Çok katlı çelik yapıların deprem performansının belirlenmesi ve beton dolgulu kutu kesitli kolonların deprem performansına etkisi
Evaluation of eartquake performance of multi storey steel buildings and effect of concrete filled tube columns on earthquake performance
Yazar: OĞUZHAN AYMAZ
Danışman: ÖĞR. GÖR. BAHATTİN KİMENÇE
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Bu tez kapsamında 1994 yılında California, Amerika'da yaşanan Northridge depremi sonrasında çelik yapılarda gözlemlenen beklenmeyen hasarların nedenlerinin anlaşılması amacı ile oluşturulan SAC organizasyonunun yürüttüğü çalışmalar kapsamında tasarlanan 20 katlı Los Angeles yapısının deprem performansının belirlenmesi ve akabinde ilgili binanın boşluklu kutu kesit şeklinde tasarlanan kolonlarının beton dolgu ile doldurularak kompozit kesite çevrilmesi halindeki performans sonuçlarıyla karşılaştırılması yapılmıştır. Akabinde ise sonuçların daha da belirleyici hale gelmesi bakımından binadaki kat adedi 25'e çıkarılarak bu çalışma tekrarlanmıştır.
Beton dolgulu dikdörtgen çelik kesitler ülkemizde son yıllarda yüksek yapıların kolon kesitlerinde kullanılmaktadır. Yüksek yapılarda bu tarz kesitlerin kullanımının temel sebebi,betonun yüksek basınç dayanımı ve çeliğin sünek davranışının kombine edilmesiyle beraber daha küçük alan kaplayan kesitlerle istenilen kesit kapasitelerinin yakalanabilmesidir.
Ülkemizde çelik yapıların deprem performanslarının belirlenmesi için DBYBHY 2007 Bölüm 4'de verilen tasarım kriterleri kullanılmaktadır. Söz konusu durumda mevcut çelik yapılar için değerlendirme tasarım esaslarına dayanmakta ve lineer yöntemler ile yapılmaktadır. Yapılan bu değerlendirme sonucunda ise çelik kesitler için  hasar seviyesi tanımlamaları yapılmamıştır. Bu nedenle bu tezde yapılan çalışmaların çelik yapıların deprem performansı ile ilgili olan kısımları  FEMA 356 yönetmeliğinde tanımlanan kriterler doğrultusunda yapılmıştır.  Bunun yanı sıra ülkemizde yürürlükte olan deprem yönetmeliği güncellenmektedir ve 2017 yılında  güncellenmiş halinin yürürlüğe girmesi beklenmektedir. Bu anlamda kullanılan FEMA yönetmeliği ile taslak çalışmanın kısa bir karşılaştırması da bu tezin içinde verilmiştir.
Binayı teşkil eden elemanların deprem kuvveti altındaki davranışlarına ilişkin hasar seviyeleri FEMA 356'da belirlenen limitlere göre tanımlanmıştır. Buna göre plastik mafsal özellikleri kesitlerin akma dayanımları veya akma dayanımları ve akma şekildeğiştirmeleri ile tanımlanmaktadır.
Kolonlar ve kirişler arasındaki moment aktarımı birleşim bölgelerinde kompleks bir gerilme ve deformasyon dağılımmı ortaya koyar. Kolonların başlık bölgelerinde yüksek normal gerilmeleri, panel bölgesinde ise yüksek kayma gerilmeleri oluşmaktadır. Panel bölgelerinin modellenmesi konusunda birçok araştırma yapılmıştır. Bu çalışmada Gupta ve Krawinkler tarafından önerilen üç doğrulu panel bölgesi modeli kullanılacaktır. Beton dolgulu kesitlerin panel bölgeleri de kutu kesitli olduğu durumla aynı olduğu kabul edilmiştir.
Beton dolgulu kesitlerin deprem performanslarının belirlenmesine ilişkin kriterler ise bugüne kadar herhangi bir yönetmelikte kendilerine yer bulamamışlardır. Her ne kadar Eurocode 8'in ilgili kısımlarında çelik kesitlerin performans kriterlerinin kompozit kesitler için de geçerli olduğu belirtilmiş olsa da, kompozit kesitlerin çeşitliliği gözönünde bulunduralacak olduğunda bu ibarenin yetersiz kaldığı görülebilir. Bu çalışmada kompozit kesitlerin deprem performanslarını belirlemek için daha önce literatürde yayınlanmış olan birtakım deneysel verilere dayalı belirli kriterler kullanılacaktır.
