Spiral Strands Research Articles

Study on performance of bended spiral strand with interwire frictional contact

The present study establishes a solution model of a spiral strand subjected to a bending load, in which the interwire frictional contact and the Poisson's ratio of the wires are considered, and the interwire friction force is automatically achieved. Based on this model, the performance of bended wire rope strand with interwire frictional contact is solved with conjugate gradient method, fast Fourier transform, finite difference method and improved Euler's predictor–corrector method. The effects of the frictional contact, bending load and lay angle on the performance of the bended strand are analyzed. The results show that the consideration of the interwire frictional contact can obtain a larger bending stiffness of the strand compared with a pure bending model. The serious diameter shrinkage of the outside wire due to the effect of Poisson's ratio, the maximum pressure and deformation due to the core-wire contact occur at the furthest part from the curvature center of the bended strand, where the tensile failure and contact fatigue are most likely to happen. Meanwhile, interwire slippage and bending fatigue are liable to happen at the neutral layer. The strand with a large lay angle has a better resistance to bending fatigue but worse tribological properties, compared with a small lay angle strand.

Spiral strand cables subjected to high velocity fragment impact

Structural cables are widely adopted around the world in offshore construction, sports stadia, large scale bridges, Ferris wheels and suspended canopy and fabric structures. However, the robustness of such structures to blast or impact is uncertain with a particular concern related to the loss of a primary structural cable when damaged by high velocity blast fragmentation. This paper presents the first ever numerical and experimental study on commonly used high-strength steel spiral strand cables subjected to high velocity fragment impact. Spiral strand cables were impacted by 20mm fragment simulating projectiles travelling at velocities between 200 and 1400m/s. Complex 3D non-linear finite element models were developed and carefully compared with experimental tests. The penetration resistance of the cables and resultant damage were studied with respect to fragment impact velocity. It was found that for all the impact velocities, the fragment penetration depth was less than half of the cable diameter demonstrating a considerable amount of resilience. Considering the damage caused, the residual cable breaking strengths were estimated and found to be still higher than the minimum breaking load of an un-damaged cable. The numerical models were also able to reproduce the main features of the impact tests, including the extent of localised damage area, the fragment penetration depth and mode of individual wire failures, thus demonstrating their potential to be widely used in industry for structural resilience and robustness assessments by structural engineers.

Dynamic torsional characteristics of mine hoisting rope and its internal spiral components

Dynamic torsional characteristics of mine hoisting rope and its internal spiral components were investigated in the present study. Theoretical models of tensions of rope segments at distinct locations were presented to obtain dynamic rope tensions. Theoretical models of torque, unit torsion angle, torsion angle, twisting parameters, and torsional stress were introduced to investigate dynamic torsional characteristics of hoisting rope and its internal spiral components under tension. Rope tests were conducted in order to validate dynamic torsional properties of the rope under fluctuation tensions. The results show three-stage fluctuating trends of rope tension and torque. An increase of hoisting time induces a decreased torsion angle of the rope, fluctuating upward trends of unit torsion angles of the rope, spiral strands and steel wires, respectively, fluctuating increases in lay angles of the spiral strand and steel wires, respectively, and the fluctuating decreased lay length of the spiral strand. An increase of the distance between rope segment and friction pulley tangent causes a decrease at first and then an increase in the unit torsion angle in cases of the rope, spiral strands and steel wires, an increase at first and then a decrease in the rope torsion angle, increased lay angle and decreased lay length of the spiral strand, a decrease at first and then an increase in the torsional stress of steel wire in every layer of the spiral strand.

