Eatherton, Ma, Krawinkler, Mar, Billington, Hajjar, and Deierlein, 2014
This paper observes the self-centering rocking frame, which reduces residual drift and concentrates inelastic drift into replaceable fuses. Different configurations can be made, but they must include replaceable energy dissipating fuses, post-tensioning, and a stiff braced frame spine. Computational analysis of this system was then used to examine an example structure.
System Concept
A rocking braced steel frame includes the following: a stiff braced frame spine to reinforce uniform story drifts, vertical post-tensioning to provide an elastic self-centering force, and a steel energy-dissipating fuse to dissipate seismic energy of the system and damen motion. These elements must always be included, but can be found in several configurations. Both a single and dual frame can be used within the system. A single frame features two energy dissipating fuses attached to the edges of the frame, while the dual frame includes energy dissipating fuses attached between two frames. This paper examines a six story building using a single and dual frame and performs computational analysis on both systems.
Experimental Study, Results, and Discussion
The methods of analysis for rocking braced steel frames were applied to a 6 story building using either a single and dual frame configuration. The analysis assumed a base shear ratio 0.125, and a self centering ratio of 1.9 for the single frame, and 1.25 for the dual frame ratio. Using these numbers, the initial post-tensioning (PT) force and fuse shear strengths were found. The system also assumed a 3% roof drift ratio under maximum considered earthquake (MCE) conditions in order to determine the fuse dimensions, and thereafter calculate stiffness, the fuse hardening ratio, hysteretic flag height, and the energy dissipation ratio, which must be greater than 0.25. Then, the self centering (SC) and uplift ratios were also calculated. After force losses in post- tensioning, the SC ratio for the single frame system dropped from 1.46 to 0.99, while the dual frame system dropped from 1.25 to 1.02. Since this ratio remains close to 1, both systems are effective in self-centering while also resisting global uplift. However, this loss indicates that researchers must examine PT losses and fuse hardening and how they affect the system in order to produce desirable results and prevent lowering the SC ratio.
Reference
Eatherton, M.R.., Ma, X., Krawinkler, H., Mar, D., Billington, S., Hajjar, J.F., and Deierlein, G.G., (2014). “Design Concepts for Controlled Rocking of Self-Centering Steel- Braced Frames,” Journal of Structural Engineering, 140. 11, pp. 5.