Dişli döşemeli sistemlerin Türk deprem yönetmeliklerinde algılanışı açısından parametrik incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 75448
- Danışmanlar: PROF. DR. ZEKİ HASGÜR
- 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 Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 188
Özet
Bütün dünyada depreme dayanı klı tasarım yönetmelikleri, sürekli olarak değişmekte ve gelişmektedir. Buna bağlı olarak ülkemizdeki deprem yönetmeliğide dünyadaki gelişmelere paralel olarak kendini yenilemektedir. Ülkemizde“Afet Bölgelerinde Yapılacak Yapılar Hakkında Yönetmelik ”adıyla 1975, 1996, ve en son olarak şu an yürürlükte olan 1998 yönetmelikleri uygulanmıştır. Bütün deprem yönetmeliklerinin amacı, yapının depremden en az hasar görmesi veya hasarın onarılabilir düzeyde kalacak şekilde yapıların tasarımını amaçlar. Deprem yönetmeliklerinin bu amaca yönelik şartlarından birisi de kat ötelemelerinin sınırlan dırılmasıdır. Kat ötelemeleri, özellikle ikinci derece yapı elemanlarında hasara yol açtığı için deprem sırasında meydana gelebilecek ölüm olaylarının ve hasar maliyetinin artmasına neden olacaktır. Kat ötelemelerinin en önemli nedeni, yapının rijitlik durumudur. Rijitlik arttırıcı önlemlerin ötelemeleri düşüreceği kesindir. Bu konuda en etkili yöntem ise yapıya perdelerin eklenmesidir. Rijitlik açısından diğer döşeme türlerine göre daha zayıf olan dişli döşemeli sistemler, kat ötelemeleri hususunda daha dikkatli davranılması gereken döşeme türleridir. Bu çalışamada dişli döşemeli sistemlerde genel olarak, yapıda oluşan ötelemelerin önlenmesi için perdelerin etkisi ve deprem yönetmeliklerimizin bu sistemler için ortaya koyduğu koşullar incelenecektir. Bu inceleme yapılırken, hesaplama sırasında kullanılan çeşitli parametrelerin de değerlendirmesi yapılacaktır. Buna göre çerçeveli yapı için oluşacak gerilmeler, ülkemizde uygulanmış olan deprem yönetmelikleri ve ve değişik deprem bölgelerine göre hesaplanmış kesme kuvvetleri ve kat ötelemeleri bulunacaktır. Daha sonra yapıya perdeler eklenecek ve kat adetleri arttırılacaktır. Böylece yapı yüksekliğinin değişmesi, taşıyıcı sistemin değişmesi, perde boyutlarının ve sünekliklerinin değişmesi perspektifinde, uygulanan herbir deprem yönetmeliğinde ve deprem bölgelesinde oluşacak gerilmeler, ou değerleri, taban kesme kuvvetleri, kat ötelemeleri ve perde donatıları parametrelerinin değişimi sorgulanacak ve sonuçların takdiri yapılacaktır. Çalışmanın sonuçlarına göre, 1998 yönetmeliğinde verilen koşullar diğer iki yönetmeliğe göre daha gerçekçidir. 1975 ve 1996 yönetmeliklerine göre hesap yapıldığında, yapıda hasar miktarı az olurken 1998 yönetmeliği uygulandığında perde yapımı zaruri hale gelmektedir. 1998 yönetmeliği, ne 1975 yönetmeliği gibi az değerler ne de 1996 gibi fazla değerler vermektedir. Yapılacak perdelerin yüksek süneklikte olması, normal süneklikte olmasından daha ekonomik ve emniyetli sonuçlar vermiştir.
