Why is the shear force Vz for a rib directly above the support smaller than close to it?

Answer

For a rib member, the shear force Vz consists of the member internal forces which are related to the eccentrically connected rectangular member as well as of the surface internal forces which are integrated over the defined integration width.


A decreasing value of the shear force Vz directly above the support (see Figure 01) thus usually results from the distribution of the surface internal forces (basic internal force vx or vy). See the diagram of the basic internal forces v-y in Figure 02. A "Zero-crossing" of the surface internal forces results above the support. This "Zero-crossing" results from the smoothing of the surface internal forces within the surface and is also reflected accordingly in the member internal forces of the rib member.

To avoid the "Problem", you can divide the continuous surface above the support into a surface before and after the support.

When the surface, internal forces are integrated, the smoothed distribution of the surface internal forces "within a surface" is applied. If you enter a surface before and after the support, RFEM provides you with a result value without zero-crossing exactly next to the nodal support. In Figure 04, it corresponds to +112.63 kN/m or -112.63 kN/m.

Keywords

Shear force Vz Shear force distribution Rib T-beam Downstand beam Upstand beam

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RFEM Main Program
RFEM 5.xx

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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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