ABSTRACT
A detailed riparian field study to assess the importance of bedrock groundwater in streamflow processes was established in the headwaters of the Afon Hafren, mid-Wales, UK. Results from this study identified distinct groundwater horizons close to the stream channel. Different flow pathways and travel times resulted in a different chemical character of groundwaters in these different horizons. Groundwater discharge from these horizons into the stream was by piston displacement in response to recharging rainfall higher up in the catchment. Groundwater upwelling into the soils indicated soil water to be sourced from both groundwater and rainfall. Soil waters closest to the stream (ca. 25 m) were predominantly groundwater controlled and may be the major source for ecologically toxic soil components such as aluminium entering the river. The role of groundwater in upland streamflow generation is far more complicated than previously considered and has important implications for upland water quality.
Songpu Bridge is a double-deck riveted continuous truss bridge carrying highway on the upper deck and railway on the lower deck. The 419.6 m long bridge, which consists of two 96 m + 112 m continuous truss girder, was completed in 1976. In 2012, a new railway bridge was built nearby and the railway on Songpu Bridge stopped running. To meet the increasing traffic demands and make the most of the load capacity of the trusses, the upper deck of the bridge will be widened to 24.5 m to carry 6 lanes and the lower deck will be reconstructed to carry pedestrian and bicycle ways.
Two main trusses will be retained and used still as the main load-bearing elements. The upper deck is replaced by an ortho-composite-slab which consists of a reduced orthotropic steel deck and a concrete layer. The concrete layer is 12 cm in thickness, covered with 6 cm thick asphalt pavement. The steel deck plate is 8 mm in thickness, stiffened by bulb plates. The long cantilever of the top slab after the widening is supported by inclined bracings at each truss joint. The ortho-composite-slab is to be connected to main trusses as a whole in the rebuilding plan. The composite deck will be bolted to upper chords and fixed at joints by steel-concrete composite connectors. The lower deck is rebuilt by orthotropic steel deck supported by bearings on bottom crossbeams between main trusses.
Some truss diagonals, vertical sticks and joints need to be strengthened due to load and stability requirements. The bottom chords, the diagonals and the vertical sticks at the side-bearing will be strengthened by sticking steel plates at their flanges with high-strength bolts, and the related gusset plates at the joints will be treated with the similar way according to the structure details which related. The sticking steel plates on the gusset plates will be extended a certain length to the diagonal flanges to ensure that enough high-strength bolts can be placed. The vertical sticks will be strengthened by sticking steel plates in their flanges with high-strength bolts to meet the stability requirements of compression members. The stiffening chords at the mid-supports are strengthened by composite section which can effectively enhance these members’ ability to bear compressive stress without affecting the force condition of the whole structure.
The three piers with foundations can continue to be used without strengthening.
