Bagheri, Hashemi, Yousef-Beik, Zarnani, Quenneville 2020
In this study, a new approach to a tension-only brace was investigated for its seismic performance in comparison to the conventional tension-only braces. The proposed brace includes a resilient slip friction joint (RSFJ) at the ends in order to eliminate the stiffness/strength degradation, pinching and slackness of the system. The system was subjected to loading protocols on a full-scale, two-dimensional steel frame that investigated both its dynamic and quasistatic performances. The results from the tests portrayed that the designed joints and frame exhibited satisfactory behavior under a 5% lateral drift which is the limit for a maximum earthquake (MCE). The base shear was also reduced due to the high ductility of the RSFJ tension-only braces. With the damage avoidance concept of the RSFJs, the system exhibited zero damage after different tests carried out in this study. According to these observations, the system was verified as a promising low-damage structural device with satisfactory seismic performance even in extreme seismic events at MCE level.
System Concept
The proposed system is a tension-only brace that uses the resilient slip friction joint (RSFJ) which can have both fixed or pinned connections. Components of the RSFJ include steel-grooved middle plates with slotted holes, grooved cap plates with simple holes, high-strength bolts and rods, and disc spring rings. When subjected to load, the device begins to open until the disc springs are locked. One diagonal member resists the tension force while the other experiences none. When load is released, the joint returns to initial position due to the restoring force from the spring rings. Simultaneously as the joint moves, energy is dissipated by the sliding friction between the clamped grooved surfaces. While the system can work in both tension and compression, the proposed system experiences only tension due to its frame design and thus, contributing to its small brace body requirement.
Experimental Study, Results and Discussion
The proposed system was tested on a full-scale, two-dimensional steel frame under five series of static, quasi-static, and dynamic loading procedures with the maximum displacement at MCE level 5% drift using MTS 500 kN up to a 60-mm displacement. All tested joints generally exhibited repeatable flag-shape linear behavior of the disc springs and closely matched the estimated displacement-force graph without any damage. Seismic base shear of the structure was also significantly reduced which was more noticeable at 2% displacement drift. As anticipated the system demonstrated no strength degradation, buckling or slackness and possesses damage-avoidance seismic criteria which is a desirable feature for a promising seismic resilient device.
Reference
Bagheri, Hamed, et al. “New Self-Centering Tension-Only Brace Using Resilient Slip-Friction Joint: Experimental Tests and Numerical Analysis.” Journal of Structural Engineering, vol. 146, no. 10, Oct. 2020, p. 04020219. DOI.org (Crossref)