Mantolanmış betonarme kolonların değişik yükleme şartları altındaki davranışları
Başlık çevirisi mevcut değil.
- Tez No: 56022
- Danışmanlar: DOÇ.DR. NECMETTİN GÜNDÜZ
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 55
Özet
ÖZET Bu çalışmanın amacı, öncelikle betonarme kolonların mantolama yöntemi ile iyileştirilmesi konusunda genel bilgi vermektir. Kolonlarda mantolama, onarılacak ve/veya güçlendirilecek kolon yüzeyinin temizlenip ilave boyuna donatılar ve etriyelerle betonlanarak enkesitinin artırılması ile oluşmaktadır. Diğer bir deyişle eski kolonun etrafında yeni bir kolon oluşturulması ile uygulanan güçlendirme ve/veya onarım yöntemidir. Bu çalışma dört bölümden oluşmaktadır: Birinci bölümde; mantolama konusu ile ilgili tanımlar ve öneriler yer almaktadır. İkinci bölümde; eksenel yük altında deneye tabi tutulan üç grup mantolanmış kolon numuneleri anlatılmıştır, ilk grupta Orta Doğu Teknik Üniversitesinde, Bahadır Aksan tarafindan yapılan beş deney yer almaktadır. Bunlar; yüksüz halde güçlendirme mantosu, yük altında güçlendirme mantosu, yüksüz halde onarım mantosu, yük altında kurulan onarım mantosu deneyleridir. Ayrıca mantolanmış kolon numuneleri ile aynı kesitsel özelliklere ve donatılara sahip olan, manto davranışını karşılaştırabilmek üzere kullanılan monolitik deney elemanı yer almaktadır. İkinci grupta; mevcut kolonun etrafının harç ve hasır donatı ile mantolanarak kesme mukavemetini ve sünekliğini artırmak üzere test edilen dört numune anlatılmıştır. Üçüncü grupta; Hüsnü Can tarafindan gerçekleştirilen kısmi mantolamanın incelendiği deneyler yer almaktadır. Üçüncü bölümde; eksenel yük ve eğilmeye maruz bırakılarak test edilen, üç grup numuneden oluşan, mantolanmış kolon davranışı anlatılmıştır. Birinci grupta; O.D.T.Ü.'nde Ramadan E. Süleiman tarafindan gerçekleştirilen deneysel çalışma anlatılmıştır. İkinci grupta; üç farklı onarım ve/veya güçlendirme tekniğinin kısa kolonların yanal yüke karşı davranışlanndaki etkileri anlatılmıştır. Üçüncü grupta; mantolama tekniği ile güçlendirilen veya onarılan kolon numunelerinin eşdeğer deprem yükleri altındaki davranışlarını anlatan deneysel çalışma yer almıştır. Dördüncü bölümde; mantolanmış numunelerin deneysel olarak elde edilen ortak sonuçlan yer almaktadır.
