Esnek-sürtünmeli temel ayırıcılı sistemin deprem etkisindeki davranışı

Abstract

Bu çalışmanın amacı; öncelikle temel ayırıcı sistemlerin (base isolating systems) yapısı, kullanılma esasları ve uygulamadaki yerleri hakkında genel bilgiler vermek, ikinci olarak sürtünme esaslı bir modeli esas alarak, temel ayırıcı sistemin dinamik titreşimini incelemektir. 1. ve 2. Bölümlerde temel ayırıcı sistemlerin genel özelliklerinden ve uygulama örneklerinden bahsedilmiştir. 3. Bölümde; esnek-sürtünmeli temel ayırıcı modeli esas alan bir sistemin dinamik analizi yapılmıştır. Burada çok katlı bir yapı, tek serbestlik dereceli sisteme indirgenmiş ve dinamik analiz için adım-adım integrasyon yöntemlerinden parçalı- tamlık yöntemi izlenmiştir. 4. Bölümde; üçüncü bölümde adım-adım integrasyonla bulunan formülasyonları izleyen bir program geliştirilmiştir. Herhangi bir deprem ivme kaydım (yatay+düşey) kullanarak; deprem sırasında kuvvetli yer ivmeleri etkisinde kaldığı düşünülen tek serbestlik dereceli bir sistemin; temel ayırıcılı ve ayırıcısız olmak üzere yerdeğiştirme, hız ve mutlak ivme karşılıklarını hesaplayan bir program geliştirilmiştir. Ayrıca program, sadece yatay deprem ivmesine göre aynı karşılıkları hesaplayıp, hem yatay ve hemde düşey ivmeye göre hesaplanmış karşılıklarla oranlarını alacak şekilde düzenlenmiştir. 5. Bölümde; Erzincan (1992), Denizli (1976) ve Dursunbey (1979) depremlerinin gerçek ivme [yatay (D-B)+düşey] kayıtları kullanılarak, tek serbestlik dereceli bir sistem için, temel ayırıcısının işlediği ve işlemediği durumlar için, davranış spektrumları hesaplanmıştır ve sonuçlar grafik olarak verilmiştir. Temel ayırıcı sistemlerin yapıyı kuvvetli deprem hareketinin zararlı etkilerinden ne ölçüde koruduğu, yapıya iletilen yer hareketinin şiddetini ne oranda azalttığı, sınırladığı gösterilmek istenmiştir. 6. Bölümde; sonuçları ifade eden tablolar hazırlanarak bazı karşılaştırmalar yapılmıştır. Yapılan örnekler sonucunda; temel ayırıcı sistemin, yapıya iletilen kuvvetleri ve yerdeğiştirmeleri sınırlamadaki etkisi gösterilmiştir. Esnek-sürtünmeli ayırıcı; düşey deprem ivmesinden yapıyı ayırmadığı için, düşey deprem ivmesinin, karşılıklara etkisi oran diyagramlarıyla gösterilmek istenmiş ve bu etkinin çok az olduğu; genellikle % 2 ~ % 10 arasında (hız ve yer değiştirme spektrumlarında) olduğu görülmüştür.

