The fire resistant properties of common building materials such as stone, brick, wood, cast iron, glass, steel and concrete are mentioned below.
Stone is a poor conductor of heat. But under the influence of fire, he suffers a lot. When heated and suddenly cooled, the stone also shatters into small pieces. Granite cracks and disintegrates easily in case of fire. Limestone breaks easily even by ordinary fire. Sandstones of compact structure with fine grains can generally successfully tolerate moderate fires without severe crack formation.
It is found that 1200 . Bricks are not severely affected by very high temperatures of0c to 13000 C has arrived. This is due to the fact that a brick is a poor conductor of heat. If the type of mortar and the quality of workmanship are good, brick masonry generally offers good resistance to fire. However, a brick has its own structural limits for use in buildings.
As a general rule, structural elements made of wood tend to ignite in the event of a fire and are rapidly destroyed. In addition, they increase the intensity of the fire. But wood used in heavy sections can attain a high degree of fire-resistance because wood is a very poor conductor of heat. This is why wood needs time to generate enough heat to cause a flame. To make wood more fire resistant, wooden surfaces are sometimes coated with certain chemicals such as ammonium phosphate and sulfate, borax and boric acid, zinc chloride, etc. Such treatment on wooden surfaces leads to an increase in temperature during a fire. Wooden molds can also be made fire resistant by using certain paints on its surface.
4. raw iron
This material is currently rarely used as a structural material. When heated and suddenly cooled, this material flies into pieces. Therefore, when this material is used in construction, it is either covered with brickwork of one brick thickness or another fire resistant material such as concrete.
This material is a poor conductor of heat and due to heat its expansion is less. When this material is heated and then suddenly cooled, cracks are formed. Glass reinforced with steel wire is more fire resistant than ordinary glass and can resist sudden changes in temperature without crack formation. Wired glass, even if it breaks, keeps the fractured glass in its original state.
Steel is a good conductor of heat and therefore heats up rapidly in case of fire. It is found that steel loses its tensile strength with increase in heat and the yield stress of mild steel is 600 . happens on0C is about a third of its value at normal temperature. Therefore, under intense fire, the unprotected steel beams sag, the unprotected steel columns buckle and the structure collapses. steel 1400 . melts completely at a temperature of0C. It has also been found that if the paint of the surface is not specially made to be fire resistant, it helps in spreading the flame on the surface and thus it increases the intensity of the fire.
If a steel plate or sheet form is fixed to the framework, it becomes ductile which is resisting the passage of flame. This type of construction is widely adopted in the manufacture of fire resistant doors and windows.
Concrete has got very good fire resistance. The actual behavior of concrete in the event of a fire depends on the quality of the cement and the aggregate used. In the case of reinforced concrete and prestressed concrete, it also depends on the condition of the steel. The larger the concrete cover, the better the fire resistance of the member.
There is no loss of strength when concrete is heated to 250°C. If the temperature exceeds 250 °C, the strength begins to decrease. Generally reinforced concrete structures can resist fire for about an hour at a temperature of 1000 °C. Therefore cement concrete is ideally a fire resistant material used.
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