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transmission towers have been subjected to alternating loads caused by the galloping of iced conductors for a long time, and their fastening bolts are easy to loosen or break, which seriously threatens the safe operation of transmission lines. Through the transverse vibration test of M20 bolts commonly used in transmission towers, the vibration frequency and amplitude are changed, and the change law of the preload of bolt joints is studied. The results show that with the increase of the initial preload, the decline speed of bolt clamping force decreases significantly; The clamping force drop curve of M20 bolt is fitted by shivakumar crews model, which is very consistent with the actual test curve.

Transmission lines are affected by the natural environment for a long time, and bolts are prone to frequent vibration, resulting in loosening or falling off. In this paper, the loose mechanism of transmission line threaded connection is analysed, and the transverse vibration comparative test of bolt locking method is carried out. A new type of locking nut has been developed, which has good locking performance and convenient installation. According to different operating environments, the principle of differential bolt locking is proposed.

The tower is the load-bearing structure of the overhead transmission line. Due to the complex operating environment and other factors, the transmission tower is prone to corrosion, which weakens the bearing capacity of the tower and affects the safe operation of the power grid. Through the investigation of the corrosion situation of the transmission towers in service, the angle steel members were removed from the in-service transmission towers, and the axial compression bearing capacity test was carried out. As the corrosion rate increases, the bearing capacity of components shows a decreasing trend, and due to the existence of corrosion, and at the same corrosion rate, due to the location of corrosion, The corrosion depth and corrosion area are different, and the axial compression bearing capacity of the components fluctuates greatly.

Summary: After completion of the construction process including wire stringing of 1,000 kV ultrahigh voltage (UHV) cat‐head electric transmission towers, the outward horizontal K‐joint deformation of one side crank arm may usually exceed 70 mm. Joint slip effects were ignored in the initial structural design of transmission towers, which induced that the calculated K‐joint displacements are much lower and the real deformation cannot meet with the requirement of the acceptant code. First, the shortcomings of the traditional unit load method used to calculate the displacements of transmission towers connected by bolt joints were analyzed. Second, a coefficient for describing the axial force state of bolted joints was proposed. The connection numbers for different types of members in the crank arms of a UHV cat‐head transmission tower were determined. The traditional unit load method was enhanced by importing the force state coefficient and specifying the detailed connection numbers. The K‐joint displacements calculated by the enhanced formula were compared with the experimental results by full‐scale tower experiment. It shows that the enhanced unit load method is suitable for calculating K‐joint deformations in the crank arms of UHV cat‐head transmission towers. Lastly, contribution weight coefficients of different members for K‐joint displacements of the UHV cat‐head transmission tower were calculated by the enhanced unit load method. For bolt joints connected with the tower members with high contribution weight coefficients, the manufacturing accuracy of bolt holes should be improved, and the bolt clearance should be decreased, which can significantly reduce the K‐joint deformation of UHV cat‐head transmission towers. [ABSTRACT FROM AUTHOR]

This paper conducts a theoretical research into bond–slip relationship between ribbed steel bars and concrete. According to whether the concrete is cracked or not, the ascending part of the bond–slip curve is divided into two sections which are calculated by two different mechanical models. Based on the wedging action mechanism, the slip is introduced as displacement boundary conditions into the model, which is the main innovation of this study. The boundary conditions of the model are changed by the changing slip, so the bond stress values corresponding to all levels of slip are obtained. According to the rebar geometrical parameters specified in National Standard GB1499‐2007, the spacing of the adjacent ribs is fitted as a linear function of the rebar diameter. Then characteristic slip with the rib spacing as the main parameter is adopted in this study. Also, a negative exponential function is proposed for the descending part of the bond–slip curve. Specially, parameters of slipping path are therefore suggested for engineering applications. Comparison between calculated values and test results shows that the theoretical model can reasonably predict the local bonding problems with different steel bar diameters and concrete strength grades. [ABSTRACT FROM AUTHOR]

This paper presents basic parameters test and an efficient numerical model for the bond between reinforcing bars and concrete after elevated temperatures. The chemical adhesive and friction coefficient are measured by self-designed setups, and the variation law of the parameters is summarized. In the 3D modeling, bar-to-concrete interface has been modeled by means of an explicit discretization of the bar ribs. Surface-to-surface contact pair elements are employed for the interface, and the tangential contact behavior is elastic-plastic with a Coulomb-type friction model. Comparison between experimental and numerical results shows that the proposed model describes the behavior of steel bar relatively well in the pull-out process after elevated temperatures. The 3D modeling makes up some deficiencies of macro pull-out test, such as the detailed stress distributions and crack patterns. [ABSTRACT FROM AUTHOR]