Tempreture stress on slabs

[perfectaccess]

Hi Community

I read part of ACI Commentary 2243r_95.And I was looking for the length of the building that don't require temperature study(I already know that is almost less than 45-50 m),but I need the reference for this data, so any suggestion?

Also AS per my reading in ACI 2243r_95 I found that expansion joint (Or as refer by the manual is isolation joint ,since expansion joint allow movement in one direction and prevent shear)should extend in the whole building up to the foundation, Actually this logically acceptable since the volumetric change that may occur to the isolated footings is negligible, but I have the following questions?
1)If I have raft foundation, is it right to separate the foundation as well, since the raft is huge and temperature changes will have huge stresses or should I reinforced it to theses stresses and never separate the raft?(Manual Saying only up to the foundation level)
2. If the raft or isolated footings is not part of expansion joints (isolation is up to the foundation ), hence I have to take mass of both adjacent building in the calculations(but designers don’t do that??)
The reason of taking both buildings mass .is they are still connected at the foundation level!!!!

Thanks

 

[Guastavino]

1. I would think in most cases no but I'm not sure I followed your question 100%. In all the building expansion joints I've done, I didn't separate the foundation. That's where the load exits the structure into the ground. You can't put an expansion joint in the ground, so it logically follows that you probably don't need one in the foundations. Plus, foundations/thermal loads should be a lot less. Something 2' down in the ground in most areas won't change temperatures much at all.

2. What exactly do you need the mass of the foundation for?

 

[perfectaccess]

njlutzwe

Thank you

Excuse my bad language....lol

1. Me two, I never see any project separated at foundation levels for the sake of alleviating and preventing volumetric changes due temperature ,but think with me when you have massive raft foundation ,and this foundation will represent the ground floor for a basement, In this case this raft will be exposure to temperature changes, especially in hot areas .So what is the practice in this situation, is it to design the foundation for temperature stresses ,since no expansion joint in the RAFT(And why code don’t separate foundation as well for this reason???)

Note: I have general question for basement open area with no difference in temperatures, do we design for temperatures stresses or only we design for closed heated floors?)

2. My second question come from my first question, if the foundation for two portion of building are not separated by expansion joint at foundation level but separated above by one, so I think that the two portions are still connected (at foundation level) and therefore there total mass has to be taken into earthquake forces, while in actual work we are modeling every portion alone with it own mass, thus it is own lateral force.
Thank you

 

[Guastavino]

perfectaccess,

Unfortunately, that goes beyond me. Hopefully someone else here can help you. I will say though, that I'm not sure why you need the foundation mass for seismic calculations. I typically only include mass above the foundation. Although, I haven't done much with basements and complex structures with atypical foundations.

 

[perfectaccess]

Thank you anyway .

Appreciate