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]

There is no difference. Stop making simple things complicated.

If I understand you correctly, you are saying Stage 1 is during construction and Stage 2 is after construction. I did not call them stage 1 and 2; you did.

Obviously, during the course of construction vertical wall reinforcement will be placed tying the wall sections together so that after construction, they will be adequately connected. That is true of any concrete wall with cold joints between subsequent pours.

You should be getting in touch with the architect and other consultants to make sure we are all on the same wavelength about parking, car-lift, open areas and story height.

Parking is completely up in the air and has been from the beginning. It appears that the architect is happy with cars overhanging drive lanes or parked in the middle of them. I am not and doubt that the authorities will be. It now appears that the turning radius for accessing the car-lift does not meet minimal requirements.

The Main Stair has more risers than the Secondary Stair. That needs to be changed.

Has the architect indicated what measures are required to ensure fire separation between floors at the car-lift location? What about the "open floor" locations?

Three meters is much more than required if flat plates are to be used on residential levels. I suspect it is also too much for the parking levels, although it is hard to say until we see the structural drawings for floor framing.

I question The need for a Show Hall on First Floor level. I suggest downsizing by removing the upper Show Hall and one level of residential space.

How are you proposing to frame the 2.85m cantilevers between Grid A and D?

These issues should be updated on the preliminary Architectural and non-existent Structural drawings, so that everyone is aware of the latest decisions without rummaging through reams of text. Perhaps the architect should be party to this thread.

 

[hoshang]

Hi BAretired,
your help is highly appreciated.
Another concern.
Suppose one uses piles to support excavation. Can one use these piles as vertical force resisting members in the places of the columns since these columns should be located on property lines? If not, i.e., if one uses piles for excavation support only and uses columns on property lines for vertical loads, doesn't these piles reduce available bearing area for mat foundation?

 

[BAretired]

Another concern.
Suppose one uses piles to support excavation.

That is a major concern, and has to be carefully assessed as neighboring basements, if they exist at all, will not likely be as deep as yours. A geotechnical firm must be retained to determine soil properties as well as foundation types recommended.

Can one use these piles as vertical force resisting members in the places of the columns since these columns should be located on property lines? If not, i.e., if one uses piles for excavation support only and uses columns on property lines for vertical loads, doesn't these piles reduce available bearing area for mat foundation?

On the east and west sides, existing buildings extend to the property lines. It will be difficult to get equipment close enough to property lines to install piles. This issue is best discussed with piling contractors in the area. I do not have the answer to your question.

 

[rb1957]

man, this is a slow moving train wreck !

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[hoshang]

Hi BAretired,
Just for discussion, suppose existing buildings don't extend to the property line and one uses piles to support excavation. Can one use these piles as vertical force resisting members in the places of the columns since these columns should be located on property lines? If not, i.e., if one uses piles for excavation support only and uses columns on property lines for vertical loads, doesn't these piles reduce available bearing area for mat foundation?

 

[BAretired]

The site plan is shown below.

Buildings to the east and west extend to property line.
On the south border, two houses are believed to be set back from the property line.
The north border is skewed parallel to Main Street.

On the north and south sides, steel sheet piling will be needed to prevent collapse of soil beyond the site borders.

On the east and west borders, sheet piling, if used, would have to be placed tight against the existing buildings, which would be damaged by vibration from the pile driver. Moving sheet piling away from existing buildings or using secant piles may be possible, but that would reduce the footprint of the proposed parking levels, which is not an option.

There appears to be no easy solution to the problem. Others may wish to comment.

 

[BAretired]

Just for discussion, suppose existing buildings don't extend to the property line and one uses piles to support excavation. Can one use these piles as vertical force resisting members in the places of the columns since these columns should be located on property lines? If not, i.e., if one uses piles for excavation support only and uses columns on property lines for vertical loads, doesn't these piles reduce available bearing area for mat foundation?

If the existing buildings do not extend to property line, the East and West border could be supported using sheet piling, same as the North and South borders. Sheet piling would extend from Ground Floor down to Elev. -7.2 (or -10.8 if the Architect adds one parking floor).

The mat foundation would extend to the sheet piling. The foundation wall would bear at the edge of the mat and would need offset piles to carry the load from above.

 

[hoshang]

On the east and west borders, sheet piling, if used, would have to be placed tight against the existing buildings, which would be damaged by vibration from the pile driver. Moving sheet piling away from existing buildings or using secant piles may be possible, but that would reduce the footprint of the proposed parking levels, which is not an option.

Using secant piles, can one use these secant piles as vertical force resisting members in the places of the columns since these columns should be located on property lines? If not, i.e., if one uses secant piles for excavation support only and uses columns on property lines for vertical loads, doesn't these secant piles reduce available bearing area for mat foundation?
Here, where I live, I found this is done frequently. Please find the images:

 

[BAretired]

and BA[/color]]Using secant piles, can one use these secant piles as vertical force resisting members in the places of the columns since these columns should be located on property lines?

Okay, I see what you are suggesting. Yes, I believe that could be done, but you would have to leave clearance between the existing building and the secant piles to avoid damaging the building.

If not, i.e., if one uses secant piles for excavation support only and uses columns on property lines for vertical loads, doesn't these secant piles reduce available bearing area for mat foundation?

