Temperature Dependence of Ultrasonic Longitudinal Guided Wave Propagation in Long Range Steel Strands

Ultrasonic guided wave inspection is an effective non-destructive testing method which can be used for stress level evaluation in steel strands.Unfortunately the propagation velocity of ultrasonic guided waves changes due to temperature shift making the prestress measurement of steel strands inaccurate and even sometimes impossible.In the course of solving the problem,this paper reports on quantitative research on the temperature dependence of ultrasonic longitudinal guided wave propagation in long range steel strands.In order to achieve the generation and reception of a chosen longitudinal mode in a steel strand with a helical shaped surface,a new type of magnetostrictive transducer was developed,characterized by a group of thin clips and three identical permanent magnets.Excitation and reception of ultrasonic guided waves in a steel strand were performed experimentally.Experimental results shows that in the temperature range from-4 ℃ to 34 ℃,the propagation velocity of the L（0,1） mode at 160 kHz linearly decreased with increasing temperature and its temperature dependent coefficient was 0.90（m·s-1 ·（℃）-1） which is very close to the theoretical prediction.The effect of dimension deviation between the helical and center wires and the effect of the thermal expansion of the steel strand on ultrasonic longitudinal guided wave propagation were also analyzed.It was found that these effects could be ignored compared with the change in the material mechanical properties of the steel strands due to temperature shift.It was also observed that the longitudinal guided wave mode was somewhat more sensitive to temperature changes compared with conventional ultrasonic waves theoretically.Therefore,it is considered that the temperature effect on ultrasonic longitudinal guided wave propagation in order to improve the accuracy of stress measurement in prestressed steel strands.Quantitative research on the temperature dependence of ultrasonic guided wave propagation in steel strands provides an important basis for the compensation of temperature effects in stress measurement in steel strands by using ultrasonic guided wave inspection.

PROPAGATION CHARACTERISTICS OF HIGH ORDER LONGITUDINAL MODES IN STEEL STRANDS AND THEIR APPLICATIONS

Propagation characteristics of high order longitudinal modes of ultrasonic guided waves in seven-wire steel strands are investigated theoretically and experimentally. According to these analysis results, proper longitudinal modes are selected for defect detection in steel strands. Dispersion curves for helical and central wires in a 17.80 mm nominal diameter seven-wire steel strand are numerically obtained firstly, and propagation characteristics of high-order longitudinal modes, such as wave structures, attenuation and dispersion, are analyzed. In experiments, the signals of ultrasonic guided wave at different high frequencies are excited and received at one end of a steel strand by using the same single piezoelectric transducer. The identification of longitudinal modes in the received signals is achieved based on short time Fourier transform. Furthermore, appropriate L（0, 5） mode at 2.54 MHz is chosen for detecting an artificial defect in a helical wire of the steel strand. Results show that high order longitudinal modes in a high frequency range with low dispersion and attenuation whose energy propagates mainly in the center of the wires can be used for defect detection in long range steel strands.

Experimental Study on Bonding Properties Between Steel Strand and Concrete at Cryogenic Temperatures

To study the bonding properties between steel strand and concrete at room and cryogenic temperatures, a series of center pullout experiments were conducted on 96 bonding anchorage specimens at the lowest temperature of-165 ℃. The impacts on the bonding property of such parameters as the temperature, concrete strength, the relative concrete cover thickness, and the relative anchorage length were analyzed. The test results indicate that the changes in temperature have a clear effect on the bonding property between steel strand and concrete. As the temperature decreases, the bond stress, which corresponds to a 1 mm slip of steel strand in relation to concrete, and the ultimate bond strength initially increase and subsequently decrease at the inflection point of-80 ℃. The impact of the concrete strength on the bonding property, as shown by the tensile strength and the moisture content interaction, indicates that the bond stress vs concrete strength curve initially increases and later decreases with a decrease in temperature; the bond stress vs concrete cover thickness curve linearly increases, but the bond stress vs anchorage length curve linearly decreases at first and finally levels off.

