Expnasion joint in L- shape RC slab ?

[tngv752]

I am design the concrete slab on ground supported by strip footings. The soil is high reactive. The slab is an L shape of 23m x 12m x 6m wide approximately (see below).
Should I provide the slab expansion joint along the dotted line and double strip footing under ?
The masonry walls are articulated joint, therefore the joints should be located there (both sides) ?
Thanks.

12m
______________
| |
|....._________| 6m
| |
23m| |
| |
| |
| |
|____|
6m

 

[hokie66]

I assume by the dimensions that this is a single family dwelling. It would be highly unusual to provide an expansion joint in such a small structure. Crack control joints, maybe, but it is more common practice to tie the whole slab together with reinforcement and reinforced slab thickenings to make the slab work as a raft. Strip footings with slab on ground is not a system which works well in highly reactive soil areas. It might be helpful to know your location, as different systems are employed in different geographical/geologic areas.

 

[tngv752]

This is an extension of a single dwelling. The soil is Class H1 (100KPa).
The bore hole:
(0.0 – 0.2m) LOAMY CLAY – Topsoil, Moist, Medium Plasticity
 (0.2 – 0.5m) SILTY CLAY – Yellow/Brown, Moist, High Plasticity
 (0.5 – 0.9m) SILTY CLAY – Yellow, Moist, High Plasticity
The geotechnical engineer recommend for strip footings should be taken through any soft to firm silt or fill and founded in the stiff silty clay.

The different level between the top of new slab and ground level is from 215mm to 415mm. As original I think raft slab can be used (beam = 500 deep x 300 wide) therefore the footing cannot be located above the silty clay. Should I increase the
deep of the beam or provide thick cement blinding under the footing ?

I belong to Sydney, NSW, Australia. Which part are you in Hokie ?

 

[tngv752]

I go for Stiffen raft + deep edge beam. Raft slab + piers is too expensive.

 

[hokie66]

Brisbane. I haven't really been involved with residential design in many years, so am certainly not the authority. My understanding is that most dwelling construction uses the prescriptive provisions of the Residential Slabs and Footings Code, or whatever it is called. Raft slabs are certainly one way, and probably applicable in your case.

 

[ooox]

As your slab is less than 30m it can be detailed in accordance with the requirements AS2870-2011 and therefore it is not necessary to introduce an construction joint at the re-entrant corner. If you're adopting a stiffened raft then make sure you look at the Commentary C5.4 for guidance on arranging stiffening beams.

Its standard practive to use a 15MPa concrete where the underside of the edge/internal beams are located above the bearing material.

 

[tngv752]

It's clear now. Thanks guys