50 foot clear span steel beam in residential construction 2

[KevinChez]

I have a high end residential project with a 50ft x 50ft garage located under the upper two floors. I was going to design a couple of 50 foot deep W-beam's to avoid posts. They want to have room for 5-6 cars and a turntable.

Seems crazy to have a W24 or deeper. It is going to be so heavy. I doubt I can talk the client into posts due to the layout. But maybe costs/constructability will govern.

What are your thoughts on cambering this beam and what is an appropriate L/??? deflection criterion?

Thank you!

 

[Eng16080]

It's easy for a client to say they want a big open space without any posts or other interior support. You can go through the entire design process with them unwilling to make any compromises. But then they see the cost, and everything very quickly changes.

I would quickly determine an approximate beam size, column sizes (at the ends) and footing sizes. Then get some preliminary costs.

For deflection, definitely use at least the code minimum, which is probably L/360 for live load and L/240 for total load. You may also want to limit the absolute deflection since L/240 is 2.5". I have, in similar situations, limited deflection to somewhere around 3/4" to 1". Cambering the beam, as you mention, might be beneficial as well. A steel supplier/fabricator should be able to give a price for cambering and then you can let the client decide if it's worth it.

If you actually end up spanning 50 ft, use the deepest section you can. Go deeper than W24, if possible. Deeper is cheaper they say (or something like that).

 

[XR250]

Can't imagine the steel cost would be an issue for a client who is installing a turntable

 

[HTURKAK]

Just a preliminary calculation shows , the beam section should be heavy built- up section if the garage level beams carry the upper two storeys. I am more familiar with Europian steel sections and the the heaviest standard section HE 1000 could be for one floor loads.

I am thinking two options ,

- Each storey beams will support related floor only ,
- The first upper floor could be full storey depth truss ( if architectural plans allows )

 

[lexpatrie]

I don't see why the cost of camber would be a question for you, as the structural designer, if it's necessary, give options - a) no camber W24, b) camber with W21 or whatever. Then on the final it's what they pick, if they don't want to ask around and figure it out, that's their choice.

Your job is life-safety, not lowest cost. And you owe it to the public, not the owner.

If you wanted to go exotic, the full height truss for the floor above sounds interesting. Similar to a staggered truss system in steel framing.

 

[TRAK.Structural]

50 ft clear span sounds pretty extreme for residential work, even high end custom stuff. Cost would be the least of my worries especially if this is supporting more than just roof load. Go heavy and safe.

 

[phamENG]

I usually try to limit live load deflection in residential floors to 1/2" or L/480, whichever is less. For girders, though, I do L/600.

In this case, vibrations will be your enemy. Frank Woeste has done some work on wood floor vibrations - I suggest you check it out. You're a bit beyond the rules of thumb, though, so you'll want to pay close attention to the actual performance.

At 50ft, your beam will need to be delivered in at least 2 pieces. You may want to do splices at third points depending on loading. Transportation is the biggest issue with the longer length. But breaking it up will let them us a smaller crane, too. Of course that eliminates camber, but camber is tough in residential. Residential loading is live load dominated - usually close to 4:1. So very little of the load can actually be accounted for in cambering it.

I don't totally agree with @lexpatrie on this one. Yes, life safety is paramount...but as engineers we should be seeking out the most efficient and sustainable ways to design structures that are reliable. Within reason, of course. And I use sustainability broadly - environmental, economic, and social (though social usually plays a vanishingly small role in our part of the design process). And engineers who don't consider constructability won't be practicing very long. So I applaud your attention to these things, @KevinChez .

 

[XR250]

Why can't 50 feet be delivered in one chunk?

 

[dold]

I feel like W24 is going to be the bare minimum I'd use for such a span and such loading. Just tell 'em what it needs to be. WbigXheavy. My folks built a house with a pretty solid clear span in the garage and the WF stuck through the bottom of the ceiling, dad mounted a trolley and chain hoist on the bottom flange. Just tell them it's a feature for the garage.

 

[lexpatrie]

I'm not aware of an outright prohibition on using camber on live loads, but one would be wise to consider "plausible" live loads in this situation. Camber is for serviceability, not strength, anyway, and the "rules" are guidelines, within reason, one can deviate from them (beyond, say, trying to camber a ten foot long W8x10 that won't even fit in the machine).

From the sound of it, this is the loadbearing direction for the floor and roof above, as well as two (?) walls, so there is some dead load, and given the large span, camber of some sort is wise and even the 3/4" minimum recommended camber (with tolerances) would help. The way we calculate deflections isn't all that realistic anyway, as some of that deflection is there before the finishes are applied, and the garage doors can be adjusted if the deflection isn't absurd.

As far as fifty foot length, I see no issues unless there is some really odd mining town between the project and the fabricator and they can't make the corner at the intersection.

