Restructuring the work process

On the first of April 2010, with the introduction of Eurocodes, everything was supposed to change for structural engineers. However, so far nothing seems to have happened. By this I am referring to the withdrawal of the previous suite of British standards and the introduction of the Structural Eurocodes which our industry seems so reluctance to adopt. For structural engineers, this is a very big deal; the way in which we undertake our designs has, in effect, been changed overnight. So why is the UK construction industry so slow to change and so resistant to change? More importantly, why are structural engineers not taking this opportunity to improve our designs when our European competitors have been doing so for many years?

Reluctance to change
The basic reason for the reluctance to change from British Standards to Eurocodes is the shear magnitude of the task and a lack of enforcement by building regulations.  

The magnitude of the change is difficult for anyone outside the industry to appreciate; 30 Codes of Practice have been replaced by 58 Eurocodes. These have been doubled again by the introduction of the National Annexes. This has resulted in a quadrupling of the number of documents to be referenced in order to achieve the same design.

Ironically, the purpose of the National Annexes is to allow the national bodies, such as British Standards Institute, to adjust the Eurocodes to suite domestic practices, i.e. to make the codes correlate with what we would expect from a ‘British Standard design.  

Another reason for not changing to the Eurocodes is cost. The general view, expressed on the internet and industry press, is that adopting Eurocodes will cost approximately three times as much as the British Standard equivalent.  

Further more, while British Standards have been withdrawn, they still represent a tried and tested method of achieving a satisfactory design. The attitude of engineers is simply then, ‘if it isn’t broken, don’t fix it’.

Forcing Engineers to use the new codes is almost impossible. Under the building regulations, engineers are under no obligation to use Eurocodes as it is acceptable to use a recognised alternative method of analysis and design – which allows the old codes to be used ad infinitum.

When I was a new graduate in 1990 the introduction of the current British Standard, BS5950, and the reluctance to accept it in lieu of BS449. Now engineers are clinging to their copy of BS5950 as the BSI try to prise it from the grasp and replace it with EC3. Similarly, new graduates have been using the Eurocodes for years and will leave us behind.
 
What’s the difference?
We will use steelwork design as a basis for this analysis although in essence these observations could apply to any of the structural materials.

For the first time ever, basic structural concepts are laid down in a code of practice, Eurocode 0.
Reference to this document will be sporadic; engineers will continue to use the theory they have learnt over their degree courses, computer analysis and simple rules of thumb.

Analysis of structures has not changed between the Eurocodes and the previous British Standards; Simple Bending, Euler’s Buckling theory, Pounders Plate Theory and so on are still valid.  The Eurocodes present a much purer form of design based on structural theories and do not rely on interpolation of tables. In fact, once we can get over the hurdle of the copious equations and their unfamiliar Greek symbols the theory is very familiar.

A hard sell?
Take the subject of loading as a way of illustrating the Eurocodes system. Loading is covered under Eurocode 1 and is largely in line with the previous British Standards. The differences only become apparent when combining and factoring loads. Some load factors have been reduced and others increased from their BS5950 equivalents.

Dead loads attract a factor of 1.35 and imposed loads a factor of 1.5 compared with 1.4 and 1.6. The Wind loads, though, are treated as ‘variable actions’, and are factored by 1.5, as opposed to 1.4 or 1.2 in the British Standard equivalent.

Load combinations further complicate the issue; the Eurocode requires all likely simultaneous variable actions to be considered.  Each one is then considered as the principle variable action with all the others considered with a weighting factor. A multitude of load combinations could be generated for all possible combinations in a complex frame. 

A simple floor beam will see a reduction in loading due to the reduced load factors for Dead and Imposed Load, a roof beam could see an increase due to the introduction of leading variable actions (imposed loads) and inclusion of all the variable actions simultaneously.  The number of load combinations for a roof beam, including snow and wind, will be at least five combinations compared to the previous two combinations. As such this is likely to prove a headache for engineers.

The major construction bodies, (TRADA, BCSA, SCI, Concrete Society) are providing guides to the new codes together with worked examples; the backbone to getting engineers to produce efficient and consistent designs.  This has been rolled out over recent years and the intensity of new documentation accelerated up to 1 April deadline.

The course I attended by the SCI in March 2010 was the initial stimulus to examine the benefits that could gain from using the Eurocode.  

Assessing the change
The publication of the Blue Book (the engineers’ bible) along with the change in the status of the existing British Standard was an important juncture for the assessment of the Eurocodes on our design process and the benefits which could be obtained from its adoption.  This was following the claim by the SCI that for some beams (as an example), economies in design of up to 33 percent could be achieved.

The effect on long spanning steel beams, those whose design is governed by their behaviour in lateral torsional buckling, is most markedly affected.

This is where savings of the magnitude suggested by the SCI could be achieved.  Most other savings from the Eurocode design will probably come from reduction of factored loads and are likely to be of the order of  5 to 10 percent depending on the dominance of the imposed loading.

For long spanning beams, we found that savings in weight could be achieved in almost all circumstances.  We were consistently finding savings in actual weight of steel beams of around 24 percent; this was defined by the increments in steel weight. Approximately 5 percent of the saving could be attributed to the reduction in loads with 19 percent attributable to enhanced performance.

If we use the Eurocode to its ultimate potential, we can make further savings by considering how the beam is loaded as well. This, however, also needs other members of the design team to buy into the efficiency of the frame being an important component of the overall design.  

In closing, it would be remiss of me not to mention sustainability in any article relating to construction and we can see that if we use the Eurocode as intended, we will use less steel and make the resulting structure more sustainable, as well as more cost efficient.
 
Eurocodes are here and they’re here to stay. It is now up for engineers and the construction industry as a whole to accept them, use them and get the most out of them.

David Knight is engineering director for ASTAM GBC, the Southwest-based multi-disciplinary consultancy of architects, engineers, surveyors and project managers. Visit: astamgbc.co.uk