It's 1928 and suspension bridges are
being built all across America new designs and new materials make for rapid construction. This is the Silver Bridge. Crossing the Ohio River at Point Pleasant West Virginia on its opening day. My father was vice president of the
corporation that built the Silver Bridge. Was a wonderful time to be a young American boy. The Roaring Twenties they called it and America hadn't had never been as prosperous they just thought nothing but the best in the future and a wonderful time for America. The st. Mary's citizens band marched at the opening of the Silver Bridge. My father and mother went to that opening and it was supposed to be a very gala event, but unfortunately right in the middle of the
parade to have some rain and everybody was running and trying to get out of the
rain, that dampened the fervor of the thing and the historic impact of it. Shortly after work commenced on the
silver bridge another bridge almost identical in design was constructed at
some merits about 70 miles upstream from Point Pleasant. The bridge was formally named the Hi carpenter bridge was really ready for a big thing to happen
at st. Mary's and people were just browsing to welcome this new thing
called a bridge crossing herever st. Mary's In a suspension bridge the uppermost supporting chains strung from tower to tower are members in tension and they exert a downwards force on the towers. The deck is supported from the cabling system using a series of vertical hangers, these hangers are also in tension. The bridge should be designed so that the degradation of any one
tension element of the structure doesn't immediately lead to collapse. Nowadays suspension bridges use cables
spun from many individual wires but in fact the suspension chains in the high carpenter and silver bridges were formed out of long lengths of steel with holes drilled out at either end. These eyebars were put together in much the same way as the links in a bicycle chain. A bolt is used to join the eyebars together. The resulting joints in the suspension chain can then move in response to the forces
placed on them. The bridges were both painted with an aluminum color and
described as a beautiful silver color although the st. Mary's Bridge never lost, the name the high carpenter bridge it always had that, never alluding to the
paint at all but the Silver Bridge was very proud of
that silver sheen that they got from their aluminum coat and when the bridge
was even repainted every time so far as I know always silver or aluminum but is referred to as a silver bridge. But the word aluminium and the fact that the silver bridge will be painted aluminum I think had more of an impact on the psyche of the public than did the fact that it was steel But after barely 40 years the design and materials used came
to haunt them On December the 15th 1967, the bridge fell in less than one minute, with the loss of 46 lives. A 20 year old eyewitness at the time was Charlene wood. I was actually on the bridge when it failed that night I was going home from work and a trembling and of the bridge, and a noise that you couldn't I couldn't even describe what the noise was like, but I realized that maybe something had hit the bridge, and I decided I wasn't going to cross - so I
threw the car in reverse and as I was backing, the car stalled on me but it kept going and when I was able to get it stopped, the bridge fell in front of me and my wheels was on the alleged chair. But what was the cause? Was it an accident? Carelessness? or inadequacy in the design? The problem couldn't just be that this bridge was a suspension bridge using eyebars, because that was a known technology with many contemporary examples. The city of Pittsburgh has three suspension bridges spanning the Allegheny River. Known collectively as the three sister bridges, all employ eyebars in their suspension chains. They were constructed at much the same time as the Silver Bridge and are clearly still standing. They do however have a marked difference in their design, this one is the Sixth Street bridge. The eyebars are configured together in clusters, meaning that several eyebars are used to form each chain and so the failure of any one eyebar won't precipitate a collapse of the structure. In fact the steel used here is of a lower strength than that used in the Silver Bridge but these bridges are said to have a safety factor of at least two that means that
they're designed to support more than twice the greatest expected load. The three sister bridges were built in 1928, and they were expected to last a hundred
years and at the rate that they're going now I'd expect them to last 25 years. The major difference between the designers of the past and a designer GF
today. The members that were designed on steel structures were over designed where the the steel members only needed to be an inch today well back then they would make him an inch and a half, so you had a fact that half inch of material
that could actually deteriorate before it even impacted the structural capacity
of the bridge. With each eyebar weighing several tons assembling them into suspension chains was no easy undertaking but clustering them together had become a time-honored technique because that way a degree of
redundancy comes from the way that multiple eyebar assemblies provide
multiple load paths. Photographs from the time of construction along with the engineering plans are still preserved in the local County Archive. This is a plan
of view at a sixth Street bridge it's approximately 995 feet long and 77 feet high. And it gives general notes to the contractor or the director on the assembly of the plan and giving it a manufacturer's name an American bridge company the Pittsburgh based American bridge company was able to employ the
practice of building from either Bank using a cantilever principle. It was necessary to stabilize the eyebars in each arm with additional diagonal braces
until that is the two arms met and the whole structure became independently
stable. Each eyebar cluster was of course clearly specified in the engineering plans. This sheet here shows you the Assembly of the eyebar in a number of bars that are in the assembly which the pin goes through. The pinning all threading was itself a difficult undertaking because of the tight tolerance between the pin and the eyebar holes. The material used was standard annealed mild steel which is susceptible to corrosion