I think you're over interpreting my comment Pham. The implication I went after was that camber needed to be considered as a cost impact to the project by the engineer. Camber is pretty trivial in the grand scheme and I'd struggle to think of any practical design engineer who sincerely provided a heavier beam because the perceived cost of camber precluded using a lighter beam with normal camber, or a practical design engineer that even considered the possibility of camber being more expensive than a heavier beam.

 

[phamENG]

Why can't 50 feet be delivered in one chunk?

Depends on the location. Where I am, a house like this is either out in the middle of nowhere on a big piece of land (pretty easy to deliver), or it's close to the water (creek, river, or ocean) down a tight, winding road or down a small alley where they have to hand carry floor trusses the last half block or so anyway if they get brought in on a large truck.

 

[phamENG]

WF stuck through the bottom of the ceiling, dad mounted a trolley and chain hoist on the bottom flange.

Without some significant effort on the part of the architect, that would violate garage/living space separation requirements for what passes as fire protection in most residential codes. I ran into that recently on a project.

 

[JoshPlumSE]

50 feet is a pretty good span. That is close to the maximum length that can be transported, I believe. Some places you can get a little bit longer. Some place it might be difficult to do anything over 30 or 40 ft.

My tendency is to think that we (structural engineers) aren't the most knowledgeable about such things. It's best to ask a general contractor that you've worked with what he thinks the cost would be for such a transport in this area.

I think it can be done. If it is done, I think camber is what you want to use to counteract the expected dead load deflections.

Depending on the depth you come up with for this beam, I also wonder if a customized joist girder might be a more affordable option.

 

[KootK]

With camber, keep in mind that:

1) It does not impact deflection, only final, vertical position.

2) Once a 50' beam, natural camber will be significant, perhaps problematically so depending on your detailing.

 

[dauwerda]

Semi trailers are allowed to be up to 53ft, so in general, anything below 53ft can be transported without any special (overlength) permits. Obviously that does not account for local conditions that phamENG brought up. We regularly ship steel up to 60ft in length but our preference is to keep it under 53ft and if at all possible prefer 48ft and below (Lot's of flatbeds are 48ft long).

A6 allows natural mill cambers to be up to 1/8" in 10ft, so the beam *could* naturally be cambered up to 5/8" straight from the mill.

I think phamEng brings up a good point on vibration - If it were my house and I'm spending that kind of money I would be pretty upset if I feel bounciness - using camber to control deflection in order to use a lighter beam will not be helping with this issue.

 

[271828]

Vibration will likely control. If you don't check it for that, you're taking your life into your own hands, especially with a residential client. They're a lot more likely to be irritated and sue you.

 

[KootK]

I'm less concerned about vibration on this than others seem to be. Unless I'm mistaken, these beams will be part of a transfer floor system that supports the superstructure above. In my experience, such systems tend to have pretty high M/K ratios and, therefore, natural periods longer than those that tend to bother humans.

By all means, pay some attention to vibration on this. I just don't feel that it needs to be a deal breaker on the scheme.

 

[lexpatrie]

I know this is going to turn into a long conversation where people try to squeeze in little pings in what I'm saying.........

Again, generally (and I'm NOT an attorney) but I'll wade in nonetheless. As a design professional (where I practice) similar to Doctors and Architects, your litigious client will need to find another persnickety engineer (perhaps more broadly a fellow "design professional", like an Architect or Contractor) to fill out that this suit has merit and the complaint against the design professional involves either incompetence, failure to meet the standard of care (that mercurial little pixie), or some kind of other issue, like a delay claim.

e.g.

PRACTICAL CONSIDERATIONS: IS THE CERTIFICATE OF MERIT STATUTE (CCP 411.35) EFFECTIVE; SHOULD IT BE CHANGED AND HOW CAN DESIGN PROFESSIONALS PROTECT THEMSELVES - Furukawa Castles LLP

CCP 411.35 (b) (1) requires that before filing a complaint or cross-complaint against a design professional for professional negligence, the lawyer representing the plaintiff and the lawyer(s) representing the cross-complainant(s) must serve a certificate declaring that the attorney has...

furukawacastles.com

Common design professional malpractice claims - Furukawa Castles LLP

Construction projects may be large and complex. Building owners and other impacted parties can sue anyone involved in the design and construction of the structure, including design professionals, if something goes or if they are dissatisfied. Design professional litigation generally involve any...

furukawacastles.com

(this is the first google hit on "complaints against design professionals" so don't think this is an endorsement or has anything to do with my state of practice, and keep in mind these folks seem to specialize in "prosecuting" design professionals as they have all manner of "you should" material throughout the page and at the bottom which 99% of design firms on a small project will not do, i.e. Peer review.

Without bothering with delay claims, as those tend to go forward without much merit regardless........ (because the burden of proof is so fuzzy they tend to survive motion for summary judgement regardless of merit, and they don't need a certificate of merit from a design professional, let alone much evidence besides somebody's feelings were hurt.....)

