Building geometry concern 11

[hoshang]

Hi all,
please find the attached thread:
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http://www.tipmaster.com/includes/refinfo.cfm?w=450&h=450')

There are no beams on gridlines D and E other than walls, acting as deep beams and shear walls combined.

The black object is hanging from the cantilevered wall above, which means that forms must be kept in place until the wall above cures.

So the black object is hanging from the cantilevered wall above, does this mean the cantilevered wall above (the dark green one) is acting as a hanger for the cantilever slab below (the cantilever slab at level +4.60) at the same time it acts as bearing wall supporting the cantilever slab resting on it (the cantilever slab at level +8.20)? If so, how it can be modeled in an FEA software?

 

[BAretired]

Section A-A shows the slab suspended from the cantilevered wall beam by means of hanger rods anchored in the concrete below the underside of slab. No need to model it in FEA software. The hanger rods are simply spaced as required to carry the slab reaction. There is no bending moment in the suspended part.

 

[BAretired]

NOTE:

For previous thread, see thread507-514978

 

[hoshang]

Section A-A shows the slab suspended from the cantilevered wall beam by means of hanger rods anchored in the concrete below the underside of slab.

Thanks for your response.
This is my concern.

Can the cantilevered wall be a hanger (tension member) and a deep beam (compression member) at the same time?

 

[jayrod12]

Why can't it do both?

Deep beams are and aren't compression members. And in this instance, it being a cantilevered deep beam, it would actually improve its ability to anchor the hanging reinforcing due to the compression in the zone right above the slab.

 

[BAretired]

Can the cantilevered wall be a hanger (tension member) and a deep beam (compression member) at the same time?

It can indeed, but the multi-colored wall beams in the picture above will be connected by vertical reinforcement, and must act as a shear wall, a bearing wall and a very deep cantilever, carrying the weight of five floor slabs and a roof in addition to lateral forces from wind and any seismic events which occur during the life of the structure.

 

[BAretired]

You still have never actually told us why the 20% open area is a requirement. It doesn't make sense to many of us, and when we ask for clarification you just repeat yourself "20% open requirement". Why is that a requirement? What part of the code that you are designing around indicates that's a requirement? It seems extremely against most of our design codes to have just open air access between parking level and habitable space above. I do not believe the openings continue below Ground Floor. It would honestly be the first time I've ever seen it.

Hoshang indicated that the 20% open area is a municipal requirement but I do not know which municipality. It seems to me to be a very severe requirement, wasting large floor areas which could be more gainfully used. The intent is to get fresh air into the building instead of relying 100% on mechanical ventilation. I do not believe the ventilation openings continue below Ground Floor, but a substantial opening is required to move cars in and out of the Parking Floors. I would expect fire walls are required for the Car Lift.

Iraq does not have its own building code and I am not sure which code, if any, has been adopted.

 

[hoshang]

The black object is hanging from the cantilevered wall above, which means that forms must be kept in place until the wall above cures.

the multi-colored wall beams in the picture above will be connected by vertical reinforcement, and must act as a shear wall, a bearing wall and a very deep cantilever, carrying the weight of five floor slabs and a roof in addition to lateral forces from wind and any seismic events which occur during the life of the structure.

My point is that:
Does that mean that forms (for slab at level +4.60) must be kept in place until the wall (between levels +4.60 and +8.20) only cures?
Or does that mean that forms (for slab at level +4.60) must be kept in place until all the walls above cures?

 

[BAretired]

@hoshang,

Forms must be kept in place until it is safe to remove them.

We cannot continue with this type of dialogue for the duration of the project. This is not a simple structural design and it is not the function of Eng-Tips to provide ongoing detailed advice about design of specific projects. The nature of your questions indicates to me that you are not capable of performing structural design in a reliable and competent manner. In the interests of safety of future tenants, you must retain a competent structural engineer to review what we have discussed to date, to work with the design team, and to see the project through to completion.

 

[jayrod12]

Depends how you want to design the wall between 4.6 and 8.2. If it were me, I'd design it for the dead load applied by each of the subsequent pours above, a staged analysis to ensure the deflection stays within tolerance.

However, you could leave the formwork in place for all the pours. It would need to be designed accordingly, and I assume by the last couple wall pours it won't be doing anything as the wall stiffness will far exceed the formwork stiffness.

 

[hoshang]

Hi all,
Sorry for not been clear.

My point is that:
Does that mean that forms (for slab at level +4.60) must be kept in place until the wall (between levels +4.60 and +8.20) only cures?
Or does that mean that forms (for slab at level +4.60) must be kept in place until all the walls above cures?