Özet (Çeviri)
THE BEHAVIOUR OF REINFORCED CONCRETE COLUMNS STRENGTHENED BY JACKETING UNDER VARIOUS LOADING CONDITIONS SUMMARY First of all, the purpose of this study is to give some general information about the retrofit of columns using reinforced concrete jackets. Secondary, success of the reinforcing techniques tested to enlighten the application of the jacketing. Several techniques for the repair and strengthening of structural elements, such as reinforced concrete columns, have been suggested in the literature. One retrofit technique for buildings has involved the jacketing of columns with additional reinforced concrete. It is also possible to retrofit the other structural reinforced concrete members except columns. Such as; beam-column joints, beams, slabs, infilled walls, etc. In addition to that the deficient bending and shear capacity of concrete moment frames can be improved by one or more of the following alternatives: a) Increasing the ductility and capacity by jacketing the beam and column joints or increasing the beam or column capacities. b) Reducing the seismic stresses in the existing frames by providing supplemental vertical resisting elements (i.e., additional moment frames, braces or shear walls). c) Changing the system to a shear wall system by infilling the reinforced concrete frames with reinforced concrete. Improving the ductility and strength of concrete frames by jacketing (alternative a) is generally not cost effective. When deficiencies are identified in these frames, it will probably be more cost-effective to consider adding reinforced concrete shear walls (alternative b) or filling the frames with reinforced concrete (alternative c). These alternatives will also typically require upgrading the foundations which may be costly. Being one of the practical methods of repair and strengthening, column jacketing has a great popularity in developing countries. Reinforced concrete buildings in seismic zones are strengthened or repaired for three principal reasons; to satisfy the building owners' concern for financial protection and XIoccupant safety; to comply with local building codes and regulations; and to repair earthquake damage and obtain improved performance during future events. Considerable changes took place in the seismic design codes of developed countries on the basis of recent experimental research. As a result of these changes a lot of existing buildings are now insufficient according to the new code requirements and the problem of rehabilitation is quite common. Various research programs are being carried out by many researchers to find an answer to the question of“How to strengthen, renew or retrofit the existing columns?”. Retrofitting of structures has been undertaken in several earthquake-prone countries after structural damage caused by strong earthquakes or because existing structures were required to comply with more recent seismic code provisions. Seismic design procedures have advanced considerably since about 1970. The main developments have been in the understanding of the nonlinear dynamic response of structures, the introduction of capacity design procedures, and the methods for detailing reinforcement in concrete structures to achieve the ductile behaviour necessary to survive severe earthquakes. The subject matter of this thesis, column jacketing, consists of putting additional bars as well as transverse reinforcement and enlarging the cross-sectional area by casting a jacket around the column after cleaning the crushed and spelled parts. In other words, it can be considered simply repair or strengthening method by forming a new column around the old one. Defects and damages in reinforced concrete structures can occur if the structure is not designed or built properly. However even if designed and properly, structures are liable to damages caused by number of events such as disasters (earthquake, fire, etc.) overloads, adverse environmental or chemical effects, etc. Due to these defects and damages, the structure needs to be repaired. Structural intervention may also be needed in some of the existing reinforced concrete which have not suffered any damage. In general, it can be said that“repair”is the intervention made to damaged members or structures. In other words repair is always associated with damage. On the other hand upgrading of members and structures which have not suffered any damage is called“strengthening”. In both repair and strengthening interventions the objective is to upgrade the members and the structure to an acceptable safety level. Design criteria which aim to bring the structure to this level is called“redesign criteria”. Repair and/or strengthening by jacketing is most commonly used method and the most preferred one since it can be used for both lightly damaged columns and heavily damaged ones. XllIn the same way it is suitable for either repair or strengthening. And also jackets may be used partially at a certain portion of the member that is to be repaired or strengthened (in which case it is called local jacketing). Before making any interventions (repair or strengthening), a detailed investigation to determine the structural characteristics of the structure as it stands should be made. This operation is called“assessment ”. Using the data obtained from the assessment, the structural engineer decides whether repair or strengthening is needed or not. If any kind of structural intervention is needed, redesign of the repaired or strengthened structure should be made. If there is any damage in the structure, redesign should not be attempted unless a diagnosis is made about the cause or causes of the damage observed. The engineer should consider the change in stiffness due to repair or strengthening which will alter the static and dynamic characteristics of the structure. If the stiffness has increased significantly, the strength demand for inertia loads, such as earthquake, will also increase. If such changes are not taken into consideration, the strength demand can exceed the strength provided. In other words, in such cases strengthening will not improve the response under seismic