Research On Physical And Mechanical Properties And Damage Detection Of Wood Structures

As one of the most commonly used building materials,wood is widely used in residential and public buildings at home and abroad.It has become a research hot spot for experts and scholars from various countries because of its renewable,light weight and high strength,easy processing,and environmentally friendly advantages.In this paper,based on the existing research,high-temperature tests and impact tests were conducted on wooden columns.The high-temperature tests include the physical properties of wooden columns after high temperature,the mechanical properties of wooden columns after high temperature and the damage detection of wooden columns after high temperature.The main contents are as follows.(1)The moisture content change,color change and mass loss of the wood columns were studied by high-temperature test.With an increase in temperature and constant temperature time,the moisture content of the wood columns showed a decreasing trend,and the mass loss of the wood columns showed an increasing trend.Compared with the constant temperature time,the temperature had a more significant effect on the moisture content and mass loss rate of the wood column,and the decline in moisture content and mass loss rate of round wood columns was generally faster than that of square wood columns.After high temperatures,the color change of the square wood column and round wood column was similar.With an increase in the temperature,the color of the wood column gradually changed from light brown to dark brown and even carbon black,and there were many small cracks on the surface.(2)Compression failure tests were conducted on wooden columns after high temperatures.The results showed that high temperature changed the failure mode of the wood column from shear failure to split failure and bottom compression failure.In addition,the high temperature increased the ductility of the square wood column,but the effect on the ductility of the round timber column was not significant.With an increase in the temperature and constant temperature time,the ultimate bearing capacity and ultimate strain value of the wood column decrease gradually.Compared with the constant temperature time,the influence of temperature on the ultimate bearing capacity of the wood column was more significant.The decrease of the ultimate bearing capacity of a round wood column was much greater than that of the square wood column,and the deformation resistance of the corner area of a square wood column was better than that of the center area.(3)Damage detection tests were conducted on the wooden column after high temperature.The results showed that the change of constant temperature time has less effect on the ultrasonic velocity of the wooden column at the same temperature.With an increase in the temperature,the ultrasonic velocity of the wood column decreased and the damage degree increased,indicating that the temperature had a more obvious effect on the ultrasonic velocity of the wood column.The ultrasonic wave velocity of the round wood column and square wood column was very close,indicating that the influence of changing the section form on the ultrasonic wave velocity of the wood column was limited.There was a high correlation between the relative wave velocity and damage degree to evaluate the performance of the wood column after high temperature,and the fitting value was in good agreement with the test value,indicating that it can accurately reflect the high-temperature damage degree of the wood column.Through regression analysis,the regression equations of relative wave velocity and damage degree after high temperature and ultimate bearing capacity damage rate of wooden columns with different temperatures and constant temperature times were established.(4)Transverse impact tests were conducted on wooden columns.The results showed that the impact process can be divided into three stages: initial contact between the specimen and falling ball,maximum deformation of the specimen and static stage.The overall deformation of the specimen is shown as bending deformation caused by tension,and the crack is firstly produced at the bottom of the specimen,then rapidly develops at the side and upward.With the impact position from the middle of the span to the support,the corresponding deflection gradually became smaller,indicating that the middle of the span is the most unfavorable impact position,but changing the impact position had a limited effect on the peak impact force and impact duration.