Monitoring damage evolution of steel strand using acoustic emission technique and rate process theory

Utilizing the acoustic emission(AE) technique, an experimental investigation into the damage evolution for steel strand under axial tension was described. The damage evolution model for steel stand relating the damage evolution to acoustic emission parameters was proposed by incorporating the AE rate process theory. The AE monitoring results indicate that damages occur in both elastic and plastic phases of steel strand. In elastic phase, AE signals are mainly sent out from the micro damage due to the surface friction among the wires of steel strand, while in plastic phase, AE signals emitted from the plastic deformation of wires. In addition, the AE cumulative parameters curves closely resemble the loading curve. The AE cumulative parameters curves can well describe the damage evolution process including the damage occurrence and damage development for steel strands. It is concluded that the AE technique is an effective and useful nondestructive technique for evaluating the damage characteristics of steel strand.

Bonding Characteristics and Flexural Stiffening Effect of Carbon Fibre Reinforced Plastics Strand Sheets Bonded to Steel Beams

Corrosion of steel structures is unavoidable and the structural performance decreases dramatically due to the corrosion. As a repairing method for corroded steel members, bonding carbon fiber sheets with resin had been developed. The purpose of this study is to propose the flexural strengthening method for steel members by using CFRP （carbon fiber reinforced polymer） strand sheets. In order to clarify the stiffening effect and the debonding characteristics of CFRP strand sheets, and to optimize the strengthening design specifications, the flexural tests using high tension steel beams strengthened with CFRP strand sheets are performed. Two cases of experiments are carried out. In Experiment 1, the result from previous research is reflected in the strengthening design. Moreover in Experiment 2, the debonding characteristics obtained from Experiment 1 are reflected. As a result, it was clarified that CFRP strand sheets have stiffening effect equivalent to the theoretical value and its debonding property is practically high enough when FRP （fiber reinforcement polymer） sheets have an appropriate bonding length.

Health Monitoring-Based Assessment of Reinforcement with Prestressed Steel Strand for Cable-Stayed Bridge

This paper presents the method of reinforcing main girder of reinforced concrete cable-stayed bridge with prestressed steel strands.To verify the effectiveness of external prestressed strand reinforcement method.Static load tests and health monitoring-based assessment were carried out before and after reinforcement.Field load test shows that the deflection and stress values of the main girder are reduced by 10%~20%after reinforcement,and the flexural strength and stiffness of the strengthened beam are improved.The deflection and strain data of health monitoring of the specified section are collected.The deflection of the second span is 4 mm~10 mm,the strain range of the upper edge of the second span is-10με~-40με,and the strain range of the lower edge is 30με~75με.These values show the deflection and strain values fluctuate within a prescribed range,verifying the safety of the bridge.The reinforcement method of prestressed steel strand is feasible and effective.It can provide reference basis for the application of external prestressed strand reinforcement technology in similar projects.

Research on stress distribution between wires of single thigh steel strand

A three-dimensional contact model of 1×7 steel strand was established. Contact point was searched by Splitting-pinball algorithm, and Augmented-Lagrangian algorithm was applied for analysis of contact loads. The exerted tensile loads to the model were analyzed using finite element method. After analyzing calculation results, the laws of steel wire stress distribution in axis direction and in its cross-section were found. Friction coefficients were set as 0.10, 0.11, and 0.12, respec- tively, to obtain the influence law of friction coefficient to steel wire stresses. Research result shows that friction coefficient has significant influence on the shear stress of steel wire. Analyzed the calculation results of steel strand with five different lay pitch multiples and got the influence law of lay pitch multiple to the stresses of steel wire in steel strand. The Von Misses stress of steel wire increases following with the increasing of lay pitches nmltiples, but the increment value is not very prominent. The shear stress of steel wire decreases following the increase of lay pitch multiple, and the changing amplitude is large when lay pitch multiple is small. Finally, carried out a steel strand tensile deformation test and the consistency of test results with the calculation results shows that the selected model is reasonable.

