Strand Tension Research Articles

Research on methods for controlling strand sag in main cables

The accuracy of main cable construction in suspension bridges is directly influenced by the sag of the strands during the erection process. Thus, effective methods for controlling strand sag are crucial. However, the current control standards and methods are primarily based on practical engineering experience, lacking quantitative analysis and a sufficient basis. This paper aims to address this gap by summarizing four commonly used strand sag control methods and proposing a quantitative analysis model that considers the influence of random factors. The model quantifies the impact of these methods on the main cable shape and strand tension after cable tightening. To illustrate the practical application, a suspension bridge is utilized as a case study. The results of the study illustrate a linear relationship between the main cable sag and inter-strand distance, with each control method exhibiting a varying linear change rate. Moreover, the discrepancy in strand distance contributes to uneven strand tension after cable tightening. Random errors contribute to the dispersion of the main cable sag and strand tension, which are further exacerbated by cumulative errors between layers of general strands. Based on the study’s results, this paper provides valuable references for the erection and control of the main cable in suspension bridges.

Tension evaluation of prestressed strand based on combined features of nonlinear ultrasonic mixing

The estimation of prestressed strand stress levels is of great significance in ensuring the structurally reasonable performance of post-tensioned concrete structures, cable-stayed bridges, and arch bridges. This paper proposes a method to evaluate the remaining tensile stress on the strand through the ultrasonic mixing technique. The relationship between the strand tension and the nonlinear harmonics is established based on the theory of contact acoustic nonlinearity, and the acoustic nonlinear parameters at different tension levels are investigated by finite element analysis and step-loading experiments. The results show that the nonlinear parameters follow a power-law decrease with the increase in the tensile stress. To overcome the shortage of decreasing sensitivity of theoretical nonlinear parameters in monitoring early loosening, support vector regression is introduced to utilize complex high-order nonlinear generations in stress evaluation. With this approach, the accuracy of early-stage stress evaluation based on wave mixing has been remarkably improved.

An NCFA-Based Notch Frequency Feature Extraction Method for Guided Waves and Its Application in Steel Strand Tension Detection

An NCFA-Based Notch Frequency Feature Extraction Method for Guided Waves and Its Application in Steel Strand Tension Detection

Swelling Effect on the Yielding, Elasticity, and Fracture of Double-Network Hydrogels with an Inhomogeneous First Network

Typical double-network (DN) gels are formed by free radical polymerization, and the constituent network strands have a wide molecular weight distribution. It is important to clarify what determines the specific mechanical behaviors of DN gels with a strongly inhomogeneous first network, including the criteria for the occurrence of yielding and strain hardening during tensile deformation, as well as their impact on the fracture toughness. In this work, we first studied the influence of swelling ratio λs of the first network synthesized from radical polymerization on the yielding and strain hardening of DN and triple-network (TN) gels by tensile tests. We observed scaling relations for the yielding stretch ratio λy ∝ λs–1 and engineering yielding stress σy ∝ λs–2, like those found for DN hydrogels with a homogeneous first-network structure. Furthermore, we found a universal relationship λyσy ∝ λs–3 that is independent of the cross-linking structure of the first network. We found that these scaling relations agree well with the theoretical predictions derived from a simple one-dimensional affine model for the fracture of a homogeneous network, suggesting the affine swelling effect on the fracture of network strands. Next, we showed that swelling induces more tension in the inhomogeneous network than in the homogeneous network, suggesting non-affine swelling behavior at the network strand scale for the inhomogeneous network. We discussed the molecular origin of the discrepancy between the affine swelling effect on the fracture of network strands and the non-affine swelling behavior for strand tension. Finally, we investigated the influence of swelling ratio λs on the local yielding behavior ahead of the crack tip and the fracture toughness of the DN and TN hydrogels using pure shear tests. We found that crack-tip yielding zone size hy ∝ λs1 and fracture energy Γ ∝ λs–2. Furthermore, we found that the relationship Γhy∝λs−3 is also independent of cross-linking structure and obeys a universal relationship with the true yielding stress λyσy ∝ λs–3 determined from the tensile tests, which is in excellent agreement with nonlinear elastic fracture mechanics theory. This work provides important insight into the specific mechanical behaviors of the DN gels with an inhomogeneous first network.