Forms must be kept in place until it is safe to remove them.

My intent is regarding this:
If forms (for slab at level +4.60) must be kept in place until the wall (between levels +4.60 and +8.20) only cures, then your SECTION A-A applies (vertical bars stop there), meaning this section A-A will be repeated at each floor. So, my thought is that the hanger force will go to the back span wall at each floor.

If forms (for slab at level +4.60) must be kept in place until all the walls above cures, then vertical bars must extend to the roof, and my thought is that the hanger force will go to the back span wall at the roof.
Is my thought reasonable?

 

[BAretired]

and BA[/color]]If forms (for slab at level +4.60) must be kept in place until all the walls above cures, that seems extremely unlikely, but speed of construction is a factor to be considered then vertical bars must extend to the roof, and my thought is that the hanger force will go to the back span wall at the roof.
Is my thought reasonable? No, but the precise distribution of forces, moments and stress in the finished wall will never be known, particularly when wind or seismic forces occur. Some conservatism in design is warranted.

1. It is time to put aside the walls on Grids D and E and give some thought to the rest of the building. This is not the time to worry about stripping forms.
2. Do you have any information about soil conditions at the site? If so, what kind of foundations are you anticipating?
3. Have you considered downsizing the building due to inadequate parking?
4. With a Show Hall at Ground Floor, do you really need one at First Floor? If not, can you reduce the height of building by one story? That would be a significant cost reduction.
5. Do you have a detail for the Car Lift?
6. Lots more to come.

 

[hoshang]

1. It is time to put aside the walls on Grids D and E and give some thought to the rest of the building. This is not the time to worry about stripping forms.

I don't worry about stripping forms.
Does the cantilever slab @ level +8.20 will be bearing on the wall in your section A-A?

 

[BAretired]

Cantilever slab is a misnomer. It is not a cantilever slab; it is a continuous one way slab supported by cantilevered beams. And yes, the Second Floor slab bears down on the green wall beam between First and Second Floor.

 

[hoshang]

yes, the Second Floor slab bears down on the green wall beam between First and Second Floor.

You mean like this:

The load path would be such this:

The hanger force from the first floor and the bearing force from the second floor will induce an in-plane moment in the back span. Am I correct?

 

[BAretired]

Quote (BAretired)
yes, the Second Floor slab bears down on the green wall beam between First and Second Floor.

You mean like this:

Yes, except you have the top and bottom steel in the 2nd Floor slab reversed.
EDIT: Also, it may be prudent to extend hanger bars into the next tier, so that the double slab load could be shared by more beams.

The hanger force from the first floor and the bearing force from the second floor will induce an in-plane moment in the back span. Am I correct?

The First Floor hanger force and the Second Floor bearing force will induce a moment in both the cantilever and back span. Delete the term "in-plane".

 

[hoshang]

EDIT: Also, it may be prudent to extend hanger bars into the next tier, so that the double slab load could be shared by more beams.

Can you elaborate more on this?

The First Floor hanger force and the Second Floor bearing force will induce a moment in both the cantilever and back span. Delete the term "in-plane".

If I understand it correctly, The First Floor hanger force and the Second Floor bearing force will induce an (out-of-plane) moment in both the cantilever and back span. Am I right?

 

[BAretired]

1. The lowest beam carries a double load, 1st and 2nd floor slab. The EOR may decide to extend the hangers into the tier above as a means of sharing that load with other beams.

2. No, you are not, as is evident from your question. The terms "in-plane" and "out-of-plane" are confusing and unnecessary. The direction of moment induced in the deep beam from gravity loads is evident without further description.

EDIT: I checked on the internet to find the meaning of "in-plane moment". According to one video, you were correct the first time. However, from my perspective, I still advise that you drop the term "in-plane" because it is confusing and unnecessary. It is not commonly used for a beam with gravity load acting on it.

 

[hoshang]

Hi BAretired,
My mistake. I thought you were considering walls acting as hangers and bearing. So, your intent is using deep beams acting as hangers and bearing. If so, may I consider this approach:

 

[BAretired]

Hi hoshang,

[ul]
[li]Yes, that would work just fine. It saves a little concrete too, but forming the orange and blue cantilevers may be more trouble than it's worth. As EOR, it's your choice.[/li]
[/ul]

[ul]
[li]If the municipality requires enough parking for four residential floors plus two sales floors, some downsizing may be necessary. At present, parking accommodates only 10 cars, five on each floor below grade. We could eliminate the 1st Floor Show Hall and one level of residential space. That may not appeal to your client, but it may be a necessity.[/li]
[/ul]