Inclined grade beam and pier foundation

[cclin]

When designing the foundation system for residential customer built house at the hill side with steep slop, say 25 degree, can the concrete grade beam be designed parallel to the slop in general (inclined the grade beam instead of stepping the grade beam)and connect the grade beam to the pier foundation as usual? Any idea, experience, or suggestion? I am thinking of using step grade beam. However, the slop is too deep and regrade is kind of difficulty.

 

[PSlem]

The wall form man would shoot you.

The optimist sees the glass as half full. The pessimist sees the glass as half empty. The engineer see the glass as too big.

 

[TpaRAF]

The depth of the beam is all that matters. After determining the depth required, make that your minimum dimension. Several steps could be used along the top of the beam. Be sure to include the steps as extra dead load on the grade beam.

Since you did not mention the framing material, I presume you are using masonry (wood framing wouldn't be an issue). Make your steps in increments to match your CMUs or bricks (usu modulo 8").

Hope that helps! RAF

 

[SperlingPE]

To help me understand this better. What keeps the foundation from sliding? Shear keys? Friction/cohesion between foundation and soil?

 

[JRESE]

Typically in the San Fran bay area, the scheme you have suggested is quite common. Twelve-inch to 24" diameter drilled concrete piers with a constant depth (18" to 24") concrete grade beam following the pad grade. If the slope is more than about 6:1, you would want to specify that 2x flat blocking be placed on top of the mudsill between each cripple stud. Grade beam forming of a constant depth on a slope is actually easier than trying to step the grade beam. Of course, pouring a sloping beam presents other challenges, especially when the concrete mix is pumpable (frequently the case when on a slope).

James

 

[J1D]

SperlingPE - The pier or pile (or whatever foundation)supporting the beam should possess certain lateral resistance. Regarding the whole horizontal reaction at a pier (or foundation), slope of a grade beam should not make big difference. Like a simply supported stair stringer, the theoretical horizontal reaction under vertical load is also zero. But the inclined beam has a tendency to slide along the local longitudinal axis of the beam. Anchorage against such a sliding possibility must be secured.