Equivalent Lateral Force Method
Equivalent Lateral Force Method:
1. I tried to disregard the self-weight density for the elements in (basement & penthouse level) by dividing the self-weight case into two parts (self-weight-seismic & self-weight-non seismic) then I used (factor = 0.00001) for self-weight –non seismic. A. is it correct that what I did? If no, could you edit the attached file with the right way and return it back to me? If yes, how do I design the elements which are disregarded their density in the same rtd file ?
For this type of analysis Robot always includes self weight which is automatically calculated based on the properties of elements defined in a model. If you want to disregard self weight of a part of the model you should define self weight of this part in a separate load case and convert it to mass with -1 factor.
2. I did the same way with other loads types (topic & live). By dividing them into parts (seismic – non seismic) to be able to convert the right loads to the mass. What is your opinion about that? …. Please, take a look to the attached model.
Makes sense
3. I used partial stiffening diaphragms but I figured out that the internal forces for instance beams (My, Fz) are less than the internal forces which can be obtained without this diaphragm. I know the reason behind that (constraints Ux , Uy ,RZ) . How do I design the structure elements (beams) with less values (My, Fz)? What should I do when I want to design elements in the same file?
I'm not sure if I understand this point correctly.
4. I have column (bar number 187) which is passing through two stories (3 and 4) . I assigned it manually to (story 4). I need to get perfect stories results (displacements & reduced forces) . Is it correct what I did?
What would you to calculate them by hand?
Eventually, General question:
5. In case if I have ( elastic ground bar or raft with elastic supports ) ( both without uplift ) in my model then could I use any implemented method ( Equivalent lateral forces , modal or seismic method ) for any one of them ?
You can use both.
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Artur Kosakowski
could I use the same trick in modal analysis instead of disregard density?
Yes, you can.
3. I am not sure if I understand this point correctly
I got the answer for this inquire from EC8, part (1), clause (5.10) the need to use diaphragms for building which are exposed to seismic.
But, I would like you to verify the following procedure to design slabs in seismic cases1. Save one floor as substructure.
2. Remove the diaphragm.
3. Remove all the lateral load cases
4. Meshing
5. Analysis
6. Design.Am I correct? Or is there any other procedure?
IMHO it makes perfect sense to run seismic analysis for the whole building with simplified models of floors and then extract a floor or a floor and walls and columns above and below for design of reinforcement against the gravity loads.
4. What would you to calculate them by hand?
Actually, when I added the column (bar 187) manually to (story 4) I got a warning message as appear in the attached capture.
So, how do I avoid this message?
Due to the geometry of this column (running through two defined stories) and the fact you assigned it to one of them you need to just ignore it. To avoid it you could split it into tow at the level of the intersection story or just define a node at this level on the column but this influence the results for stories. This is why I asked you how would you calculate them
Anyway, you can just make such change and check the results comparing it with the original model and then decide which ones you want to use for further design.
If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.
Artur Kosakowski
Also tested this with other load cases in the model i.e. applied +1 conversion factor: m increases (ok, expected) ....apply -1 conversion factor: m stays the same (not ok, not expected)... ?
Reefat ...did this work for you?
Indeed it doesn't work for the negative coefficients in the way I expected If so you need to:
1. Define material with zero density and assign them to objects which mass you want to exclude
2. Create a load case with the corresponding loads so that the weight of these objects is used for gravity load analysis.
If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.
Artur Kosakowski
1. When I assigned (zero density) to the elements of (basement & penthouse level). I have received a warning message that the load has not distributed correctly. Please took a look to the attached file and what shall I do?
Exclude panels with zero density material from 2nd load case element list
2. I am not sure if I understand your sentence correctly (2. Create a load case with the corresponding loads so that the weight of these objects is used for gravity load analysis. ).
Since the self-weight of these elements will be ignored then, how do I recompense this self-weight for gravity load analysis? Example or quick video will be highly appreciated to clarify the meaning of this point.
As self weight for these panels cannot be generated automatically (zero density material) you should replace it with the corresponding unifom surafce load of real material density * thickness value. This is the same kind of load as defined in e.g. laod case 5.
3. Concerning the column which is running through two defined stories I did what you proposed (Anyway, you can just make such change and check the results comparing it with the original model and then decide which ones you want to use for further design.) .I have found out there are several differences in the results and in particular the results related to the column design (please take a look to the attached captures).
https://www.dropbox.com/s/6s2otnz1ons173i/Captures.zip?dl=0
But indeed I believe that this column should be designed as one unit (long column).
Therefore I am wondering to know if I have to assign it to one story or leave it without any assigning.
I'm not sure if I understand you correctly. My suggestion was for seismic forces generated for particular story rather than the RC Column design whereas looking at the picture I assume you compare two RC Design modules instead.
If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.
Artur Kosakowski
