Research On The Influence Of Steel Strand Detail Structure On The Mechanical Properties Of Stay Cables

As an important mechanical component,steel strand is widely used in stay cables,prestressed concrete and space grid structures.It is of great significance to study the mechanical properties of this component.Steel strands have complex spatial geometry and contact characteristics,and the influence of these factors is usually simplified in engineering design.In this paper,the effects of twist angle,friction and contact conditions on the mechanical properties of steel strands are evaluated,and the stay cables widely used in steel strands are selected.Based on the two cable force calculation methods of frequency method and sag method,the effects of three parallel steel strand stay cables（15.2-61）with different lengths and the geometric structure of steel strands in parallel steel strand stay cables on the mechanical properties and tension calculation of the overall structure of a cable-stayed bridge are discussed.Finally,based on BP neural network,the multi-parameter cable force prediction is carried out.The main contents of this paper are as follows:（1）In order to analyze the influence of the detail structure of steel strand on its bending stiffness,a single steel strand in the stay cable of parallel steel strand is taken as the research object,and a refined contact finite element model of seven-wire steel strand is constructed.The bending mechanical properties of steel strands with twist angle and without twist angle under different detail structures are analyzed.It is concluded that the bending stiffness of the cable is related to the twist characteristics between the internal steel wires,the friction interaction between the steel wires and the tension.Research has shown that for non twisted angle parallel steel wire bundles,the mid span displacement is linearly related to the bending moment load applied at both ends,and the bending stiffness is independent of its length,which can be approximated as 1.16EI_equ.（2）For seven-wire steel strand with twist angle,the influence of different details of steel strand on its bending performance is different.Research has shown that the bending stiffness of steel strands increases with the increase of lay distance and friction coefficient,and decreases with the increase of length L.Under tension free conditions,its bending stiffness can be approximately taken asEI_min In addition,the change in the initial contact state of the steel strand has a significant impact on its bending stiffness.When the steel strand strands are not in contact with each other,the bending stiffness will undergo a certain reduction The elastic modulus of HDPE sheath is much lower than that of steel wire,which cannot provide significant bending resistance to steel strands and has no significant impact on the bending stiffness of steel strands The bending stiffness of steel strands is positively correlated with their initial tension,with a correlation coefficient of approximately 0.984.（3）In order to accurately analyze the influence of the detailed structure of the steel strand on the mechanical properties of the stay cable,improve the accuracy of the cable force calculation,and reduce the influence of other external factors on the cable force calculation,based on the related research of the frequency method and the sag method,the common formulas for the calculation of the engineering cable force are selected,and the influencing factors of the two cable force test methods are analyzed.The influence of shock absorber,bending stiffness,boundary conditions and tension on the cable force test is obtained.The results show that the cable force test error increases with the increase of the bending stiffness and the main frequency order of the cable,but this effect decreases with the increase of the cable length.In addition,the installation of the cable-stayed shock absorber and the setting of the boundary conditions will also cause errors beyond the engineering permission for the cable force test.（4）In order to study the relationship between the complex combined structural characteristics of steel strands and the frequency and sag of stay cables,based on the two cable force test methods of frequency method and sag method and the analysis of bending stiffness of steel strands,the vibration frequency and sag of stay cables under different detailed structures of steel strands are theoretically simulated and analyzed.Research has shown that during cable force testing,the lay length of steel strands has a significant impact on the frequency and sag of stay cables.Within the specified lay length range,for short and medium cables,when the lay length of steel strands is approximately 218-265mm and greater than 205mm,the accuracy of cable force testing is closer to theoretical values For long cables,the change in the twist length of the steel strand has no significant impact on the cable force test.The frequency and sag of stay cables are sensitive to changes in the pitch diameter ratio of steel strands.Within the range of pitch diameter ratio specified in the specifications,when it is less than about 22,the cable force test exceeds the engineering allowable error.This impact decreases with the increase of the pitch diameter ratio of steel strands The initial contact state of the steel strand has little effect on the cable force test of the stay cable,but the calculation error of the cable force reaches the minimum when the steel strands are in contact with each other HDPE sheath can significantly reduce the vibration frequency and sag of short cables,but has little impact on medium and long cables When the coupling distance of the stay cable is 1/16to 1/32 of its total length,the overall performance of the stay cable is good,which can further improve the accuracy of cable force detection when conducting cable force testing.（5）The BP neural network model is built in Matlab,and the multi-parameter cable force prediction is carried out for the stay cable with the prediction accuracy of the cable force of the steel strand under different stranding modes as the index.The research shows that the BP neural network can accurately predict the cable force of the stay cable,which proves the feasibility of this cable force prediction method.In addition,when specific parameters related to stay cables are known,the cable force of stay cables can be predicted based on neural networks,and compared with the results of theoretical calculation of cable force,which can provide a certain reference for the detection of cable force in practical projects.