In 1998, working as an independent consulting engineer, I was invited by The City of Calgary to design a small footbridge over a divided highway near the city’s perimeter. Alberta is not a place where there is a lot of scope for bridge engineering: of the three major clients – the Province of Alberta and the two larger cities, Edmonton and Calgary – the Province demands standardisation and knows exactly what it wants. The cities, although quite conservative, do have an interest in being attractive and thus are more responsive to architects’ and consulting engineers’ proposals. Work is assigned largely in proportion to the consulting firms’ size; fees are a percentage of the construction cost. For smaller bridges, the usual way to produce better designs is to spend more time on them – often cutting costs in construction and so effectively, but unfortunately, reducing the fee. It is not always a profitable business. Even small structures can produce unforeseen risks when unusual design or construction methods are attempted. No doubt that with more design time the three bridges discussed in the following pages could have been improved to some degree. In the Sarcee Trail overpass the post-tensioning anchors required the ends of the girders to be enlarged to accommodate their size. This was ungainly and spoilt the outline of the structure at the ramp connections – a better solution would have taken more time to research and develop, and time was severely limited. In the case of the John Laurie Boulevard overpass the permanent bearings placed above and below the deck also produced an ungainly solution. Although not a distraction to the appearance, it is not a good engineering solution, however, construction started before the design details had been completed, the contractor having agreed that there would be no extras in spite of any required detail changes, placing the engineer in a rather difficult situation. The contractor had also agreed that with the help of the engineer some savings would be made within the pre- defined budget. Custom bearings, as in the 146 Avenue overpass, would have produced a far nicer solution but would have added cost to the project. The design team for small bridges includes an architect, a landscape architect, a geotechnical engineer and the bridge engineer who leads the team. The landscape architect helps locate the structure while the architect offers whatever advice is requested. All have their strengths and uses, and contribute from their individual wells of experience. Each of the following three projects use a similar strategy for putting a bridge in place in difficult and impacted urban sites. Very few buildings are designed with plenty of time at the architect’s disposal. Although the Syney Opera House took years to develop and build, in the end the client was frustrated and the architect quit rather than settle for compromises that were becoming more and more necessary. In the automobile and appliance industries the consequences of an error are mind-boggling; even so errors continue to be made, millions of cars are recalled annually for fixes. A building or a bridge is one-off. Innovation is so risky that many clients (in the oil industry for example) put a requirement on the structural engineer that he will try nothing that has not been successfully done before and that he will use a large factor of safety against overload. Errors still occur with amazing frequency. Perhaps we should be more prepared for errors. Maybe they should be more acceptable as part of the risk of doing anything. Good luck in selling this concept to a client, although they should recognise that more time for design is an ultimate benefit. The typical bridge in Calgary is built using precast concrete girders in spite of the large premium cost of precast concrete over cast-in-place. In some cases precast concrete girders offer advantages during construction but in my experience this has been vastly exaggerated. Their main advantage is that the designer can do it quickly, make more money out of it and leave the marketing of the product to the concrete industry. My concern is the number of ungainly bridges that litter our landscape as if we were born without an imagination. All three bridges here were attempts to find solutions that not only suit the sites but also contribute something to the art of bridge design. I must acknowledge the debt I owe to those who pioneered this field and particularly Robert Maillart through his work and Sir Ove Arup who inspired so many of his colleagues and employees. He believed that engineering should be a ‘power for good’.
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