Calculation And Analysis Of Dynamic Performance Of Fourth Grade Double-span Timber Frame With Damaged Column Foot

The wooden structure of ancient buildings is the epitome of China’s five thousand years of splendid culture.It is the precious wealth left to us by our ancestors,and is the evidence of the continuous inheritance of Chinese civilization.The wooden structure has been preserved to the present time and has suffered various degrees of damage.The study of the dynamic performance of the damaged wooden structure is of great significance to the protection of the wooden structure.This article uses ABAQUS numerical simulation software to establish a four-grade double-span timber frame model according to the detailed description of the size of each component in Song’s "Building Method",and conducts dynamic simulation tests on the model.It mainly includes the following research contents:（1）The simple harmonics of different frequencies and different peaks are applied to the bottom plate of the intact wooden frame.The results show that with the increase of the acceleration input peak,the acceleration attenuation of the column top of the intact double-span wooden frame becomes more and more obvious.The maximum horizontal displacement of the column top,the vertical displacement of the column foot and the stress of the tenon end gradually increased.The vertical displacement of the column foot and the horizontal displacement of the column top meet a linear relationship,and are not affected by the input frequency.The displacement of the tenon end under 100 gal and 150 gal and the horizontal displacement of the column top meet a similar linear relationship,and the slope is greater than 50 gal.The dynamic response of the side column and the center column under50 gal and 100 gal is similar,except that the positive displacement of the center column is larger than that of the side column,and the negative displacement of the center column is smaller than that of the side column.（2）The dynamic experiments were applied on wooden frames with different damage conditions and different damage heights at the bottom of the column.The results show that with the increase of the damage degree of the bottom of the column,the attenuation becomes more and more obvious compared with the acceleration of the top of the column.The increase in input peak value and input frequency will accelerate this attenuation.When the column base is damaged at 0.5E,the dynamic response is not much different from that of good wooden frame.With the elastic modulus of the column bottom changing,the column bottom still swings mainly.As the degree of damage increases,the maximum displacement in the positive direction gradually decreases,and the maximum displacement in the negative direction gradually increases.The curve of the vertical displacement of the column foot and the maximum stress can be fitted into a three-segment straight line,The slope of the first segment K1 is greater than the slope of the second segment k2 and the slope of the third segment k3.with the increase of the damage degree of the column foot,K1 gradually decreases.Under the same degree of damage to the column foot,as the frequency increases,K1 gradually increases.Under the same degree of damage,as the frequency increases,the maximum stress on the tenon end gradually decreases.At different frequencies,the greater the damage degree,the greater the maximum stress on the tenon end.Under different input frequencies,the displacement of the double-layer damage is smaller than that of the single-layer damage.The K value of double-layer damage is significantly smaller than that of single-layer damage.（3）The dynamic test of the wooden frame with different areas of the column bottom is carried out.The results show that as the area of the column foot cutting off,the acceleration at the top of the column is attenuated more obviously,and the peak acceleration of the top of the column is "filtered out" at high frequencies.The negative acceleration decays more.As the frequency increases,there is a significant phase difference between the column top and column bottom velocities,and there is also a phenomenon of peak filtering.With the increase in the area of the column foot cutting off,the positive displacement gradually increases,and the negative displacement gradually decreases,but both are less than the displacement of the intact column top.When different areas of the column foot are cut off,the maximum stress and the maximum vertical displacement of the column foot are reduced.At the same frequency,as the cross-sectional area of the column foot decreases,the slope of the column foot K1 gradually increases.The time when the stress of the tenon end reaches the maximum corresponds basically to the time when the maximum displacement in the negative direction is reached.