Discontinuous systems are common in multi-story single-family and multi-family woodframe residential structures. ASCE7-16 defines these discontinuities of load path as either in-plane or out-of-plane offset irregulatities. Elements below the point of discontinuity that resist the horizontal effects of seismic load on the upper stories of the structure are required to be designed for seismic forces that are increased by the overstrength factor which represents an upper bound of the magnitudes of forces that a lateral force resisting system can produce during a major earthquake. There seems to be uniform agreement among design engineers that the transfer beam supporting the discontinuous wall is to be designed for the overstrength factor. What is unclear is whether the structural system supporting this transfer beam also needs to be designed considering the overstrength factor. Wood systems support heavy beams by bearing on posts, with large capacity to resist high downward forces. However, the transfer beam to post connection may be as minimal as a few toenails which cannot resist uplift of the beam if unexpected upward forces occur. Three series of full-scale two-story woodframe shear wall experiments are being conducted to clarify the effects of in-plane structural discontinuity. Preliminary results show that metal hardware installed to resist uplift at the end of the beam usually possesses sufficient strength to resist forces high enough to cause failure to occur in the woodframe system prior to failure of the anchorage of the transfer beam. The outcome of this research is clarity in actual woodframe behavior and adjustment of the wording of the building code to result in consistent, efficient design of these systems.
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