Full-scale cyclic testing of an ordinary concentrically-braced frame

Steel concentrically-braced frames (CBFs) are used extensively as lateral-force-resisting systems for low to mid-rise buildings in moderate seismic regions of the United States, such as the East Coast and Midwest. CBFs are economical because they are stiff, strong, and relatively simple to design, fabricate, and erect. Although good structural performance of CBFs for typical gravity and wind loading is well-established, there is little evidence-either from experimental research or field observation-related to CBF performance when subjected to design-basis earthquake demands. CBFs in moderate seismic regions are often not specifically detailed to achieve ductile inelastic response, so the effect of brittle limit states is largely unknown. As a result of this situation, a research project was initiated to investigate the seismic performance of CBFs in moderate seismic regions. This paper summarizes one aspect of the project: a full-scale cyclic test of a one-bay two-story Ordinary Concentrically Braced Frame-focusing on the sequence of limit states and associated system behavior. The test frame exhibited ductile response characterized by brace compression buckling and tension yielding up to nearly 1.5% frame drift and then experienced sudden strength loss due to weld fractures.