Platform + Connecting wood to I-beam questions

[kingnero]

I'm talking about a platform, about 20 feet long and 15 feet wide.
2 I-beams span the long direction (20 ft) at both sides.
Inbetween are wooden beams, one every 15"-20" in the other direction (90° to the I-beams) .
Flooring will be MDF or similar (3/4" thick) plates.

The wooden beams rest on the bottom flange of the I-beam (or wide-flange beam, depending on the answers to this question).

1) How do I know the allowable contact (pressure) area? Contact surface between the wooden beam and the bottom flange will be quite small, What do I need to know about this?
2) What would be the best way to attach wood and steel? welding tabs on the web of the beam, and cross-bolt the wood? Special weld-on/bolt-on brackets?
3) Will the eccentricity of the load (due to the wooden beams, onto the bottom flange) cause warping of the I-beam?
4) Any other things I don't know about?

Barn floor is about 8" thick, 30 yrs old concrete, that holds up great against heavy vehicles (tractors and trailers, ...), privately owned and only used by me.
Load on the platform will mostly be (rimless) tires, I'll check for 2500N/m², =~ 52 lbs / square foot - for starters or unless told otherwise.
I'll use base plates as prescribed by a SE (see below).


I will contact a SE if I pursue this idea, but I first want to know apprx. what sizes of material I will need for this (storage area in a barn), what will it cost me (in materials) and whether or not I will need a firm to do the actual installation or whether it is straightforward enough to do myself or not.

Being in Europe, I can assure you all liability will come down to me, and not to an anonymous forum that "merely" (but well-appreciated!) offers suggestions... so please bear with me and help me to do a first cost analysis of this thing...
All help much appreciated - as well as any other tips or tricks that might be of use to me.

 

[BAretired]

The wooden beams rest on the bottom flange of the I-beam (or wide-flange beam, depending on the answers to this question). If you have sufficient headroom, placing the wood joists above the beam is simpler, provides more bearing area and does not put torsion on the beam. A glulam beam might be another option.

1) How do I know the allowable contact (pressure) area? Contact surface between the wooden beam and the bottom flange will be quite small, What do I need to know about this? Bearing joists on the bottom flange of the beam can be done but is not recommended. Better to use joist hangers.

2) What would be the best way to attach wood and steel? welding tabs on the web of the beam, and cross-bolt the wood? Special weld-on/bolt-on brackets? Joist hangers are made for wood or steel beams. They would be the best.

3) Will the eccentricity of the load (due to the wooden beams, onto the bottom flange) cause warping of the I-beam? Yes, you are adding torsion to the beam.

4) Any other things I don't know about? If using a steel beam, the top flange needs to be laterally braced to prevent lateral torsional buckling.

Barn floor is about 8" thick, 30 yrs old concrete, that holds up great against heavy vehicles (tractors and trailers, ...), privately owned and only used by me.
Load on the platform will mostly be (rimless) tires, I'll check for 2500N/m², =~ 52 lbs / square foot - for starters or unless told otherwise. Sounds a bit light for storage, but it depends on how many tires you pile up there.



BA

 

[msquared48]

If the loft or platform is for storing hay, as it is a barn, then with an 80# bale giving 15 to 20 psf per bale, stacked five high, I would use a minimum of 100 psf live load.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[kingnero]

@ BA: Height is somewhat limited (already going 3m high so I can drive/park under the platform), so I'll have to walk already while bending a bit (1.5m left, about 5 ft, and I'm a bit over 6 ft).

When you say, top flange needs to be laterally braced, that means a large X inbetween the top flanges, correct?
Why the top flanges? torsion will make the beam bend so that the bottom flanges will want to spread apart, so bottom side is the tension side, so it seems logic the bracing goes there.
And when bracing the top flange, that would interfere with floor plates... Would you care to elaborate on that?

If using wide flange beams, would that be less of a problem when placing the wood beams (joists?) on the bottom flange? That saves me another 25 cm (10") in height.

@ M²: thanks for the suggestion. I might up the load to 75 lbs/sq.ft , but it won't ever see that, due to limited height and the fact its only access will be a ladder.

Thanks to both of you for taking the time for responding.

 

[BAretired]

kingnero,
No large X. The top flange would be laterally braced by joists bearing on it and fastened to it, provided the deck is rigid enough to be considered a diaphragm, but if you don't have sufficient headroom, you must use flush framing (bottom of joist flush with bottom of beam).

Placing joists on the bottom flange does not brace the top flange, although it could still be laterally tied to every second or third joist which would be considered bracing. If you don't brace the top flange, the beam must be designed with a 20' unbraced length which could add substantially to the beam weight required. Also, if the beams are in place, it is difficult to insert joists between the flanges and still get full bearing, not to mention difficulties in physically connecting the two materials.

A pair of glulam beams is probably the easiest solution. You would hang the joists between them using conventional joist hangers. There are also joist hangers made specifically for steel beams and that would be another option. Or you could bolt a wood ledger through the web of the steel beam, resting it on the bottom flange and provide joist hangers from the ledger to the joists. There are several options.



BA