Spiral Strands Research Articles

A rheological constitutive model to predict the anisotropic biaxial bending behavior of spiral strands subjected to variable axial force

Spiral strands exhibit dissipative bending behavior when subjected to external axial force. To the best of the authors’ knowledge, only the uniaxial bending behavior of spiral strands subjected to constant axial force has been studied in the literature so far. Thanks to a recently developed mixed stress–strain driven computational homogenization for spiral strands, this paper is the first to study the biaxial bending behavior of spiral strands subjected to variable tensile force. Based on the observed anisotropic behavior, a rheological constitutive model equivalent to multilayer spiral strands is proposed to predict their behavior under such loading. For an Nl-layer strand, the proposed model consists of several angularly distributed uniaxial spring systems, referred to as a multiaxial spring system, where each uniaxial spring system consists of a spring and Nl slider-springs. In a uniaxial spring system, the spring represents the slip contribution of all wires to the bending stiffness of the strand, while each slider-spring represents the stick contribution of each layer. A major advantage of the proposed scheme is its straightforward parameter identification, requiring only several monotonic uniaxial bendings under constant axial force. The proposed rheological model has been verified against the responses obtained from the mixed stress–strain driven computational homogenization through several numerical examples. These examples consist of complex uniaxial and biaxial load cases with variable tensile force. It has been shown that the proposed scheme not only predicts the response of the strand, but also provides helpful insight into the complex underlying mechanism of spiral strands. Furthermore, the low computational cost of the proposed models makes them perfect candidates for implementation as a constitutive law in a beam model. Using a single beam with the proposed constitutive law, spiral strand simulations can be performed in a few seconds on a laptop instead of a few hours or days on a supercomputer.

Study on method of controlling interaction between wires of Galfan spiral strands

This paper presents a method of controlling the interaction between the wires of Galfan spiral strands. Axial tensile tests were carried out on 1 × 7, 1 × 19, 1 × 37, and 1 × 61 strands. The material properties of the wire, the bearing capacity of the strand, and the surface strain of the outer wire were measured. The wear of the wire after loading was observed by cutting open the 1 × 7 strand and the 1 × 19 strand. The initial contact state between the wires was then determined by calculation and modelling. The contact state between the wires under load was analyzed by ABAQUS. Finally, the contact pressure caused by the interaction was investigated. The method of controlling the maximum contact pressure was developed. A formula for the complete elimination of the maximum contact pressure was also proposed.

A mixed stress-strain driven computational homogenization of spiral strands

Spiral strands subjected to tensile force and bending loading display a nonlinear dissipative behavior due to frictional interactions between their elementary wires. This study aims to provide an efficient method, based on a computational homogenization procedure, to accurately characterize the nonlinear response of such strands. By using 1D beam elements in both micro- and macro-scale, homogenization is performed along the axial direction of a representative volume element (RVE), leading to expressing a boundary value problem on RVE, driven in a mixed manner by either strains or resulting forces or moments. The boundary value problem on the RVE is solved using an in–house implicit finite element solver for finite strain, considering all frictional contact interactions. A method is proposed to predict the bending moment’s evolution for any curvature variation from the simulation results of only one bending loading test on the RVE. The nonlinear behavior of the strand in the micro-scale identified through this offline technique can then be used in the macro-model to simulate various bending loading tests under constant tensile load. Results obtained with the multiscale model are compared to those provided by direct numerical simulation to demonstrate the validity of the proposed approach.

