Stability behavior of T-shaped retrofitting cross bracings in existing transmission towers

To analyze the stability behavior of T-shaped retrofitting cross bracings, finite element models were developed and validated by full-scale experiments of cross bracings available in the literature. Effects of stress ratio, nominal slenderness ratio, width-to-thickness ratio, and yield strength on the failure mode and bearing capacity were considered for T-shaped retrofitting cross bracings without auxiliary members (TCB) and with auxiliary members (TCBA). Results show that the failure modes of T-shaped retrofitting cross bracings are out-of-plane bending of the entire brace. As the stress ratio decreases, the failure modes transition to the bending of the longer section of the brace. When the nominal slenderness ratio is below 160 for TCB, local buckling dominates and nominal slenderness ratio has few effects on the bearing capacity. Also, stress ratio has a minimal impact on bearing capacity when it is less than -0.2. In addition to above, bearing capacity is related to nominal slenderness ratio and stress ratio. A higher width-to-thickness ratio increases the nominal stability coefficient for TCB, but has a negligible effect on TCBA. Increasing yield strength can effectively enhance the bearing capacity of TCB when stress ratio is below 0, while yield strength has little impact in other conditions.