Seismic performance of buckling restrained braced frames with and without manufacturing defects subjected to combined in-plane and out-of-plane loading (2021)
Type of ContentTheses / Dissertations
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
Buckling restrained braces (BRBs) and BRB Frames (BRBFs) have become widely used in New Zealand and around the world. However, concerns have been raised about the behaviour of BRBs for various reasons.
Firstly, explicit considerations to account for all possible failure modes are not specified in current standards. For example, design equations to prevent restrainer bulging are not provided. Also, design equations to determine restrainer capacity, they are depend on the buckling wavelength and contact force, are inconsistent. Better information on this would be useful for BRB design before proof testing is conducted. This stud y describes a method to improve this. The wavelength is estimated using a deformation-based approach and the contact force is obtained using an energy approach. Equations to estimate the restrainer capacity are then provided.
Secondly, manufacturing defects may significantly affect performance. Experimental tests with defective as well as good quality BRBs are therefore conducted and compared. The primary defects considered are large voids in the core transition zone, resulting in steel core concentrated buckling, and missing axial gap, resulting in large axial compressive force. Relevant recommendations are provided.
Last but not least, according to current standard s, experimental testing is generally only required to be conducted in-plane. However, earthquakes generally cause both in-plane and out-of-plane frame displacements. In this study, the large scale BRBFs are subjected to bidirectional horizontal loading. It is shown that for well designed and detailed braces, the compression strength may be similar to the tension strength during in-plane loading. In contrast, for similar braces subjected to bi-directional loading, the compression strength may be up to 1.3 times the compression strength. Such an increase needs to be considered in the design. It is also recommended to chamfer the steel core transition zone edges to reduce the additional resistance and provide sufficient insert length to prevent restrainer end failure.
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