Concrete Fin-Back Bridge in Usa.

Abstract

The Paper describes the design and construction of a type of bridge-namely a prestressed concrete fin-back-which might be claimed to be the first of its kind ever built. The Paper begins by explaining the structural concept. It goes on to refer to several similar bridges which have been built and others which have been proposed, in order to justify the bridge's claim to be original. The background to this particular project and the considerations leading to the adoption of the design are then explained. Finally, the Paper describes, in some detail, the design of the bridge and its construction, concluding that the concept is extremely economical in materials quantities and can be correspondingly competitive in price if the details of the design provide for a logical construction sequence. ConceptA bridge deck which is fully continuous for self-weight and live load is required to resist a much greater moment at the supports than at the mid-span sections. This is particularly true if the deck is built by the balanced cantilever method.2. Conventional wisdom is that the most efficient and economical way of achieving this in prestressed concrete box-girder construction is progressively to increase the thickness of the bottom flange and also, in longer spans, the depth of the section towards the pier. Each of these also serves to lower the neutral axis of the section, and hence to increase the eccentricity of prestressing tendons. However, in a typical box-girder section, the neutral axis will remain well above mid-height, and therefore it will still be an inefficient prestressed section.3. Such variation in the depth of the section also has three potential disadvantages (a) it reduces the clear headroom under the bridge adjacent to the piers (b) it complicates and hence increases the cost of balanced cantilever construction (c) it may, in certain circumstances, be considered aesthetically undesirable; certainly in conjunction with the popular sloping external webs, it leads to unfortunate 'fish-belly' effects on the soffit. 4.The fin-back is a logical attempt to achieve the benefits of a variable depth section without these attendant disadvantages. Rather than increase the effective depth of the section by lowering the soffit, the web or webs containing the prestressing tendons are extended upwards to project above the bridge deck, accommodated within the median or the outer verges of the roadway, while the soffit remains parallel to the deck. The greatly increased efficiency of the section in the regions of negative moment over the piers leads to very significant economies in Ordinary meeting 5.30 pm.

Comportamiento estructural y criterios de diseño de los puentes extradosados: visión general y estado del arte

“…Puente Odawara Blueway en Japón, 1994 (Kasuga, 2006) Figure 4. Odawara Bridge in Japan, 1994 (Kasuga, 2006) José Benjumea, Gustavo Chio, Esperanza Maldonado Ganter Bridge served as inspiration for the construction of other similar bridges, such as Barton Creek Bridge (United States, 1987(Gee, 1991 and Papagayo Bridge (Mexico, 1991(Fernandez, 1999, considered as a Fin Back Bridge and the Socorridos Bridge (Portugal, 1993(Reis & Pereira, 1994, identified as a Cable Panel Bridge. Some disadvantages such as the impossibility of replacing strainer wires and the additional costs for concrete walls uplifting, have not allowed a spread use of such typologies.…”