Basement Wall or Canitlever Wall

[CowboyBill74]

I have a 12' high concrete wall with a pre-engineered dome roof system that sits atop the wall.

My question is would you design the concrete wall as a basement type wall assuming that the roof system is bracing the top of the wall or would you design the wall as cantilevered? I do not have the reactions from the roof system yet but I do know from inspection that there will be both a vertical and horizontal reaction atop the wall.

Any insite would be appreciated.

Thanks

 

[Lion06]

I would design the wall as cantilevered, adding in the horizontal reaction from the dome roof. If you are going to design it as braced at the location where it meets the dome, you would have to give those loads to the dome engineer so that he could design the dome to take those loads. I doubt he assumed any load from your wall.

One other note, I would make sure that the wall is backfilled, and the formwork and shoring removed before the dome is set in place. You don't want the wall putting load into the dome. If the wall moves after the dome is set, then it will put load into the dome.

 

[slickdeals]

If the roof is going to provide a lateral thrust and has no tension tie, then I think I would design the wall as a cantilever wall.

 

[JAE]

I think slickdeals has a good point. The dome structure may be self-supporting in that it has its own tension ring at the base. In that case, the structural stability of the whole assembly (wall and dome) do not require lateral stability at the top of the wall.

If the dome is loaded, and spreads a bit at the base, the wall would simply lean with it. The wall design would have to account for that lateral movement (sort of a hinge at the base) but would be designed as a simple span element - foundation to wall top at the dome base.

However, if the dome is not self-supporting and requires a separate tension ring or lateral support, then the wall should be designed either one of two ways:
1. As a cantilevered wall system that resists vertical loads and horizontal loads applied at the wall top.

2. As a simple span wall (foundation to wall top) with an integral tension tie built into the top portion of the wall (i.e. a build-up of horizontal reinforcement to take the tension). This is assuming the wall is continuous all the way around the dome perimeter.

 

[BAretired]

Is the plan view of the wall circular or some other shape?

BA

 

[msquared48]

If this is a circular geodesic type dome or similar with a tension ring at the exterior, then a basement wall is ok.

However, if it is anything else, then a retaining wall should be used with the rections from the dome structure properly applied.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ToadJones]

I do think a good questions is, is the "dome" circular and, if so, is the "wall" you are designing then cylindrical?

 

[BAretired]

Well maybe we should be asking if the dome is spherical.

BA

 

[ToadJones]

semantics

 

[msquared48]

Come on guys. You're talking in circles here...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ToadJones]

Nice Mike.

 

[BAretired]

Balls!

BA

 

[hokie66]

You need to find out how the dome is designed before you can decide how to design the wall. For instance, it may have a tension ring but not a compression ring required for uplift. In this case the top of a cantilevered wall would have to take the reaction.

 

[JLNJ]

Get some info on the dome and model it together. It works together in real life, might as well try to figure out how.

 

[CowboyBill74]

Ok maybe "dome" was not a good word to use, the building will be rectangular in shape however a cross section through the building shows the roof to look like a dome. So I guess a better term to use would be an arched roof system.

StructuralEIT - That is one of my concerns there is no back fill on the wall. Previous plans show the wall to be supported by nothing more than a spread footing. To me this seems incorrect. Exspecially since there is a horizontal force component on the top of the wall.

The previous plans of this type of building that I have seen show a 12' high wall supported on a 6' wide spead footing with the wall centered on the footing. This is the reason for my question to me it seems like the only way to design the wall is as a cantilever but looking over the previous plans it appears that they designed it as a braced basement wall.

The roof system does not have any tension rings associated with it. It is more of an arched truss clear spanning the building.

 

[BAretired]

Maybe the arched roof is the wrong system to use. If the arch supplier is expecting a twelve foot high wall to resist large horizontal forces, it might be more economical to consider a trussed type of roof instead.

BA

 

[hokie66]

Or a tied arch.

 

[JAE]

Rectangular ...


So all the discussion above about tension rings is not applicable.

With an arch (unless it is tied per hokie66's comment) would have a lateral thrust - thus you would have to use a cantilevered wall design.

 

[BAretired]

We don't know enough about the problem to give an intelligent answer.

BA