I can see two reasons to tack weld the
nut in place: to prevent the nut from turning while you turn the bolt
from the other side; and to prevent the nut from falling off or out of
alignment while you try to install the nut from the other side.
Thinking outside the box, there are a
couple of solutions to both problems.
1.) Put a spot weld on the base metal beside the
nut. This would not affect the nut but would prevent it from turning.
2.) Tack weld a small tab of steel to the main
member beside the nut to prevent the nut from turning.
3.) Stick the nut in place on the back of the
main member with silicone calking. This will keep the nut in place
while you thread the bolt through from the other side. It may not
prevent the nut from turning and it certainly will not resist any
serious shear load applied to the bolt.
4.) You could probably stick on (with silicone
calking) both the nut and a small bar of scrap metal jammed between the
nut and, say a nearby beam flange, that would even resist serious bolt
Just a couple of thoughts.
H. Daryl Richardson
Original Message -----
Tuesday, June 20, 2006 6:06 AM
Re: welding nuts follow-up
Gordin said in part, “My feeling is that the heat of such tack welding
should not be able to affect the properties of a relatively massive
Even a tack weld melts the base metal. Just because the rest of the nut
is does not become molten is immaterial. The properties of the nut have
changed. The metallurgical notch that may have been created can
propagate into the rest of the nut.
A tack weld is the worst kind of heat input into a piece of metal. It
is more akin to an arc strike than a weld. It heats a small section of
the metal then that volume cools as rapidly as it can, because it is
the only part of the metal that was heated. This rapid heating and
cooling can cause cracking. The reason for preweld and postweld heat
treating is that they help the metal maintain a consistent crystal
lattice, with less interruption by the molten weld or even the changed
properties of the heat-affected zone. A tack weld has the opposite
effect. And that is the reason that tack welds are to be incorporated
into a qualified weld.
I have not gone back through the entire thread to see the main thrust
of your posts, but the statement above got my attention this morning.
Precast Concrete Engineer