## Prying (Heel-Toe) Calculations

## Prying (Heel-Toe) Calculations

(OP)

Hello all,

I was wondering if you could help me with a question on prying load calculations.

Flabel and all of the examples I've seen so for prying in a simple tension clip (bracket design) only consider one fastener. The classic prying calculation is shown here:

Link

I would like to perform the exact same calculations, but with 3 fasteners instead of one, equally spaced out so that there are 3 fastener reactions.

I have a simple design where the distance a = 1.0" between all 3 fasteners, and the distance b = 0.5".

I'm struggling to figure out how to do the sum of moments and sum of forces equations for multiple fasteners when prying is considered.

Could anyone please help me do this?

Many thanks,

James

I was wondering if you could help me with a question on prying load calculations.

Flabel and all of the examples I've seen so for prying in a simple tension clip (bracket design) only consider one fastener. The classic prying calculation is shown here:

Link

I would like to perform the exact same calculations, but with 3 fasteners instead of one, equally spaced out so that there are 3 fastener reactions.

I have a simple design where the distance a = 1.0" between all 3 fasteners, and the distance b = 0.5".

I'm struggling to figure out how to do the sum of moments and sum of forces equations for multiple fasteners when prying is considered.

Could anyone please help me do this?

Many thanks,

James

## RE: Prying (Heel-Toe) Calculations

The answer to your question depends very much upon the stiffness of your tension clip. If it is very stiff,like a thick fitting, I would assume a linear deflection from the end of the clip all the way to the applied load. This would give you a linear relationship such that you could reduce the number of variables in your moment equation.

If it is more flexible, beware of assuming the clip effective over its full length (See Flabel Figure 5-51 regarding long base flanges). In this case, I would probably put all of the load on the first fastener, apply the reaction between the first and second fasteners, and assume two of the fasteners ineffective.

SuperStress

## RE: Prying (Heel-Toe) Calculations

The bracket is 0.040" thick 301 1/4H stainless steel.

The load, P = 388 lb.

As it is a relatively small load and the bracket is made of 0.040" thick steel, I would assume it is more on the stiff side?

I have attached a simplee FBD pic.

Where would one place the prying reaction load in such a case? Would it be 2/3 the distance between the last fastener (P3) and the end of the Clip, or somewhere closer to the second fastener if assuming a linear deflection along the entire clip?

Much appreciate your help. Still very new to the prying concept.

James

## RE: Prying (Heel-Toe) Calculations

OP... thanks for the link; I didn't realise there was an AeroWiki

Dik

## RE: Prying (Heel-Toe) Calculations

and check the clip for bending due to the 388lbs applied load ... with a 0.25" offset and 0.04" thk, I think you're good for 160*(fty/40) fty in ksi (using the typical tension clip allowable curve from McCoombs Supplement to Bruhn (and copied many places)

another day in paradise, or is paradise one day closer ?

## RE: Prying (Heel-Toe) Calculations

## RE: Prying (Heel-Toe) Calculations

Dik

## RE: Prying (Heel-Toe) Calculations

After looking at it, I agree the most conservative way to analyze it is to assume all the load is reacted by P1.

I have attached a detailed picture of the actual structure that I am analysing.

As you can see there are two types of prying going on... the one we covered before (A), plus the prying in the vertical direction (B).

The 3 rivets in the vertical web restrain the structure, and the structure is eccentrically loaded by P = 388 lb.

I have analysed condition B in the second picture attached. Now, my question is: do I assume that the first rivet also carries all of the reaction load in this scenario given that it is so close to the load?

Or will it be divided amongst all 3 rivets?

Cheers,

James

## RE: Prying (Heel-Toe) Calculations

Apologies, I could only seem to attach one at a time.

Thanks

## RE: Prying (Heel-Toe) Calculations

another day in paradise, or is paradise one day closer ?

## RE: Prying (Heel-Toe) Calculations

## RE: Prying (Heel-Toe) Calculations

Even though P1 [F1] MUST absorb tension load of P [as noted], [2] or more fasteners on the attaching flange are always mandatory for 'stability' against any eccentricities tending to rotate and/or twist the fitting about F1... which could be dramatic. NOTE: in the real-world manufacturing and load ECCENTRICITIES will ALWAYS exist!

F1 MUST have a tension rated head and tail: bolt/washer/nut or HL pin/collar... especially since the load will concentrate on the edge of the fastener head or nut/collar [whichever]. Use of a solid driven aluminum rivet is unsuitable for this application since there are NO currently published allowables. Use of a CRES or Ti blind rivet or bolt in this instance [with tension allowables] is acceptable if well designed. F2 only hast to resist planar shear, or very minor prying forces, so a shear rating is fully acceptable.

I assume that this fitting sees cyclic loading so fastener loading in all cases MUST be held well-below yield of any part of the fastener installation for durability.

NOTE.

In this instance, I personally, would install a thick [rectangular] fillet-radius 'washer' ['radius filler' if You prefer that term] underneath the fastener head/tail into the fillet radius. The edge of the 'washer' must nest tightly into, and runs-the-full-length-of the fillet. It MUST have a matching radius to the fillet [or chamfer(s)], so it snuggles in very tightly and grossly improves tension bearing, at F1, while reducing the unsupported distance [0.25" now... much less depending on the fit into the radius] to virtually eliminate the 'prying' moment at the fastener [head or nut/collar]. Also this 'washer' allows for installation/fit of a nut or collar or fastener head VERY tightly into the flange fillet.

Regards, Wil Taylor

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## RE: Prying (Heel-Toe) Calculations

My 2-cents I'll crawl back under my rock.

## RE: Prying (Heel-Toe) Calculations

That first fastener is a CR7773S-04 blind cherry Ti maxibolt rivet which has a tension allowable of 600lb. The margin of safety on that fastener is very tight after doing the math in its raw configuration. I did a FEA to verify.

Interestingly, there is actually another fastener on the top flange which is not shown in the illustration. It is a nutplate attached with AD3 csk rivets accomodating a 1/8" diameter bolt hole on the top flange about halfway between the second and third rivet. Factoring this into the analysis seems to greatly reduce the reaction loads on that first rivet.

## RE: Prying (Heel-Toe) Calculations

## RE: Prying (Heel-Toe) Calculations

and also agree that our tolls are showing us hotspots that have always existed by were below our visual (preceptible) threshold.

another day in paradise, or is paradise one day closer ?

## RE: Prying (Heel-Toe) Calculations

We also crashed a lot of them. People tend to forget that. Test piloting is almost an office job today, but that wasn't the case 50 years ago.

TTFN (ta ta for now)

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