Stability assumptions in numerical modeling of cold-formed steel-framed buildings under seismic loading

In the U.S., current seismic provisions limit the height of cold-formed steel (CFS) framing in buildings to six-stories. Utilizing component-level laboratory tests, with strength levels higher than current code-available values, a ten-story CFS-framed building archetype was professionally designed to explore the potential for taller buildings and address the increasing need for resilient, efficient, non-combustible urban residential housing. This year, a series of shake-table tests on a slice of the ten-story archetype building will be conducted at the UC San Diego 6-DOF Large High-Performance Outdoor Shake Table Facility. This archetype building capstone experimental program is part of the NSF-funded collaborative research program: Seismic Resiliency of Repetitively Framed Mid-Rise Cold-Formed Steel Buildings (CFS-NHERI). In preparation for the experimental program, a high-fidelity finite element model of the building has been developed in OpenSeesPy. The model uses a combination of phenomenological and mechanically-driven elements, enriched with findings from prior component and fastening test programs. The nature in which stability is handled in the model has an important impact on the predicted response. This paper presents the assumptions inherent in the model when considering the large variety of geometric nonlinearity that exists, including: buckling of steel sheets; local, distortional, and global buckling of CFS members and story-level P-Delta effects. Predicted response under earthquake loading is presented and compared with results generated by a design-level model. It is intended that the findings of this research can help guide the development of strategies for incorporating stability limits into the seismic modeling of CFS-framed buildings, thereby enhancing the analysis, resilience, and application of these structures.

Proceedings of the Annual Stability Conference Structural Stability Research Council 2025, Louisville, KY.