Effect of axial forces on the performance of links in eccentrically braced frames

The damage to an eccentrically braced frame due to a major earthquake is designed to be confined to a highly ductile link. The link acts as a safety valve for the structure. The post-elastic behaviour of the link and its performance up to failure has been evaluated using a finite element model, with the link subjected to a cyclic loading. The results obtained from the finite element model were verified against test data. The model was used to evaluate the effect of axial forces on the performance of the link. High axial normal forces may be developed in the link as a result of the particular configuration of the eccentrically braced frame.It was found that it is possible to develop a simple yet effective finite element model for the link. Comparison between the analytical model predictions and the test results indicated good agreement. When the link is subjected to axial forces, deterioration in both the load-carrying capacity and ductility were observed. The adverse effects of axial forces on the link performance were found to be most pronounced for link lengths close to the value of the critical shear link length limit.