Deprem etkilerine karşı geliştirilen pasif ve aktif kontrol sistemleri /
Yazar: MELTEM ŞAHİN
Danışman: DOÇ.DR. NECMETTİN GÜNDÜZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Yüksek Lisans, 1996
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Denetim sistemleri = Control systems ; Deprem = Earthquake

Özet:
ÖZET Bir yapının sismik tasarımında ana amaç, yapıda oluşan iç kuvvet ve yer değiştirmeleri güvenlik, servis ve konfor koşullan kullanarak sınırlamaktır. Bunun için deprem gibi çevresel etkilere karşı yapıyı koruma önlemlerinin alınması gerekir. Deprem etkilerine karşı yapılan korumak amacıyla pasif yöntemler ve aktif yöntemler olarak adlandırılan sistemler geliştirilmiştir. Uygulanmasının daha kolay olması, ileri teknolojinin gerekmemesi ve daha ekonomik olması nedeni ile pasif kontrol araçlar üzerinde daha çok araştırma yapılmış ve daha yaygın bir şekilde uygulanmıştır. Koruma yöntemleri uygulanmamış yapılarda kolon rijitliklerini azaltarak, kirişlere mafsallar koyarak ya da bunun gibi yöntemlerle yapıya bir form vererek depreme karşı dayanımı sağlanır. Burada amaç, depremden yapıya intikal eden enerjinin belirli yapı elemanlar tarafından sönümlenmesi veya sisteme enerji girişinin azaltılmasıdır. Bu önlemler ile belli bir koruma sağlansa bile, bazı elemanlarda oluşabilecek olan plastik deformasyonlar yapıya ciddi hasarlar verebilir. Yapıya katı veya sıvı sönümleyiciler, özel mesnetler, tendonlar, kayma elemanlar dediğimiz ilave elemanlar koyarak da yapıya giren enerjinin azaltılmasına çalışılır. Yapımn tabanına ya da içine konan ilave elemanlar ile korunmasıyla yapıda oluşabilecek ciddi hasarlar önlenebilir. Bu çalışmada yapılan depremin neden olduğu yıkıcı etkilere karşı korumak amacı ile geliştirilen kontrol sistemleri incelenmiştir. Bu kontrol sistemleri, pasif yöntemler kullanarak koruma sağlayan yöntemler ile gelişmiş bilgisayar teknolojisi kullanan aktif kontrol yöntemleri olarak iki ayrı kategoride ele alınmıştır. Birinci bölümde bu sistemler genel olarak tanıtılmış, sistemler hakkında genel bir bilgi verilmiştir. Pasif kontrol sağlayan sistemler, taban izolasyon sistemleri ile pasif enerji dağıtan sistemler olarak ayrılmıştır. İkinci bölümde, taban izolasyon sistemleri üzerinde yapılan çalışmalar anlatılmış, taban izolasyonu sağlayan sistem çeşitleri hakkında bilgiler verilmiş, sistemlerin çalışma mekanizması açıklanmıştır. Üçüncü bölümde, aktif kontrol sağlayan sistemler anlatılmış, bu sistemlere örnekler verilmiş ve sistemlerin çalışma mekanizması açıklanmıştır. Dördüncü bölümde, aktif ve pasif kontrol sistemlerinin birlikte kullanılması ile oluşturulan karma izolasyon sistemleri anlatılmıştır. Beşinci bölümde, aktif ve pasif kontrol sistemleri ve karma sistemler karşılaştırılmış, sistemlerin avantajlar ve dezavantajlar anlatılmıştır. Altıncı bölümde kütle merkezi ile rijitlik merkezi üst üste gelmeyen düzensiz dört katı betonarme bir binanın elastomerik izolatör kullanılması ile deprem etkilerine karşı davranışının değişimi üç boyutlu olarak, Sap90 programı kullanılarak incelenmiştir. vıı

Abstract:
SUMMARY THE CONTROL SYSTEMS DESIGNS AGAINST DESTRUCTIVE EFFECTS OF EARTHQUAKES In structural engineering, some structural protection concepts have been advanced to design new structures or existing ones so that they, together with their occupants and contents, can be better protected from the damaging effects of destructive environmental forces such as wind, earthquakes. Structural protective systems can be divide into three groups: Seismic Isolation Systems Passive Energy Dissipation Systems Active Structural Control Systems Many methods and several types dampers have been developed for the use passive structural response control methods with the purpose of reducing the response shear force acting on the structure frames. The dynamic properties of such dampers are to be determined according to the intensity level of the design earthquake ground motion, because the yield strength, the energy dissipation capacity and the ductility factor of the damper are highly influenced by the input disturbance level. Response control by means of passive dampers should be most effective at the design level earthquake excitation, which is the key feature of this method. On the other hand, the objective of the active structural response control lies in the exemption of structural design from the concern of the uncertainty or unpredictability of the ground motion in the future. The proposal of "Seismic Response Control of Structural Systems" is based not only on the desire of completing the structural engineering free from earthquake disasters but also on the recognition of the seismic resistant design's limitation and on the availability of new generation tecnologies such as microprocessors, sensors and actuators and so forth. Seismic Isolation Systems There are three basic elements in any practical isolation system:. A flexible support (spring) so that the fundamental period of vibration is lengthened sufficiently to reduce the force responce; IX. A damper or energy dissipator to limit the relative deflections across the flexible support to a practical design level; and. Rigidity at low (service) load levels such as wind. Seismic isolation