Experimental Study On The Fire Performance Of Half-lapped Joints In Cross-laminated Timber

Since the 21 st century,human society has paid more attention to sustainable development.The concept of green and environmental protection has continuously penetrated into the construction industry.The wooden structure built with renewable wood has also begun to attract everyone’s attention.Cross laminated timber(CLT)’s orthogonal assembly billet makes it possible to make full use of small-sized sawn timber,which has the advantages of economy and good dimensional stability.At the same time,the characteristics of the orthogonal arrangement of CLT sawn timber make the component have good mechanical properties in both directions,reducing the impact of the large difference between the mechanical properties of the horizontal and parallel grains of the wood,and making CLT board a middle-high-rise wooden structure Engineering wood products favored by architecture.As a typical CLT joints form,the CLT half-lapped joints is also an important part of the CLT structure.Its fire resistance under fire has important research significance.At present,there is little research on the fire resistance of CLT half-lapped joints,and further research in this field is also imperative.In this dissertation the CLT half-lapped joints is taken as the research object,and the CLT and selftapping screw material properties tests under ambient environment,the axial tensile ultimate bearing capacity under ambient environment,the standard fire test,and the residual tensile bearing capacity of the axial center after fire exposure are carried out successively.Experiment,and carry out finite element simulation analysis on the basis of the experiment,and finally carry out theoretical research on the ultimate bearing capacity and residual bearing capacity of CLT half-lapped joints.The main research contents of this article are as follows:(1)Summarize the research results of domestic and foreign scholars on the fire resistance performance of CLT components,mainly covering the charring rate,fire resistance limit and residual bearing capacity of components.Then combined with the research status of CLT joints under ambient environment,the significance and content of the research on the fire resistance of CLT half-lapped joints are proposed.(2)Carry out CLT material performance tests,including density measurement,moisture content measurement,grain compressive test and rolling shear test;carry out self-tapping screw material performance tests,including tensile strength test,bending yield strength test and pull-out resistance Strength test.At the same time,the mechanical and thermal properties of wood and self-tapping screws are given with reference to domestic and foreign specifications and related research results.(3)Taking the CLT half-lapped joints with two specifications of self-tapping screw diameters of 6mm and 8mm as the research object,the axial tensile test at room temperature was first carried out,and then the standard of change with or without fire protection measures and fire time was used as the standard In the fire test,the axial tensile residual bearing capacity after the fire was finally tested to study the axial tensile ultimate bearing capacity,carbonization rate,temperature distribution and residual axial bearing capacity of the CLT half-lapped joints.The results show that at room temperature,the self-tapping screws of the two specifications of CLT half-lapped joints under axial tension have double hinge yielding,and the joints have tearing along the grains at the lap joints.There is a certain difference between the charring law of the wood and the wood at the lap joint and the carbonization law of the pure wood section.The charring depth of the specimen containing the gypsum board protection is significantly smaller than that of the unprotected specimen;The force decreases in different degrees according to different fire time,and the self-tapping screw yields,and the half-layer laminate at the lap joint tears along the grain.(4)For the experiments carried out,use ABAQUS software for finite element simulation.Through standard fire test simulation,the temperature distribution law and charring of CLT half-lapped joints can be seen intuitively;through the simulation of the axial tensile ultimate bearing capacity under ambient environment and the simulation of the axial tensile residual bearing capacity after fire exposure,the joints are obtained Failure shape diagram,stress distribution diagram and load-displacement curve diagram,etc.Finally,the finite element simulation results are compared with the test results to realize the finite element evaluation of the fire resistance of the CLT half-lapped joints.(5)Refer to relevant domestic and foreign specifications,and conduct theoretical analysis based on the experiments and finite element research results of this article.Considering the effect of the orthogonal assembly characteristics of the CLT laminate on the bearing capacity,combined with the remaining section method,the ultimate bearing capacity formula under the axial tension of the CLT half-lapped joints and the residual bearing capacity formula under axial tension after fire exposure.