Welding HS bolt to plate

[Dinosaur]

A contractor has proposed an alternate connection to a piece of cast-in-place concrete. Rather than cast HS bolts into the concrete with the bolts projecting upwards, he proposes to cast a steel plate with rebar projecting into the concrete welded to the bottom of the plate and HS studs welded to the top and projecting upwards.

The entire assembly will be hot dip galvanized. What questions would you have for the contractor?

I am concerned about fatigue performance of the weld to the studs. I am concerned about the effect of HDGalvanizing on the rebar. I asked him if he had specified A706 resteel instead of A615. Anything else?

 

[metengr]

I would not recommend or endorse this design. First off, the question I would ask the contractor is what type of weld prep would they use for joining the HS bolt and rebar to the base plate? Do they have an AWS D1.1 or ASME B&PV Code, Section IX qualified welding procedure and welders?

Last, but probably most important, welding of fasteners is typically not good engineering practice. The heat from welding will adversely affect the strength properties of the fastener.

 

[ajh1]

If the studs he is proposing to use are of a chemical composition that works with welding, fine. I don't know names but I suspect there are a number of stud manufacturers who regularly do this type of thing. If what they are talking about is welding A325 or A490 bolts to the plate, then NO. Neither bolt type has a chemical composition suitable for quality welding. I would also be concerned about the ability to weld the rebar to the underside of the plate. You would probably be better off with a welded headed stud on that side with a rebar cage that could transfer forces off of the studs into the remainder of the concrete.

 

[Ron]

That's a lot more trouble than just putting in the proper anchor bolts.

Points above regarding welding are good and should be considered. No reason to do this alternate unless there is absolutely no way the bolts can be cast into the concrete.

 

[Dinosaur]

Thanks for the replies.

The contractor is proposing this so he can slip-form a concrete parapet on a bridge. Many around here would rather he simply cast the parapet without slip forming, but with one set of a-bolts every eight feet or so, that is a lot of parapet to hand form.

Dinosaur