Analysis of Factors Affecting Strand Tension in Cable-Twisting Equipment and Method for Equilibrated Control

To address the issue of tension fluctuations and deviations among the strands during cable-twisting production, it is necessary to establish a relationship model between the centrifugal force, frictional force, and tension experienced by each strand in a single span range under the state of traveling and rotating. Considering the differences of strand alignment at the distribution reel, the effects of centrifugal force and friction on strand tension under different twisting-deflection paths and cylinder-traveling paths should be analyzed. In our study, different stress states of each strand were applied to simulate and verify the tension fluctuations and deviations of every strand under various traveling and deflection paths. The experimental results show that the increasing travel path of the strand cylinder will cause an increase in the average strand tension. Different deflection paths in the distribution reel will affect the range of the strand tension fluctuation. A sliding mode controller based on a discrete system was designed in MATLAB to control the tension fluctuation and deviation among the strands. The results indicated that this control method can effectively reduce the tension deviation between strands, and the average tension fluctuation range of each strand was reduced by 79.5%.

A method for calculating strand tension in the anchor span of a suspension bridge considering the rotation of a splay saddle

This paper reports a method for strand tension in anchor spans considering rotation. A kind of co-moved coordinate system, a saddle local coordinate system, was set up. This system implemented the rotation of the splay saddle through the rotation of the coordinate system, and all calculations proceeded in this coordinate system. Considering the rotation of the anchoring surface by the rotation of the local coordinate system of the anchoring surface, the anchorage point coordinates of strands were transformed to the local saddle coordinate system. There was a two-layer iteration adopted in the calculation. In the inner iteration, the cable force at the end of the vertical bend was taken as the variable, and the ordinate of the anchorage point was taken as the target value. In the outer iteration, the vertical tangential angle at the end of the vertical bend was taken as the variable, and the ordinate of the anchorage point was taken as the target value. The method carried out the rotation of the splay saddle and anchor surface and was simple, convenient and without approximation. The effect of rotation was considered precisely; it showed stability during the process of two-layer iteration, powerful adaptation and higher efficiency and had been successfully applied in the construction control of the Wufengshan Yangtze River Bridge, the world's first kilometer-level combined highway and railway suspension bridge.

Experimental and numerical study on the axial compression performance of the prestressed sleeved members

The progressive collapse of large-span spatial structures can be triggered by the buckling of compression members. To further improve the stable load capacity of compression members, this study proposes a prestressed sleeved member by combining a prestressed stayed column system with a sleeved member. The experimental results show that the prestressed sleeved members possess a high load capacity, large secondary stiffness and moderate recovery performance, with the buckling modes of the members including first-order and second-order buckling. A nonlinear finite element (FE) model for the prestressed sleeved members is developed based on the experimental model. In addition, a series of parametric analyses are conducted to investigate the effects of the initial imperfection amplitude ratio, inner tube length to slenderness ratio, strand cross-sectional area ratio, inner and outer tube cross-sectional stiffness ratio and central support plate equivalent height ratio on the axial compression performance of the specimens. Furthermore, a simplified calculation model of the prestressed sleeved members is proposed for the case of second-order buckling, and theoretical calculation formulas are presented for three key points of the axial force–displacement curves of specimens. In contrast to the theoretical and FE results, the maximum errors of axial displacement and axial force do not exceed 15%. In addition, the steel strand tension, the contact force, and the lateral deflection of the middle section of the inner half-tube are highly consistent, which verifies the proposed relevant assumptions and theoretical calculation formulae.

Introducing a new seismic efficiency index of post-tensioned self-centering steel moment connections

Assuming that damages to buildings in earthquake are repairable, retrofitting them is not always economically justified. As an alternative solution, buildings can be designed such that damages are limited to only easily repairable elements. One of the structural systems that provide this possibility is the post-tensioned self-centering moment resistant frame. In self-centering structures, after the event of an earthquake, due to an opening in the gap of beam to column connection and with the help of highly resistant strand tension, residual drift is eliminated. In this study, an attempt is made to develop an efficiency index of post-tensioned self-centering steel moment resistant connections through the analyses of dispersion indices. After a time-history and parametric analysis of three models of steel buildings with self-centering connections, a model will be selected for evaluating the efficiency index that has the lowest sensitivity resulting from dispersion analysis in the study population. Then, between the seven introduced indices, efficiency indices will be compared and optimized. Evaluations show that the Efficiency index of self-centering frame (EISCF), calculated based on coefficient of variance, will increase the accuracy and speed of analysis.

Numerical analysis of the tension and twist of staple strands in embeddable and locatable spinning

This study reports a numerical analysis on embeddable and locatable spinning systems. The finite element method is used to quantify the relationship between the tension and twist of staple strands and the spinning parameters. The model was constructed using the three-dimensional beam element, which is capable of simulating the stretching, bending and torsion behavior of the filament and the staple strand. It was found that the staple strand shares far less load (around 13.8%) than the filament during the spinning process. The twist is mainly distributed on the composite yarns and less on other zones. The pretension of the filament, the filament–strand distance ratio, the twist of the composite yarn and the material fed-in velocity were investigated for their influence on the tension and twist of the staple strand. Numerical predictions showed that higher filament tension and filament–strand ratio lead to less load and more twist on the staple strand. This is beneficial in producing stronger and smoother yarns and avoiding end breakages. It was also determined that strand tension and twist increase with an increase in composite yarn twist and a decrease in material fed-in velocity.

