Ricles et al. 2010
This paper presents a self-centering moment resisting frame as an alternative to a conventional moment resisting frame. The design is set up to avoid large residual drive using PT beam-to-column connections for SC. For the system to be desirable it was tested against the design based earthquake for this ability to prevent collapse and sustain minimal damage allowing immediate occupancy performance.
System Concept
Within a self-centering moment resisting frame the beam-column is characterized by a gap opening and closing during a seismic event. The beams are post-tensioned to the columns by high strength strands of horizontal orientation. The energy dissipation takes place in the beam web friction devices which are attached to the column at the interface.
The PT-WFD has an initial stiffness relative to a traditional welded moment connection. The gap opening occurs when the connection overcomes the imminent gap opening moment and the beam tension flange loses contact with the shim plate at the column face. The PT force increases with strand elongation until yielding. During the unloading, the direction of friction force in the WFD is reversed and the beam tension flange returns to contact with the column.
Experimental Study, Results and Discussion
A 7-bay, 4-story prototype building located on stiff soil in the Los Angeles area was designed with the web friction devices and tested. The perimeter frames consisted of two 2-bay self-centering moment resisting frames with post-tensioned web friction device connections. The test frame consisted of a 0.6-scale prototype. Hydraulic actuators were used to apply lateral force at each level. A hybrid earthquake simulation was conducted.
Desired connection performance was achieved under the design based earthquake level tests. No significant damage occurred and the WFDs provided reasonable levels of energy dissipation. Self-centering capabilities were also demonstrated.
Reference
Ricles, J. M., Sause, R., Lin, Y. –C., and Seo, Y. –C. (2010). “Self-Centering Moment Connections for Damage-Free Seismic Response of Steel MRFs,” Proceedings of the Structures Congress 2010, Orlando, FL, May 12-15.