Özet (Çeviri)
The rapid developments in the theory and practice of earthquake engineering during the last quarter of the century as well as the lessons learned from the past earthquakes have led to the continuing development of earthquake resistant design codes throughout the world. The aim of all seismic codes is to prevent the collapse of structure and loss of life because of the most severe earthquake that could be forecasted with great probability during the service life time of the building, and no or limited and repairable damage at the structural or nonstructural components is mostly desired when the structure is forced frequently by the little or mean scaled earthquake. In order to realise this aim, one of the conditions is the limitation of the story drift. The story drift (A), is defined as the difference of maximum elastic lateral displacements of any two adjacent floors. This is also called as interstory drift. The division of story drift to the respective height that is called the story drift ratio (5). The aseismic safety of a reinforced concrete building as well as its susceptibility to nonstructural damages is primarily indexed to its ability of restricting the relative story displacements, in addition to its adequate strength, ductility, and toughness. The term“drift”has two connotations: ¦“Story drift”is the maximum lateral displacement within a story (i.e., the displacement of one floor relative to the floor below caused by the effects of seismic loads). ¦ The lateral displacement or deflection due to design forces is the absolute displacement of any point in the structure relative to the base. This is not“story drift”and is not to be used for drift control or stability considerations since it may give a false impression of the effects in critical stories. However, it is important when considering seismic separation requirements. Design for drift and lateral stability is an issue that should be addressed in the early stages of design development. In many cases, especially in tall buildings or in cases where torsion is a major contributor to structural response, the drift criteria can become a governing factor in the selection of the proper structural system. There are many reasons to control drift; one is the member inelastic strain. Although the usage of drift limitations is an imprecise and highly variable way of controlling strain, this is balanced by the current state of knowledge of what the strain limitations should be.Stability considerations dictate that flexibility be controlled. The stability of members under elastic and inelastic deformation caused by earthquakes is a direct function of both axial loading and bending of members. A stability problem is resolved by limiting the drift on the vertical load carrying elements. The drift limits indirectly provide upper bounds for these effects. Buildings subjected to earthquakes need drift control to restrict damage to partitions, shaft and stair enclosures, glass, and other fragile nonstructural elements and, more importantly, to minimise differential movement demands on the seismic safety elements. The design story drift limits reflect consensus judgement taking into account the goals of drift control. In terms of life safety and damage control objectives, the drift limits should yield a substantial, though not absolute, measure of safety for well detailed and constructed brittle elements and provide tolerable limits wherein the seismic safety elements can successfully perform, provided they are designed and constructed in accordance with provisions. The lateral displacement, or drift, of a structural system under wind or earthquake forces is important from three different persperctives : (i) structural stability, (ii) architectural integrity and potential damage to various nonstructural components, and (iii) human comfort while and after the building experiences these motions. # Structural Stability : Excessive and uncontrolled lateral displacements can create severe structural problems. Empirical observations and theoretical dynamic- response studies have indicated a strong correlation between the magnitude of interstory drift and building damage potential. Studies emphasising the fact that the potential for drift-related damage is highly variable and is dependent on the structural and nonstructural detailing provided by the designer, have proposed the following generalisation of damage potential in relationship to the interstory drift ratio 5: 1. at 5 = 0.001, nonstructural damage is probable ; 2. at 5 = 0.002, nonstructural damage is likely; 3. at 5 =0.007, nonstructural damage is almost certain and structural damage is likely; 4. at 5 = 0.015, nonstructural damage is certain and structural damage is likely. Drift - control requirements are included in the design provisions of most buildings codes. ¦ Architectural Integrity : Architectural systems and components, and a variety of other nonstructural items in a building, constitute a large portion of the total investment in the project. In many cases the monetary value of these items exceeds the cost of structural system by a large margin. In addition, these nonstructural items can be sources of injury, and even loss of life, for building occupants and those who are in the vicinity of the building. Past earthquakes haveproven that nonstructural components can also greatly influence the seismic response of the building. ¦ Human Comfort: Human comfort and motion perceptibility, which are of importance in the design of structures for wind-induced motions, are relatively insignificant in seismic design, where the primary objective is to limit damage and prevent loss of life. For every essential structures, where continued operation of facilities is desired during and immediately after an earthquake, a more conservative design or application of special techniques, such as seismic isolation may be considered. However, here again, the primary goal is to keep the system operational, and to prevent damage, rather than to provide for comfort of the occupants during a strong ground motion As it is seen, the story drifts must be limited in order to provide the safety but this is not sufficient to control the extent of damages to nonstructural elements. A moment resisting reinforced concrete frame structure can very well satisfy all strength and ductility requirements as well as the interstory drift limitations, but the extent of secondary damages during a strong earthquake may be so high that the structure may have to be demolished on account of the high costs of repair and rehabilitation. If however, the same building is designed to carry the lateral loads largely by means of a shear wall system, the structural and nonstructural damages may be so minor that the building may be readily put into service immediately after the earthquake. The use of shear walls in buildings of any height is a very effective method