Abstract: Varying temperatures significantly affect long-span cable-stayed bridges. However, quantitative studies on their temperature behaviors are limited. Existing studies focus on 2D or 3D models of bridge segments only, exclude cables from heat-transfer analysis, and utilize inaccurate environmental conditions. For the first time, this study comprehensively and accurately investigates the global 3D temperature distribution of long-span cable-stayed bridges by integrating the heat-transfer analysis and field monitoring data. A navigation channel bridge of the Hong Kong‒Zhuhai‒Macao Bridge is used as the testbed. A global 3D refined finite element model of the entire bridge is established. The external thermal boundary conditions of the outer surfaces of the structure are carefully determined based on the real-time ambient temperature, wind, and solar radiation, which are tailored for each surface to reflect the influence of the geometric configuration. The internal thermal boundary conditions of the inner surfaces of the box girder and tower are dependent on the measured ambient temperature, considering the vertical temperature difference of the girder and the uniform temperature inside the tower. Then, the numerical heat-transfer analysis and field monitoring data are integrated to calculate the detailed temperature distribution of the entire bridge in different seasons. Results show that ambient temperature, wind, and solar radiation significantly affect the temperature distribution. For the girder, the vertical temperature difference is significant throughout the year, and the transverse temperature difference is nonnegligible in winter and summer, while the longitudinal temperature difference is trivial. The internal temperature of the tower remains stable owing to the insulation of the concrete. The temperatures of the cables vary from each other, which may cause stress redistribution within the structure. The calculated temperatures are in good agreement with their measured counterparts. The temperature results will be used to calculate the thermal-induced responses in the companion paper in a unified manner.

Abstract: In recent years, there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes. However, the increased size makes tunnel support more difficult. Unfortunately, there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel, while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports. Based on excavation compensation method (ECM), model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out. The results indicate that during excavation of super-large-span tunnel, the stress and displacement of the shallow surrounding rocks decrease, following a step-shape pattern, and the tunnel failure is mainly concentrated on the vault and spandrel areas. Compared with conventional anchor cable supports, the NPR (negative Poisson's ratio) anchor cable support is more suitable for the initial support stage of the super-large-span tunnels. The tunnel support theory, model test materials, methods, and the results obtained in this study could provide references for study of similar super-large-span tunnels.

Abstract: Abstract. Ocean alkalinity enhancement (OAE) is a proposed marine carbon dioxide removal (mCDR) approach that has the potential for large-scale uptake of significant amounts of atmospheric carbon dioxide (CO₂). Removing anthropogenic legacy CO₂ will be required to stabilise global surface temperatures below the 1.5–2 ^∘C Paris Agreement target of 2015. In this chapter we describe the impacts of various OAE feedstocks on seawater carbonate chemistry, as well as pitfalls that need to be avoided during sampling, storage, and measurement of the four main carbonate chemistry parameters, i.e. dissolved inorganic carbon (DIC), total alkalinity (TA), pH, and CO₂ fugacity (fCO₂). Finally, we also discuss considerations in regard to calculating carbonate chemistry speciation from two measured parameters. Key findings are that (1) theoretical CO₂ uptake potential (global mean of 0.84 mol of CO₂ per mole of TA added) based on carbonate chemistry calculations is probably secondary in determining the oceanic region in which OAE would be best; (2) carbonate chemistry sampling is recommended to involve gentle pressure filtration to remove calcium carbonate (CaCO₃) that might have been precipitated upon TA increase as it would otherwise interfere with a number of analyses; (3) samples for DIC and TA can be stabilised to avoid the risk of secondary CaCO₃ precipitation during sample storage; and (4) some OAE feedstocks require additional adjustments to carbonate chemistry speciation calculations using available programs and routines, for instance if seawater magnesium or calcium concentrations are modified.

Abstract: In recent years, efforts have been devoted to utilizing terrestrial laser scanning for bridge spatial performance inspection, but they are still restricted to small or medium-span bridges, like some historical heritages. Due to the large-scale dimensional features of long-span bridges, applications of 3D point cloud techniques still remain challenging, such as the extra-long scan range and extreme-small incidence angle when scanning a bridge with a span over 1000 m. Moreover, rare attempts can be found for the performance evaluation of point cloud registration methods for long-span bridges as well, which is a critical basis for further spatial deformation recognition on the point cloud data. Hence, in this study, a cross-evaluation of three iterative closest point (ICP) registration methods is conducted for long-span suspension bridges, namely, traditional ICP, kd-tree-based ICP, and feature point-based ICP algorithms. We conducted field laser scanning on the Ma’anshan Yangtze Bridge, an 1880 m long suspension bridge located in China. The results show that the feature point-based ICP algorithm outperforms the other two in terms of convergence rate and execution time for a single iteration due to the smaller number of registration points compared to the other two algorithms. Moreover, it also gives more precise values in terms of bridge tower spatial deformation identification. Meanwhile, due to efficient data organization, the kd-tree-based ICP algorithm takes less time for a single iteration than the traditional ICP algorithm. Finally, two suggestions for algorithm improvement in terms of efficiency optimization and accuracy improvement of long-span bridge deformation analysis are proposed based on the assessment results.

Abstract: Overhead line icing may threaten the operational stability of power grid. In this paper, a detection method for equivalent ice thickness of 500 kV overhead lines based on axial tension measurement was proposed. Firstly, according to the tension of insulator string when the transmission lines are not covered with ice, the horizontal distance from the lowest point of the transmission line to the tower on the side where the tension sensor is installed is calculated. Secondly, the state equation of the transmission line in the whole tension section is established. Then, the state equation is solved by iterative method. The initial ice thickness is taken as 0 mm. The ice thickness when the iteration value of tension F _i is equal to the measured value of tension F is taken as the equivalent ice thickness of transmission lines. The actual cases of single span transmission line and multi-span transmission line were used for verification and application effect analysis of the proposed method. The results show that the detected results of this method were consistent with the artificial ice observation values of typical 500 kV single span and multi-span transmission line cases. The accuracy of the proposed method can be further verified through finite element simulation analysis. The variation trends of the detected ice thickness is consistent with the icing conditions created by the meteorological factors during the same period, and can be verified by the icing photos captured on site.