Designing foundation wall unbraced at top with two story opening at basement level

[HokieNation]

I would like to discuss possible options to design basement foundation walls in the middle of basement that is unbraced from top. This situation will arise when there is a open to above space in the basement at corners or in the middle of basement. There will be two approaches I would consider: 1. Design as retaining wall & 2. Design as concrete frame around that open to above area so there is a concrete beam (to have face reinforcement to support wall laterally) and concrete column reinforcement at each end. I would like to hear what others have to say. retaining wall will introduce larger footings and rebars which builders and contractors will hate. Additional reinforcement around the open to above area within same wall thickness to make the wall laterally braced by having beam at top will reduce chunk of concrete.

 

[hokie66]

By "1. Design as retaining wall", I assume you mean a cantilevered wall, and beyond the opening you are designing the walls as basement walls spanning from floor to floor.

It can be done either way, but if the opening is not too large, I prefer to keep the wall footing and wall the same, providing a horizontally spanning beam at the top to take the load into the floor diaphragm. This assumes a concrete floor at the upper level, but with a more flexible floor, my answer would probably change. So to summarize, it depends...

 

[HokieNation]

@hokie66:

If there is a flexible diaphragm and if one would use beam column method the remainder of the walls are still going to be braced with floor framing. Isn't it the same scenario as of basement foundation wall running parallel to joists direction where only bracing there is plywood subfloor and few blocking?

 

[hokie66]

Yes, I think it is, but I don't prefer this type of system. Some do, and the codes no doubt permit it, but depending on plywood to brace a reinforced concrete basement wall is not for me.