Stability of Wall-Diaphragm Connections in Cold-Formed Steel Framed Buildings

In cold-formed steel buildings, ledger framing represents the current state-of-the-practice in which floor joists are effectively hung from the walls via a rim track (ledger) and clip angle connection. Not only do full-scale shake table tests on a cold formed steel building confirm the presence of alternate load paths, but recent efforts at Johns Hopkins University to experimentally test these wall-diaphragm connections demonstrate that these load paths and resultant failure modes are complex. Observations from these experiments indicated that ledger flange buckling and wall stud web crippling are predominant limit states. Notably, these stability modes are not currently considered in design codes, where fastener shear dictates connection design. The work presented herein expands these experimental tests via a computational modeling effort using finite element analysis. Experimental parameters (clip angle location, presence of top/bottom screws, location of ledger relative to flanking studs) are broadened to capture a range of stability behavior. This study is part of a larger effort to discern diaphragm behavior and wall-diaphragm interactions in cold-formed steel systems, with the goal of motivating full system analyses and improved design recommendations.

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