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🔗 Strut-and-Tie Explorer

Near a support, a deep opening, or a concentrated load, plane sections stop remaining plane and ordinary beam theory quietly stops applying. Strut-and-tie replaces it with something you can actually see: a truss of concrete compression struts and steel tension ties carrying the load to the supports. Change the depth and watch the strut angle — and the steel you need — respond.

Deep Beam

Applied load P 2000 kN

Span L 4000 mm

Lever arm jd 1200 mm

Capacities

Concrete f_c 30 MPa

Strut width 200 mm

Member thickness 400 mm

Live Result

—

Strut angle θ—

Strut force (compression)—

Tie force (tension)—

Tie steel required—

Strut utilization—

Governing element—

Powered by ACI 318 Ch.23 strut-and-tie (engine/strut-and-tie.js). Verified before publishing: the tie force is cross-checked against independent global statics (M/jd from overall beam equilibrium — a completely separate route), and node equilibrium is confirmed in both the vertical and horizontal directions to machine precision. The ACI minimum strut angle of 25° is enforced and flagged rather than silently ignored, and CCT nodes are correctly weaker than CCC nodes.

Method

Schlaich et al. (1987)Strut-and-tie as a lower-bound plasticity method — any statically admissible truss within member capacities gives a safe strength estimate.

ACI 318 Ch.23Strut f_ce = 0.85β_sf_c', node f_ce = 0.85β_nf_c', φ = 0.75, minimum strut angle 25°.

Scope: single-panel model, simply supported deep beam, central point load. Real D-regions need model-selection judgement, anchorage checks, and crack-control reinforcement — none of which this automates. β_s and β_n are code choices; this tool uses 0.75 (bottle-shaped with transverse reinforcement) and 0.80 (CCT node).

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