Elasto-plastic Damage Constitutive Model Of Wood And Nonlinear Analysis Of Key Parts Of Traditional Timber Structures

Chinese traditional timber structures are important carriers of some aspects of Chinese culture.From the perspective of structural engineering,the construction philosophy contained in traditional Chinese timber structures has important significance for modern structural designing and innovation.In recent years,the seismic performance of such structures has been studied in depth,but there are still some deficiencies:(1)the commonly used nonlinear constitutive model of wood was established within the perfect elastio-plastic or hardening elastic-plastic theoretical frameworks,which was able to model the monotonic loading test in each orthogonal direction,but could not truly reflect the coupling mechanism of plasticity and damage during unloading;(2)in the stress analysis of traditional timber structures,the influence of material aging,decay,local damage of key components and joints,and local inclination and displacement of the whole structures on the mechanical properties was not fully considered.This thesis is devoted to the development of a nonlinear constitutive model of wood and analyze the damage mechanisms of the key parts of traditional timber structures.The main research contents are listed as follows:(1)The establishment of elasto-plastic damage constitutive model of wood.The repeated loading and unloading tests were used to study the realistic plastic behavior,the stiffness change during loading/unloading and the coupling mechanism between plastic and damage process.Combined with the monotonic loading tests,the typical nonlinear characteristics of wood were described completely.Based on the continuum damage mechanics,an orthotropic elasto-plastic damage constitutive model was established to reflect the plasticity and damage evolution of wood.(2)The nonlinear behavior of plasticity and damage of wood under complex loading conditions were revealed.The numerical algorithm of the elasto-plastic damage constitutive model of wood was developed;the UMAT subroutine was compiled and planted into ABAQUS;and the correctness of the model was verified by uniaxial tests.Furthermore,the thesis analyzed the plastic and damage behavior of wood caused by the loading reverse and the coupling of normal stress and shear stress.(3)The key components of traditional timber structures and the damage evolution under the influence of different initial damage extents were revealed.Based on the established elasto-plastic damage constitutive model,the finite element model of traditional timber structure was established and the nonlinear analysis was carried out.Compared with the existing model,it can reflect the damage initiation and evolution characteristics.Considering the influence of local decay on beams and columns,and the influence of lateral loosening and tenon pulling-out damage on mortise joints,related damage evolution laws under different damage degrees was revealed.(4)The nonlinear analysis model of traditional timber frame was established and the influence of typical component damage was considered.The nonlinear finite element models of traditional timber frame considering the damage of local decay of wood beam and wood column,lateral clearance between mortises and tenons were established,and the influence of different damage degrees on the hysteretic performance was analyzed.The static calculation method of single span wood frame considering the semi-rigid of traditional timber structure,the semi-rigid of column foot and the geometric nonlinear of wood frame was established.The elasto-plastic damage constitutive model established in this thesis can reflect the plasticity and damage nonlinearity of wood.Based on this,the relevant analysis results of key components of traditional timber structures can provide good technical support for the scientific protection of traditional timber structures in China.