Help Interpreting Base Reaction. Dead Load case produces huge Moments. 1

[serrojo]

Dear experts,

I need help in defining if my model works fine and displayed the base reaction table:

And to my surprise found that my Dead and Live loads (purely gravitational) produce huge Moment reactions.

Why if I defined that loads as superficial to floor elements, it comes as moment at the base?

Thank you for your thoughts,

Regards

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[Guest262653]

The force and moment output is given at point (0,0,0), as you can see on the last columns of your table.

 

[serrojo]

Thank you, you are so wright, I´ll move my building to the center to see what changes.

Thanks a lot!

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[serrojo]

Getting back to the model as avscorreia noted that the reactions were given at the 0,0,0 coordinate.

I have moved the building, to the origin:

So i got same results for dead/live loads:

Still trying to undestand the values for Base Reactions.

Any suggestions are welcome.

Regards,

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[Guest262653]

Have you noticed that the eccentricities (Mx/Fz and My/FZ) are now much smaller and are less than 0.5m? These values make perfect sense as they seem to be the result of an unsymmetric core, which would shift the dead load distribution a bit from the slabs geometrical centre.
You don't need to shift the entire building to its centre to get these dead load moments close to zero. Just use the first model and calculate the eccentricities (Mx/Fz and My/Fz) for each vertical load case. These should be coordinates of the centroid of the vertical load. If it is far off from what it was supposed to be, only then you'd have a problem.

 

[Trenno]

Yes, tall buildings can lean to one side if you have an offset core or differential stress / axial shortening problems. P-delta effects should especially be taken into consideration.

Simple example would be to think of the building as a lamp post with a heavy lamp hanging to one side of the post.

 

[serrojo]

Yes, I understand the point, even in column design one have to consider a minimum eccentricity and the bigger are the gravitational loads bigger will be the moment for that designated eccentricity.
thank you both!

Regards

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.