First of all, the purpose of this study is to give some general information about characteristics, properties, principle of using and application of base isolating systems. Secondary, the analysis of dynamic vibration of the resilient-friction base isolators, is given. Base isolation is a technique to protect structures from the destructive effects of earthquakes by means of mechanism that limits the forces transmitted to the structures. This approach has become practical mainly due to developments in rubber technology as applied to elastomeric bearings. The mechanisms, to reduce the seismic effects are roughly grouped into four types; 1- base isolation type, 2- energy dissipation type, 3- soft spring type, 4- automatic control type. Seismic base isolators protect structures by decoupling them from damaging ground motions and by absorbing energy. The main effects of the base isolation is to decouple the structure from the ground and increase the resonant period of the structures and bearings to a value outside the range of periods containing the principal earthquake energies. Base isolated structures concentrate high lateral deformations and hysteretic damping in special components connected between the base and the supporting foundation. For flexible structures, further increases in mode 1 periods, and high damping for mode 1, give diminishing returns. However increased base flexibility and damping, give continuing reductions in the response of the higher modes. Therefore, base isolation is best suited to shorter period structures, since their benefits include substantial reductions in mode 1 responses. XH This study consists of six chapters. In the first chapter; much of the literature on theoretical aspects of base isolation is summarized. In the second chapter, the properties, behaviour and design of several types of base isolation systems are given. Rubber bearings offer the simplest method of isolation and are relatively easy to manufacture. Elastomeric rubber bearings consist of sheets of rubber bonding to thin steel reinforcing plates are as shown below steel plates rubber sheets Laminated rubber bearing The bearings are very stiff in the vertical direction and are very flexible in the horizontal direction. Their action under seismic loading is to isolate the building from the horizontal components of the earthquake ground movement. Rubber bearings does not offer isolation against vertical ground motion. The vertical components are transmitted through to the structure relatively unchanged. Because, vertical acceleration does not normally present with any problem for building structures. Rubber bearings are suitable for rigid buildings and masonry or reinforced concrete construction of up to seven stories. For this sort of buildings, uplift force on the bearings will not occur and wind load will be unimportant. In early 1980's, there has been a considerable amount of research on the development of new base isolating systems and experimental works on the response of base isolating systems have continued at several centres. xin Using the laminated rubber bearing on the base of the structure, horizontal natural frequency of the total system is much lower and earthquake response acceleration of the superstructure is reduced remarkably. But the response displacement is generally increased and the laminated rubber bearing itself can be subjected to damage. In order to overcome these problems, a friction damper is also installed in the device. The friction damper introduces energy absorbing capability into the system to reduce resonance effects and keep deflection within an acceptable limit. Some of developed base isolation systems are; - laminated rubber bearings with friction damper, - base isolation systems including helical springs and viscos dampers, - sleeved pile systems, - shake suppression systems, - lead-rubber hysteretic bearings, - resilient-friction base isolators, Some information has been given about these systems in the second chapter. In the third chapter; the analytical model of the resilient-friction base isolation system is introduced and dynamic analysis is carried out considering both horizontal and vertical components of ground motions. Resilient-friction base isolator can be incorporated into foundation of structures. Resilient-friction base isolator is composed of a set of flat rings that can slide on each other with a central rubber core and peripheral rubber cores. Sliding rings are protected from corrosion and dust by very flexible rubber cover. The rubber cores, help to distribute the lateral displacement and velocity along the height of the isolator. The resilient-friction base isolator is characterized by the coefficient of friction of the sliding elements and the total lateral stiffness of the rubber cores. In this study, in order to show the isolation characteristics of the resilient-friction base isolators, the response of rigid structures supported on a resilient-friction base isolator is considered and the mathematical model of a shear with the resilient- friction base isolators is formulated. The model is reduced to that of a rigid structure founded on a resilient-friction base isolating system. The single degree of freedom system is subjected to the horizontal and vertical components of ground motions. Equation of motion is; [m] {Ü} +[c] [Û] +[*] {«} = -(*+*) [m] {r} (D XIV s+2t<*s + v>2s = -x-\ı(g+y)-?- (2) where, o>2 = - (3) M+E/m 2Ca>= ^- (4) M + 2-mi and, Jc : horizontal ground acceleration, $ : vertical ground acceleration, K : horizontal stiffness of the elastic core, M : foundation mass over the isolator, C : damping of the elastic core, C : damping ratio of the elastic core, u. : coefficient of friction of the isolator, g : gravitational acceleration, s : sliding displacement of the isolator, {«} : relative displacement vector, {r} : a unit vector, [m] : mass matrix of structures [c] : damping matrix of structures [k] : stiffness matrix of structures N : number of floors The step-by-step integration method has been used to dynamic response analysis of the system. In the fourth chapter; a Fortran program, to calculate displacement, velocity and absolute acceleration response values with the double precision for the both horizontal and vertical ground motions, is developed. The details of the flow chart for the computer program called BASE1, are presented. In the fifth chapter; the responses of resilient-friction base isolated single degree of freedom system, that subjected to Erzincan E-W 1992, Dursunbey E-W 1979 and Denizli E-W 1976 earthquakes, are calculated and presented graphically. Some information about the ground motion records are presented in the table; xv Ground Motion Records The response of the system is very sensitive to the starting times of sliding and non- sliding phases, implying that the digitized time interval A t should be very small. The time interval of, A t =0,0002 sec is chosen in dynamic analysis. Displacement, velocity and absolute acceleration for a damping of, C=0,05 in rubber, and five values of friction coefficients namely, H=0,00; 0,04; 0,06; 0,08; 0,10 for the system periods at the range of, T=0,l~5 sec. at interval of 0,1 sec. are computed and presented in chapter 5. The range of friction utilized covers the expected friction for teflon under the operating conditions of bearing pressure and the velocity for this system. In the sixth chapter; the results are discussed and some main characteristics observed from the graphs are fabulated. To reduce interaction with the superstructure effective period should be into considered beyond the 1,5 sec. for the base isolated system. The results presented in the table; XVI XV11 As a result; important features of the response spectrum of the base isolated system presented in the table, demonstrate the resilient-friction base isolator's potential in both controlling the level of forces transmitted to the superstructures and limiting the maximum sliding displacements to levels which can easily be considered and provided for in design.