Wandering Wallaby
Structural
- May 4, 2020
- 19
Hello everyone. The geotechnical engineer on a residential project that I’m working on suggested either pin piles or a mat foundation due to site conditions. The builder doesn’t want to use piles, so I’m designing my first mat foundation. I’ve never seen them on small light-framed wood construction, but here we are. It is two stories above grade in front with a basement that opens to the rear (a sloping lot, ie. daylight basement). The basement level and the garage above will be mat foundations. The garage mat will impart a significant surcharge on the basement wall so I will probably tie the top of the wall to the mat and design as a restrained retaining wall to keep the thickness of the wall to a typical 8” thick wall.
My questions are regarding the mat foundation. I do not have access to software for this design and do not feel it would be feasible to purchase any since this seems to be a rare occurrence for the type of work I typically do. With only one source of interior bearing walls (in blue), this seems to be a fairly easy design. I’m thinking just typical top and bottom reinforcement each way (enough for crack control), and maybe some extra steel at the interior bearing wall, will suffice for this lightly loaded mat. And then anchor the retaining walls into the basement mat as needed. Then I will idealize it as one large rigid footing and design for the overall base shear and overturning to check the soil pressure.
To give some numbers to this, the basement slab is -10’-8” below the main floor garage slab. The structure footprint is 35’ x 46’ with the garage taking up the 20’ x 24’ area of the lower left quadrant. SDC D with base shear V = 16.2k and M = 2100 k-ft. Soil bearing capacity of 1,000 psf with 150 pci modulus.
Please let me know if you think I am in the ballpark, or way off base, in regards to my proposed design approach.
Thank you in advance.
My questions are regarding the mat foundation. I do not have access to software for this design and do not feel it would be feasible to purchase any since this seems to be a rare occurrence for the type of work I typically do. With only one source of interior bearing walls (in blue), this seems to be a fairly easy design. I’m thinking just typical top and bottom reinforcement each way (enough for crack control), and maybe some extra steel at the interior bearing wall, will suffice for this lightly loaded mat. And then anchor the retaining walls into the basement mat as needed. Then I will idealize it as one large rigid footing and design for the overall base shear and overturning to check the soil pressure.
To give some numbers to this, the basement slab is -10’-8” below the main floor garage slab. The structure footprint is 35’ x 46’ with the garage taking up the 20’ x 24’ area of the lower left quadrant. SDC D with base shear V = 16.2k and M = 2100 k-ft. Soil bearing capacity of 1,000 psf with 150 pci modulus.
Please let me know if you think I am in the ballpark, or way off base, in regards to my proposed design approach.
Thank you in advance.
