renovation of Autoclaved Aerated Concrete (AAC) structure

[TDGRAVY]

I'm charged with making a few modifications to an existing 2-story commercial building comprised of loadbearing AAC block walls and precast AAC floor and roof panels. The owner would like to add a few passthrough interior door and window openings. Nothing extreme - maybe 4 to 6 foot wide interior openings. Does anyone have any experience on modifying AAC block walls in this manner? The precast floor and roof panels won't be touched. I've done this in CMU and have a good idea how to approach cutting new openings in CMU and brick masonry, but wondering if the AAC block poses any other issues. I'm thinking of cutting something like a L8x4(LLV) into each face of the new wall openings, maybe with a welded bottom plate to catch any loose debris, and having plenty of bearing at each end given the apparent low compressive strength of the AAC block. Then grouting everything solid between the steel lintel and the AAC block above, and at the bearings. The owner may actually want the new openings to be arch-topped, so I may have to get the steel angle lintels shop fabricated to be arched, with a horizontal bearing segment welded at each end. The precast floor and roof panels won't be touched.

 

[Agent666]

Not specifically familiar with AAC at all, but can you simply mimic what might be done if the opening was originally there in the first place. If you would have required a lintel bearing either side of the opening in the first place then provided you prop the floors cutting in a new lintel like you say could work.

Are these block unreinforced or reinforced? A search for AAC blocks tends to show solid blocks that would be unreinforced construction. Reason I ask is to ensure the wall left is adequately stable when you cut the hole even if you prop the floors. The way I've done with essentially unreinforced brick walls several wythes thick (URM - unreinforced masonry) before, is to install a channel either side of the wall and bolt right through and extending the channels a decent distance either side of the proposed opening, then cut the opening and if required install a plate similar to you suggest to catch any loose bits below the bolts supporting the brick (you can grout up any gaps to ensure bearing onto this plate and the channels).

If the block has a low compression strength, I'd tend more towards putting some posts either side of the opening down to ground level to support any lintel as you are potentially increasing the axial loads either side of the opening quite a lot.