Study On Fire Protection Behavior For Tunnel Structures With Fireproof Boards

Fire is a significant hidden danger affecting urban highway tunnels’ safety,as the tunnel’s interior is generally semi-enclosed.Affected by fire,the tunnel interior heating rate is fast,the temperature should not spread,causing severe damage to its lining structure bearing capacity,will not only bring more significant economic losses,more likely to cause casualties.Improving the tunnel structure’s fire resistance and the tunnel fire’s overall stability is an important topic.First,the object of study is determined as a tunnel structure without protective measures for internal fire,and the finite unit method and hydrocarbon(HC)heating curve are used to calculate the tunnel secondary lining structure numerically.The tunnel lining structure’s surface is used as the reference point to analyze the tunnel lining’s overall temperature distribution law and the temperature change curve at different depths within the lining.The fire resistance limit and fire performance of the tunnel interior after fire protection measures were analyzed.The fire resistance effect’s effect was studied by changing the thickness of fireproofing panels and fireproofing coatings and the thermal parameters of the materials.Finally,each node’s displacement and stress on the steel connection are analyzed using a sequential coupling.(1)The temperature distribution law of the tunnel lining structure without protective measures is studied,and the values of temperature change at the same position in different fire periods and at various places in the same fire time period are analyzed and compared.The results show that with the increase of fire time,the temperature transfer depth in the tunnel structure increases,and the damage to the lining structure is increasing,and the temperature curve in the tunnel lining structure is decreasing in the form of inverse function with the increasing transfer depth.(2)Comparing the lining structure’s protective effect with a fireproof coating layer and without a protective layer,in the fire period of 0~14400s,the thickness of fireproof coating sprayed on the surface of the lining structure was varied equally to study its protective effect on tunnel lining.The coating thickness was divided into six groups,i.e.,0.5cm,1.0cm,1.5cm,2.0cm,2.5cm,3.0cm,and the lining without a protective layer.The temperature values of the structure at the reference point were compared.The results show that the thicker the fireproof coating layer,the greater the temperature drop,spraying thickness of 3.0cm fireproof coating layer corresponding to the temperature rise curve drop is the most obvious.(3)lining structure with fireproof board layer and no protection layer protection effect comparison,in 0 ~ 14400 s by fire time,equal difference value change the lining structure surface external fireproof board thickness to study its protective effect on the tunnel lining,the board thickness into seven groups that is 3.0cm,3.5cm,4.0cm,4.5cm,5.0cm,5.5cm,6.0cm and no protective layer of Lining structure at the reference point temperature values for comparison,the results show that the thicker the fireproof board layer,the more significant the temperature drop,a fireproof board layer thickness of 6.0cm corresponds to the most apparent rate of temperature rise curve drop.The fireproof effect of the same thickness of the fireproof board is better than the fireproof effect of spraying fireproof coating.(4)Using the control variable method to independently analyze the effect of specific heat capacity,density,and thermal conductivity of fireproof materials on the thermal insulation effect,the results show that increasing the specific heat capacity or density of fireproof materials has a small change in the temperature amplitude at the lining reference point and the effect is not apparent;reducing the thermal conductivity of fireproof materials has a large difference in the temperature amplitude at the lining reference point,and the product is pronounced.It shows that reducing the material’s thermal conductivity is more effective for improving the fire resistance of the lining structure and further shows that the thermal conductivity of the fireproof coating has a greater weight among the selected thermal parameters.(5)In order to make better use of the air layer its natural non-thermal conductor,steel connectors were used to connect the fireproof panel with the lining structure while leaving an air layer between them,and a reasonable value for the size of the steel connectors was determined based on the study of the effect of the thickness of the air layer on the fire resistance performance of the tunnel.The results show that the air layer effectively reduces the temperature conduction efficiency after hanging the fireproof board,and the actual thermal insulation efficiency is directly determined by changing the ratio of air layer to fireproof board thickness.The larger the ratio between the two,the more significant the actual thermal insulation efficiency,but the fundamental thermal insulation efficiency growth rate decreases with the increase of the balance.(6)The displacement and stress change law under the action of equivalent uniform load and temperature field,taking the partially arranged steel joint and fireproof board assembly as the research object,exploring the fire resistance and fire resistance limit of the body,using the sequential coupling method to equate the fireproof board layer into a uniform load applied to the steel joint for force analysis,obtaining the displacement and stress change law of each node on the steel joint with time,verifying The overall stability and the spacing values of the longitudinal and transverse steel joints and the size of the fireproof panel are given.