Modelling Thermal Performance of Unloaded Spiral Strand and Locked Coil Cables Subject to Pool Fires

Structural cables are used to design critical bridge structures. These are not typically redundant; a loss or compromise of a few cables can lead to the progressive collapse. Previous experimental research has shown that the degradation of material properties and thermal expansion of structural cables is more onerous than the standard carbon prestressing steel. Despite its importance for design no well-validated methodology exists to aid in the thermal performance of structural cables in the event of a fire, particularly for spiral and locked-coil cables which inherently are complex due to their cross-sectional geometry. A state-of-the-art methodology for modelling structural cables' thermal response is presented. The methodology will enable the development of an understanding of the temperature distribution and thermal deformation in a cable cross-section and allow estimation of post-fire resilience. Validation is performed against experiments of locked-coil and spiral cables, subjected to realistic pool fires. The cables range from 22 to 100 mm in diameter and are constructed of galvanized or stainless steel. The cables are modelled undergoing non-linear thermal analysis in LS-DYNA. 2D models are found to provide conservative estimates for critical values such as peak temperature with 90% accuracy, while 3D models provide slightly more conservative estimates.

Bending Behavior of a Frictional Single-Layered Spiral Strand Subjected to Multi-Axial Loads: Numerical and Experimental Investigation

Bending deformation gives rise to interwire slippage for spiral strands subjected to multi-axial loads, and further induces wear or fatigue phenomena in practice. The interwire friction would resist bending deformation and lead to uneven tension distribution of individual constituent wires but little research has quantified these effects. To figure out this issue, a beam finite element (FE) is established, into which a penalty stiffness algorithm and a Coulomb friction model are incorporated. A series of free bending simulations are developed for parametric study on deflection near the terminations and tension distribution of individual wire for strands with different levels of length and friction coefficient as well as external loads. Based on the simulation results, it is found that strand length has little influence on bending deformation and tension distribution if the strand length exceeds six times the pitch length. A deflection formula extended from the classical Euler beam model well predicts the sag deflections and the relative error with respect to experimental measurements is less than 10%. Furthermore, additional axial tension induced by the friction is clearly characterized and an approximate expression is proposed to estimate tension distribution for outer layer wires. Its predictions are encouraging for longer strands.

Study on bending fatigue failure behaviors of end-fixed wire ropes

Torsional fatigue always exists after a wire rope is put into use, which results in damage aggravation and lifespan reduction. This study is aimed at exploring the comprehensive tribo-fatigue behaviors of wire rope considering torsional fatigue. To achieve this aim, a new type of self-made fatigue testing machine was introduced, and the bending fatigue tests were carried out. Furthermore, the diameter shrinkage ratio, the number and distribution of broken wires under different fatigue times were studied by means of manual detection and non-destructive testing. Moreover, the fractures and wear scars were investigated with the aid of the LW200-4JT optical microscope system. For the thicker outer wire of spiral strand (SS), the influences of bending fatigue times on the evolution of wear parameters were comparatively analyzed. The research results are as follows. With the increase of bending fatigue times, the diameter shrinkage ratio increases, and the increase decelerates gradually. The artificial statistical results agree well with the non-destructive testing results. To be specific, the broken wire develops slowly in the early stage of fatigue, whereas it develops rapidly when the fatigue times exceed 60,000. The broken wire is highly concentrated in the thicker outer wire of SS 1. The maximum width and depth of wear scars of the thicker outer wire of SS 1 increase with the increase of cycles. The values of the two parameters at different contact positions follow the order: contact with the pulley > contact with the adjacent SS 1 > contact with the SS 2 > contact with the wire in the adjacent layer in the same strand. This study is expected to find the fatigue failure rules of end-fixed hoisting wire rope, thus providing a basis for improving the safety of mine hoisting.

Experimental Thermal Performance of Unloaded Spiral Strand and Locked Coil Cables Subject to Pool Fires

There are no contemporary code requirements for the fire resistance of bridge infrastructure, nor is there guidance available for practitioners who wish to design cable-supported structures for the fire. This research seeks to develop an understanding of the thermal response of steel stay-cables under exposure to a pool fire. Multiple varieties of locked coil and spiral strand stay-cables are instrumented with thermocouples and heated by a methanol pool fire. Novel imaging techniques observe the cables’ surface during heating and cooling and enable the calculation of thermal strains and deformations. Results herein illustrate a normalisation of cross-sectional temperatures outside of the localised heating region for cable diameters up to 140 mm, provide comparisons of heat transfer behaviours for different cable sizes and configurations, present novel thermal rotational effects, and calculation of cable thermal expansion values. Predictive thermal expansion values provided by the Eurocode are shown to underpredict cable thermal expansion in most cases.

