| As an ancient building material,wood is an excellent renewable material compared with common building materials such as steel and concrete.It has the advantages of low density,high strength,beautiful texture,easy processing,superior seismic performance and etc.However,due to its nature of flammability,people are skeptical about the fire resistance of timber structures,which has led to the slow development of multi-rise timber structures for a long time.Foreign construction experience shows that cross laminated timber(CLT)structure is the main structural form of the current multi-story timber structure.As an important vertical force transmission member,the mechanical properties of CLT wall under fire and after fire exposure are related to whether the vertical force transmission path is interrupted and whether the structure collapses.Considering that there has been no relevant specifications and standards for CLT fire resistance design in China,it is imperative to study the fire resistance performance of CLT walls in order to promote the CLT structure in China.In this dissertation,the CLT wall was taken as the research object,and the axial compression test under ambient environment,standard fire test and residual bearing capacity test after fire exposure were carried out successively.Based on the test,finite element simulation and theoretical analysis were carried out.The main research contents are divided into the following parts:(1)The research results of domestic and foreign scholars and research institutions on the fire resistance performance of CLT wall are summarized,including charring speed,fire resistance and the failure mechanism of the speciment.(2)The Abaqus user material subroutine UMAT,which is suitable for the constitutive relationship of wood at ambient temperature and after fire exposure,was compiled.The correctness of UMAT writing was verified by some example tests,which show that the UMAT can effectively simulate the the residual bearing capacity of wood components under these situations.(3)The three-layer and five-layer CLT walls were used as research objects,and the axial compression test of CLT walls under ambient environment and after fire exposure were carried out.The results show that the wall is transformed from the axial compression at normal temperature to the eccentric compression after fire exposure,and the failure mode is instability failure.(4)The finite element analysis was carried out with the CLT wall as the object of investigation.Based on the transient thermal analysis methoud,UMAT and Riks method,the temperature field distribution of the specimen during combustion,the ultimate bearing capacity of the static load test after fire exposure,the loaddisplacement curve and other mechanical properties were analyzed.Compared with the test results,the finite element evaluation of the residual bearing capacity of the CLT wall after fire is achieved.5)Combined with the experimental conclusions and related research results at home and abroad,shear deformation,initial geometric defects,the internal temperature field distribution of the specimen and the deterioration of the mechanical properties of the wood after high temperature were considered,the residual bearing capacity of the CLT wall after fire was predicted using theoretical formula. |