Yapının değerlendirilmesinde DBYBHY 2017'de tanımlanan 475 yıl dönüş periyotlu (50 yılda aşılma olasılığı %10) deprem senaryosu için(DD-2) benzeştirilmiş yer kayıtları kullanılarak zaman tanım alanında doğrusal olmayan analizler yapılmış ve sonuçlar özetlenmiştir.
İlgili kolonların kompozit olduğu durumda da aynı depremsellik şartlarına göre zaman tanım alanında doğrusal olmayan analizler yapılmış ve her iki durum için ortaya çıkan sonuçlar karşılaştırılmıştır. Analizler neticesinde edinilen sonuçlar tablolar ve grafikler ile özetlenmiştir.

Abstract:
In 1994, to understand the causes of unexpected damage observed in steel structures after the Northridge eartquake occured in California USA, SAC organization designed 20-floor Los Angeles structure. Within the scope of this thesis, the seismic performance of this structure was defined and compared with the performance results after turning into the composite sections filled with concrete filling column designed as hollow box sections. Subsequently, to obtain more decisive results, number of floors of the building was increased to 25 and same study was repeated.
In recent years, concrete-filled composite sections, called as CFT in the  literature, are used in the column cross-section of high-rise buildings in our country.  The main reason for the use of these kind of sections,  to capture desired section capacity with small-sized sections obtained by combination of high compressive strength of concrete and ductile behavior of steel.  Steel wall of hallow section causes release of 3-axis stress by wrapping concrete core. Thus, steel tube prevent the concrete core to spread apart by staying under large loads.  Structurally, the most important advantage is the increased carrying capacity and ductility of concrete under the influence of dressing. Also, since concrete core prevents local buckling due to composit works of sections in CFT elements, it is possible to use thinner steel plates. The biggest economical advantage of CFT sections is lack of formwork costs compared to concrete sections. Steel tube takes over the role of formwork during construction.  Additionaly, the ability to construct a few floor from steel tube enables contruction to continue without waiting for the concreting puring process. Thus, in the multi-storey structure, work time and labor costs are reduced.
Column behavior of CFT members, also can not be considered independent from slenderness as in other column section.  Thus, they differ according to their slenderness ratio which are short columns, medium – slender-columns and high-slender-columns.
In this study; behaviors of CFT columns under the effect of axial load and moment and effect of H/t,P/P0,L/H parameters,  effecting collapse mechanism, on the behavior is explained.
D / t ratio is the parameter that controls the local buckling and ductility of the section. H / T's being greater than 50 will cause collapse of section because of local buckling before reaching the yield strength. When this ratio reaches the value of 24 ~ 34,  ductility of the section increases and collapse is delayed. Studies conducted to date, it has been observed that as ratio reached over 44, ductility reduced severely. (Tomi,Sakino 1979)
Another parameter that affects sectional ductility is P/P0 ratio. Although, increasing in the axial load on sections with composit work causes a slight increase in moment capacity, a quick decrease occurs with increase in this ratio. Therefore, P/P0 ratio has certain restrictions defined on related design codes. L/D ratio, although called as  the slenderness, reduces the axial load capacity of the element.
In our country, design criteria given in DBYBHY 2007 Part 4 are used for the determination of the seismic performance of steel buildings. The evaluation for current steel buildings is based on design criteria and done by linear methods. As a result of this evaluation, it is not possible to define a performance level. Therefore, parts of this thesis regarding to the seismic performance of steel structures were conducted based on criteria defined in FEMA 356. However, the earthquake regulation of Turkey is being update, new version is anticipated to be legislated by next year. In this context, a brief comparison between FEMA and draft regulations can be found within this thesis.
The damage levels of the building components under earthquake are defined according to the limits defined in FEMA 356. According to this, the plastic hinge properties are defined by the yield strengths or yield strengths and yielding deformations of the sections.
Moment transfer between columns and beams reveals a complex stress and deformation distribution in the connection joints. High normal stresses are produced in the flange zones of the columns and high shear stresses are generated in the panel zones. Several studies have been done on modeling panel zones. In this study, trilinear panel area model proposed by Gupta and Krawinkler will be used. It is accepted that panel areas of concrete filled sections are the same as the case of box-sectioned. Also, according to FEMA 356 regulation, on which the evaluation of the structure is based during research, the frame connection types are grouped as rigid (Fully Restrained) and semi-rigid (Paritally Restrained), and the damage limits are defined as rotation. In this study, it is presumed that the vertical load-carrier system connections are pinned connections and welded column-beam connections are fully rigid, as is often the case in structural models evaluated by Gupta and Krawinkler. The possible effects of welded column-beam frame connections on the plastic behavior of the structure have not been evaluated.
