Prestressing Steel Wires Research Articles

Fracture Analysis of the Spiral Ribbed Pre-Stressed Steel Wire during Pre-Stretching

In order to analyze the case of the spiral ribbed pre-stressed steel wire failure during pre-stretching, OM, SEM and EPMA was used to do the inspection and analysis of the fracture sample. The result show that the crack propagation during pre-stretching of the wire bring on the fracture, which is cased by the net carbide and phosphorus segregation in the center of the raw material 82B rod in the drawing process.

The Role of Residual Stresses in the Performance and Durability of Prestressing Steel Wires

Residual stresses developed during wire drawing influence the mechanical behavior and durability of steel wires used for prestressed concrete structures, particularly the shape of the stress–strain curve, stress relaxation losses, fatigue life, and environmental cracking susceptibility. The availability of general purpose finite element analysis tools and powerful diffraction techniques (X-rays and neutrons) has made it possible to predict and measure accurately residual stress fields in cold-drawn steel wires. Work carried out in this field in the past decade, shows the prospects and limitations of residual stress measurement, how the stress relaxation losses and environmentally-assisted cracking are correlated with the profile of residual stresses and how the performance of steel wires can be improved by modifying such a stress profile.

Influence of Drawing Straining Path on Hydrogen Damage of Prestressing Steel Wires

Residual stress and strain states, produced during cold drawing, play a key role in hydrogen embrittlement (HE) of prestressing steel wires, because of hydrogen accumulation in certain places of the material is affected by stress and strains fields. Taking into account that the drawing straining path directly affects both residual stress and plastic strain distribution, the aim of the present paper is to clarify the influence of drawing straining path in the residual state and, consequently, its influence on the HE process of prestressing steel wires.

Corrosion-Fatigue of High Strength Steel Bars: Evolution of Crack Aspect Ratio

Abstract. This paper shows the evolution of the surface crack front in prestressing steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)2+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (characterized with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan law, and using a three-parameter stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth and by the variation of the maximum dimensionless SIF at the crack front

High Performance Prestressed Polymer Mortar System in the Application of Concrete Structure Reinforcement

High performance polymer mortar and the high strength prestressed steel wire characteristics are researched and analysised in this paper. High performance prestressed polymer mortar system is proposed in the application of concrete structure reinforcement on the basis of those two existing material of china, reinforcement construction process and successful practical applications is also given. This technology organically combine high-performance polymer mortar with prestressed steel with fire resistance, good corrosion resistance, strong anti-aging, anti-cracking, durability and other advantages, so it is worth further study and extension application.

Hydrogen Degradation of Cold-Drawn Wires: A Numerical Analysis of Drawing-Induced Residual Stresses and Strains

Abstract Hydrogen degradation represents a problem of major technological concern in the structural integrity of prestressed concrete structures in which cold-drawn wires are the main structural component and can suffer the deleterious effect of hydrogen, with the subsequent risk of catastrophic failure. This paper presents an innovative numerical analysis of hydrogen degradation of cold-drawn prestressing steel wires, focused on the two relevant variables influencing the phenomenon of hydrogen transport by diffusion in the metal: residual stresses generated by manufacture and plastic strains after cold work. To achieve this goal, two real (industrial) drawing processes are analyzed with two main differences, namely, the reduction of cross-sectional area performed at the first drawing stage and the number of drawing steps used in the whole process. Generated results prove the importance of an adequate design of the cold-drawing process with regard to the residual stress-and-strain field and its relevant r...

Influence of coiling on the stress relaxation of prestressing steel wires

AbstractThe possible deleterious effects of coiling and long‐term storage of coiled wires on the stress relaxation behaviour of prestressing steel wires has been checked by means of experimental work and a simple analytical model. The results show that if the requirements of standards are fulfilled (minimum coiling diameters), these effects can be neglected. However, some other factors, such as previous residual stresses, long‐term storage or storage at high temperatures, can trigger or emphasize this damage to the material. In the authors' opinion, checking the final curvature of the wires after uncoiling prior to prestressing, as required in some standards, is to be recommended.

