Building geometry concern 11

[hoshang]

Hi all,
please find the attached thread:
javascriptpenindex(450,450,'

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?

 

[rb1957]

how about leasing some of those parking spots on the opposite side of the road ?

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

 

[rb1957]

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

dee-amn!! how on earth did you sleuth that info ??

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

 

[BAretired]

how about leasing some of those parking spots on the opposite side of the road ?

I like the idea, but would the authorities allow it? Many cities require sufficient parking to serve the occupancy within the same building.

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

dee-amn!! how on earth did you sleuth that info ??

I looked on the architect's title block, then searched near the Gulan Tower in Erbil with Google Earth.

 

[hoshang]

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.

Please find the attached image:

I meant using reduced axial stiffness for the green labeled columns since these columns are on the property line and they bear on small area 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.

Please find the attached image:

 

[BAretired]

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.

[li]We are definitely not on the same wavelength.[/li]
[li]The axial stiffness of the columns is not affected by what they bear on.[/li]
[li]Secant piles should form a continuous foundation wall on Gridline A.[/li]
[li]Columns on Gridline A start at Ground Floor and bear on a wall of secant piles.[/li]
[li]Leaving gaps for columns could allow soil to slough into the excavation.[/li]
[li]The type of soil is unknown, so we need a soil report.[/li]
[li]A mat foundation makes no sense at all. It cannot extend under the secant piles because they must be placed first in order to retain the soil.[/li]

The following was printed in light green text on the image:

Column on property line bearing on small area of mat foundation.

[li]This is not the concept shown on the architectural drawings.[/li]
[li]Columns should bear on a wall, in this case a wall composed of secant piles continuous along Gridline A. [/li]
[li]The proposed concept puts a large stress on the soil and a large shear and bending moment on the small nib projecting out of the mat. It is simply the wrong concept; do not use a mat.[/li]

 

[BAretired]

In addition to having insufficient parking stalls, the car in the Car-lift cannot make a 180[sup]o[/sup] turn in the space available. The black semicircle shown below is the minimum space required to make the turn. Good luck with that!

The site is too small to accommodate the proposed building, even if it is downsized by one or two floors.

 

[hoshang]

The axial stiffness of the columns is not affected by what they bear on.

I know that The axial stiffness of the columns is not affected by what they bear on since k=AE/L.
My intention is when one needs to find the bearing area for a single column footing,
he uses this:
A=p/q
where p is axial load and
and q is the allowable bearing pressure
So I thought if I could reduce the axial stiffness of the columns, then it would attract smaller axial load and would need a smaller bearing area Since there would be a small area available for the columns on the property line.

 

[dold]

So I thought if I could reduce the axial stiffness of the columns, then it would attract smaller axial load and would need a smaller bearing area Since there would be a small area available for the columns on the property line.

I can't believe I'm still following these threads but I just can't look away.

 

[BAretired]

I can't believe I'm still following these threads but I just can't look away.

I think I have finally learned how to look away.

 

[rb1957]

"So I thought if I could reduce the axial stiffness of the columns, then it would attract smaller axial load and would need a smaller bearing area Since there would be a small area available for the columns on the property line."

I think what you are saying (in a very clumsy way, but I think we have to remember your native language is almost certainly not English) is ...
If I make all the columns the same area, then they are equally stiff, and react the same load;
but if the columns have different areas, if the ones in the sides are 1/2 the area used previously (which would reduce the load they can support) then I'd have to increase the area (and the load reacted) for the other columns in order that I maintain the same overall load capacity.

Now I don't know buildings this doesn't sound unreasonable (maintaining the total load capacity), but I'd've thought this is probably backwards ... you want the outer supports to be more effective (I'm picturing bending moments applied from seismic loads ??).

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

 

[hoshang]

Hi BAretired,
My intention is when one needs to find the bearing area for a single column footing,
he uses this:
A=p/q
where p is axial load and
q is the allowable bearing pressure
This is for single column footing. In my case I have a mat foundation. There would be a small area available for the columns on the property line. So I thought if I could reduce the axial stiffness of the columns, then it would attract smaller axial load and would need a smaller bearing area. The reduced axial load on the columns on the property line would be distributed to the interior columns. Am I right?

 

[BAretired]

I don't think you are right. Axial stiffness of columns has little effect on load carried. Consider for example a continuous beam with two equal spans of length L, loaded with q kN/m and pin connected to three columns of similar area. Load on the exterior columns is 3qL/8. Load on the middle column is 2*5qL/8 or 10qL/8, more than 3 times the load on each exterior column.

While it is true that the central column strains a little more than the outer two, the difference is so small, it is ignored in design.

In my case I have a mat foundation.

So you say, but why? A mat foundation makes sense when soil conditions warrant, but we don't know the soil conditions. Perhaps the foundation should be footings, piles or a combination of those.

 

[rb1957]

in a statically determinate structure (a simply supported beam) the stiffness (and the relative stiffness) of the reactions points has no impact on the reaction forces.

in a statically indeterminate structure there are "too many" reaction points, so the relative stiffness of each (and the stiffness of the structure) play a part in distributing the reaction forces (that also complies with equations of equilibrium. That's why I think changing the stiffness (reducing some, increasing others) could be a possible solution. But there could be other concerns beyond simple loadpaths (local deflection limits ?) that also play a role.

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

 

[BAretired]

That's why I think changing the stiffness (reducing some, increasing others) could be a possible solution.

Axial stiffness of columns has a negligible effect on load carried by each column, compared to soil settlement or deflection of the mat. Varying axial stiffness of columns is not a possible solution. It should not even be considered.

 

[rb1957]

the structural part of the column, ok, but the stiffness of the loadpath from the building to the ground. The OP was talking about the capacity of the column as the capacity of the foundation (AIUI).

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

 

[BAretired]

[li]Normally, framing plans are prepared for each floor and roof, then circulated amongst members of the design team to find and remove possible conflicts. [/li]
[li]Column loads are then tabulated based on geometry and stipulated loads without regard to axial stiffness.[/li]
[li]With that information, plus data and recommendations from a soil report, the foundation type is selected. It is too early to assume that a mat foundation will be used.[/li]
[li]The site seems too small to provide adequate parking for the building. [/li]
[li]This information should be shared with the architect and appropriate modifications made to the architectural plans.[/li]
[li]Until the above steps have been taken, continuing with structural design is pointless.[/li]

 

[rb1957]

"tributary" areas are associated with individual foundations ? as though the building is one whole "rigid" structure ... makes sense.


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

 

[hoshang]

Axial stiffness of columns has a negligible effect on load carried by each column, compared to soil settlement or deflection of the mat. Varying axial stiffness of columns is not a possible solution. It should not even be considered.

I worked around with my model with different axial stiffness of one column on the property line.

for self-weight case without release:347.70kN

Using elastic partial stiffness coefficient of 0.05 at the bottom of the column, the column axial load became 100.91kN

 

[BAretired]

Impossible! You evidently don't understand what your software is doing. We're not even talking about the same part of the building. But I do not intend to argue about it. If you believe that result, carry on...without me.

 

[hoshang]

You evidently don't understand what your software is doing.

I hope Celt83 who have experience with the software I'm using could comment on this.
For lateral load analysis, can one use code provisions of equivalent lateral load procedure, especially for this irregular geometry horizontally and vertically to find base shear?