Application of Fiber Optic Sensor Technology in Intelligent Steel Strand

A twisted fiber optic sensor based on intensity modulation is described. The principle and structure of the sensor and the choice of steel strand modules are introduced. The sensor is used to determine the tensile strain and distribution. The experimental results show that the change of the transferring light power has an approximate linear relation with the outer force. The intelligent steel strands with this kind of sensor will have a good application in monitoring the concrete crack and deformation distribution in huge structures such as dams and bridges.

Reinforcing Effect of CFRP Strand Sheets on Steel Members

The steel structure is corroded by various mechanisms, and thus its performance decreases. As a repairing method of the corroded steel member, a method in which carbon fiber sheets is bonded to the steel member with glue has been studied. In recent years, as more efficient repairing method using FRP materials, the strand sheet bonding which has high mass per unit area has been developed. The purpose of this study is to propose the repairing method for corroded steel member by using the strand sheets. In order to confirm a reinforcing effect, the tensile and flexural tests using steel plates and girders reinforced with strand sheets were performed. Test results showed effectiveness of strand sheets for the reinforcement of the steel members.

Determination Method on Initial Pretension of Cables in Steel Mega Frame and Prestressed Composite Bracing Structure

Determining initial pretension values of pre-stressed cables is one of the key problems for a steel mega frame and pre-stressed composite bracing structure.Through the mechanical analysis of the composite bracing under vertical loading,the critical factors deciding the initial pretention value were found.According to these factors,a rule for the initial pretension value was put forward.The determination equations were acquired based on the principle of force equilibrium at nodes.The numerical results indicate that the internal force disequilibrium in composite bracings resulted from symmetrical load can be eliminated only in a symmetrical way,so that initial pretention values are decided only by vertical loads.The influencing coefficient leveling method,taking into account interactions between story and story,is accurate and feasible.

护套不同破坏形式下钢绞线的腐蚀特性研究

PE护套破坏是导致斜拉索中钢绞线发生腐蚀的直接原因。为了研究护套不同破坏形式下钢绞线腐蚀形态特征及力学性能退化规律,基于钢绞线电化学加速腐蚀试验,通过静力拉伸试验测定腐蚀钢绞线力学性能参数。结果表明:PE护套在两种破坏形式下钢绞线的锈蚀形态不同。PE护套环向破坏时,腐蚀产物在损伤口两端堆积,而纵向破坏时,腐蚀产物堆积在两侧;通过钢绞线腐蚀损伤评定,发现护套环向破坏时,钢绞线的腐蚀率随着时间呈指数增长,而纵向破坏时为线性增长,说明前者的腐蚀损伤危害要大于后者;护套两种破坏形式下,腐蚀钢绞线的力学性能不同,环向破坏后腐蚀钢绞线的承载力小于纵向破坏形式;在弹性模量和抗拉强度方面,环向破坏时,钢绞线的损伤率在20%以内时快速衰减,随后衰减缓慢,而纵向破坏时,腐蚀钢绞线的弹性模量和抗拉强度随损伤率呈线性衰减。PE套管环向破坏时,腐蚀钢绞线的力学性能损耗较大,在实际工程中应当重点关注。

烧结机煤气消耗量预测模型的性能比较研究

针对钢铁企业烧结机煤气消耗量预测精度较低的问题,研究建立差分自回归移动平均模型(ARIMA)、长短期记忆网络模型(LSTM)和极端梯度提升模型(XGBoost),用于预测烧结机的高炉煤气消耗量,利用钢铁联合企业的实际数据对比验证了预测模型性能。结果表明,XGBoost模型的预测精度高于ARIMA模型和LSTM模型。XGBoost模型的MAPE为3.45%,RMSE为703.53 m^(3)/min,R^(2)为99.91%,鲁棒性和泛化能力较强。此外,为了强化预测模型与烧结机不同运行状态间的联系,对烧结机不同运行状态的煤气消耗量进行预测。LSTM模型在烧结机正常生产状态表现出最好的预测效果,XGBoost模型则在烧结机减产和增产状态预测效果最佳。

