Shen et al. 2011
A disadvantage of the current design in MRFs is that they are expected to sustain significant damage to structural members during seismic events. A replaceable link located at expected inelastic yielding locations can provide an alternative to this. An experimental study was conducted to develop and validate the replaceable link concept.
System Concept
The links are designed with smaller capacities than the beam section. This provides a weakened section, away from the critical welds at the column interface, where a plastic hinge can form. Two link types were examined: W-sections with endplates connections and back-to-back channels with bolted web connections. A 5-story prototype building was design and analyzed for the full scale testing validation.
An advantage of the proposed system is that damaged links after an earthquake can be easily inspected and replaced which minimized disruption time of the structure. Also, this allows for more independent control of beam stiffness and required strength. This provides a more efficient and cost effective structure.
Experimental Study, Results, and Discussion
The experimental test set up represented a typical first floor exterior beam-to-column joint. A column was fabricated with a beam stub for both link type connections and mounted to a strong wall. The loading was implemented through the laterally supported beam. Four full scale tests were conducted under standard cyclic loading.
Results showed that the MRF with nonlinear replaceable links exhibited strength and ductility equivalent to current design procedures. The end-plate links provided greater energy dissipation than the bolted web links, where the bolted web links reached significantly higher rotational capacity. It is noted that additional research is needed to better understand the global behavior of a building assembled with replaceable links.
Reference
Shen, Y., Christopoulos, C., Mansour, N., and Tremblay, R. (2011). ”Seismic Design and Performance of Steel Moment-Resisting Frames with Nonlinear Replaceable Links.” Journal of Structural Engineering. 137.10, 1107–1117.