Bridge Repair by External Prestress: The Gibe Crossing in Ethiopia

摘要

The Gibe bridge is located between Addis Ababa and Jima along the homonymous highwayrnconnecting the two Ethiopian cities. The bridge is made of a continuous, 4 span, reinforced concreterngirder of 120m length and 9.6m width. The structure has 4 longitudinal beams, of variable height,rnconnected by reinforced concrete diaphragms at piers, quarter spans and midspans.rnThe bridge, built in 1976-1977, suffered major damage from a terrorist bombing in the 80's. Thernbombing caused the collapse of a whole section of the deck that had to be re-cast in situ. The bridgernhas been used since then with load restriction with an alternative crossing available a few hundredrnmetres downstream along the old road built by the Italians in '30. This latter crossing was an oldrnsteel truss girder built by the English in the '40 that collapsed in the fall of 2006 when a dozerrncrashed into the upper bracing of the main steel girders causing the spectacular collapse of thernwhole structure. Rehabilitation and strengthening of the concrete bridge became, all of a sudden,rnvital and urgent as it stands as the only connection between the agricultural South Western regionrnand other parts of the country.rnThe Ethiopian Government contacted Salini Costruttori SpA, a contractor presently engaged inrnconstructing hydropower projects in Ethiopia, with a request for technical assistance. SalinirnCostruttori SpA decided to perform the bridge strengthening as a contribution to the Country, andrnasked Integra to devise a fast, reliable and economic method to carry out the operations. Thernproposed solution makes use of external prestressing to increase the girder strength by closing thernextended crack pattern and reducing bending and shear forces in the deck. The works, performedrnwhile the bridge was in service, were completed in three months and the bridge opened back torntraffic without load restrictions in November 2007.