Risposta:
Si ritiene che sia DLT che NLT si comportino più come elementi di trave ad asse singolo sollecitati principalmente a flessione. Although realistically there is a small amount of stiffness perpendicular to the span direction, this is neglected in beam design. This is in contrast to cross-laminated timber (CLT) which includes two-way stiffness in both the directions parallel and perpendicular to the span direction. Therefore, the Multilayer Surfaces Add-on is not suitable for NLT or DLT design but rather better used for CLT design.
The best approach in RFEM 6 is to model a standard stiffness surface with modified orthotropic elastic 2D material properties. For the material model details, the modulus of elasticity in the local y-axis direction (Ey) should be set to a very small number (i.e. 0.001). The shear modulus in the local yz-plane (Gyz) should also be set to this small value. This will replicate little to no stiffness in the direction perpendicular to the DLT or NLT span direction.
The surface can then be applied in the RFEM 6 model for the full analysis. Note, design is not possible for these elements directly in RFEM 6. Internal forces, stresses, deflections, etc. from the RFEM 6 analysis can be exported to alternative programs (i.e. Excel) for further design according to the various standards.