Effects of manufacturing-induced residual stresses and strains on hydrogen embrittlement of cold drawn steels

Cold drawn wires of eutectoid pearlitic steel are widely used for prestressing concrete structures that usually work in harsh environments, so that stress corrosion cracking of prestressing steel is a problem of major technological concern. In this paper a previous model developed by the authors is applied to analyse the influence of the residual stress-and-strain profiles after cold drawing on the hydrogen embrittlement susceptibility of prestressing steel wires. Numerical results show the relevant role of both residual stress and strain field in hydrogen diffusion in this material

Fatigue performance of cold drawn prestressing steel: The effect of sudden load changes

This paper analyzes the effect produced by sudden load changes on the fatigue of cold drawn prestressing steel wires to be used in prestressed concrete. Fatigue tests were performed on cylindrical samples under load control, using fatigue steps with different stress, and observing the appearance of a transient state in the fatigue crack propagation curve (da/dN-ΔK) when the product KmaxΔK suddenly decreases, a sort of overload retardation effect that allowed the calculation of the plastic zone size. In addition, the fatigue crack growth rate in the Paris regime, da/dN, obeys mainly to the parameter ΔK and it is hardly ever affected by Kmax. The study of the fatigue fracture surface shows: (i) that the micro-roughness of ductile micro-tearing patterns is a function of Kmax; (ii) the existence, in some tests, of a small zone with fatigue initiation fractography (with a tearing topography surface), related to the decrease of crack tip opening displacement, a phenomenon similar to that of crack initiation and growth from a micro-notch.

Study on Prestressed Laminated Strand Lumber and its Load-Carrying Capacity

Owing to some problems in the existent plywood products such as weak shear capacity and weak wear intensity, as while as the large consumption of crude wood resources, prestressed laminated strand lumber (PLSL) is proposed in this paper, in which the multiple integration method and prestressed technology are adopted to obtain a higher strength. More significantly, used wood can be reused as the raw material of PLSL, then the crude wood will be conserved and the cost will be lowered. To study its mechanical properties, the commercial software ANSYS is adopted to establish the finite element models of PLSL. The diameter and spacing of prestressed steel wire, the magnitude of the prestress and the width of the lumber are some factors considered. Based on the nonlinear finite element buckling analysis of these lumbers, some major conclusions are summarized as follows: (1) The improvement of strength is comparatively obvious to use PLSL compared with the traditional plywood products; (2) The ultimate bearing load is rising along with the increase of the diameter of the prestressed steel wire and the width of the lumber; (3) The ultimate bearing load is descending with the increase of the spacing of the prestressed steel wire; (4) The ultimate bearing load is rising along with the increase of the magnitude of the prestress at first, but when the prestress reaches a certain level, the ultimate bearing load starts to descend.

Reactions and energy absorption of trees subject to rockfall: a detailed assessment using a new experimental method

A new method for investigating the detailed reaction and the energy absorption of trees during a rock impact was developed and applied to 15 subalpine Norway spruce (Picea abies L. Karst) trees. A wedge-shaped trolley, guided by prestressed steel wires, was mounted on a forested slope to simulate a falling rock. The trolley accelerates down the wires and hits a tree at a preselected stem height with variable energies. The tree displacements and accelerations during the impact were recorded to determine reactions and energy absorption for the stem, root-soil system, crown and the entire tree. Trees absorbed the kinetic energy of the trolley rapidly by mobilizing strain and inertia forces close to the impact location in the stem and the root-soil system. This energy was then gradually dissipated all over the tree through permanent deformations and damping. The stem assimilated more energy than the root-soil system. The tree's energy absorption capacity was limited by stem-bending stresses at impact height, by shear stresses at the stem base and by lack of resistance of the root-soil anchorage. It was positively and exponentially related to stem diameter at breast height and negatively related to impact height. The field experiment enabled a physical description of how a tree reacts to a rock impact and highlighted the most important and critical components of the tree for its energy absorption. Such descriptions should help make computer simulations of rock-forest interrelations more precise and thus improve management strategies to ensure that forests can provide protection against rockfall.

Numerical modelling of crack shape evolution for surface flaws in round bars under tensile loading

This paper proposes a numerical procedure for calculating the crack shape evolution in semielliptic surface flaws in round bars under tensile loading, studying how the aspect ratio (relation between the semiaxes of the ellipse) changes with the relative crack depth. It was been assumed that each point at the crack front advances in direction perpendicular to such a front, according to the Paris–Erdogan Law. The stress intensity factor was computed using a triparametric expression proposed in the scientific literature. Numerical results of the present model agree fairly well with experimental results obtain in real prestressing steel wires tested in fatigue.

