ABSTRACT
In a traditional K braced (Chevron) frame design, the braces resist the lateral earthquake loads transmitted by the beam as axial forces. Under a strong ground motion one of the braces is expected to buckle in compression while the adjacent one is expected to yield in tension. Due to differences in compression and tension capacities, there will be a non null vertical resultant transmitted to the beam as a shear force, which makes its design very costly, since the moments at the midspan are enormous. Khatib et al. (1989) suggested adding a vertical column between the beams of the frame at the joints where the braces connect. This column transmits the vertical unbalanced force from the braces after buckling, or yielding, to the upper floor beam, redistributing it to the upper braces. Thus the compression brace will be subjected to an even greater compression, triggering buckling. A new unbalanced vertical force will be created at the upper floor beam. If this floor is linked to the upper one, the process would repeat. The propagation of buckling and yielding to the upper floors seems similar to a “zipper” from which this system derived the name of “zipper frame”. The solution is appealing; however, if all the braces at all floors are allowed to buckle, then collapse of the frame
hosting the NEES Equipment Site at University at Buffalo. The model utilized is an incomplete similitude, 1/3 scale model, derived from a prototype designed by Yang and Leon (2004) at Georgia Institute of Technology.
