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Flat Plate with misplaced (too low) top rebar and 50% missing rebar in one direction

Flat Plate with misplaced (too low) top rebar and 50% missing rebar in one direction

Flat Plate with misplaced (too low) top rebar and 50% missing rebar in one direction

(OP)
thread507-242292: Cracks in Flat Plate Slab

Very similar to the 507 thread:
Two way slab with similar cracks pattern. The reinforcement appear too low. In addition we found that in one direction reinforcement was installed only 50% of what design called out.
My question is: How to economically repair this flexural and possible punching shear deficiency? The missing reinforcement has to be added. Do we have to incorporate shear due to unbalanced moment? Punching shear deficiency may be address with drop panels/capitols or so...Please comment....

RE: Flat Plate with misplaced (too low) top rebar and 50% missing rebar in one direction

Good for you in locating the 2009 thread. Some good advice there, some not so good. If you have top bars too low, and less than the required reinforcement in one direction, that is a big problem. How does this happen? Was there no on site inspection?

One approach, but one which I am not versed in, would be to use FRP (fibre reinforced polymer) strips on the top surface. Several companies, Sika included, provide design assistance in using these surface bonded reinforcing strips.

Punching shear deficiencies can be addressed by adding to the column size, or in some cases, using bolted steel brackets.

RE: Flat Plate with misplaced (too low) top rebar and 50% missing rebar in one direction

As per hokie66 advice, FRP for top flexural strengthening and stiffened steel through-bolt brackets for punching shear are probably the most economic.

I have used both techniques for strengthening slabs, and the challenge for FRP may be maintaining the required ductility for flexure strengthening, given the relatively large moment deficiency, and also meeting the fire resistance for the slab.

If fire endurance is required, you may have to consider recessing the FRP into the slab cover concrete then patching with a cementitious material. Or you could consider recessing via controlled-depth saw cutting and using pultruded FRP bar, or even steel rebar, for one direction.

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