However; The effects of composite slabs on column-beam connections and beam behavior are not considered in this study; because of the limited number of cyclic experiments performed in consideration of the contribution of the composite slabs, and the work being done mostly on bare frames.
Criteria to determine the earthquake performance of CFT sections have not been found in any regulation until now. Although the relevant parts of Eurocode 8 indicate that performance criteria of the steel sections are also valid for composite sections, it can be seen that this section is insufficient when the diversity of the composite sections is taken into consideration. In this study, certain criteria based on experimental data previously published in the literature will be used to determine the earthquake performances of composite sections. For this thesis, a wide literature survey on the subject have been done. The one with most delicate consequence of these was published by Cenk TORT and Jerome F.HAJJAR, professors of the Minnesota Minneapolis University, in 2004. For this reason, the damage limits set out in this article will be used in this study.
In the mentioned study, the results of the experiments performed in various regions of the world related to CFT sections were used as data. Among the information belonging to the samples in the data, besides the values such as material, geometrical properties, values like D / t, L / D, fc ', which are important for CFT behavior, have also given.
Two types of damage relationships can be derived for monotonically loaded elements. The first one is deformation-based. The second type of damage function is the energy-based damage function. The amount of damage felt by the structural component is related to the distribution of the energy in the component (as documented in the Experimental Test that best represents the Load-Deformation Curve). Damage limits are obtained by using energy-based damage functions in periodic tests. In general, the use of energy-based damage functions is preferred. The related formulas were developed by Kradzid in 1989.
In the evaluation of the construction, using the simulated ground records for the 475 year return period (the possibility to be exceeded in 50 years is %10) earthquake scenario defined in DBYBHY 2007; nonlinear analyzes were carried out in the time domain and the results were summarized.
It was seen that the use of artificial earthquake records would be more appropriate when conducting the relevant analyzes. For the 475 year return period (the possibility to be exceeded in 50 years is %10) earthquake scenario defined in the related regulations, %90 compliance condition is required between 0.2 * T1 ~ 2 * T2 between the spectrum and the spectrum of the selected earthquake record. This situation makes it difficult to find a suitable earthquake record in buildings with first high dominant period. It also causes the earthquake load to be affected much more than it should be. This leads to uneconomic results. For this reason, artificial earthquake records have been used.
SAP2000 structural analysis program was used to solve the related structures. The fact that the buildings used in the study are 20 and 25 storeys, it extended the nonlinear earthquake analysis times too much. In the related regulations, it is required to use at least 3 different earthquake records for nonlinear analysis method in time definition area. In this case, analysis times can be up to 1 month. In order to avoid this situation, this work was carried out through only one earthquake recording.
The examined structure is composed of 6 in the X direction and 7 frames in the Y direction, with a total of 20 floors, the framed are opened approximately 6.096 m (20 feet). In addition, with the construction of 2 basement floors under the ground, the building will be supported as lateral at each basement floor. The normal floor heights from the second floor of the building are 3.96 m (13 feet), the first floor height is 5.49 m (18 feet), and the total height of the basement floors is 7.32 (24 feet).
The frame system circulating all around the building meets the horizontal loads on both sides.The other column-beam system, however, is articulated and only serves to compensate for vertical loads. The columns are connected to the base as fixed base. The strong axes of the frame columns are formed in the X direction for the X directional frames and in the Y direction for the Y directional frames. The frame columns of the building are formed of W-sectioned profiles on the inner and outer axes, and only the columns on the four corners of the building are constructed with box sections in terms of the moments of both directions. Reinforcing plates were used in various levels in column beam joints. The frame girders are made of W-sectioned profiles and the cross-sectional dimensions vary according to the number of storey. Column and beam sections were also used in the same manner for vertical load bearing joint members.
In the case of relevant columns are composite, nonlinear analyzes were carried out in the time history analysis according to the same seismicity conditions and the results for both cases were compared. After that, number of floors were increased to 25 for the building described as 20-storey in SAC documents, required analysis were repeated.The results of the analyzes are summarized in tables and graphs.