Monitoring of a Swedish Integral Abutment Bridge
Abstract One of the most commonly discussed problems regarding bridges with integral abutments is the influence of longitudinal elongation of the superstructure as a result of seasonal temperature variations. A bridge built with integral abutments is often supported by a row of piles made of steel or concrete. The longitudinal elongation of the superstructure induces a displacement and a rotation at the top of the pile, which in turn may cause strains that exceeds the yield strain. Such seasonal variations may lead to low-cyclic fatigue failure in the pile. Therefore, it is of great interest to investigate the amplitude of these strains, as well as the general behaviour of the bridge. In 2005, the European R&D project, INTAB (RFSR-CT-2005-00041, “Economic and Durable Design of Bridges with Integral Abutments, 2005–2008”) was started. Within the INTAB project a composite bridge was built and monitored in Northern Sweden.
Design Temperature Load Spectrum for the Fatigue Verification of Composite Bridges with Integral Abutments
For (low cycle) fatigue design of steel foundation piles of composite bridges with integral abutments, not only traffic loads but also temperature loads as well have to be considered. Regarding this temperature fatigue load case, no specific rules and recommendations are given in EN 1991-2 (Eurocode 1: Actions on structures—Part 2: Traffic loads on bridges). The current paper proposes a simplified temperature load spectrum, to be used for (low cycle) fatigue design of constructional steel members of composite bridges with integral abutments. Therefore, effective bridge temperature hydrographs (100 year period) are derived by means of FE-calculations for various locations based on actual weather data. They are converted into pile strain hydrographs, taking into consideration residual strains and plastic deformations. The calculations are verified by laboratory low cycle fatigue tests and monitoring results. Finally, a design temperature load spectrum is proposed, based on classified temperature variations.
Microstructure of the solder-casting zone in bridges of dental gold alloys.
The composition and structure were studied in the cast and in the solder of bridges which had failed clinically. Both materials were gold alloys but with different contents of Pt, Ag and Zn. The metallographic investigation revealed defects mostly in the solder, situated in the subsurface layer. SEM studied of the fracture surface revealed large porosites and a structure of dense parallel lines--striations--, indicating that the material had failed from fatigue. The materials in the fractured bridges were identified by micro-probe measurements. It was stated that cast material and solder material used together, were of different composition.