of restricting the interstory drifts thereby providing safety against excessive damages to nonstructural elements. Adding shear walls to a frame structure, it is easy to reduce the strain limitations and provide adequate drift control. Frames with ribbed floor systems are less rigid according to normal type frames. Because the main beam's height is less in order to have the same height with ribbed floor. So at this type floor it is true that story drift problem is more important than the other types of slabs, and needs more attention at the stage of designing. To indicate this fact, all Turkish seismic codes put some special regulations at provisions. In Turkey, three earthquake provisions have been applied; two of them are main and the other is the temporary. The first is the 1975 Recommended Provision for Seismic Regulations (R.P.S.R.) which were applied till 1996. Then the second was 1996 Draft Recommended Provision for Seismic Regulations which was a temporary provision and was designed to be applied till 1998. Now the valid provision is 1998 Recommended Provision for Seismic Regulations. All these provisions have separate sections for ribbed floor systems:¦ 1975RP.S.R 1) The thickness of the slab must be greater than 7cm., 2) If the height of the building is more than- At 1st. level earthquake zone 12.00m., At 2nd. level earthquake zone 15.00m., At 3rd. level earthquake zone 18.00m., At 4*. level earthquake zone 21.00m., shear walls must be added to the building. ¦ 1996RPS.R If the buildings that is mentioned below which of the main frame beams of the beam and girder floor system do not satisfy the provision's requirements, earthquake forces must be carried by the shear walls: a) All buildings at 1st and 2nd level earthquake zone, b) All buildings that is the height over 15m. at 3rd and 4th level earthquake zone. ¦ I998RPS.R If the buildings which of the main frame beams and system columns of the beam and girder floor system do not satisfy the provision's requirements, should be regarded as the normal ductility level systems. This type of systems can be constructed only at 4a and 3rd level earthquake zone if the height of the building less than 13m. To construct this type of systems at 2nd and 1st level earthquake zone or at 3rd level earthquake zone with the height of over 13m., normal or high ductility level type reinforced concrete shear walls must be added to the structure. As it is seen, all Turkish seismic provisions have regulations about the construction of the ribbed floor systems but there are some differences especially between 1975 and 1996-1998 provisions. The basic difference is in the definition of the floor type as well as in the height of the building according to the earthquake zone. In this study, these three provisions will be evaluated for the subject of frames with ribbed floor systems. The aim is to decide whether the height of a building which is given to the relative earthquake zone is proper or not. For this study a four-floor moment resisting frame with ribbed floor system is taken into account. Then it is multiplied to eight floors by changing the dimension of the main frame beams and columns so four types of building are obtained ; and then the maximum story drift ratios are calculated for each structure based on the three provisions; then according to each provision the story drift conditions are examined and evaluated the regulations about the adjusting shear walls. At the second step of this work, a variety of shear walls at various dimensions, from small to great sizes, are added to the structure for each of four type. The dimensions are decided according to the 1998 provision. The same calculations are done for these samples and maximum drift ratios are found by using all dimensions of shearwalls at each building type. The stresses are tried to be calculated by an empiric formula. Also reinforcement for shear walls are found by using the last provison, 1998 provision. The results of the analysis of the three provisions are compared in order to determine the conditions of shear walls and to decide which one is more economic from the perspective of the safety. Using damage and stress variables, the regulation of adding shear walls to the moment resisting frame is tried to be evaluated for three provisions. Throughout the rest of this text, the results of this work will be summarized. In the moment resisting frame structures of second and third level earthquake zones, the story drifts obtained when 1975 and 1996 codes are applied are less than the limiting values. Therefore, it is unnecessary to construct shear walls at these types of structures. However, in the first level earthquake zone these code conditions are suitable. When 1998 code is applied on the moment resisting frame structures of third level earthquake zone, the story drifts obtained are less than the limiting values although given limits for story heights are surpassed. At the moment resisting frame structures, the minimum and maximum drift ratios are obtained by the application of 1975 and 1998 codes, respectively. When damage is deadly considered, construction of shear walls is necessary by 1998 code. The conditions to get the shear wall dimension which keeps the drifts below the limits with 1975 code in case of the addition of shear walls to the moment resisting frame are as following, SA g /S Ap >1.2, for the 1996 code NDL type £A g /£ Ap >1.5, for the 1998 code NDL type ZA g /S Ap >3.0. When security and cost are considered, the 1998 code is the mean of the other two, but with the 1996 code, NDL type seems to be better for the shear walls with am< 0.75 since NDL in 1998 code is not applicable for these kind of walls. When shear walls are constructed by HDL, the drifts occured are less than those in NDL. Minimum shear wall dimensions are enough if shear walls are constructed as HDL in the 1996 code. However, in 1998 code ZA g /S Ap >1.5should be. One of the important results from this study is the construction of shear walls has a great effect on prevention of story drifts and this effect can be increased by using the high ductility level shear walls. In order to prevent the damage, it is more economic to construct high ductility level small dimensional shear walls instead of normal ductility level large dimensional shear walls. For the same damage class, the concrete amount used is 1/3 in 1996 code and 1/2 in 1998 code of the usual amount when HDL is used instead of NDL. When shear wall dimensions are considered the 1996 code gives better economic results compared to the 1998 code, but it forces the construction as well.In conclusion, it is recommended that the shear walls are constructed with high ductility level and dimensions not smaller than certain limits according to the 1998 code, but according to the 1975 and 1996 codes small dimensional shear walls are enough.
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