) ( ) 4 Figs. 5 and 6 show the amplitude variation of the damping, elastic and seismic forces transferred from the excitation to the oscillating system as a function of the ratio between the oscillating system period and the period of the excitation, for 5% and 30% critical damping, respectively. These graphs demonstrate that increasing the damping of the oscillating system (β) leads to the increase of damping force in the system, especially in the isolation range. Analyzing the diagrams, it becomes clear that the amplitude of the power transferred from the excitation source to the oscillating system is practically equal to the amplitude of the excitation power for oscillating system vibration periods smaller than 0.4T s. For example, the very good behavior of the block of flats made of prefabricated elements in Bucharest during an earthquake in 1977 is a confirmation of the phenomenon from a real case. For vibration periods greater than 0.4T s, the oscillating system starts to build-up energy by the transferred power and the amplitude of the dissipated power reaches 1% of the excitation power amplitude (for 5% of critical damping ratio). 3 Technical solutions to reduce the systems response to dynamic actions 3.1 Theoretical aspects The analyses carried out in section show that: the dynamic response amplitude of a system to a repeated dynamic action depends on the amount of energy transferred from the dynamic action to the oscillating system and the amount of energy accumulated in the oscillating system associated to the structure. To reduce the seismic response of a system to a repeated dynamic action the following effects must be achieved repeatedly. 1. The energy transfer in an oscillation cycle from the dynamic action to the oscillating system has to be minimal.. The amount of energy (kinetic and potential) accumulated in the oscillating system has to be minimal. 3. The amount of energy dissipated by the oscillating system in a vibrating cycle has to be maximal. These issues cannot be addressed simultaneously.

Seismic Control Systems 53 Figure 5: Variation of damping, elastic and seismic force amplitude transferred from the excitation to the oscillating system versus period ratio; critical damping ratio 5%. Figure 6: Variation of damping, elastic and seismic force amplitude transferred from the excitation to the oscillating system versus period ratio; critical damping ratio 30%. According to the relation between the oscillating system s own vibrating period and the forcing cycle period, several situations can be met. In all these situations there should be borne in mind that the power transfer from the dynamic action to the oscillating system mass is accomplished by both elastic and damping forces and the energy dissipation of the oscillating system is accomplished only by damping forces. For this reason, there must be an optimum ratio of the two types of forces in order to get a minimum answer of the system to the repeated dynamic action. Possible situations in which one can find an oscillating system defined by its vibrating period T responding to the repeated dynamic action defined by the cycle period T S and the definition of these states are described next.

54 Seismic Control Systems 3. System flexible to the dynamic action T >> T S In this case the oscillating system is in isolation state when practically the dynamic action applied to the base is not transmitted to the system mass. In practical design cases, the condition T > 3T S shall be considered because the evaluation of T and T S is affected by calculation and measurement errors. We call this region of the response spectrum of the system dynamic response isolation region. In this region, small forces act on the oscillating system mass, a great percentage of these forces being represented by the damping force. The mass of the system is set in motion by the oscillation amplitudes which are much smaller than the excitation amplitude. This is due to the fact that the interaction forces (springing and damping) between excited flexible elements and oscillatory system mass are low and the mechanical work done by them and transferred to the oscillatory system does not practically lead to an increase in the energy accumulated in the system. In this case, if the damping forces are great, a large amount of energy is transferred in the oscillating system which leads to the increase of the seismic response unlike the case of the small damping system. In practical cases, the achievement of a damping capacity must be connected with the mass and stiffness of the oscillating system. Through technical design solutions, it is recommended that the damping of an oscillatory system, expressed in critical decay ratios (damping for which the system no longer oscillates) to be under 30%. 3.3 System rigid to the dynamic action T << T S In this case the oscillating system is in transport state when it is carried by the dynamic action and a relative deformation of the system is not realized. In practical design cases, T T S /3 is recommended accounting for the reason explained under case 1. For T = T S /3, the potential energy accumulated in the oscillatory system is about 10 times less than the energy of excitation in a cycle of oscillation and the kinetic energy of the oscillating system is practically equal to the energy associated with one oscillation cycle of the excitation. This region of the dynamic response of the oscillatory system is called transport region. In this state, the mass of the oscillating system has practically no motion relative to the support structure to which excitation is applied. In this case, the oscillating system is transported on either side of the equilibrium position without relative deformations. The oscillatory system mass does not have a movement relative to the basis (support structure), so there is no amplification or reduction of system response amplitude versus the excitation amplitude. In this situation, the damping of the systems does not influence the response of the oscillating system. 3.4 Elastic system to the dynamic action T T S In this case, the system is located in resonance state when the transfer of energy from the excitation to the oscillating system is maximum. The system response increases leading also to the growth of energy dissipation.

