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Articles > Cement Shoes 2

Cement Shoes
Part Two - Niagara Follies

There were already dozens of wire suspension bridges in France at the time of the 1850 disaster at Angers. Many wide, deep rivers of North America presented a greater challenge for bridge builders than those previously encountered in Western Europe. In 1843, Charles Ellet Jr. had suggested studying “…the Niagara River, below the Falls, where the gorge could be readily spanned by a beautiful edifice…”

By Don Sayenga

Published in Rope News & Sling Technology August 2015

John Roebling used local stone fo the obelisk-style towers of his bridge

It is fascinating to review the many similarities between the situation at Niagara Gorge in the 1840s and the completion of a bridge at the Si Du Gorge in China within the last five years. Both projects were classed in the world’s record category. Both projects required some sophisticated engineering to get the wire suspension cables anchored. Both projects began in a similar way: to get the first line across at Niagara Gorge they used a kite; at Si Du Gorge they used a rocket.

In 1997, Harvard Business School professor Clayton Christensen coined the term “disruptive technology”. In his explanation of what he meant by the term, he offered two depictions of how continual innovations affect our daily lives. He named them either “sustaining” or “disruptive”. The advent of iron wire rope in the 1830s exemplified both kinds of innovation. In the case of mining technology, the substitution of metal wire ropes for cordage and chains sustained and enlarged the use of ropes for excavation. In the case of suspension bridges, the same innovation was disruptive.

Bridge engineers in the 1800s were faced with making a decision about the disruptive technology of wire cables for several reasons. The application of wire cables in structures progressively reduced the use of the metal chains previously used for exactly the same purpose. Drawn wire was stronger than forged chain due to cold mechanical deformation. The greater strength of iron wire allowed the total weight of the structure to be lighter. Wire cables supporting the structure needed less weight to serve as an anchor which, in turn, reduced the size of the anchorages.

In the 1840s, the primary disadvantage of wire cables was the greatly increased total surface area exposed to atmospheric corrosion. Protecting wire cables against corrosion was mainly done by painting. Chinese engineers working at Si Du Gorge in the 21st Century had the benefit of using cables made from drawn steel wire which is even stronger than iron wire. They also profited from many advances in metallurgical corrosion prevention techniques.

FALLING THROUGH THE CRACK

In France, the commission of inquiry investigating the 1850 Angers tragedy issued their report (known as the Dupuit Report) without suggesting any good remedy. The French government declared a halt to the construction of wire bridges, pending an assessment of the other wire bridges scattered all over their nation. At first, the French moratorium was more or less ignored elsewhere. One of the three causes of the failure (troops marching in step) was already recognized as a no-no in the UK. As for the deck being flexible enough to be twisty in a windstorm, engineers were already contriving various styles of trusswork to make bridge decks stiffer. In the USA three of the most popular trusswork designs were known as Howe, Pratt, and Warren.

The French engineer Emile Malezieux made this sketch of John Roebling's bridge for his book "Travaux Publics Des Etats-Unis d'Amerique en 1870"

The cement shoes defect doesn’t seem to have attracted much scientific attention. Maybe because it was easy to reason the troops marching, and the deck twisting, were the main problem. After a decade of use, those cement seals of the anchorages had broken free of the wires, forming a rigid envelope. Tiny cracks extended to the exterior. If they were spotted they could be resealed, but there was no way to look down into the anchorage where gravity was causing moisture to collect at the ends of the cables – the worst possible place.

Following the great success of the 1842 Schuylkill wire suspension bridge, Americans were scoping out other previously uncrossable locations for wire bridges. The Ohio River drainage system was being converted into a transportation corridor where the concept of a pier-free bridge offered many opportunities. The Saint Lawrence River and the Niagara River forming a boundary with Canada were two other prime sites under discussion by transportation experts.

LIKE A CHICKEN CROSSING TO THE OTHER SIDE

The idea of getting a bridge over the Niagara River was two-fold: [1] mainly to facilitate travel into Canada more or less in the direction of Toronto, and [2] facilitate tourists who wanted to see the Canadian side (the most impressive side) of Niagara Falls, the site of which was out in the wilderness near Fort Niagara, a defensive military base. For purpose #1 the best location was between the villages of Queenston ON and Lewiston NY. For purpose #2 the best location was at the gorge just upstream from The Whirlpool. This was also the narrowest point. The debate between the two sites was never adequately settled – therefore as a result of the debate, suspension bridges were built at both locations.

