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🔄 Torsional Irregularity Explorer

Put the stiff core in the middle and the building translates. Push it to one side and the building twists — the far corner takes drift far above the average, and that corner is where the columns fail first. Drag the wall stiffness and watch the center of rigidity walk away from the center of mass.

Plan (24 m wide)

Four resisting frames at x = 0, 8, 16, 24 m. Center of mass at the plan center (12 m).

Frame 1 stiffness (x=0) 300

Frame 2 stiffness (x=8) 100

Frame 3 stiffness (x=16) 100

Frame 4 stiffness (x=24) 100

Live Result

—

Center of rigidity x_r—

Natural eccentricity (x_m − x_r)—

Torsional stiffness J_r—

Torsional irregularity η_bi—

Powered by rigid-diaphragm torsional analysis (engine/torsional-irregularity.js). Verified before publishing: a symmetric layout gives η_bi = 1.000 exactly, the center of rigidity satisfies its independent defining property Σkᵢ(xᵢ−x_r) = 0 to machine precision, and the displacement field is confirmed exactly linear in x (rigid-body kinematics). Accidental eccentricity is applied in both directions and the worse case governs, as codes require.

Method

TBDY 2018 §3.6.2.1η_bi = δ_max/δ_avg > 1.2 defines torsional irregularity A1; > 2.0 not permitted.

ASCE 7 §12.3.2.1Same 1.2 trigger, but classifies > 1.4 as "extreme torsional irregularity" rather than prohibiting > 2.0 — the consequence is code-dependent.

Scope: single story, rigid diaphragm, one loading direction. Does not model flexible diaphragms, multi-story torsional coupling, or elements with two-directional stiffness.

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