Analysis Of The Effect Of Aging On Mechanical Behavior Of Ancient Timber Structural Members

As an indispensable historical and cultural heritage in the history of architecture in China,the ancient timber buildings have a very high artistic,historical and cultural value.However,the aging phenomenon universally exists in the existing ancient timber buildings because of its own material defects and the long-term exposure to the natural environment in the process of service,and the aging is an important factor in the decrease of the bearing capacity of ancient timber buildings.Therefore,it is of great significance to research the effect on mechanical behavior of ancient timber structural members caused by aging for the protection and repair of heritage buildings.(1)Based on the mechanical characteristics of timber beam and timber column in the timber buildings,the degradation model of bending capacity of aging timber beam and the degradation model of compressive bearing capacity of aging timber column were deduced by using the way of combining the equivalent cross section method with the empirical formula of the aging metamorphic layer thickness.And the above two models were used to predict the bearing capacity degradation of timber beams and timber columns of an ancient wood structure.On the basis of this,the effect of strength reduction coefficient of aging wood material on the degradation curve of bearing capacity was studied.The results show that the material strength reduction coefficient of the aging part of the timber members is bigger,and the decreasing trend of the bearing capacity of the timber members is more serious,especially the aging part of the complete loss of strength of the timber members of the carrying capacity degradation of the most significant.Therefore,it is very important to accurately determine the aging degree of the timber members when predicting the residual resistance of the ancient building wood components.(2)The numerical simulation of axial monotone loading of aging timber column is carried out by ABAQUS finite element program.The simulation results are compared with the experimental results,and the reliability of ABAQUS simulated timber column is verified.On the basis of this,the parameters of the aging timber column are analyzed,and the mechanical behavior of the timber column under the axial load are analyzed according to the simulation results.The calculation formula of bearing capacity reduction coefficient of the timber column considering the aging effect is put forward.The simulation results show that the effect of aging on the compressive bearing capacity of the timber column is linearly related to the uniformity of aging,and is the quadratic polynomial relationship with the aging depth.The deeper the aging depth and the greater the aging uniformity,the lower the bearing capacity.The effect of aging on the compressive bearing capacity of the timber column is very small when the aging depth is not more than 5mm and the aging uniformity is not greater than 0.25,so in the actual project can be ignored.(3)The numerical simulation of the three-point monotonous loading of the aging timber beam model is carried out by ABAQUS finite element program.The simulation results are compared with the experimental results,and the reliability of ABAQUS simulated timber beam is verified.On the basis of this,the parameters of the aging timber beam are analyzed,and the bending behavior of the timber beam under the influence of the aging effect is analyzed according to the simulation results.The calculation formula of bending capacity reduction coefficient of the timber beam considering the aging effect is put forward.The simulation results show that the effect of aging on the bending capacity of the timber beam is linearly related to the uniformity of aging,and is the quadratic polynomial relationship with the aging depth.The deeper the aging depth and the greater the aging uniformity,the lower the bending capacity.The effect of aging on the bending capacity of the timber beam is very small when the aging depth is not more than 5mm,so in the actual project can be ignored.In addition,The changes of bending capacity of timber beam are not consistent when the different part of the cross-section occurred in the same degree of aging.The specific change rule is: the bending capacity decreases most when aging occurs at the top,the reduction of bearing capacity is secondary when the aging occurs on both sides,and aging occurs at the bottom with minimal reduction.