Seismic Control Systems 55 Amplification of the response settles at a maximum value when the energy transferred from excitation is entirely dispersed in the system. The system response is a maximum due to accumulation of energy from excitation. Maximum amplification occurs for T = T S but important amplifications occur for periods of vibrations of the system in the neighborhood of T S. In practical design cases, the resonance area is considered: T S / T T S. This region of the dynamic response of the system (response spectrum) is called region of resonance. In this region, almost all the energy of an oscillation cycle is transferred to the oscillating system (total transfer is accomplished for T = T S ). The energy transferred accumulates in the oscillatory system (part of it is dissipated) leading to an increase in the system acceleration, velocity and displacement response. The maximum response of the system in this case is heavily dependent upon the ability of damping expressed in fractions of critical damping. Due to the damping capacity, the maximum velocity and displacement response of the system is reached for T > T S depending on its critical damping ratio. In this region, the reduction of the oscillating system response can only be achieved if the damping capacity increases. In this case, as in case 1, the critical damping ratio of the oscillatory system is not recommended to exceed 30%. In the transport and isolation state, the oscillating systems do not have a high variation of the response with respect to their own vibration period; this, for many oscillating systems, may be due to the degradation of the materials of which the system is composed. Unlike these states, an oscillating system may be found in transient states in which an important change of the system response occurs with a variation of its period of vibration. These transient states are: transport-resonance and resonance isolation. Oscillating systems in these states change their response to avalanche depending on the modification of the vibration period. Changing the vibration period of an oscillatory system occurs when the state of stresses and deformations in the oscillating system components exceeds the limit of elastic reaction. For common materials, the degradation of an oscillating system has as an effect maintaining practically constant the elastic force for a large deformation of the material (yield) but the damping capacity increases. In this case, the force that transfers energy from the excitation to the oscillatory system mass does not remain constant and there is a growing dependence on damping capacity. This growth creates two phenomena with opposite effects on the dynamic response of the system. The first effect is an increase in total acceleration of the oscillatory system mass due to the enlargement of the interaction force resonance region and the second is to reduce the dynamic response of the oscillating system due to increasing the capacity of damping. According to the ratio of the two tendencies, the maximum acceleration of the system mass can drop or grow. This change of acceleration depends much on the position of the oscillatory system in nondegraded state opposite to the resonance area.

56 Seismic Control Systems For this reason, the dynamic response of an oscillating system grows by degradation if, in non-degraded state, it is in the transitory region of transportresonance and drops if, in non-degraded state, it is in the transit region of resonance-isolation. For the definition of these regions, it is recommended the overlapping with the technical resonance status also to be considered and to use as the limit T S rather than T S / or T S, respectively, because the transitional phenomena manifest themselves on both sides of T S. 3.5 The pre-resonance range The system is elastic and gains energy from excitability in avalanche regime. Accumulation of energy in the oscillatory system leads to an increase in dynamic response. If degradations appear in component materials in the system, the oscillating system is unstable and high amplifications of the dynamic response may appear to destroy it because this reduces the resistance capacity of the system materials at the time when the response of the system to dynamic forces increases. Dynamic amplifications of the system shall be reduced only if the natural period of vibration T has increased so much because of the degradation (reducing the rigidity) so that it becomes greater than the period of excitation cycle T s (in the case of earthquakes greater than T C ). The critical damping ratio is not increased so much in the oscillation system so that the effect of reduction is greater than the effect of amplification produced by the accumulation of energy in oscillatory system due to the proximity of the resonance region. This dangerous situation may appear in the building's seismic response so that, in their lifetime, they may be affected by slow earthquakes for which T C > 0.5 s up to s when the dominant harmonic component of the seismic movement T C (which was represented in the analysis as T S for a harmonic excitation) is greater than the vibrating period T of the non-degraded building. This case is not taken into account by the current seismic design code that results in the seismic response of building being usually underestimated for slow earthquakes, with negative consequences to the level of safety of constructions. This danger is very high for areas affected predominantly by slow earthquakes as are intermediate Vrancea earthquakes (in Romania) or earthquakes which are manifested in soft ground areas (in a large depth of field, ground layers are of alluvial type, non-consolidated and have a period of high vibration, as for example earthquakes of Kobe-Japan in 005). The seismic design concept for constructions throughout the world was imposed by the concept of design in Japan, New Zealand, USA, etc. which are countries affected by rapid surface earthquakes in which T C 0.3 s. Any construction of 3 or more levels does not enter this dangerous region of reaction/response, or if it does (those with fewer levels), constructions leave this region by increasing their own vibration period through a slight degradation. In this case, constructions auto-isolate towards fast earthquakes and their response is greatly reduced.

