PONTYPRIDD ARCH BRIDGE
COLLAPSE(S)
Pontypridd Arch Bridge

Georgian pedestrian bridge
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Spans 43m over the Taff in South Wales
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The world's largest single-span stone bridge for 40 years
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Rebuilt for the fourth and final time by William Edwards in
1756
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Prior to 1856, Pontypridd was called Newbridge
3 Collapses…
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Edwards first bridge was washed away by debris carried by the
river Taff in flood

The second attempt was to span the Taff without any
supporting pillars midstream. Staging collapse caused the
failure of this attempt when the structure that was used to
support the heavy bridge during the building phase gave way.

The third collapsed when its light crown was 'sprung' by the
pressure of its abutments (incorrect rise-to-span ratio) .
Solution

To prevent the crown from being forced upwards by the
pressure of the massive haunches, Edwards made cylindrical
holes through the spandrels.

Three such holes on each side, ranging downwards in size
from 9ft in diameter, effectively redistribute the weight on the
arch.

Edwards also used charcoal as a lightweight infill for the
spandrels to further help with weight distribution.
Cylindrical holes
The bridge today

The structure still stands to this day as a monument to William
Edward's ingenuity and perseverance
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Its use is restricted to pedestrians

The road surface was repaired and steps added

A modern bridge has been constructed alongside it
What can we learn from this?
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The third bridge collapsed during construction and Edwards
was able to learn from watching its fall.
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Many potential pitfalls can be avoided by studying past
mistakes.
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Often small details can make a big difference
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Perseverance pays off !!