Capping Beam At Mid Story Height

[Collin_St203]

I am designing this retention using capping beams on piers. Capping beams are arranged to suit the slope and because of this I have to build walls (which are up to 1.7m high) above capping beams and then connect to the ground floor slab on top as shown below.
I am not sure if this is acceptable.
My concern is that the capping beam is not at where the floor diaphragm is so I am using the torsion capacity of the capping beam to avoid the 'pin' wall-capping connection. Any comments?

 

[Retrograde]

The OP calls them columns

Agreed, what I wrote was probably confusing. What I meant is that the columns do not span the full height. The basement retaining wall is a soldier pile wall. I have never done a soldier pile wall without a capping beam. In my opinion, the capping beam is absolutely necessary. Otherwise, what supports the wall/column. As the OP stated, they cannot batter the site down.

 

[BAretired]

The soldier piles (or piers or columns) should span full height. They can be spliced at grade level, but reinforcement should be continuous, using pilasters in the wall where necessary. Capping beam is not necessary or desirable. See below.

BA

 

[Retrograde]

Oh OK. You were proposing to extend the piles. I couldn't visualise what your proposal was.

I still prefer to keep the capping beam - but at least I now understand where you are coming from.

 

[BAretired]

The moment at the base of a soldier pile is the same whether you use a capping beam or not. I do not like relying on torsion in a concrete beam to carry significant moment. If pilasters are a forming problem, make the wall thicker. It doesn't encroach on floor space any more than the pilasters already do.

BA

 

[Collin_St203]

The columns or walls can't extend to the basement level because it is right next to the boundary as I mentioned.

Basically, there are walls and columns above the capping beam (which is at ngl) connecting to ground floor slab. I did think of extending the piers but I don't think the client will accept it due to the geometry. And even if I extend the piers at where the columns are, what about the walls above NGL?

 

[Collin_St203]

I am not confident on assuming the cantilever pier providing as lateral restraint for the column or wall above.

 

[Collin_St203]

Yes that's what we normally do for shotcrete wall. The reason I am thinking of lapping the vertically bars here is to achieve some continuity for the wall.

 

[Collin_St203]

I was thinking the same when I drew the free body in the first picture (one pin support at pier end not shown)

However I am still not comfortable with this discontinuity (maybe I am just overthinking. Maybe it is because the P-Delta of the piers). How would you adapt the effective length of the walls or columns above if they are simply connected to the capping beams with L starter bars?

Similarly, below is the commonly used connection that I have seen and am not comfortable with the fact the the panels are not jointed at floor level. But this is still better than the one we are talking about here because it has dowel bars to achieve continuity.

 

[Retrograde]

I am not confident on assuming the cantilever pier providing as lateral restraint for the column or wall above.

What I thought you said was that the wall is not laterally supported at the Ground Floor. That is what I was questioning.

 

[le99]

Any reason the conventional excavation/construction method is not desirable - excavate and construct the structure within the temporary piling. The temporary piling can be retrieved or left in the ground.

 

[KootK]

How would you adapt the effective length of the walls or columns above if they are simply connected to the capping beams with L starter bars?

I'd rely on the cantilever behavior of shoring piles and call the connection between the capping beam and the vertical element above "pinned" for the stability purposes. In my experience, the shoring piles tend to be pretty stocky. Additionally, the only way for the system to buckle is inwards. And for that, the soil will massively restrain the deformation of the shoring pile back spans and stiffen things up nicely. In my opinion, if you can't reconcile yourself with the cantilever model, this probably is just not the system for you.

 

[BAretired]

Any chance for a conversation with the owner of the adjacent property? Maybe he would agree to permit some temporary excavation next to this wall.

BA