| High-rise office buildings below 50 m are an important part of high-rise buildings and an important part of a city.As an important place for people to work and live,the stairwell is the main escape channel when a fire occurs.In the stairwell of high-rise office buildings below50 m,natural smoke protection methods are mostly used,and the wind direction and wind speed of the environmental wind will affect the natural smoke protection effect of the stairwell,especially when the windows of the stairwell are all open.In this paper,combined with the "Liaoning Natural Science Foundation Project(Project No.20180550336)",a12-story office building with a building height of 48 m is used as the physical model for this simulation.Taking the staircase as the research object,all the windows of the staircase,the windows of the fire source layer in the front room,the fire source layer and the front room evacuation door near the fire source layer are all opened,a total of 288 sets of fire scenes are set,and the FDS fire simulation software is used to perform the numerical simulation research.The simulation study obtains the influence of different wind direction,wind speed,and fire source power of environmental wind on the dangerous arrival time.The research results show that:(1)The various wind directions of the environmental wind have a great impact on the natural smoke protection effect of the stairwells of high-rise office buildings.With the change of the wind direction,the time required for smoke entry in the stairwells and the front rooms of the fire source floor,the arrival time of the visibility critical value,the arrival time of the dangerous temperature will also change accordingly,which fully shows that each wind direction has a significant impact on the natural smoke protection of the stairwell.In the future research in this field,directions of the environmental wind should be considered as important influencing factors.(2)Under the same wind speed,the greater the power of the fire source,the shorter the time required for smoke entry in the front chamber.The time required for each wind direction to reach the dangerous temperature is shortened with the increase of the power of the fire source.Therefore,in daily precautions,attention should be paid to the safe storage of items with high fire source power.When a fire occurs,ways should be found in time to reduce the fire source power of the fire site and the surrounding environment.(3)Under the same fire source power condition,compared to when there is no wind,the wind speed delays the arrival time of most of the dangerous temperatures in the wind direction.Therefore,it can be explained that the wind speed has a certain obstructive effect on the arrival time of the dangerous temperature.When the wind speed and fire source power are the same,the arrival time of the dangerous temperature will also change with the change of the wind direction,indicating that the wind direction has a significant influence on the arrival time of the dangerous temperature.(4)According to the research results of this article,combined with the "Technical standards for smoke management systems in buildings"(GB51251-2017)(hereinafter referred to as "smoke label"),it can be concluded that the height of high-rise office buildings is less than 50 m,the stairwell under natural smoke protection and the environmental wind speed is5～10m/s.Under the conditions,when the wind direction is southeast-135°,northwest135°,south-southeast-112.5°,east-southeast-157.5°,all the windows of stairwell and the fire source layer are open,all evacuation doors on the fire source floor and the front room adjacent to the fire source floor are opened.The four indicators of the maximum allowable concentration of smoke in the stairwell,temperature,visibility,and CO concentration are all within the safety standard range.When a fire occurs on the first floor,it is the most conducive to natural smoke protection in stairwells.When the wind direction is west-0°,northeast45°,and north90°,all the windows of the stairwell are opened,the evacuation door of the front room is opened,and the four indicators of the maximum allowable concentration of smoke in the stairwell,temperature,visibility,and CO concentration are all in the safety standard range.When a fire occurs on the middle floor,it is most conducive to natural smoke protection in stairwells.When the wind direction is west-0°,west-southwest-22.5°,north-northwest112.5°,west-northwest157.5 °,northeast45 °,north-northeast67.5 °,southwest-45 °,south-southwest-67.5°,northwest135°,north90°,the stairwell windows are all opened,and the second high-rise front room evacuation door is opened,and the four indicators of the stairwell smoke limit allowable concentration,temperature,visibility,and CO concentration are within the safety standard range.When a fire occurs on the second high-rise,it is most conducive to natural smoke protection in stairwells.(5)Based on the prevailing wind direction and wind speed in Dalian and the above research results in this paper,it is concluded that when the height of high-rise office buildings in Dalian is less than 50 m,if the natural smoke protection system is used in the stairwell,in the planning and design of the building,from the perspective of building fire protection,it is recommended to place the stairwell in the direction of due east,due west,southeast or northwest.This will ensure that when a fire occurs,most of the four indicators will be within the scope of safety standards to ensure that the stairwell is naturally smoke protection.And he system is in an effective state,which is conducive to the safe evacuation and rescue of personnel. |
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