Augmenting a waffle pod slab on grade

[geopat69]

hi all.

I have an existing waffle slab with 385mm deep x 110mm wide internal ribs. The existing ribs have 1Y16 Top and Bottom. The existing slab is 85mm thick. The drawings show that there is F72 mesh in this slab with 20mm top cover. The edge beam is exactly the same as the internal ribs except it is 150mm wide. (This is basically a design pulled from AS2870!).

I need to extend the waffle slab outwards and act "monolithicly". My design currently utlises epoxied N10 @ 150mm bars and drilled horizontally into the side of the waffle slab. The intention for these bars is to maintain slab reo continiuty and to lap with the existing F72 mesh (ie N10s will have 300mm embedment depth) . These N10 bars will be located at mid-slab depth = 85mm/2 = 43mm.

Then I need to drill and epoxy 1N16 beam bars at the top and bottom into the 110mm wide internal beam. Again this will occur on the side of the waffle and the reo will be embedded about 400mm. The intention is to lap with existing Y16 bar already in the rib beam.

POTENTIAL ISSUES:

1) The new slab reo being only 43mm from the top and drilling in about 300mm, I am concerned that the Contractor will "deviate" and either come thru the surface or go thru the slab soffit. At 43mm he my even hit existing top reo somewhere!!

2) Similarly, with the new beam reo. He will be trying to drill within 110mm width...I am concerned that the Contractor will deviate laterally when he comes to drill in 400mm and come out thru the sides.

** Any ideas on how to control these issues?

** How good are concrete scanners to precisley locate the sides of beams from the surface?

** Should I consider NOT drilling the N10 slab bars quite so deep? Maybe only embed 120mm into the 150mm wide edge beam? In that way we can drop the slab reo a bit (say to 60mm instead of 43mm) and give him more room for movement? But this has an issue with deveopment length!!

** Any other ideas welcome**

 

[Agent666]

Any aversion to simply treating the joint as a free joint? Drill in a bar but debond the end in the new concrete (simply a deeper version of a slab on grade free joint).

Can transfer vertical loads but no significant moment transfer. At a previous employer we used to have long blocks of multiple residential units in expansive clays where we used to have a free joint every few units to primarily deal with accumulation of concrete shrinkage. But we never saw any issues as the slabs still effectively were continuous as there was little differential ground expansion and/or shrinkage along the length of the buildings to cause any rotation at footing level.

 

[geopat69]

Thanks agent 666.

But in thus case, since there will be a tiled floor and stud walls with plaster. I am trying to aviod a jointed system.

 

[hokie66]

I think you need to accept Agent666's advice. You can't create a monolithic condition as you described. The wall and floor finishes should both have control joints, which is good practice anyway.