Influence of bracings on the stability of a truss

This article analyses the stability of a three-dimensional reticulate steel truss composed of deformable bars, with the particular goal of studying the influence of bracings. The bars are assumed to be deformable by bending, axial forces, shearing forces and torsion. A computer program was developed to determine the critical loading of the structure by taking into account geometric non-linearity. The stiffness matrix technique is used to describe the structural response in three dimensions. Three-dimensional stiffness functions (stability functions) were developed to consider simultaneous bending effects, shearing force, axial force and torsion. Global instability is considered to have been achieved when a given loading introduces singularities in the global stiffness matrix. When the critical loading has been determined, it is possible to determine global instability parameters such as effective buckling coefficients. Truss examples are presented and compared with Ansys results to demonstrate the potential of the process.