Application Of Fast-growth Wood In Light Wood Frame Construction

The wooden structure buildings are still the ideal living and working place in people's mind because of its comfort.The fast-growing wood can not be directly used as structural component due to the defects in its nature.This paper begins with the modification of fast-growing china-fir and poplar,and applies them to the Triangular roof and fabricated lightweight wood frame building.Impregnation treatment on fast-growing china-fir and poplar with phenol-formaldehyde resin of low molecular weight and test the tensile strength parallel to grain,compression strength parallel to grain,bending modulus of elasticity,bending strength of primal wood and soaked wood.Experimental studies on bending resistance properties of glued laminated timber beams and the axially load bearing capacity of glued laminated timber columns were carried out.Tests shown that:(1)The mechanical property of soaked wood are better than primal wood,the tensile strength parallel to grain was increased by 14%,the compression strength parallel to grain was increased by 10%,the bending modulus of elasticity was increased by 13%,the bending strength was increased by 11%.At the same time,the standard deviation of the mechanical properties of the soaked wood is reduced accordingly,which is beneficial to the application of China fir in structural members.(2)The mechanical properties of glued laminated wood has been improved after the surface with impregnated reinforced wood,the bending strength was increased by 14%,the bending modulus of elasticity was increased by 7%,in the test,the bending failure of the glued laminated timber beams is at two loaded points,the beams were fracture destruction and adhesive layer destruction,the failure mode in accordance with the standard.(3)The glued laminated timber columns have obvious bending and the unstable failure occurred during the later loading period,the ultimate load of 4 columns are larger than the theoretical value,it illustrated that the stability coefficient of the specification is still conservative.Apply the modified fast-growing to the Triangular roof engineering,firstly,checking the strength and deformation of the fast-growing poplar purlin and the modified fast-growing poplar triangle truss according to the code for design of timber structures,secondly,the drawing software NX5 UG is used to draw the wooden truss and the finite element analysis was carried out,the analysis results shown:(1)The purlines are adopted with fast-growing poplar and the calculated strength and stiffness meet the requirements of the current specification.(2)The truss chord and web members are adopted with modified fast-growing poplar and the calculated strength and stiffness meet the requirements of the current specification.(3)The maximum displacement of the timber truss in the chord members of windward side,the maximum immunity is 3.6mm is less than the allowable value 5.744 mm.These determine the maximum elongation of the material is in the limit range and the truss structure and section size are meet the requirements according to the second strength theory.(4)The strength and stiffness of timber truss members are meet the requirements of the code for design of timber structures,the fast-growing poplar and the modified fast-growing poplar can be used in the Triangular roof engineering.Apply the modified fast-growing to light wood frame,the calculation method of the internal force of the shear wall of the light wood frame structure in the horizontal wind load is studied.Using finite element software ANSYS to simulate the effect of eccentric torque on housing when symmetrical and asymmetric structure of shear wall under horizontal wind load at the same time.Based on the finite element analysis of specific house,the stress and deformation of the house in the horizontal wind load are studied.(1)When the barycenter of the shear wall group is far from the centroids of the house and under the action of strong wind load,will produce large horizontal force in the shear wall,the longer the distance is,the greater the force will be.(2)Under the action of axial horizontal wind load,the wall parallel to the direction of the wind plays a major role in shearing,the magnitude of the shear force in the wall is in proportion to the stiffness of the shear wall,the shear stress distribution in the wall increase with the decrease of the wind load action surface.Only the wall which under the directly action of wind load and perpendicular to the wind direction can bear the shearing force,and the shear resistance of other walls can be negligible.(3)Under the action of eccentric horizontal wind load,torsional deflection occurred in the house,the regularity of torsional stress distribution is the farther from the barycenter of the wall,the stress is larger,the regularity of torsional stress distribution in the same wall is the torsional stress at two ends is very small,the torsional stress at the middle points increases and tends to be equal,the stress grown exponentially compared to no torque effect.(4)Under the action of wind load,the light wood frame house is in a state of shear and torsion,and the failure of the wall is different from the normal shear failure.Internal parallel wind walls,walls of direct action of wind load,walls far from the housing center are the weak links.It is necessary to check the shear strength of these walls.(5)According to the local frequency of wind direction,in the interior of the structure set more walls parallel to the direction of wind(longitudinal wall)and longitudinal wall should minimize openings to avoid shear failure of wall shear wall.Thirdly,make sure that the floor has enough stiffness to ensure transfer effective horizontal load.Lastly,as far as possible to retain wall between the top of the hole and the floor,the shear walls embody completeness and play a role in bearing and transferring load.(6)When designing the light wood frame houses,we should try to make the wall arrangement regular and center of gravity and centroid coincident.Multi layout walls perpendicular to the main frequency of wind direction in the area of length of the 1/3 wall with parallel main frequency wind direction wall enhance the overall stability of shear wall.In this paper,we build frame with small column span house made of modified fast-growth Chinese fir.First,it was designed and analyzed through the finite element analysis.We discussed the wood frame structure's force and displacement response under wind load;and the structure internal force under the effect of wind load are also analyzed in the paper when the transverse wall was joined in the downwind direction.The influence of the lateral wall on the overall structural stiffness is discussed,and the conclusions are as followed:(1)The light wood frame structure's stiffness of the wind direction under wind load is improved significantly when the the side wall along the wind load's direction was joined in,and also has a significant resistance to the displacement of the vertical wind direction.This is due to the addition of the side wall which makes the structure more tend to a whole,the side wall and the wood framework as a whole,so the structural stiffness of the wind and the lateral stiffness increased significantly.(2)The stress of downwind and crosswind direction under the action of wind load is lower when the downwind side is joined in.The structure form resist the force as a whole,the structure integrity is better when it was introduced into.(3)The suction of the vertical side wall has little effect on the displacement of the wind direction of the wood frame structure,which verifies the correctness of the load simulation wind load without considering the lateral horizontal force.(4)The horizontal stress of the wood frame is slightly larger than that of the horizontal force under the horizontal force of the vertical wall,but the stress result is obviously smaller than the strength of the material.The deformation capacity and stress state of the house was tested when the lateral load was applied to.The detrimental situation is that the load was applied to the house as a point load which is equal to the maximum uniform wind load.Under this case,the maximum deformation of the two floor is only 10.3mm,the maximum deformation of the roof is only 5.8mm.The deformation can be recovered in a short time after unloading,so it is elastic deformation.And the layer displacement of the house is small.(1)Test results showed that the lateral deformation is in elastic range when assembly of light wood structure buildings is under horizontal load and the lateral displacement of the maximum value is less than H/500 which is provided in the code for design of timber structures(GB 5005-2003);(2)Due to the lower and upper layer of the vertical component of the building,the steel connection piece is installed on the spot,and the joint rigidity is insufficient,so that the whole distribution and the transferring process of the house are flexible mode;(3)The lateral wall plays a major role in resisting lateral displacement under lateral loads;(4)The houses had a little torsional deformation because the site where the lateral load applied to is not coincident with the house's center position;(5)In the course of the experiment,there was no crack or damage in the main stress components.As a result,it is feasible to use the fast growing Chinese fir to build the assembly light beam structure,which can meet the requirement of the normal use of the house.