Twine Tension in High-Density Large Square Bales

Abstract.When greater density bales are made, baler manufacturers recommend using twine with greater knot strength. When twine fails, bale integrity is lost, harvesting costs increase, and productivity suffers. Twine failure typically occurs in the knot on the top strand of the twine. A better understanding of twine tension in the top strands could help reduce failures, allow for improved knot strength recommendations, and ultimately lower baling costs. A system was developed to measure the tension of the top strands while baling a variety of crops with a high-density large square baler. Depending on the bale chute design, twine tension was greatest as the bale cantilevered from the chamber but had not yet touched the chute or just as the bale fully exited the bale chamber. In either case, the absolute maximum recorded tensions were typically less than 60% of the twine specified knot strength. Pulses in synchronization with the plunger frequency were superimposed on the nominal twine tension. Tension was usually greatest in the outer left twine and the other right twine because for each, there was only one neighboring twine to share the load. Average twine tension over the first 60 s after the bale rested on the ground was linearly related to bale density. Crop stress relaxation reduced tension up to 20% within 20 min after the bale was placed on the ground. Top strand tension approached 60% of knot strength for only a short duration as the bale exited the chamber and after that, the tension was much less than the specified knot strength. Therefore, design changes or strategies that reduce tension during the critical period when the bale exits the chamber could reduce maximum knot strength requirements and lead to lower baling costs. Keywords: Bales, Density, Tension, Twine.

Strand Tension Control in Anchor Span for Suspension Bridge Using Dynamic Balance Theory

Strand tension control is essential in suspension bridge safety. However, few quantitative studies have examined the bending rigidity and boundary condition behavior of strands in the anchor span of suspension bridges because of their special structure and complex configuration. In this paper, a new calculation method for strand tension is explored by using dynamic balance theory to determine the effect of bending rigidity and boundary conditions. The accuracy and effectiveness of the proposed method are tested and confirmed with verification examples and application on Nanxi Yangtze Suspension Bridge in China. The results indicated that only low-order frequency calculation could be used to calculate the strand tension without considering the effect of bending rigidity to ensure control accuracy. The influence of bending rigidity on the control precision is related to the tension and the length of the strands, which is significantly determined by the specific value between the stress rigidity and the bending rigidity. The uncertain boundary conditions of the anchor span cable, which are fixed between consolidated and hinged, also have a major effect on the control accuracy. To improve the accuracy of strand tension control, the least squares method is proposed during the tension construction control of the anchor span. This approach can significantly improve the accuracy of the tension control of the main cable strand. Some recommendations for future bridge analysis are provided based on the results of this study.

Special Issue on Sustainable Civil Infrastructures: Innovative Technologies and Materials

Special Issue on Sustainable Civil Infrastructures: Innovative Technologies and Materials

Optimal Zone II flexor tenorraphy

Optimal Zone II flexor tenorraphy

Mathematical modelling of a bridge stay cable for individual strand tensioning in several cycles

Mathematical modelling of a bridge stay cable for individual strand tensioning in several cycles

