Integraph

Section Analyzer

Compute geometric section properties — area, centroid, second moments of area, elastic and plastic section moduli, radii of gyration, principal axes, and stiffness-weighted (transformed) properties — from arbitrary 2D cross-sections drawn on a CAD-style canvas.

What is the Section Analyzer?

The Section Analyzer — internally referred to as GCS (General Cross Section) — is a general-purpose tool for computing geometric and stiffness-weighted properties of arbitrary 2D cross-sections. Draw the outline on a CAD-style canvas, cut voids out of it, add inclusions of a different material adjacent to the outline, assign materials to each region, and the tool returns the full property set used downstream by every flexural, axial, and shear capacity calculation in the platform.

Unlike the Light Gauge Steel Designer or the Advanced Concrete Section, the Section Analyzer is not tied to a design code. It does not run capacity checks, buckling analyses, or fire-resistance verifications. Its job is to answer one well-posed question: given this shape (and optionally these materials), what are its section properties?

This is the right tool when:

  • You need section properties for a hand calculation or an external solver
  • You have an unusual built-up or custom section that does not match any standard tabulated profile
  • You want to verify the centroid and principal axes of a composite assembly before sending it into a more specialised designer
  • You are doing preliminary studies where capacity is downstream of getting the geometry right

Capabilities

Geometric properties (single-material section)

For a single-material section the tool reports the standard catalogue:

  • Area AA, perimeter PP, centroid (xˉ,yˉ)(\bar{x}, \bar{y})
  • Second moments of area about centroidal axes: IxxI_{xx}, IyyI_{yy}, IxyI_{xy}
  • Elastic section moduli at all four extreme fibres: Sx,topS_{x,\mathrm{top}}, Sx,botS_{x,\mathrm{bot}}, Sy,leftS_{y,\mathrm{left}}, Sy,rightS_{y,\mathrm{right}}
  • Plastic section moduli ZxZ_x, ZyZ_y (single-material only — see composite caveat)
  • Radii of gyration rxr_x, ryr_y
  • Principal moments I1I_1, I2I_2 and the principal-axis rotation θ\theta
  • Polar moment Jo=Ixx+IyyJ_o = I_{xx} + I_{yy}
  • Shape factors kx=Zx/Sxk_x = Z_x / S_x, ky=Zy/Syk_y = Z_y / S_y (single-material only)

Composite (multi-material) sections

When a section contains more than one material, the tool additionally reports stiffness-weighted (transformed) properties computed via the modular-ratio method (ni=Ei/Erefn_i = E_i / E_{\mathrm{ref}}). The reference material is the first outline’s material — concrete is typical for RC, but any material can serve as the reference axis.

Transformed properties cover area, centroid, second moments, elastic moduli, radii of gyration, principal moments, and polar moment. Plastic modulus and shape factor are deliberately null for composite sections because plastic capacity depends on per-material yield, not modular ratio (see #874 — silent model substitution is worse than no result). Use a material-specific designer (ACS, or LGS once it launches) for composite plastic capacity.

Multi-region geometry

Each region carries a role that determines how it contributes to the section:

  • Outline — adds area (and stiffness) to the section
  • Void — subtracts area; must lie strictly inside an outline
  • Inclusion — an additional positive-sign region carrying its own material; treated identically to an outline by the calculator. Used to flag secondary regions in a composite assembly. Inclusions are currently adjacent to outlines, not embedded inside them — the region validator rejects any overlap between outlines and inclusions today. Extending the role to allow inclusions strictly contained within an outline (rebar-in-concrete and similar embedded layouts) is tracked at #1748; for now, use the Advanced Concrete Section for embedded reinforcement

Regions are validated server-side before any property is computed: self-intersecting polygons, voids that escape their outline, overlapping non-void regions, missing outlines, and degenerate (sub-three-vertex) polygons each produce a 400 with a machine-readable code. See Drawing tools — Region roles.

CAD-style geometry input

  • Polygon drawing tool with click-to-place vertices, ESC to cancel, click-start-vertex to close
  • Distance lock — type a number while drawing to constrain the next segment length; press Enter to place
  • Direction snapping — hold SHIFT while drawing for horizontal/vertical snap
  • Grid snapping at user-set resolution
  • Per-vertex coordinate editing in the side panel — for precise input that does not lend itself to mouse work
  • Multi-element selection, hide, and delete from the left panel
  • Zoom, pan, zoom-to-fit; vertex and edge numbering toggles for cross-referencing with prints

Backend verification

Properties are computed on the client during drawing for instant feedback, then re-computed on the backend on demand. The backend computation is the authoritative source — when both agree the right sidebar shows a green Calculated badge; when only the client preview is available it shows Preview. The backend response is what is persisted in any downstream report.

What this tool does not do

Section Analyzer stops at properties. It does not perform:

  • Design-code capacity checks. No MnM_n, VnV_n, NnN_n, or utilisation ratios. For steel use LGS; for concrete use ACS.
  • Buckling analysis. No FSM signature curves, no DSM. That’s an LGS responsibility.
  • Fire / thermal analysis. That’s an ACS responsibility.
  • 3D geometry. All sections are planar 2D.
  • Mesh-based stress fields. A finite-element mesh is generated and exposed as an overlay for visual inspection, but stress fields under applied loads are not computed here.

The limitations page covers the full scope and assumption list.

Next steps