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In your article 'Keeping the faith' (NCE 20 November 1997) you refer to the Tasman Bridge, Hobart, and state 'Later it gained notoriety when it was accidentally demolished by a ship'. May I, having been in the late 1950s Maunsell's project engineer for the bridge, outline the true facts?
About a quarter of a century ago three of the 19 viaduct spans of Tasman Bridge were demolished when a ship collided with two of the 17 viaduct piers. Repairs were hampered by the wreckage of the ship on the estuary bed, at the location of one of the two demolished piers. It became necessary to provide a span of 85m over the wreckage, in place of two of the demolished 42.5m spans. Despite that difficulty the bridge was repaired within 18 months.
At the location of the bridge the river Derwent has a tidal flow of up to 5 knots and is navigable by cargo ships of up to 10,000t. The river is 1,000m wide and up to 30m in depth, and bedrock is at some points a further 30m below river bed. Obviously the choice of a multi-span viaduct was far from ideal, and consideration had been given to an alternative design: namely a suspension bridge a short distance downstream, where the river width was nearer to 700m. However such a bridge would have doubled the estimated cost of £A5M ($A10M in today's currency) of the viaduct, and was out of the question. Tasmania is not the wealthiest of the Australian states: and the bridge had to be funded by the state.
The possibility of accidental shipping impact had of course been considered in the design of the bridge, when it had been recognised that full protection against a major impact could not be provided even at the main navigation span piers, let alone the much smaller viaduct piers. Gravity fenders incorporated in the navigation span piers could absorb the impact of a 10,000t ship moving at rather less that 1 knot. More important, and more relevant to the accident that occurred, is the provision made for preventing a progressive collapse of all the viaduct piers and spans, in the even of damage to a single pier. Far from ''gaining notoriety', the bridge behaved exactly as had been expected.
Douglas A Stephenson (F), Cooma, Laverstock Park, Salisbury SP1 1QJ.
I refer to your report on tall towers in NCE 11/26 December 1997. You reported the world's tallest structure as the 645m mast outside Warsaw. Unfortunately this structure followed the habit of others you reported and collapsed on 9 August 1991, during maintenance work involving replacement of the guys.
While the statement that 'most mast collapses can be blamed on atmospheric ice accretion' is certainly true in the US, where about 140 such failures have occurred between 1959 and 1996, there are many other causes including wind storms, fabrication errors, maintenance problems etc. Of interest are the increasing numbers of failures, or near failures caused by vandals and by aircraft hitting guy wires.
The relatively high failure rate of these light, dynamically sensitive structures is one of the reasons why more reliable design criteria have recently been developed and incorporated in the UK and European Standards.
BW Smith (F), 21 Dartmouth Street, London SW1H 9BP.
I was watching the film Yanks on TV in December - about the US army in northern Britain during the Second World War - when I noticed, in the background of one scene, two large concrete shell cooling towers.
I thought they came after the war. Can any reader say when the first one was built?
RA Baldwin, 4 Coppelia Road, Blackheath, London SE3 9DB.
Your article 'Hesitant contractors rebuff New Deal' (NCE 11/25 December 1997) could not be further from the truth.
First, it was the Construction Confederation, together with the CITB, which took the initiative to produce a sector specific New Deal scheme for construction. As the article states this is the first sector scheme to be finalised.
Second, a number of companies, including my own, have been working with the confederation and the government to produce a scheme which will make it as easy as possible for the industry to take on New Deal employees and the Employment Service to place people in construction.
In addition, the outline proposals for the scheme were circulated to all members of the constituent bodies of the Construction Confederation; and, for example, all of the CECA Regional Companies supported it.
Of course we do not know at this stage what the take up of the scheme will be. At the end of the day that will be dependent on the number of New Deal employees who decide to choose this industry in favour of the other options open to them.
While it will not solve the potential skills shortages in construction by itself, new Deal offers a real opportunity for us to bring new people into an industry which has not recently been all that successful in attracting new talent.
Alan Crane, managing director, Christiani & Nielsen, Orion House, Athena Drive, Tachbrook Park, Leamington Spa, Warwickshire CV34 6RQ.
The article by Simon Delves on the Housing Grants Act (NCE Water supplement 1997) was a well-written and accurate explanation of the provisions of the Act. What was not so clear was the reasons for the exclusions regarding the process and related industries.
The process industries, many of whose projects are carried out under the IChemE Model Forms of Conditions of Contract - known to users as the Red and Green Books - are known for their non-adversarial, litigation- free ways of working. There are several reasons for this laudable state of affairs and we were concerned that in addressing the difficulties of the building and civil engineering sectors, the Bill (as it then was) would affect the main contracts of process plant projects. These would have additional dispute resolution processes implied into them by law that were not necessary: the IChemE Model Forms have for 30 years had expert determination as one method of dispute resolution, and this has proven to be highly successful. To add adjudication was, we felt, unnecessary and confusing, and would itself add costs to projects. In addition, the difficulties associated with pre-appointment of adjudicators (which is now optional where the Act applies) were magnified for the process industries because of the different disciplines on any project.
This is why IChemE was glad of the exclusions, although in the end they did not go as far as we would have hoped. We are fully supportive of adjudication as a way of combatting the problems we see our colleageus in building and civil engineering face, but we fel that our Model Forms had no need of it.
Derryn Rolfe, manager - EPSC Operations, IChemE, Davis Buidling, 165- 189 Railway Terrace, Rugby CV21 3HQ.
On the market
Your otherwise interesting article 'Action stations' (NCE Railtrack supplement' was incorrect with respect to the credits for the London Bridge section of the Thameslink 2000 works. The new viaduct over Borough Market is distinct from the station works and the architectural work for the viaduct is by this office.
Rob Naybour, Tony Meadows Architects, 40-42 Newman Street, London W1P 3PA.