21 September 2009

Low-cost bridges: 2. Bridging the Gap

Like Bridges to Prosperity, Bridging the Gap (BtG) is a charity whose aim is to build bridges in developing countries. Founded in 1996, BtG focusses its efforts on Africa, principally Kenya, and has completed around 40 spans. As with B2P, the bridges provide access for rural communities to schools, health facilities and markets, and reduce exposure to the risk of drowning or animal injury.

The charity has its own standard bridge design, a simple catenary suspension bridge similar to the Helvetas designs used by B2P, and suitable for spans up to about 45m (see above right). This uses tubular steel supports (see left), inexpensive metal hangers, plank decking, and typically a few horizontal wires to form the "parapets". While the deck and parapets are simpler than the B2P bridges, the supports would seem to require more in the way of a non-local engineering input.

In its most recent bridge, a span of 112m was called for, far beyond what the charity had previously attempted. With the assistance of B2P and Helvetas, they adopted a far more conventional suspension bridge (shown right), albeit one which is still lightweight and adapted for construction in difficult territory.


Costing US$100,000, a very large sum by Bridging the Gap's standards, this bridge is documented in an excellent article at Bridge Design and Engineering magazine. As the image on the left shows, erection of the bridge's steel grille decking requires a head for heights. The images also show that this is a highly engineered structure, with more complex fabricated towers, hangers and decking than is the charity's norm.

While it's good to see them expanding their capabilities, it's hard not to wonder how many of their more normal bridges could have been built for that sum (they estimate US$5,000 for their typical bridge). This is a classic and perhaps insoluble dilemma for any charity.

Bridging the Gap invites donations to support their work.

See also:

1 comment:

rollins said...

This bridge was funded by AIG through Presbyterian Church of East Africa for a structure at this specific location; the amount was not available for any other use. BtG was brought in as builder.