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Date: 2024-05-19 Page is: DBtxt003.php txt00008231

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Even in the supposedly precise world of engineering, miscalculations arise

Burgess COMMENTARY

Peter Burgess

Even in the supposedly precise world of engineering, miscalculations arise

Misfortune often finds its roots in the smallest of things. Such as a centimetre or two. Or is that in inch? Perhaps a foot? Swedish or Dutch?

The French had reason to blush in May as it became apparent that national rail operator SNCF had ordered 2 000 trains that are too wide for many of the regional station platforms they are due to serve.

The error seems to have happened because RFF, which owns and maintains the rail network, provided SNCF with the wrong dimensions.

RFF sent SNCF the dimensions of stations built less than 30 years ago. It was subsequently discovered that the trains, due to go into service from 2014 to 2016, were too big by several centimetres for stations built more than 50 years ago, reports British newspaper The Guardian.

The blunder will cost the French rail service more than €50-million, as around 1 300 station platforms out of 8 700 on the network have to be reconfigured to accommodate the rolling stock.

Some commentators blame SNCF for not verifying the measurements, and some politicians fume at the decision to separate the management of the rail network from train service operations.

Swiss Imprecision

The Germans and Swiss, famed to be meticulous nations, have also made some measuring errors of their own. Or is poor communication perhaps to blame?

Laufenberg is the name of twin towns in Germany and Switzerland, separated by the Rhine river. When a bridge was built to connect the two towns, it was found, in 2003, that one side was 54 cm higher than the other.

The problem arose because construction teams on each side used a different method of calculating the elevation above sea level. The Germans apparently based their sums on the North Sea, not knowing the Swiss were using the Mediterranean.

The German side had to be lowered to enable to construction work to be completed.

Yet another measurement that fell short was the construction of the biathlon track built for the 2014 Sochi Winter Olympics.

The track should have been a loop of 2.5 km, but was found to be too short, even after con- sidering the 5% deviation allowed.

Race organisers had to quickly add 40 m to the track, the day before the opening of the Olympics. Perhaps one of the most infamous miscalculations of modern times was recorded in Canada.

The Gimli Glider, as it has become known, was not, in fact, a glider, but an Air Canada Boeing 767, scheduled to fly from Montreal to Edmonton, with a stopover in Ottawa.

In July 1983, maintenance crews discovered that the plane’s on-board fuel gauges were not working. The flight was to continue, however, with the crew deciding to refill the tank based on a drip test, which determined how many litres of fuel remained in the tanks.

The flight required 22 300 kg of fuel, an amount expressed as mass because of the importance of knowing an aircraft’s weight.

The mechanics needed to work out how many litres made up 22 300 kg. They could then subtract the litres already in the tanks, and use the fuel gauge on the refuelling truck to tell when they had reached the right number of litres to make up 22 300 kg.

However, the 767 was the first aircraft in Air Canada’s fleet to use metric units (kilograms) rather than imperial units (pounds).

Metric units were, at that stage, being phased in across Canada.

Through calculation errors involving pounds and kilograms, Flight 143 ended up not having 22 300 kg of fuel on board, but about 10 000 kg – less than half the amount of jet fuel needed to fly to Edmonton.

Captain Robert Pearson was faced with landing the plane when the fuel ran out. Trained as a glider pilot, he tasked his first officer to calculate the optimum gliding speed for an 80 t Boeing.

Using this expertise, Pearson landed the plane in Gimli, metres away from a crowd gathered at an old runway that had become a drag racing strip.

The plane was dubbed the Gimli Glider. The crew and passengers all survived the landing.

Bridge Wobbles

Less than 20 years later, there was the case of the wobbly Millennium Bridge.

The Millennium Bridge, central London’s first new river crossing for more than a century, opened in 2000, but was shut three days later.

Engineers decided to close the 350-m-long bridge after it began swaying alarmingly.

More than 160 000 people used the bridge during its opening weekend.

Experts blamed the synchronised footfall effect. As the bridge began to sway, people adjusted their footsteps to the rhythm of the bridge’s movements, inadvertently magnifying the effect.

Designers reportedly took into account the up-and-down synchronised footfall effect, but not the side-to-side effect.

Modifications to remedy the situation included 91 dampers, similar to car shock absorbers, says the BBC, which were designed to reduce the movement of the bridge.

Following marching tests using 2 000 volunteers, the bridge was reopened in 2002.

London was also the scene of another engineering challenge but, this time round, in the 1800s, when a new Big Ben bell was cast in 1856. It was transported to London, and pulled across Westminister Bridge by 16 white horses.

Hanging in New Palace Yard, it was tested each day until October 1857, when a 1.2 m crack appeared.

No one would accept the blame. One theory pointed a finger at the heavy hammer, at 660 kg, and another at the alloy the bell was made from: seven parts tin to 22 parts copper.

