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Even with strong-column-weak-beam design requirements, story mechanisms have been observed in Moment Resisting Frames (MRF), resulting in concentrated drift demands that can result in severe structural damage to drift-sensitive components. Frame-Spine systems can redistribute demands with building height, but near-elastic higher-mode effects tend to contribute to floor accelerations, affecting damage to acceleration-sensitive nonstructural components. To mitigate this tradeoff, Force-Limiting Connections (FLCs) have been proposed to reduce accelerations through yielding components between the Frame and Spine, thereby limiting the magnitude of the forces. This study examines the sizing and placement of FLCs in a four-story Frame-Spine system using stochastic simulations. The T-shape yielding element dimensions in the FLC were modeled as random variables at each floor, and Monte Carlo simulations were used to explore their effect on drifts and accelerations. Results show the dominant role of the first-story FLC on balancing drifts and accelerations, while upper-story devices offered limited benefit. Design recommendations are provided to constrain first-story yielding element dimensions within effective bounds that reduce peak accelerations relative to the baseline Frame-Spine configuration.
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Research Experiences for Undergraduates (REU), NHERI 2022: 3D Model of a Concentrically Braced Frame for Real-Time Hybrid Simulation
This project provides an in-depth study into how floor isolation systems (FISs) perform when subjected to floor accelerations from a 3D building model of a special concentrically steel braced frame (SCSBF) building during real-time hybrid simulation (RTHS). The project details the creation and study of a 3D model of a SCSBF building using HyCoM-3D, a 3D modeling software created for use at the NHERI Lehigh Experimental Facility. Data in this project can be reused to further assess how FISs behave when subjected to accelerations and their ability to isolate large nonstructural components of buildings and lessen their damage when subjected to different accelerations due to different building configurations. This project is unique because it considers the multi-directional response of a FIS subjected to floor motions simulated from a 3D, nonlinear model of a SCSBF building. The main audience is researchers and professionals interested in learning more about how FISs can limit damage to nonstructural building components.
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- PAR ID:
- 10379785
- Publisher / Repository:
- Designsafe-CI
- Date Published:
- Subject(s) / Keyword(s):
- NHERI Lehigh Lehigh University 3D Model Earthquakes Floor isolation system Real-time hybrid simulation Concentrically braced frame Nonlinear Multi-directional
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Concentration of drifts due to story mechanisms can lead to severe structural damage and economic loss. Frame-Spine systems have been proposed to mitigate these effects by redistributing drift demands with building height; however, systems can also exhibit near-elastic higher-mode effects, resulting in forces and floor accelerations that remain largely unreduced by inelastic behavior, thereby adversely affecting acceleration-sensitive nonstructural components and occupants. To address near-elastic higher-mode effects, Force-Limiting Connections (FLCs) have been introduced limiting force transfer between the frame and the spine and reducing acceleration demands through controlled yielding components. This study presents observations from full-scale shake-table testing of a four-story Frame-Spine and a Frame-Spine-FLC specimen at E-Defense. Results highlight higher-mode effects under strong shaking, with emphasis on (1) story shear resisted by the spine, (2) force–deformation behavior of the spine-to-frame connections, and (3) vertical distribution of forces. These findings provide experimental evidence of higher-mode participation in Frame-Spine systems and support the development of improved design guidance and controlling mechanisms.more » « less
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