Research On Bending,torsion And Stability Properties Of Space Truss Structures With Triangular Section

Space truss with triangular section are widely used as crane jib.The calculation and analysis of this kind of complex beam system composed of many links often rely on largescale finite element analysis software,which generates a lot of economic costs,causing huge amount of time during structure selection,program comparison,performance estimation and initial decision-making procedures in the new product development process.In this paper,the structural layouts of such space truss is parameterized in order to study its overall performance.This work can greatly reduce the time and effort that designers spend on engineering design and verification on such space truss structures.In this paper,the bending,torsion and stability properties of space truss structures with triangle cross sections are studied respectively.The equivalent bending moment of inertia and the equivalent torsional stiffness formula of such structures are deduced,and two methods to calculate the critical axial force of tower jib consisting of such structures are proposed.After adequent verification with finite element models,the accuracy of the formulas and calculation methods are proved.In the second chapter,in order to study the bending performance of space truss structure with triangular section,the space truss structure is taken as a solid beam,and its equivalent bending moment of inertia is investigated.Firstly,the latreral displacement of spass truss under transverse force on the tip is discussed,considering 4 different layouts of space truss and different conditions regarding in-plane and out-of-plane bending;Then the equivalent bending moment of inertia is obtained by equaling lateral displacements of the tip of both space truss and the solid beam.Chapter 3 studies the torsional performance of space truss structure with triangular section by taking it as a solid circular shaft,and its equivalent torsional stiffness is examined.Firstly,the torsional angle of the tip of the space truss is investigated,considering 4 different layouts.Then the equivalent torsional stiffness is obtained using the equaling principle of same torsion angle.Chapter 4 studies the stability performance of space truss structure with triangular section by calculating its critical axial force.Firstly,the in-plane and out-of-plane buckling of space truss is discussed and it is found that the overall buckling of space truss is decided by its out-of-plane buckling condition.Then 2 methods of calculating the outof-plane buckling force are presented,in which the first uses the traditional Euler critical force formula by substituting the equivalent out-of-plane bending moment of inertia,and the second used the revised Euler critical force formula considering the shear effect caused by diagonal and transverse tubes by substituting the unit shear angle,which is obtained by investigating the relationship between out-of-plane lateral displacement of spass truss and standalone plane truss.Chapter 5 serves as the verification chapter of the above 3 chapters.The influence of geometric variables of the triangular section space truss is fully included.Results based on finite element models shows that the two formulas of equivalent bending moment of inertia and equivalent torsion stiffness,as well as the instability critical force derived in the above 3 chapters meets high accuracy,which means they are applicable in engineering practice.Furthermore,while the equivalent bending moment of inertia is derived only when concentrated force is applied on the truss end,it turns out to have high accuracy when distributed force or end-bending moment is applied.