search

Steel canopies

Exterior canopies penetrating the envelope typically occuring in schools, universities etc. are another critical thermal bridge which leads to significant heat loss. Schöck Isokorb® type KST is the solution to thermally separate the exterior steel structures from interior steel strcutures.

Seite_18_Bild_21

Figure 21: Schöck Isokorb® type KS/QS for steel beams

Seite_18_Bild_22

Figure 22: Typical building with supporting structure made of steel. Steel canopies are thermally broken by Schöck Isokorb® type KST.

The highly conductive structural steel (λ = 50 W/(mK)) at the connection is replaced with expanded polystyrene (EPS, λ = 0.031 W/(mK)) with a thickness of 80 mm to give an effective thermal separation of the steel beam. This is non-structural and constitutes the main body and surface area of the thermal break.
Stainless steel is used within the Isokorb® module for the structural elements (bolts and a hollow section) to transfer the loadings, while further reducing the thermal conductivity, since stainless steel λ = 15W/(mK) has a thermal conductivity 30% that of carbon steel carbon steel 50W/(mK).

Typically two Isokorb® type KST/QST are used per beam connection. Appendix chapter 4.2 shows the equivalent thermal conductivity λeq and the equivalent thermal resistance Req respectively. Note that heat transfer through the connection is reduced by about 85% compared to the heat transfer through a continuous steel beam.

The following 3D thermal models have used Schöck Isokorb® for concrete structures and steel structures.

A modelling study was undertaken by Oxford Brookes University to determine the effectiveness of Schöck Isokorb®. The aim of this investigation was to determine the heat loss, minimum surface temperature and temperature factor (fRsi), and equivalent conductivity resulting from use of Schöck Isokorb® type KST units connecting a steel beam, and to compare these values with alternative connection methods and with a continuous beam. Calculation was by means of three dimensional finite difference analysis.

Seite_18_Bild_23a

Figure 23a: HEA200 beam passing through 80mm insulation

Seite_18_Bild_23b

Figure 23b: Thermally broken steel beam with KST22

Further information about the boundary conditions and the thermal conductivity of the used components can be found in Reference 1.

Seite_19_Bild_24a

Figure 24a: Direct connection (Case 1): temperature distribution (section). This detail does NOT conform to UK Building Regulations Part L requirements for minimum temperature factor in dwellings (fRsi = 0.75)

Seite_19_Bild_24b

Figure 24b: KST16 connection: temperature distribution (section). This detail conforms with UK Building Regulations Part L requirements for minimum temperature factor in dwellings (fRsi = 0.75)

Seite_19_Tabelle_3

Table 3: Thermal modelling results

It can be seen from the results that the KST16 units, with fRsi = 0.75 respectively, exceed the minimum value of 0.75 and will therefore meet the requirements of Building Regulations Approved Documents L1 and L2. whereas the continuous beam falls far short of the requirements. The heat loss by incorporating Schöck Isokorb® type KST is reduced by almost 65%.

Seite_19_Bild_25

Figure 25: Schöck Isokorb type KST installed between the interior and the exterior beam.