Mechanism And Mechanical Behavior Of Delamination And Slippage Between Wires Or Strands Of Cables For Large-span Bridges

Cables serve as the main load bearing and transmission components for cable supported bridges. They are usually considered as perfectly flexible strings with well integrity between wires or strands; however, this assumption does not hold in some cases. For example, cables are subjected to local bending at the place of cable saddle of a suspension bridge or at the anchor end of a cable-stayed bridge. Slippage will occur once the shear force exceeds the limiting value of friction resistance beeween layers, which sequentially will influence the mechanical properties of cables. For parallel strand cables, the strands are separate and unbounded, so they will contact with each other under the influence of outer pipe and anchor members; in addition, slippage phenomenon between strands will appear along with deformation, and these will affect the mechanical properties and force control work of parallel strand cables.This paper focus on delamination and slippage phenomenon between wires or strands in cables to study the influence of these phenomenons to the mechanical properties of cables and force controlling by simplifing cable into a laminated beam model. The following work has been done:(1) According to force analysis of a laminated beam element considering interfacial friction, the shear stress distribution formulation of section was deduced for coulomb frictional laminated beams, and then the mechanical condition and development process for slippage were determined based on the theory of layered-slipping. The method of solving slip length for laminated beams was proposed and a calculation programe was complied with MATHEMATICA. Compared with the data calculated by ANSYS, the results demonstrated the proposed algorithm is accurate and efficient.(2) By modeling actual cables to laminated beams, the effection of slippage to the deformation and stress of cables under local bending was investigated aided by the algorithm in(1). Through the influential factors analysis, constructive suggestions on advoiding local secondary bending stress were recommended.(3) Interlayer slip changes the stiffness of a laminated beam; it also contributes to energy loss at the same time. Beginning with dynamic equilibrium analysis on the micro segment of a laminated beam, vibrational equation of laminated beams was obtained. By the Newmark-β method and spectrum analysis, the influence of variation of stiffness to the vibration of laminated beams was got; energy loss phenomenon was also demonstrated through the analysis of a two-layer laminated beam.(4) According to static equilibrium conditions and the principle of the isotenson method for parallel strand cables, two basic problems involved in the stretching process and the corresponding numerical computing method were fully discussed. The program of solving installation force for parallel strand cables was compiled with MATLAB; by contrast with the measured data of the Tongling Bridge, it is found that the algorithm has an advantage on accuracy and efficiency. Meanwell, this paper presented the force uniformity test method for parallel strand cables.(5) Concentrating on the separation and slip phenomenon between strands, after abstracting parallel strand cables to laminated beam model, the contact regions were determined by contact analysis with ANSYS, also taking the structural features of parallel strand cables into consideration. The analysis results of the modal that contains contact effect indicate that layer contact ensures the displacements of strands couple with each other, so the vibration of strands shows a great deal of consistency. This can be verified by measured vibrating signals, throuth which the self-damping of strand cables can also be determined.(6) A numerical method for estimating cable tension was developed based on finite element theory, and parameter sensitivity analysis was done by this method. The test results from the Tongling road-rail bridge show that this method is accurate. Combining with the Tongling road-rail bridge, several common tension measurement methods for such type of cables were introduced. Case study on assessment of these tension measurement methods was done through the statistical comparative analysis of the field test data collected from the Tongling road-rail bridge; the conclusion can provide good reference for similar projects.