Ductile Fracture Simulation and Risk Quantification of Buckling-Restrained Braces under Earthquakes
Creators: name: Terashima, Masao
name: Deierlein, Gregory G.
Publisher: name: Stanford Digital Repository
Year: 2024
Subjects: earthquake engineering
structural engineering
buckling-restrained braces

description: Since their ﬁrst use in Japan in 1980s, Buckling-Restrained Braces (BRBs) have been widely implemented in steel-framed structures throughout the world. A BRB consists of a steel core enclosed by mortar and a steel casing tube. The steel core resists the axial loading applied to the BRB, while the mortar and casing tube prevent the steel core from globally buckling under compressive loading.

Since BRBs do not buckle under compressive loads, they display stable and nearly symmetric behavior in tensile and compressive excursions. Thanks to their superior ductility capacity, BRBs have been applied to variety of structures and conﬁgurations, such as diagonal braces (i.e. BRBFs), outriggers for high-rise buildings and energy dissipation fuses for rocking-frames. Since the safety of the structures with BRBs heavily relies on the ductility of BRBs, it is important to ensure that BRBs have suﬃcient ductility capacity as compared with the ductility demand.

The ductility capacity of BRBs is usually controlled by fracture of the steel core since BRBs are designed to avoid other failure modes (e.g. global buckling). Under earthquakes, BRBs will experience relatively small number of cyclic loadings (less than 100 cycles) with large deformation amplitudes, which may lead to failure by Ultra-Low Cyclic Fatigue (ULCF). Therefore, to fully understand BRB ductility capacity, evaluating the fracture of the steel core caused by ULCF is essential.

To date, most of the development and validation of BRB ductility has relied extensively on full-scale cyclic loading tests. This nearly exclusive reliance on empirical test data is due in part to the limitation of computational methods for evaluating fracture under inelastic cyclic loading.

Ductile fracture caused by ULCF has been studied for a few decades, especially after 1994 Northridge Earthquake and 1995 Kobe Earthquake, during which a number of structural steel com-ponents and joints fractured due to ULCF. Several ULCF criteria have been proposed and shown to successfully evaluate fracture caused by ULCF under a wide range of stress states. However, previous validations were mostly limited to cyclic loadings with relatively large amplitudes, during which specimens failed in less than 20 cycles. In addition, the loading histories used for the validation of these criteria were usually constant amplitude cyclic loadings or the combination of stepped constant amplitude cycles. Therefore, the applicability of the ULCF criteria under earthquake-induced random loadings has not yet been fully validated. Motivated by the limitations of existing computational methods for evaluating BRB capacity, this study develops, validates and applies a computational fracture simulation method using a local ULCF criterion, referred to as Stress-Weighted Damage Model (SWDM), through detailed FE simulations of both coupon-scale tests and full-scale BRB tests...