Careful attention to joinery and geometry brings a work of art (and a functional pedestrian bridge) to a busy intersection in Colombia
This unusual fabric and bamboo structure has several sustainable design advantages going for it, starting with the design of the intersection it crosses. The intersection is a mini cloverleaf with clear and practical separation of auto and pedestrian circulation systems. A modified “roundabout”—a traffic control concept known to reduce pollution and gas consumption by avoiding stoplights and idling engines—it is located at a major crossroads in the city of Cúcuta, near Colombia’s northeastern border with Venezuela. To minimize gasoline use, the exit and entrance ramps from two directions rise only 3.5m above the pedestrian grade (or “zero-level”) while the main four-lane thoroughfare descends 3.5m to make a total of 7m difference between the lowest and the highest roadbeds. In a subtle nod to the concept, the steep slopes leading down to the lowest road level are planted with an anti-erosion ground cover of clover.
Like a handcrafted wooden puzzle, the bridge relies on each piece of bamboo to contribute to the integrity of the structure. Two broad arches, one each side of the pedestrian deck and each composed of a trio of large-diameter bamboo, carry the weight of the bridge and rest on major foundations set into the embankments. Three is the favored number, as bundles of three medium-diameter bamboo support the deck transversely at regular intervals, while a secondary arch of shallower curvature undergirds the deck assembly. Bamboo struts point diagonally up above the two bridge ends to provide cross bracing and structural support for the tensioned saddle-shaped fabric cover.
“Working with bamboo is a pleasure,” says Jörg Stamm, a German-born carpenter who did the bamboo construction, “as it is already a finished product and it feels good in your hands: no splinters, no roughness and it is very light.” Bamboo is an ideal construction material for a number of reasons. Unlike metal, with bamboo there is no mining of raw material, no melting of ore, no anti-corrosive paint required to protect it and thus has a relatively low carbon footprint. Structurally, bamboo is a tube with mechanical properties similar to light steel. As for Life Cycle Assessment (LCA), according to Dr. Jules Janssen of Eindhoven University of Technology, bamboo has an LCA 50 times lower than steel and three times lower than dimensional lumber for equivalent strengths.
For the protective fabric roof, Castro Rojas Ingenieros y Arquitectos Ltda., Bogotá, Cmarca, Colombia, designed a gently curved saddle form with outrigger steel cable tie-downs at each corner securing the roof to the embankments as well as contributing to the overall structural stability of the bamboo.
As far as anyone knows, this is the first time that a tensioned fabric roof of this size has been combined with an all-bamboo structure of such magnitude. The refined connection details and craftsmanship prove that the bridge in Cúcuta is more than a pedestrian structure, it is a work of art that has become a much-loved landmark for the community. The project won an Award of Excellence for projects less than 558m2 in the 2009 International Achievement Awards sponsored by the Industrial Fabrics Association International.