Stress Ribbon Bridges Philosophers, thinkers, intellectuals all appeal, please build bridges and not walls between different communities, nationalities, countries, languages etc, to achieve universal brotherhood. This can be achieved by constructing stress ribbon bridges.
Stress ribbon bridges are very economical, aesthetic and almost maintenance free structure. They require minimal quantity of materials. They are erected independently from the existing terrain and therefore they have minimum impact upon the environment during construction.
Stress ribbon bridge is the term used to describe structures formed by a very slender concrete deck in the shape of a catenary. They can be designed with one or more spans and are characterized by successive and complementary smooth curves. These curves blend in to natural environment and their forms, the most simple and basic of structural solutions. The stress ribbon bridge can be erected without undue pressure on the environment.
Stress ribbon bridges looks at how slender concrete deck are used in the design of suspension and cable stayed structures. It looks at their characteristic feature; their rigidity, which is mainly given by the tension stiffness of prestressed concrete decking so much so that movement caused by pedestrians or wind does not register as discomfort by users. As opposed to suspension bridges, where the cables carry the load, in stress ribbon, by tensioning the cables and the deck between the abutments, the deck shares the axial tension forces. Anchorage forces are unusually large since the structure is tightly tensioned.
2. FINSTERWALDER’S STRESS RIBBON BRIDGE THEORY
Stress Ribbon Bridge uses the theory of a catenary transmitting loads via tension in the deck to abutments which are anchored to the ground. This concept was first introduced by a German engineer Ulrich Finsterwalder. The first stress ribbon bridge was constructed in Switzerland in the 1960s. The new bridge at Lake Hodges is the sixth ribbon bridge in North America, with three equal spans of 330 feet is the longest of this type.
The stress ribbon bridge combines a suspended concave span and a supported convex span. The concave span utilizes a radius of about 8200 ft while the convex span, depending on the design speed of the bridge, utilizes an approximate radius of 9800 ft (1965).
The stress ribbon itself is a reinforced concrete slab with a thickness of about 10 inches (25.4cm). This reinforcement consists of three to four layers of 1 inch (2.5cm) to 1 ¼ inch (1.2cm) diameter, high strength steel. The layers are spaced so that the prestressing pipe sleeve couplings can be used as spacers both vertically and horizontally. To resist bending moments from traffic, the slab is heavily reinforced at the top and bottom in the transverse direction.
The high strength steel tendons are stressed piece by piece during erection to produce the desired upward deflection radius of 8200 feet (2500m) under dead load of the superstructure plus the pavement. A temporary catwalk is provided to stress the first tendons. The formwork for the bridge is hung from the tendons and then removed once the concrete is cured. Concrete is placed from the middle of the freely hanging 63 suspended concave part and continues without interruption to the supports (Finsterwalder 1965).