Flux pinning in REBCO (rare-earth Ba-Cu-O) by self-assembly of BZO (barium zirconate) nanorods has emerged as one of the most prominent techniques for improving the in-field performance of 2G-HTS wire in terms of I_c and angular I_c anisotropy. In our previous study on metalorganic chemical vapor deposition REBCO wire, an optimum performance was found for 7.5% Zr at 1 T, 77 K, while further increase in Zr content resulted in I_c and T_c degradation. However, recent results indicate that the pinning performance at high Zr content actually surpasses that of the 7.5% Zr wire at intermediate and low temperatures. In-depth understanding of the effect of high Zr levels on REBCO provides a strong potential for further substantial increase in pinning performance at high Zr content if the unwanted effects can be minimized by process modification. In this study, we analyze the effect of high Zr doping levels on REBCO properties with emphasis on microstructure analysis. Structural properties as a function of BZO dopant level have been analyzed using X-ray reciprocal space maps and transmission electron microscopy, while the performance has been characterized using angular in-field I_c characterization up to 9T at temperatures of 20-77 K.

Zangmu Bridge is a concrete‐filled steel tube (CFST) arch bridge along the Sichuan‐Tibet railway in Tibet, with a main span of 430 m. Owing to the unique temperature conditions in Tibet, there have been no large‐scale experimental studies on the thermal load design of CFST bridges in this area. Therefore, to determine the thermal load calculation parameters and thermal effects of Zangmu Bridge, a long‐term continuous field test was conducted to measure the temperature variations in a test arch with the same pipe diameter. The test results were then compared with current design specifications and relevant literature. Finally, the thermal effects in a CFST arch bridge were analysed using the finite element method. According to the results, the following recommendations were made: (1) the average temperature of concrete in the pipe after the formation of concrete strength should be used to calculate the closure temperature of CFST arch bridges in Tibet; however, the standard calculation formula was still applicable; (2) the daily average temperature in extreme weather should be taken as the maximum and minimum effective temperature; (3) we presented recommended values for the influence range and gradient temperature for a single large‐diameter pipe; and (4) a refined finite element model that included the arch base should be used to verify the temperature effects during bridge design.

In order to obtain the construction technology of concrete construction at extreme low temperature and ensure the construction quality of concrete in winter, this study investigated the temperature field and compressive performance of concrete specimens cured in the laboratory at a temperature of 10°C using different thermal control measures. A finite element model of the observed temperature field was then established and shown to be in good agreement with the test results. This model was applied to analyse the factors influencing thermally controlled low-temperature concrete curing in winter. The results showed that concrete cast at 10°C using rock wool insulation covering and heated formwork for thermal control met the relevant performance requirements. Finally, the proposed temperature field model and thermal control measures were successfully applied to the construction of a concrete box girder in winter conditions.

In order to study the influence of corrosion rate and shear span ratio on reinforced concrete beam, a numerical analysis method of corroded reinforced concrete beam was put forward. Bond‐slip relationship formula between reinforcement and concrete was suggested. A three‐dimensional finite element model of corroded reinforced concrete beam was established. Calculation method of ultimate bearing capacity for reinforced concrete beam was suggested. Ultimate bearing capacity experiment on 14 corroded reinforced concrete beams with different corrosion rates and shear span ratios was carried out. Numerical analysis results and experimental results were compared and analyzed. The results show that, for reinforced concrete beams with different corrosion rates and shear span ratios, load‐deflection curve can be divided into elasticity stage and plasticity stage. With the increase of corrosion rate and shear span ratio, ultimate bearing capacity of corroded reinforced concrete beam decreased. When shear span ratio was 3.0, if corrosion rate increased by 1%, experimental value of ultimate bearing capacity decreased by 1.002 kN. When shear span ratio was 2.4, if corrosion rate increased by 1%, experimental value of ultimate bearing capacity decreased by 1.849 kN. The numerical analysis method put forward in this paper was feasible, and the suggested ultimate bearing capacity calculation method for reinforced concrete beam has a high accuracy.

To study the construction of concrete‐filled steel tubular (CFST) arch bridges in Tibet, China, the hydration‐temperature field of nonshrinkage concrete in large‐diameter CFST arch ribs was evaluated in a temperature‐testing box to simulate a low‐temperature environment. A finite element simulation was then conducted to replicate the experimental results. Finally, an improved formula with the parameters related to the diameter, the position, and the retarding time of concrete for predicting the hydration heat generated by non‐shrinkage concrete in large‐diameter CFST arch ribs cured at low temperatures was proposed. The formula results were shown to be consistent with the experimental results for low‐temperature conditions and large diameters. This research method can be extended to predict the hydration heat at all locations in different‐diameter CFSTs with different concrete mixes cured at various temperatures.

Taking the construction of a concrete‐filled steel tube (CFST) arch bridge (part of the Sichuan‐Tibet Railway) in low temperatures as the test site, firstly the deformation performance test of concrete was carried out. Following this initial testing, measurement of compressive strength and shrinkage performance was conducted in large‐diameter CFSTs under a variety of curing conditions. Experimental results showed that the expansion effect of Ca‐Mg composite expansive agent in concrete was better than that of other expansive agents at any stage. Under low‐temperature curing (0°C), the sampling strength of the large‐diameter CFSTs reached 73.5% of the design strength at 28 d in the presence of a nonthermal curing system. The design strength itself was reached, when a curing system involving a thermal insulation film was applied, and use of this film also led to improvements in concrete shrinkage. The results suggested that a Ca‐Mg composite expansive agent, combined with an insulation film curing system, should be the technique selected for concrete pumping construction of CFST arch bridges in Tibet.