A cantilever spar cable-stayed bridge is a modern variation of the cable-stayed bridge. This design has been pioneered by the structural engineerSantiago Calatrava in 1992 with the Puente del Alamillo in Seville, Spain. In two of his designs the force distribution does not depend solely upon the cantilever action of the spar (pylon); the angle of the spar away from the bridge and the weight distribution in the spar serve to reduce the overturning forces applied to the footing of the spar. In contrast, in his swinging Puente de la Mujer design (2002), the spar reaches toward the cable supported deck and is counterbalanced by a structural tail. In the Assut de l'Or Bridge (2008), the curved backward pylon is back-stayed to concrete counterweights.
Puente Atirantado (sometimes called Puente de la Unidad or Viaducto de la Unidad), opened in 2003, is a cable-stayed bridge that crosses the Río Santa Catarina and joins San Pedro Garza García with Monterrey. Although impressive and elegant, its construction was highly controversial due to its cost, its design (very similar to the one by Santiago Calatrava), and the fact that the river it crosses is dry.
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