Simulating hollow core slabs in 1D-model

[Sami Roikonen]

Hello!

I need to simulate couple of floor types. One of the floor types has a hollow core slab at the bottom as supporting structure and on top of it, there is thermal insulation, in-situ cast concrete slab, screed and floor covering. It's a bit like a concrete sandwich panel as a floor.

I have to make many models of this one since the different floor coverings (tiles, moisture insulation, epoxy, paint...) change how dry the concrete has to be before adding the covering, and they have their own specs as well.

Since making many models in 2D is quite tasking, I thought to make a new material in 1D that simulates a hollow core slab as a homogeneous concrete slab. I changed the concrete's material data so it would take the air cavities into account. I did this using the ratio between areas of concrete and air cavities, so the new material has about 55% - 45% ratio of density, thermal conductivity, u-value, water content and the relation between RH and water content.

Of course there's the possibility of making twice the number of models and simulating the hollow core slab in one case as just concrete and in other as an air layer. The truth then lies between those two cases. I think, however, that this is too tasking as well.

Do you have any suggestions on this? Is there anything right now that I'm forgetting?

Regards,
Sami Roikonen

[Daniel]

Dear Sami,

sorry - your request got lost in my inbox.

I think a material representing the hollow core slab with effective properties for both concrete and air is a good approach. We have already some materials in the data base which follow that principle (for example hollow clay bricks).

One possibility is to measure effective values in the lab, the other one is to calibrate the 1D material by the 2D simulation. Also effective properties for thermal conductivity, vapor and liquid transport are important - here it's not always sufficient to reduce (or increase) the values just by densitiy ratio, but you should try to verify the resulting fluxes by the ones calculated in WUFI 2D.

best regards
Daniel