Beam Sizing Help.

Started by DaveOrr, October 16, 2013, 10:56:47 PM

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DaveOrr

Trying to figure out sizing for a cross beam to support my loft in the cabin I'm designing.
Cabin is going to be a 24X36 with 2nd floor loft.
Span is 24' and the section of loft it needs to support is 8'.
There is a structural wall that will support the section from there to the back wall of the cabin (about 10').

I'm not an engineer (well structural  ;) ) and the charts and specs are Greek to me.  ???
Dave's Arctic Cabin: www.anglersparadise.ca

Don_P

A sketch would be a good idea, I can read the description a couple of ways.
First way, there is a 24' long load bearing wall 10' off the back wall and the beam is 8' in front of that. In that scenario the beam is supporting a tributary area of 4' x 24'.
Second way, there is a 24' long load bearing wall 10' off the back wall and the beam is 16' in front of that. In that scenario the beam is supporting an area of 8'x24'.

By those assumptions the joists are running the length of the cabin and are not providing any tie action for the roof... I'm assuming a structural ridgebeam is above?


Squirl

I once did a quick post on how to read girder/header span charts.
http://countryplans.com/smf/index.php?topic=10511.0

It sounds like you are trying to do a beam in the center to hold 1 floor above.  It sounds like you want TABLE R502.5(2) GIRDER SPANSa AND HEADER SPANSa FOR INTERIOR BEARING WALLS

http://publicecodes.cyberregs.com/st/ny/st/b400v10/st_ny_st_b400v10_5_par018.htm

If you need further explanation on any items, just ask.

flyingvan

  Dunno if this is useful or not....For my first O/B project I had a 24' height limit to deal with, and the size beam needed to support the upstairs (like I think you're doing) was so thick something had to give---I needed to meet the minimum ceiling height requirements, without going over for the whole building. 
  The solution was to hang the upstairs floor joists flush with the bottom of the beam.  Of course, laying them on top is strongest, bit I couldn't afford the 12".  I just used Simpson hangars primed and painted.  10 years gone by now--no squeeks, sags, or other problems. 





   It also provides a nice 'stop' before the rail boards at the floor.  It's good because that's always a really tough spot to keep clean, where 2x2's come up over the edge
Find what you love and let it kill you.

DaveOrr

Thanks for the help so far everyone.
Here are some drawings to help visualizing my set up.

This is the 1st floor plan.



And the 2nd floor plan.



And finally a doll house view of the 2nd floor with the beam location in red and the 1st floor walls in green

Dave's Arctic Cabin: www.anglersparadise.ca


Don_P

#5
Try this for the framing plan. Load bearing walls are in dark blue, joists are in black, LVL's are in red, the tributary area loading the long beam is in light blue. The beam at the stair head is delivering a point load to the long beam at about midspan. I'm assuming stair support from below.

Doing that I'm coming up with a double 11-7/8" LVL for the long beam and a single 11-1/4" lvl for the beam at the stair head. The supplier would do the final engineering and I'd investigate a glulam for looks but LVL's are probably more available to you. I'm assuming the roof is not bearing on any of this.

DaveOrr

Thanks for that Don.    [cool]
Makes sense to me.
What are the thickness of the beams you're thinking?
I know they are available in many different sizes.
Yes, the stairs are supported from below.
Dave's Arctic Cabin: www.anglersparadise.ca

Squirl

The LVLs are a pretty expensive option.  Personally I would just use 2 - 2x12x8s and put in a 4x4 post.  It would save a whole lot of work too.   I usually work alone. Two 24 foot long 12" LVLs would be a pain to install.

Don_P

If we have our druthers I'd work towards centerlining the plan and run a beam into that tall gable wall of windows, taking advantage of the 2nd floor diaphragm to help brace that wall.


DaveOrr

Think I'll pull the second floor bump out back in line with the stairs and support on the load bearing wall that hold the stairs up.
I'll lose a bit of space but won't need to buy expensive long beams. ;)
I can easily carry the point load @ the stair junction down to bedrock easily.
I think this will make life a lot easier.
Dave's Arctic Cabin: www.anglersparadise.ca

Don_P

It looks like you'll need to rework the bedroom entry to get a load bearing wall out there at that juncture. I'm also not seeing the washer/dryer in this?

DaveOrr

No washer and dryer.
It's just a weekend cabin.
Off grid as well as the nearest town is 15 miles away.
All appliances are going to be propane and lighting will be LED.
Going to have a solar setup with 2KW generator backup.
We don't get much sun in the winter here. Heck, we don't get much daylight.   :)
Dave's Arctic Cabin: www.anglersparadise.ca

Don_P

I doubt solar is much in the winter there. Generators are a ball in subzero as well. As far as expensive beams go... they are heavier and harder to work with but I imagine there are a few just standing around in your back yard,  we can size "in the round" if you want to go that route.

DaveOrr

The generator is a little Yamaha 2000is.
It will stay indoors when not in use.  ;)
Never get it started if it was left outside the whole time.
Going to need it running to get the truck running after sitting in bitterly cold temps over our winter weekends.
Dave's Arctic Cabin: www.anglersparadise.ca