A simplified finite element model for structural cable bending mechanism

A simplified finite element modeling method for structural cables on bending and wire sliding problems are proposed and formulated. The model is characterized by a beam-spring composition that uses helically arranged short-beam elements to simulate spiral wires, radially-placed rigid beams to replace wire sections and spring elements to capture contact extrusion and friction between adjacent wires. Winding and contacting patterns for semi-parallel wire cables and spiral strands are discussed and then used to formulate the model establishments. In semi-parallel wire cable, any selected wire section can be simplified as a seven-node set to represent the center wire and the surrounded six contact spots. While in spiral strand, wire section can be replaced by four rigid beams that connect the four contact points to wire center. Helical wire compression, sheath pinch effect and contact friction are all considered and calculated, and then bending simulations are conducted on large dimension cables with different end conditions, wire constructions and pretension levels. Simulation results are compared to the test data, and prove that the proposed model can well predict the bending behavior and the varying trend of flexural stiffness. Both cables all express a bilinear elastic–plastic like flexural strength–deflection response. Semi-parallel wire cable has sinusoidal deflection out of the bending plane, and the range of bending gradient is influenced by the cable end conditions. Galfan strand shows little unwinding and torsion effect due to the canceling out effect from alternative twisting between adjacent layers. The model can efficiently simulate long and large dimension cables in a short time, implying its promising applicability in cable studies.

Finite element simulation of creep of spiral strands

In the presented paper, the creep of steel spiral strands with a construction of 1×7 and 1×19 round wires subjected to constant axial loads is studied numerically. The principal aim of this contribution is to define and describe a novel design computational tool for the numerical simulation and prediction of creep strains in spiral strands. For this purpose, finite element models are developed using ANSYS software. Wires of the strands are modelled using 3D geometrically nonlinear beam elements. An approach is based on the Timoshenko beam theory and Saint Venant torsion theory. The wire material is both linearly elastic and isotropic. Creep strain of strands is caused by the creep strain of wires due to the tensile load acting on them and by extension due to the construction of the strand when the strand is tightened. The constitutive creep equations of wires and selected initial clearances between wire layers are incorporated into the finite element models. The models are set up and calibrated on the basis of data obtained by the creep tests. In principle, the required functionality and performance have been implemented in the software and a good agreement with test results has been obtained.

An analytical approach to model the hysteretic bending behavior of spiral strands

Spiral strands are lightweight and flexible structural elements, widely employed in many different applications, moreover, they are the basic components of stranded wire ropes. Bending behavior can play an important role in modeling slack cables and in “critical” regions of flexible ropes, such as in the neighborhood of clamping devices. When a strand is bent, wires tend to slip relatively one to each other. In the present work, the critical conditions for the onset of inter-layer sliding are investigated by defining the limit domain for wire slipping (the domain of “admissible values” for the axial force of a generic wire, accounting also for the contribution due to bending of the strand). The special case of uniform bending of the strand is considered and a closed form expression of the limit domain is presented. The non-holonomic nature of the strand mechanical model developed in this work leads to a lacking of symmetry for the tangent stiffness matrix. In the paper it is proved that this condition can be de facto relaxed in practical applications and that an elastic potential function, relating the generalized stress and strain variables of the strand in bending, can be defined only under the limit kinematic hypotheses of “full stick-state” or of “full slip-state”. The aforementioned results are used as the starting block from which the strand full mechanical behavior for coupled axial force and bending is derived. Knowledge in closed form of how the limit domain depends upon the strand construction parameters and current stress conditions paves the way to design optimization of the strand.

Experimental research on bending performance of structural cable

Studies on bending properties of cables have long history but those researches are mainly around electrical conductors with very limit experimental discussions on structural cables. One approach on dynamic problems are through understanding changes in bending stiffness and utilized the varying bending rigidity into beam theory or beam finite element analysis. Therefore, a serial of quasi-static bending tests on semi-parallel wire cables, stranded ropes and steel spiral strands (Galfan) were performed to understand the cable bending response, with considering different factors like end conditions and the present and magnitude of pretension. The effective flexural stiffness of those structural cables were then determined and compared. Test results indicated that the unstressed cables under bending had an elastic–plastic like force–displacement response, which was analogous to an elastic–plastic metallic beam. Galfan strands showed better wire bounding behavior and cooperative bending due to different winding method. Welded end measurements can add integrity to the cable but this strengthening effect is weak and limited. Flexural response of the cable under a constant tension force was more like a linear relation with sag deflection. Pretension can increase the cable flexural stiffness, and this strengthening effect increased with the pretension level but decrease with the cable dimension. A simplified evaluation method of effective flexural stiffness was also proposed.

