The connection detail for the Scottish Parliament building beams (NCE last week) shows the bolts to be screwed into the end grain of the timber struts.
As any joiner or carpenter will tell you 'never screw into end grain since it has no strength'. The tightening of the bolt in such a detail will tend to shear the wood around the screw threads leading to an ineffective and loose connection.
And so it would not surprise me if the investigation finds the timber strut to have slipped out of the steel bracket under its own weight following some drying shrinkage in the timber. The search for an external loadcase to explain tension in these members is likely to be futile.
Richard Dinsdale-Young (M), 9 Penrith Avenue, Giffnock, Glasgow, G46 6LU