[TheForge] Wooden Beam strength for Rigging

[Walter Mullett]

Bill,

Not enough info here.  You say the beams are 3x11.5 but you don't give span
or slope.  You also say beams and then you say rafters.  What are they?  
- Is this a sloping roof with ridge or single slope? (If you have a ridge,
do you have collar ties on your rafters? - Over-loading a ridge rafter
system can push out the sidewalls and sag the ridge.) 
- How far from the end of the beam/rafter do you want to hang your beam? (
Mid-span is a worse condition than 1/4 span. )

Given the above .... You really aren't talking about a lot of load.  If you
are living in a snow environment, your roof will probably support at least a
snow load of 30lb/sf.  If you can spread your load over +/- 30 sf, you could
just be replacing that load.  However, I doubt your 6" 'I' will do that.
You can test out that by loading the beam on the ground and seeing how much
deflection it has.

Your existing 3x members are probably stout enough to take up the point
loading they will have.  My concern with these would be to make sure your
connections are in the middle of the side of the beam.

You can build it then load test it.  Wood is great because you have a
running factor.  Unless you have some really bad flaws (knots - holes in
wrong locations), it deflects and groans a lot before it fails.  Just check
your deflection as you add load.  If you get too much deflection, you can
sister the joists or add fletch plates to them.  

Walt

-----Original Message-----
From: theforge-bounces at mailman.qth.net
[mailto:theforge-bounces at mailman.qth.net] On Behalf Of Woolley
Sent: Sunday, January 29, 2006 10:49 PM
To: theforge at mailman.qth.net
Subject: [TheForge] Wooden Beam strength for Rigging

Greetings,

I seem to remember a thread about beam strength a while back but don't have
any info.  I'm not sure if this is the right forum but here goes.  I want to
hang small steel I beams(6"?) under my roof joists to rig from. I'm hoping
to get up to 1/2 ton or so capacity.  The beams measure 3x11 1/2 with no
room above (obviously butt up to roof deck), so I have to drill to bolt
through or lag in to hang straps down and under to support steel.  The
joists are spaced 2 feet apart. I hope to span at least 5 or 6 of them. Does
anyone have a known reference for engineering specs on this or any practical
experience doing something similiar?  Any help would be appreciated.

Regards,
Bill Woolley
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