Kurşun Ekstrüzyon Sönümleyicinin Çelik Bir Birleşimin Davranışına Etkisi

Abstract

Deprem hareketi sırasında yapı sistemine önemli deprem enerjisi girişi olmaktadır. Bu enerji yapı sisteminde ortaya çıkan hasarlar, sönüm vb. mekanizmalar tarafından harcanmaktadır. Ancak bu durum yapıda çatlamalara ve büyük hasarlara neden olabilmektedir. Modern yapısal tasarımında, yapı sistemine yerleştirilen özel eleman veya aygıtlar ile ilave enerji tüketimi sağlanabilmekte, deprem enerjisinin bir bölümünün bu elemanlar tarafından harcanması sağlanabilmektedir. Bu çalışmada; İstanbul Teknik Üniversitesi Yapı ve Deprem Mühendisliği Laboratuvarında bir doktora tezi kapsamında geliştirilen kurşun ektrüzyon sönümleyicinin, çelik kolon - kiriş birleşiminde kullanılması halinde yapısal davranışa etkileri deneysel ve kuramsal olarak incelenmiştir. Çelik birleşime çapraz olarak yerleştirilen kurşun ekstrüzyon sönümleyicinin deprem enerjisi tüketme kabiliyeti incelenmiştir. Yalın çerçeve ve kurşun ekstrüzyon sönümleyicinin yerleştirildiği çerçeveye, yapılan ön hesaplarla belirlenmiş bir yerdeğiştirme protokolü uygulanarak, kuvvet - yerdeğiştirme ilişkileri elde edilmiştir. Deney sonucu elde edilen verilerden, birleşimin genel davranış biçimi, tüketilen enerji ve rijitliği belirlenmiştir. Kurşun ekstrüzyon sönümleyicinin bulunduğu birleşime ait ulaşılan en yüksek kuvvetin yalın birleşimden %50~%75 daha fazla olduğu gözlenmiştir. Kurşun ekstrüzyon sönümleyicili birleşim tarafından tüketilen toplam enerji miktarı, yalın birleşim tarafından tüketilen toplam enerji miktarından yaklaşık olarak %175 mertebesinde fazla olmuştur. Bununla birlikte kuvvet – yerdeğiştirme çevrimlerine ait rijitlik değerlerindeki artış %39-98 arasında değişmektedir. Yapılan deneyler sonucunda elde edilen bilgiler ışığında, kurşun ekstrüzyon sönümleyici büyük ölçüde deprem enerjisi tüketmiş ve yapıya önemli bir miktarda rijitlik katmıştır. Deneylerden elde edilen bilgilerin kuramsal olarak da ispat edilebilmesi için, bir bilgisayar yazılımı kullanılarak deneyde kullanılan yalın birleşimin modeli oluşturulmuştur. Bu modelde doğrusal olmayan statik analiz yapılarak birleşime ait kuvvet - yerdeğiştirme ilişkisi elde edilmiş ve deneysel çalışmada bulunan ile karşılaştırılmıştır. Yapılan deneysel çalışmalar ile kuramsal çalışmalar sonucunda birleşime ait genel davranış biçimi, tüketilen enerji ve rijitliklerinin kabul edilebilir düzeyde benzer oldukları görülmüştür. Bu matematiksel modele, deneysel çalışmada kullanılan kurşun ekstrüzyon sönümleyici eklenerek ikinci model elde edilmiştir. Seçilmiş bir kütle ve ivme kaydı durumu için yalın ve sönümleyici yerleştirilmiş durumlardaki tepe yatay yerdeğiştirmesi sonuçları karşılaştırılmştır. Sonuçlardan sönümleyicinin sistem yerdeğiştirmelerini yaklaşık %50 düzeyinde azalttığı gözlenmiştir.

