University of Colorado Bridges to Prosperity
CONSTRUCTION
Centerline
The very first construction task when building a bridge is setting the centerline. The survey report gives an idea of where the bridge will lay to within a few meters. The last few meters of wiggle room are chosen to create the easiest path, allay excavation work, and ensure a safe distance from cliff edge. Once a line is chosen that is in accord with all criteria a rope is strung across for reference.
Towers
Once a centerline is laid out, first shovels are dug for tower erection. Towers provide a saddle over which the cables will be strung over. They are structural members built to transfer resultant compression from the cables to the ground. At the top are a pair of steel and grout reinforced brick assemblies supporting handrails. At base of the bricks is the tier top which supports the rest of the cables. The tier is a cube of concrete and carefully placed stone measuring one meter in height. Supporting the tier and providing the final link to the ground is the foundation, which is essentially a tier placed underground.
Anchors
Anchors are tasked with resisting the cable tension necessary to hold the bridge up. To accomplish this an excavation pit was dug to house a large concrete block through which the cables are tied. At the center of the anchor is a rebar cage of (8) 20-millimeter longitudinal bars and (11) 12-millimeter stirrups. Cables are wrapped around the rebar cage and clamped to themselves a short distance outside of the anchor. To complete the anchor, a large amount of concrete was poured to completely enclose the rebar cage. A total of 29 and 25 batches of cement were used for the westerly and easterly anchors respectively. Once the concrete had sufficiently hardened and the cables were set, over 2 meters of backfill was placed on top of the anchors. This was done to ensure adequate bearing stress was achieved in order to eliminate sliding.
Both anchors were not built to the same specifications, as one needs to be ‘adjustable’ in order to string cables up to their appropriate heights. To achieve this hollow plastic tubes were wrapped around the rebar cage in locations the cables would later sit. The fixed anchor on the opposite side differs in that cables were wrapped around the rebar cage and tied off before pouring concrete.
Typical Work Day...
Wondering what a typical day working in Ichoca was like? We usually woke up at 7 in the morning. Breakfast was usually a piece of bread with a cup of tea. Afterwards we walked a mile from town to the site and began safety talks and pre-work stretches. Once all safety hazards have been identified we began work. For the first four to five weeks work consisted of hand-mixing concrete, gathering large stones, and excavating with shovels. After a few hours of work the entire group would take a “descanso” (or break in English), where we would take on some water and the locals would chew coca leaves. Once rested we would work until lunch at around 12:30. Typical lunches consisted of soup and a plate of rice or pasta. Afterwards we continued working until sunset, taking another break in the middle of the afternoon. After work we would play soccer with the locals in the little soccer court and grab dinner before heading to bed.
