I develop simple model 1 story structure consist of slab and column only (no beam). Then I apply vertical load on the middle of the slab.
After that I put rigid diaphragm using master slave and run the model. As the result, I got all support reaction at every column is exactly same.
Contrary, when I'm using floor diaphragm, the supports reaction are different for each column. Column near applied point load have higher reaction.
My question, why the result different? Manual said that both method can be used. So, what condition suppose master slave or floor diaphragm to be used?
Thank you for the answer.
Please attach both models.
Structure 1 using floor diaphragm
Structure 2 using master slave
First of all plate thicknesses are not constant in your model '6443.Structure1.std'. Make sure that thickness of all plates are constant and equal to thicknesses in the model '7457.Structure2.std'.
Another thing - FLOOR DIAPHRAGM command would lead to the same results compared to the command SLAVE ZX MASTER, but not SLAVE RIGID MASTER. In other words, the MASTER/SLAVE links have to be created in ZX plane only to simulate an inplane diaphragm behavior. So if you would do the mentioned modifications, the reactions in both models would be the same.
Please note that diaphragm behavior can be noticed when there are lateral forces in the model. Also, if you model slab using plates, that would simulate the diaphragm behavior too, so there is no need to use a FLOOR DIAPHRAGM or MASTER/SLAVE commands in such model. These commands should be used in the models where you do not want to model plates.
Thank you for the explanation. Please help to clarify some of my doubt:
1. Mean to say, FLOOR DIAPHRAGM and MASTER/SLAVE to be used only on frame structure that modelled without plate? Is it like that?
2. If I want to model thick pilecap (2 meter depth) for tank foundation, is model '7457.Structure2.std' correct assumption (using MASTER/SLAVE RIGID)?
3. Or please explain in which condition MASTER/SLAVE RIGID can be used?
Many thanks for the feedback.
1) You can use FLOOR DIAPHRAGM and MASTER/SLAVE commands for the structures with plates too. However, if the slab is already modeled from plates, the rigidity will already be accurately considered, so I don't think that FLOOR DIAPHRAGM and MASTER/SLAVE would still be needed. The FLOOR DIAPHRAGM command however would be required if the is a need to perform a soft story checks or check irregularities per the IS 1893 2016 and ASCE 7-05/10/16 seismic codes.2) You can model the pile cap using plates or even solids. I don't see the reason why Master/Slave should be used.3) Rigid Master/Slave feature can be used in various different scenarios when you want to model a rigid connectivity between 2 different nodes (i.e. member offset or load transfer through some very rigid member which is not modeled).
1. Well noted
2. The reason such assumption made was the load I got from tank vendor is only Vertical Point Load, Horizontal Point Load and Moment Point Load. Whereas, the actual load supposed to be applied uniform at the base. That's why I applied Master Slave Rigid, to obtain proper behaviour (applied point load but behave similar to if uniform load applied). However, I'm wondering whether it's correct method or not. So, I would like to know your perspective in this matter.
3. Well noted.
Thank you for the feedback.
Yes, I think you can apply the load in that way by using the master/slave specification.