Buckling-Restrained Braced Frame Connection Design and Testing Buckling-Restrained Braced Frame Connection Design and Testing

by Coy, Bradly B

As typically designed, the beam-column-brace connections of buckling-restrained braced steel frames have undesirable failure modes that compromise the integrity and performance of the frames and are costly to repair. To decrease the time and resources needed to repair the frames following an earthquake, a new connection design was developed that attempts to confine yielding to replaceable frame components. The design incorporates a gap in the beam beyond the edge of the beam-gusset weld that acts as a hinge and reduces moment forces transferred to the connection; it is bridged by splice plates that are bolted to the beam top flanges. The splice plates and buckling-restrained braces are the only frame components that are expected to yield.

To investigate the performance of the proposed connection design, a prototype bay was designed and two test specimens were fabricated and tested. Each specimen represented a corner of the prototype braced bay and consisted of a beam, column, gusset plate, brace core extension assembly, splice plates, and lateral bracing angles. Both standard design procedures and newly developed criteria were used to design the connection.

In preparation for testing, a method was developed for estimating the hysteretic response of a buckling-restrained brace. By using this method to program an actuator, the specimens could be tested without using actual braces, resulting in a significant reduction in testing cost.

Testing was conducted using two 600 kip actuators; the first followed a static loading protocol with a maximum design drift of 6.5%, and the second replicated the prototype BRB’s response. The tests yielded promising results: both specimens withstood the maximum displacements and avoided yielding in the beams, columns, and gusset plates; yielding did occur in the splice plates and BRB core extension assembly, as anticipated.

Possible limitations in the design may arise under the presence of increased shear loads, concrete floor slabs, or out-of-plane loading. Additional testing is recommended.