Seismic Hybrid Experimental Testing of Three-Story Special Concentrically Braced Steel Frame with Improved Column Design

A 1/3 scale three-story special concentrically braced frame (3SCBF) was subjected to two back-to-back maximum considered earthquake (MCE) ground motions performed quasi-statically using hybrid simulation to investigate the effects of increased column section design on inter-story drift demand distribution. The specimen frame was designed and detailed according to the AISC Steel Construction Manual and Seismic Provisions. Increased column sections allow lateral forces to redistribute along the height of the frame as strength and stiffness degrade due to damage in the braces. This prevents the formation of a soft-story collapse mechanism commonly observed in modern SCBF designs under MCE loading.

All tributary gravity framing, including mass and gravity loads, was modeled as a single column in the Open System for Earthquake Engineering (OpenSees, 2012). This model was subjected to ground motions selected from the SAC ground motion bins for the LA site. Target displacement values were imposed by actuators attached to the physical specimen at each floor elevation, and measured forces in the actuators were communicated back to the analytical model for calculation of the next target displacement. The physical substructure and laboratory hardware were integrated with the analytical substructure through the Open Source Framework for Experimental Setup and Control (OpenFresco, 2008).