Module section_lower

Lower parameterised structural sections into exact contours (ADR 0057).

Why the fillets are not optional

For a rolled steel section the web-to-flange root fillet is real material. Measured on a 0.4 x 0.3 I-section with an 0.021 root radius, the four fillets carry 2.40% of the cross-sectional area. Dropping them yields a section that looks correct and whose area, second moment and mass are all wrong, so they are built as exact arcs rather than ignored or approximated.

Structure

Every variant reduces to a closed counter-clockwise ring of corners, each carrying an optional radius. One shared router turns that into a contour, inserting a tangent arc at each rounded corner. Concave root fillets and convex toe radii are the SAME operation – the sign of the turn decides which way the arc bends – so neither gets a special case that could drift from the other.

Functions

circle_contour

A circle profile, and its bore when it has a wall thickness, as exact contours of four quarter arcs each (#111).

rectangle_contour

Lower a rectangle – rounded, hollow, or both – into an exact contour.

section_contour

Lower a parameterised section into an exact contour.