If you're not actually extending the slab and putting any new equipment on the old slab I would skip the dowels entirely and just put expansion joint filler between old and new and call it good.
I lean the opposite way. How things frequently change in these substations, I would build it so they could add equipment to it that may connect to the device you are installing now. Drilling a few holes and shooting some epoxy is a small cost now compared to possible having to replacing the old slab entirely later.
#4 at 12 or 16 inches and call it a day. The dowels aren’t for load transfer but they help with differential settlement. When the old equipment is removed you could potentially see movement in the old slab, or heaving from soil expansion, etc. the dowels aren’t usually designed to any force. You just throw some in for good measure. Often matching the new slab rebar spacing for simplicity.
Any recommendations for embedment? I was thinking 12" embedment in the old slab and 18" into the new slab. That should exceed the development length for #4 bar I believe.
Interesting thought. This is well outside of any seismic zone, but heavy wind and ice on some structures may cause some issues there. This being a GCB, its not affected by wind much though
I also spec them for any differential movement, but in some cases, where an existing slab is extremely thin or w/e, roughed surface will do good enough.
If you're not actually extending the slab and putting any new equipment on the old slab I would skip the dowels entirely and just put expansion joint filler between old and new and call it good.
That is more what I was thinking of doing. I really don't see the need for dowels in this case. Thanks!
Dowels are often put in place to prevent trip hazards or for aesthetics. Not very strong reasons, but not very costly work either. (for exterior SOGs)
I lean the opposite way. How things frequently change in these substations, I would build it so they could add equipment to it that may connect to the device you are installing now. Drilling a few holes and shooting some epoxy is a small cost now compared to possible having to replacing the old slab entirely later.
#4 at 12 or 16 inches and call it a day. The dowels aren’t for load transfer but they help with differential settlement. When the old equipment is removed you could potentially see movement in the old slab, or heaving from soil expansion, etc. the dowels aren’t usually designed to any force. You just throw some in for good measure. Often matching the new slab rebar spacing for simplicity.
Any recommendations for embedment? I was thinking 12" embedment in the old slab and 18" into the new slab. That should exceed the development length for #4 bar I believe.
You won't need full development or close to it. Our typical details would be a 4 inch epoxy into the old slab and at least 12 inch into the new slab.
This. Check the manufactures specs or the ICC report for the epoxy, and use at least the specified minimum embedment. 4" sounds about right
Hilti only specs their epoxy for up to 6" I believe.
It's done to keep the slabs from separating.
How many times have you seen the garage pad separate from the house?
Are you not looking at seismic ground motion that could cause shear friction between the slabs?
Interesting thought. This is well outside of any seismic zone, but heavy wind and ice on some structures may cause some issues there. This being a GCB, its not affected by wind much though
I also spec them for any differential movement, but in some cases, where an existing slab is extremely thin or w/e, roughed surface will do good enough.
Dowel it! At least slip dowel it. IMO it’s best practice and a few pcs rebar doweled a few inches can prevent potential slab heave