Design optimization

[Anonymous]

Hi,

I am working on a project (attached), to do modal and seismic analysis on a building form the 1900. I have some challenges with the Rel.mas.UY (%) and in general with the stiffness of the building. When i go to the diagram results it look ok for mode 1 but does not look normal for higher modes, and only the roof is moving not the rest of the structure with it, as shown on the attached picture.

Does anyone have any suggestions to help me out to make sure the building is good for both the Rel.mas.UY (%) and also Rel.mas.UY (%), without increasing the number of modes and no change of the structure as it is, but bracing can be added to the roof or somewhere else, as i have already done it for some place in the model. (minimal changes as possible)

Note: The model is supposed to have masonry walls, but i will make it with concrete B10 first.

Thank you!

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

If you don't want to increase number of mode to accommodate local vibrations of the elements of the roof the possible solution could be:

1. Mark disregard density in the modal analysis parameters

2. Create self-weight case for all but these elements

3. Convert it into mass

4. Assign mass of these roof element to the top edges of the wall at the locations where the roof is supported

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

hi, thanks for the answer,

i did the suggestion 1, but it gave worse values, and also i have done the rest of the suggestion before, but the UY direction won't get higher, what is the reason for that?, when only the UX direction is good.

Can i conclude due to the way the structure looks this is the best results that can be generated, and there is no possibilaty make it higher. It might work with higher number of modes, but this will be unrealistic in the real world. do i understand it correctly? 

Regards,

Roz

[Artur.Kosakowski]

Hi @Anonymous

The steps I posted are not alternatives but supposed to be a sequence. The idea is to 'exclude' shapes of vibrations of unbraced elements of the roof which contribution towards participation mass limit is small.

Your assumption is that such local modes for seismic analysis are neglected but in Robot they are not therefore you either need to increase number of modes or 'move' their weight to the locations where they will not generate local vibrations of single elements of a model.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Thank you for your answer.

I am not sure how to do this for the roof. Do i have understod it correctly, that the reason for the value in UY direction is low is due to each elements of the roof is vibrating, and since it is not rigid enough that this is the reason for the low value. Will this be the same case in a real life. Or since correct connections and more detailed design is used in real life that this would not be the case, where each element can not vibrate, but instead the whole roof will vibrate as a unit. If it is possible , i appreciate if you could show me with a video how the steps is done for the roof, or at least do the correction on the UY direction?, in the attached file uploaded in the first post.

Thank you!

[Simau · Accepted solution]

Hi @Anonymous

Why did you choose only 10 mode for modal analysis?

In Y direction 400 mm shear wall are having huge rigidity vs X direction, so you need to increase the number of mode ( and then the frequencies) in order to activate mass in this Y direction.

Let’s make a test by assuming that in Y direction shear wall have only 110 mm instead of 400mm, then we need only 13 modes you activate 70% in both direction.

Model with reduced thickness in Y direction attached.

[Simau · Accepted solution]

Here some deformation shape