Yangının çelik taşıyıcı sistemler üzerine etkisi ve bir uygulama örneği

Abstract

İnsanoğlu varolduğundan bu yana çeşitli tehlikelerle karşı karşıya kalmış ve bunlarla mücadele etmeye çalışmıştır. Bu tehlikelerden biri olan yangın, toplumda can kayıplarına ve maddi zararlara neden olmasıyla insanlar için sürekli bir tehdit ve tehlike unsuru olmuştur. Kullandığımız yapılar bugün geçmişe göre farklılık gösterse de her zaman için yangın tehlikesiyle karşı karşıyadır. Ancak ne tür önlem alınırsa alınsın bugün ve gelecekteki yapılar için yangın çıkmama olasılığı kesinlikle yoktur denilemez. Önemli olan yangın başlangıcının en kısa sürede saptanması ve müdahale etme olanaklarının çözülmüş olmasıdır. Bu nedenle henüz tasarım aşamasında iken yapılarda yangın güvenliğinin nasıl sağlanabileceği düşünülmeli ve yapım sonrasında da kullanıcılara olası bir yangında neler yapmaları gerektiğine ilişkin uyarılarda bulunulmalıdır. Teknolojik gelişmelerle ve enerji kullanımının artmasıyla, yangınların oluşma biçimlerinde farklılık ve sayılarında artışların görülmesi, buna karşı yeni önlemlerin alınmasını gerektirmektedir. Özellikle endüstri devriminden sonra, çeliğin yapılarda taşıyıcı sistem elemanı olarak kullanılmasıyla istenilen tasarım biçimi rahatlıkla gerçekleştirilmeye başlanmışken, meydana gelen bir kaç önemli yangında çelik taşıyıcı sistemin yangına karşı dayanımının yetersiz olduğu ortaya çıkmıştır. Bu doğrultuda yaklaşılan tez çalışmasında, çelik taşıyıcı sistemin yangına karşı dayanımının nasıl iyileştirilebileceğine yönelik, yabancı literatürde yer alan yangından korunma yöntemleri, kullanılabilecek yalıtım malzemesi türleri ve kalınlıklarına ilişkin hesaplama yöntemleri ve çeşitli ülkelerin konuyla ilgili yönetmeliklerinin incelenmesi yönünde bir araştırmaya gidilmiştir. Araştırmadan elde edilen bilgilerle, taşıyıcı sistem elemanı olan çeliğin yalıtımlı ve yalıtımsız durumda yangına dayanım sürelerinin (kullanılan yalıtım malzemesi ve kalınlığına göre değişebilen) hesaplanması (Eurocode'a dayalı) çalışmalarına örnek bir uygulama verilerek, yangın yalıtımının önemine ve bunun uygulamaya geçirilmesinde yönetmeliklerin ciddi bir şekilde ele alınıp incelenmesi ve hazırlanması gerektiğine dikkat çekilmek istenmiştir.

