Ned,

I think I caused a bit of confusion.

The BIG cranes I mentioned earlier I did NOT design, nor was I
responsible for, their fabrication.

They were part of the facilities (Dominion Bridge - Sulzer in Lachine,
Quebec) where I was manager of manufacturing engineering, responsible
for the economic fabrication and machining of hydraulic turbine and
nuclear reactor components. I was instrumental in the procurement of
one 132 ton crane...we had two. All the big cranes I mentioned earlier
were double beam double web custom design / fabrications (box sections
with internal stiffening), with trolleys on top of the beams.

Fast forward 17 years. I now run my own engineering office where I am
'chief cook and bottle washer', with one employee: me!

I offer my services to local businesses that can profit from my
engineering services, which nowadays are often mandated by legislation.

On occasion I am asked to design a small overhead travelling hoist, or
to certify an existing one cobbeled together by who-knows-who.

The 12" I-beam with 30 ft span in my example was a case-in-point of the
latter. I take all relevant dimensions, make sketches and
calculations, and certify the hoist (or equipment requiring
certification) as having a safe working load of xxx lb. For hoists of
unknown origin an inspection is then required by a certified NDE
technician (not me) who checks the welds, bolts, cable, etc. He issues
his report, puts appropriate labels on the hardware, and the hoist is
good to go. Where I design stuff I use material that's available in
the fabricator's yard as much as possible. Keeps the costs down and my
client happy.

Since I design only small hoists it would be uneconomic to custom
design a beam that could meet the differing requirements for the
tension and compression flange. With the load and span specified by the
client and basic calculations, it is easy to simply pick an
appropriately sized beam from the published tables, keeping an eye on
the unsupported length.

It is during analysis of an existing installation that I get into
difficulties. I have to explain to the owners/managers that while their
equipment may not be in danger of crashing down about their ears
(because it has been in use for xx years before the ministry of labour
caught up with them) it nevertheless does not meet regulations, ie. the
legally required factor of safety. Then they want to know why.....

To summarize: Yes, custom designed beams are used for the big stuff;
off-the-shelf material is used on small hoists because of the large
range of standard sizes of beams available, which cover the most often
encountered, smaller, requirements.

Trust this clears the fog somewhat.

Wolfgang

Ps.: I NEVER certify anything I haven't personally inspected. My
errors and omissions insurance is a little too expensive for that.
This is also the reason I do not offer free design advice/information
on this discussion group. WFH