Seismic Control Systems 57 3.6 The post-resonance range The system is elastic but receives from excitations less amount of energy than that of an oscillation cycle. This energy accumulates at a smaller amount in the oscillating system. If there are overloads of component materials, they lead to an increase of the vibration period of the oscillating system T and consequently its dynamic response is reduced. All high constructions affected by rapid earthquakes are situated in the postresonance or isolation region and through degradation (if these phenomena appear), their seismic response is reduced considerably. For this reason, the solution of acceptance of controlled degradations in constructions affected by rapid earthquakes, T C < 0.5 s, is a good one in terms of construction safety and saving human lives. Applying the same seismic design solutions for constructions in areas affected by slow earthquakes (as is the case in parts of Romania, where slow Vrance earthquakes occur) is a scientific and technically legalised error in seismic design codes (Code P100 in Romania). The solution to secure buildings against earthquakes with the acceptance of structural controlled degradations (plastic hinges) can be accepted only if the design ensures that the building structure can sustain, in terms of safety, relative level deformations which ensure the exit of the resonance region and the passage to the isolation zone where seismic response reduction shall be reached for the construction. 3.7 Practical aspects To reduce the dynamic response of a system, many solutions have been devised, which are applied selectively. A technical solution applied in particular to constructions is accepting controlled degrading which leads to a reduction in their rigidity so that the construction reaches the isolation region with respect to dynamic action. In this case, the relative level deformations must be under the ultimate limit of the construction resistance in order to achieve a minimum degree of safety. Another solution consists in the control of structural dynamic behaviour by means of special mechanical devices. These devices are inserted into the system and/or between the system and the support-structure; they allow the modification of the dynamic characteristics of the system and reduce its dynamic response without structural degradations having to appear in the systems. These devices must sustain high static and dynamic loads, allowing control of the systems deformations and have optimum damping capacity. Conceptually and practically, two types of devices have been developed for the control, limitation and damping of the dynamic response of a system: Devices for dissipation of energy and control of deformations of the system subjected to a dynamic action; Devices for the isolation of the system towards the dynamic action.

58 Seismic Control Systems These devices must meet a series of requirements so they do not affect the stability and safety of the system and the foundation. To satisfy such requirements, SITON and SIGMA SS has developed a new type of devices with geometric non-linear elastic characteristics and large damping, that are capable to sustain the static and dynamic loads and to selfadjust to the large installation deviations and errors (Serban [1, ], Serban et al. [6]). Such a device was developed on the basis of the Invention Patent no. 119845/9.04.005 protected by OSIM. SIGMA SS and SITON has been developing and applying the new method and technology to reduce shocks, vibrations and seismic movements in buildings, equipment and pipe networks for more than 0 years. The first industrial application was the isolation of forging hammers (36 tons each) against shocks, vibrations and seismic movements, located in IUS SA Brasov, in 003 (figs. 7 10) and 004 (figs. 11 14 and table 1) (Serban [8]). The operation of the isolation system in IUS-Brasov without maintenance and repairs for a period of 10 years represents a guarantee certificate for the new technology developed by SIGMA SS and SITON. Figure 7: IUS 003. Foundation. SERB-194-3C. Figure 8: IUS 003. Hysteretic curves for SERB-194-C. Figure 9: IUS 003. Wave shape recorded on the foundation in the old solution. Figure 10: IUS 003. Wave shape recorded on the foundation in the new solution.

