Stavebnicový systém MB 9 - EN

686 19 The following equations apply for calculating the torsion angle ϑ : Example load 1 ϑ = ​ 180° x M t x l  ___________   π x G x  t x 10 ​ Example load 2 ϑ = ​  180° x M t x l  _____________   π x 4 x G x  t x 10 ​ Where: M t = Torsional moment in Nm l = Free profile length in mm  t = Moment of inertia in cm 4 G = Modulus of rigidity in N/mm 2 G AI = 25,000 N/mm 2 ϑ = Torsion angle in decimal degrees Construction profiles: Determination of the torsion angle The values for the profiles’ torsional moments of inertia were determined experimentally or through an approximate calculation. Component tolerances and simplifying assumptions mean the actual torsion angles can differ from the calculated value by up to 15%. Check of the torsional stress In practice, the criterion for a profile to fail under a torsional load is less the fact that the permissible torsional stress is exceeded, but rather the presence of excessive twist (torsion angle) even though it is still within the elastic limit. This deformation greatly impairs correct functioning of the components. Consequently, a more torsionally rigid profile must be selected long before the permissible stress values are reached. The example shown on the nomogram opposite is based on the free profile length and a given torsional moment. The result is the torsion angle as a defor- mation of Profile 8 80x80. It is naturally also possible to use the nomogram in reverse and begin with a maximum permissible torsion to calculate the required profile sizes or the maximum loading moments for a specified profile length. Example: Given: M t = 20Nm l = 2,000 mm  t = 136.98 cm 4 (Profile 8 80x80) Find: ϑ = Torsion angle in decimal degrees Results: Example load 1 ϑ = 0.07° Example load 2 ϑ = 0.02° T E C H N I C A L D A T A