Miller, Fahnestock, and Eatherton 2011
This paper investigates the performance of self-centering buckling restrained braces. These braces provide the ability for a structure to return to their initial position after a seismic event and minimize damage. The research presented is geared to develop an innovative self-centering brace for advanced seismic performance.
Experimental Study, Results and Discussion
The self-centering buckling restrained brace consist of a typical BRB component with is supplemented with pre-tensioned superelastic NiTi shape memory alloy rods, providing the self-centering. The unit can be substituted for a conventional steel brace or a BRB brace without changing the global structure. This system does not contain many of the challenges associated with PT moment frames or rocking braced frames.
As the brace deforms, the middle and outer tubes act as struts that push the anchorage plates apart. The self-centering force is increased as the anchorage plates move apart. The BRB core yields in tension and compression, the energy is dissipated. The pre-tension selection is greater than that of the yielding force producing the self-centering.
Analytical Study
A numerical model was created using OpenSees and a SC-BRB was designed for a prototype building matching a 5-story BRBF design example. The model used gap elements to represent contact between the tubes and anchorage plates. Stages were assembled to allow for pre-tensioning. The analysis was tracked for both the buckling restrained brace and the self-centering component.
Specimens were tested using increasing strain cycles. The two variables studied were length of time of the heat treatment and sequence of machining and heat treatment. It was found that strength decreased as heat treatment time increased. The smallest amount of residual elongation occurred when the shape memory alloy bars were heat treated for 60 minutes after machined.
Reference
Miller, D J., Fahnestock, L. A., and Eatherton, M. R. (2011). “Self-Centering Buckling-Restrained Braces for Advanced Seismic Performance,” Proceedings of the Structures Congress 2011, Las Vegas, NV, April 14-16.