Research On The Mechanical Properties Of Wood-framed Shear Walls

Most of the rules on light wood structure house which are added to “Code for design oftimber structures” published in China in2003(GB5005-2003) come from the experimentalresults and standards of North America. Light wood structure house is still on a developingperiod in China, and the systematic research on light wood structure house has yet to be carriedout. The experimental research on mechanical properties of wood frame shear walls can providetheoretical and experimental basis for the popularization and standards of light wood structurehouse in China.This thesis is on experimental research into panel-wood frame nail joints and wood framenail joints.To study the effect of the upper part stiffness on mechanical properties of wood frameshear walls, the load spreader adopts three forms, which are flexible load spreader and rigidload spreader as well as new type of load spreader.Experiments are carried out on full size wood frame shear walls. The specimens aredivided into two groups. In the first group, eleven specimens are designed according to differentcombinations of the opening size, the upper story stiffness and the vertical load. In the secondgroup, three specimens are designed by using new load spreader. The monotonic load tests areconducted on each specimen, and cyclic load tests are conducted after the renovation ofwood-frames and the change of wallboard.The wood frame shear wall analysis model is set by using ANSYS. The actual wood shearwall is composed of the wood-frame and panel, which are connected by nails. The experimentalresults show that the load-bearing capacity of wood-frame is very small, and shearingdeformation of panel is also small owing to the large shearing stiffness on the plane of itself.The shear wall’s load-bearing capacity and deformation ability are mainly dependent on the nailconnection between the wood-frame and panel.The model produces nonlinear parameters of nail joints after the experiments onpanel-wood frame nail joints and wood frame nail joints, and mainly analyzes the load bearingof wood frame shear walls under one-way load.The thesis reaches the following conclusions through the above experimental study:The numerical model of nail joints which adapts to two-way panels of Chinese nails(panel-wood frame nail joints and wood frame nail joints) is set on the basis of exponentialmodel of Foschi. This model provides fundamental data for analyzing the structure of lightwood frame shear walls with finite element software.Increasing the stiffness of the upper part of the wall and imposing vertical load can improve the shearing strength of wood frame shear walls. The new type of load spreader doesnot restrain wood frame shear-wall specimens, which makes the shearing strength of thespecimens using new load spreader weaker than other specimens of the same configurations.The deformations that happen when wood frame shear walls are failure can be dividedinto the whole deformation and local deformation. The whole deformation happens within thewood frame when the stud is completely separated from bottom plate, which enlarges the lateraldeformation. The local deformation of the wood frame shear wall is caused by the slidingmovement of nail joints between wallboard and wood frame. Each piece of wallboard revolvesaround its central axis, and the wallboard becomes tilted rectangular.The flexible stiffness of specimen to resist lateral force by using the new type of loadspreader is smaller than the elastic stiffness by using flexible load spreader and rigid loadspreader specimens. The shearing strength and limit displacement by using the new type of loadspreader are both smaller than the shear strength and limit displacement by using flexible loadspreader and rigid load spreader specimens.That wood frame shear walls produce considerable force in the rigid load spreader underthe monotonic and cyclic load shows that the upper story wall can produce considerablereaction force to against the uplift caused by lateral load.The accurate imitation of nail joint nonlinear properties is the key to the finite elementcalculation of wood framed shear walls.The analysis of the finite element of wood-frame shear walls with the help of the ANSYSdemonstrates stress distribution and deformation of wood-frame shear walls, deepens theunderstanding of wood-frame shear walls’ resistance to lateral load, and provides basis forwood-frame shear wall design.