Behaviour of the T-Beam at Temperature Changes

Apart from the resistance capacity against loads the temperature behaviour plays an essential role. A second T-beam was exposed to 25 temperature cycles according to standard DIN EN ISO 9142 – Ag­ing Cycle D3. This resulted in a longitudinal in the centre of the 50 mm wide glass sheet of the flange. This crack ran 150 mm before the end of both beam sides. At the marked point in Fig. 10b the crack divides and cuts out a wedge-shaped piece of glass at the ends of the upper flange. The detailed image in Fig. 10a shows spots where very fine glass pieces can be seen which are the result of the steady opening and closing of the crack (probably formed in the first temperature cycles) because of the tem­perature change. This process could be confirmed by a FEM-analysis of both temperature conditions (20°C and +70°C). At a temperature of -20°C tensile stresses of such a magnitude occur at the upper side of the flange which let the glass break in the static experiment. When the T-beam is exposed to a temperature of +70°C a high tensile stress occurs at the underside of the upper glass sheet of the flange. This high tensile strength leads to a crack which opens and closes in the following cycles.

The deformation in the opposite direction as a consequence of both temperature conditions is shown in Fig. 9. The movement of the upper flange was a result of its unsymmetrical design, (upper glass sheet continuous, lower glass sheet interrupted), it was worsened by the different heat expansion coefficients of glass and plastic. When further developing glass-plastic hybrid elements one has to find construc­tive solutions that neutralise effects of such deformations in the opposite direction.

a) beam at temperature -20°C b) beam at temperature +70°C

Fig. 9: stress in cross direction of a hybrid beam at different temperatures

a) crack in the center of the beam b) crack at the end of the beam Fig. 10: path of crack in the upper glass sheet of the flange

Acknowledgements

The department of steel structure, Bauhaus-Universitat Weimar, thank the companies Glaskontor Er­furt, Rudolstadter Stahlbau, Innovative Klebtechnik Zimmermann, and the Institute for Joining Tech­nology and Material Testing Jena (IFW Jena) for the support.

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