Search

U75V rail steel is widely used in railways in China, including train tunnels in mountain and subsea projects, where it suffers from selective corrosion near welded joints. To ensure adequate railway service life, this study examines the effect of the normalisation process on the electrochemical behaviour of U75V rail-welded joints (URWJs) manufactured by flash butt welding (FBW) using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Corrosion morphology and elemental distribution analyses were performed to investigate the corrosion behaviour. The results show that the grains within the joints became finer and more homogeneous after normalisation, with a lower corrosion rate and higher corrosion resistance. It is demonstrated that fewer corrosion products were formed on the surface of the normalised joints after electrochemical test, and the corrosion resistance of the URWJs improved, owing to the formation of denser passivation films caused by normalisation. These mechanisms of corrosion response help explain corrosion failure in railway lines, as well as also help optimise the welding process and normalising processes to obtain a corrosion-resistant microstructure and ensure the quality of welded joints. [ABSTRACT FROM AUTHOR]

GJ steel is a high-performance steel manufactured in China, and its thick plates are widely used in building structures. The first companion study examined the material properties of the thick GJ steel plates (t ≥ 60 mm). This study focuses on the mechanical properties of butt welds in thick GJ steel plates (t ≥ 60 mm). Monotonic and cyclic tests were conducted on butt-weld specimens made of 60-mm and 100-mm thick Q345GJ steel plates in the longitudinal and transverse directions. In addition, the layered specimens obtained from five different thickness locations were tested. Based on the cyclic test results, the Chaboche constitutive parameters were calibrated and verified via the finite element analysis (FEA). Moreover, the differences in the static and cyclic mechanical properties of the base metal and butt welds were analysed. Compared with the base metal, the static tensile strength and hysteretic energy dissipation under the same cyclic loading protocol were better in the weld specimens; however, their ductility was significantly lower. Furthermore, the distribution of the mechanical properties along the thickness direction was more uniform in the weld specimens. Moreover, the weld specimens had higher yield surface reduction ratios. However, their initial and final yield surface sizes were larger than those of the base metals. [Display omitted] • The mechanical properties of butt welds in 60-mm and 100-mm thick Q345GJ steel plates were tested using layered specimens. • Totally 160 weld specimens were tested under monotonic and five different cyclic loading protocols. • The static and hysteretic properties of the butt welds and base metals were compared. • The constitutive parameters of the Chaboche model were calibrated and validated against test results. [ABSTRACT FROM AUTHOR]

Rehabilitating corroded or seismically damaged reinforced concrete (RC) bridge columns often involves replacing the longitudinal steel rebar. Welded joints offer a practical and efficient in-situ solution for connecting new rebar segments to existing undamaged rebar, even with irregularities in the steel reinforcement. However, traditional approaches to rebar joint welding have paid little attention to the overstrength of the welding seam, which can result in a brittle response. Properly designing such joints should aim for a ductile rebar failure. However, in-situ rehabilitation solutions often require reducing the seam length to save time and material costs and, not secondarily, avoiding the plastic hinge formation in the rehabilitated column. Therefore, providing the seam with adequate overstrength is crucial to achieving a ductile failure of the welded joint. This study presents an experimental investigation into the most effective methods for connecting existing and new rebar segments through welding, addressing on-site welding challenges such as limited operational space and weld orientation. Over 100 tensile tests have been conducted at Fuzhou University's laboratory in China to understand the response of nine welded joints. Among indirect butt joints, the study identifies two performance groups based on the ductile failure rate as the welding seams reduce. The symmetry of the joint and the presence of additional direct butt welding also in asymmetric joints can significantly improve the joint performance, determining a ductile failure with minimal welding lengths. In a second step, following a probabilistic approach, the study assesses the overstrength of indirect butt joints as a function of seam length for the two identified performance groups. Empirical failure probabilities of the rebar and the seam are estimated to fit probability density functions representative of the tensile strength of the rebar and the seam. Based on a target reliability class, the overstrength factors are estimated. • Tensile tests on 152 rebar welded joints. • Two groups: brittle (prevalent weld failure) and ductile (prevalent rebar failure). • Optimal configuration is R4V*: indirect butt joint with V coupler and additional butt weld. • R4V* has the minimum welding length with optimal ductility. • Probabilistic estimation of overstrength factors to prevent weld failure. [ABSTRACT FROM AUTHOR]

