Research On The Effect Of The Damage Of Wood Knots On The Seismic Behavior Of Timber Beam

The wooden beam element is the main force-bearing components of the Chinese traditional wooden frame system buildings,and its performance directly affects the safety of the structure under the action of earthquakes.Especially in the region of strong earthquakes near-fault,the structure is severely damaged by significant vertical earthquakes,and the seismic performance of the wooden beam plays an important role in ensuring the structural safety.The wooden knots are natural defects of wood,which significantly affect the mechanical properties of the wooden elements.In order to study the influence law of wood knot defects on the seismic performance of the wooden beams,the study takes Douglas-fir as the object of research,and combines the pseudo-static testing and numerical simulation technology to explore the influence law of the geometry of wooden knots and the location of wooden knots on the hysteresis,energy consumption,stiffness degradation and other mechanical characteristics of the wooden beams.The main work includes the following parts:(1)To carry out the material properties test and design the test components.According to the relevant test standards,it measures the moisture content,density,tensile strength parallel to grain,compression strength parallel to grain and compressive strength perpendicular to grain,MOE and bending strength and other parameters of the specimen of Douglas-fir.The test results show that the destruction of compression strength parallel to grain and compressive strength perpendicular to grain are typical ductile damages,whereas the tensile strength parallel to grain is brittle damage.Based on the results of the research on the natural defects of wood,it adopts an artificial method to simulate the wooden knots.And it designs 11 groups of wooden beam members with different knot diameters and knot positions.(2)To conduct the pseudo-static testing on the test components.For wooden beam elements including those without wooden knots and with wooden knots in the span,it conducts the pseudo-static testing,and obtains the hysteresis curve,skeleton curve,stiffness degradation curve and equivalent viscous damping curve of each element.It analyzes the influence on the seismic performance of the beams by the diameter of the wooden knots and the location of the wooden knots.The results show that the larger the diameter of the wooden knots and the farther the distance from the neutral axis,the greater impact on the seismic performance of the wooden beam elements.(3)To establish a fine-grained finite element simulation.It uses the finite element method to establish the same numerical model as the test member,simulates its mechanical behavior under low circumferential reciprocating load,and compares it with the test results to verify the reliability of the simulation results.Regarding the boundary position of bending and shearing and the presence of wooden knots in the bending and shearing region of the beam,it simulates the mechanical behavior of the beam under the low circumferential reciprocating load.The results show that when the wooden knots are located at the boundary of bending and shearing area,the more the wooden knots deviate from the neutral axis,the greater the effect on the peak load of the beam;when the wooden knots are located in the bending and shearing area,the more the wooden knots deviate from the neutral axis,the less the effect on the peak load of the beam.It compares the skeleton curves of wooden beams when wooden knots of the same diameter are located in different positions,and the results show that when the wooden knots are located at the boundary of bending and shearing position,they have the greatest influence on the peak load of the beam elements;when the wooden knots are located in the middle of the span,they have the second greatest influence;when the wooden knots are located in the bending and shearing section,they have the least influence.