After a steel member is set to be designed using the Advance Stability solver from Advance Design Bedding conditions can be imposed in the definition box.
The Bedding tab allows the user to define continuous springs along the member, in case of steel sheets (shear diaphragms) acting as restraint, for example.
Figure 1 - One Span Function
By default, the “Bedding” option is not activated. In order to activate it, the “One Span” function auto-detects the intersections of the selected element with other elements (like it does in the Nodal Springs tab). The bedding conditions can be added, deleted or reset.
The bedding “Position” is by default set to “Neutral” (in the shear center of the section), but it can also be modified by the user along the Z axis and set to “Upper fiber”, “Lower fiber”. It can also have an value imposed by the user, which can be set as reported to the neutral point.
Figure 2 – Bedding position
According to EN1993-1-3 (§10.1.1), the influence of sheeting can be considered by providing the appropriate stiffness value (rotations, translations):
Figure 3 – Stiffness definition
Shear diaphragms originate, for example, if trapezoidal steel sheeting or similar components are continuously connected with the construction underneath at all four edges. Often, the compressed upper flange of girders is considered to be supported laterally in this way. The supporting effect does not rely on a disability of displacement as is the case with translational springs, but on a decrease of rotations.
Figure 4 – Shear field definition
The shear field stiffness of trapezoidal sheeting connected to the purlin at each rib and connected in every side overlap may be calculated as:
Where:
- t is the design thickness of sheeting
- broof is the width of the roof
- s is the distance between the purlins
- hw is the profile depth of sheeting