Study Of Failure Probability For Fire-proofing Steel Element Under Sprinkler Application Based On "Equivalence" Concept

With different operating mechanisms and fire development assumptions, sprinkler system and fireproof coating are widely used in fire protection of steel structures. Generally, they are designed respectively without considering the interaction between them. Scientific basis and quantitative assessment methods are still lack in how to consider the use of sprinkler system and fireproof coating for optimizing cost-effective fire protection strategy of steel structures, especially in reconstruction of fire protection system in those buildings whose fire risk class were transformed due to the changing of construction applications. So it has practical significance to carry out research in this area.Fire-resistant performance of steel element is determined by its temperature rise in fire, so the heat transfer process is an important part of structural fire safety. This paper analyzed the effect of the reliability of sprinkler application on the characteristics of fire development, as well as the uncertainty of fire fighting conditions. And event tree analysis was used to get the fire scenario which can lead to the failure of fire-proofing steel element. Combining with the temperature rise characteristics of fire-proofing steel element in this thermal environment, the failure judging flow of fire-proofing steel element?under sprinkler application was proposed. So the evaluation method of failure probability for fire-proofing steel element under sprinkler application based on"Equivalence"concept was established.In this paper, the main influence factor which impacted the development of fire, such as water density, sprinkler response time and the arriving time of fire brigade were analyzed. Fire control capability of sprinkler system is determined by local water density at fire source. However, water density distribution is non-uniform and uncertainty. The distribution of water density is affected by radical distance to the nozzle and the operating pressure of sprinkler system. In this paper, water density distribution characteristics was used to study the fire control capability of sprinkler, and the parametric model of water density distribution which contained the parameters of radical distance and operating pressure was established, based on the experimental data. The probability distribution of water density was obtained by considering the stochastic property of parameter in model. The effect of water density distribution characteristics on fire control capability was studied by referring the ?required critical water density for various class fire control using sprinkler and percent of effective fire control with number of sprinkler nozzles activated. Results indicated that the fire control capability was significantly affected by the probability distribution of water density. With the increase of radical distance, the occurrence probability of smaller water density increased and fire couldn't be controlled under some serious fire situations.Sprinkler response time is uncertainty. In this paper, based on the statistical analysis of simulation data of sprinkler response time, the parametric model of sprinkler response time which contained fire growth factor, radial distance and sprinkler response time index was established. The probability distribution of sprinkler response time was obtained by considering the stochastic property of fire growth factor, as well as radial distance. The results indicated that the probability distribution of sprinkler response time was significantly affected by fire growth factor and radial distance. With the increase of fire growth factor and the decrease of radial distance, the probability of the sprinkler response time in short period was increased. As the radial distance reduced, the impact of the sprinkler response time index on the distribution for sprinkler response time became smaller.Since the arriving time of fire brigade is uncertainty, the fire accidents in 2009 were collated and driving time of fire brigade was analyzed in this paper using SPSS statistical software. The results indicated that the arriving time of fire brigade had characteristics of probability distribution. And their effect on fire development was analyzed.Finally, the assessment method of failure probability for fire-proofing steel element under sprinkler application based on"Equivalence"concept was used to study the fire security of the steel elements with different fire coating thickness in a 3-storey 3-span continuous steel frame structure. And a series of cost-effective strategy for fire protection of steel elements were obtained.Such research can provide effective methods and tools for evaluating the steel elements fire safety in real environment and optimizing the strategy of steel fire prevention.