Dilworth Footbridge - twin asymmetrical arches

Dilworth footbridge is part of Auckland’s Newmarket Viaduct Replacement project, which involved the deconstruction and reconstruction of a 700m long viaduct on one of the busiest sections of motorway in New Zealand. The existing footbridge had to be replaced because its central support did not suit the new motorway lane arrangement and because of its low height clearance and the risk of bridge strike by over-height vehicles. Replacement of Dilworth footbridge was undertaken as an alliance contract for the NZ Transport Agency.

The new bridge is constructed of steel hollow sections with a precast concrete deck. The twin asymmetrical arches: a tied arch over the motorway and a second underslung arch over the railway came about because of the difficulty in reconciling the appearance of alternative options such as two twin tied arches or a single arch over the motorway and a beam over the railway. This paper discusses the particular challenges associated with the design of the asymmetrical arches.

Also discussed in the paper is the careful planning that went into construction. The footbridge is on a popular school route and has fairly heavy pedestrian traffic, particularly around 8:30 am and 3:30 pm. Construction of the new footbridge was staged with the demolition of the original one to ensure continual access for pedestrians throughout the works. The design of the new footbridge was configured for rapid erection so that delays would be minimised to the busy section of motorway beneath it.