Smoothing of results on beam and rib elements

Table of Contents

Phenomenon #

However the smoothing is turned on under the display parameters under the settings of the statics analysis results view, diagrams for beam elements are not smoothed, but have steps between finite elements.

Reason #

The reason is that, ribs and beams are different finite elements with special behaviors.

The rib is an isoparametric element, that approximates the displacements with a quadratic function, which especially in the case of a distributed load or a concentrated load inside the rib element is really only an approximation. For this reason, we cannot calculate the internal forces accurately inside the element, and as a direct result of the calculation, the internal forces do not fit in the common nodes either. To improve this, smoothing is applied.

The beam is a Navier-Bernoulli element with a third-order displacement function. This gives an accurate deflection and stress diagram at the endpoints and inside the bar element only for node loads. Moreover, it allows us to superimpose the effect of the loads inside the elements on the third-order function if we know the distributed and concentrated loads inside the element. As a result of this, we can show an exact bent shape and an accurate stress diagram even for internal loads. The beam element, therefore, does not need smoothing.

However, this is not true if there is line support defined to the beam.

The load acting on the beam from the line support as a distributed force inside the element is not taken into account when calculating the corrected beam stress diagram. Thus, in the case of line support, the bar stress pattern will be so intermittent. The shear force that is continuously absorbed in the support is not smeared on the rod, but appears in the form of steps between the elements.

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