Fire dynamics - Dissertation Example

At 250-300 degrees room temperature, creep has little effect on the performance on the steel structure since the amount and distribution of the effects of steel remain uniform hence any deformations occur at a slow pace. As the fire crib is set to temperatures of 0.25/0.5 MegaWatt, recorded by a thermal imaging camera, creep starts to become a dominating factor (Totten, 2007). Deformation starts to occur as the vacancies in the crystal structure diffuse to the location of a dislocation hence the dislocations move faster to an adjacent slip plane.

As the temperature of steel increases so does the creep deformations. Depending on its material composition, steel’s melting point stands at 1400 degrees Celsius. Therefore, creep deformations will become noticeable at temperatures corresponding to 30% of its melting point. Creep strain has three phases which include: Primary creep/ Initial phase Steady-state creep/ Secondary creep Tertiary creep At the initial phase, the strain rate is high and increases at a steady rate, that is, it is directly proportional to temperature.

On almost entering the secondary creep phase, it decreases gradually. At the steady state creep, the strain rate reaches a minimum and is almost constant. At the tertiary creep phase, the strain rate increases exponentially as temperature increases. . sius), time zero (0), the strain on the structure is minimal, and as the curve shows, strain is always present even at normal conditions that are; steel is always undergoing strain in its normal conditions due to it general makeup which contains soluble atoms (Totten, 2007).

A retardant rock wool which is welded to a steel structure aimed at adding extra heat protection reduces the effect of exposing a steel structure to long hours of heat. Although creep has a great detrimental effect on this steel structure, the extra fire protection (retardant rock wool) that is welded to the structure main objective is combating this effect (Totten, 2007). This material, which is fire resistant, tolerates temperatures of up to 1000 degrees Celsius and does not burn. It remains stable when exposed to such high temperatures.

The retardant rock wool acts as an insulator in the sense that; it has an R-value which means that it has a resistance to heat flow providing rates as from 4.4dB for the 5mm thickness of steel. Metals do not react well when exposed to fire for a very long time. When it is heated, the molecular structure of the metal becomes weak and loses its strength at over five hundred degrees Celsius. This cause the collapse of metal buildings as the metal warps and melts slightly under extreme temperatures.

However, this takes a longer time and has no effect on the evacuation of the metal structure (Totten, 2007). Under normal circumstance, water reacts with metal to form rust. The surface rust is not harmful, but when exposed continuously to unprotected metal it leads to severe corrosion. Additionally, when the building is exposed to heat source for a long time, their mechanical strength of the building will decrease and thus their properties will become more dependent on