Study On Nonlinear Bending Character Of Parallel Wire Strand

Bridge cable structure consists of a large number of discrete steel wires,the mechanical characteristics are different from those of the homogeneous one.Especially when the cable section is subjected to bending action,steel wires of the same cross section may cause slippage.At this time,the cross section deformation will no longer satisfy the plane cross section assumption,and the calculation of bending stress requires the aid of complicated nonlinear finite element method.In this thesis,the parallel steel wire strands are studied under the combined action of tension and bending force.The actual situation of layered and staged sliding of wire were considered.A method for analyzing the mechanical properties of parallel steel wire strands under the combined action of tension and bending force is established.In addition,a simplified method for calculating nonlinear bending of parallel steel wire strands is established by comparing the experimental and nonlinear finite element results.The main contents of this thesis are as follows:The main reason for lager bending stress calculation difference according to beam theory is that slippage between wires is not considered.For a cable with wire slip,by the thought of segmental research,the inertia moment remains unchanged between the initial slip rotations of two adjacent wire layers.It is derived that the relationship between cable bending curvature and section rotation angle,the same as a calculation formula is derived about bending shear force along unit axial length of the cable.Based on physical relationship equation,the cable strain,stress and internal force are decomposed into linear and nonlinear terms.Then tangent stiffness matrix is derived through relation between intenal force and deformation.And linear and nonlinear terms of bending stiffness are obtained,as well as the variation of bending stiffness.The bending shear force formula of wire strand is given by segmental study.The relationships between wire axial force and interlaminar shear force and strand bending curvature or rotation are deduced by studying strand wire slippage layer by layer.The rotation angle corresponding to slip position is derived according to the condition of wire layer slip judgment.Then the moment angle diagram and the bending stiffness angle diagram of simplified model are given.Combined with the tensioning and bending model test,the ANSYS delamination slip model of of parallel wire strand is established then the factors influencing strand bending behavior are discussed.When initial axial stress increases or equivalent winding force decreases,the first slip angle of strand decreases,and the sooner the strand slips and the faster the slip rate changes,the earlier the bending stiffness decreases.When the steel wire does not slip,the bending moment and bending stress of the section will increase with the increase of initial axial tensile stress,but it will not be affected by the equivalent winding force.When equivalent winding force gets bigger,the friction slip limit force becomes bigger,the wires slips more slowly,the cross section uneven stress gets bigger,rotation angle variation scope of full slip process gets larger,so as the moment gets lager after full slip.