Investigation Of Fire Spread Characteristics And Prediction Model Of Building U-shaped Facade Insulation Layer

With the rapid development of urbanization in China,U-shaped structures are increasingly used in the design of building facades to pursue the requirements of light and appearance beautification of buildings.At the same time,to meet the demand of energy saving of buildings,organic insulation materials are also more widely used in the field of building exterior insulation.However,due to the special structure of the U-shaped facade,once the insulation layer is ignited in a fire,the stack-like effect will make the fire burning more intense and accelerate the spread of the fire,causing great difficulties to escape and rescue.In the actual fire scenario,downstream fire spreads faster and more dangerously because the fire spreads in the same direction as the external airflow.Therefore,it is of great significance to study the downstream fire spreading behavior of U-shaped structures.In this paper,the validity of the small-size experimental study was verified by the full-size experiment,and the effects of the structural dimensions of the U-shaped structure（backwall length W,sidewall length L and height H）on thev_f,ΔT_max and q’’’_maxwere investigated by the small-size experiment,and their relationships with the structural dimensions were derived as a function of the structural dimensions.In addition,the dimensionless global structure factor:αH/（?）A,was proposed to synthesize and characterize the effect of the structural dimensions of the U-shaped structure on the characteristics of the fire spread behavior.The effects of the limitation of air entrainment in the side or bottom of u-shaped structures and flame interaction on the downstream fire spread behavior of U-shaped structures are studied.It is found that the lateral air entrainment restriction increases thev_f,ΔT_max andq’’’_max,the reason is that the lateral air entrainment restriction increases the induced airflow velocity,increases its elongating effect on flame and promoting effect on fire spread,and the side wall also reduces heat loss to both sides;the presence of flame interaction between the backwall flame and the side wall flame increases thev_f,ΔT_maxand q’’’_max;the bottom air entrainment restriction reduces thev_f,increasesΔT_max andq’’’_max,the reason is that the bottom roll restriction will limit the loss of heat from the bottom,the temperature and heat flow is increased;but at the same time,the bottom roll restriction reduces the elongation effect of the induced airflow on the flame and the promotion effect on fire spread,so thev_f is reduced.In this paper,by modifying the previous theoretical model,introducing the influence of the structure height and considering the influence of the bottom air entrainment restriction and flame interaction on the fire spread rate,a fire spread rate prediction model that can predict the actual building U-shaped facade was established.The research results of this paper can help to predict the development of fire in polyurethane insulation of building U-shaped facades.It can provide reference for the assessment of fire risk and guidance for the fire safety design of U-shaped structural facade insulation systems.