Stress Ribbon Bridge in Freiburg, Germany

A three span continuous stress ribbon bridge of 75, 130, and 138 ft, was built in downtown Freiburg, W. Germany, for pedestrian traffic. Structural analysis is similar to that of suspension bridges. However, because deck and stress-ribbon are combined into one, the gradient and dip of the stress-ribbon must be small. Dip to span ratio in the middle span, varies from 1:63 to 1:15 under various loadings. Required tensile force in the stress ribbon is very high. It varies from 1,700,000 lb to 3,520,000 lb. The deck is post-tensioned longitudinally to provide higher stiffness for the stress-ribbon. Temperature is the most significant loading. Change in midspan deflection can amount to 6.3-in. due to a 36°F rise and fall in temperature. The abutments are designed as gravity anchor blocks with anchoring force of approximately 2,500,00 lb. Stress ribbon bridges are extremely slender, and are sensitive to vibrations excited by traffic or wind.