Research On Seismic Damage Identification And State Assessment Method Of Ancient Wooden Building

In the long history,ancient wooden building were repeatedly damaged under the action of earthquakes,which resulted in cracking of components,pulling out of tenon,skewness of Dou-Gong,tilting and slipping of wood columns,damages of structural system and potential collapse risk.Based on the shaking table test for a scaled ancient wooden building model,finite element model analysis and theory derivation,the seismic damage evolution characteristics and inversion recognition of materials,components,mortise-tenon joint and sub-structure systems were studied in order to monitor and assess the damage of ancient buildings.A kind of overall structural state assessment method was established.The main research contents and results are as follows:?1?On the basis of the theory of wood damage,deterioration mechanism and influencing factors,the wood mechanical properties was tested,and vibration multiple frequency and frequency information of the hydrogen-containing group C-O,O-H N-H was collected by Fourier Transform Infrared spectroscopy?FT-IR?.Partial Least Squares was used to analyze the correlation between near-infrared spectral information and wood elastic modulus,and the identification relationship between spectral information of cracking wood damage and wood mechanical properties was established.The results showed that the elastic modulus of old building was lower than that of the new materials.With the increase of the degree of material damage at different positions of the old wooden members of ancient buildings,the attenuation of wood elastic modulus increased.The peaks of the absorption intensity of the original spectral mean spectra,including 1510-1912/cm^-1,1423-1428/cm^-1,1055-1058/cm^-11 and 615-619/cm^-1,were increased to different degrees.?2?12 rectangular wooden beams and 8 circular wooden columns with different positions and different depths of fan-shaped cracks were designed.And then the finite element models of columns and beams were established.Through the finite element analysis,the natural vibration frequency,curvature mode,modal strain energy and sensitivity coefficient were studied.The damage location and degree of members with longitudinal crack can be identified in the view of the structural damage first-order perturbation theory of elemental modal strain energy.?3?Based on the shaking table test and finite element model of ancient wooden building,the simplified mechanical model of the structure was built.In addition,the structural measurement matrix,observation matrix,state equation and measurement matrix were derived.The evolution law of the rotational stiffness of the mortise-tenon joint under the action of earthquake can be confirmed by the shaking table experiment,and static and dynamic cohesion method was used to establish the relationship between structural stiffness and joint rotational stiffness.Through the hammer test and simulation calculations,the displacement,velocity and acceleration response of the structural column layer and the bracket layer were obtained.Considering 5%horizontal noise interference,the MATLAB program was used to detect the rotational stiffness of the mortise-tenon joint by using Singular Value Decomposition Partial Least Squares?PLS-SVD?and Extended Kalman Filter?EKF?method.?4?Based on a two-dimensional simplified mechanical model of Dou-Gong and the motion equation of force-slip displacement and bending moment-angle,the measurement matrix,observation matrix,state equation and observation equation were derived.The ABAQUS was used to simulate the three-dimensional finite element model with the slanting angles of 0,2,4,and 5.The deformation,fundamental frequency and damping coefficient damage evolution characteristics of Dou-Gong layers under horizontal earthquakes and impulsing excitations were analyzed.Based on the priori value of the Dou-Gong slipping and rotating interlayer stiffness,the Dou-Gong slipping and rotating interlayer stiffness under 5%horizontal noise interference were identified.?5?According to the shaking table test for a hall-type ancient building with a scale of 1:3.52,the equivalent lateral stiffness,lateral displacement response damage evolution characteristics,and lateral displacement sensitivity to stiffness damage under different earthquakes and impulsing excitations were analyzed.By considering the simplified mechanical model of the column foot slip,the structural measurement matrix,observation matrix,state equation and measurement matrix were derived,and the equivalent lateral stiffness was quantitatively identified.The state observation equation and the damage identification method of considering the column foot slipping could be applied to the damage identification of ancient wooden buildings.?6?By fuzzy comprehensive evaluation theory,the damage evaluation coefficient vector of wood structure and its evaluation matrix,with considering the weight factor and membership influence of damage index,were established.Furthermore,a kind of classification standard and assessment method of ancient wooden building was proposed based on seismic damage.Based on the micro-vibration response tests and identification of each layer of Yingxian wooden tower structure,the current overall state of the wooden tower was evaluated,and the evaluation result can provide scientific basis for repairmen and reinforcement of ancient wooden building.