Constructing Concrete Walls In Existing Building

[Jackcsh]

I have a 12" thick concrete wall about 20ft in height spanning between two existing concrete slabs. The wall must support the slab above which will have a large opening cut in it for a new stairway. Taken into account shrinkage in the wall, should the contractor allow for grouting the top of the wall to assure support? How else can the wall be constructed to assure proper support of the existing slab?

 

[msquared48]

Well, I think that grouting would be a very prudent thing to do. But...

I assume too that you have considered how you are going to add new top steel over the new wall in the existing slabs?

Mike McCann
MMC Engineering

 

[CELinOttawa]

Yup; Dry-Pack with grout for the top 50mm on top of the new wall is my go-to solution. Mike is worried about the new behaviour being imposed on the existing slabs... You should be too.

 

[Ingenuity]

I usually specify 150mm/6" cores holes through the upper slab at 1200mm/48" centres/centers and depending on wall height and thickness use 10mm(3/8") aggregate and appropriate concrete slump and admixtures.

If the wall height is too high for adequate placement/concrete freefall, sometimes a mid-height horizontal construction joint is appropriate - or a temporary placement window - but this gets into "means and methods" that the contractor usually takes care of.

I have seen some very crappy infill conc wall placements: particularly bad example was on the US Naval building on Ford Island, Hawaii - historic pre-1940 building that was seismically upgraded/retrofittedf with concrete walls placed between gravity concrete frames with large voids evident at the underside of the slab over, even though they used overhead placement 'windows' (bird mouths). Fast forward 15 years and recent re-use fit out found the results of the poor techniques and the voids had to be grouted, and in some cases epoxy injection of the 'crack'. Client was not pleased to retrofit the retrofit!