Lateral Force Distribution in ETABS

[zeemas]

Does any one know that How ETABS calculate the shear wall rigidity for distributing Lateral forces? which equations ETABS use for taking care of torsional effects?

Thanks.

 

[Diquan]

Good question!, that's why between F5 and the results is a big black box where now one knows how the program works.

But, if you have the Wilson book there it shows how they calculate that. One thing is whats in paper and another whats inside the program it self

Diquan

 

[stressed]

The shear wall is typically modeled with area finite elements. The wall stiffness and mass is based on the material and area section properties that you defined.

 

[zeemas]

Diquan
Thanks for your reply. I have wilson book for "Three dimensional static and dynamic analysis of structures" but I cannot find out any thing about shear wall in there. Are you talking about the same book?? has CSI release the paper for shear wall force distribution?

Thanks Stressed for your reply but my concern is more related to the equations ETABS is using for distribution for example if one wants to verify some distribution by hand calcs.

 

[WillisV]

Here is the equation ETABS uses: P=k*Delta.

3-d matrix analysis programs do not explicitly have to solve for the location of the center of rigidity and calculate applied torsions etc. The force distribution is calculated automatically (including all torsional effects etc) by creating and solving stiffness matrices. Stiffnesses of individual elements, including shearwalls, are determined using the element stiffness formulations (such as K=AE/L for a tension rod).

 

[zeemas]

WillisV.....Thanks for your reply.

Can I check manually by hand calc that how ETABS is distributing forces or it is not possible because of matrix size?

 

[Diquan]

It is posible to solve "manually", using Mathcad or any other program to solve matrix.

If you solve the shear wall like a frame with 3 DOF on each side is posible to solve but the same shear wall with FEA depends on how many parts you divide the wall the matrix will increase exponential.

But on both cases you can solve it by "hand" with a program that will show you wants happening inside the matrix.

Diquan