马鞍山长江公铁大桥2100 MPa高强度钢绞线斜拉索及锚具研制

巢马铁路马鞍山长江公铁大桥副汊航道桥为(58+168+392+168+58)m双塔三索面钢桁梁斜拉桥,斜拉索设计采用抗拉强度2100 MPa、抗疲劳应力幅280 MPa的∅15.2 mm低松弛PE镀锌钢绞线拉索。为保证高强度钢绞线斜拉索的力学及锚固性能,根据其技术指标要求,在1860 MPa钢绞线基础上,研制2100 MPa钢绞线及配套锚具。通过提高钢绞线原材料盘条中C、Si、Mn元素含量及改进钢丝拉拔工艺,选择直径14.0 mm的PQS92Si-HT盘条为2100 MPa钢绞线原材料。为提高钢绞线的锚固性能,夹片选择20CrMnTi钢,夹片长度52 mm、牙高0.45 mm、锥角6°10′、表面粗糙度R a3.2以上且表面硬度不低于56 HRC。根据2100 MPa钢绞线锚具的载荷变化和现行锚具锚板的材料性能,锚板选择40Cr钢,并进行调质处理。对研制的2100 MPa钢绞线及配套锚具进行单孔锚及斜拉索锚具组件疲劳试验及疲劳后静载试验。结果表明:研制的2100 MPa钢绞线及其锚具组件均满足规范要求,可应用于马鞍山长江公铁大桥副汊航道桥。

蚀坑尺寸对高强钢绞线应力集中影响研究

使用有限元软件ABAQUS 6.14-1建立1860级七丝高强钢绞线的实体模型,并在其上预设蚀坑,针对应力集中现象做仿真分析。通过改变半圆球蚀坑和三轴椭球体蚀坑的尺寸参数,研究其对应力集中的影响,并在椭球蚀坑中综合比较长宽深对高强钢绞线应力集中系数的影响程度。结论如下:在半圆球蚀坑中,逐步增大半径尺寸,应力集中系数也随之增大。在蚀坑半径较小的时候,增长速度较快,当尺寸增大到一定值后,增长速度变缓。在椭球蚀坑中,长度增加,应力集中系数随之不断减小,而宽度和深度增加,应力集中系数则随之增大,对各尺寸变化所对应的应力集中系数进行拟合,都表现出明显的线性关系。其中,深度对应力集中影响最大,而宽度因子和长度因子差异不大。对比蚀坑对钢丝的影响规律并结合吊杆疲劳试验结果,验证了模型的可靠性。

后插无粘结钢绞线U形管承压型抗拔桩工程应用

后插无粘结钢绞线U形管承压型抗拔桩技术是一种新型研发的抗浮技术,该技术具有桩身混凝土在使用周期内始终处于受压状态,充分发挥了混凝土的抗压性能,桩身不产生裂缝,无需进行裂缝宽度验算,耐久性好,使用范围广、工期快、造价低等优点。本文结合工程应用实例,详细介绍了后插无粘结钢绞线U形管承压型抗拔桩工程施工工艺,为后续类似工程的高质量施工提供参考。

基于永磁效应的钢绞线应力检测方法研究

基于永磁效应提出一种新的钢绞线无损应力检测方法,由永磁体的分子环流模型推导了矩形永磁体磁场强度分布,建立反映钢绞线应力与传感器内永磁体磁感应强度的力-磁关系理论模型。利用Ansys Maxwell电磁有限元软件对力-磁关系理论模型进行了数值分析。结果表明,钢绞线的受力状态与永磁磁感强度存在函数对应关系,以轴线中点为原点,原点起始磁强数值最高,此时钢绞线应变应力增大,磁感应强度数值沿两侧按一定规律逐渐减小。据此,提出一种新型的应力检测传感结构,并搭建了试验验证平台。试验数据分析表明,在多次加、卸载循环下,加载时磁通量随应力增大而减小,卸载时磁通量随应力减小而增加,线性函数和二次函数均能较好地描述磁感强度与应力应变值之间的相互关系,验证了笔者提出的检测理论和传感结构的可行性和有效性。

