Asce 7-10, Eurocode 1-4 Ve Ts 498 Yönetmelikleri Kullanılarak Yapılara Etki Eden Rüzgar Yüklerinin Karşılaştırılması

Abstract

İnsanoğlu yaşamların büyük bir kısmını atmosferin en düşük 600 metresinde sürdürür ve bina, köprü, kule gibi inşaa ettiğimiz tüm yapılar atmosferin bu bölümünde yer alırlar. Etrafımızda bulunan hava, çeşitli mekanizmalar sonucunda, yapıların üstüne, altına veya direkt olarak etki ederler. Bu etkiler sonucu, yapıların dayanım göstermesi gereken rüzgar yükleri meydana gelir. Yapıların hizmet süreleri boyunca maruz kalabileceği bu yükler karşısında dayanım ve dayanıklılıklarını sürdürebilmesi için bu yükler tasarım sürecinde mutlaka göz önünde bulundurulmalıdır. Rüzgar yükleri, yapının maruz kalabileceği en önemli yük gruplarından biridir. Yapılara etkiyen rüzgar yüklerinin hesaplanmasında standartların kullanılması büyük kolaylık ve ekonomik çözümler sağlar. Çünkü her yapı tipi için en yüksek rüzgar yüküne göre tasarım yapmak, optimum olmayan çözümler meydana getirir. Yapı tipleri ve bulunduğu topoğrafyalar, rüzgar yükünün hesabında önemli parametrelerdir ve optimum çözümler için dikkate alınmaları gerekir. Bu tez kapsamında, Amerika'da kullanılmakta olan ASCE 7-10, Avrupa Birliği ülkelerinde kullanılmakta olan Eurocode 1-4 ve Türkiye'de kullanılmakta olan TS 498 yönetmeliklerinde belirtilen rüzgar yüklerinin hesap yöntemleri incelenmiş, iki farklı yapı tipi için rüzgar yükleri hesaplanmış ve elde edilen sonuçlar şekil ve çizelgeler yardımıyla karşılaştırılmıştır. Son olarak ise ortaya çıkan farkların sebepleri irdelenmiştir. Birinci bölümde, rüzgar tanımı yapılmış ve farklı rüzgar tiplerine değinilmiştir. Rüzgar hızı, rüzgar yükleri ve bu yüklerin yapılar üzerinde oluşturduğu etkiler incelenmiştir. İkinci bölümde, ASCE 7-10 yönetmeliği rüzgar yükü hesabı bakımından incelenmiş, hesap yöntemleri ve parametreler çizelge ve şekiller aracılığıyla açıklanmıştır. Üçüncü bölümde, Eurocode 1-4 yönetmeliği rüzgar yükü hesabı bakımından incelenmiş, hesap yöntemleri ve parametreler çizelge ve şekiller aracılığıyla açıklanmıştır. Dördüncü bölümde, yüksek katlı yapı ve endüstri yapısı örneği olmak üzere iki farklı yapı tipi için, incelenen yönetmeliklere göre rüzgar yüklerinin hesapları yapılmıştır. Hesaplanan rüzgar yükleri şekil ve çizelgelerle belirtilmiş, son olarak hesaplanan yükler çizelgeler yardımıyla karşılaştırılmıştır. Beşinci bölümde, TS 498 yönetmeliği rüzgar yükleri bakımından incelenmiş, ASCE 7-10 ve Eurocode 1-4'e göre rüzgar yükleri hesabı yapılan yapı örnekleri için, rüzgar yükü hesabı tekrarlanmıştır. Altıncı bölümde, her iki yönetmelik için belirlenen rüzgar yükleri için hesap akışları ve parametreleri verilmiştir. Hesaplanan rüzgar yüklerine göre elde edilen sonuçlar belirtilmiş, TS 498 için hesaplanan rüzgar yükü değerlerine değinilmiş ve TS 498'in eksikliklerinden bahsedilmiştir.

