GROUP 13
4A6(1) Disaster Report
Point Pleasant Bridge Collapse
Emma Finlay 08353069
Darragh Noble 07327757
Paul O’Neill 08592209
Figure 1 - Point Pleasant Bridge after Collapse
Group 13 - Point Pleasant Bridge Collapse
Introduction
The Point Pleasant Bridge, also known as the ‘Silver Bridge’ due to the aluminium paint used,
was an eye-bar chain suspension bridge built over the Ohio River. Built in 1928, the bridge which was
built to connect the towns of Point Pleasant, West Virginia, and Kanauga, Ohio. At the time it was
one of three such structures built in the world with eye-bar bridges being a relatively new concept of
design. It was designed by the society of civil engineers and constructed in 1928 by General
Corporation and American Bridge Company (Corrosion Doctors, 1999).
On the 5th of December 1967 at 5pm the Silver Bridge collapsed during rush hour traffic
claiming 46 lives and injuring 9 persons. The Christmas rush applied an extra load to the 40 year old
bridge causing a cleavage fracture in one of the eye-bars. The structure reportedly only took one
minute to completely fall into the murky water of the river Ohio directly below. An investigation
immediately followed the collapse of the bridge which led to the discovery of cracks and extensive
corrosion which were not visible to the eye.
The collapsed bridge was replaced by the Silver Memorial Bridge which was completed in
1969. This structure, to no surprise is not of the ill-fated eye-bar chain suspension bridge design but
rather a cantilever bridge design.
Bridge Design
The bridge was built as an eye-bar chain suspension bridge. Such bridges had usually been
constructed from redundant bar links, using rows of four to six bars, and sometimes using several
such chains in parallel (Wikipedia, 2011). The eye-bars in the Silver Bridge however were not
redundant, as the links were only composed of two bars each. The reason why the engineers
thought they could get away with this is due to the new high-strength, heat treated rolled carbon
steel out of which the eye-bar was made. This had more than twice the tensile strength of common
mild steel. The main problem with this was that with only two bars, failure of one could impose
excessive loading on the other, ultimately causing total failure. This would be unlikely if more bars
were used as redundancy. While it is possible to design a low redundancy chain, the safety is totally
dependent upon correct, high-quality manufacturing & assembly (Wikipedia, 2011).
The suspension bridge itself was supported by two “rocker towers”, which are designed in
such a way to allow the bridge to respond to various live loads by a slight tipping of the supporting
towers. They were parted at deck level rather than passing the suspension chain over a lubricated or
tipping saddle, or by stressing the tower in bending. The towers required the chain on both sides for
support. Failure of one link, on either side would result in complete failure of the entire bridge span.
(Wikipedia, 2011)
The bridge was initially designed during the 1920s and built in 1928. At the time, the typical
family automobile was the Ford Model T, which weighed only 680 kg. the maximum permitted truck
gross weight was roughly 9,000 kg. however, by the time collapse occurred in 1967, a typical family
car weighed approximately 1,800 kg. and the large truck limit had increased to over 27,000 kg.
furthermore, bumper-to-bumper traffic jams had become commonplace, occurring several times a
day. The initial design loading conditions were severely less than the conditions the bridge was
operating under in 1967.
Group 13 - Point Pleasant Bridge Collapse
Failure Mode (Collapse)
The total catastrophic failure of the bridge ultimately occurred due to a minor flaw in just
one of the eye-bars on what formed the suspension chain. The eye-bar responsible was no. 330 on
the north face of the Ohio side of the bridge. The eye-bar was defective due to the high levels of
residual stress that it was subjected to. The design of the eye-bar assembly meant that water was
able to collect at the bottom. The combination of the tensile residual stress and the corrosive
environment enabled a stress corrosion crack to form. The crack was allowed to grow steadily over
39 years until it reached a critical depth of approximately 1/8th of an inch in length. The steel used in
the eye-bars had very low toughness in the near freezing conditions when the failure occurred,
which meant that the member was susceptible to a brittle fracture. The combination of the high live
loading on the bridge and the reduced toughness of the steel meant that the crack caused a brittle
failure of the eye-bar. This caused the eye-bar to separate from the pin on one side. The resulting
asymmetric load on the pin caused it to twist, and the single remaining eye-bar vibrated off the
other side of the pin. The adjacent “rocker” tower, which needed the eye-bars on both sides as
support to keep it in equilibrium and remain upright, was now destabilised and started toppling,
falling to the north. The bridge deck then twisted over to the north, pulling the other rocking tower
with it, and leading to a complete structural collapse of the bridge. A step by step schematic of the
bridge failure is shown in the Appendix (McGuinness Publishing, 2004) – *taken from BBC
documentary.
Stress Corrosion Cracking is defined as the unexpected sudden failure of normally ductile
metals subjected to a tensile stress in a corrosive environment (Wikipedia, 2011). In this case, the
eye-bar had been subjected to an excessive live tensile strength and had developed a stress
corrosion crack of critical depth of 1/8th of an inch thick upon failure. This crack was developed over
39 years before it eventually reached critical size!