Well yes, they would reduce bearing area, but if each column load is being carried by piles, why would you need a mat foundation at all?

Here, where I live, I found this is done frequently. Please find the images:

That is interesting. Thanks for the photos. I have never used secant piles on a project. I see no reason why the secant piles could not be used for vertical loads as well as lateral support for the neighbor's soil provided they are drilled deep enough to develop enough skin friction.

 

[hoshang]

I see no reason why the secant piles could not be used for vertical loads as well as lateral support for the neighbor's soil provided they are drilled deep enough to develop enough skin friction.

If so, how (two) basement floor slabs and beams are supported on secant piles since secant piles are already poured up to ground level before (two) basement floor slabs are poured? Would one use shear friction concept for this?

 

[BAretired]

Of course not! The bottom floor is slab on grade, so does not need structural support. The upper parking level floor could rely on the pile at each column location (a temporary gap in the secant pile wall) to carry a floor beam. The secant piles carry their own weight plus the Ground Floor slab. Detailing to accommodate the upper parking level floor may require a little thought. That is why you get paid the big bucks!

 

[hoshang]

The bottom floor is slab on grade, so does not need structural support. The upper parking level floor could rely on the pile at each column location (a temporary gap in the secant pile wall) to carry a floor beam. The secant piles carry their own weight plus the Ground Floor slab. Detailing to accommodate the upper parking level floor may require a little thought. That is why you get paid the big bucks!

Can you elaborate more on this:
The upper parking level floor could rely on the pile at each column location (a temporary gap in the secant pile wall) to carry a floor beam.
Also, what about the floor slab indicated in the image below:

 

[BAretired]

Using secant piles, can one use these secant piles as vertical force resisting members in the places of the columns since these columns should be located on property lines?

The answer is yes...secant piles can be used for resisting vertical loads in addition to supporting the neighbor's soil.

What about this floor slab? (P1 floor shown)

Well, what about it? Look at your own photos. Does that answer your question? Can you come up with a framing plan which supports that floor slab? Draw the framing plan for that floor. If you find that it cannot be done, forget about using secant piles.

 

[hoshang]

The answer is yes...secant piles can be used for resisting vertical loads in addition to supporting the neighbor's soil.

If secant piles can be used for resisting vertical loads in addition to supporting the neighbor's soil, what about the floor slab indicated in the image below:

Can secant piles support this floor slab? If so, how do you recommend?

 

[BAretired]

I have never used secant piles. You should talk to a piling contractor.

Just for discussion, suppose existing buildings don't extend to the property line

Well, do they or don't they? Don't keep us in suspense. If the gap is large enough, I think it would be more economical to use sheet piles rather than secant or tangent piles.

 

[BAretired]

This appears to be the proposed building site in Erbil, Iraq.

The building on the left (east) extends all the way to the property line (see below). Using secant piles would reduce the usable floor area in levels P1 and P2 of the proposed building. Driving sheet piling close to the property line would damage the existing building.

 

[hoshang]

So how do they do this?

What do you mean? I can't figure the query.

Can Floor P1 bear here?

How can Floor P1 bear on the back side of the image? On the piles?

What is this material?
Does it retain the soil?

This is the basement wall of the existing building.
I used a reduced axial stiffness at the bottom of the columns that are on the property line since these columns bear on small areas of the mat foundation. Am I right? Or should I consider flexural stiffness reduction of these columns?

 

[rb1957]

at least you have a full size model of the basement floors ... you can try parking in it. The image, with the cars parked on the vacant lot, already tells you a lot.

at least the road the building fronts onto isn't a main street, so backing out may not be as hazardous as first thought.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[BAretired]

The architect's parking plan (20% opacity) was overlaid on the Google photo (see below). The white cars in the Google photo appear slightly larger than those in the parking plan, but the overlay gives a rough idea of the relationship of proposed to existing.

[li]The car in the Car Lift cannot make a 180 degree turn in the space available, assuming a minimum outer turning radius of 7.77m, even if the cars between Grid 1 and 2 are moved to Grid A.
[/li]
[li]Above Ground Floor, Stair #2 extends east to Grid A. Below Ground Floor, Stair #2 must move to make room for the two cars adjacent to it. [/li]

 

[BAretired]

BA[/color]]This is the basement wall of the existing building. Okay, but in your case, there is no basement wall. The secant piles, if used, would be cantilevers 7.2m high.

I used a reduced axial stiffness at the bottom of the columns that are on the property line since these columns bear on small areas of the mat foundation. The columns do not extend below Ground Floor and so far as I know, there will not be a mat foundation. Am I right? No! Or should I consider flexural stiffness reduction of these columns? That question makes absolutely no sense.

We don't know how deep the existing footing is and we don't know how much load it is carrying from the two story building. That affects the lateral pressure on the piles. We know nothing about the type of soil the secant piles are intended to retain. If a soil report exists, I have not seen it.

I do not believe that either sheet piling or secant piles are feasible on the east property line.

I am not sure where the south property line should be. I may have assumed it too far north on the overlay.

The parking arrangement is inadequate for the occupancy, even if it functioned perfectly, which it will not. The site is simply too small for the proposed structure.