Road Bridge across the Uruguay River

Abstract

IntroductionThe Santo Tome -Sao Borja road bridge between Argentina and Brazil over the Uruguay River has two vehicle lanes and two pedestrian walkways.It was opened to traffic in January 1998 after 16 months of construction and consists of 33 simply supported spans of 42.5() m. The superstructure. formed by three precast post-tensioned U-shaped girders and a cast-inplace concrete deck slab. is supported by planar portal-frame piers made of two piles embedded into the sound basalt foundation. The piles of the central 18 spans (1.50 or 1.80 m in diameter. 24 m above the top of the foundation rock) were built with steel casings from a barge moored in the river. The river has a flow of about 2.5 m/s and a water depth of 10 m. Because it is difficult to perforate the foundation rock under such conditions, static and dynamic tests were performed during and after completion of construction. These tests assessed the effectiveness of the provisions adopted during the design stage in order to keep horizontal displacements along the bridge axis within acceptable values. The longitudinal layout and a typical transverse section of the bridge are given in Figs I and 2. The piers close to the river banks (piers 1-7 and 27-32) have piles of smaller diameter (1.30 m and 1.50 m. respectively) due to the considerable lateral restraint provided by a layer of sand overlaying the foundation rock. Since the piers within the course of the river do not have any lateral restraint from soils, the stiffness of piers 8 and 26 was increased byproviding them with four piles. instead of two, in a spatial arrangement. This added stiffness, although not accounted for in the original design. was aimed at limiting second-order effects in the piles at the ends of the central sector of the bridge. A typical pier in the main river channel is shown in Fig. 3.