In this study, relative load-carrying capacity (RLC) evaluation system in which the change of load-carrying capacity of a bridge structure can be estimated through the variation of the dynamic property, which is induced by the stiffness change due to the deterioration of the bridge, by using ambient traffic-induced vibration was proposed. The system uses the natural excitation technique in conjunction with the eigensystem realization algorithm for identification of modal parameters. Indoor test using a truss-typed model bridge and field measurement were performed to verify the suggested system and it was shown that the RLC estimation system is suitable for the safety assessment of bridge structures in a simple and efficient manner.

During repair welding of steel bridge under service load, vibration occurs due to the dynamic loads like wind and vehicles, etc. However, the effect of vibration during welding on the fatigue strength of weldments is not yet clearly understood. In this paper, the effect of vibration during welding on the fatigue strength of structural steel weldments was investigated in order to improve reliability in the repair welded joints of steel bridge. The base material used in this investigation was SM 490A steel of weldable grade. Flux Cored Arc Welding (FCAW) process was used to fabricate the single ‘V’ butt joints. Welding was performed on the steel under the mechanical vibration of given frequency. The applied frequency was resonant frequency. Also, weldments under no vibration during welding were prepared. Fatigue tests were conducted using a servo hydraulic controlled 50tonf capacity UTM with a frequency of 5Hz under constant amplitude loading. Effect of vibration during welding on the fatigue strength of weldments was analyzed in detail.

No abstract

TMCP steels produced by thermo-mechanical control process are now spot lighted due to the excellent combinations of strength, toughness and weldability. Recently, in Korea, high strength SM570-TMCP steel whose tensile strength is 600MPa has been developed and applied to steel structures due to its excellent nature. But, for the application of the TMCP steel to steel structures, it is necessary to elucidate not only the material characteristics but the mechanical characteristics of welded joints. In this study, high temperature tensile properties of the SM570-TMCP steel were investigated through the elevated temperature tensile test and the characteristics of residual stresses in welded joints of the TMCP steel were studied through the three-dimensional (3-D) thermal elastic-plastic finite element (FE) analysis on the basis of mechanical properties at high temperatures obtained from the experiment. The results are then compared with the conventional quenched and tempered high strength SM570 steel.

ABSTRACT： In this study, the Charpy impact test along with metallurgical observation was conducted to evaluate low temperature impact toughness of structural steel welds with different welding processes to find out the optimal welding process to guarantee the required impact toughness at low temperatures. The welding processes employed are shield metal arc welding (SMAW) and flux cored arc welding(FCAW), which are commonly used welding methods in construction. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. To investigate the impact toughness at low temperatures of the steel welds, specimens were extracted from the weld metal and the heat affected zone. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The low temperature impact performance was evaluated based on the correlation between the absorbed energy and the microstructure. Analysis of the results showed that the optimal welding process to ensure the higher low temperature impact toughness of the HAZ and the weld metal is SMAW process using the welding consumable for steels targeted to low temperature use.