Humans spend most of their lives within the lowest 600 m of the atmosphere. Our buildings, bridges, towers, and chimneys are nearly all contained in this region known as the atmospheric boundary layer. This portion of the air around us moves over, under, and through our structures, due to a variety of mechanisms such as hurricanes ,thunderstorms, and tornadoes. These higher speed winds generate loads that must be resisted by the buildings we create, and form one core component of the structural design process. For this reason, the responsible designer needs to be fully aware of the destructive power the wind contains. In this study, ASCE 7-10 for USA, Eurocode 1-4 for European Union countries and TS 498 is for Turkey, are compared in terms of wind loads. In line with views of these codes, wind loads are calculated for two different type of structures and the results are compared with tables and figures and finally the reason of the differences between the results are discussed. In the first chapter, wind definition is given and mentioned about the different wind types. Factors which could be effect to wind velocity and response of the wind loads for different type of structures are also specified. Design strategies for resisting or minimizing wind forces or response are described. The extreme wind events that control the design of buildings and structures come from several sources in the planetary atmosphere. Large rotational flows several hundred kilometers across form in the tropics and typically move to cooler climes before dissipating. These major atmospheric disturbances cause a huge amount of damage, from gusting winds to extensive flooding, when they pass over populated coastal areas. Fortunately, in the modem world there are usually several days of warning before a hurricane, cyclone or typhoon hits. Extreme winds that come with less warning are caused by thunderstorms and tornadoes, and so they may pose more of a threat to life. All three storm types are capable of generating extreme design wind and the winds are effect to building responses. These response are different for the structure type. For example, wind loads which are applied at the horizontal direction, are important wind loads for the tall building but for structure with large roofs, such as arenas and stadium, the important wind loads are lift or down force which is applied in the vertical direction on the roofs. Wind loads has two component; the first is static wind loads and the second is dynamic wind loads. The static wind loads are the results of mean wind pressure and they are sensitive to the building geometry. For typical buildings, static wind loads are usually dominant in alongwind direction. Crosswind static loads can be significant for some buildings with special shapes. The basic dynamic loads are due to unsteady wind pressures. These unsteady wind pressures can be caused by wind turbulence in the approaching wind, or by flow separations off the building surface. These dynamic loads are called “background loads” or “non-resonant loads” and due directly to the wind pressures on the building surfaces. For flexible structures the unsteady wind pressures can also excite the building structure into motion and this causes inertial loads, as the building mass accelerates during the motion. These inertial loads are generally called resonant loads because they occur at the building’s natural frequencies only, and they are greatly magnified relative to the direct pressure loads coming from the wind at those frequencies. Design strategies, for resisting or minimizing wind forces and response of structure, are aerodynamic strategies, structural strategies and storm shelters. In the second chapter, ASCE 7-10 has been analyzed. In consequence of this analysis, the information in the standard has been summerized and explained with tables and figures. In the third chapter, Eurocode 1-4 has been analyzed. In consequence of this analysis, the information in the standard has been summerized and explained with tables and figures. In the forth chapter, wind loads are calculated according to examined codes for two different type of structures which are tall building and industrial structure. The calculated results are indicated by figures and tables. Finally results are compared due to the codes by tables. The wind loads are calculated for tall building, using ASCE 7-10 and Eurocode 1-4 respectively. The building's dimension is 40 m in X direction, 60 m in Y direction and 100 m in Z direction. The wind velocity is taken 30 m/s. By the virtue of ASCE 7-10, velocity pressure exposure coefficient, directionality factor and wind velocity pressures are determined by using roughness category. The walls pressures are evaluated according to windward wall, backward wall and side walls. The pressures at the windward wall are calculated seperately due to varying heights. For the other walls, a single pressure is calculated. The walls external pressure coefficients are determined according to the building length to building width ratio. The roof external pressure coefficients are determined according to the building height to building length ratio. The internal pressure coefficents are taken +0.18 and -0.18 which are given for enclosed buildings. According to Eurocode 1-4, basic wind velocity, velocity pressure and mean wind velocity are determined,turbulance factor is calculated and than peak velocity pressure is evaluted with these parameters. Based on the walls, the structure is divided into 5 zones which are A,B,C,D,E zones and the external pressure coeffcient, cpe is determined. The roof is divided into 5 zones too, which are F,G,H,I,J zones and the external pressure coeffcient, cpe is determined.The internal pressure coefficients which are depend on buildings classification and dimension, are taken +0.2 and -0.3 according to worst case scenario. The wind loads are calculated for industrial structure, using ASCE 7-10 and Eurocode 1-4 respectively. The building's dimension is 60 m in X direction, 75 m in Y direction,10 m in Z direction and peak height is 20 m. The wind velocity is taken 30 m/s. By the virtue of ASCE 7-10, velocity pressure exposure coefficient, directionality factor and wind velocity pressures are determined by using roughness category. The walls pressures are evaluated according to windward wall, backward wall and side walls. The pressures at the windward wall are calculated seperately due to varying heights. For the other walls, a single pressure is calculated. The walls external pressure coefficients are determined according to the building length to building width ratio. The roof external pressure coefficients are determined according to the building height to building length ratio. The internal pressure coefficents are taken +0.18 and -0.18 which are given for enclosed buildings. According to Eurocode 1-4, basic wind velocity, velocity pressure and mean wind velocity are determined,turbulance factor is calculated and than peak velocity pressure is evaluted with these parameters. Based on the walls, the structure is divided into 5 zones which are A,B,C,D,E zones and the external pressure coeffcient, cpe is determined. The roof is divided into 5 zones too, which are F,G,H,I,J zones and the external pressure coeffcient, cpe is determined.The internal pressure coefficients which are depend on buildings classification and dimension, are taken +0.2 and -0.3 according to worst case scenario. In the light of these codes, the magnitudes of wind loads which are calculated for these two examples, are compared with figures and tables. In the fifth part, TS 498 for Turkey, is studied according to calculations of wind loads and examples are repeated for the TS 498. In the six part, differences between calculation process of the ASCE 7-10, Eurocode 1-4 and TS 498 are discussed. Base shear forces, which are calculated due to these standards are compared with tables and reasons of the differences between results and deficiencies of TS 498 have been discussed.