Research On Mechanical Property Degradation Of Damaged Wooden Beam

As the traditional architectural and structural type in ancient China,ancient timber structure has a very high historical,cultural and social value.However,after years of baptism,coupled with the erosion of the natural environment,the ancient timber structure has appeared damage varying different degrees,and the situation is worsening with time growth.So it is very necessary to evaluate the structural safety and to undertake repairing and reinforcement measures.The wooden frame formed by the connection of beams and pillars with mortise-tenon joints is the main load-bearing system of the ancient timber structure,And the load-bearing system of wooden frame has good energy dissipation characteristics.As the main bending member of the load-bearing system,the mechanical properties of the wooden beam directly affect the mechanical performance of the whole wooden structure,and the damage of the wooden beam usually leads to the collapse of the whole wooden structure.Therefore,it is very important to study the degradation of mechanical properties of damaged wooden beams to evaluate and repair the existing ancient timber structure.Based on the platform of finite element analysis software of ABAQUS,a threedimensional solid finite element model(FEM)of wooden beam is established in this paper,which can achieve the anisotropy and different mechanical properties for tension and compression of wood by calling UMAT material constitutive subroutine.The rationality and applicability of the numerical calculation model are analyzed and verified from three levels.Firstly,it is proved that the finite element model can reflect the different mechanical properties for compression and tension of wood by extractingthe stress-strain relationship between the tension zone and the compression zone.Secondly,the elastic-plastic theory is used to analyze the flexural capacity of wood beams,which is in good agreement with the finite element calculation results.Thirdly,through the test and analysis of the bending behavior of the small specimen of the wooden beams,the mechanical properties of the test results such as the deflection,strain,load-displacement curve and ultimate bending capacity of the wood beam are compared with the finite element simulation results,and the results are in good agreement.Based on the verified finite element model(FEM)of wooden beam,effect laws of the factors on the flexural behavior of the wooden beam,such as depth,position and length of damaged area were analyzed by single parameter analysis.On the basis of this,the relative height,the relative length and the position coefficient of the damaged zone are defined and the reduction coefficient of the bearing capacity of the damaged wooden beam was introduced by regression analysis,and then a method for evaluating the remaining carrying capacity of damaged wooden beams with considering the reduction coefficient is proposed.