FAQ 002434 EN

Design RFEM

What do I have to consider when determining weld stresses at surface interfaces?

Answer

To obtain the stresses in a weld in RFEM, it is important to know which surface stresses are used for it. The figure shows a simple example. The lap joint applied in z-direction is subjected to a line load of 100 kN/m at the upper end in x-direction and to a line load of 10 kN/m in y-direction.

To determine the correct stresses, it is necessary to know the local coordinate system of the surface. You can activate it in the Display navigator under "Model" → "Surfaces" → "Surface Axis Systems x, y, z". All stresses with "+" in the index indicate the stress at the top surface, i.e. the side of the positive local z-axis. When showing the surface moments, notice that there is a fundamental difference between surface and member internal forces: While a member moment My "rotates" about the local member axis y, a surface moment my is acting in the direction of the local surface axis y, i.e. about the x-axis of this surface.

For the given example, this means that the bending moment of the lap joint is acting in the direction of the global y-axis and therefore a value of 2 kNm/m is required as result. The average in the depicted diagram confirms this assumption by a value of 1.95 kNm/m (deviations can be reduced by a finer FE mesh). The average of the shear flow is 100 kN/m and therefore corresponds to the applied load.

The stress σy,+ thus represents the compressive stress of the lap joint at the top surface and τxy,x represents the shear stress in the interface on the same side. The stresses should only be evaluated if the weld thickness is equal to the surface thickness; otherwise it is recommended to determine the stresses manually from the adjacent internal forces.

Keywords

Weld, Stress, Surface Interface

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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