Çok katlı bir otopark binasının kompozit ve çelik çözümlerinin karşılaştırılması

Abstract

Yüksek lisans tezi olarak hazırlanan bu çalışmada, çok katlı bir otopark binasının çelik ve kompozit kirişli çözümleri karşılaştırmıştır. Sistem, enine doğrultuda 4 açıklıktan oluşmaktadır, her bir açıklıkta 11 m uzunluğunda basit kirişler düzenlenmiştir. Boyuna doğrultuda ise her bir açıklığı 7.5 m olan rijit çerçeveler düzenlenmiştir. Yapıda araçların katlar arasındaki ulaşımını sağlamak amcıyla rampalar düzenlenmiştir. Rampaların bulunduğu doğrultuda bina 4 katlı iki blok şeklinde düzenlenmiştir. İlk blok 45mx16.5m ikinci blok ise 45mx27.5m'dir. Kat yükseklikleri birinci blokta, ilk katta 3.975 m diğer katlarda 2.65 m'dir. İkinci blokta, ilk tüm katlarda 2.65 m'dir. Döşemeler çatı katında 10 cm normal katta 12 cm kalınlığında seçilmiştir. Malzeme olarak çelik St 37 beton BS20, kiriş profilleri NPI, kolon profilleri ARBED HD, kararlılk bağlan diyagonalleri [ profilleri seçilmiştir. Yapı ikinci derece deprem bölgesindedir. İkinci bölümde kesit tesirleri ve kompozit hesapta kullanılan bilgisayar programları tanıtılmış ve akış diyagramları verilmiştir. Üçüncü bölümde kompozit kirişli otopark hesabı yapılarak sonuçlar tablolar halinde verilmiştir. Dördüncü bölümde çelik kirişli otopark hesabı yapılarak sonuçlar tablolar halinde verilmiş, ayrıca tipik detay hesapları da yapılmıştır. Beşinci bölümde her iki çözümün metraj hesabı yapılmış ve sonuçlar karşılaştırmıştır.

