Civil Engineering Reference
In-Depth Information
The nature of design
1.1 Design and analysis
The origin of the word design is the Latin 'designare', to draw. In classical times, the
stability of a structure depended on its shape, which could be drawn by those with
the special skills. Design now has a much-widened meaning embracing the concept of
anything from bridges to fl oats for a carnival.
In the context of bridge engineering, design means the conceptual phase, where
harmony is created out of the tumult of data which includes:
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the physical characteristics of the site;
the technical aspects concerned with the strength of materials and the theory of
structures;
the specifi ed design life of the bridge and the maintenance regime;
the various regulations that must be complied with;
the economic and time constraints that have to be met;
the form of contract under which the bridge is to be built;
the effect the new bridge will have on the community, either by its scale, its
appearance, or by the changes it will make to the local environment;
the wishes of the bridge owner.
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An inspired designer may attain a state of grace, where original ideas combine with
technical expertise and past experience to create the perfect solution that best fi ts all
the data, and which in hindsight appears obvious.
Design must be followed by the detailed justifi cation of a project, the analysis, to
demonstrate that it is safe and complies with the relevant regulations. This analysis
is followed by the preparation of drawings which are needed to communicate to the
contractor the information required to build the structure, and the preparation of
the contractual documentation. Although requiring skill and care, these latter phases
of the process are different in nature to the initial conceptual design; they are more
mechanical, and do not require the combination of technical expertise, aesthetic sense
and imagination that are characteristic of conceptual design.
However, in many cases, design is the name given to the mechanical analysis of
the structure, and even to the whole process. This is more than a semantic quibble.
Analysing structures is principally a mathematical, mechanical procedure, whereas
design is largely a matter of judgement in weighing up the importance of the many
