Pontypridd Arch Bridge
Disasters
Group 20
Introduction
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Pontypridd is situated North West of Cardiff,
Wales
Religious Groups
Requirements: Minimum 7 years
William Edwards
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Born in 1719, his father died when William was
very young
Deeply religious man, self-taught mason
Learned further skills off blacksmiths an was
asked to undertake the project
Design
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Spans 43m (140 Feet)
Remained world’s longest single span arch bridge
for 40 years
Height of approx 10.7m and chord length of
42.7m
4 circular tunnels of diameters 9,6 and 3 feet
1st Attempt
 It
took 4 attempts in total
 First bridge made out of wood
Debris became lodged near the
supports
 Caused Edwards to think of a
more radical design
2nd Attempt
 The
bridge was almost completed when
it collapsed
 The problem for Edwards lay with
vertical load distribution
 Remember there were few
mathematical models and design
standards
3rd Attempt
 For
the 3rd attempt, Edwards built a
very thin arch
 Due to the thin arch, the spandrel
weight could be reduced accordingly
 This time, it lasted 6 weeks
 Parapets had not been put in place
Final Attempt
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Edwards contacted John Smeaton, another up
and coming engineer
Came up with alternate design of spandrels
Design
Unique design, Single spanned bridge with
4 circular voids of 9, 6 and 3 feet
diameter. The fourth is walled and cannot
be seen
 Voids acted to decrease weight of bridge
while also reducing the hydraulic force on
the bridge during a flood
 Reputed to be backfilled with charcoal lighter
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Technical Assessment
 Top
surface forming a hill with steep
gradients at either side – chain and
drag system for carriages.
 Narrower at crown than at
abutments.
 Arch ring is very slender, even by
modern standards.
 Considerable support provided by
spandrel walls
Technical Assessment
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In Snell’s Paper
“Stability of
Arches”, he
considers 3 main
modes of failure
for masonry built
structures.
Slipping of
Voussoirs - centre
of thrust never
approached a
critical condition.
Technical Assessment
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Rotation of the
joint
Failure of the
material
Success
Beautiful, elegant bridge which gained
Edward much fame and prestige.
 The final modal was completed in 1755,
spanned 140ft (42.7m).
 At the time of construction it was 9m
longer than any other bridge in the UK.
 It was the longest single-spanned bridge
for half a century.
 Bridge still stands today.
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Conclusion
Used lessons learnt from past mistakes –
important in engineering.
 His failures provided information and
insight about arch bridges, not only to
Edwards but to future bridge designers.
 At the time, a single arch bridge spanning
140ft was unheard of.
 Edward served as a pioneer for stronger,
longer, lighter arch bridges.
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References
http://webapps.rhondda-cynontaff.gov.uk/heritagetrail/big_anthem_fawr
/old_bridge_history.htm
 Hughes, T. G. 2005, William Edwards
Bridge, Pontypridd, UK; Bridge
Engineering 158, Pages 71–80.
 Snell, George, Stability of Arches, plates
27 & 28.
 http://www.atyponlink.com/doi/pdf/10.1680/bren.158.2.71.6
5906?cookieSet=1
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