Rotterdam’s future flood defences will literally hinge on two of the
world’s biggest ball-and-socket joints. The joints, each as big as a house,
are vital components of ingenious floating gates that will swivel into the
360-metre-wide ship canal leading to the port city in order to shut our
flood tides.

Dutch engineers are building the two steel gates on the banks of the
New Waterway canal downstream of Rotterdam, near the Hook of Holland. The
gates will be 210-metre long hollow boxes, longer than the Eiffel Tower
is tall and containing twice as much metal. They are fixed to ball joints
set in giant concrete blocks on the bank.

After work on the £310 million project ends in October 1997,
the gates will spend most of their time in docks in the canal banks. When
a flood tide looms, electric motors in the docks will push the floating
gates into the 17-metre-deep canal.

Then valves will open, flooding the gates internally, which will sink
to block the canal. When the danger has passed, pumps will empty the gates,
which will float back to the surface.

The gates form the last major tidal barrier to be built in southern
Holland following the floods of 1953, which killed more than 1800 people.
Since then, the government has been building a series of barriers in tidal
inlets in the delta where the Rhine and Maas rivers converge, to prevent
another disaster.

The Rotterdam canal carries, on average, one ship every seven minutes.
The government originally planned to leave the canal open and raise all
the surrounding dykes instead. But raising the dykes involved demolishing
houses and causing environmental damage, which generated enough opposition
for the government to review its policy in 1987.

As a result, the government decided to build a barrier that would cause
the least disruption to navigation, and called for ideas from construction
companies. The two favourites were both curved gates, rotating from the
banks.

One which ran on tracks on the canal bed, lost the competition because
of fears that the tracks would be blocked by silt. The winner, now being
built, is self-cleaning. As the gates sink, canal water flowing through
the narrowing gap beneath will accelerate, washing silt away automatically.

‘What’s really innovative, and gave us a lot of headaches, is the ball
joint,’ says Jos Kerstens, a senior designer with the consortium building
the barrier. The joints must allow the gates to move horizontally, vertically
and to twist. Each joint must also withstand a thrust of 35 000 tonnes from
the flood tides.

The solution was to use 10-metre-diameter steel ball-and-socket joints
with cast-steel bearing surfaces lubricated with a molybdenum-based coating.

Water companies can overcome this by enlarging sewers to act as temporary
underground reservoirs. But researchers estimate that cities in the European
Community may have to spend up to £80 billion improving sewers to
prevent overflows. Now Danish engineers are putting the finishing touches
to a computer system that monitors the weather to predict storm water and
then controls sewage flows to make the best use of existing sewers.

The Danish city of Aalborg had predicted that to improve its sewer system
it would need new storage tanks with a capacity of 10 000 cubic metres.
But instead, engineers are commissioning a computerised system to control
the gates in a main sewer.

The system, developed at the Danish Hydraulics Institute (DHI) in Horsholm,
improves the storage capacity of existing sewers by optimising the control
of flow regulating devices, such as valves, gates and pumps.

The system is based on software, called MOUSE, originally written at
DHI for analysing flow in sewers. Designers usually use MOUSE to provide
snapshots of flows for various possible sewer configurations. DHI has now
modified the software to control the flow as it happens.

Now MOUSE logs real rainfall data, transmitted electronically from gauges
around the catchment area. With this information it can predict sewage
flows, then plan the best sewer configuration and activate the equipment
automatically.

‘The new part of our concept is that any sewer run by the system is
based on forecasts of flows,’ says Jurgen Bo Nielsen of DHI. ‘The computer
model tells you what will happen in the next few hours. It also looks at
the entire system rather than each local item. The potential is enormous.
Sewer rehabilitation is needed on a vast scale in Europe and the rest of
the world.’

The European Commission has just committed over £2 million from
its SPRINT technology transfer programme to test the system on sewers of
four European cities, and to promote the technology. In Bolton, the system
will manipulate 30 control devices directing storm flows into a series
of storage tanks.

Every year salmon and sea trout migrating to spawn in North Wales try,
and fail, to jump up the 12-metre-high Conwy Falls near Betws-y-Coed. From
this summer, they will be able to zigzag up a novel sloping tunnel to the
top of the falls.

