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!

 

[BridgeSmith]

For a beam that size, a plate girder may be more economical than cambering a WF.

If the floor above is concrete, consider making it composite with the floor slab. That will greatly reduce the live load deflections and reduce the weight of the beam required, especially with a plate girder.

 

[XR250]

I ran into a weird one yesterday. Helping out on a pretty average residential project where the EOR is on "vacation".
20 ft. span beam supporting 20 ft. trib. of roof and 14 ft. trib. of floor. A W10x100 was specified. Can't imagine why. Maybe he did a vibration check lol?

 

[phamENG]

A W10x100 was specified. Can't imagine why.

I haven't seen one this bad, but I've run into a lot of 'residential' engineers that just don't know how to size or detail steel.

For the sake of giving the EOR the BOD...maybe the original design had big point load on it in the original design? A large, steel observatory dome with a rotating base that was "value engineered" out of the project?

 

[lexpatrie]

Torsion? W10 is a “column” section…. Designed fully unbraced?

 

[XR250]

Torsion? W10 is a “column” section…. Designed fully unbraced?

Flush in the floor system

 

[lexpatrie]

Jersey, where’s the thread?

3/4” camber is the recommended minimum, if it has 75% of the specified camber on arrival, no further cambering is to be done, etc. (See Downey).

Beam shouldn’t have been cambered as the required camber is too low, so they probably got 3/4” or more from the shop (-0, + 1/2” tolerance under 50’), and then given it’s a W18 40’ long, the (80% effective dead) load wasn’t enough to overcome the “excessive” camber.

 

[lexpatrie]

Xr250, even so…. He might have neglected bracing.

 

[Flotsam7018]

XR - slider below or possibly a relative deflection issue? Even if, I'd have to be backed into a real corner to put a W10x100 on a residential plan.

 

[XR250]

Non

XR - slider below or possibly a relative deflection issue? Even if, I'd have to be backed into a real corner to put a W10x100 on a residential plan.

I wish that was the explanation. Middle of a room extension.

 

[canwesteng]

Camber is 100% a mistake here. Camber is for dead loads, can help reduce the weight of concrete above the beam and can improve the appearance of beams under sizeable dead loads. Assuming the floor is wood frames, it achieves nothing but wasting money, giving a false sense of security that you designed something properly, and for the expert witness to point at as an easy mistake on the plans. Beyond IBC deflection checks and AISC vibration checks, I would make sure deflection is <1/4" when you have a reasonable group of people on the floor. For example, L/240 is 2.5" - but absolutely no one will feel safe on the floor if they feel that much deflection. If you have like 6 people walking on the floor above and they feel it shift under them you'll be getting calls regardless.

 

[dauwerda]

I've never seen vibration problems in modern houses. (jerseyshore)

My house has a W12x45 spanning 27ft supporting a second floor bedroom and bathroom - While I wouldn't call it an issue, I have definitely felt it vibrate, if it were the living room/kitchen I would say it would be an issue.

A W10x100 was specified. Can't imagine why (XR250)

The plans for my house showed either the w12x45 beam (which is what was used) or a W10x60. The W10x60 would have allowed the ceiling below to remain flush - I'm guessing that might be why such a beam would have been specified?

 

[Canuck65]

I think JoshPlumSE might be on to something. A joist girder instead of a steel beam. It likely warrants at least a discussion with a company like CANAM to see if it is a viable option. If you provided them with the design loadings and deflection parameters, they would likely run some preliminary numbers to confirm joist girder depth and be able to comment on maximum shipping length.

 

[Tomfh]

100% some other systems should be investigated other than a massive beam. How much depth is there for structure?

 

[jerseyshore]

Jersey, where’s the thread?

3/4” camber is the recommended minimum, if it has 75% of the specified camber on arrival, no further cambering is to be done, etc. (See Downey).

Beam shouldn’t have been cambered as the required camber is too low, so they probably got 3/4” or more from the shop (-0, + 1/2” tolerance under 50’), and then given it’s a W18 40’ long, the (80% effective dead) load wasn’t enough to overcome the “excessive” camber.

It should be under my profile of threads I've started. Haven't messed around with the new website to see if all of the old stuff is still on here.

 

[phamENG]

@lexpatrie https://www.eng-tips.com/threads/too-much-camber.508127/

 

[Flotsam7018]

You could implore an old school method and suspend the floor beams from a steel frame in the roof structure, assuming you've got some aligned walls between the upper levels. Just don't take any requests from the fabricator to separate the load path of the tie rods...

 

[phamENG]

I toured a historic house company store built like that in a West Virginia coal town while I was in school. They said that, during the renovation, the engineer couldn't figure out how the house worked and had to call in a bridge engineer to help design the repairs.

 

[lexpatrie]

Cheers pham, Looks like another thread where folks didn't "read the manual" on camber.

Tolerance on (induced) camber varies with beam length,
"natural" camber is a tolerance that also varies with length (I believe installing it "up" is either standard practice or required somewhere in the Code of Standard Practice, but I'm going off brute recall... verify that.

But one should not camber less than 3/4". For typical situations camber should be for 80% of the dead load to allow for the unintentional rigidity induced at the ends by normal bolted connections (perhaps this is less applicable for beam on top of column). Camber is also not wise for moment frame beams and typically for purlins as well.

Lini, Does this Beam make my building look too heavy?, Modern Steel Construction, November 2012.

You can go outside this, as these are generally guidelines and suggestions to avoid trouble, but they are decent in preventing construction or field hiccups, that's why those articles were written in the first place.

I just tweaked the Camber FAQ over in the AISC forum, so that's going to disappear for a bit. I expect it to return.... I just added the Lini article as I'd forgotten he mentions camber in that document (I referenced Lini in the practicality FAQ).

 

[Flotsam7018]

@phamENG That's a sad day for that engineer.

I've come across this type of framing a few times in old timber structures before SCL, glulam, rolled shapes and all the other fun options we have at our disposal now for open floor concepts. I have never used it for new construction, but if I did, I'd think about some way to prevent manipulation to the tie rods. Having those critical elements in a non-load bearing wall is analogous to hairpins in a slab for PEMBs, though probably worse.

 

[jerseyshore]

Thanks for posting lexpatrie. Good article.

I know our old firm always had a "natural camber up" note for the past 40+ years. We adopted a similar note these days.

We used to do a lot of steel structures and I rarely rarely saw camber noted. Never did it on one of my projects. But as you can read in my old thread, stupid programs like Beamchek just have a check box and boom camber, an architect special.

So regarding the OP, it seems like general consensus is to avoid additional camber and just design a big beam (if it can be transported). And don't forget natural camber up.