Seismic design of buckling-restrained brace welded end connection considering frame action effects: Theoretical, numerical and practical approaches

The negative effect of in-plane frame action on the performance of buckling-restrained brace (BRB) end connections was confirmed experimentally in the authors' prior work. The triggering moment induced by rigid-body rotation of BRB ends, and the amplified moment resulting from bending and semi-rigid effects of the connections, were found to be responsible for premature in-plane buckling of the BRB end connections. These effects, however, have not yet been incorporated into the current design procedure. This study aims to further discuss the amplified moment from theoretical, numerical and practical perspectives. As a companion research, the frame action effects of non-moment braced frame and their influences on the cruciform BRB end section using full penetration groove weld connection to the gusset plate are discussed. An analytical model is first proposed for derivation of the BRB end moments considering the concerned frame action effects. Theoretical analysis is conducted to highlight the key parameters affecting the amplified moment factor, an index for evaluating the contribution of the amplified moment. To avoid direct prediction of the complex semi-rigid effects between BRB end and gusset plate, an equivalent rigidity concept is proposed to combine the contributions of both flexural and rotational rigidities of the entire connection. Simple formulae for estimation of the equivalent rigidity and the effective length factor of the connection are determined by finite element analysis. The theoretical BRB end moments using such an equivalent approach are validated experimentally and numerically. A practical approach to simply estimation of the amplified moment factor is also presented. Seismic design procedure for the BRB welded end connection considering the concerned effects are summarized finally.