The heat-affected zone (HAZ) is an unmelted region of a welded joint that has changed in material properties because of high temperatures during the welding process. HAZ has a lower strength than the base (parent) material (BM) and the weld metal (WM). The lower material strength is more significant if BM is made of high strength steel and the undermatching filler metal is used. Therefore, the constitutive model of HAZ is essential for predicting the mechanical behaviour of the welded joint. In this paper, a method for determining the true stress–strain relationship of HAZ is proposed. The effect of the transverse constraint on the longitudinal deformation of HAZ imposed by BM and/or WM is eliminated by a linear modification factor correlating to the true strain. Standard tensile coupon tests were used to obtain the constitutive model of HAZ using digital image correlation (DIC). The modification factor proposed for reducing the true stress is calibrated based on finite element analysis (FEA). The modified constitutive model of HAZ is validated against the experimental results obtained by DIC. The validated HAZ material property can be used in advanced numerical simulation of welded joints.@en

Ballast layer defects are the primary cause for rapid track geometry degradation. Detecting these defects in real-time during track inspections is urgently needed to ensure safe train operations. To achieve this, an indicator, the track degradation rate (TDR) was proposed. This rate is calculated using track geometry inspection data to locate and predict railway-line sections with ballast layer defects. The TDR is determined by the monthly standard deviation of the rail longitudinal level, which is one aspect of track geometry. The Ballast Layer Health Classification (BLHC) is designed by assessing the two successive TDRs before and after track geometry maintenance actions. The BLHC is used to categorize the conditions of the ballast layer, including normal periodic deterioration, abrupt deterioration, effective maintenance, rising deterioration, and severe deterioration. Both the TDR and BLHC were validated through field assessments of ballast layer conditions, where the two indicators were found to be effective in revealing defects. The results indicate that the TDR is sensitive to ballast layer defects, while the BLHC can quickly identify the location of these defects. Consequently, the BLHC can provide real-time guidance for ballast layer maintenance.@en

Strengthening fatigue damage of orthotropic steel decks (OSDs) needs to comprehensively consider the strengthening effect and the dead weight introduced during the strengthening process, especially for OSDs in super large-span bridges or old renovated bridges, where the dead weight cannot be significantly increased during repair and maintenance. This paper proposed a new CFRP prestressed reinforcement method, that does not significantly increase dead weight while effectively inhibiting fatigue crack growth. The strengthening effects of various strengthening methods on the fatigue crack propagation of rib to deck joint in OSDs were compared. Besides, the strengthening effects of different crack sizes were also analyzed. The results showed that the proposed method is effective in reducing fatigue damage at the rib to deck joint in OSDs.@en

This paper reports an investigation on the tensile resistance of fully-penetrated butt-welded connections of (ultra-)high-strength steels considering the strength softening of the heat-affected zone (HAZ) and the strengthening due to the transverse constraint. Firstly, a parametric study is carried out to analyse the tensile behaviour of fully-penetrated butt-welded S700 connections using validated finite element (FE) models. Based on the FE results, the effect of the investigated parameters on the ultimate resistance of the connections is quantified. Consequently, a Macro prediction model is proposed, neglecting the detail of HAZ inhomogeneous microstructures but considering five design parameters, which are the width and thickness of the specimen, the width of HAZ, the softening ratio, and the matching ratio. Finally, the proposed Macro model is validated against the available experimental data of fully-penetrated butt-welded (ultra-)high-strength steel connections in literature. The results show that the Macro model is proven successful in accurately quantifying the effect of HAZ, concerning the strength softening and the transverse constraint strengthening, on the tensile resistance of fully-penetrated butt-welded (ultra-)high-strength steel connections. It is also found that 157 and 96 out of 185 experiments are predicted within a 5% deviation range using the Macro model and prEN 1993-1-8:2021, respectively, proving that the Macro model is more consistent with the experimental data compared to the prediction of prEN 1993-1-8:2021.@en

The overall competitiveness of offshore wind turbine towers is significantly influenced by the selection of the connection. The following three types of connections: a conventional bolted ring flange (RF) connection, ring flange connection with defined contact surfaces (RFD), and C1 wedge connection (C1-WC) are considered. A quantitative comparison is made to enhance performance in a specific condition and enable further optimization of these connections in engineering practices. The study compares the tensile behaviour and fatigue performance of these connections by validated finite element (FE) simulation and analysis. The proposed FE modelling is based on a realistic geometry including all contacts present in the connections, steel full-range stress–strain relationship and ductile damage model. The efficiency and accuracy of the FE models are validated through the comparison with the performed tests. Then, a series of parametric FE analyses are carried out to examine the impact of the applied boundary conditions, bolt pretension level, and steel grade on the behaviour of connections. Load-displacement curves, bolt evolution curves, and stress responses are analysed to compare their tensile behaviour. The effectiveness of conventional segment specimen testing is evaluated thoroughly. For the fatigue performance of connections, the results indicate that the segment specimen testing substantially underestimates the fatigue performance of C1-WCs. This discrepancy is essential to be considered in the tower design. It is also noted that C1-WCs are rather insensitive to the variation of pretension force level, which show superiority to avoiding the difficulties associated with typically bolted joints. This research provides in-depth knowledge for the practical application of such connections and further optimization.@en

In practice, the assessment and treatment of rail corrugation are quantitatively based on the corrugation depth. Wheel–rail vertical forces (WRVF), as a direct reflection of wheel–rail interaction, can give expression to the corrugation depth and thus serve as a key parameter for assessing the corrugation. In this paper, we propose an evaluation method for rail corrugation based on the WRVF. First, a 3D wheel–rail dynamic finite element (FE) model was developed with typical parameters of CRTS II slab track and CRH3 vehicle for high-speed railways in China. The accuracy of the model was then validated with the measured WRVF data in the field. Second, using the validated model, the time–frequency domain distribution of WRVF (vehicle speed: 300 km/h) was obtained with consideration of the corrugation wavelength in the range of 40–180 mm. The non-linear least squares method and rational equation were used to fit the function between the large value of WRVF and the corrugation depth value under the conditions of different corrugation wavelengths. Next, effects of the Pinned–Pinned resonance frequency and vibration mode on the fitted parameters were analysed, by which an indicator for corrugation treatment (grinding) was proposed. Finally, the indicator was applied in the monitoring of rail corrugation for high-speed railway lines in the field. The results show that the misjudgement rate of rail grinding decisions (using the proposed indicator) is low with the accuracy at 92.5%. The proposed method can provide a basis for the rail corrugation evaluation and grinding decisions-making.@en