Shield-driven tunneling has been playing a significant role recently as a standard method in urban tunnel construction. As the main road tunnels have to be connected with ramp tunnels efficiently, engineers have sought to develop steel-concrete composite structures using the longitudinal ribs of the steel segment as shear connectors. However, the shear connector at the connection between different types of members has hardly been studied and its stress transfer mechanism is not well understood. The authors carried out fracture experiments with scale down models for this connection, and examined the stress transfer mechanism and the shear transfer capacity carried by shear connectors and studs. A stress-transfer model for easily calculating shear transfer capacity was developed and verified through the comparison with experimental results and analytical results based on the nonlinear finite element method.

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Various types of fatigue cracks have been found in steel bridges. To maintain steel bridges, repair and retrofit methods of such fatigue cracks have been developed. The authors developed a technique which generates plastic deformation of steel surface near the crack in order to close crack opening by an impact air tool. This method is called Impact Crack Closure Retrofit treatment (ICR treatment). Plate bending fatigue tests of out-of-plane gusset specimens were carried out. Fatigue cracks at turn-around welds and those which have propagated 10 and 20 mm were ICR-treated. Fatigue test results showed significant improvement in the fatigue life of specimens due to ICR treatment.

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