The Silver Bridge disaster
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 high 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. AI bars, were, put together in much the same way as the links in a bicycle chain a. Bolt. Is used, to join the AI bars 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 raw 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, AI bars 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, I bars 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. AI bars are configured, together in clusters meaning. That several AI bars are used to form each chain, and so, the failure of any one eye bar 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 125, 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 Ibar 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, I bar 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 plant 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 I bars in each arm with additional, diagonal, braces, until. That is the two arms met and the, whole structure, became independently. Stable. Each. I bar cluster was of course clearly, specified, in the engineering plans. This. Sheet here shows you the Assembly of the I bar 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 I bar holes, the. Material, used was standard, annealed, mild, steel which, is susceptible to corrosion, like many Steel's. Also. Each I bar 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, eye bars 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 330i. Bar 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 eye bar assembly, albeit. One that has been cleaned and painted to look like new. This. Is a typical Aybar joint from the Silver, Bridge which. Was rescued, after the desert disaster. It. Comprises, a central, pin over. Which the, eye bars, 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 Aybar's would rotate and, there.
Is Considerable, pitting, under the track of one. Of the outer fibers 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 weren'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. I bar 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 eye bar 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. I bar. 330, was defective, because it had particularly, high levels of residual, stress left, after its manufacture, the. Design of the I bar 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 cracking. Hidden. Away the. Crack had grown slowly. Over, 39, years until. It was about three millimeters long, also. The steel used in the eye bars 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 I bar. 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 I bar 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 a bars 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 dick 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 clothes of 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 AI bars 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 eye bars 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.