The Silver Bridge disaster

It's 1928 and suspension

bridge

s are being built all over the United States. New designs and new materials allow for rapid construction. This is the Silver Bridge crossing the Ohio River in 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, the roaring twenties they called it and America had never been so prosperous, they were just thinking of the best for the future and a wonderful time for America. Mary's Citizens Band marched at the dedication of the Silver Bridge.

My father and mother went to that inauguration and it was supposed to be a very gala event, but unfortunately right in the middle of the parade it was raining and everyone was running and trying to get there. In the wake of rain that dampened the fervor of the affair and its historic impact, shortly after work on the Silver Bridge began, another

bridge

of nearly identical design in some merits was built about 70 miles upriver from Point Pleasant. , the bridge was formally named Alto. carpenter bridge was really ready for something big to happen in st. Mary's and the people were just looking to welcome this new thing called the bridge that crosses heresee st.

Mary's on a suspension bridge the upper support chains hung from one tower to another are members in tension and exert a downward force on the towers the platform is supported from the cabling system using a series of vertical supports these supports are also in tension The bridge must be designed so that degradation of any stress element of the structure does not immediately lead to collapse. Today, suspension bridges use cables made up of many individual wires, but in fact, the suspension chains on tall carpenter and

silver

bridges were formed from long lengths. Made of steel with holes drilled into each end, these AI bars were assembled much like the links of a bicycle chain.

A bolt is used to join the AI ​​bars. The resulting joints in the suspension chain can move in response to the forces exerted on them, the bridges were painted with an aluminum color and described as a beautiful

silver

color, although the st. Mary's Bridge never lost the name, Carpenter's High Bridge always had that never alluding to the paint at all, but Silver Bridge was very proud of that silver shine they got from their aluminum coating and when the bridge was repainted every time until now . As I always know, silver or aluminum but raw is known as a silver bridge, but I think the word aluminum and the fact that the silver bridge will be painted aluminum had a greater impact on the public psyche than the fact that it was steel , but after just 40 years, the design and materials used came to haunt them on December 15, 1967, the bridge fell in less than a 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 there was a shaking and the bridge and a noise that you 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 backed up the car stopped but kept going and when I was able to stop it the bridge fell in front of me and my wheels. was in the supposed chair, but what was the cause was an accident, carelessness or insufficiency in the design, the problem could not simply be that this bridge was a suspension bridge that used AI bars because it was a known technology with many contemporary examples in The city of Pittsburgh has three suspension bridges spanning the Allegheny River, known collectively as the Three Sister Bridges, all employ I-bars in their suspension chains, were built around the same time as the Silver Bridge, and are clearly still standing;

However, they have a marked difference in their design. This is Street's sixth bridge, the AI ​​bars are configured together in groups, meaning that multiple AI bars are used to form each chain and therefore the failure of any eye bar will not precipitate the collapse of the structure, in fact the steel used. This has a lower strength than that used in the Silver Bridge, but these bridges are said to have a safety factor of at least two, meaning that They are designed to withstand more than twice the expected higher load at which the three sister bridges were built. 1928 and were expected to last a hundred years and at the rate they are going now I would expect them to last 125 years the main difference between the designers of the past and a GF designer of today the members that were designed in steel The structures were over designed where the steel members they only needed to be an inch today, well back then they would make it an inch and a half, so you had a fact that half an inch of material that could actually deteriorate before it impacted the structural capacity of the bridge with each Ibar that weighed several tons, assembling them into suspension chains was no easy task, but grouping them together had become a time-honored technique because that way a degree of redundancy comes from the way multiple sets of I-bars provide multiple loading paths.

The time of construction along with the engineering plans are still preserved in the local County Archives. This is a view plan of a Sixth Street Bridge, measuring approximately 995 feet long and 77 feet high, and provides general notes to the contractor or manager regarding the erection of the plant and the name of a manufacturer or manufacturing company. American Bridges 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 I-bars in each arm with additional diagonal braces until the two arms met and The entire structure became stable independently, each group of I bars, of course, was clearly specified in the engineering drawings.

This sheet here shows the assembly of the I bar in a series of bars found in the assembly that the pin passes through the pin, the entire threading was in itself a difficult task due to the close tolerance between the pin and the holes of bar I. The material used was standard annealed mild steel which is susceptible to corrosion like many other steels. Furthermore, each I bar contained high levels of tension. residual stress from the manufacturing process and that residual stress could be significant at the points where the eye holes were drilled. A combination of tensile stress of a material such as mild steel and the corrosive environment of a bridge exposed to the elements and industrial pollution can cause Rosen stress cracking, so incorporating more material in the form of multiple bars of eye makes the overall design of the bridge safer against factors like these.

