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Intersecting Cantilever

Intersecting Cantilever

(OP)
Hello everyone,

For a cantilever building structure:


The cantilever extends for 12m (3.5m wide)and at 90 degrees angle it meets ends with another cantilever that extends for 7m (3.5m wide). It will be used for social meetings, so large imposed loads support is required.

1) Is this construct possible with steel/reinforced concrete frame or are there better materials which could provide strong support for it?

2) What floor thickness would be the result of it?

3) If it was attached to a steel frame reinforced concrete block wall, what would be the necessary thickness of the wall?



Many thanks,
Pete

RE: Intersecting Cantilever

Going to need some more information. Can you post a floor plan with the column locations. Dual 3.5m cantilevers is no easy feat.

RE: Intersecting Cantilever

(OP)
Hi jayrod12,

I don't have access to the computer I usually work on to provide a sketchup or cad model, but I have made a very basic outline that should give you an idea of the plan.

Structural elements are not included as of yet, because they will depend on how the cantilever is constructed.

The small corridor next to the stairs needs to remain open as it is, but the space where stairs end can be used for columns etc. Also (see: elevation) the space to the left of the arch is intended for use in the cantilever, so columns and support can be placed within.

Sorry for the lack of detail, but I hope this is enough for you to help me estimated what loads this could take and what materials to use best.

I am also open to suggestions as to how to make it more structurally viable without providing ground support for the cantilevers.


Many thanks,
Peter

RE: Intersecting Cantilever

Although that begins to illustrate the constraints, we really need more of the plan and sections. Where do the main floor walls below this line up? under the inside wall of the corridor?

RE: Intersecting Cantilever

(OP)
The walls below begin at the ends of dimension lines.

I will have access to my usual computer at the beginning of next week and then I will give you the acutal model draft.


Many thanks,
Peter

RE: Intersecting Cantilever

So there needs to be a 12m x 7m area with no columns below it at the corner of a building?

I wouldn't even begin to try and size something for that, I bet the required depths would be astronomical and the resulting backspans and uplift reactions would be a bear to deal with as well.

RE: Intersecting Cantilever

(OP)
That was my worry.

Thanks for your help jayrod


Peter

RE: Intersecting Cantilever

The way I read it, he has a 3.5 metre cantilever, and it turns a corner. The 12 and 7 metre dimensions matter little. The backspan dimensions matter a lot.

I could be wrong in my interpretation, and a full floor plan would help.

RE: Intersecting Cantilever

You're probably right, and that's how i originally interpreted it. The elevation threw me though, it shows nothing beyond the front wall,

RE: Intersecting Cantilever

The very large windows in both outside walls, with no columns or visible frames between the window panes, create a significant part of the problem.

Thus, the outside "walls" are limited by the visible architectural features to be only 36-42 inches tall. Not a full-sized 10 foot high single structural entity.

Now, if those walls could be very thick - as if made up of a very high single WF shape or TS prestressed concrete shape - or if they were 12 - 18 inches thick, then maybe the extra weight caused by the thickness of the wall member could make up for the shortened height.

Also, since the architectural feature appears to require a walkway through the cantilevered area between the entry and exit stairs, there can be no bracing or rigid structure linking the outside beam with the inside beam. That too make things more difficult, less rigid as a whole. (Does the inside wall have to have the same windows as the outside wall?)

RE: Intersecting Cantilever



Quote (hokie66 (Structural))

13 Jan 16 21:14
The way I read it, he has a 3.5 metre cantilever, and it turns a corner.

It would be much easier if the thing were straight ... forces could balance out between both ends - as long as they could be anchored firmly.

RE: Intersecting Cantilever

Everything hinges on the size of your backspan but here's what I would explore (given enough backspan):

1) Create a Vierendeel truss (rectangular truss shape with rigid connections) using the floor and roof framing as the chord members and add vertical steel members as your web at the window mullions.

2) I would do this on the 7m side only. The reason being is that the 7m truss will be so much more stiff than the 12m truss it will end up partially supporting the 12m truss unless you take great care in how you separate the two (not easy). This could lead in under predicting the load in the 7m truss and pushing it over reasonable deflection limits or worse, strength limits...

3) For lateral support you provide a horizontal truss (traditional triangle web shapes) at both the floor and roof. You may also be able to utilize the concrete floor diaphragm to do this. Axial load will be transferred back to the two story space where you can resolve it to the foundations with a braced frame hidden in the exterior wall.

I'm not sure if there are other restraints stopping you from doing this framing scheme but that's as much as I can come up with without more info.

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