On 23/02/2012 22:32, Steve B wrote:
"Jim wrote


Have you considered wood?
http://www.awc.org/technical/spantables/tutorial.html
In Fig 3 a 2x12x16' falls within the range you are looking for. Pressure
treated syp (Southern Yellow Pine) is nearly as strong as oak and doesn't
need protection from the weather. You do have to brace it to stop twisting
but the H center bar helps. Pick two without knots on one side and make it
the bottom.

jsw

No, I have not. I have this steel in stock, and the means of working with
it. That's the main reason, plus, I like to just paint it good, and not
fool with it for a long time. Wood is good, but for this, I think I trust
steel a bit more.

Steve


Can't disagree, but in the olden days they used timber rather than steel
for mining for good reasons. Firstly, wood gives early warning by making
noises before it lets go, and secondly it will usually tolerate much
larger deflections before collapsing. But, since you have the steel, go
with that but back up your instincts with some basic calcs. In
particular, watch out for buckling (which is what tends to get missed
when bridges collapse while they are being built).