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Minimum thickness of steel embed plates

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		I have not heard of anyone suggest there is a minimum
thickness of plate to keep the concrete from spalling due to weld heat. It
is a difficulty that we have not been able to resolve. If the plate is
thicker, the minimum fillet weld size increases and the amount of weld heat
increases. Of course that may mean more passes so a maximum interpass
temperature could be called out. Tapping on the embeds to listen for a
hollow sound to try to determine if damage to the embed to concrete joint
has occurred will result in lots of hollow-sounding plates with no other
indication that anything untoward has occurred.
		If you are thinking about a groove weld against concrete,
there are other issues. If the design requires the full strength of a
certain thickness plate, then the embed should be thickened so a partial
joint penetration weld will suffice to keep the weld from contacting the
concrete. Water in the concrete will boil and spall, creating popping
sounds. I do not know the thickness required to prevent this, but thick
steel spreads heat well, so I would imagine that it does not have to be very
thick. The difficulty is that the root pass should usually be backgouged to
clean metal, so a weld procedure that does not require backgouging should be
employed. This is usually GTAW (TIG), which is not usually onsite for other
		A bead of caulk around the embed will usually allow enough
expansion to eliminate spalling due to weld heat. This will result in a
permanent small groove around the plate, which would be an infestation
location if in a food-processing plant.
		Stainless steel, with its different heat transmission and
coefficient of expansion is more difficult to weld.
		Design fillet welds if possible and require caulk around the
embed if the service condition can tolerate the groove and minor spalling is
not acceptable.
	Jim Getaz
	Precast Engineer
	V: 540-665-3204
	F: 540-665-3250

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