Flattened ends are out

By Spencer Erling
Education Director, SAISC

Tubular construction is not exactly a new science. As early as the 1890’s iconic bridges such as the rail bridge over the Firth of Forth between England and Wales was constructed using circular hollow like sections for the main components. Of course in those long gone days welding was not in existence so the pipes were made from two halves – each half consisting of extended semi-circles. The halves were joined together by riveting them together through the extension pieces. Today, some 115 years since opening, all be it that the bridge has been reinforced, it is still doing regular and normal rail duty.

The arrival of seam welded pipes made their use in structural applications a given, after all, other than circular solid sections, no other structural profile has an equal strength in every direction making tubes the ideal profile for, especially, compression members.

But the circular hollow profiles were dogged for years by the perception of high prices. These were in many instances of real concern especially when the rate per ton price of tubes was considerably higher than hot rolled profiles. But that of course was not really a true measure as tubes often have a mass much lower than their equivalent alternative hot rolled profile.

The next most commonly raised argument about expensive tubular construction was the expense of joining members together. Yes, when it came to developed profiled connections this was relatively true, especially in pre-computerised drawing times. The effort to develop such connections by hand on paper was laborious and slow. Wrap around templates were made from cardboard or firm paper, and the steel once marked was cut by hand, usually with oxy-acetylene torches, resulting in an enormous amount of grinding and general cleaning before the piece could be used.

Oh, and if, as quite often happened, the wrap around template at one end of the pipe was not concentric with the other end: imagine the use of strong language; throw it away and start again.

The net result was tubular construction was not what every fabricator wanted to do, few contractors got it right, and as you can expect they charged for their services!

There was an alternative, but that became regarded as an industrial solution by architects. That was the well developed and documented flattened end method of truss construction. In this method the ends of the pipes were flattened so they were no longer round but almost a flat rectangle like and because this end was quite narrow it was now possible to cut these members in a saw (before or after flattening).

So whilst quite a few industrial projects were built using flattened ends, this method really did not do justice to the high quality finish architects had hoped for with tubular construction.

Between the ‘industrial look’, the partially true perception of high prices, the fact only a few fabricators really ‘got it right’ tubular construction just did not get its fair share of the market.

But this is the second decade of the 21st century. Some wide awake tube manufacturers and steelwork fabricators are keeping up with modern developments and over the last 5 years we find that numerous NC controlled laser cutting machines have made Tubular ‘boat shaped’ trusses under fritted glass. their way to the foot of Africa and now, all that is rapidly changing.

The advent of the fact that modern 3D detailing software packages speak to the NC laser cutting machines means that gone are days of making wrap around developments, gone are the days of flattening ends of tubes. Here are the days of NC machines automatically cutting, shaping and preparing the ends of members to accurately allow for pipe to pipe connections in every which way imaginable, in quicker time than it would have taken to use the wrap around template to previously mark a pipe, let alone cut and clean it.

Do not forget that laser cuts clean, so no grinding and cleaning before assembling. The comment of a workshop manager when asked was this a difficult job to put together (on being complemented on his very complex shaped entrance canopy sloping up and curved combination) says it all: ”We detailed the steelwork on 3D, we sent the files to our favourite tube maker who delivered the pipes cut and fully shaped a few days later. We did a quick layout and two days later the whole job was assembled and welded.”

There is no doubt that                                                                                                                                                                          1. despite the enormous investment cost in the new equipment;
2. the fact that these machines are not available only to the few as some machines sit at service centres;
3. the speed with which they cut,
4. the cleanliness of the cuts;
5. the accuracy with which they cut and so fit when assembled;
6. the resulting ability to do clean and effective welds the new machines are going to be a great boost for the tubular industry.

So, be you architect or engineer, quantity surveyor or developer, or just a fabricator, make it your business to get to grips with this new technology, let your imagination fly because the new technology will eliminate lots and lots of the pain associated with the weird and wonderful projects of the past.