psychedomination
Structural
- Jan 21, 2016
- 119
Hi there,
I'm working on a project where the client would like to add an additional storey to their existing 1 storey residential home.
The existing building is built with 8"(203mm) hollow CMU block and doesn't appear to have any foundations. The building appeared to have just been built on grade.
I'm planning to underpin this building with a suitable mass concrete foundation to hold the two storeys.
I did a load take down and the unfactored line load on the strip footing will be around 65kN/m.
Assuming a permissible bearing capacity of 100kPa, this would require a foundation thickness of 650mm.
Most guidance online seems to state the depth should be equal to or greater than the projection. In this case the projection would be (650-203)/2 = 224mm.
This would result in a footing 650mm wide and 224mm deep.
I see in my local building code, typically strip footings are reinforced. However mass concrete footings would be muvh cheaper and easier to construct with the underpinning pour sequencing. The wall length is only around 20' long max. I'm just wondering if these numbers seem reasonable for a two storey residential foundation and if not, if there is any guidance in any US/CAD/UK code for a minimum thickness for mass concrete foundations. Also is there any practical reason for me to use a reinforced concrete strip footing instead of mass concrete in a situation like this?
I'm working on a project where the client would like to add an additional storey to their existing 1 storey residential home.
The existing building is built with 8"(203mm) hollow CMU block and doesn't appear to have any foundations. The building appeared to have just been built on grade.
I'm planning to underpin this building with a suitable mass concrete foundation to hold the two storeys.
I did a load take down and the unfactored line load on the strip footing will be around 65kN/m.
Assuming a permissible bearing capacity of 100kPa, this would require a foundation thickness of 650mm.
Most guidance online seems to state the depth should be equal to or greater than the projection. In this case the projection would be (650-203)/2 = 224mm.
This would result in a footing 650mm wide and 224mm deep.
I see in my local building code, typically strip footings are reinforced. However mass concrete footings would be muvh cheaper and easier to construct with the underpinning pour sequencing. The wall length is only around 20' long max. I'm just wondering if these numbers seem reasonable for a two storey residential foundation and if not, if there is any guidance in any US/CAD/UK code for a minimum thickness for mass concrete foundations. Also is there any practical reason for me to use a reinforced concrete strip footing instead of mass concrete in a situation like this?