provides an economic alternative for the seismic design of new structures and the rehabilitation existing buildings, bridges and equipment. Rather than resisting the large forces generated by earthquakes, seismic isolation decouples the structure from the ground motion, providing the ability to reduce earthquake forces. The conventional approach requires that structures passively resist earthquakes through a combination of strength, deformability and energy absorption. The level of damping in these structures is typically very low and therefore the amount of energy dissipated during elastic behaviour is very low. During strong earthquakes, these structures deform well beyond the elastic limit and remain intact only due to their ability to deform inelastically. The inelastical deformation takes the form of localized plastic hinges which result in increased flexibility and energy dissipation. Therefore, much of the earthquake energy is absorbed by the structure through localized damage of the lateral force resisting system. This is somewhat of a paradox in that the effects of earthquakes are counteracted by allowing structural damage. Conventional construction techniques can cause very high floor accelerations in stiff buildings and large interstory drifts in flexible structures. These two factors make it difficult to ensure the safety of the building components and contents. Mounting a building on an isolation system can prevent most of the rapid horizontal movement of the ground from being transmitted to and amplified by the structure above. This results in a significant reduction in floor accelerations and interstory drifts, thereby providing protection to the building contents and components. Numerous designs for base isolators have been suggested. All of these systems have certain features in common, the most important of which are the horizontal flexibility and energy dissipative capacity. Pure friction base isolation systems have been proposed in which the isolation mechanism is sliding friction. These base isolators are the simplest base isolation systems of all and there has been a large body of theoretical work on their performances. The most extensively studied base isolation system is the laminated rubber bearing with and without a lead core. The main isolator of the LRB system consists of alternating layers of rubber and steel with the rubber being vulcanized to the steel plates. Another base isolation system is the resilient-friction base isolator. This base isolator consists of concentric layers of Teflon coated plates that are in friction contact with each other and contains a central core of rubber. The system provides base isolation through the parallel action of friction, damping and restoring springs. An important friction-type base isolator is the system developed under the auspices of Electricite de France. This system is standardized for nuclear power plants in regions of high seismicity and is constructed by the French company Framatome. The main isolator of EDF system consists of a laminated Neoprene pad topped by a lead-bronze plate which is in frictional contact with a steel plate anchored to the structure. An attractive feature of the EDF system is that for lower amplitude ground accelerations the lateral flexibility of the Neoprene pad provides base isolation. Athigh levels of excitation, however, sliding will occur which provides additional protection. Another base isolation system which has found wide application in New Zeland as well as Japan, Iceland, Italy and the United States is the lead-rubber (NZ) base isolator. This base isolator is composed of a laminated elastomeric bearing with a lead core. The function of the lead plug is primarily to dissipate energy while the lateral flexibility is provided by the laminated rubber bearing. Combining the desirable features of the EDF base isolator and the R-FBI system, which was called sliding resilient-friction base isolation system was proposed. It was suggested to replace the elastomeric bearings of the EDF base isolation system by the R-FBI units. That is, the upper surface of the R-FBI system in the modified design is replaced by a friction plate. As a result, the structure can slide on its foundation in a manner similar to that of the EDF system. For a low level of seismic excitation, the system behaves as a R-FBI unit. The sliding at the top friction plate occurs only for a very high level of ground acceleration. That provides an additional safety measure for unexpectedly severe ground excitation. One typical example of hysteretic steel dampers is Honeycomb Damper, which is a steel plate damper with many honey shaped opening in the middle of it. There are several application examples such as wall installation, pillar installation and beam installation. Each of them utilizes the relative defprmation between the main structural members so that the damper deformation dissipates the vibration energy and reduces the responce motion of the main frames. Passive Energy Dissipation Systems Passive energy dissipating devices can be used within a structural system to absorb seismic energy. These devices are capable of producing significant reductions of interstory drifts in