To create bridges over a boundary line two companies were needed; one in each country, functioning jointly. It wasn’t a comfy arrangement. The first bridge across was at the gorge site, built in 1848 by US engineer Charles Ellet, Jr., and the second was at Queenston / Lewiston built in 1851 by US engineer Edward Serrell. Both bridges used French-style multiple parallel-wire cables fabricated at the site. Neither bridge was strong enough to be used by a railroad train, but we should not forget at the time there were no railroads anywhere near either site.

Sidu River Bridge

Both bridges used underfloor wire stays to hold the bridge deck steady in a windstorm. One of the problems faced by bridge-builders at Niagara occurs in a severe winter when Lake Erie freezes over. After a thaw, enormous masses of ice propelled by gravity churn through the gorge. In the winter of 1853-54, ice in the gorge threatened the underfloor stays of Serrell’s bridge at Queenston / Lewiston. To preserve them, they were disconnected, allowing the ice to pass, but before they could be reconnected a windstorm wrecked the bridge floor. Ellet’s bridge was at a higher location. Its underfloor stays were safe. Meanwhile, both bridges had demonstrated success crossing the river, causing many developers to contemplate putting a railroad across.

In 1852 John Roebling got involved. He proposed to use Ellet’s bridge as a work platform to build a double-deck bridge with a railroad on the top deck. He had received a patent in 1847 for a method to stretch a doubled length of wire across an open space allowing him to build up a cable approximately in place. The cable was one long piece of wire doubled again and again by the process. In 1855, he built his bridge at Niagara in this manner, removing Ellet’s bridge in the process, but re-using the wire from Ellet’s cables. The rest of the wire was purchased in the UK.

John A Roebling’s final report to the owners of the bridge is dated May 1, 1855. On Page 19 he gave the following summary of how he constructed his anchorages: “The chains end at the level of the coping, where they connect with the cables, which are also enclosed in grout and masonry for a length of 12 feet, the latter terminating in ornamental blocks above the coping. The strength of the wire is not affected by sudden changes of temperature; no further protection of the cables therefore is required.”

AN ACCIDENT WAITING TO HAPPEN?

Because no one had any experience with repairing cement shoes such as those installed at Angers and Niagara, the 1850 conclusions the Dupuit Report caused very little excitement in the USA. Few technical journals were being published in the States, the Americans had just concluded our war with Mexico, and everyone was distracted by the California gold rush. British engineers, however, were more alert. Canada partly belonged to both England and France. The Canadian railroad using Roebling’s unique double- deck structure studied the subject. For a variety of reasons, questions began to be raised about Roebling’s wire cables at Niagara Gorge almost immediately after the bridge went into service in 1855.

According to Washington Roebling, who was attending college at Rensselaer Polytechnic Institute in Troy, NY during the time of the Niagara Gorge project, his father realized it was extremely important to dispel any doubts about his bridge.

“Mr. Roebling felt it his duty to go there in the summer of 1860 and make an inspection. This resulted in the writing of a pamphlet entitled the “Condition of the Niagara Bridge” published Aug. 1, 1860 …In this paper he … lays great stress on the preservative effect of cement on iron bars when imbedded therein.”

Photo Courtesy Niagara Falls Public Library
The Suspension Bridge used different combinations of three rails to serve three different railroads.
Photo shows the crossing of a locomotive over the Niagara Suspension Bridge, along with the
triple gauge railway on the bridge. The sealed anchorages can be seen in the foreground.
Photo courtesy Niagara Falls Public Library

John A. Roebling wasn’t wrong very often, but when he was wrong he seems to have believed he could be wrong at the top of his voice to shout down any opposition. His 1860 report concludes with these words:

“The cables of the Niagara Bridge… will last as long as the nature of good wrought iron will permit, when subjected to a moderate tension, not exceeding one-fifth of its ultimate strength. This durability I am unwilling to estimate at less than several hundred years… I will close this report by repeating once more… that they are free from vibration; that they are well preserved and taken care of; and consequently that they may be safely trusted for a long series of years.”

