Exhibition Hall Truss

[dcw815]

I'm doing some preliminary sizing of steel trusses for an exhibition hall. One set of them spans 150' and has 30' tributary width with 300psf live loading (yes it's big) and a 5.5" slab on deck. Unfortunately, for various reasons, our firm wasn't able to be responsible for layout so I can only have control over member sizes.

Any creative ideas for the top chord? The factored compression in the top chord works out to 4900kips so wide flanges are getting ridiculous and there arn't common tubes that can handle that. Just wanting to get a few ideas bouncing around. Thanks.

 

[dcw815]

Ya I'm not sure if our firm is doing the decks or not but I will definitely bring that up. I agree it's way too small.

We also have only 2 days to do preliminary design of all steel for the building. AISC magazine loves a project with a tight deadline!

 

[dik]

It's past your two days...but, many deck suppliers do not recommend deck for heavy moving loads...

Dik

 

[msquared48]

DCW:

Since thie is probably Chinese Steel, I trust you threw in an additional 50% moment of Inertia in each member for good measure...

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[connectegr]

Wide Flange chords, with wide flange diagonals and verticals, all web horizontal. Where necessary reduce the unbraced length of the chords, with short diagonal members running from the chords to the diagonals. We have worked on trusses with similar loading and even longer spans.

http://www.FerrellEngineering.com

Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.

 

[hokie66]

Agree with connectegr. The steel sections will be large...whatever is required. You might as well wait until the slab is designed, because that will have to change a lot from 5.5" if it is to span 30' and carry trucks.

 

[slickdeals]

Although I agree that a 5.5" slab will not work spanning 30', but it might work if you have steel beams at 5' o.c. or steel joists at 5' on center that span the 30' between trusses.

I have worked on a similar concept design for large loads, by using a trichord truss, where the top chord was formed by two W14's laced together and a 12-14" slab that helped to act as a composite top chord. This way you have cut down the 30' foot span to something like 24', assuming you have used a 6' wide composite top chord.

 

[JAE]

Even with a 5 ft. span, what happens is that highly concentrated wheel loads create localized stress peaks which crack the concrete. After cracking, the flex in the slab accentuates the cracks and also creates impacts as wheels run across the cracks which in turn adds to the cracking.

I've seen a number of slabs over the years with roughly 5 to 6" slabs that were torn apart by this type of degradation.