Seismic Performance and Design of Steel Multi-Tiered Buckling-Restrained Braced Frames

• Author / Creator

  Bani, Moad A

• Steel Multi-Tiered Buckling-Restrained Braced Frames (MT-BRBFs) are commonly used in
  moderate-to-high seismic regions of Canada and United States as the lateral-load resisting systems
  of tall single-storey buildings, such as sports facilities, airplane hangars, and warehouses, as well as
  in tall stories of multi-storey buildings. MT-BRBFs consist of two or more bracing panels stacked
  vertically between column out-of-plane support locations. A multi-tiered configuration is utilized
  when the use of a single bracing panel within a storey height is not practical nor economical.
  Although MT-BRBFs enjoy robust cyclic performance and large ductility capacity of their BucklingRestrained Braces (BRBs), their seismic response differs from standard multi-storey BRBFs.
  Namely, lateral deformation under seismic loads may not evenly distribute along the frame height in
  MT-BRBFs as the tiers with tension-acting BRBs tend to deform more than those with compressionacting BRBs. This response may induce in-plane flexural demands on the braced frame columns,
  which may lead to plastic hinge formation or even column instability in the presence of a large axial
  force induced due to gravity loading and BRB capacity design forces. Furthermore, uneven
  distribution of frame lateral deformation can impose excessive strain demands on the BRBs yielding
  in tension, which can potentially cause fracture in the BRB core. In Canada, there are no design
  guidelines for MT-BRBFs in the 2019 Canadian steel design standard, CSA S16-19. Special design
  requirements were introduced for MT-BRBFs in the 2016 edition of AISC Seismic Provisions in the
  U.S. to improve column stability response and control tier drift demands. However, very limited
  supporting research data is available to verify these requirements. Given the extensive application of
  MT-BRBFs, often times in critical structures, there is an urgent need to develop a better
  understanding of their seismic response, estimate seismic force and deformation demands on their members, evaluate the current U.S. seismic design provisions and propose potential improvements,
  and develop an enhanced design method in the framework of CSA S16.
  This M.Sc. research project aims to evaluate the seismic response of steel MT-BRBFs designed to
  the Canadian and U.S. provisions and propose enhanced analysis and design methods to better
  represent MT-BRBF seismic response with the focus on column force and BRB strain demands. A
  combination of mechanics principles, structural analysis techniques, numerical simulation and
  experimental testing is used to achieve these objectives. A full-scale test program is conducted on a
  two-tiered BRBF to verify experimentally the behaviour of MT-BRBFs under seismic loading. The
  test frame is part of a prototype tall single-storey building located in Seattle, WA (AISC 341-10
  design) or in Vancouver, BC (CSA S16 design). The results show that frame lateral deformation is
  unevenly distributed between the tiers and that the columns experienced significant in-plane bending
  due to this response. Moreover, large deformation demands develop in the BRBs, but no low-cycle
  fatigue fracture was observed under the applied loads. The results of the experiment also confirmed
  the need for an improved seismic design method for MT-BRBFs. A fibre-based numerical model of
  MT-BRBF is then developed and used to perform an extensive nonlinear response history analysis
  on a wider range of frames. The analysis results confirm that frame inelastic deformation tends to
  concentrate in the tier(s) undergoing tension yielding as they exhibited relatively lower post-yield
  stiffnesses and storey shear resistances than the tier(s) undergoing compression yielding. This lateral
  deformation pattern induces significant in-plane bending on the columns resulting in yielding or
  column buckling in some cases and causes excessive deformations in BRBs. A set of analysis and
  design methods is proposed in the framework of Canadian and U.S. seismic provisions. The proposed
  methods predict column moment demands and BRB strain with sufficient accuracy resulting in a
  safer and more economical design.

• Subjects / Keywords

  • Multi-tiered buckling-restrained braced frames
  • Buckling-restrained braces
  • Seismic performance
  • Full-scale testing
  • Column stability
  • Nonlinear analysis
  • Seismic design

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-7ak1-qw84

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.