Iron Bridge
1779 · Cast Iron Arch · Work 41 of 1,871
The Iron Bridge at Coalbrookdale spanning the Severn gorge: five parallel cast iron ribs, each a semicircular arch springing from stone abutments on either bank, the roadway resting on top of the crown of the arches with only a low railing above it, the spandrels between arch and deck filled by slender upright members with cast iron rings and ogee curves, its members joined by carpenter dovetails and wedges, tollhouse standing at the far abutment.
- What it was used for
- A toll bridge over the Severn at Coalbrookdale, built by a subscription company to replace the ferry between Broseley and Madeley. It carried the cart and foot traffic of an industrial district: coal, iron, pottery. The ribs were raised in 1779; the bridge opened to traffic on 1 January 1781. The table of tolls at the toll house exempted nobody - soldiers on duty, baggage wagons, the mail coach and the Royal Family all paid. Vehicles crossed until 18 June 1934; pedestrians paid tolls until 1950.
- What was new
- Cast iron had been used before in individual components; here it carried the whole structure of a wide-span bridge for the first time, 30.63 m in a single arch. The real achievement was in the foundry: roughly seventy per cent of the parts were one-offs, each slightly different so they would fit together. The joints still followed carpentry practice - mortise and tenon, dovetails - not the riveting that came later. 378 long tons of iron went into it, more than the structure required; later cast iron designs used less.