Doctoral Dissertations
Date of Award
8-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Civil Engineering
Major Professor
Mark D. Denavit
Committee Members
Nicholas E. Wierschem, Timothy J. Truster, Matthew R. Eatherton
Abstract
When subjected to strong earthquake ground motions, conventional steel braced frames are vulnerable to soft-story mechanisms, whereby the weakest story accumulates more damage relative to the rest of the structure. This reduces the overall strength of the structure and increases the cost of repairs.
One method for mitigating this behavior is the use of a stiff vertical “spine” with a more ductile, energy-dissipating system. The spine typically spans the height of the structure and is designed to remain elastic, distributing earthquake demands across the height of the structure and bridging weak stories. One proposed frame is the “strongback” braced frame (SBF), which merges a steel buckling-restrained braced frame and an elastic truss, using the buckling-restrained braces for energy dissipation and the truss for force distribution.
Three studies are presented here on the behavior and design of strongback braced frames.
The first considers the effect of the strength and stiffness of the spine in SBFs, and how methods to design the spine vary. Designing the spine is challenging, as higher mode effects and partial nonlinear mechanisms have been shown to be significant. The results show that two proposed SBF-specific design methods provide value over a control procedure. Both SBF-specific methods produce designs with reserve strength in the strongback, but one is much more conservative.
The second considers the effect of the vertical distribution of the energy dissipators in the frame, and introduces a design method for the energy dissipators that supports the design of frames with non-standard dissipator configurations. The design method shows promising results, but the existing methods for design of the strongback members have inconsistent results when used with the non-standard dissipator configurations.
The third considers the mitigation of higher-mode effects by using multiple pivoting segments in the spine, and how passive control devices between the segments impact the behavior of the frame. The results show that multiple segments reduce demands on the strongback braces, but increase other demands such as maximum story drift, and the use of passive control devices allows finding a medium configuration between one- and two-segment spines, with benefits over both.
Recommended Citation
Talley, Peter, "Studies on the Design and Behavior of Strongback Braced Frames. " PhD diss., University of Tennessee, 2024.
https://trace.tennessee.edu/utk_graddiss/10515