Finite element analysis of spiral strands with different shapes subjected to axial loads

In this paper a new mathematical geometric model of spiral one or two-layered oval wire strands are proposed and an accurate computational two-layered oval strand 3D solid model, which is used for a finite element analysis, is presented. The three dimensional curve geometry of wires axes in the individual layers of the oval strand consists of straight linear and helical segments. The present geometric model fully considers the spatial configuration of individual wires in the right and left hand lay strand. Derived geometric equations were used for the generation of accurate 3D geometric and computational models for different types of strands. This study develops 3D finite element models of two-layer spiral round, triangular and oval strands subjected to axial loads using ABAQUS/Explicit software. Accurate modelling and understanding of their mechanical behaviour is complicated due to the complex contact interactions and conditions that exist between individual spirally wound wires. Comparisons of predicted responses for the strands with different shapes and constructions are presented. Resultant stress and/or deformation behaviours are discussed.

The riddle of free-bending fatigue at end terminations to spiral strands

The importance of design against free-bending fatigue at points of end fixity to multilayered spiral strands used in various onshore and offshore structural applications is emphasised. A fairly extensive set of large scale test data covering a wide range of spiral strand construction details with the cables subjected to widely varying mean axial loads and bending amplitudes is used to critically examine the generality of the contact stress–slip versus fatigue life (S–N) model of Raoof which, unlike the traditional maximum bending stress models, takes the crucial effects of interlayer fretting on the strand free-bending fatigue life into account. The possible practical limitations of the Contact Stress–Slip approach are also discussed in some detail with much emphasis placed on the question of potential size effects associated with the free-bending design S–N curves.

Experimental investigation and finite element analysis of a four-layered spiral strand bent over a curved support

Cable saddles are devices used to allow the cable to be continuous over a support. This paper presents the results of experimental and theoretical analyses of the spiral four-layered strand, with a construction of the 1+6+12+18+24 (1×61) round wires, subjected to tension and bending, where stresses expected to occur at the part of the strand over a saddle are investigated and compared with those under pure tension. In order to precisely model the complex geometry of the strand necessary for its finite element analysis, the geometric parametric equations have been implemented in the CATIA V.5 software to generate the 3D strand mathematical geometric model. To simulate and predict the behaviour of the strand subjected to tension and bending, a 3D model has been implemented in a finite element ABAQUS/Explicit software. An axial tension and bending static test was carried out on a full-size strand specimen that was fully representative from a point of view of used materials, details and anchorages. Comparisons of the resultant stresses in the selected positions of the strand (directly over and closely behind the saddle where the strand was subjected to tension and bending and apart from the saddle where the strand was subjected to pure tension) obtained by the proposed finite element analysis with those obtained by the test were presented. A good agreement between individual approaches was observed. Principally, the required functionality and performance have been implemented in the software and a good agreement with the test results was obtained.

The Behaviour of Cast Rope Sockets at Elevated Temperatures

Modern building structures are making increasing use of high performance tension members in steel spiral strand. The terminations to the strand typically employ a steel fitting, a "socket", to transfer the load to other structural members, where the interface between strand and a conical recess in the socket is filled either with a cast metal alloy or (more recently) a complex resin compound. The cone grips the wires of the strand and is pulled into the conical recess in the socket by the axial load to generate a wedging action that transfers axial load between strand and socket.The present paper addresses the performance of these sockets and their filling media at elevated temperatures, so that their performance in fire conditions can be assessed. A substantial programme of tests that has focussed on the creep-temperature-time relationship in metal and resin filled sockets is reported.It is concluded that resin filled sockets are likely to fail within 60 hours if their core temperature is held at 160°C or above, while the critical temperature for alloy filled sockets is nearer 210°C.

Full 3D finite element modelling of spiral strand cables

Spiral strand cables are widely used in lightweight cable-supported structures such as sports stadia and bridges. Accurate understanding of their mechanical behaviour is complicated by their complex geometry and the complex contact conditions that exist between the many individual spirally wound wires. This study develops full 3D elasto-plastic finite element (FE) models of the multi-layer spiral strand cables subjected to quasi-static axial loading using LS-DYNA. A novel procedure to generate their complex geometry and FE meshes was devised and two cables with different diameters and numbers of wires were modelled in detail. The predicted axial load–axial strain curves and failure loads were in good agreement with experimental data.

