Feats of engineering are, for the most part, not even noticed in the U.S. Did you drive across a bridge to get to work today? Exit the freeway in a tangle of ramps? Do you know how hard those things are to build?
In developing nations, a relatively simple footbridge can make the difference between getting an education and staying at home, between receiving health care and being sick. Peace Corps Response Volunteer Nate Bloss has been working with Bridging the Gap Africa as a project supervisor in Kenyan communities where people and economies are affected by the ability to cross waterways safely. Check out these pictures from the “walking world” – and see how a bridge can make all the difference.
↑ After receiving a bridge request from a community, Nate surveys the site and collects geotechnical information. He investigates an area of the river and selects the most suitable site for a bridge. If the community is interested in helping, the project moves forward.
↑ The next step is to design the bridge, which typically spans between 30 and 60 meters. Data collected after preliminary surveys help to design the bridge. Nate completes the design by himself and sends it to a group of volunteer engineers in the U.S. to check the design. After the design is complete, Nate determines what materials are needed and gets them to the bridge site, and will sometimes prepare them himself.
↑ Nate then meets with the community and local administration to come to formal agreements so there are no misunderstandings about expectations and the final product. As they wait to begin construction, materials are gradually delivered to the site. Villagers manually help move materials such as gravel, sand and cement to both sides of the river.
↑ As construction gets underway, Nate supervises the labor with the help of two Kenyan foreman. Labor teams don’t typically have construction experience, so much of the time they need to be taught about the processes to ensure the construction is done safely and correctly.
↑ The next step is to build towers to support the cable and the anchors that hold the bridge up. This can take anywhere from one to three weeks. Before breaking ground on construction the team lays out the bridge based off the original survey and a center line that remains in place throughout construction. Holes are dug for the anchors and tower footings. The time to dig depends on the type of soil, which is anywhere between soft soil and hard rock. If it involves hard rock sometimes villagers dig the holes prior to Nate and his team’s arrival.
↑ After the holes are dug, the team strings the cable across the river. They then layout the reinforcing steel in the anchors and foundations and pour the concrete. When all the concrete has been poured and the steel towers erected, Nate and his team leave the site for one month to allow the concrete to properly cure.
↑ After one month the building team returns the bridge site and hangs the cables from the towers.
↑ They then set the sag of the cable to the design elevation and tighten down the cable.
↑ When the cable is secure they begin hanging the deck.
↑ After the deck is complete, concrete is placed around any cable that will be buried under ground to protect it from moisture, and then holes are filled.
↑ Completion of the bridge is almost always followed by a large village celebration.
Bridging the Gap Africa has constructed over 55 bridges in Kenya during its 10 year existence. Currently they are in the process of designing and constructing four suspension and suspended bridges throughout Kenya and Tanzania.