February 9, 2011
How free designs can improve footbridge quality
contributor: Rob Goodier
When the cables dangling from the enormous ship-to-shore gantry cranes can no longer hoist cargo in ports, they get a second run supporting footbridges in rural villages. Bridges to Prosperity, a bridge engineering organization, collects and load-tests the used cable, scraps the frayed parts and ships it by the container to bridge construction sites worldwide. Bridges to Prosperity’s engineers have built 4500 footbridges with recycled cable. They also donate it to other bridge projects. The organization shares both its experience and its resources as part of a mission to improve and standardize footbridge quality.
“There’s no room for error in a bridge,” Avery Bang, the organization’s executive director, tells E4C. That is why she is pushing for better collaboration in the development community. She would like for bridge builders to pool their resources, use proven designs and commit to follow up on bridges built in developing countries even years after they are complete.
As a step in that direction, Bridges to Prosperity has posted two well-tested designs online, freely available to the public. One is a suspension and the other is a suspended bridge. There are variations available for components such as decking, anchors, stringers, crossbeams, deck width and tower height. But the basic designs represent a baseline of quality, Bang says. This service and future efforts to pool resources can improve efficiency in international development. It can also keep bridges intact. “It’s scary to see some of the designs that have failed in the last 10 years,” Bang says.
“It’s good that engineers are innovative and want to design something from scratch, but without a common repository of information and idea exchange, you have people reinventing the wheel over and over again.”
The organization also provides free cable to successful applicants for bridge construction. The application process is rigorous, however. It aims to reduce wasteful spending and ensure quality. Before any project is approved for donation, it must also pass inspection before a committee of engineers.
Segera mission, Nairobi, Kenya
When a sound, safe bridge is finished, it can change lives. One of the organization’s designs is in place over the Ewaso Ng’iro river, serving a community near Mount Kenya, north of Nairobi, Kenya. The Orange County Professional Chapter of Engineers Without Borders built a footbridge there to give the residents easy access to the Segera mission clinic on the other side of the river. It cuts hours or days off of their travel time to medical and other services.