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?

 

[BAretired]

Normally, the foundation wall starts at basement floor level. Section A-A indicates that the basement area is not enclosed between piers. How can that be?

BA

 

[Collin_St203]

Between piers are shotcrete walls. But it is not continuous with the walls above but terminated by capping beams, which is why I am concerned.

 

[BAretired]

The usual (and best) solution to that problem is to continue the basement wall from foundation to ground floor, eliminating the hinge between floors. It also eliminates the need for piers and capping beams. If the foundation consists of piles, the wall can span as a beam between piles.

BA

 

[Retrograde]

I've seen it done like you have sketched it all the time. The capping beam will have a large torsion capacity, so it should not be a problem.

 

[BAretired]

The way it is sketched makes no sense.

BA

 

[Retrograde]

Makes perfect sense to me.

 

[BAretired]

Section B-B makes more sense and is more economical.

BA

 

[Retrograde]

To be able to construct Section B-B you would first need to batter the site down to the footing level. I am assuming this cannot be achieved due to site constraints which is why they are using a soldier pile wall with shotcrete between the piles.

 

[BAretired]

Could be. I made no such assumption. Maybe we'll find out.

BA

 

[Collin_St203]

What Retrograde said is correct. The retention is right next to site boundary so I have to use capping beams.

I have seen people using capping beams at mid height with walls above too but I am concerned about discontinuity at where capping beams are. Maybe I am overthinking?

 

[Retrograde]

If you make sure the depth of your capping beam is sufficient to fully develop the reinforcement (both the pile reinforcement and the wall reinforcement) then it won't be a hinge.

 

[Collin_St203]

I guess my concern comes from the fact that reinforcement of the walls above are not lapped with the shotcrete walls' below.

Wall reinforcement and pier reinforcement can be fully developed by the providing cog/hook. No problem with that.
Not a hinge if the torsion capacity of capping beam is adequate but the walls above are not supported at floor level where diaphragm is, or do you assume the diaphragm at capping beam location can be achieved by the cantilever pier system?

 

[BAretired]

The column is not braced by the capping beam. In fact, the capping beam, if used, is laterally supported by the columns. Columns span from basement floor to ground floor carrying all of the lateral load. Walls span horizontally from column to column carrying earth pressure. Capping beams should not be used.

BA

 

[Retrograde]

There is no need to lap the wall reo with the shotcrete reo. The shotcrete spans horizontally between the piles, and the piles span vertically.

but the walls above are not supported at floor level where diaphragm is

Why not?

 

[KootK]

I feel as though this is the relevant structural model and that the hinges shown do not render it unstable. If you can get some flexural continuity across the capping beam, that's peach. In my opinion, however, that's just icing on an already stable cake.

 

[BAretired]

KootK,

The capping beam is not required. The columns can simply span from basement to ground floor, with walls spanning from column to column. The base of column can be laterally supported by basement slab and rigidly connected to the pile for a somewhat less than "fixed" connection.

BA

 

[BAretired]

I am wondering if anyone has considered a waterproofing detail for the wall. This is briefly discussed in thread507-491338.

BA

 

[Retrograde]

The capping beam is not required. The columns can simply span from basement to ground floor, with walls spanning from column to column.

There are no columns - it is a soldier pile wall.

 

[BAretired]

There are no columns - it is a soldier pile wall.

The OP calls them columns, Retrograde, but it doesn't really matter; call them whatever you wish. They span the full story height. Capping beam is unnecessary.

BA