The recent talk about engine hoists prompted me to talk to a friend (who is
a civil engineer) concerning his use of his rafter+comealong method of
pulling engines (from his TR4 and MG Midgets). I plan to "borrow" his
garage to do a clutch job on an MGB. Anyway, here's his description of
how he designed the setup:
------------------------------------------------------------------------------
I did a very interesting (only to a structural engineer)
analysis of the rafter system, modelling it as a beam on
elastic foundation... this allowed me to estimate how much
load would be transferred to each rafter, which depends on
the relative stiffness of the 2x6 tee-beam I bolted to the
ceiling joists (they are not rafters). It is a rather
technical exercise, but was fun for me.
The essence of the problem is the relative stiffness of the
joists (2x12x20ft or so, simply supported beams) to the load
at the point in question, compared to the stiffness of the
spreader beam (I used two 2x6, in a Tee section). If the
tee beam is very flexible, it does not do a very good job of
transferring load to the adjacent joists. So, you have to
calculate the joist stiffness, then design an appropriately
stiff spreader beam, then determine how it loads adjacent
joists.
I was designing mine for safe load of 750 pounds, but had to
cheat a bit. It might exceed allowable stress a bit if I
pull my Chevy 350 engine, but should still hold up.
-------------------------------------
Ray W. James, P.E., Ph.D.
Texas Transportation Institute
Civil Engineering Department
Texas A&M University
College Station, TX 77843
Phone (409)845-7436; Fax (409)845-3410
E-mail: r-james@tamu.edu
Date: 8/11/98 Time: 9:26:23 AM
-------------------------------------
------------------------------------------------------------------------------
Lee M. Daniels Laboratory for Molecular Structure and Bonding
daniels@tamu.edu Texas A&M University
'74 TR6 '77 MGB http://acs.tamu.edu/~lmd1191
|