Exhibition Hall Truss
Exhibition Hall Truss
(OP)
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.
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.






RE: Exhibition Hall Truss
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Exhibition Hall Truss
You can use a welded plate girder... one of my current projects uses one 8' deep with 4" thick top and bottom flanges... just need to get 'big'... It's a consequence of having a silly design criteria...
Dik
RE: Exhibition Hall Truss
What is your truss depth? Ideally you want to be around L/8 to L/12, but you are dealing with some high loads.
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
I found some cases when establishing the moment strength of composite beams in which the limit value did NOT exceed the bare structural steel moment strength. This I then reasoned was because the slab was adding as little stiffness that trying to count on it to stiffen the "hard" beam under it was like trying to do so with a slab of butter. Hence the steel moment strength was showing as the limit as well for the composite action. That was using the LRFD 1992 code.
If such is the case, to minimize steel aspect you may use first box chords or void chords with hidden steel at some material cost.
Of course when minimizing size of the chords their slenderness grows and bracing becomes very paramount; the secondary members plus slab system needs be able to provide the required bracing. That system is analyzable for the bracing forces plus those of the secondary system, or just making the complete 3D model showing the initial imperfections etc ... after direct analysis only what not properly addressed in the model needs be looked at from a bracing viewpoint, since all bracing forces will be already extant for what properly addressed in the model.
RE: Exhibition Hall Truss
Dik
RE: Exhibition Hall Truss
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
This is one of those cases where you need the AISC Certified Erector and Fabricator.
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
Consider using jumbo W14 sections and grd. 65 steel as chords. Positioning the chords in a minor axis position simplifies connection design if you use W14 sections for the web members too.
Also is you proposed deck 5.5" fill above the deck or 5.5" overall? I agree with the others that 5.5" overall sounds a little too thin for the proposed loading and use.
regards,
Michel
RE: Exhibition Hall Truss
Like Jed said, do something like this and you are SURE to get into one of the magazines!
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Exhibition Hall Truss
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!
RE: Exhibition Hall Truss
Dik
RE: Exhibition Hall Truss
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
RE: Exhibition Hall Truss
www.FerrellEngineering.com
Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.
RE: Exhibition Hall Truss
RE: Exhibition Hall Truss
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.
RE: Exhibition Hall Truss
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.