In retrospect, there are very few ways to explain why a brilliant engineer like John A. Roebling would deliberately build a spectacular bridge containing a design flaw condemned by the Dupuit Report. Roebling’s designs differed from the French practice in several ways. His wooden decks were deliberately built more stiff. His multiple main wire cables were compressed into circular cross-section and wrapped end-to-end with a wire serving, everywhere except at the saddles and inside the anchorages. He connected the ends of his cables to iron eyebar chains which descended into the anchorages on a curving slant instead of plunging vertically.

If we seek an explanation, we might guess he was unaware of the Dupuit report but that is almost unthinkable. He was constantly reading technical literature and was publishing his own theories where everyone could read them. It becomes more obvious if we see this as a territorial stake-out. Roebling was financially successful as a wire rope manufacturer. He didn’t need the money, but he was desperate to gain prestige as a bridge-builder. One element of his turf-protection strategy was to obtain U.S. Patent protection on what he thought were the best of his ideas.

There it is: he was granted Patent 4710 on August 26, 1846 for “Improvements in the Wire Cable or Chain Suspension Bridge”. The text of Patent 4710 begins “My plan of anchorage differs very materially from the mode hitherto pursued.” After describing how and why he had devised a superior anchorage, he summarized like this: “It is also my practice to surround all the iron below ground by hydraulic cement and wall it in with solid masonry, in place of leaving an open channel as is the case in most suspension bridges. The cement with which I surround the chains or cables preserves them against rusting effectually.”

PASSING THE BUCK

Despite the strident assertions of Roebling’s 1860 report, uncertainties about the cement shoes of Roebling’s Niagara main cables continued to be bothersome to the railroads. The owners of the international bridge were watching it carefully. They were mainly concerned about the steady deterioration of the wooden structural elements but the unknown status of the main cable anchorages added to their anxiety. Unlike other wire bridges, it wasn’t a major transportation artery. The owners were faced with losing oodles of tourist revenue if any repair work interrupted use of the bridge.

Eight years after Roebling’s unexpected death in 1869, the Canadian railroad that was using the bridge demanded a study of its condition. The bridge company called in a group of brilliant American engineers including T.C. Clark, W .H. Paine, L.L. Buck, T.E. Sickles, and Milnor Roberts to assess the cement shoes. They got to the bottom of the matter very quickly. Although they made their studies quietly, without interrupting traffic which would have alarmed tourists and honeymooners using the bridge, they had to report some extremely bad news about cable corrosion inside the anchorages. The discovery of cable corrosion caused a commission to be formed to make a decision about what to do next. Everyone realized a quick fix was impossible, and mum’s the word.

According to L. L. Buck, who summarized the findings with a complete historical wrap-up in 1881, the situation at Niagara was identical to what the French panel found at Angers two dozen years earlier: “…the whole pit being solidly filled with cement masonry…the strands were also covered with masonry and the whole grouted, the intent being to preserve them from oxidation… The evident cause of this corrosion was the elongation and contraction of the strands under passing loads which had loosened the cement from the outside strands, allowing moisture to work in and finally reach the lowest point”.

THE RIGHT MAN FOR THE JOB

L.L. Buck (1837 - 1909) served as an enlisted man in the Union Army during the Civil War. Although he was already in his late 20s when the fighting ended, he enrolled at Rensselaer to get his CE degree in 1868. None of the older, better established civil engineers was eager to risk his reputation on a scary fix like Niagara. Buck, however, had gone to Peru after college, where his innovative work on the Verrugas Viaduct attracted lots of attention among his peers. He was eager to tackle the challenge. The bridge company gave him a contract in September 1877 to correct the anchorage. They also had him consider removing the wooden deck truss to be replaced with ironwork.