考虑风速概率的防风拉线风振疲劳损伤分析

为了掌握大风作用下地锚式防风拉线疲劳损伤特性,以新疆吐鲁番110 kV草杨一线为工程依托,构建了杆塔-导线-防风拉线体系整体有限元模型,分析了大风荷载作用下防风拉线的风振响应,建立了防风拉线线夹出口处节段有限元模型,研究了拉线钢股丝疲劳应力空间分布规律,分析了大风区防风拉线疲劳损伤。研究结果表明:风速对防风拉线轴向变形和应力影响较大,拉线外层钢股丝与内层钢股丝的轴向振幅时程变化具有高度一致性,在大风作用下,拉线外层钢股丝与内层钢股丝轴向振幅时程呈现强烈波动,风速越大,拉线内外层钢股丝的应力波动越大;在风荷载作用下,防风拉线内层钢股丝承受的轴向应力相对较小,而外层钢股丝应力相对较大;随着风速的增大,防风拉线的应力越大,拉线内外层钢股丝的应力波动也愈发剧烈;大风作用下防风拉线内外层钢股丝的疲劳损伤并不相同,拉线内层钢股丝的疲劳损伤小于外层钢股丝的疲劳损伤。

预应力钢绞线感应加热及其丝间接触模拟研究

预应力钢绞线感应加热是一复杂工艺过程,利用多物理场仿真软件对该过程进行模拟,可为工艺优化提供基础。对于几何方面,由于工艺的连续性,难以确定钢绞线丝间接触情况;对于物理场方面,感应加热是涉及多场的强耦合、强非线性过程。针对以上情况,根据两种丝间接触情况建立了三维钢绞线几何模型,描述了非线性材料参数,建立了相对磁导率关于温度和磁通密度的数值模型,测定了现场温度数据,判断了边丝间是否接触,分析了接触面宽度对加热效果的影响。结果表明:边丝之间是接触的,且现场温度数据与模拟结果较为吻合,验证了模拟的正确性。

钢绞线吊杆弯曲转角对其力学性能及疲劳寿命的影响

为了得到不同轴偏转角对拱桥吊杆力学性能及疲劳寿命的影响,对吊杆的基本单元1860级Φs15.2七丝钢绞线进行了研究。对钢绞线进行6个轴偏转角(0、3、6、9、12、15mrad)的静载拉伸试验,并利用ANSYS Workbench进行有限元模拟验证,随后利用ANSYS Workbench与Ncode Design联合仿真模拟得到不同轴偏转角对钢绞线疲劳寿命影响规律。结果表明:钢绞线的破坏发生在锚固端,其破断力随轴偏转角增大而减小,并且减小的幅值也随之增大。轴偏转角为15mrad时,破断力降低约12%;钢绞线的疲劳寿命随轴偏转角增大而减小,疲劳破坏点主要出现在外丝锚固端。轴偏转角达到15mrad时,当应力幅分别为250MPa和300MPa时,钢绞线疲劳寿命均减小15%以上。

缓粘结预应力钢绞线的应用与研究

研究分析了缓粘结预应力钢绞线在建筑工程中的优势和挑战。优势主要体现在其提高了结构稳定性、延长了使用寿命、减少了维护成本以及较强的适应性。然而,施工中仍存在技术要求高、周期长和成本高等挑战。研究进行了成本效益评估,并提出了相应的成本控制和效益提升对策。最后,展望了该技术在建筑工程中的应用前景,并指出随着科技和工程技术的发展,该技术将进一步得到拓展和完善。