-0.5-0.4-0.3-0. -0.1 0.0 0.1 0. Seismic Control Systems 59 Forta[kN] 100 90 80 70 60 50 Suport Forja-lubrificat Forta-deplasare F=0000N, D=*10-3 m, k=10*10 6 N/m M=6000Kg, f n =6.5Hz 40 30 0 Deplasare [mm] Figure 11: IUS 004. CM150 foundation as per SERB-375C. Figure 1: IUS 004. Hysteretic characteristic for SERB- 375C. Figure 13: IUS 004. Time history of the acceleration on isolation foundation vat (practically the null-line) and bed plate. Figure 14: IUS 004. Time history of the acceleration on isolation foundation vat (practically the null-line) and bed plate. Table 1: IUS 004. The SERB-SITON isolation solution. Attenuation, transmissibility and isolation. No. Bed plate (location 1) a 1, m/s Foundation (location ) T = a /a 1 % I = 1-T % A = a 1 /a 1 6,9 0,185 37,30,68 97,31 3,4 0,067 50,75 1,97 98,03 3 3,0 0,071 4,30,36 97,63 Average value 97,65 Among the performances of the system, it is worth mentioning: the 98% isolation ratios of the system; the suppression of the vibration to 1.5 oscillation cycles; the removal of the jumping effect; the reduction of the vibration amplitude in the near-by houses located at about 150 m from the production hall by more than 800 times, i.e. from 56 mm/s with the old foundation isolation solution to 0.069 mm/s with SERB-SITON new foundation solution.

60 Seismic Control Systems The isolating devices, designed and constructed in Romania, have not suffered modification of their elasticity and damping characteristics although the operation conditions are very heavy ones (110 blows/minute generated by a 450 kg forging hammer that is developing an energy of 36 kj/blow). In 006 and 009, the isolation of 10 electric and I & C cabinets, associated with the H S compressors by SERB-device against shocks, vibrations and earthquakes, was implemented in ROMAG-PROD (figs. 15 and 16). Figure 15: ROMAG-PROD. Cabinet isolation SERB device 006. Figure 16: ROMAG-PROD. Cabinet isolation SERB device 009. Also, in 006, the most important application of SERB-SITON solution was carried out, namely the first non-traditional seismic strengthening of a building in Romania where the seismic loads are sustained and damped by SERB mechanical devices installed into a network of telescopic braces and having a controlled elasticity and damping. The strengthened building, extended and refurbished, is the Ward B in NAVROM BUSINESS CENTRE Galati, a 6-storey building made of reinforced concrete frames, having a 300 m surface and built on an old foundation supported on 1 m long oak wood pillars in 193. The building, constructed during the period 1968-1970 and aimed to be a sailors lodging house, was affected by the earthquakes in 1977, 1986 and 1990 (fig. 17), and after strengthening and rehabilitation, it is meant to house a business centre, a hotel and a restaurant. For the quality control of SERB device, tests to assess the stiffness and damping characteristics were conducted on a specimen, randomly selected (fig. 18). Figure 17: NAVROM Ward B. Damage of reinforced structures.

