Concrete Piers Above Floor Slabs
I have a project that requires the placement of 6 steel columns. We cannot penetrate the existing basement slab.
Can a reinforced pier be constructed on the existing slab that will suffice?
Thanks - MarkAnswer:
The answer will depend on how heavy the load that are carried by those steel posts or columns which will transfer the load to the slab and in turn most likely tied to walls or columns that are directly anchored to the footings below.
The weak link here is the slab which in most cases is not designed for point load created by the steel columns. No matter how strong the piers will be it will still not going to increase the carrying capacity of the slab.
Think about it this way, suppose a 5 gallon bucket of water is the maximum you can carry. Your carrying capacity will remain 5 gallons regardless whether the bucket is made from plastic, tin or any other stronger material. The only time that you can increase the amount you can carry is if you have another person help you.
This is the exact same scenario with the steel columns in your case. Penetrating the slab to add piers to the footings will be the equivalent of adding another person to carry the additional load.
As mentioned above if the load is not too heavy for example posts for fences or display items which do not carry a lot of load, than the existing slab will be ok without penetrating into the existing slab.
If the load comes from floor or roof of an addition, chances are the floor slab is not adequate to support the new columns.
There is no easy answer that can be used as fix for this type of situation. You pointed to the difficulty of penetrating the existing slab. Whether you penetrate the slab and extend the column downward or build another column directly below the new column with footings will be extremely difficult.
Another option is build concrete or steel beam on top of slab that span from wall to wall or column to column which will transfer the new load directly to the columns or walls. Again, none of these is an easy fix
Hope this helps