Research On Overall Mechanical Performance Of Assembled Truss Purlin Structural System

Assembled truss purlin has been widely used because of its high stiffness and high bearing capacity.However,there is short of experimental research of mechanic performance of assembled truss purlin at present in China.Assembled truss purlin is connected with roof profiled steel sheet to stress together by self tapping screws in practical engineering.But the study of the function of diaphragm effect of roof panels and the research of support's quantity to constrain purlin's stability out of plane is relatively lacking,and there is no mature or unified solution to all kinds of problems in engineering.Therefore,it is necessary to carry out systematic experimental study of assembled truss purlin to to ensure its application in engineering practice.The overall mechanical performance of assembled truss purlin proposed lately is studied in this paper,and the main contents are as follows:(1)To study the overall mechanical performance and stress mechanism of assembled truss purlin,20 specimens of 6m span purlins and 8 contrast groups are designed in the experiment scheme,and the research contents include four parts:(1)The effects the factors,such as height of purlins,quantity of support,different cross section of web members under gravity load,the node connection form,the function of diaphragm effect of roof panels and the space of self tapping screws,on the overall mechanical performance of purlins are studied;(2)The stress mechanism and mechanical performance of assembled truss purlin under gravity load and axial force are studied;(3)The effects of the change of height under the action of wind suction and the number of supports on the overall mechanical performance of purlins are studied.(4)The stress mechanism and mechanical performance of assembled truss purlin under the action of wind suction and axial force are studied.(2)In this paper,assembled truss purlin with span of 6m,height of 300 mm is studied by static performance test and the failure modes,failure characteristics and mechanical properties of purlin specimens with one and two support under gravity load are analyzed,through which the effects of number of support on failure modes and mechanical performance are obtained.That provides a useful reference for the following research.(3)The tested purlin specimens were numerical-simulation analyzed and optimized by using the finite element software ABAQUS and the results are in good agreement with the test results,which verifies the validity of the numerical simulation method;each truss purlin specimen under gravity load is numerical-simulation analyzed and optimized by a large number of optimization models and the effects of factors,such as the ratio of height to span,the form of the cross section of web members,the number of supports,the strength grade of steel and the skin effect of roof panel,on failure mode and mechanical properties of assembled truss purlin.The results show that the ratio of height to span of truss purlin has great effect on its bending performance and that effect should be considered in structural analysis and design process;the change of belly bar's section diameter under the same failure mode has on significant effect on the bearing capacity of purlin;the larger number of support and the larger out of plane stiffness of the purlin,the more difficult occurrence of upper chord plane's instability,with which the stable bearing capacity will be improved accordingly.To a certain extent,the strength grade improvement of steel can make flexural capacity improve;Roof profiled steel plate,with its significant diaphragm effect,has internal shear capacity and flexural capacity of the section,which can provide some of the lateral support and torsion constraint for purlin.With the decrease of self tapping screw spacing,upper chord compressed is difficult to lose out of plane stability,and the synergistic effect of purlin and roof panel become more obvious.Therefore,the bearing capacity of purlin also improves.(4)This paper also discussed the bearing capacity and stress mechanism and failure modes of assembled truss purlin under the action of wind suction.The results show that upper chord of truss purlin is pulled and the lower chord is pressed,therefore buckling instability of the lower chord is easy to occur.In engineering practice,support can be used to improve the overall stability of the structure and the ability of large span purlin against wind suction should be considered,because of the significant effect of purlin cross bracing and high-span ratio on the bearing capacity of purlin bending.(5)In this paper,the current computing methods about truss purlin are analyzed based on experimental study and numerical simulation analysis.Verified by numerical examples,some reasonable design ideas are put forward.These design ideas,coupled with construct measures for reference for designers,can make the assembly type truss widely popularized and applied.