A second bell was cast in 1858. It was 2.5 t lighter than then the first, but its dimensions still meant that it was too big to fit up the tower’s shaft vertically. Big Ben was turned on its side, and winched up. This took around 30 hours.

The bell first rang out in July 1859, but, in September, also cracked. Big Ben was silent for four years before a solution was found.

The bell was turned by a quarter so the hammer struck a different spot. The hammer was also replaced with a lighter version, and a small square was cut into the bell to prevent the crack from spreading.

By then, the entire exercise had cost £22 000.

Deadly Errors

An even more costly mistake was the sinking of Swedish warship the Vasa in 1628.

The Vasa, with two gundecks, loaded with 64 bronze cannons, sailed 1 300 m on its maiden voyage, keeled over and sank. As it keeled over, water rushed in through the open gunports and the ship’s fate was decided.

It is estimated that 30 people died.

The Vasa was raised in 1961.The Vasa Museum today offers many possible and probable reasons for the calamity.

The underwater part of the hull was too small and the ballast insufficient in relation to the rigs and cannons.

The ship was well built, but found to be incorrectly proportioned.

One surprising result of recent modelling shows just how asymmetrically the Vasa had been constructed.

It is now clear that the ship was built more askew than previously believed, and that the gun ports on the port side were not particularly well lined up with those on the starboard side.

There are some interesting explanations for this phenomenon.

The Vasa was not built from any drawings, which meant it was difficult to fine-tune its construction. Another reason for the distortion is that the carpenters’ rules used different measurements.

The carpenters came from Sweden and Holland. A Swedish foot differed from a Dutch foot in the 1600s and each construction team found its own solutions to the different problems that arose during the shipbuilding process.

Also to blame was the captain, perhaps. He demonstrated how crank (tending to roll easily) the ship was by having 30 men run back and forth across the upper deck. On their third pass, the ship was ready to capsize at the quay.

It would, probably also have been safer to sail the ship with the lower gunports closed, since the captain knew the ship was unstable.

King Gustav II Adolf, of course, ordered the large ship, to begin with, including the heavy- calibre cannons, and also approved the ship’s dimensions.

It was also found that master shipwright Henrik Hybertsson probably had too little experience of building ships with two gundecks.

Freeway to Nowhere

South African engineers and city planners are also not immune from making highly visible miscalculations.

The concrete skeleton of the Foreshore freeway ends literally midair in the Mother City. How did this happen?

In this instance, budgeting appears to be the main culprit.

The reason the elevated Foreshore freeway was not completed in the late 1970s was that the missing inner viaducts were not economically justified in terms of the cost/benefit analysis at that time, and funding was more urgently needed elsewhere, City of Cape Town transport MMC Brett Heron reflects.

The conceptual thinking around the Foreshore freeway began in the 1960s, with an elevated freeway along the foreshore proposed as part of a ring road for the central business district, he explains.

Further investigations led to the evaluation of eight different schemes. The preferred option consisted of three-lane outer viaducts and dual four-lane inner viaducts, with freeway connections to Sea Point and connections up along Buitengracht street.

The first phases of the elevated Foreshore freeway were designed and constructed during the early and mid-1970s.

Implementation of the central viaducts and the ramp connections from the parking garage to Western Boulevard were, however, delayed owing to a lack of funds and limited justification in terms of traffic demand at the time.

Planning proceeded on the connections with Buitengracht street. The studies recommended an elevated grade-separated scheme as far as Riebeeck Square.

“As in all previous reports, the assumptions were heavily biased towards intensified development and parking demand along the Buitengracht corridor,” says Heron.

“A lack of funds and environmental concerns, however, played a major role in discouraging any further progress and final decisions on this part of the freeway scheme.”

Picking up the Pieces?

Inheriting, and then fixing, someone else’s funding mess is not easy.

Heron and his colleagues at the city council have decided to launch the Foreshore precinct and freeway project, in an attempt to find use for the unfinished infrastructure.

To achieve this, the City of Cape Town’s transport authority, Transport for Cape Town (TCT), partnered with the University of Cape Town’s (UCT’s) Faculty of Engineering and the Built Environment.

The Foreshore precinct stretches from Helen Suzman boulevard to the Culemborg district and the immediate surrounds between these two areas.

TCT, through this partnership with UCT, “has harnessed the diverse talent of students to influence the future design of urban space in the city”, says Heron.

UCT has handed the student proposals to TCT, and the assessment of all the proposals will now start. “At this stage, we are in the process of putting together an adjudication panel to assess the work produced by the students,” says Heron.

No budget has yet been identified for the project. If one, or a collection, is found to be suitable, “they will be costed accordingly”, he adds.

The students’ suggestions range from demolishing the freeway to free up land for vibrant social housing to creating public spaces.

Edited by: Creamer Media Reporter

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