Turkey is located on an active fault zones in Anatolian Plate. Eventually, Turkey has suffered from earthquakes for ages. Severe catastrophic earthquakes have affected various areas of Turkey in past, such as Erzincan (1992), Kocaeli (1999) and Duzce (1999). So, in Turkey, modern structural designs for decrasing the earthquake related losses is needed. Especially, expected Istanbul earthquake risk increases the modern desing and retrofitting demand. During the earthquake ground motion, an amount of energy imparted to the structures. The energy disbursed by plastic deformations (cracking of concrete, yielding of steel, etc.) on the members and some frictional forces between the members. This causes cracks and major damages on the structural members and joints. Occurrence of damage on structural system is undesirable situation. Experimental studies and structural damages based on site assessment show that structural damages significantly occur on beam to column connections and this caused undesirable results such as total failure in an earthquake. There are important studies about behaviour of beam to column connections under seismic loads and results show the importance of preventing the damage concentration at the connections. The basic method to remove the damage from the connections is energy dissipating devices. The modern structural design seeks to absorb the energy through the dissipater elements and devices that are located in proper positions in the structure. Therefore, energy dissipating devices that are placed properly to the beam to column connections prevent damage concentration on connections. Energy dissipating devices are giving the chance to concentrate the energy dissipation on these devices and minimize the possible damages on structural and non-structural elements. There exists various type of energy dissipating devices, which are using different mechanisms of energy dissipation. The development of these devices realized with the researches and studies in the industrial and academic arenas. Innovative concepts of control systems based on the protection of structural and non-structural elements against dynamic loads can be considered in three main classifications. These are seismic isolation, passive control systems and active control systems. Passive control systems are also known as passive energy dissipation systems. These systems are using the principles such as frictional sliding; yielding of materials, phase transformation in metals, deformation of viscoelastic solids, fluid orificing. Also tuned mass and tuned liquid dampers are mentioned with these systems. Lead extrusion damper (LED) is one of the passive energy dissipating devices which takes the advantage of the hysteretic behavior of lead when deformed into the post-elastic range. Extrusion is a process of deformation by the way enforcing of lead to pass from a hole or narrow place. The deformations on lead are turned back to first original situation and this provides long life to lead extrusion damper. These types of devices convert the earthquake energy to kinetic and deformation energies by material behavior of the metal that is used in device. For this reason, modulus of elasticity of the material used in energy dissipating device should be smaller than the modulus of elasticity of the material that the structural system is made. Through the smaller modulus of elasticity, damages firstly occur on the passive energy devices instead of the structural system. Lead extrusion damper could be used for retrofitting of earthquake-related damaged structures as well as it can be placed in newly constructing buildings. Passive energy dissipating device that makes better of damping characteristic of structure, decreases the sizes of structural system and causes the structure to be designed with low cost. On the other hand, passive energy dissipating devices have to be applicable in size and connections details to damp the earthquake energy. In other case, it may be necessary to prefer alternative retrofitting technique. An experimental study has been initiated as a PhD study on the lead-extrusion dampers in Structural and Earthquake Engineering Laboratory of ITU. This thesis has been developed as paralel to this PhD study. This thesis includes six chapters. In the first chapter, purpose and scope of the study is presented. Also, it is given a detail literature survey about dampers. In the second chapter, testing set-up and experimental procedure is described. In the third chapter, the details and the results of the experimental study are provided. In the fourth chapher, the experimental results are compared with each other. In the following chapter, Chapter fifth, an analytical study is carried out in accordance with the experimental results. And finally, results and suggestions are given in the sixth chapter. In this M.Sc. thesis, lead extrusion damper (LED) is used diagonally in a steel beam to column connection to absorb seismic energy imparted to the joint. Displacement cycles have been used for obtaining the force-displacement relationships of the connection with and without lead extrusion damper. ATC24-1992 displacement protocol for the steel joints is adopted in experimental studies. This protocol, which was specifically developed for components of steel structures, was one of the first formal protocols developed in the U.S. for seismic performance evaluation of components using a cyclic loading history. It uses the yield deformation, δyield (δy), as the reference for increasing the amplitude of cycles. This displacement control testing procedure has been applied to the structures to compare their response with and without lead extrusion damper. There were five specimens in the experimental part of the study. The pilot test has been conducted to obtain behavior of the beam to column connections as well as to catch the problems that may occur while conducting of the other four experiments. Two of the four tests are performed with the lead extrusion damper and the remaining tests are performed without lead extrusion damper. From the results obtained, general behaviour, the amount of dissipated energy, rigidity and damping characteristics of the connections are determinated. The dissipated energy intensities have been reached by the area discretized the loops of force vs. displacement relationships. According to experimental result, the effect of the lead extrusion damper has observed starting from the first step. The maximum force at the connection with lead extrusion damper’s, is reached 50% ~ 75% more than the force without lead extrusion damper’s. Lead extrusion damper absorbes major earthquake energy and increase the rigidity of the structure. The amount of dissipated energy, rigidity and damping characteristics of the joints are evaluated. The total energy dissipated by the connection equiped with lead extrusion damper is approximately 175% greater than the total energy dissipated by the bare joint. However increments of the rigidity of the force vs. displacement cycles are varied between 39~98%. According to the results of the experimental study performed, lead extrusion damper has consumed important part of the imparted seismic energy to the joint, as well as the lateral stiffness of the joint is considerably increased. Moreover, two mathematical models of the steel beam to column connection have been produced by using a well known structural analysis program, namely SAP2000. Before the analytical works, four specimens had been taken from the steel profile. The standart tensile tests are conducted in Structural Material Laboratory of Istanbul Technical University to reach the real material characteristics. The joints with and without lead extrusion damper were analyzed in the structural analysis program. The first mathematical model represents the experimental studies that are carried out without the lead extrusion damper and the second mathematical model was prepared by adding the lead extrution damper to the existing model. A link member was assigned to represent the lead extrusion damper in the theoretical study. This link member was used in the analysis in accordance with the dimensions of test specimen. By using the mathematical model, nonlinear static analyses performed to compare the results with the experiments, namely the lateral load vs. top displacement. It is obtained a good correlation between the experimental and analytical results. It is obtained that the maximum top displacement decreased by 50% for the case of lead extrusion damper added specimen. Nonlinear time history analysis was carried out. Nonlinear time history analyses are performed for a selected mass and acceleration record and the obtained top displacement histories are compared between the specimens. KOBE 1995 Earthquake Acceleration Record was used in the analyses.