Experiment and Analysis on the Mechanical Behaviour of PC Simply-Supported Slabs Subjected to Fire

Experiments on the fire resistance of 9 unbonded and 1 bonded prestressed concrete (PC) simply-supported slabs are completed. Calculation formula of the stress in the unbonded prestressing steel wires in PC simply-supported slabs subjected to fire is obtained based on the experimental results. Dividing the section of the slab into strips along its depth according to the distribution of temperature field, on the basis of invariable width of the slab in the surface exposed to fire, the transformed section of the slab subjected to fire can be obtained by multiplying the width of each strip by the elasticity modulus ratio of the strip concerned and the extreme strip in the surface exposed to fire. The stress in concrete and curvature in the researched section caused by load can be obtained based on equilibrium equations of force and moment on transformed section. Then, the methods for calculating concrete thermal strain, transient strain and creep at elevated temperature were introduced, and total strain of a point in the concerned section and total curvature caused by load and temperature can be calculated considering time-dependent effect. After the total curvature of the mid-span section was calculated, the actual stiffness of the critical section in the mid-span can be determined, moreover, the mid-span deflection of the PC slab can be calculated by the virtual displacement principle. The practical calculation formulas for the mid-span deflection of PC simply-supported slabs subjected to fire is presented considering the influences of the deflection of slabs at the ambient temperature, ratio of concrete cover to depth of slabs, load level, combined reinforcement index and span.

Cleavage Stress Required to Produce Fracture Path Deflection in Cold-Drawn Prestressing Steel Wires

Cold-drawn prestressing steel wires exhibit strength anisotropy in the form of fracture path deflection towards a direction approaching the wire axis, or cold drawing line, as a consequence of the pearlitic microstructure orientation induced by the manufacturing procedure. Such a crack path deflection is initiated at certain nuclei (fracture origins) at which axial cracking appears in the cold drawing direction (or wire axis) in the form of micro-cleavage units that produce in the load-displacement curve a macroscopic phenomenon of pop-in. This paper shows that such fracture initiators appear at a certain distance from the fatigue pre-crack tip at which a local maximum of the cleavage stress is located.

Influence of residual stresses and strains generated by cold drawing on hydrogen embrittlement of prestressing steels

Hydrogen embrittlement plays an important role in environmental cracking of prestressing steel wires. The ammonium thiocyanate test (ATT) was implemented as a standard for determination of their susceptibility to environmentally assisted fracture. However, ATT reveals neither how hydrogen induced fracture (HIF) goes on in steel nor the roles of important manufacturing and service factors. To this end, the knowledge of the residual stresses and plastic strains in wires due to cold drawing, as well as the hydrogenation from harsh environments, are the keys to successful predictions of wire lives. This paper advances previous analyses of HIF in cold drawn prestressing wires via numerical modelling, firstly, of the cold drawing process to obtain the distributions of residual stresses and plastic strains, and secondly, of the stress–strain assisted hydrogen diffusion in wires towards creation the conditions for HIF nucleation. Generated results prove the relevant role of residual stress-and-strain field in hydrogen diffusion in the wires, as well as their possible consequences for HIF.

Experimental research on the mechanical property of prestressing steel wire during and after heating

The mechanical property of prestressing steel wire during and after heating is the key factor in the design of fire resistance and after-fire damage evaluation of prestressed structures. Tensile experiment of 16 prestressing steel wires (f ptk = 1770 N/mm2, d = 5 mm, low relaxation of stress) at high temperature and tensile experiment of 14 prestressed steel wires after heating are carried out. According to the experiment, the shapes of stress-strain curves of steel wire at high temperature go smooth and the mechanical property indexes of the steel wire such as strength, modulus of elasticity, etc., degenerate continuously as temperature increased. According to the experiment after heating, the mechanical property of steel wire varies little when the highest temperature that the steel wire has ever been heated to is lower than 300°C; while the stress-strain curves of steel wire become more ductile and the mechanical property indexes of the steel wire degenerate gradually when the highest temperature is higher than 300°C. By applying the theory of viscoelastic mechanics, stress-strain curves of steel wire at high temperatures without loading rate influence are obtained. The law of mechanical property indexes of the wire is presented. The mathematical models of the stress-strain relationship of the pre-stressed steel wire are established. All can serve as basic data for the analysis of fire resistance and after-fire damage evaluation of pre-stressed structures.

