Planda düzensiz yapıların deprem davranışının incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 75209
- Danışmanlar: PROF. DR. ZEKAİ CELEP
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Yapı Mühendisliği Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 132
Özet
ÖZET Depremlerden sonra yapılan incelemelerde taşıyıcı sistem düzensizliklerinden dolayı pekçok hasarın meydana geldiği görülmüştür. Bu amaçla, deprem riski olan ülkelerde Deprem Yönetmeliklerinde düzensiz yapılar için özel şartlar getirilmiştir. Bu şekilde depremin zararlı etkilerinden korunma amaçlanmıştır. Bu çalışmada, taşıyıcı sistem düzensizlikleri hakkında bilgiler verilmiş, planda düzensizlik durumu ayrıntılı olarak incelenmişir. Düzensizlik durumları ve hesap yöntemlerinin seçiminde Deprem Yönetmeliği 1997, Uniform Building Code 1994 ve Eurocode 8 1994 Deprem Yönetmelikleri incelenmiştir. Çalışmanın örnek 1 kısmında ise Deprem Yönetmeliği 1997 esaslarına göre, düzenli bir yapı; Eşdeğer Deprem Yükü ve Modların Birleştirilmesi Yöntemine göre SAP90 bilgisayar programı ile çözülmüş, elde edilen kesit tesirleri karşılaştırılmıştır. Ayrıca bu bölümde Eşdeğer Deprem Yükü Yöntemine göre çözümde, ülkemizde yazılımı gerçekleştirilen İDE STATİK 6.01 EXTENDED bilgisayar programı ile SAP90 bilgisayar programının verdiği kesit tesirleri karşılaştırılmıştır. Kesit tesirleri karşılaştırıldığında, Eşdeğer Deprem Yükü Yöntemine göre çözüm daha güvenli tarafda kalmış, ancak dinamik hesabın burulma etkilerini daha iyi ortaya koyduğu görülmüştür. Eşdeğer Deprem Yükü Yöntemine göre çözümde; SAP90 bilgisayar programı ile İDE STATİK 6.01 EXTENDED bilgisayar programının hesap sonuçları karşılaştırıldığında birbirine yakın değerler elde edilmiştir. Çalışmanın Örnek 2 kısmında ise Deprem Yönetmeliği 1997 esaslarına göre planda A2 düzensizliği bulunan bir yapı ele alınmıştır. Yapı, döşemelerin rijit diyafram olarak çalışdığının kabul edildiği ve edilmediği duruma göre; Eşdeğer Deprem Yükü ve Modların Birleştirilmesi Yöntemlerine göre SAP90 bilgisayar programı ile çözülmüş elde edilen kritik kesit tesirleri karşılaştırılmıştır. Döşemelerin rijit diyafram olarak çalışmadığının kabul edildiği durumda; yapıdaki düzensizlik belirgin olarak ortaya çıkmış yapının deprem davranışını daha iyi temsil ettiği görülmüştür. Deprem yüklerinden oluşan kesit tesirleri karşılaştırıldığında kritik kesitlerde daha olumsuz sonuçlar elde edilmiştir. XII
Özet (Çeviri)
SUMMARY A STUDY OF THE SEISMIC BEHAVIOUR OF STRUCTURES HAVING IRREGULARITIES IN PLANE Observations of behaviour of structures during past earthquakes have demonstrated that in most cases damage is due to irregular configurations of the structural system or non-structural elements, which lead to an unfavourable overall behaviour of the structure. The basic design problems affecting the seismic performance of buildings can be stated as follows:. Building form irregularities in both the horizontal and vertical planes,. Discontinuities in strength between the major structural elements of the building,. Inadequate diaphragms, which distribute the earthquake forces to the vertical structure elements,. Effects of nonstructural elements on the structural system,. Deficiencies in the connections that tie the elements of building together,. Damage to the nonstructural components and contents of the building. Those who have studied the performance of buildings in earthquakes generally agree that the structural configuration of the building greatly influences its performance under ground motion. This is because the shape and proportion of the building have major effect on the distribution of earthquake forces that is, on the relative size and nature of the forces as they work their way through the building. A simple and symmetrical building form allows for the most even and balanced distribution of forces, but symmetry of form will not ensure low torsional effects due to the excentricity of the mass distribution. For instance, even in simple symmetrical rectangular buildings the location of stiff stair and elevator cores, solid and glazed walls, or other design elements that add mass to only one part of the building can result in different locations of the center of mass and the center of rigidity, and the torsion or twisting that results during an earthquakes has frequently caused substantial damage. A common building form that presents seismic design problems is that of the“re-entrant corner”. The re-entrant corner is the common characteristic of overall building configurations that, in plan, assume the shape L, T, U, H, +, or a combination of these shapes. These building shapes permit large plan areas to be accomodated in relatively compact form while still providing a high percentage of perimeter rooms with acces to air and light. Because of these characteristics, they are commonly used in school design. These configurations are so common and familiar that the fact that they represent one of the most difficult problem areas in seismic design may seem surprising, but examples of earthquake damage to re-entrant corner type buildings xiiiare common. First noted before the turn of the century, this earthquake problem was generally acknowledged by the experts of the day in the 1920s. These shapes tend to produce variations of rigidity and, hence, differential motions between different portions of building that result in a local stress concentration at the“notch”or re-entrand corner (Figure 1a). In addition, the wings of a re-entrant corner building often are of different heights so that the vertical discontinuity of a setback in elevation is combined with the horizontal discontinuity of the re-entrant corner in plan, resulting in an even more serious problem. The setback form a tower on base or a building with“steps”in elevation also has intrinsic seismic problems that are analogous to those of the re-entrant corner form. The different parts of the building vibrate at