I searched hard for something on this unusual situation, but no luck. I appreciate anyone's help or input:
We have a old storefront built around 1885 with a grand entrance that were common in commercial areas in Chicago back in the day. It had large 12 foot windows and a middle entrance with a ramp that goes up 6 inches in about 10 feet from the front (1:20). The entire entrance area about 35 feet into the space had roughly a 4" slap of concrete with old top embedded tile work. This slab was poured over about 2" of dirt with some gravel in it. It is 6 inches in total height. The joists were actually lowered 6 inches in this area to accept the concrete and meet the section beyond the 35 feet level which has no concrete and is just wood 6" higher. The joists are about 22 feet but they are split with a steel i-beam down the center, so each joist panel is about 11 feet on each side of that and they are 11 1/2" wide. This is for the front 35 feet because each 11 foot joist is notched and dropped into the i-beam. The joists past the 35 feet, are a solid long 22 feet laying completely over the i-beam and up that 6" higher.The old wood is solid with no cracks or significant dips and 1 3/4 thick. They are spaced about 14 inches on center. Much weight I know, but it has supported it for over 100 years! I guess they used the gravel dirt as a barrier and a cushion over the 7/8 sub floor planking. It's very solid.
When we ripped out the front storefront windows, we also ripped up the ramp and concrete flooring back about 12 feet. We are trying to move the door and ramp to meet ADA requirements off to the side next to the staircase. ADA does not enforce other code requirements on a ramp of a incline of 1:20 or less because it is actually not then classified as a ramp. We do not want to have to rip up the rest of the concrete ( a real pain in the a) and do not want to redo the whole ripped area in concrete. We plan to install new 3/4 plywood t&g over that 12 foot area on the joists. Then we plan to frame a box to the side of the ramp with 2 x 6's on 16" center, topped off with another t&g floor. The box side that meets the concrete down one joist line will be backed off about 10 inches. We will try to put 1/2" rebar every 2 feet epoxy anchored into the old slab and leading out towards the wood box frame. Also we will add concrete fortifier and bonding solutions. The wood box would have 3" Tapcons every foot W staggered towards the old slab to hold it steady. It would also have Simpson ties to the t&g (or should we go through to the joists?) We then would coat the wood water treatment solution over that 3/4 t&, a poly barrier, then 2" of the old dirt gravel and then pour 4" of a concrete slab to level off. We would have an expansion joint on the opposite side of the ramp and staircase where the concrete would meet a brick wall.There is a 1x6 trim against the staircase wall on the other side.We were thinking of cutting and replacing that with cement backer board and later coat with a cement paste to give it a cement wall look on that support side of the ramp. Later, we will add a 6" x 6" wall perpendicular across the joists and form a 4'6" wide ramp down to the door on the side away from the staircase. The ramp will be poured with 5000 psi crack resistant concrete and reinforced as well (or Rapid set 9000 psi?). To finish we will pour self level Edison coating 52 about 3/8" thick to level the whole area outside the ramp and over the entire 2800 sq ft floor. Are we crazy? What would you do? I'll try to get a couple of photos soon. I am just trying to give details of a difficult situation that is hard to explain, but you need photos to see what I mean.