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The 7th German-Japanese Bridge Symposium, July 30-August 1, 2007 Osaka, JAPAN (GJBS07)

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Bridges with orthotropic steel decks have been built across the world over the past 60 years because they provide high strength and stiffness at a relatively low cost. However, a number of these bridges have sustained fatigue fractures. The investigation described in this thesis was carried out in order to identify cost-effective fatigue crack mitigation techniques by using the deck surfacing to reduce the stresses in the steel deck. Epoxy asphalt with an expanded metal mesh was investigated with small- and large-scale laboratory tests. Finite element analyses were also performed. The small scale tests conducted at different temperatures and loading frequencies showed that asphalt stiffness increased with decreasing temperature and faster loading. The expanded metal mesh in the epoxy asphalt layer noticeably increased asphalt stiffness. In the large scale tests and finite element analyses, critical loading positions to cause stress concentrations at the fatigue prone rib-to-deck welded connections were determined with different tyre configurations. The stress reduction due to the deck surfacing was estimated for the critical loading positions. The full scale test specimen was subjected to actual truck tyres. With the effectiveness of mitigation techniques for fatigue cracks on orthotropic steel bridge decks known, a probability-based fatigue lifetime evaluation methodology using Monte Carlo simulation was developed. The deck surfacing effects with seasonal and hourly temperature variations were considered. The fatigue lifetime extension using the epoxy asphalt was quantified. For a particular bridge, cost-effective maintenance scenarios were investigated. A simple calculation method for fatigue lifetime was introduced for engineers or bridge owners to assist understanding of decision support tool concepts.

Coatings are widely used to mitigate corrosion of structural steel in aggressive humid environments. However, the service life is often diminished in aggressive environments. Repair of coatings can be costly due to materials, labor and environmental controls. So, in search for novel coatings, Chemically Bonded Phosphate Ceramic (CBPC) coating was investigated for marine bridge application. The research on CBPC coating considered various exposure environments such as inland, beach, salt-fog, wet and alternate wet and dry exposure to identify the degradation mechanism. To assess the corrosion damage, the coating was evaluated by visual inspection, thickness, adhesion, microscopy and X-ray diffraction. The CBPC coating degraded initially due to alternate wet and dry exposure. The unreacted coating constituent reacted further in moist environment to form magnesium phosphate hydrate and enhanced bulk coating porosity. That facilitated moisture to the coating substrate and formed apparent protective iron phosphate hydrate by interaction with steel substrate to the coating constituents. Passive-like conditions were observed in wet test of chloride-free solutions for the formation of hydration product of magnesium but that type of hydrate was not identified in chloride solution for the apparent high solubility. The resolved coating impedance parameters were introduced to characterize the bulk ceramic degradation. The solution resistance did show a decrease for all samples due to leaching of minerals from the bulk material. The resolved pore resistance did not show any distinct change, though there was an indication of bulk coating degradation by MIP. Water saturation level during exposure was also calculated from the resolved capacitance. An approach was proposed to transfer the pre-exponential term, Yo to coating capacitance, CC for ceramic coating. The estimated value of the coating capacitance from the developed technique indicated early saturation with water during exposure due to the porosity. So, the extent of CBPC coating permeability and degradation could not be resolved only by conventional analysis approaches. However, the formation of iron hydrogen phosphate hydrate and iron phosphate hydrate from reaction of unreacted coating constituents was thought to provide apparent enhanced corrosion protection but there is a probability of steel substrate corrosion in extended exposure in humid environment.

This master thesis content is alternative design of one span single-railed steel bridge. The bridge is located in km 44,179 on the track Jaroměř - Dvůr Králové. Crossing barrier is roadway I/33. The teoretical distance between supports is 42 m. Main bearing structure is designed as Langer beam. Structure consist of beams, arcs, suspenders, bridge deck with longitudinal and transversal bracings. Elements of the structure are made out of steel S355J2+N, S235J2+N, S355NL. The bridge is designed according to current standards ČSN EN.

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