Concentrically Braced Frame Provisions in AISC 342: Evaluation and Retrofit

Concentrically braced frames (CBFs) have been used as seismic lateral force resisting systems for many years, but current seismic design provisions were not instituted until about 1995. Hence many older braced frames in seismic regions do not meet current seismic design requirements. The seismic rehabilitation design standard, ASCE 41, is nominally intended to address the seismic performance and retrofit of these older buildings. However, the ASCE 41 provisions for braced frames were developed in early 1990’s, which both preceded development of current AISC 341 for SCBFs and current research on older and retrofitted CBFs. The AISC 342 standard has been approved and is being further updated to replace ASCE 41 provisions for seismic evaluation and retrofit of steel buildings. AISC 342 will update all steel provisions, but it particularly updates provisions for braced frames, since there has been extensive research on the seismic performance of braced frames in the past 20 years. This session will show the background to these AISC 342 braced frame provisions, the changes made in the provisions, the consequences of the changes, and an example application of the new provisions.

1. Brief review of current SCBF capacity-based design requirements including historical development of current braced frame design provisions
2. Review of common deficiencies of braced frames designed before AISC 341.
3. Discussion of experimental research results for frames with these deficiencies
4. Development of improved retrofit provisions to address these deficiencies
5. Braced frame modeling provisions adopted by AISC 342
6. Example application