Vent transition for clay flue liner

I chose to use clay flue liner for my chimney, and I noticed a relative dearth of information about how to structure the vent transition to bear the load placed on it by the weight of the flue liner. There?s lots of stuff on stainless steel anchor plates, but I didn?t find much on clay liners. I?ve posted the attached pictures and narrative to give others ideas of how to do it.

I started with the proposition that I had to effectively transfer the perpendicular load of the chimney into the horizontal arch. Since my arch is pretty flat, I knew that a perpendicular load would collapse it. First, I buttressed the sides of the arch. I drilled into the slab, dropped in ?? rebar, butted cinder block against the arch, and filled the cores with concrete.

Second, I created a template from a firebrick split. It was easier to work out the shape with a split than a full brick, and they?re cheaper. I figured that the downward force of the chimney could be transferred horizontally into the arch if the vent transition pieces would essentially ?pivot? into the arch as the load was place on them. So I came up with what I call the ?scissors??the brick that sort of looks like the Star Trek insignia (they reminded me of scissor trusses, so that?s where I got the label). I reasoned that scissors allowed the transition to essentially collapse inward under the weight of the chimney, and the legs would ?catch? on the arch bricks and transfer the downward load horizontally.
On the end pieces (those that would be in contact with the inner and outer arches), I cut one of the scissor legs in half along the long side (which faced the interior of the vent) so that the end pieces would be in contact with the arches rather than ?float? like the pieces in the center of the transition. The original plan was to place most of the weight on the end pieces, so I wanted a lot of contact with the arch.

Once I had the scissors cut, I figured that I needed some bracing across the open span for the ?floating? pieces. I cut some ?ledgers? (long horizontal pieces) to rest on the lip I had cut at the top of the scissors. Then I cut two fat ?T? shaped pieces and placed then perpendicular to the ledger on top of the end pieces, and the whole thing was locked together.

In the final assembly, I modified the ledgers to be ?L? shaped pieces and I shortened the ?T? shaped pieces so that the top would be level. I built up a ?sleeve? for the flue liner using half bricks, and cut a shelf into each of the four sleeves pieces for the flue liner to rest on.

Hopefully the pictures and narrative are sufficiently descriptive. Pardon the ugly masonry work; I?m a lawyer, not a mason.

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