Idealization of the Steel Structure.

The finite element idealization should represent the real structure as closely as possible with regard to geometrical shape, loading and boundary conditions. The geometrical form of the structure is the major factor to be considered when deciding the shape of elements to be used. In two-dimensional analyses the most frequently used elements are triangular or rectangular shapes. The triangular element has the advantage of simplicity in use and the ability to fit into irregular boundaries. Figure 9.29 shows an example using triangular elements and Fig. 9.30 shows a combination of triangular and rectangular elements. These figures also demonstrate the need to use relatively small elements in areas where high stress gradients occur. In many such cases the geometrical shape of the structure is such that  a  fine mesh of  elements is required in order to match this shape.

Circular hole in uniform stress field
Fig. 9.29 Circular hole in uniform stress field
Perforated tension strip (plane stress) – a quarter of a plate is analysed
Fig. 9.30 Perforated tension strip (plane stress) – a quarter of a plate is analysed

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