Engineers will of course be familiar with the need to identify a reasonable means of building a structure – but in my experience this is rarely the method that contractors eventually choose.
Complex structures such as lightweight cable roofs or tall buildings are generally at their most vulnerable during the construction phase – a concept that bridge engineers understand well.
The final sequence of construction often needs to be carefully evaluated by complex structural staged analysis which can reveal that alterations are necessary in the design. Design consultants are understandably sometimes reticent to become involved for commercial and legal reasons.
Contractors are therefore having to carry out long and complex analysis after contracts are awarded with all the problems that this entails.
Clients may not realise the complexities and costs involved with this type of work as it is often classed as a contractor overhead, but the reality is that, as structures become more complex to build, it is not unnatural for there to be an engineering cost attached to innovative construction methods.
The number of engineers able and willing to carry out this type of work is relatively limited.
Flint & Neill was recently involved with the new roof of the London Olympic Stadium where we provided erection analysis and engineering services to main contractor Balfour Beatty.
The roof now covers approximately 45,000m2 and is the largest cable net roof in the world.
This involved analysing some 600 load stages during the build process. A construction sequence was developed to ensure that the final structure had the same stresses in it that it would have had if the entire structure had been magically built in the air and gravity had been suddenly “switched on”– no small task.
The traditional approach of a design team giving a contractor a design to build is giving way to a more collaborative approach involving many more professionals, some on the clients’ side and some on the contractors’ side, but in more niche areas.
This collaborative approach ultimately results in some of the most innovative and exciting structures around, but it is essential that the right input is given at the right time from the right person.
The design process is a cyclic one and this needs to include the erection analysis. Computer software is becoming more and more adept at reducing the design cycle within the design team.
My hope for the future is that we can develop tools that allow the contractor to assist and collaborate with the design team so that a particular method of construction can be evaluated not just in cost terms but in design terms as well.
We may need some re-evaluation of contractual mechanisms to allow this to happen, but it will ultimately be to the benefit of the industry as a whole.
- John Cutlack is Flint & Neill project director
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