Canadian Deflection Limits of a Cantilever Structure

[CanuckPE]

I've worked on several jib crane structures and although the Canadian design guide for cranes (Crane Supporting Steel Structures) recommends a deflection limit of L/225, I've reverse engineered several "manufactured" jib cranes and I've landed on L/150 as a deflection limit for unpowered trolleys (even though some of the manufactured units are closer to L/100). The risk is a runaway trolley if it's unpowered. I'm now working on a structure that's similar but used to land a heavy compressor in a potash mill plant. I'm design-reviewing on behalf of the operator, and deflection of this structure is more in the range of L/50 to L/70. Although there's ways we can mitigate the deflection (i.e. pre-camber), I think it will look a bit like a bent banana immediately following landing of the compressor.

So, I'm familiar with Annex D from S16 which applies strictly to beam supported at each end (L/180 is the most relaxed displacement limit). I'm also familiar with the CISC's crane-supporting steel structures design guide (see above). I'd like to give this cantilevered structure a thumbs-up, but I'm hoping to be able to reference relevant deflection limits for cantilevered structures from a Canadian design standard. I'd settle for an international design standard.

Is anyone able to help?

 

[dik]

I generally go for L/180. I have a current project where the jib crane has two load conditionsa. One 0.5K at 14' and the other 2.7K at 5'. The concern is how the crane is labelled for capacity and the other is a temporary and reliable stop for the 5' loading condition. The jib is attached to the base of a 6T monorail.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TLHS]

I suspect that there is at least an implied requirement in CSA B167, but I can't find my newer copy of it. It has to be a more recent one, as the design portions were only added to it in the late '00s and I think they added some stuff in 2016 as well. Prior to 2008 it was just for testing and maintenance. I agree that if it's a jib with a trolley there are going to roughly be the same deflection requirements as with a monorail or similar.

I think it either references the Crane Manufacturer's Association of America standard that most closely suits for most things, or copies requirements from it. Also, look at the provincial operational health and safety regs. They will often have a requirements, whether that's a reference to B167, or to something else. Barring specific jib crane requirements I'd follow the monorail or bridge crane requirements but using a length of twice the cantilever length to determine the allowable deflection.

 

[TLHS]

Oh, dik, can you triple down on obvious signage? Like, over the top clear. Paint the first part of the crane yellow and label that with 2.7K, then paint the rest of the crane red and label it with something like "NOT TO EXCEED 0.5K"

Then make a drawing of what the different loading conditions are (2 or 3 example sketches) with clear descriptions and have it made up into a permanant plastic sign that's posted huge at the operator position. Then put a lockout or something on the stop and require an operational control by the owner, like a signoff in a log book that includes a review of operating requirements before anyone can get the key. Even better if you can somehow figure out a way that that the stop you take off also has the rating label on it with a different one underneath, so that if you pull off the stop assembly the rating label changes.

You're going to want to cover things several different ways, because a setup like that is not going to be a hundred percent compliant with everything. The labelling is never going to be 100% to standard and you're not going to be able to comply with the requirement that the hoist can't have a rated capacity higher than the supporting structure's rated capacity. Most of the OHS stuff has some sort of statement about "unless approved by an engineer" but you still want to make sure it can't be confused.

That's all assuming the 2.7K case is the standard operating case. If the standard operating case is 0.5K across the whole length, I'd tag it just as that with an operating manual that explains how to temporarily use it for the higher load when required as a special lift.

 

[dik]

Thanks, TLHS, I think I will use that approach. I've not seen the set up, yet, and am concerned (a bit) about the crane running away down the deflected slope. The crane must have a positive braking system or there has to be a temporary 'real stop'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Are there standard colours, either RGB or hexidecimal values for safety yellow and safety red? and a means of speccing the light reflectance for a high gloss enamel for stipulating the loads? I'm thinking of safety red and white lettering and safety yellow with black lettering in a high gloss coating... the red for the outer part which would be more dangerous for the higher loading... using max loading of 500 lbs.