action, on the contrary it will result in lowered safety. Although repair and strengthening are made to provide satisfactory performance of the structure under different load effects, in countries located in seismic regions seismic action becomes the main concern of the engineer at the redesign stage. In such countries considerable funds are allocated for the repair of damaged structures after a major earthquake. Since the cost of seismic repair is quite high, in many countries seismic strengthening of existing buildings to reduce hazards of probable future earthquakes is finding more support each year. This study consists of four chapters; In the first chapter; definitions and advises about the topic: jacketing is summarized. In the second chapter; three groups of specimens tested on the jacketed columns under axial load are explained. In the first group five tests take place which were made in Middle East Technical University by Bahadır Aksan. These are; unloaded strengthening jacket, unloaded repair jacket, loaded strengthening jacket, loaded repair jacket and to compare the jacketed column behaviour with a reference, a monolithic specimen was included, having the same cross-sectional properties and same longitudinal and transverse bar configuration with the jacketed ones. The experimental results indicated that the strengthening jacket ( undamaged column) was very effective in both cases, constructed under load or unloaded. Repair jacket was found to be effective if applied to an unloaded column but rather poor if applied to a column still under load. XIIIIn the second group; four specimens which were tested to increase shear strength and ductility by strengthening the surroundings of the existing column with mortar and welded wire fabrics in order to prevent the column from brittle shear failure, are introduced. With reference to this investigation, strengthening methods were refined to be more effective for application to the existing reinforced concrete columns that can be evaluated to be short of earthquake resistance and have been carried out for several buildings in Japan. In the third group; experimentally investigated, partially jacketed (two, three, four sides) reinforced concrete column behaviour and strength under axial loading takes place. Twelve test specimens were researched by Hüsnü Can. Although four sided jacket is the most desirable type, partial jacketing with two or three sides is sometimes inevitable due to space limitations. Edge and corner columns of buildings surrounded by close neighbours are typical examples. In the third chapter; the three groups of, experimentally tested specimen behaviour of reinforced concrete columns repaired or strengthened by jacketing and subjected to combined axial load and bending take place. In the first group; the experimental research made by Ramadan E. Suleiman in M.E.T.U. is explained. Three virgin column specimens were tested under either monotonic or reserved cyclic loading (basic column), and retested after being jacketed by enlarging the cross-section. The intervention (jacketing) was classified as repair or strengthening depending on the damage caused. In addition to these, two reference specimens were tested in which the column and the jacket were cast monolithically. Monolithically cast reference specimens had identical cross-sections and reinforcement as the jacketed specimens. The main variables investigated were the degree of damage prior to jacketing (repair or strengthening) and the type of loading (monotonic or reserved cyclic). In all jacketed specimens, jacket longitudinal bars were welded to an angle section attached to the beam stub by pull bars. The effectiveness of jacketing for repaired and strengthened specimens which was studied with respect to strength, ductility, energy dissipation and stiffness by comparing the results with those of the monolithic reference specimens is summarized. In the second group; the effectiveness of three different repair and/or strengthening techniques in enhancing the lateral load response of identical reinforced concrete short columns is given. One of the specimens were strengthened by jacketing and than retested. The remaining two specimens were strengthened by jacketing prior to testing. A single lateral displacement history and the repaired columns performed better than the XIVoriginal column. Column performance was compared in terms of lateral strength, stiffness and inelastic load-deformation behaviour. Columns strengthened by jacketing, both with or without supplementary crossties, were much suffer and stronger laterally than the original, unstrengthened column. The column repaired by jacketing was also much stiffer and stronger laterally than the original column and performed almost as well as the strengthened columns. In the third group; the results of an experimental study of the improvement in seismic behaviour of reinforced concrete columns repaired and/or strengthened by concrete jacketing is given. The tests involved both the as-built columns and the columns strengthened by concrete jacketing with added longitudinal and transverse reinforcement. The as-built columns as were typical of building columns designed and constructed prior to 1970. The column units represented the column region between the midheights of successive stories. A stub was present at the midheight of each unit to represent a portion of the two-way beams and slab at the beam-column joint. Two column units were tested, repaired and strengthened by jacketing and retested. The other two column units were strengthened by jacketing and tested. The new longitudinal reinforcement was placed through the floor slab. Two arrangements of transverse reinforcement in the jacket were investigated. The as-built columns displayed low available ductility and significant degradation of strength during testing, whereas the jacketed columns behaved in a ductile manner with higher strength and much reduced strength degradation. The retrofit of columns using reinforced concrete jackets was found to be successful but labor-intensive. XV
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