A wooden I-stud as a member of a light-frame timber wall is modelled with reducing flange width to simulate fire exposure. The stud is loaded with a vertical load and the effect of restraints from one gypsum board and the top and bottom rail is considered. Geometry and material values are chosen to correspond to a stud with flanges of solid wood and web of OSB (oriented strand board).

A model with shell and beam elements is implemented in Abaqus. A buckling analysis is performed on a perfectly straight stud and then a geometrically nonlinear analysis is performed on a stud with an initial curvature. Both the buckling analysis and the geometrically nonlinear analysis show that even a large reduction of the flange width results only in moderate changes of the load-carrying capacity of the structure.

In the report diagrams are presented from the geometrically nonlinear analysis where the critical load is easy to read once a failure stress is determined, but an estimate of the the failure stress is not given here.