different rates, and where the setbacks occur, a“notch”is created that results in stress concentration (Figure 1b). Figure 1. (a). Movement of L-shaped building under ground motion and (b) point of stress concentration in setback building. It is not generally recognized that large discontinuities (for abrupt changes) in the strenght (Figure 2) or stiffness of a building can cause adverse seismic responce effects. cast-in-place concrete steel joints-metal deck rigid diaphragm flexible diaphragm Figure 2. Discontinuity in strenght This iş particularly the case where there are abrupt changes in the vertical arrangement of the structure that result in discontinuities (changes) of strenght or stiffness from floor to floor. XIVThe most prominent of the problems caused by such a discontinuity is that of the“soft”first story (Figure 3), a term applied to a ground level story that is more flexible than those above. Although a“soft”story at any floor creates a problem, a stiffnes discontinuity between the first and second floors tends to result in the most serious condition because forces generally are greatest near the base of building. D D D D (a) (b) (c) Figure 3.“soft”first story : (a) tall, flexible columns, (b) interrupted vertical columns, and (c) heavy superstructure over slender frame Three typical conditions create a“soft”story can be given as follows:. The first occurs when there is a significant discontinuity of strenght and stiffness between the vertical structure of one floor and the remainder of the structure. This discontinuity may occur because one floor, generally the first, is significantly taller than the remainder, resulting in decreased stiffness (Figure 3a).. Discontinuity also may occur when some vertical framing elements are not brought down to the foundation but are stopped at the second floor to increase the openness at ground level. This condition creates a discontinuous load path resulting in an abrupt change of strenght and stiffness at the point of change (Figure 3b).. Finally, the“soft”story may be created by an open floor that supports heavy structural or nonstructural walls above. This situation is most serious when the wall above is a shear wall acting as a major lateral force resisting element (Figure 3c). The basic problem with all these variations of the“soft”story is that most of the earthquake forces in the building, and any consequent structural deformity, tends to be concentraded in the weaker floor or at the point of discontinuity instead of being more uniformly distributed among all stories. The result in that, instead of the building deflection under horizontal forces being distributed equally among all the floors, it is accomodated almost entirely in the lower floors. This causes tremendous stress concentrations at the lower floor connections; failure may occur at these points and result in the collapse or partial collapse of the upper floors. The earthquake loads at any level of a building will be distributed to the vertical structural elements through the roof and floor diaphragms. The roof/floor xvdeck or slab (the horizontal diaphragm) responds to loads like a deep beam. The deck or slab is the web of the beam carrying the shear and the perimeter spandrel or wall is the flange of the beam resisting bending (Figure 4). Three factors are important in diaphragm design:. The diaphragm must be edequate to transfer the forces and must be tied together to act as one unit.. The collectors (members or reinforcing ) must transfer the loads from the diaphragm into the shear wall.. Openings or re-entrant corners in the diaphragm must be properly placed and adequately reinforced. Inappropriate location or excessive size of openings (elevator or stair cores, atria, skylights) in the diaphragm create problems similar to those related to cutting a hole in the web of a beam. This reduces the natural ability of the web to transfer to forces and may cause failure in the diaphragm. earhtquake. force diaphragm Figure 4. Openings in diaphragms The present thesis deals with the irregularities in structural systems of buildings where a special attention is paid to the irregularities on the plane. The definition of irregular structures are given by considering National Earthquake code 1997, Uniform Building Code 1994 and Eurocode 8 1994. After a detailed discussion of the behaviour irregular structures by considering the behaviour of structural system under earthquake load, two examples are presented. In the first example a regular structural is analysed by using the computer program SAP90 and IDE STATİK 6.01 EXTENDED a program which is developed in Turkey. The analysis is carried out by applying Method of Equivalent Static Load and Method of Superposition of Modes and the internal xviforces at cross sections are obtained and compared. The comparison yields that the Method of Equivalent Static Load gives more conservative results than those of the other method. On the other hand, as it is expected, the Method of Superposition of Modes grasps the torsional motion of the system much more realistically. Furthermore it is found that the two computer programs SAP90 and IDE STATIC 6.01 EXTENDED yield approximately the same result for the practical design purposes. The second example investigates an irregular structure of type A2 as it is defined in National Earthquake Code 1997. In order to recognise the the rigid diaphragm assumption of slabs, two solutions are carried out under the rigid and elastic assumption of the slabs. Both of these cases are analysed by using Method of Equivalent Static Load as well as Method of Superposition of Modes. The results are given comparatively by the inspection of the numerical results it can be seen that the realistic behaviour of the irregular structures can be recognized when the assumption of rigid slabs is omited and when the slabs are assumed to elastic. XVII
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