Taşıyıcı sistemi düşeyde düzensiz bir binanın statik ve dinamik davranışının incelenmesi

Abstract

Bu çalışmada, taşıyıcı sistemini kolon ve kirişlerin oluşturduğu düzensiz çerçevelerden oluşan bir bina söz konusu edilmiştir. İlk bölümde böyle bir çalışmaya neden gereksinim duyulduğunu, bu çalışma konusunun yurdumuzda ve dünyada kullanım alanlarından bahsedilmiş ve çalışma boyunca kullanılan bir takım yöntem ve düşünceler anlatılmışır. ikinci bölümde binanın en önemli özelliği olan düzensizlik kavramı üzerinde durulmuş, düzensizlikle ilgili örnekler şekiller yardımıyla tartışılmış ve depremin bu kavram üzerindeki önemi vurgulanmıştır. Yine bu bölümde "dinamik hesap yöntemi" adlı yöntemden ve neden kullanılması gerektiğinden bahsedilmiştir. Üçüncü bölümde dünya üzerinde halen başlı başına bir tartışma konusu olan çeşitli düzensizlik tipleri ve bu tip düzensiz binalar üzerinde çeşitli bilim adamları tarafından yapılan araştırmalara yer verilmiştir. Dördüncü bölümde çeşitli ülkelerde halen uygulanan, konu ile ilgili yönetmelikler ve ülkemizde uygulanması düşünülen "Afet Bölgelerinde Yapılacak Yapılar ile İlgili Yönetmelik" taslağının konu ile ilgili bölümü sunulmuştur. Beşinci ve altıncı bölümde konsol ucunda kolon uygulaması şeklinde tarif edilen düşeyde düzensiz tip bir yapı, örnek olarak ele alınmış, problem ana hatlarıyla statik ve dinamik olarak incelenmiş, önemle üzerinde durulması gereken elemanların betonarme hesaplan yapılmıştır. Son bölümde ise varılan sonuçlar tartışılmış, konsol ucunda kolon uygulamasının getireceği olumlu ve olumsuz durumlar anlatılmıştır.The name of the present study is " static and dynamic behavior of a buildins having a vertically irregular structural system ". This study consists of the investigations of the static and dynamic behaviors of irregular structural systems. It is very important for all the elements of structural system to have regularity and continuity so that simple methods of calculation can be used as well as preventing some parts of the structure such as connections between columns and beams from overloading. However because of architectural design or aims for the use of the structures, civil engineers may meet cases of irregularity and discontinuity. Structures having irregularity or discontinuity as described above are called "irregular structures". Staggered floor arrangements, nonsymetrical design of beams and columns, discontinuity of the vertical elements carrying lateral forces ( i.e columns and shear walls ) throughout the ground floors and upper floors are some examples of irregular structures. In the first chapter an introduction of the theme is given. In the second chapter, the definition of irregularity and some examples of irregularity is discussed. Structures having irregularity have to be investigated much more carefully than those which are horizantally and vertically regular. For analyzing the seismic response for this type of structures and also those having 75 m height or more, a dynamic method has to be applied instead of using lateral static forces as dynamic loads. The use and basic principles of dynamic method is also mentioned in the second chapter. Some types of irregular structural systems are shown in Figurefl] and Figure[2]. Figurefl] represents irregularity on the plan. Some vertical irregularity examples are represented by Figure[2]. Also preferred and undesirable horizantal and vertical configurations are compared in these figures. Figure 1(a) shows that because of the location of a stiff wall at the west end of a building, very large displacements, as a result of floor translations and rotations, will occur at the east end. As a consequence, members of a frame located at the east end may be subjected to excessive inelastic deformations. Excessive ductility demands at such a location may cause significant degradation of the frame. This will lead to further shift of the center of rigidity and consequently to an amplification of torsional effects. A much improved solution is shown in Figure 1(b) where the service core has been made nonstructural and a structural wall added at the east end will ensure that the centers of mass and stiffness virtually coincide. Vlll Undesirable CR (c) (hi °CR^ M [öjjCM * Preferred -7-4 - 1 -J C/?=CM © rw CR-.CH id) (el Of=Oî D © D r9; r-, O? CM ? o. r/; /.7#. / Mass and lateral stiffness relationship willi lloor plans. ( Hori/anlnlly im-nulai ') ~İaİ lb) A (cl 19) Pr clcrrcd (r.l (d! (U (hi W"-**T"!\T (ji in Fİf>. 2 Ycılırnl ninlijimalkins. Analysis may show that in some buildings torsional effects, Figure 1(c), may be negligible. However as a result of normal variations in material properties and section geometry, and also due to the effects of torsional components of ground motion, torsion may arise in theoretically perfectly symmetrical buildings. Although a reinforced concrete or masonry core [Figure 1(c)] may exhibit good torsional strength, its torsional stiffness, particularly after the onset of diagonal cracking, may be too small to prevent excessive deformations at he east and west ends of the building. Similar twists may lead, however, to acceptable displacements of the perimeter square plans with relatively large cores, seen in Figure 1(d). Closely placed columns, interconnected by relatively stiff beams around the perimeter of such buildings [Figure (e)], can provide excellent control of torsional response. The eccentrically placed service core [Figure 1(f)] may lead to excessive torsional effects under seismic effect in the east-west direction unless perimeter lateral force resisting elements are