Partially Precast Solutions for Medium Span Bridges: the Case of the Bridge Over the River Tâmega

Abstract

Various conditionings, such as crossing of rivers or crossing at a great height of places with bad foundation conditions, can determine the conception of bridges with span lengths in such a way that it is not practicable to build them with precast beams of the same length as the span. Indeed, beams longer than a certain limit value (normally 30 to 40 metres), are too long or too heavy, so that their transportation and erection are not feasible. Some solutions to the construction of these bridges with precast beams have been found, being an alternative for other construction methods, such as the balanced cantilever method. One possible solution may be the use of precast beams slightly less lengthened than the span, spliced after erection. When this technique is used, the longitudinal beams placed upon the supports have, normally, variable height [1, 2, 3, 4, 5]. Another possible solution is the adoption of inclined columns, with a "V" or "Y" form [6, 7, 8]. Some authors used a different solution: the cable stayed bridge [6, 9]. Solutions with exterior prestress (below the deck) have also been studied [10]. This work presents the solution used in the bridge over the river Tâmega, in Northern Portugal (E3 branch of the Interior North SCUT - IP3). At the moment this bridge is under construction, according to the solution presented here (that is, indeed, an alternative to the initial plan simply supported composite steel and concrete bridge deck with a 80m span). Due to hydraulic requirements, there must be a wide separation between the central columns of this bridge and the river banks. This fact makes it inevitable to form an 80 m central span. This article shows briefly the structural solution used in the construction of this bridge with precast beams. This work also justifies the structural conception and describes concisely the prestressing system and the sequence of construction adopted.