Foundations For A Building Sitting From Plot Boundary To Boundary

[YuleMsee]

This is a foundation layout for a 4 storey building sitting on the entire plot, boundary to boundary.
Its essentially an eccentricity problem. When I consider a combined footing running from Gridline A-C, some columns e.g on Gridline 2 & 4 are left orphaned. Been scratching my head for the better part of today and I still have no solution.
Anyone with ideas on a layout that can work.

 

[Ron247]

Never had to deal with what you are showing but I may have a near future job that it appears may have a similar problem. Building between 2 existing buildings and it will be 3 story.

What about a drilled shaft along the line of 2 and 4? The shaft could be considered an upside-down column. The skin friction could be considered similar to gravity weight? I am spit-balling here. I have done very few combined foundations in the past and never one with this complexity.

 

[Ron247]

Just out of curiosity, is your building between 2 existing buildings? If so, I have some questions about how would you handle overlapping soil pressures from existing and new.

 

[jayrod12]

What is the typical/expected foundation type? Piles or footings? What kind of subgrade are we bearing on?

 

[YuleMsee]

Ron, the other lots are not develops, and one short side is the access road.
I have never worked with piles, so I haven't really considered it due to lack of experience.
@Jayrod, I'm looking at strap foundations, combined or strip footings. The soil is lateritic with an amount of clay, the clay is non expansive and the strength is 150KN per sqr metre.

 

[hokie66]

I think you are on the right track in using rectifying beams to resolve the lot line eccentricities. If you run a beam along grid B, that will give you reaction points for the beams from the "orphaned" columns.

 

[jayrod12]

I was thinking the same thing as Hokie, big bram down the centre and beams goes left and right as required to grab the columns

 

[KootK]

Took a swing at a layout using the "spine" system proposed my colleagues above.

- It's certainly workable but may come at a considerable cost relative conventional systems if those have already been priced into the project.

- Piles definitely deserve some consideration if that's viable here. Often, with some geotechnical help, piles can be loaded eccentrically without the rectifying beams.

- The system shown below is obviously in danger of morphing into a true grillage/raft slab. And that may be worth consideration as well. I've seen versions of this where you'll have slab thickening on grids A/B/C with an SOG in between with some flexural capacity. Stiffness considerations with this cause me some discomfort but it's certainly been done.

- Try not to hate me for saying this but another attractive alternative would be a more rational column layout paying homage to precisely this issue. No doubt you're not the only party involved in setting the column layout however.

 

[YuleMsee]

@kootk, some column locations I can play with, some I cannot due to architectural considerations. The columns I can play with were positioned so as to give the cheapest cost to the suspended floor slabs. So moving them them to get savings in the foundations will just be offset by increased costs to the 5 suspended floor beams.

Will do something similar to your layout, then advice the client to get a quote from a piling contractor then compare costs.

Thanks all for you contribution.

 

[kieran1]

Had a similar building a number of years ago.
Considered the combined beams as suggested above. In the end it was more economic and much easier to construct a raft slab.

Kieran