Limit State Resistance Factor for Hollo-Bolts 1

[Yao1989]

I am currently working with a project where canopy structure is being hung to base steel using a hollo-bolt. Does anyone know what is the appropriate safety factor to use in limit state for this blind-bolt product? I practice in Canada, where we use CISC S16-14, which says we should use resistance factor of 0.80 for bolts, while the American AISC 360-16 states resistance factor is 0.75 in LRFD, However, I am not sure if that is the correct resistance factor to use. Has anyone else ever dealt with this before?

http://www.lindapter.com/american/Downloads/Get/Product_Focus_Flyers/HB_flyer_811.pdf

 

[jochav52802]

Hello Yao1989,

I'd check out the RCSC Bolt Specification within the AISC 360 manual, (see the section that immediately follows the commentary section, which is the gray section you can see from the side of your manual.) See if those bolts are even covered as that's the governing spec for structural bolts. You could contact RCSC directly as well if you don't have any luck; I've found them to be quite responsive considering they're a volunteer organization...you can grab their contact info via a quick Google search.

Hope that helps; please update you post if you figure out the answer as I've considered using those bolts before too and am interested in what you find.

 

[Agent666]

This SCI guide (check page T160) has some structural capacities in accordance with Eurocode 3 plus a whole lot of other useful information on hollo-bolts. I'd use whatever strength reduction factor is applicable to bolts in your local code, or compare eqn from Eurocode with your local code (you can probably back calculate area for example). Also contact lindapter they should be able to help with specific technical queries on what is appropriate.

Otherwise lindapter has published values of "allowable" values but they tend to have a safety factor of 5 applied which results in extremely restrictive capacities if using them for primary structure.

Also keep in mind the size stated for the thread is not the overall diameter of the bolt due to the sleeve configuration. Consider the hole diameter when looking at calculating min edge distances, bolt bearing and tearout, and the loss of strength in your section due to the loss of material.

I think for a M16 bolt the hole is 24mm or so from memory, so you lose quite a bit more material than a std bolt. This can restrict some detailing like you need larger bolt spacings/edge distances.

They also require a very tight tolerance hole to get them to clamp correctly (0.5mm from memory greater than the bolt outer diameter), something to be aware of. I've specified drilling of the holes through both plies on site before if I expected tolerance issues.

 

[Agent666]

By the way in Eurocode (for UK anyway) the partial factor of safety is 1.25 for bolts, so 1/1.25=0.8 traditional strength reduction factor.

 

[TLHS]

Compare the LRFD method 'allowable loadings' (a terrible use of terminology) as per their brochure to your factored loads. Their values already include the phi value, as per the ICC report. I haven't done an extensive review of the Canadian vs US bolt provisions, but I'm pretty sure they're close enough that I'd write two sentences in my notes justifying the equivalency of the code provisions rather than trying to back calculate equivalent values for a proprietary product. Leave a bit of breathing room if you want to be careful.

If you don't want to do that, convert your loads into working stress loads and compare to the allowable. At that point, you're basically just working with a load rated product.

This is not a product that is explicitly covered by S16. I would use my engineering judgement and not try to calibrate their numbers to make up for minimal code differences.

A couple of minor things to think about:
-For this kind of product, I'm assuming it's a retrofit type of application and you're only installing a few. In that case, the material cost difference between bolts is small so I doubt it matters if you size up your bolts. If you are worried, go up a size. It's cheaper than screwing around with code comparisons.
-This type of application is also more likely to be base material governed, because you're generally bolting into material that wasn't initially sized for bolting.

 

[JLNJ]

A hung canopy may be a place to sneak a little extra factor of safety into your design, if possible. Especially if the additional cost is nil.

 

[KootK]

I would use the US design values including the US partial safety factors for the materials. CISC has instructed me to do exactly this for similar situations in the past. They seek to avoid having designers mixing and matching elements of different design standards/procedures. And that, of course, makes pretty good sense. That said, if you want to be a little more conservative, that is certainly your prerogative.