Results Interpretation: Gauss Point Extrapolation and Averaging

Description

Unlike results such as displacements and reactions, which are calculated directly at the nodes, plate and brick results such as moments and stresses are calculated at the so-called Gauss integration points. For example, the figure below shows four connected Quad4 elements, their nodes and their respective Gauss integration points. (For a list of elements and their respective positions of Gauss points and weights, see the Straus7 Theoretical Manual.)

To get plate and brick results at the nodal positions, result values are extrapolated from the Gauss integration points (see Extraplating section below).

After extrapolation, each element may report a different result value at common nodes. The difference, referred to as Jumps, can usually be reduced by increasing the density of the mesh. Monitoring the changes in result Jumps between mesh refinements can give a good picture of the adequacy of the mesh for the given loading. In any case, the result difference is usually removed by averaging those extrapolated results at the common nodes. Referring to the above figure, if the result at Node 1 extrapolated from Gauss point 2 of Plate A is 23.1 while the result extrapolated from Gauss point 3 of Plate B is 21.5, the averaged result at Node 1 is (23.1 + 21.5)/2.0 = 22.3, and this is reported as the nodal result (see Averaging below).

Extrapolating

To extrapolate the Gauss point results to the nodes, the following options are available in Straus7:

Averaging

To following averaging options are available in Straus7 to produce a nodal value after the extrapolation step:

Averaging and Plate Face Angle

The Facet angle angle setting found in Result Settings: Entity Tabs is always considered when averaging results on plate/shell elements. If the results on two connected plate elements are to be averaged, the averaging operation will proceed only if the angle between normals on the plates is less than the facet angle.

See Also