Experimental and numerical study on stress distribution in a cross section of Galfan spiral strand

The stress distribution law of the cross section of a Galfan spiral strand is studied in this paper. Axial tensile tests are carried out on four types of strands to obtain the relationship curve between the surface stress of the strand and the axial tension. The three-dimensional strand model is established by ABAQUS and verified by experiments. Based on the finite element model, the stress distribution in the cross section of a strand under different stress ratios is studied. The stress distribution coefficient is used to evaluate the degree of non-uniform stress distribution. The effects of wire diameter, wire lay length, and wire layer number on the distribution coefficient are then analyzed. The equation of the stress distribution coefficient of the core wire is obtained by regression, and the method for calculating the maximum stress of the strand is put forward.

Seismic response of low-rise 3-D steel structures equipped with the seesaw system

The efficiency of the seesaw system when applied to low-rise 3-D steel structures is presented in this paper. This efficiency is judged by several seismic response results coming from inelastic seismic time-history analyses of 2-, 5- and 8-storey steel structures. These response results involve height wise distributions for peak interstorey drift ratios (IDR), peak residual interstorey drift ratios (RIDR) and plastic hinge formations in frame elements as well as peak forces to spiral strand ropes and viscous dampers of the seesaw system. For the foundation of the steel structures, different soil types are considered in order to assess the effects of soil-structure interaction (SSI). The seismic incident angle is also taken into account. From the results presented it is concluded that the seesaw system, essentially working always in tension, constitutes a bracing solution that can be potentially proposed by seismic codes as an alternative seismic force resisting system for low-rise steel structures.

Loss of prestress in spiral strand guy ropes in masts

ABSTRACTIt's known since long that guy ropes in masts lose prestress over time. In many cases this leads to increased utilization of the mast. The problem is usually solved by regularly retightening the guys. The cause of the loss of prestress is not entirely clear, but guys in masts exposed to frequent and large vibrations, seem to be the most affected.Lately at manufacture, the guys undergo a number of large load cycles, thereby enabling the threads to get relocated and tightened in the spiral strand guy rope, in order to reduce the loss of prestress. Certificates describe the load cycles, strains and calculated Young's Modulus during this process. Apparently Young's Modulus doesn't only vary with the load range, but it also differs when loading and unloading. All together this means, when unloading the guy during a large enough load cycle, it will not completely regain its previous length, but instead gain a small remaining elongation.By being exposed to large vibrations in masts, guys can be elongated, something that in this paper is referred to as an explanation for the loss of prestress.This paper presents an analytical model, describing the loss of prestress over time in a guy, exposed to large vibrations in a mast. Prestress measurements from mast inspections also show consistency with the model.Based on three prestress measurements of a guy, carried out with a minimum of a few years interval, the model offers an efficient strategy for choosing when to retighten, or estimating if the expected loss of prestress is small enough not to require adjustment. In addition, the model offers guidelines for choosing guy dimension and initial prestress, in order to actively reduce the loss of prestress and extend the time between retightenings.

Study on temperature dependency of spiral strand properties

Prestressed cable is widely applied in various long-span prestressed spatial structures as a high-efficiency tension member. Prestressed cable easily suffers prestress loss under high temperature, and this condition results in the progressive collapse of the entire structure. This study aims to investigate the temperature dependency of properties of prestressed cables and the influence laws of twisting on cable components. Static tensile test under and after high temperatures and load creep test under high temperature were carried out using high-strength steel wires (1860 MPa) and 1 × 7Φ5 spiral strands (1860 MPa) to determine the influences of temperature on the mechanical properties and twisting of cables. Results demonstrate that the mechanical properties of cables decrease considerably when the temperature exceeds 300 °C, and the residual performance of cables deteriorate considerably after 400 °C. The twisting process improves the mechanical properties of cables under high temperature. The proposed method can predict the mechanical properties and residual performance of cables accurately. The creep process was simulated by ABAQUS, and a method for effective simulation of creep behavior of cables was proposed. The prediction method was put forward in consideration of temperature and stress. In conclusion, 300 °C is the creep boundary because of lattice deformation.