like many Steel's. Also each eyebar contained high levels of tensile residual stress from the manufacturing process and that residual stress could be significant at the points where the eye holes were drilled out. A combination of tensile stress a material like mild steel and the corrosive environment of a bridge exposed to the elements and industrial pollution can lead to stress Rosen cracking. So incorporating more material in the form of multiple eyebars makes the overall design of the bridge safer against factors such as these. The construction engineers in Pittsburgh knew what they were doing and could rely on their own tried and tested expertise. At this time the American bridge company also went on to construct both for silver and high carpenter
bridges. However those bridges were engineered by
a different designer, who embraced a new high strength high carbon heat treated steel which presumably he thought meant that you could build a less substantial
structure. Undoubtedly he expected lower live loading than in Pittsburgh, but each bridge was a much longer span and so the loads at the tops of the chains in the towers would have been greater than in the bridges in Pittsburgh. The towers themselves were less substantial structures as well yet the designer felt sufficiently confident in the new material to proceed. The new design did have a safety factor of 1.5 when they were built but that didn't account for
the increasing weight and amount of traffic that each bridge would carry as cars and lorries were to become heavier and more prevalent with time. Jack Fowler a resident of Point Pleasant at the time of the disaster now runs the local museum. The new bridge of course it was owned by local people and they
publicized and promoted it as a very high strength material bridge so the
residents had no reason not to doubt that it was not going to be a nice
strong bridge similar though thinner and design not the big chunky bridge that
existed in some of the other areas. but they had complete confidence in it and
this nice silver shiny bridge that we had here, people loved it and we throughout the 39 years of existence people over had pride
in the Silver Bridge. Following the Silver Bridge collapse it was imperative to identify the cause precisely and identify the safety critical parts of the structure. The big problem facing the investigators was that 90% of the bridge
was submerged in fast flowing river. The next day people came from every place
the state of federal government Ohio West Virginia, they had crews in here the
National Guard and they were out trying to drag and recover bodies and they were
bringing in the Corps of engineer, Derrick's boats to start removing the
steel. Well after they recovered bodies they wanted to reconstruct the bridge
and as they pull pieces out they numbered them marked them and then they took them and laid them all out in a field to try to find the culprit what
happened where was the failure. When they recovered the 330 eyebar when they found the two pieces, that's when they started realizing that one of those must have
fractured and separate or blew apart and caused the failure so they focused on
that and I think from the investigation that appears to be what happened we
that's the analysis that we received about the the failure and that's the one we promote and talk about here at the Museum. Most of the material that was
recovered from the scene as long gone but the museum did save at least a
sample of an eyebar assembly albeit one that has been cleaned and painted to look like new. This is a typical eyebar joint from the Silver Bridge which was rescued after the desert disaster. It comprises a central pin over which the
eyebars would have been pivoted and the whole assembly is encapsulated by the very solid end caps which themselves are attached by one inch through the center of the pin. There's some interesting evidence of pitting corrosion on the bearing surfaces this would be the bearing surfaces at the pin
over which the eyebar's would rotate and there is considerable pitting under the
track of one of the outer eyebars and also underneath the cap even deeper
corrosion pitting caused during its lifetime on the bridge itself. So what were the weather conditions on that evening of December the 15th 1967, and how was the bridge being used at the time? The weather was kind of chilly there was snow flurries coming and it was getting dark it was around well it was time when everyone was getting off work in the
evening time Traffic lights on a bridge changed the pattern to the traffic flow
once it changes then you've got all the traffic that's backed up and they come a
wave of them rush across the bridge and whatever's in that line that's the load
that you're going to get at that time and it was on both sides and it would
work both ways because so as you can tell from our model that there was a
great many coming through from that last change of light in Point Pleasant. When there was heavy traffic on the bridge there was a motion of going up and down
but I was told that that was normal so I wasn't afraid of the bridge. The bridge I don't think anyone ever crossed it that they didn't feel movement that was
a discussion of the community of the area because it was always swaying it
had the up-and-down motion from so much weight on and everybody always said wow
this bridge is gonna fall someday but then you look back at the design it was
a different design and we felt that it because of the design it had that built
in motion so to speak so you talked about it but did you worry about it
but the motion was there. We experienced that personally. This is where the bearing surface would connect with the pen and it's from roughly a position
right angles to the shank of the bar where the critical brittle crack which
brought the bridge down actually started. On the inner bearing surface there is
extensive pitting corrosion very similar to the one on the corresponding part of
the pin and also traces of fretting marks caused by particles of rust wearing away the surface as the bearing moved. The eyebar that failed number 330 was positioned on the Ohio end of the bridge on its northern side. Back at the West Virginia end Sharleen wood was approaching in her car but with the failure of that eyebar she was heading into trouble. As I stopped the bridge was coming forward like dominoes swaying back and forth the
tower went to the north when it fell and as I was seeing all this unbelievable II