Fish ladders are not a new idea. It is quite common for builders of
dams in rivers where fish spawn to build a stepped series of pools with
small waterfalls between them. The fish can make the short leap from pool
to pool and so get around the dam.

The Conwy Falls Trust originally planned to build a fish ladder inside
a tunnel for the fish to get round the falls. To avoid tiring the fish,
the height difference between the pools could be at most 45 centimetres,
which meant that 28 pools would be needed. But fitting this many pools in
one line would have required a tunnel so long that the trust would have
exceeded its £375 000 budget, says Roger Thomas, a member of the
trust.

Then David Donaldson, a civil engineer, came up with a simple, but radical
solution, Thomas says. To dig a tunnel 48 metres long, wide enough to accommodate
a bus, with two sets of 14 pools side by side. Water will flow down the
tunnel in zig-zag cascades over small weirs in the pool walls. This halved
the tunnel length, cut the cost, and in August it will increase the size
of the spawning grounds by 40 per cent.

Previous tests only shook models in the planes of the outer walls, reproducing
structural responses in single planes. The Bristol tests simulate three-dimensional
behaviour by shaking the model from corner to corner, made possible by the
university’s large ‘shaking table’.

The 1’15 in scale, steel model of a tower block has been built on the
shaking table by engineers from Ove Arup & Partners and the university.
The table is big enough to support a model weighing 10 tonnes and shaking
it to simulate a wide range of tremors. They have fitted the 3-metre-high
framework with a battery of instruments to measure how individual components
react.

‘We are carrying out the tests further than have ever been done before,’
says Edmund Booth, a senior engineer at Ove Arup, which is providing some
staff and about half the funding for the 150,000 Pounds programme. The firm’s
engineers developed basic computer programs to analyse the response of buildings
to earthquakes, and they also buy more sophisticated software from US companies.
‘In all good faith we advise our clients that the software gives the correct
results, but how confident are we that it does predict the building’s behaviour
correctly?’ says Booth.

Comparing the computer predictions with the real behaviour of a model
is a key goal of the three-year study at Bristol, partly funded by the Science
and Engineering Research Council. Previously, testers have modelled buildings
using two dimensions, says Booth. They have also assumed that the beams
and columns behaved elastically, regaining their original shapes after being
shaken. But real buildings are three-dimensional and some components can
be so distorted that they become elastic and stay deformed. ‘Most design
methods make only very approximate allowance for this sort of behaviour,’
he adds.

Apart from validating the software, the engineers also want to see if
they can use the shaking table to help design individual buildings. Designers
already use wind tunnels to check the effect of different air pressures
on accurate models of specific buildings, and they would find it useful
to do the same with tremors. ‘But there are quite severe problems of scaling,’
says Booth.

The penetration of harmful chemicals such as chlorides, which are carried
in water, is one of the major worries facing civil engineers. Countless
road bridges in the US, along with marine structures and tunnels in the
Middle East, have been severely attacked in this way. Nearly three-quarters
of English and Welsh concrete bridges are seriously impregnated with chlorides,
according to a Department of Transport study (Technology, 29 April 1989).

Inventor Anthony Tutundjian, president of the company Concrete Hitech,
says that the new concrete is also resistant to other damaging chemicals,
such as sulphates. The concrete would also halt the ‘concrete cancer’ caused
by certain types rock used in concrete making, he says. And because there
are none of the usual pores in the concrete, known as voids, it has ‘terrific
freeze-thaw resistance’, says Tutundjian.

The new process centres on a secret pink powder. This is a mixture of
compounds, including phosphorus, potassium, manganese and a catalyst, which
modifies the concrete. A small amount of the powder added to concrete in
a mixer alters the material so that the voids become filled with crystals.
The powder formula is so sensitive commercially that even associated patents
are ‘concealed’, says Tutundjian.

Construction engineers and scientists agree that the concrete could
have a great potential, but they still need convincing that it will live
up to its claims. ‘If successful it would expand the use of concrete. Theoretically
it could work,’ says Ken Bezant, technical director of Blue Circle, one
of the world’s top three cement makers.

