Fire Resistant Design High Rise Building - Essay Example

FIRE RESISTANT DESIGN FOR HIGH RISE BUILDING Name Professor Institution Course Date Introduction High rise buildings have tremendously increased in the recent past. The forces behind the increase have been the increase of population and the limited land space. However, fire has been a major threat to life and property in high rise buildings, something that has made even the building designers to re-examine the material to be used in order to reduce the fire risk. The buildings are so high, making it difficult for fire extinguishers to reach the upper storeys. Most ladders and fire-fighting trucks can only reach up to about firth, sixth or seventh floor. Further, it is hard to evacuate high rise buildings because elevators are not supposed to be used during fires. Thus, these buildings inspire a lot of fear despite the fact that they are awesome when it comes to land utilization. Because of the fire incidents of the past, the safety concern for high rise buildings has heightened. A number of fire cases across the world, including the famous World Trade Center Fire, have drawn the attention of different fire organizations, community members, and the government onto a common platform of discussing the design procedures which should be adopted to mitigate this risk. A number of legislations have been enacted in response to fire risk. Engineers should recommend the right materials for the construction of high rise buildings. Some of the properties of concrete and steel have suited the building codes. Most of the building codes advise designers on what to do, and not on how to do. For instance, the UK building codes require that the designers of buildings should design structures that can remain stable for a reasonable amount of time in the event of fire (Frank, 2010). This information is contained in the Approved Document, Part B. Fortunately, high rise buildings benefit from the structural approach of the building codes. Proper choice of material offers a robust solution to fire risks for high rise and complex buildings. The structures used should resist fire for some time. For this reason, attention has been drawn to both steel and concrete. The thickness of the concrete and steel material increases the overall time the material lasts in fire before collapse. Concrete and steel can also be reinforced to come up with a secondary structure that is better in resisting fire. A fire action plan that starts with the construction process is more reliable. The structural members in high rise building, such as the beams, walls, partition, columns, and floors play a central role of safety when there is fire. When both concrete and steel are used to construct fire resistant barriers, this provides an option that can stop or delay the propagation of fire from one place or room to another. Fire barriers can easily reduce the size of fire (Frank, 2010). The history of fires on high rise buildings has ranked high the performance of concrete and steel. Some of the cited features of concrete and steel include their low thermal conductivity, and high heat capacity, among other features. The technologies on how to insulate steel and encase it in concrete, has created a significant achievement towards fire safety (Lincoln & Guba, 1985). Further, the two materials do not support burning. During fire, a lot of activity may take place, right from spreading of fire to new areas, to escape and rescue operations. Therefore, the bonding of material for high rise buildings should remain strong for a long time before collapse. This will give confidence to fire-fighters and other rescuers. Also, strong bonding of the material should be encouraged in order to discourage collapsing of hot debris to lower floors. The fire risk in high rise buildings can be compared to other buildings. The flames and smoke from one floor is capable of causing further spreading of fire to upper floors. Also, the falling debris out of fire can spread fire to lower floors, thus magnifying the fire risk. The distance the occupants can travel to the outside in order to escape is obviously large, meaning that it is better the fire to be controlled or prevented than to occur at all or if it occurs, the structure of the building should prevent fire spreading. Also, the building should remain stable for a long time before collapsing. Additional mechanisms should also be put in place to assist fire-fighters in putting out the fire. Using Concrete Material as an Approach to Fire Safety Concrete material is preferred for construction of high rise buildings because of its desirable properties in fire. Following the primary objectives of having an overall structure which can prevent the development of fire, limit the spread of smoke and fire, ensure stability of the building for long hours, support the evacuation of occupants to a safe ground, and support the intervention of fire fighters, concrete is the preferred choice (Hancock & Algozzine, 2006). The material has been used right from the historical times. The structural members for high rise buildings support a lot of load and should, therefore, be constructed out of large reinforced concrete columns, walls, floors, and even the ceiling .Concrete is non-combustible, cannot lead to fire droplets on the lower floors and above all, has got high resistance to fire (Gillham, 2001). Its inert properties, compounded with its good bonding and insulating properties, make it extremely robust in retaining the structural integrity for reasonable amount of time. The material does not become molten at elevated temperatures when attached by fire. It is for this reasons that most designers of high rise buildings prefer concrete. There are several loads or forces that a high rise building is subjected to- the live and dead loads. Wind, for example, can exert a lot of force on a building. The lower structures must support the upper structures in order for the building to stand. Unfortunately, rise in temperature caused by fire will lead to decreased strength and the modulus of elasticity of the concrete. The bonding between the reinforced materials may decrease. What actually matters is the time the material can withstand the effect of heat before weakening. Also, severe fire in high rise buildings can cause the expansion of the structural components. The resulting strains and stresses must be resisted by different concrete structural members Concrete contains some free water in it. When the temperature rises, this water heats up and changes to a gaseous form. The change