Viewpoint: risk in structural engineering

The replacement of the suspended structure of the Lions' Gate Suspension Bridge in 2000-2002 was the culmination of a long study of the bridge that revealed information about suspension bridges not generally known before, notably in the areas of bridge dynamics, aerodynamics (including criteria), traffic loading, load factors, cable stretch, seismic effects, and bridge temperature compared to ambient. The need to rehabilitate the bridge while keeping traffic flowing resulted in some innovative designs, including replacing the concrete deck of the viaduct with a wider steel orthotropic deck, rotation of some foundations, and replacement of the entire suspended structure. Constraints on the reconstruction options provided some fascinating challenges. These were overcome by going back to first principles, and by some creative solutions – exercised with great care. Peter G. Buckland, LLD, CEng, FCSCE, MICE Buckland & Taylor Ltd, North Vancouver, BC, Canada