Delamination fracture of prestressing steel: An engineering approach

This paper provides a composites engineering approach to explain the stress corrosion behaviour of high-strength prestressing steel wires. To this end, two eutectoid steels in the form of hot rolled bar and cold drawn wire were subjected to slow strain rate tests in aqueous environments in corrosive conditions corresponding to localized anodic dissolution and hydrogen assisted cracking. While a tensile crack in the hot rolled bar always propagates in mode I, in the cold drawn wire an initially mode I crack deviates significantly from its normal mode I growth plane and approaches the wire axis or cold drawing direction, thus producing a mixed mode propagation. In hydrogen assisted cracking the deviation happens just after the fatigue pre-crack, whereas in localized anodic dissolution the material is able to undergo mode I cracking before the deflection takes place. Therefore, a different behaviour is observed in both steels and even in the same steel under distinct environmental conditions. An explanation of such behaviour can be found in the pearlitic microstructure of the steels. This microstructural arrangement is randomly-oriented in the case of the hot rolled bar and markedly oriented under the wire axis direction in the case of the cold drawn wire. Thus both materials behave as composites at the microstructural level and their plated structure (oriented or not) would explain the different time-dependent behaviour in a corrosive environment.

Residual stresses and durability in cold drawn eutectoid steel wires

Prestressing steel wires have excellent mechanical properties but there is a need to improve their durability in aggressive environments. In this work, the influence of residual stresses on the environmentally assisted cracking of these wires is studied. A good correlation has been found between residual stresses at the surface of the wires and the time to rupture during stress corrosion test proposed by the International Federation of Prestressing. Wires with the same microstructure, surface quality and mechanical properties show very different behaviour in aggressive environments depending on their residual stress state. Research shows that environmentally assisted cracking can be improved significantly by acting on the surface residual stresses produced by wire drawing. In addition, in this study a post-drawing treatment to generate compressive residual stresses at the surface of the wires is proposed.

Detection of SCC on prestressing steel wire by the simultaneous use of electrochemical noise and acoustic emission measurements

Electrochemical voltage and current noise were measured simultaneously with acoustic emission (AE) measurements during the stress-corrosion cracking (SCC) of prestressing steel wire. Elongation of the specimens was also measured. Constant load tests were performed on specimens made from prestressing steel with a diameter of 3.2 mm: the central wire of a seven-wire strand was used. The specimens were exposed to diluted sodium thiocyanate (a modified version of the test as proposed in EN ISO 15630–3), with and without the addition of an organic corrosion inhibitor. EN was measured between the stressed central cold-drawn wire and the neighbouring wires which acted as reference electrodes for the electrochemical current and voltage measurements. AE was measured by two AE sensors fixed to the specimen. In order to characterize the SCC processes on the prestressing steel wire, the results of all the used techniques were analysed and compared. The effect of the inhibitor on these processes was also studied. A significantly longer time to failure was observed in the experiments with the added inhibitor. The results of the techniques, in combination with SEM and metallographic inspections, confirmed that the inhibitor had a specific influence on SCC. It was concluded that measurements of combined methods are promising for the reliable detection of SCC.

이축반복하중을 받는 2주형 철근콘크리트 교각의 내진성능과 보강

Seismic performance and retrofit of reinforced concrete (RC) two-column piers widely used at roadway bridges in Korea was experimentally evaluated. Ten two-column piers that were 400 mm in diameter and 2,000 mm in height were constructed. These piers were subjected to hi-directional cyclic loadings under a constant axial load of . Test parameters were the confinement steel ratio, loading pattern, lap splice of longitudinal reinforcing bars, and retrofitting method. Specimens with lap-spliced longitudinal bars were retrofitted with steel jacket, pre-stressing steel wire, and steel band. Test result showed that while the specimens subjected to bi-directional lateral cyclic loadings which consisted of two main amplitudes in the transverse axis and two sub amplitudes in longitudinal axis, referred to as a T-series cyclic loadings, exhibited plastic hinges both at the top and bottom parts of the column, the specimens subjected to bi-directional lateral cyclic loadings in an opposite way, referred to as a L-series cyclic loadings, exhibited a plastic hinge only at the bottom of the column. The displacement ductility of the specimen under the T-series loadings was bigger than that of the specimen under the L-series loadings. Specimen retrofitted with pre-stressing steel wires exhibited poor ductility due to the upward shift of the plastic hinge region because of over-reinforcement, but specimens retrofitted with steel jacket and steel band showed the required displacement ductility. Steel band can be an effective retrofitting scheme to improve the seimsic performance of RC bridge piers, considering its practical construction.