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Re: Rivets

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RJConley(--nospam--at) wrote:
> I am looking at disassembling an old riveted joint bridge truss and
> reassembling at another site.  My question is can rivets be replaced with
> bolts?
> Thanks
> Bob Conley, P.E.

Yes, it usually is conservative to replace rivets with bolts on a 1:1
basis. I have an old code from the early 1900's which indicates that the
shear capacity of 7/8 rivets was 8 kips. A 7/8 bolt in friction
connection would be 10 kips.

It has been mentioned that rivet holes should be reamed to a larger
size  before bolting. In our practice, we only do this on tension
members with significant stresses where fatigue is a concern (for
example middle third of bottom flange). A riveted hole is often
considered a D fatigue detail (even though there is some debate about
this). Replacing the rivet with a bolt would slightly improve this as
long as the hole is not damaged during rivet removal (see also below).
Reaming the hole and replacing with a high-strength bolt fully tensioned
will bring back the accumulated fatigue damage at the bolt hole to zero
and updrade the detail to a B fatigue detail.

You might want to consider the following in your specification to ensure
proper workmanship.

The best procedure for rivet removal is to cut the rivet head with a
rivet buster equipped with a chisel point and then back it out of the
hole with the same rivet buster after replacing the chisel with a
backout punch. This works well when the connection is two or three plys
thick. When there are more plys in the connection, this may not work in
all cases. If the rivet cannot be removed than the preferred alternative
procedure is to drill a 1/2 inch hole in the center of the rivet. This
will allow the rivet shank to be squeezed when  backout is attempted. In
most cases (70-80%), this will solve the problem. If it does not, then
the rivet should be drilled full size with a magnetic drill and the hole
should be reamed oversize.

Contractors will often use the torch on hard to remove rivet. This is
seldom justified and specifications should indicate that this practice
is not acceptable.

Attention should be given to damage in the vicinity of the rivet head
and on the perimeter of the hole. Nicks and burrs in the vicinity of the
head no deeper than 1/16 inch thick can be ground smooth with a 10:1
slope. Members with more severe defects should be replaced. If damage is
present on the permimeter of the hole, the hole can be reamed oversize.

Bruno Côté