Cyclic Testing of Damaged 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 cyclic loading to failure after the completion of hybrid seismic testing. A uniform drift of 4% in both directions with a saw tooth displacement time history was imposed by actuators attached at each floor elevation. Four complete cycles were required to fracture all braces, and an additional cycle was performed to obtain the bare damaged frame's hysteretic response. The objective of this test was to characterize the degradation of inter-story strength and stiffness as the braces--the primary lateral force resisting system (LFRS)--accumulate damage and eventually fracture.

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.