# FRP bonded connection calculations

Discussion in 'Boat Design' started by boats_designer_fr, Jan 31, 2019.

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1. Joined: Jul 2003
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### AlikSenior Member

Design the detail properly and only then calculate. This is basic, TANSL is right!

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### Mr EfficiencySenior Member

It does look for all the world, like a sandwich panel.

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Structural design is very simple.

1) Draw/"design" an arrangement...and then calculate if it is strong enough using the material properties for design.
or
2) Calculate the amount of material required for a joint, from material properties, then draw/"design" it to match the number.

Once cannot detail it "properly" until one has calculated whether it is suitable or not. Cart before the horse.

The OP is asking for...how to calculate it. Nowt else.
Subjective opinions on whether it is suitable or evidence from other boats etc doesn't answer the question at hand - how to calculate its strength.

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### rxcompositeSenior Member

Draw, analyze, calculate, determine amount/strength of material.

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### TANSLSenior Member

Ad Hoc, with all due respect, I believe that your prejudice against me does not allow you to be objective. Reassure yourself, think a bit, forget your ego, and recognize what any structural designer knows. The first thing is to design a correct structure for the loads that it must support and then, only then, calculate it.

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So Tanls, still can't answer what your opine has to do with structural facts of how to calculate....no surprises there - as always. Endless drivel and misdirection to save face.

And so...again...the OP is asking....HOW TO CALCULATE...that's for the hard of reading, since all you know is to post endless nonsense that never answers the question asked by the OP.
This is not a faith based religious forum of subjectivity and beliefs...it is and engineering based one. But im sure you beg to differ as it just exposes your lack of engineering rigour and critical thinking.

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### AlikSenior Member

TANSL is absolutely right, design is first, calculation is second, then - maybe some re-design and re-dimension. In practical engineering world, design defines calculation scheme and assumptions.
Design of detail means good working arrangement for the purpose.

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### TANSLSenior Member

Thanks for your support Alik. I would never have thought that we should explain obvious things like this to an "expert" in structures. The people, the egos, are amazing.
Ad Hoc, it is not necessary to disqualify me with great words and with what you believe is the truth (I suppose you believe what you say, and that you do not say it just for attacking me). Temper your nerves, my friend and, simply, prove to me that I am wrong. As simple as that.
On the other hand, the first thing I have tried is to respond to what I thought the OP needed to know, once a correct solution is designed. I think my answer in post # 3 is enough for someone, with knowledge in the calculation of composites, to calculate what he needs. I hope you are technically prepared to understand it. Otherwise, say so, and I will try to explain it to you with patience, kindness and without despising you. Promised.

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### AlikSenior Member

Engineer or naval architect is creative profession, not a man who operates the calculator (and only reads the Holy Class Rules, hehe).
The design is creative part of the job - define proper structural design, and only then calculate. We do that in office every day - sketch the structure, then come with first guess of laminate, then calculate and adjust.
Say, this week we were designing chainplates for 15m sailing cat, so we had to put proper stiffening members, shape the chainplates/brackets so they can take the load in proper way, and only then calculate.

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### TANSLSenior Member

You do not know to what extent I agree with you.

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Geessss…..this endless self-flagellation makes me want to duck and grab some tissue for cover!!
So whilst you bask in the warmth of your own self-flagellation about how your answers are so informative, let’s take a step back and look at this from an engineering perspective – wouldn’t that be novel!

We have:
and then:
Oh wait...and then:
Hmmm..still do not see an answer to the question yet. But wait, there is more:
Oh.and then:
So if one is designing the detail properly…what does that mean “design”...is it merely just drawing it…sketching it.., but if this done ‘properly’…what does that mean - properly…?? How can it be designed and properly if there are no calculations to support the properly defined joint….?? How can something be properly designed, if there is no supportive evidence for the statement...since this is done, as you note, BEFORE any calculations? Interesting..

But then we have:
And the purpose of this joint is.....as you must know it purpose, so please enlighten everyone, since the OP hasn't stated it anywhere.

My oh my what a wonderful myriad of replies. So do any of these actually answer the question being asked. No…none of them. But I must admire the self-flagellation and prowess and demonstration in the expertise of the replies. Most illumining in the lack of comprehension of a very simple engineering question….which in case everyone has forgotten is:

Just so I am clear, the endless replies about good solutions, or doing it properly etc etc – is that how you 'calculate'..?

The lack of engineering rigour and objective replies is breathtaking!
But hey, 10 out of 10 for self-flagellation though..mighty impressive, shame that it doesn't answer the question being asked. But i suspect that wasn't the objective...

The OP must be thinking...i only asked how to calculate the strength of the joint i posted, yet i get endless opines on whether it is a good joint or not or it will peel - ad nauseum. But no answers to the Q

I'll shall just get a nice cup of coffee, sit back..and bask in the warmth of the informatie replies which still do not address the question being asked...since it is winter here, i need some rays of warmth, no matter how misguided

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### TANSLSenior Member

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### Mr EfficiencySenior Member

Maybe the OP will return, eventually, to clarify his diagram.

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### AlikSenior Member

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### fallguySenior Member

Not much useful from anyone save rx.

How do you calculate the shear strength of the system?

So, for example; you have a plate of area A x B, and you epoxy the plate and you lay 1x 1708 glass with epoxy over the plate.

You have a Force F.

Simple formula for shear

Shear strength = F/(a x b). e.g. 100# pull over 100"^2 area is 1 psi.

But this just tells us the need and not what OP asked.

I personally don't know how to calculate the glass need, so have been watching and still haven't seen it.

Sure the plate has a strength in bonding, but so does the glass and those probably add, but what I don't understand is how you would calc the shear of the glass because the shear would occur on the perimeter of the plate and not over the full area.

The limits and constraints and better methods are all noise if you don't offer the calculation. Here, where I am from, these are considered copouts. Like this answer -> ...backing plate!

Kind regards and I was really only watching to see a calculation, so wondered why none so far.

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