Seismic Control Systems 61 Figure 18: NAVROM tests; hysteretic characteristic and products delivered with Batch. Due to the great damping capacity of SERB devices installed in telescopic braces (fig. 19), the seismic acceleration amplification in the vertical direction is small, making the seismic loads and sectional stresses also small. In 011-01, SITON and SIGMA SS have developed isolation solutions for noise, shocks, vibrations and earthquakes for the Integrated Centre for Advanced Laser Technologies CETAL Bucharest-Magurele-Romania. The isolation was made for: a dynamic high precision measurements lab, a shaker platform and clean room characterization; laboratory standards frequencies-lengths. The developed solution practically ensures a total isolation towards the entire range of noise, shocks, vibrations and earthquakes affecting the CETAL building. Figure 19: NAVROM Ward B. Detail of telescopic bracing anchoring metal and concrete columns. The developed isolated system provides a high reduction of noises and vibrations for the entire range of frequencies that affect the site. In normal operating conditions, the amplitude of the vibrations is less than 3 10 6 m/s. During earthquakes, the isolation system ensures the integrity and reliability of constructions and insulated equipment. In S0 and S06 rooms, the insulated system is accomplished by means of SERB devices of high flexibility and a telescopic device with high damping capacity and limitation of lateral displacements at pre-established values. Isolation of noise transmission from

6 Seismic Control Systems room S0 to the rest of the CETAL building is accomplished by means of a multilayer structure with which the walls of the room are covered. Fig. 0 shows the mechanical isolation and devices for control of relative displacements used in CETAL and their hysteretic characteristics. Figure 0: Devices used in CETAL for mechanical isolation and control of relative displacements in vertical direction and their hysteretic characteristics. 4 Conclusions The paper presents an analysis in the frequency domain of the dynamic behaviour of an oscillating system (buildings, equipment, pipe networks, etc) considering a model with one degree of freedom to determine the dynamic response of the system under various dynamic excitation conditions. The paper points-out the fact that a system may build-up energy several times greater or smaller than the excitation energy associated to one oscillation cycle, depending on how its eigen-vibration periods are situated with respect to the dominant periods of the excitation. The results of the analysis show that there are many ways to reduce the dynamic response of a system. The most effective solution is to make the system flexible for dynamic action. In the event of this solution not being applicable for functional reasons, the recommended solution is to increase the damping capacity of the system in order to obtain a large reduction of the dynamic response amplification of the oscillating system. According to the experimental data obtained from the industrial applications, the SERB-SITON solution used to reduce the dynamic response against shocks, vibrations and seismic movements in buildings, equipment and pipe networks, is ranked among the most efficient solution applicable today. References [1] V. Serban, Brevet de inventie OSIM nr. 119845/9.04.005, Structura sandvis, dispozitiv avand in componenta aceasta structura pentru preluarea

Seismic Control Systems 63 si amortizarea incarcarilor pentru controlul comportarii unei structuri si retea de dispozitive. [] Agrement Tehnic nr. 016 03/144, Disipatori mecanici de energie seismica Tip SERB- B Consiliu Tehnic Permanent Pentru Constructii. [3] P 100-1/004. Cod de proiectare seismic. [4] Serban, V., Androne, M., Ciocan, G., Zamfir, M., Pavel, C., Pavel, M., Sireteanu, T., Baldovin, D., Mitu, A.M., Mohora, C. & Stoica, M., Solutia SERB-SITON de consolidare a cladirilor prin izolare. A XVII-a Conferinta Nationala AICPS, Bucuresti, Romania, Iunie, 007. [5] Serban, V., Androne, M., Ciocan, G., Zamfir, M., Pavel, C., Pavel, M., Sireteanu, T., Baldovin, D., Mitu, A.M., Mohora, C. & Stoica, M., Solutia SERB-SITON de consolidare a cladirilor prin controlul, limitarea si amortizarea deplasarilor relative de nivel. A XVII-a Conferinta Nationala AICPS, Bucuresti, Romania, Iunie, 007. [6] Serban, V., Androne, M., Cretu, D., Pavel, C. & Pavel, M., Controlul, limitarea si amortizarea miscarilor seismice ale unei constructii cu ajutorul dispozitivelor SERB. A 3-a Conferinta Nationala de Inginerie Seismica, Bucuresti, Decembrie 005. [7] Serban, V. & Panait, A., Isolation and damping of shocks, vibrations, impact load and seismic movements at buildings, equipment and pipe networks by SERB-SITON method. ICONE14-89189, MIAMI FLORIDA, USA, July 006. [8] Serban, V., - Patent application Device for the protection of structures from overloads Nr. A/01093/31.10.011. [9] Project Integrated centre for advanced lasers technologies -CETAL.