present to limit torsional displacements. The advantages of the arrangement, shown in Figure 1(g). in terms of response to horizantal forces are obvious. While the locations of the walls in Figure 1(h). to resist lateral forces, the large eccentiricity of the center of the mass with Figure l(j) and (k), both stiffness and the strength of these walls may well be adequate to accommodate torsional effects. The examples of Figure[l] apply to structures where walls provide the primary lateral load resistance. The principles also apply to framed systems, although it is less common for excessive torsional effects to develope in frame structures. A selection of undesirable and preferred configurations is illustrated in Figure [2]. Tall and slender buildings [Figure 2(a)] may require large foundations to enable large overturning moments to be transmitted in a stable manner. When subjected to seismic accelerations, concentration of masses at the top of a building [Figure 2(b)] will similarly impose heavy demands on both the lower stories and the foundations of the structure. In comparison, the advantages of building elevations as shown in Figure 2(c) and (d) are obvious. An abrupt change in elevation, such as shown in Figure2 (e), also called a set-back, may result in the concentration of structural actions at and near the level of discontinuity. The magnitudes of such actions, developed during the dynamic response of the building, are difficult to predict without sophisticated analytical methods. The separation into two simple, regular structural systems, with adequate separation Figure 2(f) between them, is a preferable alternative. Irregularities within the framing system, such as a drastic interference with the natural flow of gravity loads and that of lateral-force-induced column loads at the center of the frame in Figure 2(g), must be avoided. Although the two adjacent buildings may appear to be identical, there is no assurance that their response to ground shaking will be in phase. Hence any connections between the two that may be desired [Figure 2(i)] should be such as to prevent horizantal force transfer between the two structures [Figure 2(j)]. Staggered floor arrangements, as seen in Figure 2(k), may invalidate the rigid interconnection of all vertical lateral force resisting units, which are very important for the structure. Horizantal inertia forces, developed during dynamic response, may impose severe demands, particularly on the short interior columns. While such frames may be readily analyzed for horizantal static forces, results of analyses of their inelastic response to realistic groun shaking should be treated with suspicion. A problem having a discontinuity is solved for static and dynamic cases in the fifth and sixth chapters. The structural system of the building is vertically irregular as described above. And it consists of five orthogonally framed stories. The vertical irregularity is due to the discontinuity of the columns throughout the ground and the top floors. That is to say the axis of the columns around the periphery of the building do not coincide with eachother on the ground and first floors. The columns placed on the corner and on the sides in plan of these two floors are connected with corbels. In contrast, the inner columns of the building are continious from the ground floor to the upper floors and don't need to be examined. The structural system is taken to account by using three dimension and is solved by the program SAP90 ( structural analysis program ) for static and dynamic cases. Joints which are appointed within coordinates by the user are used by the program through a matrix method for hyperstatic systems. The loads are multiplied by factors 1.4 and 1.6 as described in Turkish Standards and are applied for all the system. Mass of the system is collected in these joints which is an effective approach. The first ten modal shapes are taken into account in obtaining the final free vibration modes and periods. Seismic response of such a building is analyzed under external loads caused by 1992 Erzincan earthquake. The results obtained in the numerical analyses are given in tables to demonstrate the behavior of the system. In this study the design of the reinforcement is also investigated after the demonstrations of the tables about static and dynamic analysis. The normal resistance of a corbel is shown in Figure[3]. The figure consists of a simple truss model composed of a tension tie across the top with an inclined compression strut forming a triangle, with normal bending making only slight variations. The inclination of this strut determines the tension in the tie by simple truss analysis. The flexural calculation at the face of the column gives essentially the same tension, but the triangular truss idea emphasizes the anchorage problem at the node. In the last chapter, conclusions of the topic are discussed. The inner forces of the corbel have a significance, especially for the beam placed next to the corbel so this kind of beams bonding the corbels to the inner columns must be carefully analyzed ( Figure [4] ). The shear forces of the columns are in the same direction and causes a large amount of a tension force comparing to the other kinds of beams, in that beam. For this reason, the section near the corbel of the beam must be increased in order to make the rijidities equivalent. Also the corbels on the corner columns can be selected in two main directions to decrease the effects of the corbel. XI -V »-ı f I - - N. Fig. 3 Resistance of a corbel m. ?rr J \ Fİg. d Internal forces in a corbel