Hi
I was wondering how exactly are the pushover loads applied in FEA programs?
For instance, in SAP2000 you can apply the following load patterns
- user-defined
- modal
- accel
The first case is trivial but in modal and accleration load patterns, is th eload applied to all the elements? I.e. is it applied individually to each beam and column proportional to mass?
In MIDAS the available load patterns are similar. On their website on uniform acceleration they say the following:
Uniform Acceleration: The load is distributed relative to the inertia forces developed in the structure, which has been subject to a uniform acceleration. If the acceleration is uniform, the load pattern is determined proportionally to the mass at each story level.
Since above they mention storey levels I wonder whether the programs try to lump the forces at individual floors.
Thanks
In Finite Element Analysis (FEA) programs like SAP2000 and MIDAS, load patterns determine how loads are applied to the structural elements in a model. In the case of modal and acceleration load patterns, the load is distributed based on the dynamic characteristics of the structure.
For modal load patterns, loads are typically applied to the mode shapes of the structure. These mode shapes represent the natural vibration modes, and the loads are distributed according to the participation of each mode shape in the overall structural response.
Similarly, for acceleration load patterns, the loads are distributed based on the inertia forces developed due to the specified acceleration. The loads are proportional to the mass at each story level, which means that they are distributed in a way that takes into account the mass distribution in the structure. This often results in loads being lumped at individual floors, reflecting the way the structure's mass is distributed vertically.
In both cases, the loads are not applied individually to each element, but rather distributed based on the structure's dynamic properties. This approach allows the FEA program to account for the structural response to dynamic loads more accurately.
So, yes, both SAP2000 and MIDAS, as well as other similar FEA programs, consider the mass distribution and dynamic characteristics of the structure when applying loads using modal and acceleration load patterns.
Hi Likhon! Thanks for the reply.
Regarding your point on:
In both cases, the loads are not applied individually to each element, but rather distributed based on the structure's dynamic properties. This approach allows the FEA program to account for the structural response to dynamic loads more accurately.
So if the loads are not applied individually on each element how is the analysis performed? The loads ultimatetly have to be somehow applied in the model. This can happen under the hood but there needs to be some process. Say for the uniform accelerations, we know we're carrying out a nonlinear static analysis, so the term "accelerations" is technically irrelevant. Although you could perform a quasi-static dynamic analysis. But as you said, the concept is to reproduce the dynamic properties of the structre.
My thinking is, what the program does, is to apply forces equivalent to the element mass x specified acceleration for every member. So I wonder whether this is the proces incorporated in Midas/SAP2000?
- Badges
- Science topic