Study on stress relaxation of simple spiral strand subjected to tensile load based on semi-analytical method

Based on the structural characteristics of the simple spiral strand, the stress relaxation of the strand subjected to tensile load is studied with the semi-analytical method (SAM). In doing so, using the creep and relaxation theories, and elastic theory, the stress relaxation model for the strand is established, into which the Poisson's ratio effect, interwire contact deformation and space spiral contact between wires are incorporated. Meanwhile, the proposed model is validated. Then, the stress relaxation behaviors of the strand are solved with the SAM, in which the conjugate gradient method (CGM) and fast Fourier transform (FFT) are employed for analyzing the contact behavior of the strand. The numerical results show that decreasing the axial tensile strain and the helix angle, and increasing the outside wire diameter are all beneficial to reducing the creep strain and axial stress of the strand. But the latter dealing brings out increments in the contact deformation and contact pressure.

Bending Behavior of Axially Preloaded Multilayered Spiral Strands

AbstractThis paper presents a new analytical formulation to predict the bending stiffness of multilayered spiral strands. The effect of interwire contact forces and slip between wires have been ful...

Influence of wire’s surface topography on interwire contact performance of simple spiral strand

PurposeThe purpose of this study is to research the influence of wire’s surface topography on interwire contact performance of simple spiral strand.Design/methodology/approachThe mechanical model of the simple spiral strand imposed by a tensile load is first established, into which the surface topography, Poisson’s ratio effect and radial deformation are incorporated simultaneously. Meanwhile, the Gaussian and non-Gaussian rough surfaces of the steel wires are obtained with the fast Fourier transform (FFT) and digital filter technology. Then, the rough interwire contact performance of the simple spiral strand is calculated by using conjugate gradient method and FFT.FindingsAs compared with smooth wire surface, both the longitudinal orientation for the Gaussian wire surface and large kurtosis or small skewness for the non-Gaussian surface yield a small contact pressure and stress.Originality/valueThis study conducts detailed discussion of the influence of wire’s surface topography on the interwire contact performance for the simple spiral strand and gives a beneficial reference for the design and application of a wire rope.

Experimental study on stress relaxation properties of structural cables

Cable stress relaxation causes tension loss at high stress in high-strength structural cables, thereby influencing the stiffness and strength of cable-supported or tension structures. Previous studies have mainly focused on steel wires (SWs) and spiral strands; however, several new types of structural cable, such as semi-parallel wire strands (SPWS), Galfan spiral strands (GSSs), and steel tie rods, have emerged and have been widely applied in recent decades. The axial force during normal service state occasionally reaches 55% of the ultimate tensile strength. Relaxation data on structural cables are rare and are urgently required for structural design and lifetime safety evaluation. Therefore, experimental studies on five types of structural cable were conducted, in which the initial stress levels were 70%, 55%, and 40% of the ultimate tensile strength. Three different working ambient temperatures of 15 ± 2 °C, 20 ± 2 °C, and 25 ± 2 °C were considered. Special onsite anchoring methods and anchorage devices were established and proven effective. Results showed that logarithmic expression could well express the relationship between relaxation rate and time duration. The relaxation rates of SPWSs were larger than those of SWs. GSSs had considerably larger relaxation rates than other cable types due to their material properties and special twist characteristic. The relaxation rates of all types of cable increased with the initial stress and temperature. The recommended values for the 50-year relaxation rates for different structural cables were predicted and calculated.