Recent tests in Britain support Tutundjian’s claims, although they have
been carried out only on a small sample. Mike Ridout, laboratory manager
at Contest Melbourne Laboratories in Maidstone, Kent, confirms that tests
showed that water did not penetrate the new concrete. He says the concrete
also retained its other useful characteristics, such as its ability to flow
into moulds easily. Optical and electron microscope examinations by Bill
French at Queen Mary and Westfield College of London University show the
concrete to be surprisingly free of continuous voids, he says.

Concrete Hitech has spent over five years developing the concrete. Tutundjian
says authorities in Florida have used the concrete to repair the damaged
cooling water inlet and outlet at a nuclear power station. Meanwhile, engineers
rehabilitating crumbling sewers in Cairo have used the new product, says
Tutundjian.

The DoT had put aside up to Pounds sterling 1500 million for major repairs
to bridges over the next 15 years, but this latest report claims this underestimates
the cost of coping with the problem by nearly Pounds sterling 400 million.
It says that one-fifth of England’s road bridges are so badly affected that
their corroded patches will have to be cut away and rebuilt.

The DoT is responsible for nearly 9000 bridges in England on trunk roads
and motorways, most of which are concrete. In August 1986, the department
commissioned a consulting engineering company, G. Maunsell & Partners,
to carry out a detailed survey of a random sample of 3 per cent of these
bridges.

The engineers’ report finds evidence of extensive degeneration with
a number of different causes in its sample of 200 bridges. These include
poor practices in the original construction and chemical reactions in the
concrete itself. But the greatest damage comes from the sodium chloride
used for de-icing in winter. ‘It’s not a problem of safety, but of durability,’
says a senior engineer from the DoT.

The report says that poor design, both of the joints which accommodate
thermal movements and of other openings in the bridges, has allowed salt
to leak in.

Although sodium chloride is extremely damaging, nobody has found an
economic alternative for making roads safe in winter. One possible alternative,
urea, would not corrode concrete but engineers at the DoT see little future
for it, because they say that urea costs 10 times as much as salt and is
less effective in severe conditions.

The engineers also claim that urea can filter into water supplies, contaminating
them with ammonia. The department now uses urea only on the Severn Bridge
and at ‘Spaghetti Junction’ in Birmingham, both of which have suffered severe
corrosion. According to the report, little can be done to stop such corrosion
once it has started.

For the most serious cases, the consultants recommend that the department
uses a technique called ‘cathodic protection’. More than 150 bridges and
car parks have been protected in this way in the US, but in Britain the
technique is still experimental.

Concrete is alkaline. In normal conditions, a coating of stable oxide
will form on the steel reinforcing bars that run through it. The problems
start when chloride ions in the water that has seeped into the bridge react
with the oxides and break them down, exposing the raw metal.

Concrete is not a homogeneous material. It contains pockets of air and
patches of crushed rock. ‘The pH varies considerably along the bar,’ explains
Nick Buenfeld, a specialist in concrete from Imperial College, London. These
variations in acidity set up potential differences between the different
zones of the bars. The zones can then act as anodes and cathodes for an
electric current. Parts of the bar act as electrodes and the concrete acts
as the electrolyte (see Diagram). Ferric ions are released at the ‘anodes’
and hydroxyl ions are released at the ‘cathodes’. The hydroxyl ions migrate
through the concrete to the anode, where they combine with the ferric ions
to form rust. Rust takes up more room than the original steel, so it pushes
against the surface concrete and cracks it.

Engineers can prevent this by coating the surface of the concrete with
a very stable, conductive material, such as a polymer or a resin. The engineers
set up a ‘rival’ potential difference to those along the bar, by connecting
the surface of the concrete to the positive terminal of a direct-current
supply of electricity. This turns the surface into an anode. Connecting
the bar itself to the negative terminal of the source of electricity turns
it into a cathode.

If the negative charge on the bar is sufficiently strong, then no anodes
will form along the bar and the localised electrolysis should stop. If the
surface anode is stable, it will not ionise and there should be no electrolysis
between the surface and the bar.

* The Performance of Concrete Bridges – A Survey of 200 Highway Bridges,
HMSO, Pounds sterling 11.95