Is there a high gloss white that is a 'safety white'?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[CanuckPE]

I've opted to back calculate the maximum allowable simply-simply supported beam angle (at the tips) considering a simply supported beam based on the Annex D requirements for the least onerous (L/180) requirements. I trust (viewers) you'll agree this is a tip slope of 1.019-degrees (4/225-radians) if you run through the calculations. It's independent of beam length, stiffness, and area moment of inertia by substituting the uniformly distributed load from setting midspan deflection to L/180 into the slope at the tip equation. It also sniff tests relatively well to me at about 1.02-degrees (approximate slope of 1.78 in 100). Roller friction would be in this range for the runaway condition.

 

[dik]

thanks... my concerns may have been a bit reaching.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TLHS]

I don't think there's actually a reflectance requirement. It's just a colour. I've seen a lot of flat safety yellow out there. CSA Z123 has colour recommendations for signage but it gives you a table excerpted from ANSI Z535.1 and then sends you to that standard for more details. The ANSI standard is the one that should probably get called out on notes if you want to avoid RFIs.

 

[dik]

Thanks for the reference...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[TLHS]

Where are you getting L/180? In Annex D for crane girders I'm seeing L/600 for cranes of under 225kN. So I'd be assuming jib tip of (Cantilever Length/300) as the limit. The range of L/600 and L/800 in Annex D is comparable with the CMAA requirements too (different triggers for which one to use).

It looks like I'm more conservative that crane manufacturers, though. Spanco talks about what they do here:

https://www.spanco.com/blog/understanding-overhead-crane-deflection-and-criteria/

https://www.spanco.com/blog/how-does-crane-deflection-impact-your-bottom-line/

I'm going to use R for Radius for the cantilever length, since I used L slightly differently above.

Gorbel appears to be R/200 - R/320 for ones with trolleys.

However, completely ignoring all the above, I just realized that we've somehow missed the recommendation in the crane supporting structures standard, which you could actually hang your hat on. Screenshot's from the 2004 version (first edition), so you should review the latest one. I would be fine designing to this.

 

[dik]

For free standing jib cranes it's different (from one site):

"At Spanco, we have five different jib crane series, and each series has several installation types that impact the deflection limit. For instance, our 100 Series Freestanding Jib Crane has a deflection limit of L/150 (or R/150). That number is the same for our 200 Series Mast-Style Jib Cranes and our 300 Series Wall-Mounted Jib Cranes. However, our 400 Series Articulating Jib Cranes have a deflection limit of L/200 (or R/200), and our 500 Series Workstation Jib Cranes have a deflection limit of L/150 OR L/225, depending on the way the crane is mounted. For Freestanding Workstation Jib Cranes, there’s a higher deflection limit. But for our 501 Series Wall-Cantilever Workstation Jib Cranes, we use a lower deflection limit of L/225 due to its wall-mount. For a 501 Series Wall-Cantilever Workstation Jib Crane, the deflection for a crane with a 12-foot span can be calculated similarly to the abovementioned systems. First, we would need to change our unit of measurement to inches. In this case, a 12-foot span (or reach) is equivalent to 144 inches. If we divide 144 inches by the deflection limit of 225, we get a deflection of a little more than a half an inch (.64 inches)."

They use the L/225 for jib cranes attached to walls. For real cranes I use L/400 or L/600 as req'd. I often encounter L/200 from Gorbel. One of my current projects is a Gorbel crane with L/200 from a 'rigid' jib connection. It's mounted on a 25' high column at about mid height. I had to plate the column across the toes to minimise deflectons.

My signage notes:

FIRST 5’ FROM JIB POST SUPPORT AND JIB SIGNAGE COLOUR IN SAFETY YELLOW (ANSI Pantone 109C-RGB: 255, 209, 0; HSL: 49, 100, 50; HEX: #ffd100; LRV > 50) AND LETTERING “2.7K MAX” IN BLACK, BALANCE OF JIB SIGNAGE COLOUR IN SAFETY RED (ANSI Pantone 186C-RGB: 200, 16, 46; HSL: 350, 85, 42; HEX: #c8102e, LRV > 50) AND LETTERING "0.5K MAX" IN WHITE (LRV > 80) LETTERING.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik