The seismic response of moment frame building considering the gravity connection type

Past studies investigated the seismic response of steel moment frame buildings, consideringthe contribution of the gravity framing system. Although limited, these studies noted the po-tential role of the gravity framing system in preventing/delaying story mechanism formationand mitigating story drifts along the building height. In these studies, the numerical behaviorof the gravity framing connections was either parametrically represented or calibrated basedon limited test data for specific connection types. The present study evaluates the influence ofgravity framing considering various semi-rigid connection types, including shear tab, flushendplate, and header plate connections. Recently developed accurate phenomenological mod-els are employed for that purpose. These models can capture the various degradation mecha-nisms and ductility of semi-rigid connections under cyclic loading as a function of theirgeometry. A 4-story archetype building is investigated under static pushover and nonlinearresponse history analyses. The effect of the gravity connection type -and the gravity system asa whole- on the stiffness, strength, and ductility is quantified. The study shows that the effectof the gravity framing system strongly depends on the employed gravity connection. It is con-cluded that flush endplates are the most favorable in reducing drifts and residual drift ratio.These benefits can be realized without imposing further construction costs. The results high-light the potential of incorporating the gravity framing effect as part of the design procedureas well as analysis procedures, where ignoring them can be highly conservative.