Seismic performance of eccentrically braced frames designed to AISC341 and EC8 specifications

© 2020 Institution of Structural EngineersIn the United States, steel eccentrically braced frames (EBFs) are designed according to AISC341 Specification while in Europe EC8 provisions are used. The European provisions were developed mostly based on the research works conducted in the US. While EBF design recommendations in AISC341 and EC8 have similarities, marked differences exist in the amount of lateral force reduction and distribution of member over-strength among the stories. In addition, the effect of link over-strength on non-dissipative members is treated differently in the two specifications. A study has been undertaken to evaluate the performance of EBFs designed according to AISC341 and EC8. Pursuant to this goal, EBF archetype buildings with 3, 6, and 9 stories were designed using US and European provisions taking into account different force reduction factors. The archetype buildings were subjected to 44 far-field ground motions at the maximum considered earthquake level as recommended by FEMA P695. Nonlinear time history analyses were conducted by OpenSees analysis platform to obtain the link rotation angle, residual frame drift and column axial forces. The results showed that using larger force reduction factors and disregarding the distribution of member over-strength among stories result in large residual frame drifts and non-uniform link rotation angles along the height of the building. Considering a force reduction factor of 5 and imposing a limit on link over-strength among the stories were found to improve the performance considerably. Design recommendations were developed to enhance the performance of EBFs by unifying the rules given in AISC341 and EC8. The study was complemented by investigating the behavior of EBFs subjected to near-field ground motions with pulse. The results showed that near-field ground motions with pulse produce much higher link rotation angles when compared with the demands produced by far-field ground motions