Big strip foundation under wall

[genieyas]

Hello

i found a big strip foundation under wall (cage d'ascenseur)  : 20mx5m

i ask for help in french forum but all answers was not usfull for me

could you held me please english community?

[mustafahesenow]

Hi @genieyas

I had checked your model. you get big strip foundation because you have big tension force coming from seismic force . so in order to balance this force robot is increasing the strip foundation till become bigger than the uplift force. 

I think your seismic force is very exaggerated its almost 10 % of all loads.

If your seismic force is correct then this foundation type you choose is not suitable for this foundation.

I think you need to you need to have deep foundation such as tension piles to resist the tension force. 

[genieyas]

Hello;

Think you verry much for your answer;

Yes my seismic force is 0.1xg according to my sesmic area (see pdf pls)

What do you think about eccentricity (see shart pls), may this eccentricity causes this problem?

What about torsion in columns and beams ?

Sincerly

[mustafahesenow]

Hi @genieyas

As I told you before the huge seismic force will induce huge overturning moment and will make one of the building side under tension and the opposite side under compression . and to absorb this tension reactions you need to have deep foundations like pile foundation.

Torsion effect on the building will cause shear on external columns and walls  and It has to be considered and verified as per the used seismic code .

[genieyas]

Hi Mr Mustapha;

Think you very much for your interest et your reply

I tray to delete walls and the model is good, it means without big footing, acctaully i can't use deep foundation because it will seems unusual use here in the city i live in, also it will make the project expensive.

One of my friend tell me to use, instead of walls, collomns and beams, and to construct a not rigid wall between collomns and beams.

Another problem, i learn from the forum that robobat can't calculate collomns taking in consederation torsion, so how could calculate theme?

Thinks

[mustafahesenow]

Hi @genieyas

Another problem, i learn from the forum that robobat can't calculate columns taking in consideration torsion, so how could calculate theme?

Usually the torsion in the columns is not critical (its compression member ) in your model the maximum torsion is 1.26 T.m. (shear is much more critical than torsion especially for the external columns which will absorb the building torsion).

anyway you can verify the torsion in any excel sheet if you feel its really critical and you need to consider it.

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[genieyas]

Hello

What do you think about the design espacialy the big difference between Masse gravity and Rigid gravity.  I learn that a good desiegn must take in consediration the distance between this tow points.

A good design must respect MG=RG  

What du you think?

Sicerly 

[mustafahesenow]

Hi @genieyas

Its really like that that the most optimum design should be consider this issues. 

But sometimes the complexity of the building and architectural shape make this issue hard to adopt 

anyway this issue will induce more shear which will require bigger sections of vertical elements especially the external one.

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[genieyas]

Hello;

"Anyway this issue will induce more shear which will require bigger sections of vertical elements especially the external one"

Torsion induce shear or Torsion bending? could you pls explain if is shear or toorsion bending

Sincerly

[mustafahesenow]

Hi @genieyas

What I mean the building torsion (which resultant of difference coordination between cent of gravity and center of rigidity ) will induce shear on the vertical elements (columns and walls ) especially the external ones.

[genieyas]

Hello Mustapha,

How the torsion of the building will induce shear in the vertical elements, could you pls make this idea easer for my comprehension?

Sincerly

[Artur.Kosakowski]

Hi @genieyas

I hope this picture will illustrate what happens (MZ moment stands for seismic force acting on some eccentricity)

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