Experiments and Modelling of Starred Angle Braces

A starred angle is a built-up shape composed of two angles joined intermittently by welded plates (stitch plates) at the heels, forming a cross-shaped section. Starred angles braces advantages include simple fabrication, easy installation on the frame, and easier clean up and maintenance. For these reasons, these braces are widely used in steel industrial construction in Chile. However, a number of these braces failed during the 2010 Maule earthquake in Chile either by local buckling, lateral torsional buckling, or connection fracture. These failures, although not yet completely explained, have made engineers steer away from the use of starred angles as braces. Six scaled specimens with the same cross section but different lengths were tested under cyclic loading of increasing amplitude. The failure modes varied depending on the slenderness of the specimen from flexural to flexural-torsional buckling. After several cycles of inelastic displacement, the specimens developed fracture in only one of the angle legs, maintaining significant tensile strength, but low residual compressive strength. No failure on the connections or stitch plates was observed. A numerical model developed by previous research for tubular and I shaped braces was adapted for starred angle braces and calibrated to represent the response of the braces, using the experimental data. This model can be used to study the performance of structural systems that include starred angle braces.