Actin filament severing by cofilin is more important for assembly than constriction of the cytokinetic contractile ring

We created two new mutants of fission yeast cofilin to investigate why cytokinesis in many organisms depends on this small actin-binding protein. These mutant cofilins bound actin monomers normally, but bound and severed ADP-actin filaments much slower than wild-type cofilin. Cells depending on mutant cofilins condensed nodes, precursors of the contractile ring, into clumps rather than rings. Starting from clumped nodes, mutant cells slowly assembled rings from diverse intermediate structures including spiral strands containing actin filaments and other contractile ring proteins. This process in mutant cells depended on α-actinin. These slowly assembled contractile rings constricted at a normal rate but with more variability, indicating ring constriction is not very sensitive to defects in severing by cofilin. Computer simulations of the search-capture-pull and release model of contractile ring formation predicted that nodes clump when the release step is slow, so cofilin severing of actin filament connections between nodes likely contributes to the release step.

Performance comparison of track ropes in contemporary ropeway installations

Non-destructive testing is an important means for assessment of the performance of track ropes in a bi-cable zig-back ropeway installation. The visual method produces the possibility of inadequate inspection due to its subjectivity. Electromagnetic and visual wire rope inspections complement each other. Both are essential for safe operation. Periodic in-situ measurement of faults in ropes would help to determine the effects of various parameters on rope life. Track ropes are generally locked coil ropes. Full locked coil (FLC) ropes are made with a spiral strand as the main core and are finally covered with one or more layers of shaped wires. The final covering layer is made from full locked sections of wires which interlock with each other and present a smooth surface. Wire ropes wear out eventually, gradually losing work capability throughout their useful life, making periodic inspections, lubrication and tensioning necessary. Magnetic flaw detectors, which measure the loss of metallic area (LMA) and detect local faults (LF) such as broken wires and other faults, are used to determine rope wear. In this paper, an attempt has been made to describe the performance of track ropes in contemporary ropeway installations.

Experimental Study on Repair Methods of Corroded Bridge Cables

AbstractThe cables and hangers of old suspension bridges and the stays of cable-stayed bridges often suffer from steel corrosion. It is important to repair them by proper methods to prevent the further progression of corrosion. In this paper six repair methods were proposed and applied to cable specimens. Then, the specimens were exposed to severe corrosion environments and the effectiveness of the proposed repair methods was compared. Two different types of test cables were used in this study: parallel wire strands and spiral strands. The first test group used parallel wire strand cables consisting of 19 nongalvanized steel wires. This test was aimed at the main cables of the suspension bridges. Six repair methods were applied to these cable specimens: coating with zinc-rich paint, coating with epoxy resin paint, coating with zinc powder paste, filling with epoxy resin, filling with oil, and a dehumidification method. Then, the specimens were accelerated to corrode in a laboratory for 15 months. By inves...

Swaged Fittings Under Tension and Fatigue Loads

Although swaged terminals have become increasingly important for structural engineering and mechanical handling, no technical standards exist either for production or for structural analysis. Owing to the complex behaviour of the components (terminal and wire rope) analytical calculations are not available to estimate the load capacity of swaged terminals under tension or fatigue loads. Only a few design recommendations are available, which are based on geometric parameters and experimental data. Therefore the load capacity of the swaged terminal was investigated in a PhD thesis1 at the University of Stuttgart. The task was split into theoretical and experimental sections. Analytical formulas were derived with the Finite Element Method to describe the behaviour of wire rope and sleeve after swaging. For this wire rope termination in combination with open spiral strands, the fatigue properties were investigated in a systematic test program. Owing to non-uniform methods of analysis, available test results cannot be applied directly to other rope constructions and terminations. Current standards defined endurance loads for defined rope types and termination such as cast sockets. For safe dimensioning, it is necessary to specify mechanical closure and fatigue conditions considering stress and amplitude depending on swage parameter and material.

Fretting-fatigue behaviour of bridge engineering cables in a solution of sodium chloride

Bridge engineering cables are subject to potential damage, mainly due to fretting-fatigue and corrosion. This paper deals with the study of drawn steel wires submitted to fretting-fatigue in a solution of sodium chloride. Experimental tests were conducted to reproduce the contact conditions in spiral strands undergoing free bending deformations and submitted to corrosion. Previous tests showed that lubrication and zinc coating improve the resistance of wires to fretting-fatigue. The results of fretting-fatigue tests in a NaCl solution are compared with those of fretting-fatigue tests carried out in air. In terms of lifespan, in the retained conditions, no significant influence of the NaCl solution is observed. The recorded tangential force shows stabilized partial slip regime after about 10,000 cycles. The observation of fretting scars and of fracture surfaces shows the presence of corrosion products.

