e-mosty September 2017: Mersey Gateway Bridge. Arenales Bridge. Mersey Gateway Bridge. Arenales Bridge. BLWT. - Page 31

4. CONSTRUCTION The team worked with the locally-sourced materials they were provided by the municipality and community, enlisting quality control aids in managing materials that are often of low strength and durability and completing the bridge’s superstructure in just two weeks. The final bridge product, however, showed redundancy and resiliency despite these challenging materials, a testament to the team’s focus and dedication to create a structure that would stand for years to come. Wooden nailer boards were attached to the steel crossbeams to allow for a lag screw to be used to attach the wooden decking boards to the crossbeams. The rebar suspenders were attached to the crossbeam and wooden nailers to form swings that were launched from the top of the scaffolding (Figures 10 and 11). Excavations were dug by hand, the largest of which were for the anchors, with dimensions of 9m x 1m x 2.5m. For the foundation works, all rebar was cut and bent by hand and 127 cubic meters of concrete was mixed using only drum mixers (see Figure 9 below). Figure 10: Volunteers from Kiewit and KPFF launch suspenders and cross beams from the scaffolding Figure 9: Bridges to Prosperity staff and community laborers pour cement for the anchors Because the suspenders are not positively attached to the main cables, an additional smaller cable, called a restraint cable, was used to restrain movement of the swings along the bridge. The restraint cable follows the profile of the main cables and is attached to the suspenders with cable clamps. The swings were installed and launched in sequence from each tower. The steel towers were prefabricated at a fabrication yard in Nicaragua and assembled on-site in a horizontal position with the “T section” of the tower resting in hinges embedded in the substructure. Because cranes are not readily available in rural Nicaragua, scaffolding was erected with a series of ropes and pulleys to allow a ‘tirfor’ winch to raise the towers from the horizontal position to their designed canted vertical position. Using the scaffolding as a working platform, the main cables were then lifted over the tower saddles and one end was secured at the anchor. The cables were tensioned one-by-one until they reached their design hoisting sag. Rebar ́ݕɔЁѼѠЁ䁡)%ɑȁѼٔɕɽ)݅́չՔѠ(̼)ɔQɥ́Ѽх́͡)ɽ͉́ɔչɽͥ