The task was complicated because the double-deck bridge had four main cables, not just two. According to bridge historian Frank Griggs, writing in Structure Magazine (2010) Buck “…arrived at the site September 13, 1877. He finished the anchorage rehabilitation and later replaced the wooden deck structure with iron, in less than eight months.” As an extra burden, after beginning the job Buck discovered “the old walls extended back further than was shown in the plates of Mr. Roebling’s report … which would necessitate very expensive trenches...”. He figured out a way to get around the problem, allowing him to cut out corroded wires, one by one, and splice in new ones.

While the anchorages were being fixed, he examined the deck which was in worse condition than he expected: “In short, there were very few tight joints in the structure. It had, consequently, become extremely flexible … it was evident that any attempt to repair the structure would only result in the rapid destruction of the new work.” Buck got the go-ahead to create a new iron truss and deck. He made a careful evaluation of possibly using steel instead of wrought iron. For his own reassurance, he submitted his ideas to Washington Roebling who approved his plans.

Buck was ahead of his time. He reported: “the use of steel for structural purposes had not yet reached a stage at which all of the required shapes could be promptly and economically obtained – at least in this country. Consequently my specifications were …for the use of either iron or steel or a combination…” The substitution of a metal deck aroused another specter. Examination revealed the limestone blocks at the tops of the towers had begun to spall. In Washington Roebling’s words: “Mr. Buck then addressed himself to the remarkable engineering feat of replacing the stone towers…and yet keeping the traffic uninterrupted.”

Frank Griggs explains: “Buck decided to build new wrought-iron towers around the existing stone towers…Engineering News called it ‘the most delicate and daring piece of bridge-work ever undertaken’. The Engineering Record wrote ‘his reconstruction of the towers of the bridge in 1886 is probably one of the most remarkable engineering achievements of our age… performed so modestly … few people knew that such an enterprise was even contemplated”. Because of the publicity black-out, Buck never has received the praise he deserves, which is truly unfortunate.

THERE’S MORE TO THIS STORY, FOLKS

After 1825, the Erie Canal launched faster transportation between population centers on the Hudson River and the Great Lakes, but it was Cornelius Vanderbilt’s New York Central Railroad which greatly eased the journey. In the years following the Civil War, a trip to Niagara Falls became the trope linked to thousands of honeymooning couples from the USA. Tourist traffic mandated faster and more frequent train service. The population of Erie County was multiplied by four in the years 1850-1900.

The two cities known as Niagara Falls, one in each nation, grew rapidly at both ends of the bridge. As the weight of railroad locomotives steadily increased it became clear there would soon be an expiration date for Roebling’s bridge. One of the band-aids applied toward the end was the substitution of streetcars. Ultimately, about twenty years after Buck was called in to get rid of Roebling’s cement shoes, he replaced the entire thing with a completely new bridge. The story of how he achieved this, again without interrupting traffic, is among the greatest stories of civil engineering.

Buck’s saga is a tale told rarely because he worked without publicity. Anchorages for the Brooklyn Bridge had just been completed when Buck started the job. Washington Roebling later commented on the irony that his father wasn’t around to read Buck’s report:
“Dying when he did he was spared the mortification of finding that the cable wires were very badly rusted where they connect with the anchorages - large numbers had to be replaced - and if the mischief had gone on much longer, the cables might have fallen long before the predicted two hundred years”.

The anchorages of the Brooklyn Bridge were designed by Washington Roebling to omit cement shoes, because, as he put it: “The best plan is to leave everything open free of access, only covered against the weather so that it can be inspected and painted from time to time.” Prior to designing and building the Brooklyn Bridge, Washington Roebling had observed his father in action at two other bridges. One over the Allegheny River and one over the Ohio River. Both were built with cement shoes.

Further Reading

  • Cement Shoes Part 1 Angers 1850
  • The story of the Si Du Bridge was presented in 2008 by Chongxu Wang, Dr. Yuancheng Peng, and Dr. Yinbo Liu at the International Bridge Conference in Pittsburgh PA. It was reprinted in the form “Crossing The Limits” by Civil Engineering magazine (Reston VA January 2009 Vol 79 No 1 pp. 64-80)
  • L. L. Buck’s Report on the Renewal of the Niagara Suspension Bridge (1881) is now downloadable from the internet at: https://archive.org/details/cihm_26454 Frank Griggs’ 2010 bio of L.L. Buck can been seen at www.structuremag.org
 
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