Damage Identification in Elastic Suspended Cables through Frequency Measurement

Structural cables in cable-stayed systems are subject to potential damage, mainly due to fatigue phenomena and galvanic corrosion. The paper analyzes how the dynamical behavior of cables is affected by diffuse damage, and investigates whether the damage can be identified through information selected from the dynamical response. A continuous monodimensional model of a damaged cable is used for this purpose. Damage is described as a reduction of the cable cross section, and defined in terms of its intensity, extent and position. The major effects of these different damage parameters on the cable static response and spectral properties are evidenced and discussed to verify the observability of the damage. The frequencies of the dominant transversal motion of the cable are chosen as damage indicators, since they are sufficiently sensitive to the damage intensity and extent, while the damage position requires additional information. The damage identification problem is formulated by defining an objective error function between the measured and the model frequencies, to be minimized in the space of the damage parameters. Pseudo-experimental data are initially used to test the effectiveness and resolution of the procedure. The results confirm the uniqueness of the problem solution and its correctness. The robustness of the solution is discussed while considering the presence of random errors of increasing amplitude. The procedure is also positively verified with experimental measures from a prototype model of an artificially damaged spiral strand.

Axial fatigue design of sheathed spiral strands in deep water applications

Using the previously reported axial fatigue model of Raoof, and by carrying out extensive theoretical parametric studies on large diameter (i.e. realistic) sheathed spiral strand constructions which very nearly cover the full manufacturing range of lay angles (with the lay angle being the primary geometrical parameter controlling the strand axial fatigue performance), a new set of design S– N curves for sheathed spiral strands in deep water applications have been developed. These S– N curves provide a very simple means of predicting the axial fatigue life of sheathed spiral strands (under uniform cyclic loading) to first outermost (or innermost) layer wire fracture, both at (or in the vicinity) of the end terminations, as well as in the free-field (i.e. away from the detrimental effects of end terminations), with the sealed strands being subjected to simultaneous actions of a wide range of external hydrostatic pressures, such as those in deep-sea conditions with water depths of up to 2000 m. It has been shown that, although the fatigue life to first innermost layer wire fracture is largely unaffected by the magnitude of the applied external hydrostatic pressure, the fatigue life to first outermost layer wire fracture may be significantly reduced (cf. corresponding in-air conditions) under the influence of sufficiently high levels of external hydrostatic pressure. The proposed design S– N curves have been compared with others (which are based on tests under in-air conditions) and it has been shown that the application of such previously available in-air design S– N curves to sheathed spiral strands in deep water applications may lead to unsafe designs.

Possible shortcomings of the calibration methods for certain non-destructive monitoring devices for helically wound steel cables

Coupled extensional–torsional behaviour of axially pre-loaded helically wound steel cables (wire ropes and/or spiral strands) under specific forms (i.e. unit-step, triangular, and half-sine) of impact loading are considered in some detail. The final closed-form formulations can handle both the no-slip and/or the traditionally used full-slip coupled extensional/torsional constitutive equations for helically wound cables, and describe the various characteristics of the resulting pairs of axial or torsional waves at any location along the cable with one end fixed against movement and the other end subjected to impact loading. By using extensive numerical results, which cover the full range of current manufacturing limits for the lay angle (with this being the sole controlling geometrical parameter as far as the axial/torsional stiffnesses are concerned), it is shown that significant differences exist between a number of axial/torsional wave characteristics, depending on whether the no-slip or the full-slip version of the constitutive relations is used in the analysis. It is demonstrated that modest increases in the magnitudes of the lay angles can lead to significant increases in the differences between the no-slip and the full-slip wave propagation characteristics. The present findings may have significant practical implications in relation to the currently adopted techniques used by industry for calibrating the electronic boxes, which are subsequently used as permanently installed devices, for the in situ detection of individual wire fractures under, say, fatigue loading associated with cable-supported structures.