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Rivet Design

Rivet Design

Rivet Design

(OP)
Anyone ever seen rivets designed as see in the attachment? Seems overly simplistic.
(I know that no one uses rivets anymore).  

RE: Rivet Design

Certainly a beautiful way to describe the shear flow to be taken by the rivets. It doesn't say anything about what a concentrated load would require (probably a separate structural device fitted to the web); otherwise would add to shear stress at the rivets.

However for a modern design better one would check for one of the latest specifications dealing with them, that would have the latest knowledge incorporated. Yet awareness of the old pertaining facts would be paramount if for rivet works predating the era of the specification.

RE: Rivet Design

yeah, it looks ok ... we rivet all the time (and wouldn't think to weld !)

RE: Rivet Design

(OP)
rb1957-
Numbers I'm getting using a classical shear flow formula and including the web are considerably lower. But I guess that makes sense if I am using VQ/I and 'I' includes the web.
 

RE: Rivet Design

yes, i'd expect VQ/I to be less than V/h (if that's what you mean !?)

RE: Rivet Design

No, not exactly that way, but it seems reasonable.

As an aside, but not for Toad's eyes:   The interesting thing about the 'old fashioned' rivet (which some people do still use) was, that when driven, the rivets actually tended to fill the holes, so they did take there proportional share of the load.  Unlike bolts, and bolt holes and fit-up, where some percentage of the bolts are either yielding in shear, or causing plate/hole bearing yielding, to bring the other half of the bolts into real loading and bearing, thus joint slip.

RE: Rivet Design

(OP)
We have actually discussed that very topic in my office a time or two. I have heard some people incorrectly refer to that phenomena as "shear lag".  

RE: Rivet Design

Toad,

For Case I, "Web Member Disregarded", V/h is identical to VQ/I.  For Case II, "Web Member Considered", presumably on the next page, they probably use VQ/I.

BA

RE: Rivet Design

(OP)
Yep- Thanks BA

I was being a dummy... I checked VQ/I using 'I' for the pair of angles only, matches exactly.

And yes, you are correct, they show two cases "Web MOMENT Disregarded" and "Web MOMENT Considered".

For the case where they take into account the web, they don't use VQ/I but rather an approximation taking into account 1/8 of the web depth....

H.I. = V/h x {Af/(Af + 1/8Aw)}
Af= area of flange
Aw= area of web

 

RE: Rivet Design

yes, the simplification is the web is effective for shear only (so the angles are doing all the bending), and the shear in the web is V/h.

the web Might be fully effective in bending, depending on the buckling of the thin sheet under the bendng compression stresses.  At a minimum the web stabilised by the angles won't buckle, so a estimate of h/8 doesn't sound unreasonable.  but then the tension side would be fully effective.

the problems of using old textbooks ...

RE: Rivet Design

This is a very riveting thread...

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Rivet Design

(OP)
must still be feeling sick huh Mike? smile

RE: Rivet Design

I LOVE the simplicity of the old books.

RE: Rivet Design

Taking into account the full web depth,

Q = Af.h/2

I = Af.h^2/2 + t.d^3/12
  = Af.h^2/2 + Aw.d^2/12

I/Q = h + (Aw.d^2/12)/(Af.h/2) = h + Aw.d^2/6Af.h

If we assume that d = 1.22h, then d^2 = 1.5h^2

so I/Q = h + Aw.h/4Af = h(Af + Aw/4)/Af

and Q/I = Af/h(Af + Aw/4)

VQ/I = V.Af/h(Af + Aw/4) seems reasonable for Case II.  I wonder why they didn't come up with that.  Anyone know?

BA

RE: Rivet Design

Maybe they did, BAretired. Make Aw=0 and you have a marginally bigger "shear flow" estimate, their formula V/h

RE: Rivet Design

ishvaaag,

I was referring to the Case II formula at the end of Toad's 15 April 11 16:07 post.  They had Aw/8 instead of Aw/4.

BA

RE: Rivet Design

(OP)
I'll look at the text when I get back in my office....I think they said it was a "reasonable estimate"

RE: Rivet Design

(OP)
any of you ever check the actual bearing stress on a rivet itself in a connection?

RE: Rivet Design

Not me!

BA

RE: Rivet Design

(OP)
BA-
Is that because you are not old enough to have designed a rivet, or for some other reason smile

RE: Rivet Design

Toad.  You got it...not old enough.

BA

RE: Rivet Design

(OP)
I see old texts that list the allowable shear and allowable bearing values for rivets.
Unless I'm over thinking this, its not making sense to me.

check rivet shear, bearing at the rivet hole. Should I be checking bearing on the rivet itself?>  

RE: Rivet Design

I have to confess to designing a few riveted joints, The rivet is assumed to, and usually did, fill the hole so it is correct to check the hole size. It really doesn't matter, if the rivet size was checked, then slightly higher stresses would have been allowed. Intuitively, it might have been better to use the rivet size.

The best thing about rivets, for me, was drawing the girders, I worked with a designer who was assigned to the "Cat Cracker" structure for Fawley Refinery, I had just enough drawing experience that he let me do the drawing. The vessels weighed in the region of a thousand tons so the structure was massive.

I found a picture of the actual unit that I worked on:
http://resources.schoolscience.co.uk/ICI/14-16/catalysis/catsch3pg10.html

 

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Rivet Design

We get so soon old, and so late smart, was what my Father always said.  But, BA has it all, a quick 39 year old mind and about 70 years of experience.  I'm guessing that's total years BA, not years of engineering, because you started computer programming a few years before I did.  It's a shame we can't bottle it and sell it, right BA?

My take on soft pins, rivets or bolts; without the benefit of Toad's "allowable shear and allowable bearing values for rivets" is that given a dia. and a matching steel grade, the shear stress at yield or ultimate is generally enough lower than the bearing stress at ultimate, that the shear stress usually governed the design.  I considered bolt bearing in some joints because, given fit-up and over sized holes, I knew that some bolts would be causing considerable yielding in bearing on the hole edges (and thus high shears at those bolts) before all the bolts were brought into play, thus joint slip.  This was not a perfectly rigid joint it had to move some before it became fully effective.  And, this same thinking is likely what causes some of the cracking you see in your crane rail girder webs.  Despite the fact that you didn't read that into one of my earlier posts.  That's very high localized stresses and fairly low cycle fatigue or fracture problem.  This same thinking is why bolts and welds in a joint are not additive for a total joint capacity, the bolted joint must move and the weld is rigid and takes all the load.  If we cared, and particularly on plate girders, we decreased the hole oversize and match drilled the holes on splice plates and webs or flanges.  This minimized the joint movement and gave us more confidence that most of the bolts were acting.  Since rivets filled the holes they tended to act in proportion to their number too.
 

RE: Rivet Design

And, I already see that I missed Paddington, and there are others too, who could most certainly supply some of that knowledge and experience for the bottling.  

RE: Rivet Design

dhengr & paddingtongreen,

Maybe we should collaborate on a text book and save the bottle for the good stuff.

BA

RE: Rivet Design

(OP)
hurry up guys!

RE: Rivet Design

Toad, is the hurry up cause their too old or you want the info?  :)  ha! ha!

Brad

RE: Rivet Design

(OP)
...just wanted an advanced copy

RE: Rivet Design

Toad:

You didn't mention the author of the book the page is from, could you??

RE: Rivet Design

(OP)
I'll try to look when I get back in the office.  

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