Ok, my 10,000lb reactions per point load on the garage dormer trusses
are known to require a 3-1/2 cubed footing of concrete to support the
load. So, I have the tough job of cutting into the garage floor,
digging a big hole around and under the existing perimeter foundation
footer of the garage, and pouring a lot of concrete and rebar. It's
been suggested that I go ahead and consider cutting through the
existing footer to make the job easier.
But, now I'm interested whether or not the two 8' long 4x12 garage door
headers (plus double top plate across both) can support the point load
of the trusses. I can't figure out how to convert reactions numbers
into load or forces down on the header. Span tables aren't of any
apparent help. Obviously, I want minimum deflection and no structural
breakage for these headers.
I have been told by my truss designer that my 2x4 stud wall will hold
the point loads, so it seems possible, but I'm still concerned about
whether the headers can. To clarify, I have two 8' wide garage doors
with 4x12 headers, and a central 8" wide post of several 2x4s (I may
swap this out for a 3" steel post, swapping headers is more difficult).
In any case, each door header takes the load of one of the heavy truss
point loads, and the point loads of lighter trusses, all spaced 24"OC.
I'm trying to solve this while my engineer finds time to fit me into
his schedule. Previous help was interesting, so I'd like to understand
more about how the trusses will affect my existing headers.