현수교 PPWS 가설중 형상관리를 위한 PPWS 새그 및 장력민감도 산정법 개발

현수교 주케이블은 완성시 교량의 구조적 건전성을 나타내는 중요한 지표이다. 주케이블은 가설완료시 자유 매달림(free hanging) 상태의 형상이 되며 교량완성시 행어, 보강형 등의 고정하중을 지지하여 가설완료시 형상과는 차이가 발생한다. 따라서, 주케이블의 가설완료시 형상이 교량완성시 형상에 직접적인 영향을 미치므로 가설중 형상관리가 매우 중요하다. 주케이블의 가설중 형상관리는 중앙 및 측경간은 새그조정으로, 정착경간은 장력조정으로 수행된다. 새그조정은 새그조절량에 대한 스트랜드 길이 조절량을 나타내는 산정값인 새그민감도가 필요하며 장력조정은 온도변화에 대한 장력변화량을 나타내는 장력민감도가 필요하다. 이에 본 연구에서는 케이블 형상가정에 따라 유도된 기본식과 이로부터 도출된 미분 관계식으로부터 새그 및 장력민감도를 산정하는 방법을 제안하였다. 그리고, 다양한 새그변화 요인에 대해 현수선 기본식을 사용한 비선형 수치해석 새그민감도 계산 흐름도를 제안하여 미분관계식을 적용한 새그민감도 결과와 비교하였다. 또한, 각 새그변화 요인이 복합적으로 발생함으로 이를 고려하여 케이블의 최종 새그변화량을 산정하는 방법을 제안하였다. PPWS 공법으로 시공중인 실교량을 대상으로 PPWS의 길이변화 및 온도변화, 경간장변화 등의 다양한 시공여건의 변화에 따른 새그 및 장력민감도를 산정하였다. 본 연구내용이 주케이블 가설중 형상관리 방법에 대한 체계적인 지침이 되기를 바라며, 향후 실교 현장적용 및 실증에 의해 완성도를 높일 것이다. Main cable of a suspension bridge is the important member which shows the overall structure integrity at bridge completion. Configuration of main cable is a free hanging state at cable erection completion and is different from that at bridge completion supporting the dead loads such as hanger, girder, and so on. Accordingly, the configuration control under cable erection is considerably significant because the configuration at cable erection completion has direct influence on that at bridge completion. That is performed by sag adjustments at center, side span and tension adjustments at anchor span. The former needs the sag sensitivity which represents the control quantity of strand length corresponding to that of sag. The latter requires the tension sensitivity which shows the change of strand tension according to that of strand temperature. In this study, the fundamental equations of cable were derived with the assumption of either catenary or parabola shape, the differential-related equations using chain rule on horizontal tension were drawn from those and finally the estimation methods of the sag / tension sensitivity were proposed from both those. The nonlinear numerical analysis flow charts of sag sensitivity based on the catenary equations were proposed and the sag sensitivities grounded on the differential-related equations were compared with the results using them for various parameters of sag change. Also, considering the combinations of sag change parameters, the calculation method of the final variation for the cable sag was suggested. For the real suspension bridge under construction with PPWS method, the sag/tension sensitivity were estimated considering the construction conditions like the change of PPWS length, PPWS temperature, bridge span, etc.. We hope that this study will be a systematic guideline for the configuration control under main cable erection and improved highly by field verification in the real bridge site.

Shortcuts in Arthroscopic Knot Tying

Background: Shortcuts for throwing 3 alternating reversed half-hitches on alternating posts (RHAPs), in which the post is switched by alternating strand tension to “flip” the knot, have been advocated but never validated in a biomechanical study. Hypothesis: Shortcut tying techniques will affect knot security or loop security. Study Design: Controlled laboratory study. Methods: A single surgeon tied 90 knots using No. 2 FiberWire through an arthroscopic cannula. Half had a static “surgeon’s base,” and half had a Tennessee slider base. Three techniques were used to create 3 RHAPs: (1) rethreading, (2) knot “flipping” where half-hitches were tensioned by past-pointing, and (3) knot “flipping” where half-hitches were tensioned by alternating past-pointing and over-pointing. Each knot was subjected to a preload of 5 N, followed by 1000 cycles of 5 N to 45 N at 1 Hz, and a single load to failure. Results: When compared with Tennessee knots, surgeon’s knots had a lower incidence of knot slippage and catastrophic failure as well as higher loads to clinical and ultimate failure. Shortcut techniques did not affect the properties of surgeon’s knots. However, when used to secure Tennessee knots, past-pointing decreased load to clinical failure and ultimate load to failure. Over-pointing increased the incidence of knot slippage and catastrophic failure and decreased load to clinical failure and ultimate load to failure. Loop security was marginally increased by both past-pointing and over-pointing. Conclusion: When all tying techniques are considered, surgeon’s knots outperform Tennessee sliding knots. Shortcut techniques do not alter the properties of surgeon’s knots. However, when used to secure Tennessee sliding knots, shortcuts lead to unacceptably high rates of knot slippage and catastrophic failure as well as decreased knot security. Clinical Relevance: The outcomes of arthroscopic rotator cuff or labral repairs can be compromised when using shortcut tying methods to secure sliding Tennessee knots.

