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Because of excellent mechanical properties, thermal insulation and ideal radiation resistance, polyimide (PI) is one of the best choices as a flexible solar backsheet in photovoltaic systems. In this study, accumulation characteristics of surface charge of PI backsheet under temperature-controlled corona polarization were investigated both theoretically and experimentally. In order to investigate the surface charge accumulation of PI backsheet under the effect of different temperatures, finite element method (FEM) was used. The mechanisms by which the temperature influenced accumulation and decay processes of the surface charge of the PI backsheet were investigated. The results show that the carrier mobility of PI backsheet increased in the stages of charge accumulation and charge decay, which then has an indirect effect on the dynamic characteristics of the surface charge. Charge accumulation decreases with the increase of temperature, and both accumulation process and decay process occurred simultaneously. The results of this study provide theoretical support for the modification of PI backsheet. At the same time, a practical theoretical method for modeling and simulating the charge diffusion of insulating PI backsheet under the influence of temperature was explored. [ABSTRACT FROM AUTHOR]

Space charge behavior in polymeric materials is of interest to the electrical engineering community and has significant effects on the behavior of the polymers that are used in gas-insulated transmission lines (GILs). For example, the space charge in certain insulating materials can cause severe distortion of the electric field that may even lead to breakdown of the materials. It is therefore important to understand the trapped charge distributions in these materials because they can be used as novel indicators for effective evaluation of the aging status and the electric withstand strength of these insulating materials. This paper addresses recent developments in the modeling of charge transport in polymers for use in GIL applications. A numerical model of bipolar charge transport in polymeric insulators is presented in this paper. This model was studied based on use of multiple trap levels and consideration of symmetrical parameters for the generation and transport of electrons and holes. [ABSTRACT FROM AUTHOR]

The concrete-filled wide rectangular steel tube (CFWRST) columns, with the aspect ratio of cross-section greater than 2.0, have attracted much attention in practice. Existing studies on the concrete-filled rectangular steel tube (CFRST) members have shown that the aspect ratio of cross-section is a main parameter controlling their behaviors under various loads, which means that the behaviors of CFWRST columns may be different from the common CFST members (the aspect ratio of cross-section not greater than 2.0) considered in existing studies. The behaviors of CFWRST columns under the combined constant axial compression and cyclic lateral loadings were investigated in this paper. Six full-scale columns were tested, with which the failure modes, hysteresis curve, skeleton curve, ductility, lateral stiffness and energy dissipation capacity of the specimens were analyzed and discussed in detail. For all tested specimens, the ductility indexes are between 2.028 and 3.433, and the equivalent damping ratios usually exceed 0.3 at the last of loading cycle. The finite element model was also developed and validated using the test results, and the parametric analyses were carried out with the influences of main parameters discussed. Furthermore, comparisons between the predictions of the solution of EC4 for CFST beam-columns and test results show that the solution of EC4 can provide safe predictions for the CFWRST columns under constant axial compression and cyclic lateral loading. [Display omitted] • The tests on CFWRSTs subjected to the constant axial compression and cyclic lateral loading were carried out. • The failure mode, hysteresis curve, ductility, stiffness and energy dissipation capacity of the CFWRSTs are investigated. • FE models considering material damage are established using ABAQUS. • The seismic behaviors of CFWRSTs with different parameters are reported based on FE analyses. • The M-N relationship of EC4 is examined. [ABSTRACT FROM AUTHOR]

Steel-concrete composite frames have been widely used in high-rise buildings. To improve the utilization efficiency of the indoor area, irregular-shaped concrete-filled steel tubular (CFST) columns were proposed for an alternative of the traditional rectangular CFST columns. In this paper, the L-shaped multi-cellular CFST (LM-CFST) frame was proposed, consisting of LM-CFST columns and H-shaped steel beams. Firstly, four LM-CFST frames were tested under combined axial compression and cyclic lateral loads. The local buckling was observed at both the top and bottom ends of the column, and fracture of steel occurred when the drift ratio was large. The hysteresis curves were spindle-shaped with the ductility indexes of 2.61–3.24. Then, a refined finite element model was established and validated against the test results. A parametric analysis was conducted to study the effect of axial compression ratio, web cell length, concrete strength and steel tube thickness on the seismic performance of LM-CFST frames. It was found that the axial compression ratio could affect the seismic performance of LM-CFST frames significantly, while the concrete strength had little effect. Finally, the compression-bending capacities obtained from the sectional analysis method specified in EC4 were compared with those obtained from tests. It was found that this method could predict the compression-bending capacity of the LM-CFST frame under combined axial compression and cyclic lateral loads with reasonable discrepancies. • Four 1/2 scale LM-CFST frames were tested under combined axial compression and cyclic loads. • The failure modes and hysteretic responses were discussed. • A validated FE model was established for further investigation. • A parametric analysis was conducted to investigate the influence on the seismic performance of the LM-CFST frames. • A simplified method was proposed to evaluate the compression-bending capacity of the LM-CFST frame. [ABSTRACT FROM AUTHOR]

[Display omitted] • A large-scale model test is used to study the mechanical properties of joints. • The failure process of the joints is quantitatively analysed. • The failure modes of the joints are explored with screws and without screws. Although prefabricated frame tunnels are widely used, research on their structural performance is limited, especially research on the weakest joints in prefabricated tunnels. In this study, a large-scale physical model test is used to study the mechanical properties of joints with bolts and without bolts under static loading, mainly considering the joint concrete and steel strain, opening amount, deflection, rotation angle, toughness, and ductility. The failure of the two joint types is quantitatively analysed using the virtual hinge angle and plasticity index. In addition, a finite element model is established, the model test results are compared, and the effects of the axial force and bolt preload on the joint performance are evaluated. The results show that the concrete strain and steel strain of the two joint types do not exceed the limit values under the ultimate load, providing sufficient ductility. The mechanical properties of the bolted joint are improved by the anchoring and crack arrest mechanism of the bolt. The deflection produced in each stage is lower and the deformation resistance is stronger for the bolted joint than for the boltless joint. Due to its larger damage area and greater number of cracks, the bolted joint exhibits a smaller rotation angle and stronger load-bearing capacity, and the material performance of the joint concrete is fully utilized. Increasing the axial force of a joint can significantly improve its bearing performance, but increasing the bolt preload has no significant effect. In the design of prefabricated frame tunnel joints, bolts can be added to improve the bearing capacity and deformation resistance. [ABSTRACT FROM AUTHOR]