High Fidelity Monotonic and Cyclic Simulation of a Woodsheathed Cold-Formed Steel Framed Floor Diaphragm

Abstract eng:
Non-linear finite-element models of monotonic and reversed cyclic wood sheathed cold-formed steel (CFS) framed diaphragm tests recently conducted at McGill University are developed using the commercial finite element software ABAQUS. Cantilever-type monotonic and reversed cyclic tests to failure were conducted on 3.5 m x 6.1 m wood sheathed cold-formed steel framed diaphragm specimens. The diaphragm construction details matched those used for previous full-scale shake table experiments performed on a two-story building under the CFS-NEES project. Oriented strand board (OSB) sheathing, cold-formed steel joists, tracks, blocking and clip angles are modeled as elastic shell finite elements. Sheathing-to-steel screw connections are modeled as non-linear shear spring elements that were characterized using single fastener tests. The spring models are multilinear with two ascending branches and two descending branches. For the reversed cyclic analysis, the fasteners are modeled with recently developed User Element Library that can capture unloading-reloading response under reversing loads. Contact is modeled between the OSB panels using a combination of bearing and frictional springs. The analysis results are compared to the laboratory tests for initial stiffness, peak load, ductility and energy dissipation. Force distributions in individual fastener components that are critical to system behavior are studied. This work gives insight into the seismic response and flow of forces in floor diaphragms and verifies a cyclic modeling protocol for cold-formed steel framed structural systems.

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