Analysis of the construction process of cable-stayed bridges built on temporary supports

The temporary supports erection method is a fast and economical way of building cable-stayed bridges. In this method the bridge deck is first erected on a set of temporary and permanent supports and then, the stays are successively placed and tensioned according to a predefined tensioning sequence. A proper definition and analysis of this sequence is very complex as the structure is highly statically indeterminate, exhibits a non linear behavior and has a changing static scheme.Despite its importance, no specific research referring to the modeling of the temporary support erection method has been found as most of the modeling procedures are proposed for the alternative erection technique, the cantilever erection method. The modeling carried out by most of these methods is based on the opposite construction sequence followed on site, this is to say, the structure is disassembled from the desired final stage (Objective Completion Stage, OCS).A procedure, the Backward Algorithm (BA), is formally presented in this paper for calculation of the erection of cable-stayed bridges built on temporary supports. Because of its simplicity the BA can be reproduced by any structural code that enables the modeling of the prestresses of the stays by means of imposed strains or imposed temperature increments. Another advantage is that no separate models are needed to calculate the evolution of stresses in the strands when the strand by strand tensioning technique is used. Furthermore, the stay elongations when prestressed can be easily obtained when the stays are prestressed in a single operation or strand by strand. This information is important to control the correct and safe prestressing of the stay on site. In addition, it also help the designer to control if the anchor wedge bites the strand in the same position several times during the prestressing process.

The impact of tensioning device mal-positioning on strand tension during Anterior Cruciate Ligament reconstruction

BackgroundIn order to confer optimal strength and stiffness to the graft in Anterior Cruciate Ligament (ACL) reconstruction, the maintenance of equal strand tension prior to fixation, is desired; positioning of the tensioning device can significantly affect strand tension This study aimed to determine the effect of tensioning device mal-positioning on individual strand tension in simulated cadaveric ACL reconstructions.MethodsTwenty cadaveric specimens, comprising bovine tibia and tendon harvested from sheep, were used to simulate ACL reconstruction with a looped four-strand tendon graft. A proprietary tensioning device was used to tension the graft during tibial component fixation with graft tension recorded using load cells. The effects of the tensioning device at extreme angles, and in various locking states, was evaluated.ResultsStrand tension varied significantly when the tensioning device was held at extreme angles (p < 0.001) or in 'locked' configurations of the tensioning device (p < 0.046). Tendon position also produced significant effects (p < 0.016) on the resultant strand tension.ConclusionAn even distribution of tension among individual graft strands is obtained by maintaining the tensioning device in an unlocked state, aligned with the longitudinal axis of the tibial tunnel. If the maintenance of equal strand tension during tibial fixation of grafts is important, close attention must be paid to positioning of the tensioning device in order to optimize the resultant graft tension and, by implication, the strength and stiffness of the graft and ultimately, surgical outcome.

Parameters Influencing Corrosion and Tension Capacity of Post-Tensioning Strands

A 12-month long strand corrosion test program with 298 specimens was conducted to identify and quantify parameters influencing corrosion and tension capacity of strands in post-tensioned bridges. The parameters investigated were grout class, moisture content, chloride concentration, void type, and stress level. The test specimens were 41 in. (1041 mm) long, in unstressed or stressed conditions, partially or completely embedded in cementitious grout, and exposed to various environmental conditions representing possible field conditions. After the exposure period, the grout material was removed and the strand surfaces were cleaned and visually evaluated for corrosion damage. The tension capacities of the strands were then determined. Results indicate that the corrosion was most severe at or near the grout-air-strand (GAS) interface. Corrosion evaluation and statistical analysis of the strand tension capacity results show that orthogonal, inclined, and bleedwater void conditions caused more corrosion and tension capacity loss than parallel and no-void conditions. The change in grout class did not result in statistically significant changes in the tension capacity of the strand samples evaluated. Statistically significant changes in tension capacity were observed with changes in the GAS interface, stress level, moisture content, and chloride concentration.

Study of a steel strand tension sensor with difference single bypass excitation structurebased on the magneto-elastic effect

With many steel strands used in various important machines and architectural structures,health monitoring of strand tension becomes more and more important to ensure theequipment or structures’ safety. Contrasted with the method of vibration frequencyand strain gages, the method of measuring the steel strand tension based onthe magneto-elastic effect is more capable of meeting the requirements of healthmonitoring. Yet the structure of the sensor is mainly a sleeve structure, and the steelstrand to be measured serves as the core of primary and secondary solenoids. Thisstructure is very difficult to fix and maintain. On the other hand, a change oftemperature will strongly affect measurement results, and experiments prove thattemperature error compensation by using a temperature compensation curveis not effective enough. Therefore in this paper the principle of a cable tensionsensor based on the magneto-elastic effect is expounded, the theory of temperatureinfluence is explored, a difference structure by single bypass excitation is devised,its magnetic loop is analyzed, an experiment is designed, and experiments ontemperature compensation and pulling tension are carried out. The experiment resultsindicated that the structure of the sensor is feasible, temperature errors can becompensated for automatically, after which temperature errors become less than0.012 MPa °C−1, and repeating errors of tension are less than 0.15%, which meet the measurementrequirements.