Bridge weathering steel produced in China has been used in bridges worldwide. Bridge weathering steel Q345qNH is the most common steel grade used in China and for export, the fatigue crack growth thresholds and fatigue crack growth rate (FCGR) parameters of Q345qDNH are investigated in this paper. The FCGR tests are conducted on 9 compact tension (CT) specimens of base metal and butt welds respectively, the fatigue crack growth threshold tests are conducted on 3 CT specimens of base metal. The fatigue crack growth threshold decreases as stress ratio increases, Q345qDNH has considerably higher fatigue crack growth thresholds than Q345qD and universal thresholds given in BS7910. Two data processing methods are employed to calculate characteristic FCGR parameters. The FCGR parameters determined by small sample method are more conservative than those obtained by group sample method. The FCGR of butt weld increases faster than that of base metal as stress intensity range increases, therefore butt weld is more brittle than base metal. Q345qDNH has slower FCGR than Q345qD and the universal parameters given in BS7910, hence Q345qDNH has better fatigue resistance. The fatigue crack growth was numerically simulated, the largest difference between predicted fatigue life and tested fatigue life is 11.3%, therefore fatigue life can be predicted reasonably accurately by numerical simulation on the basis of measured FCGR parameters, which illustrates the potential and effectiveness of numerical simulation for fatigue assessment of complex bridge structural details based on fracture mechanics and the significance to obtain accurate FCGR parameters. • Fatigue thresholds and FCGR parameters of Q345qDNH have been measured. • Bridge weathering steel Q345qDNH has proved to have excellent fatigue resistance. • This paper provides essential data for fatigue assessment of bridges using Q345qDNH. • Fatigue life of CT specimens are accurately predicted by numerical simulation. [ABSTRACT FROM AUTHOR]

• The plastic zone in the weld metal, fusion zone, heat-affected zone, and base metal was measured through a digital microscope, and the plastic zone length a P versus the distance from the weld centre was presented. • The fracture toughness of the four zones in the Q235 butt weld joint was obtained and it was found that the weld metal had the highest fracture toughness value around 130 MPa√m, followed by the heat-affected zone of 109 MPa√m, the base metal of 83 MPa√m, and the fusion zone of 77 MPa√m. • The fracture mechanism of the welded joint was revealed, indicating that the weld metal, fusion zone, heat-affected zone, and base metal underwent an elastic–plastic fracture. Yielding loads (P y) from small three-point-bending (3-p-b) specimens with notch tips in the heat-affected zone, fusion zone, weld metal, and base metal of Q235 (common carbon steel in China) were used to estimate the corresponding fracture toughnesses. To model the elastic and plastic fracture around the Q235 welded joint, the boundary effect model initially developed for quasi-brittle fracture of heterogeneous solids with a large crack-tip fracture process zone was adopted in this study, bypassing the stringent ASTM standard requirements on the specimen size, initial crack length, and un-notched ligament. It was found that the weld metal had the highest fracture toughness value around 130 MPa√m, followed by the heat-affected zone of 109 MPa√m, the base metal of 83 MPa√m, and the fusion zone of 77 MPa√m. Microstructures and notch-tip plastic zones in each section of the welded joint were measured and used to explain the fracture toughness measurements. [ABSTRACT FROM AUTHOR]

The Tianjin Haihe movable bridge in China has the largest span among similar bridges in Asia. Owing to the dual characteristics of being both a bridge and heavy machinery with mechanical, hydraulic, electric and intelligent control devices, the construction of its steel box girder requires appropriate installation and control technology. Because of the stringent on-site navigation restrictions and blockage conditions, as well as mechanical characteristics during construction, a semi-supported cantilever installation and erection scheme is proposed, in which a bridge-erecting machine, temporary steel pipe support, bridge cantilever construction and other traditional methods are used in combination. Unlike traditional bridge closure technologies, new alignment closure and central locking closure control technologies are employed. The latter requires that the locking device be precisely assembled and adjusted to be horizontal for the suitable operation of the central locking equipment. The execution of this construction practice shows that the technology is feasible and effective. [ABSTRACT FROM AUTHOR]