A complaint about the floor "vibrating" is going to be particularly ..... a reach, to pursue. Sure, they can potentially find some Ph. D. somewhere to "prove" you suck, (or they may spend six months trying to find somebody uptight enough to swear out that complaint, or never find the guy, or he'll be a vibration expert and somehow nobody is going to notice until the 11th hour that he's not a P.E.....), but as life-safety and design within the standards, unless this is a dance floor, or a building with sensitive equipment that is disclosed, (and yes, I've done those, on elevated floor systems, specifically medical centrifuges on wood trusses), or something specific in your contract that "elevates" the standard of care (i.e. "hey do you guys want me to design it so it doesn't vibrate at all???" emails), or you willfully ignore the issue knowing full well they're intending to put an MRI, yogurt centrifuges or whatever on the floor and then it cannot be calibrated because the floor vibrates too much, (i.e. loss of function of the building) there isn't anything in the building code or AISC that REQUIRES you design for vibration. From the "attorney" standpoint, this is going to be a difficult claim to pursue for their client.

Of course, this whole thread where people are adamant vibration needs to be considered, should it be discovered, would be "helpful" to the plaintiff's claim, so to speak. But this discussion has demonstrated (to me) that there's no clear consensus on the subject. And it's not a four out of five dentists recommend brushing your teeth with toothpaste (because the fifth dentist wants to bill insurance companies for filling cavities all day long).... some engineers get more excited about vibration, others do not.

There are actually standards in the code for deflections..... the "standards" on vibration are supplemental documents published by various groups, design practices and such, and are really not standards. Even "best practices" are not standards. There are design guides on it, (Thomas Murray is The Guy, or, rather, WAS the guy. Fantastic speaker and engineer, by the way, I can't think of who will replace him, my first thought when the news broke about the VT shooter was Please Not Frank, and second was Please Not Thomas), just like there are (now) design guides for ponding and camber (the distinction here is that the IBC actually has language about ponding and so does ASCE 7 which is a code referenced standard, but the AISC ponding guide isn't code-referenced that I know of).

(As an aside, there are times where things are just so bloody obvious as to not be bothered with in a standard, i.e. Don't leave surgical sponges or surgical instruments in your patient, put the plug back into the drain hole after you drain the oil out of a car's engine while doing the oil change, put on ALL the lug nuts after you change the tire rim, so it's a bit murky).

Now, that doesn't mean that somebody who can afford a 50' garage beam won't feel like pouring money at something futile in the attempt, or specifically on the theory that you will exhaust your attorney defense coverage on your O&E rather quickly, which then forces a settlement, so to speak, regardless of the merit.....

A6 allows natural mill cambers to be up to 1/8" in 10ft, so the beam *could* naturally be cambered up to 5/8" straight from the mill.

The camber specification "includes" this, so if the camber is "close enough" they aren't required to camber it further, by the way, though this is unlikely as the 5/8" would be the worst case camber of any beam, basically, ever, and hypothetically you can get "over" camber as well, unless you specify a tolerance, as I recall, so you can get more than you asked for.

Have I already referenced the FAQ on camber or did I not write it yet?

2006 - Specifying Camber

I think the camber discussion, as we get further into it, is perhaps moot, as it feels like this beam is the LFRS on this end of the buildling, which means it's best to avoid cambering it, or, alternately, the beam has to be framed over the top of the column which makes the moment transfer tougher for the moment frame.

If it's more deflection controlled, one could explore a top plate or a bottom plate or both.

 

[271828]

It is not a reach that an owner would pursue a lawsuit over floor vibration. I've worked on multiple such lawsuits.

The AISC Specification Section L4 requires that vibration be considered, so it is a formal building code requirement for steel-framed floors. A wood floor with steel framing? That's not as clear. It doesn't matter because the expert on the home-owner's side will make a field day out of "standard of care" and "vibration wasn't checked."

A home owner isn't going to tolerate a bouncy floor. When they walk and the big-screen TV jiggles or dishes rattle in the sink, they'll only tolerate that for so long and then they'll demand the floor be "fixed." If the contractor or engineer tells them to shove off because that's not a requirement, the next phone call is to a lawyer.

OP, vibration is most definitely something to consider. Like someone above said, it might not end up controlling the design, but it needs to be taken seriously.

 

[jerseyshore]

I've mentioned this here before (started a thread actually), but last year I got called in on a high end residential project where they specified a ~40 ft long steel beam holding 2 stories above. It was a W18x175 and they also specified 1/2" camber.

Guess what happened when they installed it? Huge belly in the middle. 2nd floor framed and built. Didn't move a millimeter. Attic floor and roof built. Still didn't move. The dead load on residential is really low compared to LL as pham mentioned above. They had to cut custom studs on this first floor to match the slope of the steel beam. Nothing they did could flatten it out. Flooring guy had to level the 2nd floor above it so that it wasn't noticeable.

I've never cambered anything in a residential setting and definitely won't after seeing this beam. As Koot said natural camber is significant on it's own for a beam that long.

I am also not too worried about vibrations unless it's going to be a gym or something right above it. I've never seen vibration problems in modern houses.