[TheForge] riveted joints aren't flexible

[David E. Smucker]

Tom,  Point very well taken, and my choice of "Worked" was very poor.  In 
fact I should have said that the structures were design to be some what 
compliant.  In terms of movement of the structure it is the movement of the 
total structure that is important and movement (separation, rotation etc.) 
at any "joint" will result in failure through fatigue.  You point of early 
welds being excessively brittle is also well taken and the real cause of the 
failures.
As you noted a correctly made riveted joint is as strong as a preloaded 
bolted joint.  The hot applied rivets cools and develops a preload in the 
rivet just as the torque applied to the bolt develops a preload in the bolt. 
As long as the joint does not see a load that is greater than the preload in 
either the bolt or the rivet then these items do not see any additional 
load.
The only failures I have seen in riveted structural building steel have been 
fatigue failures of the steel beam itself and not the riveted joints.  These 
failure have all been in overhead crane runways with many many load cycles 
from moving heavy loads with the crane -- 40 plus years of such loading.

Tom, Once again thank you for sharing your experience and insight.

Dave Smucker
----- Original Message ----- 
From: "Thomas A. Troszak" <tom at tomtroszak.com>
To: <theforge at mailman.qth.net>
Sent: Thursday, March 03, 2005 9:48 PM
Subject: [TheForge] riveted joints aren't flexible


>
> On Mar 2, 2005, Dave Smucker wrote:
>
>> Use of the riveted construction that allowed ships to "work" was an
>> extension of the timber construction that did the same.
>
>
> Dear Dave,
>
> I have done a lot of riveting since age thirteen, mostly on locomotive and 
> traction engine boilers, including constructing riveted and welded 
> pressure vessels where I designed the joints myself.
>
> In a riveted pressure vessel, the riveted joints are actually NOT as 
> flexible as the rest of the plate(s) due to the added thickness at the 
> joints, but the material in the joints and the rivets themselves are no 
> more or less likely to crack from flexure than the plates themselves, only 
> from internal wasting (from various causes) or caustic embrittlement.
>
> The only reason that the early riveted hull and boiler joints were assumed 
> to be more "flexible" than welded structures is because the early welds 
> and welded steels were excessively brittle, and couldn't survive thermal 
> cycling, especially cold temps. Nowadays, a GOOD welded steel joint will 
> bend and flex and expand and contract right along with every other part of 
> the structure, whatever it may be, and survive environments that would 
> could damage a riveted joint.
>
> Hand (hammer) riveted joints are not watertight or pressure tight unless 
> properly caulked, but they may still be mechanically rigid, and are 
> definitely stiffer than the rest of the structure. Pneumatically riveted 
> joints still need to be caulked at the seams, and the only occasional 
> rivet head. The hydraulically clinched rivets found on late model 
> locomotive boilers generally do not leak at all, but the seams can.
>
> Very early riveted ship hulls probably did work (move) some visible amount 
> at the joints, but not intentionally, the scale of the structure simply 
> exceeded the technology of the joinery. You may find that the accounts of 
> leakage are often precursors to immediate or catastrophic failure of the 
> particular joint, which is more likely evidence of inadequate structure or 
> execution of the joints, not the amazing flexibility of riveted 
> structures. The poor bastards were simple floating around in some very 
> poorly assembled hulls.
>
> Very early riveting sucked. Boilers exploded, bridges fell. After decades 
> of practice, riveting technology fully matured. By the time electric 
> welding processes were first used in large scale practice, such as the 
> Liberty ships of WWII, structural riveting had been a science for more 
> than a century, and the Liberty ships were stick welded together outside 
> in the open air by housewives with three days training, then tossed into 
> the icy Atlantic. They actually performed fantastically well considering 
> the circumstances.
>
> A riveted joint is in fact structurally very similar to a bolted joint, 
> but rivets are much less expensive than bolts, and they can be made water 
> tight (sort of). No engineer would intentionally design or tolerate a 
> bolted structure with every bolt "working" visibly in it's hole as the 
> structure flexed, the bolts would soon fail from a variety of causes.
>
> Please save all flames. I am very aware of the fact that all structures 
> move and flex to a great great degree constantly. Some of the boilers that 
> I worked on physically grow 1-1/2" or more in length from cold to working 
> temp. By "working" is specifically refer to joints or fasteners that move 
> visibly, or cause visible wear of the components. Fasteners that move in 
> their holes are always a bad thing, IME (In My Experience)
>
> The wing of a 747 flexes up very visibly during flight, but not because 
> all of the thousands of little rivets are squirming in their holes, but 
> because the entire structure is flexible, just like a bridge. A composite 
> wing can flex even more than an aluminum one, and it has no rivets at all, 
> just intentionally flexible material and structure.
>
> All of the early riveted ship hulls were hand riveted, and manually 
> bucked, and the science of designing riveted structures was in fact still 
> very primitive. The simple lap seams of very early hulls were simply 
> scarfed at an angle and bashed together. This means that every plate and 
> joint is subject to constant bending with every load and change in 
> temperature. In short: early riveted joints really sucked, and often 
> failed.
>
> The double butt strap of the 1920's is a 'ting o' beauty, and is in fact 
> stronger than the plate it joins.
>
> In summary (from my experience):
>
> Properly executed riveted joints are always LESS flexible than the 
> surrounding material.
> All riveted joints can and will leak water no matter how stiff they may 
> be, but they sure aren't flexible.
>
> Just my two cents worth,
>
> Tom Troszak
>
> _______________________________________________
> Manage membership or unsubscribe at:
> http://mailman.qth.net/mailman/listinfo/theforge
> theforge mail list group photo site is
> http://www.photoaccess.com
> Login:  blacksmithblacksmith at hotmail.com
> password:  anvil
> ___________
>
>
>