Post installed anchors into existing 2 way slab

[mjs611]

My client would like to install jitney guards on an 11.5" elevated slab with post installed anchors. The capacity of the slab can support the jitney and storage. I am concerned that when drilling for the anchors, the contractor may cut through some of the reinforcement. The slab is a 2 way slab with only 3/4" cover on top and bottom (built in 1914). To complicate matters, I have 4 1/5" of industrial wood block above the slab. I considered removing the block under the base plates and grouting to install the anchors but that doesn't provide much resistance.

ACI permits openings in two way slab systems but you have to maintain the required reinforcement. Should I be overly concerned about cutting ~1 rebar every 20'? How has any one else anchored in elevated concrete slabs?

Side note: When using current design standards with the existing reinforcement, I calculated the same allowable psf load that the 1914 designer did. Guess some things don't change all that much....

 

[BridgeSmith]

Without knowing how close to its capacity the slab is, I can't say whether cutting a bar would be an issue. If you're concerned, and you're a little flexible on the anchor placement, there are scanning techniques readily available to locate rebar. With only 3/4" cover, you might even be able to identify the reinforcement locations visually by discoloration or cracking.

 

[mjs611]

The concrete slab is covered by a 4.5" layer of wood block so there will be no way to visually inspect. The racking comes in at 220 psf on a 250 psf slab but only covers about 1/4 of the floor area. The rest is unloaded except when a jitney is present.

 

[BridgeSmith]

The wood may create a problem for the scanning technologies as well, unless the bottom of the slab is exposed. You may be stuck with drilling small test holes to check whether there is rebar, if you can't afford to sacrifice some rebar for a development length each side of the hole locations.

 

[mjs611]

I know I have rebar since I have the existing drawings. Also, there would be no way I would allow a jitney to drive on an unreinforced elevated slab.

Given the rebar is present and I don't want to pay to map it out exactly (probably couldn't anyway), is there an issue with cutting through reinforcement in a couple areas?

 

[jayrod12]

If you have the existing drawings, it should be fairly simple to analyze the slab and see what the loss of a bar means to the slab. In many cases, slabs can accommodate the loss of a bar or two at reasonable spacings.