Aftermath & Conclusions
This disaster focused a lot of attention on older bridges and bridges built in the same fashion
(eye-bar type construction). There were two other bridges built to a similar design, one further
upstream at St. Mary’s, West Virginia and one in Florianopolis in Brazil. The bridges in Florianopolis
and the Hi Carpenter Bridge in St. Mary’s, which was built by the same company, were immediately
closed. The use of the bridge in St. Mary’s was different, in that it didn’t carry the same heavy traffic
loads. The National Transportation Safety Board had to condemn the bridge because they could not
prove its structural stability. The Hi Carpenter Bridge was demolished in 1971 with controlled
explosions on the main charges. The Brazilian bridge remains but is still closed to traffic although it
was designed to a higher factor of safety than the bridge at Point Pleasant (Lonaker, 2006).
The legacy of the Point Pleasure Bridge collapse was in bridge safety in general. In 1967
President Johnson established the National Bridge Inspection Standards. There are definitions used
in the NBIS regulation to ensure all bridges are checked to a specific standard.


Quality assurance (QA): Effectively means that measures such as sampling check the
adequacy of quality control procedures which are used to measure the quality level of the
bridge and how it’s designed for loading.
Quality control (QC): Effectively the quality of the inspection on the bridge and the load
rating to be at or above a required level.
These are the guidelines used on all bridges inspected in the U.S. It requires that every
bridge be inspected at least every 2 years and if any problems are found the frequency of those visits
Group 13 - Point Pleasant Bridge Collapse
should be increased depending on the problems found in the specific structure (U.S. Department of
Transport, 2011).
There are over 1,000,000 bridges in America, which are all checked in accordance to the
guidelines. The structural integrity of a bridge can now be found using modern non-destructive
testing methods such as sonogram reading with a gel and a sound probe, as well as x-raying the
frame. Any minor cracks or defects can be acknowledged with maintenance carried out where
necessary on older bridges. A lot of older bridges of similar distinction have been replaced with
various other modern styled bridges (McGuinness Publishing, 2004).
Lessons Learned & Prevention
The first lesson to be taken from this tragedy should be to always include some type of
redundancy in structural design as a type of safety net against potential failure due to faulty design,
underestimation of loading conditions or other such problems. Furthermore, another lesson to be
learned is that all structures should be designed and constructed so that all parts of the structure
can be easily inspected and maintained. In addition, regulation should be increased and constantly
and thoroughly policed and enforced by the relevant governing bodies.
It is also evident from this report that structures should be designed with the future in mind.
Design loading conditions should be thoroughly reviewed and a design load of 4 or 5 times what is
currently required should be designed for. This allows for a change of use of a structure in the future.
The Silver bridge was designed for cars that on average weighed 680 kg, and at the time of failure,
the average weight of a family car was almost three times that number. Furthermore, the levels of
traffic expected greatly increased. This is also applied in environmental engineering in the design of
Wastewater Treatment Works (WwTW). A WwTW is designed for an expected population of 2 or 3
times. If the population is predicted to increase in excess of this, then the WwTW needs to be
redesigned.
References
Corrosion Doctors. (1999, August). Corrosion Doctors. Retrieved October 19, 2011, from Corrosion
Doctors: http://corrosion-doctors.org/Bridges/Silver-Bridge.htm
Lonaker, T. (2006). Silver Bridge Collapse. Retrieved October 19, 2011, from Silver Bridge Collapse:
http://www.freewebs.com/silverbridgeaccident/thebridgecollapse.htm
McGuinness Publishing. (2004). Mothmen.us. Retrieved October 20, 2011, from Mothmen.us:
http://www.mothmen.us/silver-bridge.htm
U.S. Department of Transport. (2011). U.S. Department of Transport. Retrieved October 20, 2011,
from U.S. Department of Transport Federal Highway Administration :
http://www.fhwa.dot.gov/bridge/nbis/nbisframework.cfm
Wikipedia. (2011). Wikipedia. Retrieved October 19, 2011, from Silver Bridge:
http://en.wikipedia.org/wiki/Silver_Bridge
Note: Screen shots taken from BBC documentary “The Point Pleasant Silver Bridge History”
Group 13 - Point Pleasant Bridge Collapse
Appendix
Figure 2 - Stress Corrosion crack formed
Figure 4 - Brittle fracture of eye-bar causes it to separate
from pin
Figure 6 - The twisting of the pin causes the eye-bar on the
other side to vibrate off the pin
Figure 3 - Combo of high live loads &
reduced steel toughness causes brittle
fracture failure of eye-bar
Figure 5 - Resulting asymmetric load
on pin causes it to twist
Figure 7 - Eye-bar now completely dismantled causing a
domino effect type failure of the suspension structure
Figure 8 - the adjacent tower is now destabilised and starts to topple, falling to the north. The bridge deck
twisted over, pulling the other rocking tower over with it leading to a complete structural collapse of the
bridge