Structural consideration of window profiles in accordance with DIN EN 14351-1
Structural calculations need to consider the structural integrity of the load-bearing profiles and main attachments as well as the fitness for purpose.
This is to be ensured by means of the deformation limit under external loads.
Resistance to wind load is a particularly important criterion here.
Normative limit of deformation:
Windows and external doors must be tested in accordance with DIN EN 12211. The deflection of frame components (e.g. mullions and transoms) must be determined by means of calculations or tests (reference method).
The relative frontal deflection of the most strongly deformed frame section is classified as follows in DIN EN 12210:
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Class
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Relative frontal deflection
|
|
A
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< 1/150
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B
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< 1/200
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C
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< 1/300
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The respective requirements for the unit are generally fixed by the architect in the specification for the individual project.
In addition to the external wind loads, a window unit can also be subjected to horizontal live loads if a safety barrier function is required due to the installation position.
Safety concept:
As the currently valid verification procedure for thermally broken profiles in accordance with the IfBt guideline (guideline for the proof of structural integrity of metal/PVC-U composite profiles, version 1986-08) is not based on the partial safety principle, all certifications are given in accordance with the global safety concept.
Load combinations:
The necessary overlap under external loads (wind + horizontal live load) is derived from the specifications of DIN EN 1990 and DIN EN 1990/NA.
To be on the safe side, the following load combinations are taken as a basis within the program for the measurement of frame components:
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Load combination for structural integrity and fitness for purpose
1.0 G + 1.0 Qk,1 + 1.0 ψ0,i Qk,i
-
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G
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is the value of constant influence
(e.g. loading by means of dead load, permanent equipment)
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|
Qk,1
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is the characteristic value for the dominating changing effect
(e.g. wind, horizontal live load)
|
|
Qki
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is the characteristic value for the accompanying changing effect
(e.g. wind, horizontal live load)
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|
Ψ0,i
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Coefficients for the combination of accompanying changing effect
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-
As is evident from the above formula, the required cross-sectional values for structural integrity and fitness for purpose are calculated from the significant overlap of the changing loads (wind and
horizontal live load).
Based on DIN EN 13830:2003 (product standard: curtain walling) more advantageous load conditions are conceivable with regard to fitness for purpose:
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Structural integrity:
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1.0 G + 1.0 Qk,1 + 1.0 ψ0,i Qk,i
|
|
Fitness for purpose:
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1.0 G + 1.0 Qk,Wind
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Here the load proportion of the horizontal live load is disregarded for the proof of fitness for purpose. Briefly exceeding the profile deformation in the most unfavourable loading combination (wind + horizontal live load) is tolerated if the structural integrity of the unit continues to be ensured.
As these load conditions are not clearly documented in standards, however, they require prior official consultation with the structural engineer for the project or the project test engineer, and cannot be accounted for by Schüco as part of a preliminary structural calculation.
