The Iron Bridge: Anatomy of a Cast-Iron Arch

INTERACTIVE RECONSTRUCTION — ISOMETRIC

30.6 m SPAN5 CAST-IRON RIBSRIVER SEVERN

CAMERA

APPLIED LIVE LOAD409.0 kN

ARCH THRUST · EST.— kN

LEFT SUPPORT— kN

RIGHT SUPPORT— kN

INTERACTIVE LAB

Explore the structure

01 / 04

Explore how a simplified arch transmits vertical loading into reactions at the abutments.

Distributed load 12.0 kN/m

Moving point load 40 kN

Load position 50%

Show force vectors on the model

VERTICAL EQUILIBRIUM CHECK

Σ reactions409.0 kN

Applied409.0 kN

Residual 0.000 kN · balanced

Illustrative planar, two-support arch model; not a structural safety or condition assessment.

OBJECT NOTE

A bridge cast in pieces

Five semicircular iron ribs share a crossing that was assembled using large individually cast components and carpentry-inspired joints.

DOCUMENTED

Science, provenance & sources +

Arch-load equations

With span L = 30.6 m, rise f = 15.3 m, load per metre w, point load P at a from the left:

W = wL + P
R_L = wL/2 + P(L−a)/L
R_R = wL/2 + Pa/L

Approximate arch thrust is determined by minimizing the bending residual along a parabolic reference arch:

H ≈ ∫M(x)y(x)dx / ∫y(x)²dx
y(x) = 4fx(L−x)/L²

The independent equilibrium check compares R_L + R_R against W. The experiment omits 3D effects, self-weight, material stiffness, settlement and joint mechanics.

Evidence confidence

Documented: the crossing, c. 30.6 m span, five principal cast-iron ribs, ornamental circles and ogee frames, and timber-derived joint details. Reconstructed: precise beam profiles, joint spacing, deck layering and terrain slopes. Artistic: tree placement, weathered colour variation, river surface and time-of-day lighting.

Sources

Historic England — The Iron Bridge, Scheduled Monument 1015325
English Heritage — History of Iron Bridge
ASCE — Iron Bridge
English Heritage — Future Secure for Industrial Icon

Educational reconstruction; details marked as reconstruction are interpretive.

The Iron Bridge over the Severn