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Is CAD/CAM the greatest advance in construction?

After reading that CAD/CAM got top vote in the recent poll to find the greatest advance in construction (NCE last week), I was left wondering as to the age spread of those who voted?

Yes I am one of those older engineers who were brought up on a drawing board, and I do appreciate that CAD can be more efficient. How many times have readers gone back to an architect after receiving a new layout asking for dimensions to be told: “Its drawn full size just overlay it and scale off the dimensions you need,” and this is when we all tend to have a general note saying: “Do not scale this drawing!” In my opinion CAD/CAM should be used in the same way as a good set of pens, as a tool, not a be all and end all solution which appears to be the attitude of some.

It is all very well, to quote your article, being told we are: “Old fashioned and dismissive to say the craft is lost,” and “People can craft things with a mouse the same as you might with a pencil,” but I would hazard a guess that most engineers of my age still produce hand-drawn sketches either for their own visualisation or to clarify a point when talking to other people.

Don’t get me wrong I am a strong advocate of technology, to the point of being a gadget geek, but please, as came across in the article, do not try and portray CAD/CAM as the future of engineering – Brunel et al managed quite well without it!

  • Robert Lye Robert.lye@fairhurst.co.uk

By all means use Computer Aided Design (NCE last week) as long as the end result is good. The “little kiosk” outside St Paul’s Cathedral is dreadful and could have benefitted from a lot more intelligent human input. We must make sure that the computer is our servant, not our master.

  • Hugh Burn (F) 15 Greenfield Road, Devizes SN10 5BP   

Recognition where it is due

Regarding the news that the Thames Barrier is good to 2070, as a retired engineer from RPT/ HPR, I am proud to have been on the Barrier team. It was a tremendous project to be on and this latest report proves its worth. Unhappily in the closing stages it suffered from a political battle between Margaret Thatcher and Ken Livingstone so the acclaim due to the engineer and the contractor was forgotten.

The project was however honoured by being commissioned by the Queen, but no honours to engineers followed from it. However, by any standards those that headed the teams deserved recognition and this latest report confirms this fact, to me at least.

Illumination marks the spot

The instant islands system (NCE Spotlight 26.03.09) has much to commend it, as does the traditional pedestrian refuge island that it might replace. Both the traditional and instant provide increased safety for the pedestrian, but unfortunately in the process they both provide an extra hazard for the motorist.

In daylight they should be accompanied by a marking that widens out to guide the motorist towards the narrowed lane that is the result of the refuge, but particularly at night the refuge should be far better marked.

One suggestion is to place reflective bands on the upstanding kerb but more important is the position of the illuminated or reflective bollard. In the centre of the refuge it is of little value to the motorist, indeed it can be misleading. The bollard should be placed to the left side of the refuge and should always have a clear arrow marking giving the motorist ample time and distance to move into the narrowed lane.

Looking at the whole picture

With the article “The Shape of Things to Come” (NCE 26 March), under the banner of Road Safety and Technology, there is a photo of the bridge on Dobwalls Bypass. I would suggest that the operative standing on the end of the tunnel wall, some 3m off the ground, is clearly compromising his own safety and possibly those around him. With risk assessments and method statements aimed at reducing risks, we must all ensure that we police and reinforce the need for safety throughout the design and construction period.

  • Paul Thompson Paul.thompson@interroutejv. co.uk

Precast concrete still arches over rivals on railway lines

I am very pleased to see the continuing use of precast concrete arches over railway lines (The Shape Of Things To Come NCE 26 March), despite the much publicised problems at Gerrards Cross.

These structures can be very economical, make good use of soil-structure interaction and can minimise the inference to the running of the railway. However, the article asks: “Could the Dobwalls tunnel herald a new era?” and quotes a claim, that: “It is the first of its kind in the UK.” This is a bit too generous! The longer span Bebo design is stitched together at the crown to create a two-pinned arch which makes it different to a number of three-pinned arches which have been constructed in the UK, including that at Gerrards Cross.

However, early in the 1990s, long before proprietary precast arches were available in the UK, we (Benaim, now part of Scott Wilson) designed two bridges in Scotland using two-pinned precast arches with a crown stitch – I even held a patent for one of them jointly with the contractor, Balfour Beatty. These were alternative designs prepared for the contractors and, while the analytical techniques in those days were not as sophisticated as those we now have available, they were very economical structures costing about half as much as the traditional structure that they replaced.

  • Mark Raiss, head of Metros Scott Wilson Railways  

Which is the right fork?

On the Clyde Arc Bridge it would be interesting to know how the maximum load was assumed to be carried by the forks (NCE last week). Because of the stiffness of this type of connection it is highly probable that in many cases it cannot yield sufficiently to share the load equally between the two prongs of the fork. The whole load may be carried on one prong of the fork, which fails, followed by the second one.

  • Peter Jackson pdm.jackson@btopenworld.com
  • NCE welcomes letters from readers. We attempt to print as many as possible, which means letters longer than 200 words are likely to be condensed

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