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Steel/timber beam with reduced height
5

Steel/timber beam with reduced height

Steel/timber beam with reduced height

(OP)
Hello, I hope for some suggestions.

I have existing inverted RC beams (b/h = 40/50 cm, slab is 12 cm thick).

Im designing a new terrace so I need new steel or wood beam (they are 1,20 m apart). Spans between RC beams are not that large - cca 3 - 4 m. I already calculated beams - they can be from timber or steel. But Im wondering what problems / issues there may appear.

What is a better choice?

I know timber is far more cheaper. But what about details?

I have reduced height of beams because I have some height problems between terrace and a roof.

There are wood panels on top so I need flat surface above existing concrete beams.

What do you guys suggest - steel or timber? im open to new details, better options.

What issues can develop there?

There also may be some additional small torsion force on existing RC beams because of uneven loading of beams... right?




RE: Steel/timber beam with reduced height

Can you put a sleeper in the middle of the lower portion of concrete and use shallower timber, so you don't have to do that notch and the steel angle. If you use timber, you need to address how to keep the timber from rolling over. Possibly raise everything and use a timber nailer on the concrete beams with a continuous rim of blocking.

Steel is an option but does sound expensive, is this for a small project or a big 50yr life + duration building?

RE: Steel/timber beam with reduced height

How about a nailer (or two) on top of and parallel to the RC beam and then top flange hangers for the wood beams. Just use blocking atop or across the nailers to support the wood panels.

RE: Steel/timber beam with reduced height

For fairly light loads, here is a wooden tee-beam concept that could be prefabricated from dimensional lumber.
Make the flange wide enough to provide an adequate amount of wood for shear loading.
Make the web deep enough for sufficient moment capacity and deflection control.
Thickness of the wood bearing blocks as needed to get the proper top of beam elevation.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Steel/timber beam with reduced height

(OP)
Tnx for advices! really appreciate it.

EngineeringEric: Steel is an option but does sound expensive, is this for a small project or a big 50yr life + duration building?
Its a terrace (150 m2) for a coffee shop.

'Can you put a sleeper in the middle of the lower portion of concrete and use shallower timber'

English is not my first language so i have some trouble with some expressions. What is sleeper?


azcats - thats an interesting option. Will check it out.

bhiggins- Im not sure if i understand the detail you made - why do i need furring blocks on a slab? I also dont know how blocking between joists would help either. Also, span is 3 or 4 meters so deck would be pretty thick in that case.

SlideRuleEra - tnx for suggestion but i think its too complicated. There will be quite a lot of those beams, so designing them (number and spacing of screws based on the shear flow) and making them would be a problem.

RE: Steel/timber beam with reduced height

Regardless of how you build the deck, make sure you vent it too or it will not last long.

Mike McCann, PE, SE (WA)


RE: Steel/timber beam with reduced height

(OP)
good advice... well there will be waterproofing on timber panels... But the condesation might be a problem...

RE: Steel/timber beam with reduced height

Actually, here is an easier detail. Simply use a top-flange joist hanger fastened to a wood nailer.

In the previous detail, furring blocks may be required to get the necessary depth for the joists. In addition they give you wood to shim to because the concrete will not be perfectly level. Plus any moisture that does get trapped between the joists can be directed elsewhere. The blocking is to prevent the joists from tipping over.

RE: Steel/timber beam with reduced height

Greznik91:
You said..., and your sketches seem to show...; the beams are 400mm wide (15.75") and 500mm high (19.68"), the slab is 120mm thick (4.72"), thus the beams project 380mm (14.96") above the top of the slab. The beams are spaced 3m apart, clear, or about 3040mm on center. You haven’t really told us much more about this structure. Is it an existing roof to be turned into a terrace, how does it drain between the upturned beams? This drainage and some form of venting under any spanning deck system should be continued/maintained. I don’t understand your steel or wooden beam spacing, DL and LL, design loads, or the decking thickness vs. its spanning ability. Why don’t you fill the void btwn. the upturned conc. beams with structural foam blocks to within about .5"-1" below the top of the conc. beams. Then, cast a 3-4" light weight conc. slab, sloped to drain, on top of the whole thing, and be done with it? You’ll save another 4"-5" in deck height. The structural foam I’m thinking of can be bought in light weight rigid blocks 2, 3, 4' wide, by 4, 6, 8' long, by a number of different thicknesses, and just stacked in place to fill the upturned voids. It is easily cut to fit and fill. I would consider some positive drainage system for this foam fill too, down at the existing conc. slab.

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