moment-resisting frames. Furthermore, these devices, under elastic conditions, reduce the design forces. In these systems which has been passive energy dissipating devices, mechanical devices are incorporated in the frame of the structure and dissipate energy throughout the height of the structure. The means by which energy is dissipated is either yielding of the mild steel, sliding friction, motion of a piston within a viscous fluid, orificing of fluid or viscoelastic action in polymeric materials. A friction device is located at the intersection of cross bracing. When seismic load is applied, the compression brace buckles while the tension brace induces slippage at the friction joint. This, in turn, activates the four links which force the compression brace to slip. In this manner, energy is dissipated in both braces while they are designed to be effective in tension only. These devices provide a substantial increase in energy dissipation capacity and reduce drifts in comparison to moment resisting frames. The reliable yielding properties of mild steel have been explored in a variety of ways for improving the seismic performance of structures. Energy dissipation is primarily concentrated at specifically detailed shear links of eccentrically-braced frames. These links represents part of the structural system which is likely to suffer localized damage in severe earthquakes. XIAnother element called ADAS device consists of multiple X-steel plates. The shape of the device is such that yielding occurs over the entire length of the device. This is accomplished by the use of rigid boundary members so that the X-plates are deformed in double curvature. ADAS elements improve the behaviour of the moment-resisting frame to which they are installed by; a) increasing its stiflhess, b) increasing its strength, c) increasing its ability to dissipate energy. ADAS elements yield in a pre-determined manner and relieve the moment frame from excessive ductility demands. Active Control Systems Active control system consists of; (a) sensors located about the structure to measure either external excitations, or structural response variables, or both; (b) devices to process the measured information and to compute necessary control forces needed based on a given control algorithm; and (c) actuators, usually powered by external energy sources, produce the required forces. When only the structural responce variables are measured, the control configuration is referred to as closed-loop control since the structural responce is continually monitored and this information is used to make continual corrections to the applied control forces. An open-loop control results when the control forces are regulated only by the measured excitations. In the case where the information on both the response quantities and excitation are utilized for control design, the term open-closed loop control is used. To see the effect of applying such control forces to a structure under ideal conditions, consider a building structure modeled by an n-degree of freedom lumped mass-spring-dashpot system. The matrix equation of motion of the structural system can be written as; Mx(t)+Cx(t)+Kx(t)=Du(t)+Ef(t) (1) where M, C and K are n x n mass, n x n damping and n x n stiffness matrices x(t): n- dimensional displacement vector f(t): applied load or external excitation u(t): applied control force vector D: n x m matrix defining the location of the control force vector E: n x r matrix defining the location of the excitation xuSuppose that the open-closed loop configuration is used in which the control force u(t) is designed to be linear function of the measured displacement vector x(t), the velocity vector x(t) and the excitation f(t). The control force vector takes the form, u(t)=Kıx(t)+Cıx(t)+Eıf(t) (2) where Ki, Ci and Ei are respective control gains which can be time-dependent. The substitution of equation (2) into equation (1) yields Mx^+CC-DCOxCO+CK-DKOxC^CE-DEOftt) (3) Comparing equation (3) with equation (1) in the absence of control, it is seen that the effect of open-closed loop control is to modify the structural parameters (stiffness and damping ) so that it can respond more favorably to the external excitation. It can be seen easily that the concept of active control is immediately appealing and exciting. On the other hand, it is capable of modifying properties of a structure in such a way as to external excitation transmitted to the structure is also possible through active control. Hybrid Control Systems Intensive research efforts have been made in the application of passive and/or active! control systems to reduce the response and damage of civil structures caused by earthquakes and strong winds but it has been shown that a combined use of active and passive control systems, referred to as the hybrid control system, is more effective, beneficial, and practical in some cases. The idea of hybrid control systems is to utilize the advantages of both the passive and active control systems to extend the range of applicability of control systems to protect the integrity of the structure. In particular, under extreme environments, e.g., strong earthquakes, hybrid control systems are superior. Xlll