For many years, steel beams and reinforced concrete slabs were used together with no consideration being made for any composite effect. In recent years, however it has been shown that a great strengthening effect can be obtained by tying steel beams and reinforced concrete slab together to act as a unit in resisting loads. Steel beams encased in concrete, were widely used from the early 1900's until the development of lightweight materials for fire protection in the past 30 years. In the early 1930's bridge construction began to use composite sections. After 1960's, the uses of composite construction for buildings became economical. In composite construction steel and concrete are placed to maximize the moment arm for resistance against bending. The bending moment is mainly resisted by the compressive force in the concrete slab and the tensile force in the steel. The ultimate strength of a composite section is depended upon the yield strength and section properties of the steel beam, the concrete slab strength and the interaction capacity of the shear connectors joining the slab to the beam. The procedure for determining the ultimate moment capacity depends on whether the neutral axis falls within the concrete slab or within the steel beam. If the neutral axis falls within the slab, the slab is capable of resisting the total compressive force. If the neutral axis falls within the steel beam, the slab is able to resist only a portion of the compressive force, the remainder being taken by the steel beam (Fig. 1). Fig. 1. Stress diagrams of the composite section VI A particular advantage of composite floors is that take advantage of concrete's high compressive strength. At the same time, a larger percentage of the steel is kept in tension. The result is less steel tonnage required for the same loads and spans. Composite sections have greater stiffness than non composite sections and they have smaller deflections. Deflections under loading may be calculated by elastic analysis using a transformed section approach assuming full interaction. Just as for reinforced concrete sections, the elastic analysis assumes that plane sections remain plane and that the concrete can not carry tensile stress. In addition shrinkage and creep of concrete will also contribute to service deflections. The modular ratio should be obtained from n=Es/Ec (ES,EC =modulus of elasticity for steel and concrete respectively). In the case of continuous beams, the advantage of composite behavior is reduced in the region of negative beam moments. Longitudinal additional reinforcing steel within the effective width of the concrete slab may be assumed to act compositely with the steel beam. In composite beams, the steel beam is designed to act with a part of the slab. For this to happen, it is necessary that slip at the interface be prevented. This normally achieved by the use of shear connectors. An important aspect of the design of the composite beam is therefore the provision of adequate shear connection. Various types of shear connectors have been tried including spiral bars, channels, angels and studs. Economic considerations have usually led to the use of studs welded to the top flanges of the beams. These studs can be quickly attached to the steel beams with stud welding guns. The overall economy of using composite construction when considering total building costs appear to be good. Because of this, in this study the steel and composite solutions of a multistorey parking building are compared. Parking buildings are generally builded with reinforced concrete in Turkey. This limits the column spans of such buildings. However, the composite beams are available for long spans. Parking structures serve office buildings, shopping centers, banks, universities, hospitals, etc. and they are located in urban areas. Parking structures have many things in differences. A very elemental one is that there must be some circulation system that provides access from one floor to the next. In this study the parking building is designed as a split level car park with combined entry and departure circulation and with end ramps. The up ramp system being the one on which drivers enter, and the down ramp system being the one by which the leave. The parking levels are flat decks VII and the rise between them is half the floor to floor height. Aisles are designed one way. Ramps are arranged 12 percent slop. The settlement area is 44 m x 45 m In the longitudinal direction the system consists of 6 spanned rigid frames and each beam span is 7.5 m In the transverse direction, 4 spanned simply supported beams are designed. Each beam span is 1 1 m. The building consists of 4 stories. For the first block fist storey is 3.975 m high and normal stories are 2.65 m high, for the second block all the stories are 2.65 m high. In both solutions steel St 37 and concrete BS 20 were used as a construction materials. In the calculations, 350 kg/m2 of live loads were taken. The main type of flooring used is cast in situ concrete in one way spanning slabs. The cast in situ slabs constructed to act compositively with the steel beams. The thickness of the reinforced concrete is chosen as 10 cm in roof floor and 12 cm in normal floor. The section effects of all the beams were calculated by a computer program, which is prepared for the vertical loads. Before that, the sections were approximately chosen from the preliminary calculations. Optimization programs were prepared for the composite and steel section calculations. The composite calculation of structure was only done for the steel beams which generally dominates the overall structure weight. The moment bearing capacity of composite beam sections were calculated in the positively and negatively moment zones. The effect of the shear force is considered. The deflection analysis of the composite beam was also done by well known elastic method. During the calculations, vertical loads were increased by a load factor of 1.7 in the composite and steel plastic solutions. For the solutions NPI sections for beams and ARBED HD sections for columns were used. All of the vertical loads were carried by beams and columns. However all of the horizontal loads, which are effected in two directions were carried by bracing walls. In the bracing, provided to stabilize multistorey buildings, the panels have cross diagonals. It is considered that the truss as statically determinate with only the set of diagonals in tension assumed to be effective. When the horizontal force reverses the other set become active. For bracing wall beams lateral buckling calculations are carried out and the sections were enlarged. Since the floor heights are too small where the two blocks are intersected, reinforced concrete walls are arranged in the main direction. The construction was imagined to be located in the second degree earthquake area. VIII The earthquake coefficient C was calculated as C=CoxKxSxl C0: is the earthquake area coefficient. K : is the structure type coefficient. I : is the importance coefficient. The lateral forces acting on the building were calculated by the formula Wxh F, = CxWx ' ' ZWiXh, W: is the total weight of the building. Wji is the weight of the i th. storey. For the plastic calculations of steel section; Total weight of simply supported beams: 41 841 8.4 kg Total weight of continuous beams: 387735 kg For the elastic calculations of steel section; Total weight of simply supported beams: 453145.2 kg Total weight of continuous beams: 423204.3 kg It shows that plastic calculation is take an advantage against elastic calculation for the steel sections. For the composite calculations of steel section; Total weight of simply supported beams: 309888.8 kg Total weight of continuous beams: 358434 kg It shows that simply supported beams are economical than continuous beams, but it must known that internal forces are obtained by elastic calculations. For the overall structure, the following results have been obtained from steel solution. Beams : 387735 kg Columns : 165462 kg Bracings : 90908 kg Total Weight :644715 kg Total Area of Building:7920 m2 The Weight per 1 m2:81.33 kg/m2 IX For the overall structure, the following results have been obtained from composite solution. Total Weight : 564402 kg Total Area of Building:7920 m2 The Weight per 1 m2;71.26 kg/m2 In this study, it has been concluded that the composite solution supplies an economy approximately 14 percent for the overall structure and 25 percent for the beams. I am very grateful to my teacher Prof. Dr. Tevfik Seno ARDA whose knowledge I made used of.