Research On Mechanical Performance Of Light Poplar Laminated Veneer Lumber Truss Roof

Poplar Laminated Veneer Lumber(hereinafter referred to as poplar LVL),which is derived from abundant fast-growing poplars and has good application prospects for constructional engineering,is an engineering material with high reliability and low variability.However,there are few studies on LVL and its application in China.For the purpose of expanding the application scenarios of poplar LVL in Chinese wood-structure buildings,this paper conducts an experimental study on the mechanical behaviors of poplar LVL and on the mechanical behaviors of a roof structure with the light-weight poplar LVL truss member used as the load-bearing member,and also discusses truss spacings and truss slope on structural performance.The major research work and achievements of this paper are as follows:(1)The experiments on the compression,bending,shearing and pulling of poplar LVL test specimens in all directions are carried out,and the failure modes thereof are analyzed.Through the above experiments,the material parameters such as bending strength,compression strength and tensile strength of poplar LVL are obtained,and the constitutive relationship of the material is revealed,which provided the basis for parameter selection in the subsequent finite element analytical calculation model.(2)The experimental study of poplar LVL dimension lumber and Oriented Strand Board(OSB)panel nail connection is carried out,and two types of the load tests under uniaxial tensile with 20 specimens for each type(one type is in the direction that the load is parallel to the glue layer,and the other type is in the direction that the load is perpendicular to glue layer)are carried out.Through experiments,it is found that poplar LVL dimension lumber has high nail-holding ability,and it has good connection performance with nail-fastened node.Based on the commonly-used Foschi model,the calculation formula for the nail connections in the two directions of poplar LVL dimension lumber is established.(3)The static loading experiments of four groups of light poplar LVL truss roofs with different truss spacings and truss gradients are carried out,the failure modes and failure mechanisms of the light poplar LVL truss roofs are explored,the whole loading process of light poplar LVL truss roofs is systematically analyzed,and the ultimate bearing capacity,the load distribution mechanism under various working conditions,and the change rule of load-displacement are studied.The experiment results show that:the failure modes of single members in the roof structure system are all brittle failure,but the structural system makes the unbroken truss in the roof structure still have a certain load redundancy by the means of load redistribution;different from the loaded trusses designed according to the principle of subordinate area in the existing specifications,the parallel trusses of the roof structure system are arranged according to the different positions of the loaded trusses,and only about 16%to 46%of the load on the loaded truss is accepted by other trusses that are arranged in parallel;and the light poplar LVL truss roof has small displacement change,large overall rigidity,and good performance under vertical force.(4)Through the theoretical analysis,the numerical calculation model for the connection characteristics of poplar LVL dimension lumber and OSB panel nail connection is obtained,the calculation method of the effect coefficient of the roof structure system,the calculation method of the load distribution,and the calculation method of the ultimate bearing capacity under the single-component failure mode are determined.(5)Based on ABAQUS finite element software,a finite element model is established for four groups of light poplar LVL truss roofs,and corresponding numerical simulation is carried out.The simulation results of the roof structure system coincide well with the experiment results,and the simulation results of the load distribution also coincide roughly with the experiment results.Therefore,the correctness of the finite element model is verified,and an analytical method is proposed for the study of the structural performance of the light truss roof that is prepared by poplar LVL dimension lumber.