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Residential Steel Beam common practice 1

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COEngineeer

COEngineeer

Structural
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Sep 30, 2006
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I work in Colorado. When you use steel beam (ie. W10X), what maximum or maybe comfortable to work with length do you usually specify? Sometimes I wonder if I should just continue the beam or stop it at a column and specify other smaller/bigger beam (with connection on top of the column).

 
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The longest span that I have used in residential work is an 18' simple span using a W12. The beams are not the problem, just size them as usual; full load allowable deflection is often the criteria that dictates beam size. Coming up with (carpenter-friendly wooden) columns that can carry those loads is more of a challenge - I consider that to be the limiting factor.

[idea]
 
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Due to bulk plane limitation I get a lot of projects where 2nd floor plan foot print is about 2' smaller than main floor. So theoratically on this project I can use up to 70 continuous beam with 2 columns in the middle. Just wondering whether I should analyze it as 3 continuous span and put splicing locations OR size them as simple span and size them individually. OR 2 continuous span and 1 simple span. I hope you understand my dilema :).
 
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Opinion: I would never size any beam in "typical" residential construction to be either 2 or 3 span continuous - at the construction level the understanding and quality control to make that happen (in a structurally correct way) is just not there.

Suggest that you consider simple spans, but see if economics will allow using one beam size for all applications. In the field, getting various beam sizes mixed up and putting them in the wrong places is a very real possibility.

If you must use different sizes, one way to help minimize field errors is to try to use only one weight beam for each nominal beam height, ie. one size W8, one size W10, one size W12, etc.

[idea]
 
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I wouldn't go with a 70' continuous beam. Transportation and erection are really your limiting concerns. For analysis try to model the actual in situ condition; after all you specify splice locations.

For residential, I would probably break a 70' foot span into three spans with shear splices.

 
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When dealing with wood construction, especially residential, I call out contin. steel beams with caution. Sometimes, you have trouble getting the bottom flange bracing you need for cont. beams. If I can get by with simple spans, that is the way I go. You don't have the bottom flange bracing to worry about and you may be able to keep the crane off the job.
 
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Good point slide. I just thought it would be nice to make it continous so I can make the size of beam smaller. I thought about using 2 continuous span and 1 simple span. But then I need 44' long beam. Is that too long for a residential? Then I began to think to design it as 3 continuous span and put the splicing at the 0 moment. that would make maximum beam length roughly about 22'.

The columns are going to be rectangular steel pipes. I like to avoid wood/lvl column on heavy steel. So if you have 3 simple spans, they still have to splice the beams right by the support right? If they have to do this anyway, why not just design it as 1 continous beam (smaller member) and splice it at 0 moment (2 splices).
 
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rday.. thats what i meant. 70 ft with splices (longest member will be about 24 ft).
 
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I would make them all simple beams. Keep it simple.
 
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well... if I make it continuous I will only need W 10x88. If I make it simple than one beam I need up to W 12x96.
 
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That's the trade-off you have to deal with and why you need to use your engineering judgment. You're talking about a lot when you want a residential contractor to deal with the details associated with continuous steel beams and bracing and so forth. SlideRule gave some very good advice.
 
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96/88 ~= 1.091.... 9.1% cost increase on a single component (even if principle to a project) would not make me blink if I believed (as clearly is the case here) that it would simplify the contractor's job and be more certain of acheiving a safe and structurally compatible solution.

I do have to say that I have specified cantilevered beams with a drop in span before on residential. It's the sort of lego-like construction that can appreal to a contractor's common sense quite safely. These guys are virtually never dumb, just busy doing the stuff we don't have to deal with. I would not do that on such a long project though, and agree completely with UcfSE and SlideRuleEra.

Good luck,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
 
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Most steel framing is simple span or articulated framing (with a tiny cantilever) for commercial and residential projects for exactly the reasons given. Namely, SE does not want to detail the kicker braces and the contractor does not want to erect a multi-span beam and deal with the kickers either. More so for wood butchers than a real steel erector I would say.

How many folks bear steel beams on built up wood stud columns? I have a philosophy issue with bearing a stronger material on a weaker material, even if the code stresses are OK. Steel beam gets a steel column.

I saw a steel beam bearing on a LVL beam a few months ago "designed" by another SE. It passed the framing inspection, and the stresses looked Ok from a cursory view, but I thought it looked real strange...
 
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yeah, I dont use stud pack for steel beam. i usually use TS 3x3x3/16. so I figured, if I design it as simply supported, they have to connect the 2 beams anyway because you cant really bear 2 beams on TS 3x3x3/16. So I decided to design it as continuous beam and put the splice at 0 moment instead. To be frank, im pretty new engineer my self, so I dont really know what u mean by kicker braces.
 
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We have sucessfully used continuous beams in residential applications several times. We don't go over about 40 ft or so for a single piece. The only complaint we get is when we too refuse to bear steel on wood. For W10x88 or W12x96, you can bet they'll have a crane no matter what length, and really, all the erectors have to do is bolt the thing up. We check to make sure the bottom compression flange over columns can span unbraced, and then design the splices at location of zero moment. It goes together quickly, and the continuity really helps with deflections.

Those beam sizes sound really heavy for residential applications, and are not the most efficient beam sections. Are you being limited by headroom or something? On the other hand, they have enormous flanges which should help the unbraced length issue.
 
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PMR, I put other choices on my plan. Typically they want W10x because with 2x nailing plate, it will be flushed with the floor joists. But I do give them options on my plan (up to W16) if they are willing to see the bottom of the beam (wrap it or just drop the ceiling a little at certain spot).
 
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It has been 30 years since I have done much on the Front Range. I am assuming that about 1/4 of the contractors who would be building something requiring a heavy beam, would have some steel experience.

My experience in the mountains (resorts) and Grand Junction is.....Depends on the contractor, if I can know this. A lot of the upper priced residences are essentially small commercial, from a structural standpoint. Cranes are commenly used and some amount of steel construction is also commen. I go for continuous lengths unless uplift becomes a problem. I also tend to minimize mixing of sizes due to the field connection problems.

I have also been known to show an alternate size/assembly. I have found this can create minor problems of communication but, it usually has served to focus the contractors on what can be done and they can seriously consider the consequences of each alternate.
 
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Holy smokes, you are calling out some big beams for residential work! I have been doing residential engineering for years and have not come up with anything close to those sizes. I would talk to the contractor and/or architect and try and come up with some alternatives. Steel work in the residential world is a completely different animal than with commercial, and simpler is definitely better.
 
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From the Mid-west - different parts of the country often do things differently.

Yes - those beams seem a bit big for residential construction. About the biggest I have ever needed was something like a W10 x 33 - maybe W12 x45

Don't forget that many times those beams are wrestled into place by hand. So shorter simple span designs make sense. Max trucking length is about 48'. Typical residential post spacing is usually in the 10' to 15' range - though I have done up to 25' for a pool table room. A column and a few cubic feet of concrete footing are rather cheap.

Keeping them the same size also makes sense - if the dollar penalty is not too big. Ever try to figure out if it is a W8x10 or W8x13 -- not easy.

Always use steel columns with concrete walls - but I usually put second floor steel beams on wood columns if using wood stud walls. That way - when the wood walls shrink AND they will - the beam will come with them - or hopefully.

 
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We do a lot of big houses up in the mountain so the snow load is 80-100 psf. Plus the side upper exterior walls usually dont stack with the lower exterior wall so yes... big beams and not a lot of walls.

 
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