Courtney Thomas wrote in message ...
I want to reinforce the bed of a trailer whose bearing surface is about
26' long and 8' wide to support about 10Tons.

How can I determine the proper BEAM SIZE and an adequate DESIGN, e.g.
longitudinal beams with cross bracing; or, lateral cross members
interspersed with bracing, I beams, tubular steel, etc. [without hiring
a mechanical engineer just for the purpose] ?

I'm aware I can look at other trailers and make assumptions about what
they've done but I'd like to "know" that what's to be done is sufficient.

It may shock & astonish you to find that us engineers often do about
the same thing (i.e., learn from what has worked). I am not a vehicle
or trailer designer, but there is more to consider in a trailer's load
than live & dead weight over a span. Shock loads, conditions of
service, type of load & it's distribution, lading & unlading issues,
reasonable corrosion wasting factors and other things all are in play
in such a selection. The good news, is that you don't have to deal
with a haughty Classification Society's rules too (may my friends at
the Bureau forgive me). :-)

Engineering also has it's often-neglected limits. For example, while
the structural properties of most woods are well known & understood, a
traditional timber-framed house has many oversized and undersized
timbers - yet these houses have stood for 300 years, while
highly-engineered homes next door have fallen down or blown away in
the first bad storm because they were strong but fundamentally
unstable and not robust in design. The very same thing has happened
with ships, over & over again, which is why those of us who have
designed and built a few become humble people & try not to stamp more
drawings than we have to.

IMO&E, if you have enough fabrication skills to build the damn thing,
your gut feeling as to the adequate beam size, and even any gussetting
required, will be remarkably reliable. I would trust the opinion of a
fabricator before the advice of an engineer who had never built &
operated a trailer himself. Even if both were wrong (happens). No
engineering text about beams is going to tell you how to build or
reinforce an adequate trailer. 10-ton trailers are as common as crows
in a cornfield - go look at a few.