How to distribute point load from glued laminated timber column onto existing foundation?

[Kubikton]

Planning for the renovation and extension of a garage, including replacing the existing gable roof with a glulam beam at the ridge, where the load is directed down to the existing foundation through three glulam pillars.

The foundation is a cast slab on the ground from 2014.

The roof is 8000mm long, with pillars placed in the wall on the short sides and the third one 2500mm from one short side.

The support reaction is calculated to be 45kN for the "middle pillar." This pillar will also stand in an interior wall.

I'm considering what options are available to distribute the point load from the glulam pillars down to the foundation (besides the option of cutting the foundation and reinforcing it). Since the current foundation is not designed for this point load. Steel beam on the floor? Or any other alternatives?

I can add that function takes precedence over appearance here, and as mentioned, there will be an interior wall here, so it is possible to encase a potential load distributor.

 

[a_w]

Planning for remodeling and extension of the garage, I will be among other things, supporting the existing gable roof with a glulam beam at the ridge where the load is directed down to the existing foundation through 3 glulam columns.

The foundation is a concrete slab on ground from 2014.

The roof is 8000mm long, the columns will be located in the wall on the short sides and the third 2500mm from one of the short sides.

The support reaction is calculated to be 45kN for the "middle column". This column will also be in an inner wall.

I'm considering what options are available to distribute the point load from the glulam columns down to the foundation (apart from the option of cutting up the foundation and reinforcing it)? Since the current foundation is not designed for this point load. Steel beam on the floor? Or some other alternative?

I can add that function takes precedence over appearance here and as mentioned there will be an inner wall here so it can possibly be clad

Assume you distribute the ground pressure over an area of 0.5m2, then the pressure is 90 kPa that the foundation should handle. This is relatively low unless you have a lot of clay or peat under the building. The insulation must not be too soft either, but with an s80 it should be ok.

Relevant failure modes of the slab apply:
- Crushing under the column: Is most likely not a problem.
- Bending failure of the slab: is probably not a problem either.
- Punching shear: Is probably the governing failure mode. To handle this, it’s not a bad idea to install a steel beam on top of the slab. Just make sure to get plenty of dowels between slab and beam. Then ensure a good underpour with expanding grout. Hard to say exact dimensions of the beam. But if I were to take a stab, maybe an HEA140 with web plates at the connection to the column and end plates. Length maybe 1.5 meters.

 

[Kubikton]

Assume that you distribute the ground pressure over an area of 0.5m2, then you get a pressure of 90 kPa that the foundation should withstand. This is relatively low as long as you don't have a lot of clay or peat under the building. The insulation must also not be too soft, but with an s80 it should be okay.

Relevant failure modes of the slab are:
- Crushing under columns: Is most likely not a problem.
- Bending failure of the slab: Is probably not a problem either
- Through punching: Is probably the governing failure mode. To handle this, it is not a bad idea to mount a steel beam on top of the slab. Just make sure to get a good amount of dowels between the slab and the beam. Then achieve a nice underpinning with expanding mortar. Hard to say exact dimensions on the beam. But if I were to take a guess, maybe a HEA140 with web plates at the connection to the column and end plates. Length maybe 1.5 meters.

Interesting! Sounds like there are possible solutions without cutting up the floor, and if a beam can solve this, I'm satisfied. I will consult my plans with a structural engineer before I start but am looking for some ideas to consider.