of state that occurs leads to transfer of heat from the surface to the interior concrete components. However, concrete does not burn and the time taken for this water to burn is very long due to the insulation effect. The properties of concrete change with increase in temperature, and these changes depend on the type of the coarse aggregate used. The coarse aggregate of concrete is classified into three forms: lightweight, carbonate, and siliceous. Lightweight aggregate is manufactured after heating slate, clay or shale. The siliceous aggregate is made up of silica, such as granite and sandstones. Carbonate aggregate consists of limestone and dolomite. The diagram below shows the effect of temperature increase on Compressive Strength of Concrete (carbonate, siliceous, and sanded lightweight concrete). An Illustration of How Temperature Increase Affects the Compressive Strength of Concrete An Illustration of the Effect of Higher Temperatures on the Modulus of Elasticity of the Concrete Material (carbonate, siliceous, and sanded lightweight concrete) Reasons as to Why Concrete is Suitable for High-Rise Buildings The performance of concrete in fire makes it suitable for construction of high rise buildings. Further, concrete cost is low as compared to other materials. It has a good appearance. Designers have given it an upper hand. The following are some of the particular reasons as to why concrete is preferred in the construction of high rise buildings: Concrete has got high resistance to fire and is less costly. The load-bearing properties of concrete material make it appropriate for supporting the building for long hours in a remarkable way without need for more protective material, like the intumescing paint or plaster coatings. Concrete use in buildings remains permanent at no extra maintenance cost. Concrete does not burn when subjected to severe fires. It does not change to molten state, does not emit poisonous gases or smoke, and does not support the spreading of fire even when the temperatures are extreme. Concrete elements can withstand elevated temperatures for a long time and with little or no deformation. For reinforced concrete slabs to reach their critical temperatures, they must be subjected to a temperature of over 500oC, in a duration of more than two hours, and at a depth of about 3.5 cm. Lightweight concrete is in a higher demand because of its effective barriers against spreading of fire. Concrete consists of some reserves in its structure. These reserves offer protection against fire. Since concrete does not consume in fire, this prevents the spreading of fire, especially when concrete is used in compartmentalisation. The large amount of water that is used in extinguishing fires does not negatively affect the strength of concrete structure. High rise buildings have to be provided with load-bearing members in order to sufficiently meet the fire resistance threshold. This reduces the risk of the trapped occupants, minimizes the risk of fire attacking the vicinity, and makes it easy for fire-fighters to approach the attacked building without fear that it would collapse on them. Concrete is used in construction of high rise buildings because it renders the load-bearing materials with the ability to withstand fire, resist collapse of the building, resist fire penetration to other rooms within the building, and prevent the transfer of unreasonable heat ( Helmstadter, 1970). Therefore, in the pre-design stages, architectures and engineers must take this into consideration in order to come up with reliable structures such as the floors, walls, columns and even the frames. If the building legislations on fire safety are overlooked, it would be a big mistake that would lead to creating of dangerous high rise buildings. The thickness and the mixture of the concrete should support the building for about two hours. Other fire-fighting systems should also be incorporated into the building for easy fire management. From the various fire incidents of the part, concrete has proved strong in resisting fire. For instance, in 2005, the Windsor Tower in Madrid Spain was attacked (Gray & Larson, 2008). A total property value of about 122 million Euro was destroyed by the fire. The tower comprised 29 storeys, with two technical floors and five basement levels. The tower was first constructed between 1974 and 1978. At this time, building legislations that existed did not include the installation of sprinklers in high rise buildings. After some subsequent amendments, the tower was refurbished. The refurbishment entailed construction of entire steel perimeter columns that are fireproof. New escape routes and new external stairs were installed and the entire fire alarm system was upgraded. Normal concrete material was used in the construction of a number of its structure, with some reinforcement from steel. The building was attacked by fire, two years later. Fortunately, the building was unoccupied when the fire broke out. The fire started from the 21st floor, and spread upwards through openings, and downwards due to falling of some burning debris which entered the building through some windows below. The building was raged by fire for over 26 hours, and almost all the floors were engulfed. When the building finally got extinguished, almost everything had been burnt from the 5th floor upwards. Rumours went round that the building would collapse. However, the building remained stable till it was demolished. The concrete columns and the core provided the building with passive resistance to fire, and that is why the building never collapsed. This reconfirmed the building codes that had been put in place. When concrete floors are situated at regular intervals, the risk of fire is prevented. The diagram below shows the remaining structure after the fire incident. An Image Showing the Windsor Tower before it was Demolished Using Steel Material as an Approach to Fire Safety Steel can be used to reinforce concrete structures. Though steel is somehow sensitive to high temperatures as compared to concrete, it can be used together with concrete in order to give desirable properties. Building standards that govern fire issues dictate that the steel material be rated according to its behavior when subjected to high temperatures. The choice of steel that should be considered in construction of high rise buildings depends on the fire rating. Appropriate steel should be the one that is capable of standing the fire for longer before completely losing its mechanical properties. The figure below shows the effect of