advanced building skins 14 | 15 June 2012 - lamp.tugraz.at - Graz ...

Advanced Building Skins
Figure 10: Principal tensile stresses on the glass surface as a function of the temperature distribution and the
stiffness of the frame
7 Summary and Outlook
The mechanical load test according to IEC 61646 with only one specimen leads to a much lower
safety level than the application of the structural design standards for glass constructions (TRLV,
DIN 18008).
To consider the scattering of the glass strength, the number of specimens should be increased
significantly to reach a comparable safety level to DIN 18008 (see Table 3 and 4). Instead, according
to IEC 61646, only a safety factor of γ = 3 is taken into account referenced to a characteristic wind
load of 0.8 kN/m². Thus, the allowable installation and application situations that may be covered by
the staggered test load according to IEC 61646 with 2.4 kN/m² and 5.4 kN/m² have to be discussed.
Nevertheless, it is common practice to install PV-modules, which were tested according to IEC 61646
without any additional structural calculations. The consequences are already evident in numerous
cases of damages. Only the positive post-breakage behaviour of laminated glass ensures that the
damages did not cause greater hazards to people so far.
It was shown that temperature loads and especially variable temperature profiles over the cross-section
can lead to design relevant principal tensile stresses.
For the future, besides the need of a suitable structural design method for PV-modules, the postbreakage
behaviour of laminated glass has to be analysed systematically to develop appropriate
mechanical models. Moreover, specific loads on PV-modules, such as thermal stresses due to the high
solar absorbance of the thin film and the associated thermal stresses in the glass, have to be
investigated further.
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