how to identify shear studs in existing building?

[hs2112]

We have a drawings for the existing building, Building has a composite slab resting on steel beams & girders. we are calculating the allowable load for this existing building. But we don't know that building has shear studs or not. so i want to know is there any procedure to get info. about the shear studs in existing building?

 

[ThePenguin]

Did you say that you had the drawings? If so I would imagine that the shear studs would be called out on the drawings? If no drawings are available you can look to the existing structure for clues. If some of the member sizes are too small for the original loads when analyzed as non-composite it was either a design error or there are shear studs. Don't know the connection design customs in your neck of the woods, but if the connections are stronger than the typical "1/2 maximum total uniform load" you may have shear studs. In my opinion the only way to know for sure is to dig one out of the slab. Once you confirm that you do infact have studs you may be able confirm the number and position by non-destructive means. Not sure if it would pick up shear studs, but I've located rebar in slabs on grade with Ground Penetrating Radar (GPR), and despite what the name would imply I belive GPR can be performed on elevated slabs. Hopefully thats a start.

 

[hs2112]

Thanks!! do you know what would be the cost for GPR testing?

 

[msquared48]

A simple rebar detector would work to a 2" or so depth of the concrete. You could locate the top bars over the beam, draw those lines on the slab, and see if you got any additional bleeps in between that would be the stud heads.

Mike McCann
MMC Engineering

 

[StructuralEd]

Have you determined that you need to use the composite design?

Unfortunately you need to know the size and also the total number on each member.

It seems that the studs take quite a bit of heat to install and you might see burn marks on the bottom of the top flanges.

You might also chip some concrete out to see what one actually is once you think you've located one using another method.

I'm not sure if there is a standard or minimum concrete cover required on top required to have the studs (or whatever shear item was used) fully effective? Maybe it wouldn't be far down to chip in your exploration.
Anyone know about the cover?

 

[ThePenguin]

hs2112,

I'm in the US Northeast, and the last time I had a GPR done inside a building it was something like $1,200 for the day. There was a general contractor in the middle of it, and it was a government job so I'm not sure how the markups compare to your situation. The purpose of the GPR was not just to locate rebar, but also to locate electrical ducts and various utilities in the floor of a machine shop to install a new machine foundation. Think of it as a dig-safe indoors. As msquared48 mentioned you may be able to do this with simpler equipment, but I am always impressed with the level of detail you get from GPR with a skilled operator. From the fuzzy images on the screen the operator was able to locate the rebar in the shop floor, the two layers of rebar in an existing 24" thick machine foundation to be removed, and all of the electrical ducts encased in the floor. When we cut the floor open everything was exactly as described.
As I mentioned I am not sure what it will pick up on an elevated slab, if anything at all? But I think it would be worth your while to discuss it with a GPR company in your area. You will still need to dig out some studs to confirm their size etc, but the GPR might locate all of the studs for you.