Experimental Study On Fire Resistance And Mechanical Properties Of Wood Structural Component

Wood is not uniform,and easy to be corroded and moth-eaten,resulting in the weakening of the mechanical strength of wood structural members,especially under the state of fire,easy to burn,load force decline,and eventually lead to the instability of the building collapse.In this paper,the main load-bearing components in timber structure buildings are taken as the research object.Through fire resistance test and compressive bending test,the change law of their fire resistance characteristics and mechanical properties after combustion is studied,so as to master the fire resistance characteristics of components and provide theoretical and technical support for the fire protection design of timber structure buildings.The main research conclusions are as follows:(1)Experimental study on fire resistance of wood structure.According to the common tree species and the wood used in construction in Guizhou,this paper selected local Chinese fir to carry out the fire resistance test of the wood structure with the section size of 100mm*100mm and 120mm*120mm respectively.The temperature changes of wood components under different combustion times were analyzed.The results show that the closer to the flame center,the faster the heating rate.For wood components with different combustion time and the same section,the shorter the combustion time,the faster the heating rate,the larger the section size,and the significantly improved fire resistance.The flame spreads faster in the height direction than in the width direction.(2)Experimental study on carbon rate of wood components.The carbonization rate of the member after fire resistance test is studied.The results show that,at the same measuring point,no matter the horizontal carbonization rate,vertical carbonization rate or average carbonization rate,the carbonization rate of the member with the section size of 100*100mm is greater than that of the section size of120*120mm.The maximum vertical carbonization rate is 1.1mm/min,and the maximum horizontal carbonization rate is 0.35mm/min.The vertical carbonization rate is greater than the horizontal carbonization rate.With the increase of fire time,the carbonization advances to the interior of the section,and the carbonization velocity decreases.Because the corners are subjected to heat transfer in two directions,the lower corners of the components turn into arcs after carbonization,and the carbonization depth here is significantly greater than other positions.(3)Experimental study on compressive properties of wood components.The results show that the compressive strength of the components with different section sizes is different,and the larger the section size,the greater the compressive strength.In terms of residual carrying capacity,the smaller the section size,the smaller the compressive strength coefficient is.The average compressive strength coefficient of the member with the section size of 100*100 is 0.958,and the average compressive strength coefficient of the member with the section size of 120*120 is 0.973.The coefficient of variation of the small section size is relatively large,reaching 2.92%.The correlation coefficient R~2after fitting is almost greater than 0.99.(4)Experimental study on flexural properties of wood components.The flexural property of the burned component is studied.In the aspect of flexural strength,through the curve of load and displacement,it is obtained that the displacement of the wood component increases with the increasing of fire time.As the size of the section increases,the load borne by the member increases.In terms of residual bearing capacity,the smaller the section size is,the smaller the bending strength coefficient is.The average bending strength coefficient of members with section size of 100*100 is0.562,and that of members with section size of 120*120 is 0.896.The coefficient of variation of small section size is larger,reaching 4.27%.