The construction engineers in Pittsburgh knew what they were doing and could rely on their own proven experience at the time. The American Bridge Company also built silver and high carpenter bridges; However, those bridges were designed by a different designer who adopted a new high-strength, high-carbon heat-treated steel, which he presumably thought meant that a less substantial structure could certainly be built. He expected a lower live load than at Pittsburgh, but each bridge had a much longer span and therefore the loads on the tops of the chains on the towers would have been greater than on the Pittsburgh bridges.

The towers themselves were less substantial structures, and yet the designer felt confident enough in the new material to continue. The new design had a safety factor of 1.5 when they were built, but that did not take into account the increasing weight and amount of traffic each bridge would carry as cars and trucks became more common. heavier and more frequent over time Jack Fowler, a Point Pleasant resident at the time of the

disaster

, now runs the local museum. The new bridge, of course, was owned by the local population and they advertised and promoted it as a bridge made of very high strength material, so the residents had no reason not to doubt that it was not going to be a pretty bridge and strong, similar although thinner and not designed like the big thick bridge that existed in some of the other areas, but they had complete confidence in it and this nice shiny silver bridge that we had here people loved it and throughout the years 39 years of existence, people were proud of the Silver Bridge after the collapse of the Silver Bridge, it was imperative to identify the cause accurately and identify the critical safety parts of the structure, the big problem facing investigators. was that 90% of the bridge was submerged in a fast flowing river, the next day people came from all over the state of the federal government Ohio, West Virginia, they had teams here, the National Guard and they were out trying to drag and recover bodies and they were bringing in the Corps of Engineers Derrick boats to start removing the steel long after they recovered the bodies they wanted to rebuild the bridge and as they were pulling out pieces they numbered them, marked them and then took them and placed them all in a field to test . to find the culprit, what happened, where the failure was, when they recovered the 330i bar, when they found the two pieces, that's when they started to realize that one of them must have fractured, separated or exploded and caused the failure, so They focused on that and me.

Let's think about the investigation that seems to be what happened, that is the analysis that we received about the failure and that is the one that we promote and talk about here at the Museum, most of the material that was recovered from the scene no longer exists, but the The museum saved at least one specimen of an eye bar set, although it was cleaned and painted to look new. This is a typical board from Aybar del Puente de Plata that was rescued after the desert

disaster

. Includes a center pin on which the eye bars are placed. would have been rotated and the entire assembly is encapsulated by the very solid end caps which in turn are attached by an inch through the center of the pin.

There is some interesting evidence of pitting corrosion on the bearing surfaces. These would be the bearing surfaces on the pin over. that the Aybar would rotate and there are considerable pits under the race of one of the outer fibers and also under the cap, even deeper corrosion pits caused during its life on the bridge itself, so what were the weather conditions on that afternoon of December 15, 1967? and how the bridge was used at that time the weather was a little cold, snow flurries were coming and it was getting dark, it was already close, well, it was time when everyone was leaving work in the afternoon, the traffic lights on a bridge changed the pattern to the traffic flow, once it changes, then you have all the traffic that is backed up and there comes a wave of them running across the bridge and whatever is on that line, that is the load that you are going to receive at that time and it was on both sides and it would work both ways because as you can see in our model, there were a lot of people coming from that last light change at Point Pleasant, when there was a lot of traffic on the bridge, there was a go movement. up and down but they told me that was normal so I wasn't afraid of the bridge the bridge I don't think anyone has ever crossed it that they didn't feel movement that was a discussion in the community of the area because it always swayed, it had a movement up and down because of so much weight and everyone always said, Wow, this bridge is going to fall down one day, but then you look back and look at the design, it was a different design and we're sorry because of the design. it had that built-in movement, so to speak, so you talked about it, but did you worry about it?

But the movement was there. We personally experienced that this is where the bearing surface would connect to the pen and it is approximately from a right angle position to the rod shank where the critical brittle crack that brought down the bridge actually began, on the inner surface of the bearing, There is extensive pitting corrosion very similar to that on the corresponding part of the pin and also traces of friction marks caused by rust particles. away from the surface while the bearing moved the I bar that failed number 330 was placed on the Ohio end of the bridge on its north side back at the West Virginia end Sharleen Wood was approaching in her car but with the failure of that eye bar was I got in trouble when I stopped, the bridge was moving like dominoes swinging back and forth, the tower was heading north when it fell and while I was watching all this amazing stuff, I didn't know what was really going on, I didn't know what it was. happening, but it had not yet been recorded, so what did the forensic investigation conclude had happened to cause the bridge to fall?

