Ground beams and differential settlement 1

[Gus14]

In my local practice where sandy soil is common. Ground beams, ( see attached file ) serve three purposes:
1) Bear the heavy brick partition load ( weight = 7 kn/m )
2) Bear the ground slab loads. ( I design the ground slab as if it were a roof and neglect any backfill soil strength as contractors can't be bothered to follow the backfilling procedure required to achieve any reliable bearing capacity )
3) Prevent differential settlement.


When there is a long distance between columns as in the attached sketch example. It's logical to put columns that end at the ground floor level ( CN ) to reduce the ground beams' length.
My question is, would assigning these CN columns also reduce differential settlement, and why?

Sketch link,

https://files.engineering.com/getfi...8-a16a-49cf-8007-5b384e471c23&file=Sketch.pdf

 

[BAretired]

The additional columns would reduce the cost of the beam significantly because of the span reduction. By reducing beam deflection, differential settlement is reduced between C1 columns, but the main benefit would be cost reduction in the grade beam.

BA

 

[dik]

Is this interior, and do you need frost protection or competent bearing layer?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Gus14]

Thank you dik and BAretired for replying. C1 columns are exterior columns, while the new CN columns will be interior. I don't need frost protection. However, most contractors are not familiar with the backfill compaction requirements, and I am trying to limit the overall settlement of building and differential settlement by increasing steel and concrete rather than going to war with contractors.

 

[HTURKAK]

If frost depth and soil bearing capacity are not issue, what is the reason for to excavate around 2.0 heigh and backfill with loose sand again?

Why not just perform grading excavation and local pit excavations for individual footing , so the grade beam can be supported by undisturbed soil?

Why the compaction of sand backfill is a big issue ?

IMO, it is not reasonable to provide short coulmns and ftgs under the grade beam to support against wall and SOG loading etc.

 

[Gus14]

Thank you HTURKAK for replying.
1) The high depth is because most clients are asking for high ground floor level of 1 meter above pavement so for typical building where soil level is the same as pavement. The soil strength report begins at 1 meter depth. leaving the depth of embedment 2 meters.

2) If the soil is not compacted well enough, such settlements could happen

3) Most contractors use the ground floor to stack bricks and building material ( props, cement bags... ), and typically used walls are heavier ( the wall linear load is approximately 7 kn/m. )

 

[HTURKAK]

If GFL is 1 meter above pavement , the depth of the grade beam should be in the range of 1.20 -1.4 m. If the soil safe bearing stress is defined 1.0 m below the grade, with the use of spread ftg having depth 0.6 , the 1.4 m depth of grade beam would be necessary..


I 'm saying the same... the fill SHALL BE compacted !!.

 

[Gus14]

Damn it I keep mistakenly submitting posts.
Dear HTURKAK, I think I misinterpreted your words regarding fill compaction. Contractors just don't know how to do it, and my office only supervises the final stage of grade beam construction right before concrete pouring, and it's really difficult to object at that stage. Most clients choose the cheapest contractor they could find, and I can't ask them for something they were not paid to do.
Regarding the beam depth, I was trying to set an example as I mentioned in the original post, so yes maybe a 1-meter clear height between grade beam and footing is more reasonable.

 

[dik]

So, spec it, and require that it be tested.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Gus14]

I tried but I can assure you that no one reads the specs, I consider myself lucky if they even look at the details. Their motto is to finish the stage, get the money and put the blame on the office.

 

[dik]

What country? Simply reject work not done to spec...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Gus14]

I am an expat in the gulf area, and maybe I should start rejecting work more often.

 

[dik]

They smarten up pretty quick... Have a preconstruction meeting outlining your objectives and stipulating the consequences for failure.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik