- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
The time-equivalence method is one way to determine the appropriate fire severity in buildings. One of the input parameters required is the fire load energy density (FLED) and in a deterministic design this is taken to be a fixed value. This paper illustrates the use of a simple Monte Carlo tool that accounts for statistical variations in car energy content as a function of vehicle size to determine probabilistic FLED values for a risk-based calculation approach to the design of car parking buildings. The paper briefly discusses FLED values for car parking buildings that can be found in the literature and results from the Monte Carlo tool suggest that 260 MJ/m2 could be used as an appropriate design value in lieu of using a probabilistic approach.
The paper demonstrates how a probabilistic approach to obtaining FLED values can be applied by bringing together a number of recent studies related to car parking buildings. The application of the Monte Carlo model allows for a future reassessment of FLED values for car parking buildings should there be new energy content measurements for cars or changes in the composition of a vehicle fleet. The approach could also be modified to account for the occupancy of car parking spaces as a function of the time of day. Since the change in FLED from the Monte Carlo tool is directly related to the static efficiency then deciding what is an appropriate value becomes important. However the linear relationship from the probabilistic model means results can be easily applied to any static efficiency that is deemed suitable. In addition the ratio of the median FLED to the 80%, 90% and 95% fractile values allows fractile values to be estimated for a given static efficiency. Therefore a simple calculation method is presented in the paper to estimate the median FLED and associated percentile values for a given static efficiency in lieu of performing a Monte Carlo analysis. Using a static efficiency of 25 m2 /space, a 100% parking space occupancy, the distribution of curb weights obtained by Anderson and Bell  and the vehicle energy content distributions from Tohir and Spearpoint , the 80% fractile FLED is 260 MJ/m2 (rounded up to the nearest 10 MJ/m2 ). It is interesting to compare the FLED values from the Monte Carlo model to values quoted in the literature given this work has used energy content values from vehicles subsequent to the 1980s and also adjusts for the apparent higher percentage of heavier vehicles in modern fleets. Thomas  gives an average FLED value for ‘Garaging, maintenance and exploitation of vehicles’ as 190 MJ/m2 and 200 MJ/m2 for ‘Parking buildings’ which are of the order of 20% less than median values obtained in this study. However the method proposed by Thomas to obtain 80% fractile values means values of 270 MJ/m2 for ‘Garaging, maintenance and exploitation of vehicles’ and 250–300 MJ/m2 for ‘Parking buildings’ are comparable with the 260 MJ/m2 value suggested in this study. Using a time-equivalence calculation for the structural fire design of car parking buildings may not always be the only approach that should be considered and the effects of travelling fires and/or severe localised fire in the vicinity of structural elements may also need to be investigated.