The I 330 bar was defective because it had levelsparticularly high residual stress after its manufacture, the design of the I-bar assembly meant that water could accumulate at the bottom of the eye hole and that the combination of tensile residual stress and a corrosive environment had caused a crack to occur. Hidden stress corrosion cracking, the crack had grown slowly over 39 years until it was about three millimeters long, also the steel used in the eye bars had low toughness at the near-freezing temperatures of the night of the disaster, making them susceptible to brittle fractures. Due to a combination of the high live load on the bridge and the reduced toughness of the steel, the relatively small crack caused a brittle fracture. fracture of bar I at the point of failure, a brittle crack grew almost instantly to the outer edge, this overloaded the top side which separated with some signs of ductility, the resulting asymmetrical load on the pin caused it to twist and the only bar I which was left to vibrate on the other side of the pin, at which point the chain was completely severed, the adjacent tower that was destabilizing began to collapse and fell towards the north, the path below twisted and the other tower it was washed to the bottom.river also what we thought after the event was how was it inspected and if it was and you found something then what do you do to replace it?

How do you come in here and replace them on these bars or one of the joints that if something is corrosion or you saw failures and how do you replace that, but I guess the chronometer people were so confident in the process of this new high strength steel that that was not a fear and I'm sure they included factors, but you know we found out later that was not what was supposed to follow after the Silver Bridge disaster. An immediate legacy was that the High Carpenter Bridge was closed and the sister bridge had to be closed. closed because you know it was a similar design, the same company built it, now we know they knew there was some way to inspect it and correct any findings they might have, so the public almost demanded that the bridge be closed a little fantastic, so I sneaked through the bars of the barrier and crossed the bridge and the people who were waiting to cross some weight just followed me like little chicks following a mother's hand and she just a trail of us pedestrians, but Dick He asked me and said is it you?

Aren't you afraid to cross the bridge just to show you how people were affected by the clothes from the fall of the Silver Bridge? They thought the bridge could fall at any moment. I guess you could argue for not closing it. the st. Mary's bridge as soon as they did it, it had a different use, you know, it doesn't have the traffic lights at the end, it didn't have the interstate traffic that our bridge had here, the tractor trailers, all the heavy loads that were hauled there could have been. means to inspect if there were faults, if there were faults in the bridge, if it could be used in another way, but I think that public opinion would not have accepted that there was too much pressure for this terrible disaster that we had. here I think public opinion would have overruled anything they had found they couldn't get it out of their heads the fate of this bridge was sealed the National Transportation Safety Board had no other recourse but to say they had to condemn the bridge because they couldn't prove that it was safe and they were wrong and came to that conclusion, so aside from the subsequent demolition and removal of the high carpenter bridge, the Silver Bridge disaster at least had a lasting legacy in terms of overall bridge safety when the Silver Bridge collapsed 1967 President Johnson established national bridge inspection standards, which are the guidelines used throughout the United States for all bridges that are inspected.

National bridge inspection standards require that each bridge be inspected every two years and if that bridge has any problems, it is increased to 12 months or it could be once a month depending on how serious the problems are with that structure. . The three sister bridges have already been inspected more than 20 times and their safety will continue to be reviewed in the past. The designers. had designed this bridge to last a hundred years with a safety factor of around two and due to the heavy loads traveling across the bridge today that safety factor is probably decreasing but it is still a safe bridge to travel on to replace these particular AI bars because their intention, you would have to design another support system to support it while you remove it, so you would actually build a fake job; it will be another bridge next to the exact same bridge you have and then you would delete that fake job.

When they are 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 ultrasound where a gel is used on the metal with the sound probe. In the near future we are going to do some minor repairs to hold us steady until we have time to develop plans for a major rehabilitation on the bridge and in that major rehabilitation we are going to replace the deck and all the steel members that are deteriorated and paint the structure again In the United States alone there are more than a million bridges and thanks to the silver bridge they all now receive regular inspection and maintenance in the case of the three sister bridges redundancy was built in from the beginning in the form of additional eye bars that reduce criticality of highly stressed joints, it is equally important today that engineers responsible for the design and maintenance of bridges are aware of the need for redundancy where the inevitable weakest links occur in a structure and also know those weakest links to protect them from impact. . effects of corrosion and fatigue and thus guarantee the integrity of the structure