temperature increase on the yield strength of steel. The Effect of High Temperature increase on the Yield Strength of Steel The modulus of elasticity of steel can also be affected by temperature increase, subsequently affecting the steel structure. The diagram below shows the impact of temperature increase on the modulus of elasticity of steel. The Effect of Increase of Temperature on the Yield Strength of Steel Reinforced bars retain a lot of their yield strength up to 800oC, while the cold-drawn steels begin to lose their strength even at about 500oC. If a slab gets subjected to severe fire, the strength of reinforced steel decreases due to temperature increase. Some of the principle materials used to protect structural steel include the sprayed fire-resistive material, thin-film intumescents, intumescent mat wrap material, epoxy based intumescents, and board type products. Thin-film intumescents are added to structural steel, thus increasing some thin thickness on it. When this steel is exposed to some heat, the thin film undergoes some chemical changes leading to formation of an insulation layer of char. This provides more fire resistance for about two to three more hours. The history of intumescent paints is 10 years old. In the UK and USA, they are commonly used for construction of high rise buildings. The main components in this paint are: resin binders and a mixture of chemicals that easily breakdown under intense heat and give off some gas. When a high rise building is raged by fire, intumescent paint melts, and this leads to a reaction that produces gas at a temperature corresponding to the melt viscosity of the resin. The release of the gas makes the resin to melt, and the form released develops an insulating layer. For instance, the 88 storey Twin Towers of Petronas has got each side soaring to about 452 m into the sky and above the street level. The towers have four basement levels, massive concourse levels, and concourse mezzanine levels. A lot of both steel and concrete material has been used in the construction of this building, for instance the barrette piles together with a 4.5 m thick raft foundation of reinforced concrete. The main columns, floors and walls were framed with concrete and steel trusses. The entire structure was then completed with stainless steel and vision glass. Such a structure has higher chances of remaining stable in the event of fire. There are several fire causes, such as gas leakages, electrical shocks, among others. No matter what cause, the impacts of fire remain almost the same and depend on the factors that lead to the spread and how the fire was managed. When The First Interstate Bank Building in Los Angeles was attacked by fire in 1988, a lot of things were leant (Gillham, 2001). The building had 62 storeys. The fire lasted for about three and half hours. Several fire-fighting companies battled with the fire and there was a lot of window damage. This complicated the fire-fighting efforts. Despite the destruction of a lot of property, the investigations that were done reveal that the principle structural elements which were constructed out of reinforced steel, remained intact. Only few structures were destroyed. There are several steel-related technologies meant to offer fire resistance to high rise buildings. Some of these technologies involve the insulation of steel, and the use of membrane protection parallel to other systems for the purpose of circulating and discharging water in order to cool the overall building structure. For the purpose of increasing the overall strength of steel, the design process of high rise buildings must take into consideration the insulation process. Insulation protects the steel structure from any direct exposure to fire. A good insulator should be a poor conductor of heat. This will increase the time taken for heat to reach the structural elements. Some of the best insulators that have been used in the past include: bricks, tiles, concrete, and asbestos. The materials perform better even at elevated temperatures. Gypsum has a lot of water that is chemically combined in it, something which makes it a good insulator. A lot of energy must be expended in order to dislodge this water from gypsum. How Steel and Concrete Work Together When both steel and concrete are used together, they share some similarities and differences in terms of their role of ensuring fire safety (Kathy, 2010). Steel is normally encased in concrete and in this case, it is insulated. However, both of them have very high melting points and jointly form a stronger structure that cannot easily collapse in the event of fire. When steel is encased in concrete, it gets protected from any direct exposure to fire. More insulation can be provided by increasing the thickness of the concrete. The technology of encasing steel in applied in many parts of the world. Conclusion The pressure on land resource due to increase of human population has led to increased number of high rise buildings. These buildings inspire a lot of awe in the modern world except for the danger posed by the fire risk. High rise buildings increase the escape distance of the occupants in the event of fire. The occupants may also be trapped and even the complexity of the building makes it impossible to rescue the occupants or extinguish the fire. Several building legislations have acknowledged the need for incorporating proper design features into the building. Following the excellent properties of steel and concrete, they are commonly used in the construction of steel structures. The materials can resist fire for a reasonable amount of time, and do not burn easily at elevated temperatures. The fire incidents of the past have reconfirmed the structural impact of steel and concrete on high rise buildings. References Frank, T 2010, Fire Officers Handbook of Tactics, APB Group, Norwich. Gillham, B 2001, Concrete and Fire Resistance in Buildings, Continuum, London. Gray, CF, & Larson, EW 2008, Fundamentals of Fire Protection. 4th Edition, McGraw-Hill Educations, Singapore. Hancock, DR & Algozzine, B 2006, Modern Approach of Building Tall Buildings, Teacher College Columbia University, New York. Helmstadter, GC 1970, The Mechanical Properties of Steel and Concrete, Appleton-Century- Crofts, NY. Kathy, S 2010, Tall Building: Criteria and Loading, Course Technology Ltd, Boston. Lincoln, YS, & Guba, EA 1985, The Building Legislations for Fire Safety, Beverly Hills, Sage, CA. Robert, A & Arthur, I F 2009, Fire Safety for High-Rise Buildings: The Role of Communications, Zaltbommel, Van Haren. Read More

