I am designing spread footing for a single column that will see relatively high moments at the base. The client wants the footing to start at grade, and so we're left trying to meet frost depth.
My thought would be to use an approximately 42" thick footing and put enough steel top and bottom to meet minimum steel, which could be quite a lot of rebar. We also want a replicable solution, so I'm not convinced we should rely on a shallow footing with a thick granular base to meet the frost requirements of different locations.
My co-worker suggested designing a standard 20" thick isolated footing at grade and add essentially a grade beam down to frost depth. He suggested designing the dimensions as if it were just 20" thick, and then arbitrarily add the trench on all 4 sides (sketch attached). However, I feel the grade beam on all sides would significantly change the soil interaction and we wouldn't see a triangular soil pressure distribution like we would typically expect. Because the footing is stand alone and only about 8'x13', this doesn't seem like a solution where the behavior will be predictable, but I've also never seen it done before.
Am I missing something rejecting his assumption of designing it as a stand along 20" thick footing?
My thought would be to use an approximately 42" thick footing and put enough steel top and bottom to meet minimum steel, which could be quite a lot of rebar. We also want a replicable solution, so I'm not convinced we should rely on a shallow footing with a thick granular base to meet the frost requirements of different locations.
My co-worker suggested designing a standard 20" thick isolated footing at grade and add essentially a grade beam down to frost depth. He suggested designing the dimensions as if it were just 20" thick, and then arbitrarily add the trench on all 4 sides (sketch attached). However, I feel the grade beam on all sides would significantly change the soil interaction and we wouldn't see a triangular soil pressure distribution like we would typically expect. Because the footing is stand alone and only about 8'x13', this doesn't seem like a solution where the behavior will be predictable, but I've also never seen it done before.
Am I missing something rejecting his assumption of designing it as a stand along 20" thick footing?