didn't know what was really happening I didn't know what was happening but it
just hadn't registered yet So what did the forensic investigation conclude had happened to make the bridge fall well eyebar 330 was defective because it had
particularly high levels of residual stress left after its manufacture the design of the eyebar assembly meant that water could pool at the bottom of the
eye hole and the combination of the tensile residual stress and a corrosive
environment had caused a stress corrosion crack to form. Hidden away the crack had grown slowly over 39 years until it was about three
millimeters long. Also the steel used in the eyebars had a low toughness at the near freezing temperatures on the night of the disaster making it susceptible to
brittle fracture. Under a combination of the hi live loading on the bridge and the reduced toughness of the steel the relatively small crack caused a brittle
fracture of the eyebar. At the point of failure a brittle crack grew almost instantaneously down to the outer edge. This overloaded the upper side which
separated with some signs of ductility. The resulting asymmetric load on the pin
caused it to twist and the single eyebar that was left vibrated off the other
side of the pin. At which point the chain was completely severed. The adjacent Tower being destabilized started toppling and fell to the north. The road below twisted over and the other Tower was pulled down into the river as well. What we thought about after the event
was how was inspected and if it was and you found something then what do you do
to replace it how do you how do you get in here and replace them on these eyebars
or one of the joints that if something is corrosion or you saw found failure
and how do you go about replacing that but I guess that the people the timer
had so much confidence in the process of this new high-strength steel that that
wasn't a fear and I'm sure they built-in factors but you know we found out later
that it wasn't as purported to be. Following in the wake of the Silver Bridge disaster one immediate legacy was that the high
carpenter bridge was closed The sister bridge had to be closed because you know
it was a similar design the same company built it we know now that they knew
there was any way to inspect it and to to correct any findings that they might
have so public opinion almost required that
bridge be closed a bit terrific. So I sneaked through the bars
the barrier and walked across the bridge and the people that were waiting to get
some weight across they just followed me like little chicks following a mother
hand and her just a trail of us pedestrians but Richard asked me, he said,
are you aren't you afraid to cross the bridge just to show you how the people
were affected by that the falling of the Silver Bridge that they thought that bridge could fall at any time. I suppose a case could be made for not having closed the st. Mary's bridge as
soon as they did there was a different use you know it doesn't have the traffic lights at the end he didn't have the interstate traffic that our bridge had
here the tractor trailers all the heavy loads that it carried there could have
been means of inspecting to find if there were failure if there was failure
on the bridge if it could be used in a different manner but I believe that
public opinion would not have accepted that there was too much pressure because
of this terrible disaster we had here I think public opinion would have
overridden whatever they may have found. They couldn't get it out of their minds
the fate of this bridge was sealed The National Transportation Safety Board had
no other recourse than to say they had to condemn the bridge because they
couldn't prove it was safe and they were no Doubt's right and coming to that
conclusion. So apart from the subsequent demolition and removal of the high
carpenter bridge the Silver Bridge disaster did at least have a lasting
legacy in terms of bridge safety in general When the Silver Bridge collapsed
1967 President Johnson established national bridge inspection standards
which are the guidelines that are used throughout the United States for all
bridges that are inspected. The National bridge inspection standards require that
every bridge be inspected on a two-year frequency and if that bridge has any
problems it's increased to 12 months or it could be once a month depending on
how severe the problems are with that structure. The three sister bridges have already been inspected over 20 times and they will continue to be checked for
safety in the past the designers had designed this bridge to last a hundred
years with a factor safety around two and due to the heavy loads that are
travelling across the bridge today that factor safety is probably going down but it's still a safe bridge to travel To replace these particular eyebars
because their intention you'd have to design another support system to support
it while you're removing it so you'd actually build some false work. It'll be another bridge next to the exact same bridge that you have and then remove
that false work when you're all complete. The different techniques that we use to
inspect the steel members, would be non-destructive testing where we can x-ray the metal or we can use on sonogram where you use a gel overtop of
the metal with the sound probe. In the near future we're going to make some
minor repairs to hold us over until we have time to develop plans for a major
rehab on the bridge and that major rehab we're going to replace the deck and all
the steel members that are deteriorated and paint the structure over again. In America alone there are over a million bridges and thanks to silver bridge they
all now receive regular inspection and maintenance. In the case of the three sister bridges redundancy was built in from the outset in the form of additional eyebars reducing the criticality of highly stressed joints it's just as important today for those engineers responsible for designing and
maintaining bridges to be aware of the need for redundancy, where the inevitable weakest links occur in a structure and also knowing those weakest links to
protect them from the effects of corrosion and fatigue and thus ensure
the integrity of the structure
Thanks for posting! Very informative video. Maybe low-rise, community-driven development isn't that bad, lmaooo
Good documentary. This bridge failure is the subject of the Mothman Prophecy movie - a pretty good spooky show.
Worth the watch. TY.