Failure Analysis and Safety Protection of a Certain Type of Wire Ropes under High-Speed Impact Loads

As the key bearing components in engineering projects, wire ropes often suffer from high-speed impact loads in service. In the majority of applications, wire ropes are subjected to the loads with the following characteristics: alternating impact loads, short-time overload, and small movements among adjacent spiral strands. Typical failure modes of wire ropes include fracture, wear, corrosion, geometric failure and thermal failure. In this work, the corresponding failure mechanisms were analyzed. For a certain type of wire ropes, the fracture morphology, surface quality, microstructure and internal defects of steel wires were analyzed, and failure causes were discussed. Accordingly, the precautions in relation to the safe use of wire ropes were proposed.

Failure Analysis and Safety Protection of a Certain Type of Wire Ropes under High-Speed Impact Loads

As the key bearing components in engineering projects, wire ropes often suffer from high-speed impact loads in service. In the majority of applications, wire ropes are subjected to the loads with the following characteristics: alternating impact loads, short-time overload, and small movements among adjacent spiral strands. Typical failure modes of wire ropes include fracture, wear, corrosion, geometric failure and thermal failure. In this work, the corresponding failure mechanisms were analyzed. For a certain type of wire ropes, the fracture morphology, surface quality, microstructure and internal defects of steel wires were analyzed, and failure causes were discussed. Accordingly, the precautions in relation to the safe use of wire ropes were proposed.

Optimization of FPSO Glen Lyon Mooring lines from vessel positioning to detailed stress analysis

Optimization of FPSO Glen Lyon Mooring lines from vessel positioning to detailed stress analysis

An innovative approach for numerical simulation of stress relaxation of structural cables

Relaxation test on cable with large diameter is usually difficult and money consuming due to its extremely large ultimate tensile strength. A simplified finite element modeling method for stress relaxation simulation of steel wire, semi-parallel wire strands and spiral strands was proposed. Simplified relationship between stress relaxation and creep of steel wires was derived and a simplified modeling method on spiral wire composition was proposed. The whole numerical approach incorporated the steel wire creep model and the simplified cable compositions to realize the simulation of stress relaxation behavior of structural cables. The effectiveness of proposed creep calibration and cable stress relaxation simulations were verified through relaxation test data of single-wires and 19-wire semi-parallel wire strands. The 19-wire, 37-wire, 61-wire, 91-wire and 127-wire semi-parallel wire strands and spiral strands at different initial stress levels were all simulated. Due to the spiral wire composition and corresponding gradient wire stress distribution under axial tension, relaxation rate of semi-parallel wire strands and spiral strands were all larger than that of single steel wire. Semi-parallel wire strands presented a decreasing relaxation rate with the increase of cable dimension. Spiral strands had larger relaxation rate than similar-sized semi-parallel wire strands, and present a slight relaxation increase trend with cable dimension. The proposed finite element modeling method can realize the stress relaxation analysis of large diameter structural cables, with only stress relaxation test data of single wires or small diameter cables.

Shear strength properties of cable bolts using a new double shear instrument, experimental study, and numerical simulation

A newly developed double shear apparatus without contact between concrete blocks was developed to conduct a series of double shear tests. This new double shear apparatus is capable of determining the pure shear strength of pre-tensioned fully grouted cable bolt without friction between sheared concrete blocks. Five different types of cable bolt, with various pretension loads, were tested to investigate the influence of surface profile type and pretension load on the shear strength of cable bolt. Concrete blocks of 40MPa strength and the Stratabinder HS grout were used for consistency across the entire tests. The results showed that the plain cable bolts had higher peak shear load compared with the indented and spiral strand cable bolts. The shear displacement and peak shear load decreased by increasing the pretension load. A numerical analysis was carried out, based on the Fast Lagrangian Analysis of Continua (FLAC 2D) and the result was compared with the experimental data. It was observed that FLAC 2D is capable of simulating the performance of cable bolt satisfactorily.