Seismic design of multi - story cold - formed steel buildings : the CFS - NEES archetype building

Lightweight cold-formed steel (CFS) framing is an effective building solution for low and mid-rise structures. However, systems level response and component contributions as well as their interactions such as those from lateral-load resisting systems, floor diaphragms, studs to track connections, etc., are not fully understood. Existing building codes for the CFS frame buildings are based solely on the stiffness of the lateral-load resisting frames and do not explicitly incorporate systems response. This paper presents the first-phase of a multi-year project aimed at generating knowledge and tools needed to increase the seismic safety of CFS frame buildings. The first phase of the study focuses on the design, instrumentation plan, and preliminary analysis of full-scale two-story CFS frame buildings that are tested on shake tables at University at Buffalo NEES Facility in the second phase. Design of the two-story CFS buildings incorporates a “state of the practice” ledger framing system that attaches floor and roof joists to the inside flanges of the load-bearing studs via a combination of track and clip angles. The instrumentation plan for the shake table tests is developed to capture both systems and component level response of the buildings. The preliminary analysis includes development of new modeling capabilities that incorporate cross-section limit states (local and distortional buckling) into frame analysis engines such as OpenSees to enable more accurate incremental dynamic analysis. This paper provides detailed design of a prototype CFS frame building and instrumentation plan for the shake table tests at Buffalo.