How to model a thermal break

(Balconies with thermal breaks – source: Plaka)

A thermal break is a reinforcement system with the main function of eliminating thermal bridges caused by structure elements overhanging reinforced concrete structures (balconies, cornices, canopies, etc.).

To design thermal breaks, manufacturers usually request the moment and shear force at the break. So what should you model and which internal forces should you give to the manufacturer?

• As seen on the image aboven, the reinforcement is not continuous over the total length of the balcony. But in a pre-design, we make an abstraction of this. We assume that the thermal break has the same propeties over the entire length of the balcony.
• The reinforcement present in the thermal break, is drawn on the Diamonds model below. This reinforcement ensures that moment Mxx ( = moment about the local z’-axis = orange arrows) can be transferred.
  Note: determining which forces can (or cannot) be transferred can only be done correctly by making the local coordinate system of the plates visible!

• Select the thermal break together with the plate and click on  .

• The orange arrows (two images above), have the same orientation as the moment framed in red:
  The red framed moment represents M_xx.

• If we then assume that the other moments cannot be transferred, then the two moments at the bottom must be unchecked:

• If we then assume that only the out-of-plane shear can be transmitted, then the normal force and in-plane shear must also be unchecked:

• If the manufacturer then asks what force is present in the thermal break, you draw a cut line over the entire length of the thermal break and request the average value for Mxx and Vx (= the shear force in a plane perpendicular to the x’ axis).

If you also want to assess the cracked deflection of the balcony, you must request the rotational capacity of the thermal break from the manufacturer (the 1kNm/rad/m in the printscreen below is an arbitrary value).