On Wed, 23 Mar 2005 12:27:36 GMT, Tony Bryer
wrote:

In article t, Bob
Morrison wrote:
Now for a really interesting problem, let's say you want to take
out a post and increase the span of the 3-2x12 from 13 feet to 18
feet, but you must leave the 3-2x12 in place. "Flitch" beams are
allowed. Do you compute combined section properties of wood and
steel or do you simply let the steel carry all the load and the
wood becomes "filler"? This problem has a trick in it that I will
not divulge.

I look forward to the trick. In the meantime we have a page on the
approach to flitch beam design we use in our UK SuperBeam program at
http://www.sda.co.uk/info/sbw/flitch.htm.

One of the crunch things in your question is that the steel plating
to an existing beam will do nothing unless you jack the timbers first
to remove the load they are carrying.


I am not exactly enthused about the timber beam application code
approach to flitch plates. Seems like an inefficient use of material
to sandwich a verical plate between two wood beams.

I think it might be worth considering "flange doublers" top and bottom
- which is an aircraft main spar approach. Leave the timber as shear
and anti buckle and apply steel strips top n bottom of each side,
bolted through I haven't worked the numbers, it's true.

Brian Whatcott Altus, OK