Research On Wood Dynamic Mechanical Property Based On SHPB Test And Under Impact Behavior Of Wooden Beam

There are many wooden structures in the south of China.These structures are not only subjected to quasi-static loads,but also inevitably subjected to some dynamic impact loads.In daily life,there are natural disasters such as torrential rain and earthquake,which are easy to cause rock slippage and debris flow,lead to impact loading on wooden structures and even damage the structure to varying degrees.However,at present,there are few studies on the dynamic mechanical properties of wood.In this paper,dynamic mechanical characteristics based on Split Hopkinson Pressure Bar(SHPB)Test and impact performance of wooden beams base on Drop Hammer Test are studied,focusing on two kinds of wood commonly used in residential houses in southern China,Merbau and Chinese Fir.It has important theoretical significance and social value for the theoretical perfection of wooden structure,the exploration of the dynamic behavior of the wooden structures under dynamic impact,and the safety insurance of wooden structures.The main research contents are as follows:(1)For wooden property,static and dynamic properties of Merbau and Chinese Fir are studied.Specimens with different impact pressures(0.10 MPa,0.15 MPa,0.20 MPa,0.25 MPa,0.30MPa)and different material directions(Longitudinal,Radial,Tangential)are designed for SHPB Test.The test results show that the strain rates of Merbau and Chinese Fir are similar under the same impact pressure and the same material direction,when the impact pressure is 0.10 MPa to 0.30 MPa.At high strain rate,the dynamic compressive strength of most wood specimens is higher than that under static condition.The dynamic compressive strength of Chinese Fir specimen is about 2 to 3 times that of Merbau specimen under the same material direction and same impact pressure,while under the same kind of wood and same impact pressure,DIF of the radial specimen and the tangential specimen is about 3 to 4 times that of longitudinal specimen.The dynamic increase factor(DIF)curve of compressive strength of Merbau and Chinese Fir is fitted in three material directions.The fitted curve,which has small overall error and high agreement,is consistent with the development trend of the test value.(2)For wooden member,static and dynamic performance of Merbau beam and Chinese Fir beam is studied.This paper designs a total of 10 Merbau beams with different impact heights(velocities)and different drop weights(including radial cross section and tangential cross section),designs a total of 10 Chinese Fir beams with different impact heights(velocities)and different cross-sectional dimensions(including vertical direction and horizontal direction).Furthermore,the monotonic static load test is carried out on two kinds of wooden beams respectively with a total of 4 beams as compared beams.The test results show that most of specimens of Merbau beam are mainly sheared damage along the grain,while Chinese Fir beam specimens are mostly cracked or broken by bending failure.The peak impact force of wooden beam is higher than the ultimate bearing capacity under static load mostly.The peak impact force increases with the increase of height.For Merbau beam,under the condition of approximate kinetic energy the peak impact force fluctuates up and down in a certain range by increasing the drop hammer mass and reducing the impact height.For Chinese Fir beam,under the condition of same height(0.4m),the peak impact force increases with the increase of crosssectional height.The shape of the impact force time history curve in test includes first peak stage(main peak stage),platform stage,and descending stage in Merbau beam,while the curve shape includes first peak stage,main peak stage,and secondary peak stage in Chinese Fir beam.(3)With reference to the study of the dynamic mechanical properties of Merbau and Chinese Fir materials,the comparative analysis of Merbau beam and Chinese Fir beam between monotone static load test and Drop Hammer Test.The mechanical behavior of wooden beam under monotone static load and drop hammer impact is discussed and analyzed.Four methods are suggested to analyze and calculate the ultimate bearing capacity of wooden beam under concentrated load.For Merbau beam,the theoretical calculated values of method 2 and method 4 are close to the experimental values,and the beams are mainly damaged by shearing along the grain.For Chinese fir beam,the theoretical calculated values of method 1 and method 4 are close to the experimental values,and the beams are mainly subjected to bending failure.Method 4,considering strain rate effect,is reasonable and accurate to estimate the peak impact force of Merbau beams and Chinese fir beams in Drop Hammer Test,and can better predict the ultimate bearing capacity of wooden beam.