Fatigue Prone Details- Rivets 1

[greendrake]

I am currently categorizing Fatigue Prone Details (FPD) on older rivited truss. After not seeing anything AASHTO LRFD 2012 Tbl. 6.6.1.2.3-1 addressing rivited connections.
I may have missed something. Description 2.3 is the closest thing I can find.
I had concluded, based other reading in the Manual for inspecting bridges for fatigue damage
conditions, January 1990, Huang, Fisher etc. that rivited connection are FPD Category D.

Wanting something more current i came to this site and after reading some previous threads on this site. I'm became uncertain of my conclusion. A post from 2011 wrote."If I can change my analysis to the LRFD specifications my problems disappear because rivets are a Category C rather than D; the fatigue life would be infinite from day one." No basis for this decision was given.

Can anyone provide some additional guidance on this subject. Thank you

 

[bridgebuster]

I'm dealing with this problem as well; not a truss but a riveted viaduct.

Two good sources of information are NCHRP 299 and NCHRP 302; the latter states in cases of cracking in riveted joints the fatigue strength was consistent with Category C ranges. This never made it into the original AASHTO fatigue manuals, although the committee was aware of it.

The main concern with riveted joints is not so much the rivets themselves, rather the base metal. Rivets don't provided the same clamping fporce as bolts and may not fill a hole completely, resulting in slippage of plates. However, if the holes were drilled or punched & reamed there's less likelihood of cracking.

 

[bridgebuster]

I forgot to add that in the AASHTO Bridge Evaluation Manual Section 7.2.1 says existing existing riveted connections are evaluated as Category C.

 

[greendrake]

It appears to be industry std that riveted connections are to be considered Cat D, as it relates to the inspection of bridges.

 

[bridgebuster]

The problem isn't the rivet, per se. It's the base metal that is prone to cracking due to slippage of the plates. I've seen plenty of cracked connection angles - stringer to floorbeam - the thinking is that insufficient gage reduces the flexibility of the connection.

In a built up riveted girder or floorbeam it's difficult, if not impossible, to find a crack in an interior plate, unless you have X-ray vision. I've only seen a cracked plate once, about 30 years ago. It was tie plate over a column attached to a pair of stringers. I suppose it provided some degree of continuity; I think there were only four rivets at each end. The condition was discovered during a rehab project after the deck was removed.

I've done a lot of bridge inspection; generally clients require "hands-on" inspection of D, E, E', non-redundant, and fracture critical members. However, the provision for hands-on inspection of D to E' conditions is sometimes waived if safe-life calculations have been performed.

 

[TomDOT]

There is an example of a cracked plate and some rivets from a riveted bridge stored in the Fayette County, TX historical archives (located on the floor above the LaGrange public library.)

These items are from the recent rehab of the 1885 "Piano Bridge" just west of Dubina, TX.

http://thebridgehunter.areavoices.com/2012/02/28/piano-bridge-restoration/

http://thebridgehunter.areavoices.com/2012/04/03/piano-bridge-reopened/