I was hoping to get some thoughts on the following situation. We are designing some work inside concrete walled trenches, and there are some concrete lids being replaced. In the process of replacing the lids, the contractor has to demo the surrounding asphalt surface back a few feet, and resurface it after the lid is replaced. There will be future projects in the same tunnel which would then require the asphalt to be demo'd and replaced again. In order to fix this, someone proposed a concrete beam/slab bordering the trench wall. This area is subjected to HS25 loading (20 kip wheel loads).
The contractor proposed the attached concept, a concrete beam on grade essentially, which is doweled into the side of the trench wall. The problem I immediately pointed out is that the 4" wall is not nearly thick enough for dowels, and the dowels would probably just do more harm than good at that shallow depth. Now I am trying to propose alternate options. My two thoughts are 1) extend the concrete out to something like 4-5 feet, and design like a slab on grade, or 2) design the beam as a beam on elastic foundation. The problem with option 1 is that we likely can't extend out that far, and the problem with option 2 is that I am getting very large rebar, both longitudinal and shear, when designing a beam on elastic foundation subject to a 20 kip wheel load.
I am unsure if the beam or slab on grade design would change at all, being butted right up against the side of the wall. Also, I am unsure how wheel loads would transfer across a dowel-less joint between the trench lid and new border structure.
The contractor proposed the attached concept, a concrete beam on grade essentially, which is doweled into the side of the trench wall. The problem I immediately pointed out is that the 4" wall is not nearly thick enough for dowels, and the dowels would probably just do more harm than good at that shallow depth. Now I am trying to propose alternate options. My two thoughts are 1) extend the concrete out to something like 4-5 feet, and design like a slab on grade, or 2) design the beam as a beam on elastic foundation. The problem with option 1 is that we likely can't extend out that far, and the problem with option 2 is that I am getting very large rebar, both longitudinal and shear, when designing a beam on elastic foundation subject to a 20 kip wheel load.
I am unsure if the beam or slab on grade design would change at all, being butted right up against the side of the wall. Also, I am unsure how wheel loads would transfer across a dowel-less joint between the trench lid and new border structure.
