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Holes in a roof beam. What is the purpose?
8

Holes in a roof beam. What is the purpose?

Holes in a roof beam. What is the purpose?

(OP)
I recently saw this roof beam with circular holes in an airport. What is the reason to cut out those holes? Reduce weight? Make it stiff?

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

(OP)
Thanks JAE. Learnt something today.

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

I've seen this claim before and it's always struck me odd (2nd link above)

"Better strength and stability – their crenellated design makes castellated beams more resistant to bending and deformation."

I feel it should include the words "for the weight of the material that is used."

I recall seeing it as a way to take an I-beam from the rolling mill and convert it to a deeper beam using a trapezoidal zig-zag that is shifted and then welded along the middle at the tops of the trapezoids. It left them with hexagonal openings.

The bit with circular holes is wasting material that is cutout and discarded, but they have an interesting look and reduce installed weight, so why not?

RE: Holes in a roof beam. What is the purpose?

(OP)
Yes, round or hexagonal cut-outs and then anti corrosion painting the cut edges is a pita cost rider. May be resulting lighter beam reduces the column sizes and easier erection offsets the costs?

Wonder how the size and spacing of cut-outs is calculated.

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

It's along the neutral axis so it has to resist the shear between the upper and lower portions.

I only did direct mechanical design, not regulated and codified structural design, so I'd ensure there was sufficient shear area and then divvy it up some interesting way. Same thing happens to main spars in aircraft wings - lots of holes. I would not be surprised if the standards have more to say on the subject.

RE: Holes in a roof beam. What is the purpose?

(OP)
Looking at the photo, guesstimating about 60% weight reduction?

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

3

Quote (3DDave)

The bit with circular holes is wasting material that is cutout and discarded, but they have an interesting look and reduce installed weight, so why not?

Not as much wastage as you might think.

RE: Holes in a roof beam. What is the purpose?

Edison
Good place for you sparkies to run stuff through, like in the photo you posted. More often pipes and ducts.

And then, some architects like the look.

RE: Holes in a roof beam. What is the purpose?

(OP)
hokie

lol, yes, us sparkies ruin the aesthetics with our works. I am planning a new 50 ft wide x 500 ft workshop and might go for this castellated beams design.


Retrograde

That seems like a lot of work driving up the cost, weld distortion etc. and finished product is not gonna be pleasing to the eyes.

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

I don't believe they are used much these days, in Australia at least, (but I could be wrong) exactly because of edison123's comment.

They were popular in the 80's and 90's.

RE: Holes in a roof beam. What is the purpose?

Increases the depth of the beam also. Blodgett has good chapter on them.

RE: Holes in a roof beam. What is the purpose?

In an airport. It does look "aircrafty" :)

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Holes in a roof beam. What is the purpose?

They should be stiffer than the source beam, if one ignores the holes.

There's a Best Buy in Hawai'i that has them as roof beams with a parking garage on top

Edit: its a single, it's not a garage. So an elevated parking lot that sits on a roof.

RE: Holes in a roof beam. What is the purpose?

(OP)
lexpatrie

Do these beams sit on top of the parking garage or is the parking garage sitting on top of these beams?

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

(OP)
IRstuff

Yes, flanges weigh 40 to 50% of total. (Metric beam 125 to 600 depth).

Assuming 70% of the web is cut, that leaves a decent 30 to 40% weight reduction.

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

Do they ever just cut a bunch of circles, as they do with regular beam penetrations? Or is it always cut and rewelded for material saving?

RE: Holes in a roof beam. What is the purpose?

The parking isn't a garage per se it's a single level on the roof.

Edison, it's not typically done that way, they cut the beam mid depth then weld it back together to make a deeper beam with the holes in the new midline. See the figure above.

Now, that photograph above, I'm not convinced that's a standard castellated beam. that looks like what you describe, straight up cut out holes.

3ddave, I think the comment is accurate, within the context of creating a larger moment of inertia (potentially larger strength as the flanges are farther from the centroid, provided shear in the web doesn't govern), and increasing the effective stiffness for the same weight (deflection)

RE: Holes in a roof beam. What is the purpose?

(OP)
Thanks lex.

The ones in my photos cellular steel beams with holes cut out. I did not see any welds.

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

Concur.

RE: Holes in a roof beam. What is the purpose?

Like SnT, knowing it's an airport, I believe this case is primarily an architectural choice to mimic the aesthetic of a wing spar.

Clearly it wasn't planned (or planned well enough) for MEP penetrations -- look at that fire line!

RE: Holes in a roof beam. What is the purpose?

I have a couple of questions here:

1. I know in the days of cheap fabrication, castellation was used to save on material cost. With the cost of fabrication these days, might this just be holes cut in a beam instead of castellation? I can't see the picture well enough to see if the web is welded at mid-height.

2. Has anyone noticed the span direction of the ceiling? Must be a ceiling because it spans in the same direction of the beams (more likely girders). I'd love to see the framing plans for this one.

Just my input.

RE: Holes in a roof beam. What is the purpose?

Yes, there must be a series of purlins above that ceiling. But in the picture, I can't see fasteners.

RE: Holes in a roof beam. What is the purpose?

Like edesin123 says. They seem to me to be holes cut out of a beam and not castellated beams, hard to see from the photo.

RE: Holes in a roof beam. What is the purpose?

A key advantage like some of you mention is to have space within the depth of the beam to run services through. This means there is no need to hang services below the beams and therefore you can have a larger open area or reduce the overall height of the building. The removal of the weight can in theory help achieve larger spans?

RE: Holes in a roof beam. What is the purpose?

Only in theory. Practically, it makes no difference.

RE: Holes in a roof beam. What is the purpose?

(OP)
It is circular holes cut in the web with no welding. It is just a roof with no superstructure. One more photo.

Muthu
www.edison.co.in

RE: Holes in a roof beam. What is the purpose?

Edison,
Those are properly called rafters. And they form the superstructure, along with the purlins which support the roofing. The purlins also support the ceiling which you see in your nice photos.

RE: Holes in a roof beam. What is the purpose?

(OP)
Thanks hokie. The design looked interesting and hence my photos.

Muthu
www.edison.co.in

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