Evidence collected for peer review of buckling-restrained braced frames in New Zealand

Abstract

Buckling-restrained braces (BRBs) form a bracing system that provides lateral strength and stiffness to a building. These systems have been shown to provide larger energy dissipation in severe earthquake events compared to concentrically and eccentrically braced frames (CBFs and EBFs). However, unlike CBFs and EBFs there is no guidance document or specific instructions in regulatory standards for the design of buckling-restrained braced frames (BRBFs) in New Zealand. This makes it difficult for structural engineers to be aware of all the strength and stability considerations required for the safe design of BRBFs. Currently, structural designs that include BRBFs require a peer-review to gain building compliance. The American standard ANSI/AISC 341-16 is the adopted document used in New Zealand for guidance in how to collect evidence showing a BRBF system will perform as intended. However, as ANSI/AISC 341-16 is not a governing document in New Zealand, instructions within the document are not enforced and can be made to fit within the constraints of a building project. By way of example, this paper presents the experimental test process and results acquired from pre-qualification testing of three different commercially available BRB architypes. Of the three BRB designs investigated, one failed prematurely due to global buckling. A manufacturing error was the likely cause of this premature failure. This failure highlights the need for strict quality control during fabrication. All remaining BRBs performed well, meeting the acceptance criteria set out in ANSI/AISC 341-16. Positive pre-qualification results meant the BRBs were installed in medium to high-rise buildings throughout New Zealand. The importance of sub-assemblage testing to assess the performance of a BRB and its frame components is also discussed. Finally, the capability of high fidelity modelling to supplemental physical testing is also presented.