Plate girders

[MIStructE_IRE]

I was in Orlando airport the weekend and saw what I believe are some really cool looking plate girders. A deep web plate as expected but the bottom “flange” comprises a CHS. Very nice looking detail.

I would assume that the design of this would be the same as a standard plate girder? Are there any local effects/checks to ensure that the entire cross sectional area of the CHS “flange” is mobilised in tension? No different than a truss in that respect I guess..

 

[BridgeSmith]

I would think you'd have to pay close attention to the stresses in the wall of the CHS just below the weld, but for overall capacity it would be similar to a plate for the flange.

 

[Agent666]

I'd approach it in the same way as any plate girder, instead of being a typical flat plate the bottom flange just happens to have a void and be a different shape. Provided the shear flow can be dealt with at the connection for the welding I don't fundamentally see a difference in the way you would approach it.

 

[KootK]

1) Shame on you for tabling this without a picture of one of these cool girders. Shame. Your phone better have died on the plane.

2) Much depends on the relative proportions of things but I would say that the major nuance is the phenomenon that I've shown below.

3) For what it's worth, this is just like a truss so long as that truss has chords that are uncommonly stocky and flexurally continuous. You know, to the extent that every truss is really [1 Truss + 2 Crappy Beams].

 

[MIStructE_IRE]

I know Koot!! I feel the shame!! For what its worth, my phone did in fact die..

I did however find this pic on google of the girders.

You can see they’re relatively close together but covering a crazy span! I’d love to see what the top flange is made of. I doubt its a CHS.

Thanks for your sketch. It certainly makes sense alright. Im wondering how great this effect would be however when you consider the stiffness of the CHS Flange in comparison to the stiffness of the overall girder?

 

[KootK]

At those proportions, I don't see it being a big deal. Given the spans, I wonder if it's not tubes because there's prestressed reinforcing inside.

 

[KootK]

When I googled this, I came up with the framing below from the same airport I believe. Equally bad ass if not more so. Airports are a structural engineer's paradise. I used to have a photo collage going of all the neat stuff that I'd seen. Vancouver, Toronto, Denver, Chicago. SF & MKE are a little disappointing in my opinion owing to their dating back to an age when that kind of stuff seemed to often be done in oppressively heavy looking precast.

I've bowled over a lot of petite, female business travelers while walking quickly and staring up at the ceiling.

 

[jayrod12]

I took out a 7 year old kid in the Victoria airport because I was too busy admiring the heavy timber and steel trusses that were framing that roof. Poor kid didn't stand a chance.

 

[KootK]

It's actually the local giga-plex Costco that gets me the most. I get tricked into going there with the family once or twice per year.

- Exposed PEMB on a massive scale.
- Packed like a human ant farm on the weekend.
- Grocery shopping is super boring.

My abnormally long arms and penchant for gesticulation don't help. I end up brushing my hands against a lot of things that I shouldn't. One time, while pointing out diaphragm trussing to the kids, I managed to slip my hand inside the partially unzipped coat of a fellow shopper. Thankfully it was a dude.