Section Profile

Sections are most conveniently edited using the Section Wizard. This allows the user to either select sections from a catalogue, to define standard section shapes or explicitly define the section properties.

The first step is to select the basic section definition – catalogue, or standard shape, etc. Depending on this choice the profile wizard will load either catalogue sections, standard sections, or geometric sections (perimeter sections, or fabricated and line segment sections). Finally the defined section properties are displayed and an option is given to convert the section to a perimeter.

Section Definition Axes and Element Axes

Sections are defined with respect to section definition axes, shown in this diagram as $x_{def}$ and $y_{def}$. The section is used in GSA such that the section appears as defined, when viewed with the element x axis pointing into the page. This has the, perhaps unintuitive, consequence of GSA having to translate the specified $(x_{def}, y_{def})$ section definition coordinates to (0, $-x_{def}, y_{def}$) element axes coordinates. (I.e. ($x_{def}, y_{def}$) translates to ($-y_{el}, z_{el}$).) The translation occurs automatically within GSA, requiring no action from the user. The distinction between section definition axes and element axes is particularly relevant when considering geometric sections. Display “Section Shapes” labels in a Graphic View to confirm the orientation of sections.

Principal Axes

For a doubly non-symmetric section principal axes are not aligned with element axes. In this circumstance loading applied in element axis directions will produce deflections in the plane orthogonal to the loading unless there are constraints on the section to prevent this behaviour. If there are such constraints the user can choose, when defining the section, to prevent this effect by ignoring the $I_{yz}$ term in which case the $I_{yy}$, $I_{zz}$, $K_y$ and $K_z$ values would be used to calculate the element stiffness as if they were principal 2nd moments of area.