Algorithm weighs up strategies for bridge management

The method helps decision makers choose which bridges to focus on by assessing several key factors.

‘Most bridges in North America are in really bad shape,’ said Sabah Alkass of Concordia University in Canada. ‘We talked to different municipalities, and the reason is that they just don’t have funds. The budget is so limited that they only do corrective maintenance. But in the long run, although it requires more planning, it’s actually cheaper and more effective to avoid problems now rather than fix them later.’

The method takes into account the fact that some criteria are more important than others: a bridge that is in poor condition would be prioritised over one that has an inefficient drainage system.

A bridge that gets a lot of traffic, has an inefficient drainage system, is at seismic risk and is in poor condition would be at the top of the list. After assessing which bridges require the most attention, the next issue facing decision makers is whether to rebuild the bridge, repair it or increase maintenance.

With three different rehabilitation options — each with its own price tag — and an entire network of bridges, figuring out which bridges to rebuild and which to repair while staying within the budget is a challenge. 

Alkass and colleague Abu Dabous calculated that there are more than three billion rehabilitation possibilities when considering just 20 bridges. They then commissioned experts to choose the best option — rebuilding, repairing or maintenance — for each bridge in their sample and then entered the information into a computer program that simulated all the different possibilities and calculated the cost of each.

‘It is a powerful tool that can incorporate both expert opinion and a systematic assessment of bridges to identify the best strategy within a limited budget,’ Dabous said.