diaphragm design

[n39]

hi everyone, I was working on a job in which there are 2 types of building that is going to be held by one column. They both were adjacent to each other and were connected structurally.

So, as you can see, both of the building have different slab elevation. My question is:
1. I modelled the building using ETABS, should I divide column2 into 7 segments while column1 into 4 segments and both column3 and column4 into 3 segments?
2. Will there be 7 diaphragms?? That is divided by the different elevation of the slab?
3. Could you possibly do this analysis? I mean, there are 2 different building with different elevation in each floor but it is going to build adjoin to each other. Should you do the analysis as an idividual building or as a adjoin building? >> I think I need to prioritize checking on as an individual building, because adjoining it with other building will increase it's stiffness, therefore an adjoining building will be able to have SMRF with more capacity than an individual building.
4. Lemme know if you have any other thoughts

Thank you

 

[dik]

In dealing with parkades where the deck level can vary from a few inches to a few feet with spans on opposite sides of the column, I've nearly always used corbels; the beams on either side could be spanning 58' to 60' and the flexural moments created can be huge.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

You did not supply a lot of info. here.. The size of the structure, seismicity, the beams and sab PC or monlytic etc..

Regarding your questions,

1- Yes..You should divide column2 into 7 segments while column1 into 4 segments and both column3 and column4 into 3 segment etc. as long as the column 2 is common for both sides. Can you consider double column at column axis 2 ?

2-Yes. There will 7 diaphragms . But only column 2 is restrained by 7 diaphragms. You are expected to make free the other columns for irrelevant diaphragms .
3- I could not get the question. You are expected to do the analysis. I would prefer double coulmns and EJ at coulmn axis 2.

Just my opinion ..




Use it up, wear it out;
Make it do, or do without.

NEW ENGLAND MAXIM

 

[n39]

Do you know how to make free my other column from the influence of irrelevant diaphragm in ETABS?

 

[JoshPlumSE]

1. I modelled the building using ETABS, should I divide column2 into 7 segments while column1 into 4 segments and both column3 and column4 into 3 segments?
**Yup. You should divide those columns up (whether it's with an internal mesh or manually) so that the columns connect to every spot where you have a diaphragm connecting to it. In some ways, the difficult part will be ensuring that you DON'T have connectivity between columns and certain diaphragms.**

2. Will there be 7 diaphragms?? That is divided by the different elevation of the slab?
**Probably. At times, I have eschewed using built in diaphragms because I don't like the way they distribute forces. And, just "fudged" some X bracing or such to represent the diaphragm. In particular, I'm talking about sloped ramps on parking garages. Or, maybe cases where I've got a flexible metal deck or word diaphragm area. **


3. Could you possibly do this analysis? I mean, there are 2 different building with different elevation in each floor but it is going to build adjoin to each other. Should you do the analysis as an individual building or as a adjoin building?
**You didn't mention any reasons why I might want to analyze them as different buildings. Maybe if there was a lot of effort built into detailing the two buildings to be seismically separate or something. I did an inspection on a building (hospital) where they had a huge expansion joint in the hallway / diaphragm and it took us awhile to figure out what the engineer was thinking.... But, it was just that this wing of the building was supposed to be seismically separate from the rest of it.**

 

[Greenalleycat]

My question is not "how" but "why" as in "why the fuck would you do this"
I'm going to hope that this is a non seismic zone as that is an undesirable setup for an earthquake

 

[KootK]

If you're doing SMRF then I would have to think this is a structure meant to resist significant seismic demand. That being the case, I would want to either:

a) Separate the buildings laterally at the diaphragm offset or;

b) Design the columns at the offset to, effectively, stitch the offset diaphragms into contiguous diaphragms. This would mean a very punishing/ over strength design of the columns common to the two diaphragms.

 

[n39]

Thank you everyone for replying
I've done some trial and error and came to a conclusion. The red diaphragms will affected column2 and vice versa. But since the building with green diaphragms is much more stiffer, some of the seismic load from red diaphragms were absorbed by the green diaphragms. I agree that column2 need to be very stiff and to be design to able to withstand the seismic load from both sides. BTW this is in SDC D, so I think the design will be very over design