The fire has always been a treat and a danger to human beings. The number of those who died due to heart attack or poisonous gases in the event of fire is higher than those who die from actual burns due to panicking or blocked exit way. Fire can break out anywhere; at home, at office, at school, in the car, on board of streamer or plane, etc., but this work deal with the problems of and the protective measures to be taken against the fire that might occur in buildings. For the purpose of this work, the phenomenon of fire in buildings is investigated in general and then the resistance of steel structures to fire is particularly studied. Besides, fire and safety codes implemented in some foreign countries are included and a comparative study between the Turkish practice and that of foreign examples is attempted. Whatever the measures are taken, the possibility of fire in any type of building can not be determined. The fundemantal issue is to detect the start of a fire as soon as possible and is to provide every likely mean of fire tackling measures in a proper manner. The possibility of fire incident is likely related to the type of buildings in use. According to the recent statistical findings, the majority of the fire incidents that amounts to 53 - 63 % of all fire cases, involves house fires. By increasing use of electrical appliances and wide spread use of electrical power in todays' modern life, the volume of fire incidents has relatively increased. The Industrial Revolution was followed by the application of steel in large scale as building material for structural purposes. The well known Chicago fire, which devastated the city in 1871 demonstrated well how steel structures were vulnarable in the case of fire. It is only after the 18.th century that means of fire escape have been given serious considerations. Since the start of the 19.th century, the building materials and the building connections have been subject to investigations in order to identify the fire prevention measures so that the fire incidents would be minimised.Following the Second World War, such issues as the capacity of building evacuation; fire tests, and the mode of fire testing and test conditions; smoke spreading potential and movement pattern; fire proofing of structural systems, especially in steel and building elements; etc., have been dealt with by the official bodies like CIB, ISO, et.al, through international cooperation and joint operations. Within the first chapter of this study, the phenomenon of fire is investigated. It is known fact that human beings can only stand the temperature which is above 65 °C for a short period of time. The human body can withstand the ambient temperature of 120°C for 15 minutes. If the ambient temperature rises up to 143°C within 5 minutes, it creates an untolerable enviroment for human beings. In case of heat level reaching up to 177°C in less than 1 minute, human being suffer uncurable fire burns. In the first chapter, it is also studied how a fire breaks out and spreads around. It is esential that the gas of 02 should be present together with sufficient heat temperature in an enviroment to spark off a fire. The aspects fire resistance and fire load are also highlighted in the first chapter. The category of fire resistance and duration of fire resistance with respect to DIN 4102 are given as follows: F 30 Fire deterrent F 60 Fire deterrent F 90 Fire proof (low) F 120 Highly fire proof (moderate) F 1 80 Absolute fire proof (high) It is noted in this chapter that main reason behind the consequent stages of fire outbreak, spreading and extinguishing is radiation. It is also pointed out the effects of poisonous gases and smoke resulting from the fire in this chapter. Chapter 2 includes the fire proofing aspects and related code of practices. The precautions which can be taken in terms of building itself are presented by a table. The main intention behind the fire proofing measures as follows; to provide user safety to stop fire spreading from its origin to minimise the damage to property and to prevent casualities. In this context, the fire walls between adjacent buildings are discussed and illustrated. Besides, some examples for the code of practice for fire precautions applicapable in other countries are emphasised. The cost of fire prevention measures is also demonstrated in chapter 2 by compairing two fire prevention system implemented at two buildings in Istanbul.Chapter 3, however, investigates the potential capacity of flammability of building materials together with the procedure for selecting appropriate material for fire proofing. In this chapter, it is also included the physical and chemical changes that building materials undertake in the course of fire. For designers, the safety ceiling level for fire resistance buildings, in terms of building temperature fluctuation is between 20 to 700°C. The majority of available building materials, tend to yield before surviving the top ceiling level. It is for this reason that pacularities and behaviour of both concrete and steel at higher temperatures are studied. The temperature fluctuation of building materials is also illustrated. The building materials are classified with reference to fire safety potentials in Germany standarts DIN 4120 - Section 1 as follows ; Inflammable Class A Class A1 Class A2 Flammable Class B Class B1 (fire proof) Class B2 (moderate fire proof) Class B3 (non-fire proof) In chapter 4, it is attempted to describe how to select appropriate material in lines with German standarts and the code of practice for fire precautions. In chapter 4, the effects of fire on building structures and the fire precautions that might be taken together with the modes of fire protections are discussed. The deformation and deflection which building elements and in turn building frames do suffer because of the heat, caused by the fire are illustrated. It is also highlighted in this chapter 4, how coloums as structural members and reinforced concrete and steel loose their structural properties in case of fire. It is therefore, the significance of fire proofing is emphasised. The fire proofing materials, their classification and application for the purpose of providing fire proof building components are also included in this chapter. The superiority of structural steel for coloums, beams, trussers, etc., over reinforced concrete and timber together with disadvantages inherent in steel are discussed. The steel production in Turkey is briefly touched upon. Apart from all the above considerations, the numerical data and the tables which identify the rise of temperature in steel, in course of fire and which are used in chapter 5 in the context of a case study are presented here. As it is known, steel looses its structural strength when subjected high temperature. It is generally accepted that critical temperature for structural steel is 550°C, for reinforcement steel is between 400 - 500°C. For the above given facts, it is particularly essential to protect steel against fire hazards. In this chapter, it is also included the means of fire proofing that are applicable for steel members.These are namely: _ Concrete encasement _ Board encasement _ Vermicular spray application _ Liquid filled column fire protection Chapter 4 includes the methods of calculation of fire resistance capacity of both fire protected and non protected structural steel, which are found in foreign literature. Besides, it is also described in this chapter, how to test the structural capacity of steel. In Chapter 5, a case study is conducted with the object of demonstrating the fact that structural steel members should be protected against fire. The type of fire proofing materials; the thicknesses of materials required; the procedure in which the resistance period of steel to rising heat and transformation of all related information resulting from above into the code of practice for fire precautions in foreign literature are highlighted by this case study. At the end of the case study, the fire resistance periods of the building with / and / without fire precautions are determined. The fire resistance periods are also presented by a table and a grafic diagram. It is observed that where insulation is used, an additional time of approximately 87 % is obtained and this additional time is enough for the fire brigades to arrive to the scene. Consequently, the loose of human lives and money, caused by the fire hazards, can be prevent by the coordinate works of persons who deals with fire precaution. The regulations for fire precaution must be prepared seriously, examining the international examples and technological developments. These precautions must also be revised periodically in order to loose its actuality. Today, in international regulations, the tables of fire resistance periods and insulation thicknesses for the used processes and materials, for the precaution of the structural systems against fire are ready. Also fire brigade, building users, architects and engineers, etc., must show a great effort on obeying to these regulations. According to all these, by making and generalising the necessary supervisions for the fire preservation, either before or after the construction, precautions that are taken in Turkey will be as high as the international quality.