Joint between high and low part of a building

[hoshang]

Hi
Please find the attached link.

https://www.screencast.com/t/cxlfTrtg

This is a reinforced concrete building. There isn't a joint between the high and low part of the building. The mat foundation is 70cm thick (top #20 @ 25cm both direction and bottom #20 @ 17.5cm both direction). I've not designed the building. Do you think there will be problems if the joint doesn't exist between the high and low part of the building?

 

[hoshang]

Hi
If there are problems, how it can be solved? I don't think sawcut can solve the problem. My thought is that using lightweight partitions in the high part and using hollow masonry concrete block in the low part of the building may be one of the solutions if the beams and columns can carry the loading.

 

[hoshang]

Hi
Isn't there any reply?

 

[hoshang]

Hi KootK, Ron, HotRod,
Are there any suggestions?

 

[Retrograde]

Do you think there will be problems if the joint doesn't exist between the high and low part of the building?

Do you think there will be problems? What problems? Why are you worried?

No point bumping your post 4 times in one day.

 

[JAE]

A stepped building like this can be designed appropriately without a joint to separate the low and high sections.

A separation joint would probably keep you from an irregularity for seismic. A full expansion joint could be considered but you’d want to weigh the costs between joint and no joint.

Depends on a lot of different parameters.

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[hoshang]

A stepped building like this can be designed appropriately without a joint to separate the low and high sections.

This building is designed previously (not me) and the RC frame (foundation, columns, beams, and slabs) is constructed. The client asked us to check the design before starting finishing works.

 

[robyengIT]

... why not asking the designer ??

 

[hoshang]

... why not asking the designer ??

Because

The client asked us to check the design before starting finishing works.

does three floor difference make problems with regard to the foundation?
And

If there are problems, how it can be solved? I don't think sawcut can solve the problem. My thought is that using lightweight partitions in the high part and using hollow masonry concrete block in the low part of the building may be one of the solutions if the beams and columns can carry the loading.

 

[struct_eeyore]

sounds like you are doing a peer review. If you are worried about foundations, run the loads and see how they compare to the bearing pressure - also, looks like the joint occurs at elevator shafts, which could be(?) your shear walls - in which case, I would like the floor diaphragms to attach w/o a joint. Hard to say w/o detailed plans - this just looks like an architectural profile.

 

[calvinandhobbes10]

1. Building looks small in this transverse direction, not wide enough to warrant an expansion joint that way. Check longitudinal length too.
2. Agree with the above about seismic irregularity especially if youre in high seismic. In design I would rather just check/accommodate the irregularity provisions, instead of adding a joint and now having two structures.
3. If you have concerns, voice them. Consider calling the original designer to ask how they approached it.
4. I strongly discourage simply “OKing” this because thats what the owner wants. Do due diligence, check it.

Good luck

 

[hoshang]

looks like the joint occurs at elevator shafts

No, There isn't any joint there.

Hard to say w/o detailed plans

Please find the attached link:

https://www.screencast.com/t/EQd4nr98yFZD

Building looks small in this transverse direction, not wide enough to warrant an expansion joint that way. Check longitudinal length too.

This direction is the longitudinal direction. The transverse direction is 10m wide.
Should I consider differential settlement of the soil for this mat foundation? If so, should rotation of the mat be one of the considerations?

 

[bob33]

The structure is built. A Client wants Hoshang to provide a second opinion before completing the building. There is a concern about the mat foundation and expansion joint. I would suggest the following. First examine the structure for any signs of distress now that a large portion of the dead load is in place. Next analyze the mat using spring constants obtained from the geotechnical engineer. The spring constants should take any long-term settlements into account. Then discuss with the EoR, if there is a problem. I would not question another engineer's work without discussing it with him/her first if possible. Finally, report findings to Client and await further instructions.

 

[hoshang]

Next analyze the mat using spring constants obtained from the geotechnical engineer. The spring constants should take any long-term settlements into account.

After analyzing the mat using spring constants if there's a problem in the mat, how it can be solved? I suggested in previous posts using normal weight partitions in the low part of the building and using light weight partitions in the high part of the building if the beams, columns can be safe for these new loading.

 

[bob33]

You have to analyze the mat first with the specified loads. If there is a problem, you could easily run the mat analysis again with changes in partition loads and see if it helps significantly. There are other options as well, but I would not want to consider any until I had done all I had suggested in my previous comments.

 

[Ron]

You will need a flexible joint for waterproofing purposes at the roof to wall transition

 

[hoshang]

There are other options as well

What other options?
I thought about another option today. What about thickening (strengthening) the raft foundation (adding 20-30cm concrete on top of mat foundation with reinforcement anchoring into existing columns and mat foundation).

You will need a flexible joint for waterproofing purposes at the roof to wall transition

Can you explain this more?

 

[bob33]

Hoshang, why are you looking for solutions when you have not done the investigation yet? As I said, I am not willing to consider any solutions until the investigation is complete. For all I know, there may not be a problem. Perhaps you should consult with a senior structural engineer who can give you more help with the investigation and any remedial work required. All I can give you are tips.

 

[Ron]

Hoshang....Waterproofing at roof to wall transitions are notorious for leaking and moreso when there is a potential for structural movement between the two sections. The joint should be flexible and allow for movement between the sections while remaining waterproof.

Water flows down the wall of the higher section and is blown by wind against the wall from the lower section....all of this creates a significant leak potential.


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[hoshang]

Hoshang, why are you looking for solutions when you have not done the investigation yet?

For all I know, there may not be a problem.

Is the later quote is written after an investigation?
If you did the investigation, can you post your remarks on the investigation?
I haven't completed the investigation yet because I haven't gathered all data I need. I search on solution earlier so it can be available a lot of options when there should be problems with the mat foundation so I shouldn't post another thread regarding this project.

Wall flows down the wall of the higher section and is blown by wind against the wall from the lower section....all of this creates a significant leak potential.

Thanks Ron.