Experimental Study On The Fire Resistance Of Crosslaminated Timber (CLT) Floor

Compared with steel and concrete,wood is a green,renewable material that has advantages of low density,high strength,good elasticity,beautiful texture,and easy processing.It is widely used in many fields.In terms of mechanical properties,wood has high tensile,flexural,and compressive strengths,and exhibits good plasticity in bending and compression resistance.The new released code(Technical Standard for MultiStory and High Rise Timber Buildings)provides strong support for high-altitude timber buildings in China,and expands the application market for wood structures in certain districts with lower population.According to statistics,in recent years,the occurrence of building fires in China has increased,which is extremely harmful,causing massive property losses and casualties.As one of the mainstream structural materials used in multi-story high-rise wood structures,CLT slabs also face severe fire issues.Some foreign scholars have studied theoretically and experimentally on the fire resistance performance of CLT slabs.However,the domestic research on this part is still limited,and there is no fire protection design method and specification for CLT slabs.In light of the above,it is of great significance to study the fire resistance of CLT slabs.In this thesis,the fire behavior of three-layer and five-layer CLT slabs are studied.The fire test based on ISO834 standard temperature curve and the thermal-mechanical coupling analysis in fire based on ABAQUS are carried out.The main research contents are divided into the following parts:(1)Research results of other scholars on the fire resistance of CLT slabs are summarized,including the charring mechanism,charring rate,and fire resistance.(2)Finite Element Analysis software ABAQUS is hired using the temperature and mechanical sequential coupling analysis method to simulate and analyze through comparing the test results with the references’ CLT fire resistance test.The cohesive elements are used to simulate the adhesive in the CLT slabs.The calculation results verify the effectiveness of the modeling method based on the cohesive elements.(3)Three and five-layer CLT slabs were used as test objects,and the ultimate bearing capacity of the CLT slabs and the fire-resistance tests at different load ratio were performed.The results show that the threelayer CLT slab shows good ductility at lower load ratio,and the fire resistance of three-layer CLT slab with high load ratio drops significantly.The five-layer CLT slab load ratio has a relatively small effect on the fire resistance.Reducing the load ratio of the specimen and changing the number of layers can effectively increase the fire resistance of the CLT slabs.(4)The finite element analysis was conducted on the CLT slabs.The distribution and response of the internal force under the normal temperature were analyzed.The temperature distribution,structural response and internal force change under elevated temperature were considered.(5)Combining domestic and foreign wood structure design codes,this thesis proposed methods for fireresistance design of CLT slabs under bearing load,and use “Reduced Section Methods” and “Simplified Calculation Methods” that do not consider the contribution of transverse layers to capacity.It is applicable to determine the value of zero strength layer of CLT slabs and calculation method of the fire resistance of CLT slab under fire conditions.