During fire, a lot of activity may take place, right from spreading of fire to new areas, to escape and rescue operations. Therefore, the bonding of material for high rise buildings should remain strong for a long time before collapse. This will give confidence to fire-fighters and other rescuers. Also, strong bonding of the material should be encouraged in order to discourage collapsing of hot debris to lower floors. The fire risk in high rise buildings can be compared to other buildings. The flames and smoke from one floor is capable of causing further spreading of fire to upper floors.

Also, the falling debris out of fire can spread fire to lower floors, thus magnifying the fire risk. The distance the occupants can travel to the outside in order to escape is obviously large, meaning that it is better the fire to be controlled or prevented than to occur at all or if it occurs, the structure of the building should prevent fire spreading. Also, the building should remain stable for a long time before collapsing. Additional mechanisms should also be put in place to assist fire-fighters in putting out the fire.

Using Concrete Material as an Approach to Fire Safety Concrete material is preferred for construction of high rise buildings because of its desirable properties in fire. Following the primary objectives of having an overall structure which can prevent the development of fire, limit the spread of smoke and fire, ensure stability of the building for long hours, support the evacuation of occupants to a safe ground, and support the intervention of fire fighters, concrete is the preferred choice (Hancock & Algozzine, 2006).

The material has been used right from the historical times. The structural members for high rise buildings support a lot of load and should, therefore, be constructed out of large reinforced concrete columns, walls, floors, and even the ceiling .Concrete is non-combustible, cannot lead to fire droplets on the lower floors and above all, has got high resistance to fire (Gillham, 2001). Its inert properties, compounded with its good bonding and insulating properties, make it extremely robust in retaining the structural integrity for reasonable amount of time.

The material does not become molten at elevated temperatures when attached by fire. It is for this reasons that most designers of high rise buildings prefer concrete. There are several loads or forces that a high rise building is subjected to- the live and dead loads. Wind, for example, can exert a lot of force on a building. The lower structures must support the upper structures in order for the building to stand. Unfortunately, rise in temperature caused by fire will lead to decreased strength and the modulus of elasticity of the concrete.

The bonding between the reinforced materials may decrease. What actually matters is the time the material can withstand the effect of heat before weakening. Also, severe fire in high rise buildings can cause the expansion of the structural components. The resulting strains and stresses must be resisted by different concrete structural members Concrete contains some free water in it. When the temperature rises, this water heats up and changes to a gaseous form. The change of state that occurs leads to transfer of heat from the surface to the interior concrete components.

However, concrete does not burn and the time taken for this water to burn is very long due to the insulation effect. The properties of concrete change with increase in temperature, and these changes depend on the type of the coarse aggregate used. The coarse aggregate of concrete is classified into three forms: lightweight, carbonate, and siliceous. Lightweight aggregate is manufactured after heating slate, clay or shale. The siliceous aggregate is made up of silica, such as granite and sandstones.

Carbonate aggregate consists of limestone and dolomite. The diagram below shows the effect of temperature increase on Compressive Strength of Concrete (carbonate, siliceous, and sanded lightweight concrete).

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