This post relates to sloped wood roofs framed with sawn lumber or
manufactured I-joist rafters supported by a ridge beam. Does anyone know of
a case where the connection between the rafter and the ridge beam failed due
to axial load in the rafter?
The axial load, which equals the vertical load times the sin(slope), can
exceed 2,000 pounds for I-joist rafters. The typical details provide by the
I-joist manufacturer calls for a Simpson LSSU variable angle seat hanger,
which has an allowable tension of zero pounds. The staff engineer at the
I-joist manufacturer believes the roof diaphragm carries the axial load from
all the rafters into the roof diaphragm and over to the end walls.
I would like to know if other engineers size the tie strap at the ridge beam
based on the calculated rafter axial load and if anyone knows of a failure
resulting from an inadequate connection. If you would like a spreadsheet for
determining this axial load request it from the e-mail address shown below.
Mark Oakford, P.E., oakfordm(--nospam--at)RSEC.com
RSE Consulting, Federal Way, WA 98093-1417
T 253-927-6169 F 253-838-3823