Cantilevering Structural Grating
Cantilevering Structural Grating
(OP)
I have a prefabricated building that i am designing an elevated structure for it to sit in. The client wants a deck around the full perimiter. This building has lifting lugs that stick off the side so my support beams have to be outside of these lifting lugs for it to fit in place. This means for my platform to be close to the building, i need to look at cantilevering the grating about 8 inches past the support beam. Has anyone seen this done before or have any literature on a possible standard for this situation? I've attached a model view showing where the grating needs to extend over the lifting lug and also a sketch of what i am trying to accomplish. Any insight is appreciated. [/link]






RE: Cantilevering Structural Grating
That being said, I probably wouldn't think twice about it, I'd be overly conservative on my bearing bar spec and be done with it.
RE: Cantilevering Structural Grating
RE: Cantilevering Structural Grating
RE: Cantilevering Structural Grating
Dik
RE: Cantilevering Structural Grating
The ability of decking to handle negative flexure will vary based on the specifics of the deck.
The deck we typically specify has bearing bars in one direct, and small rounds in the other direction. These rounds will brace the compression side of the bearing bars for positive flexure, but not negative flexure. Like the cantilever beam over a column/inflection point bracing question that comes up routinely, if you're using this type of deck you`ll have a huge unbraced length for the compression (bottom) flange, and hence very little capacity.
RE: Cantilevering Structural Grating
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Cantilevering Structural Grating
If grating goes, say, 1/4" from the building, you could probably eliminate the toe plate. But your detail is fine if you need it.
Looking at your detail, would it be possible to run a small channel to support the grating end rather than having it cantilever? I think 8" should provide enough space for connection clearance.
RE: Cantilevering Structural Grating
RE: Cantilevering Structural Grating
As far as the mechanical properties, I had to check some grating just today, and from what I can tell it's just a simple section modulus calculation. They must assume 24,000 psi allowable due to lateral bracing, because that what their spans indicate.
I'm not sure how many engineers or technical staff are left working for the grating companies anymore. I've tried calling and all I've gotten is someone who can go to the same page of the online catalogue that I'm already on.
RE: Cantilevering Structural Grating
Thanks for the replies, I'm not too concerned with the strength of the cantilevered section as I agree i believe it is just a simple span situation, my main concern is anchoring as JedClampett has described. We usually call out grating clips to secure grating but I was wondering if in this situation if those would be sufficient or not if someone were to stop on that edge. I will probably do as Once suggested and just call the manufacturer and see what they would recommend. It is good to know that this is not uncommon though. Thanks again.
RE: Cantilevering Structural Grating
Thaidavid
RE: Cantilevering Structural Grating
The cantilever distance is quite small.
Dik
RE: Cantilevering Structural Grating
And I agree with others that you should check the uplift reaction on the end of the grating piece opposite the cantilever edge, and see whether your typical saddle clips would have the appropriate capacity. This reaction might not be very large if your back-span is significantly larger than your cantilever length.
RE: Cantilevering Structural Grating
RE: Cantilevering Structural Grating
RE: Cantilevering Structural Grating
I have also used those grating clips myself, at times. However, I don't really like them much because in the environments in which I work they tend to loosen, and then they can be dislodged, or even fall off. I sometimes use them for securing small electrical support posts and such on grating, or securing small removable grating sections, but I've mostly quit using them for regular fastening.
Dave
Thaidavid
RE: Cantilevering Structural Grating