Demonstration projects are intended to show innovation in at least one of four areas: product development, project implementation, partnering with the supply chain or production of components. But innovation is not confined to regular building types, where lessons learned on one project can be carried to the next. It can also be found on unique landmark projects, where the structure and design themselves ought to have been innovative enough. That is the case with the Lowry Footbridge in Salford, linking the Lowry Centre and the planned Imperial War Museum of the North across the Manchester Ship Canal.
The competition-winning design for the recently completed 92 m span bridge had to cater for the large ships that use the canal; the solution was a steel footbridge and cycleway 22 m above water level that could be raised hydraulically. The design team consisted of consulting engineer Parkman in association with Spanish architect/engineer Casado.
But when client the Lowry Trust Development Company put the bridge out to tender in early 1997, the lowest bid came back £2m above its lottery and grant-funded budget of £5m. At that stage, as project manager Simon Laffan of lowest tenderer Christiani & Nielsen confirms, the Lowry footbridge was “dead in the water”.
However, the client had sufficient faith in the ingenuity of the construction industry to proceed to a cost-cutting redesign of parts of the bridge. Christiani & Nielsen, the designers and key steelwork subcontractor Fairport set up partnering workshops where ideas for reducing costs were floated in brainstorming sessions, then given rankings. Those judged most likely to bear fruit were then pursued.
The bridge’s four support towers, originally designed in curved pre-stressed concrete, were given a radical makeover. Cheaper tubular steel was proposed, which had the added advantage of a more open appearance that put the counterweights and winding gear on show. “It has become quite an educational feature,” says Parkman’s resident engineer Charlie Parkinson. Another change was in the bridge’s drive mechanism, where the decision was taken to swap the specified single electric motor for six smaller hydraulic ones. These brought several advantages: the bridge could still be operated if two were out of commission; the motors were standard, easily available and easily repaired; and the bill came in at £100 000 less than for the single bespoke motor.
Lateral thinking was called into play when the footbridge team considered what to do with a hollow concrete structure sitting exactly where it wanted to land its bridge. Demolition and removal was the obvious, if expensive, answer, but the engineers decided to drill and concrete their piles through holes cut in the structure, then break the surrounding concrete away. This saved £100 000. The accumulated savings helped bring the project in just above its target cost. The design team is satisfied that although the cost-cutting redesigned the bridge’s four corner supports, it did not compromise the innovative design and engineering. “It’s an excellent project – a real one-off,” says Parkinson proudly.
Client Lowtry Development Company Contractor Christiani & Nielsen Steelwork Contractor Fairport Steelwork Designer Parkman, in association with Casado M&E Designer and Contractor Bennett Associates