Structural health monitoring of long-span suspension bridges using wavelet packet analysis

During the service life of civil engineering structures such as long-span bridges, local damage at key positions may continually accumulate, and may finally result in their sudden failure. One core issue of global vibration-based health monitoring methods is to seek some damage indices that are sensitive to structural damage, This paper proposes an online structural health monitoring method for long-span suspension bridges using wavelet packet transform （WPT）. The WPT- based method is based on the energy variations of structural ambient vibration responses decomposed using wavelet packet analysis. The main feature of this method is that the proposed wavelet packet energy spectrum （WPES） has the ability to detect structural damage from ambient vibration tests of a long-span suspension bridge. As an example application, the WPES-based health monitoring system is used on the Runyang Suspension Bridge under daily environmental conditions. The analysis reveals that changes in environmental temperature have a long-term influence on the WPES, while the effect of traffic loadings on the measured WPES of the bridge presents instantaneous changes because of the nonstationary properties of the loadings. The condition indication indices VD reflect the influences of environmental temperature on the dynamic properties of the Runyang Suspension Bridge. The field tests demonstrate that the proposed WPES-based condition indication index VD is a good candidate index for health monitoring of long-span suspension bridges under ambient excitations.

The hamster egg penetration test may decrease intracytoplasmic sperm injection utilization while maintaining high conventional fertilization rates

This was a cohort study of in vitro fertilization(IVF)subjects at the University of Utah,Salt Lake City(UT,USA)utilizing partner sperm.Cycles where both the hamster egg penetration test(HEPT)and semen analysis were performed within 2 years prior to IVF cycles were stratified into four groups based on a normal or an abnormal HEPT and morphology.The mean conventional and intracytoplasmic sperm injection(ICSI)fertilization rates were calculated in each group.We performed a univariate analysis on the primary outcome comparing clinically interesting subjects.We performed a cost-effectiveness analysis of a policy of HEPT versus universal ICSI in couples with an abnormal morphology.Among patients with a normal HEPT,there was no difference in the mean conventional fertilization rates between those with a normal and an abnormal morphology.There was no difference in the mean conventional fertilization rates between subjects with a normal morphology without a hamster test and those with a normal HEPT without a morphology assessment.In 1000 simulated cycles with an abnormal morphology,a policy of HEPT was cost saving compared to universal ICSI,yet produced similar fertilization rates.The HEPT is similar to the World Health Organization edition 5(WHO-5)morphology in predicting successful conventional fertilization while allowing decreased utilization of ICSI.A policy of HEPT for males with abnormal morphology saves cost in selecting couples for a fertilization method.

Investigation of active vibration drilling using acoustic emission and cutting size analysis

This paper describes an investigation of active bit vibration on the penetration mechanisms and bit-rock interaction for drilling with a diamond impregnated coring bit. A series of drill-off tests(DOTs) were conducted where the drilling rate-of-penetration(ROP) was measured at a series of step-wise increasing static bit thrusts or weight-on-bits(WOBs). Two active DOTs were conducted by applying 60 Hz axial vibration at the bit-rock interface using an electromagnetic vibrating table mounted underneath the drilling samples, and a passive DOT was conducted where the bit was allowed to vibrate naturally with lower amplitude due to the compliance of the drilling sample mountings. During drilling, an acoustic emission(AE) system was used to record the AE signals generated by the diamond cutter penetration and the cuttings were collected for grain size analysis. The instrumented drilling system recorded the dynamic motions of the bit-rock interface using a laser displacement sensor, a load cell, and an LVDT(linear variable differential transformer) recorded the dynamic WOB and the ROP, respectively. Calibration with the drilling system showed that rotary speed was approximately the same at any given WOB, facilitating comparison of the results at the same WOB. Analysis of the experimental results shows that the ROP of the bit at any given WOB increased with higher amplitude of axial bit-rock vibration, and the drill cuttings increased in size with a higher ROP. Spectral analysis of the AEs indicated that the higher ROP and larger cutting size were correlated with a higher AE energy and a lower AE frequency. This indicated that larger fractures were being created to generate larger cutting size. Overall, these results indicate that a greater magnitude of axial bit-rock vibration produces larger fractures and generates larger cuttings which, at the same rotary speed, results in a higher ROP.

Detection of the support damage of spatial steel structures under earthquakes based on shaking table test

There are always some local damages in spatial steel structures induced by strong earthquakes, such as welding cracks of steel nodes,anchor loose of supports etc.If these local damages of spatial steel structures occur,there will be serious dangers to the structural safety.In order to detect the position of local damage under earthquake quickly and accurately,the method of support damage diagnosis of spatial steel structures under earthquakes is studied by using wavelet packet decomposition,data fusion and cluster analysis.Furthermore,a scale model of spatial steel structure was tested on a seismic simulation shaking table to detect the position of damaged support.Results show that the damaged support position can be detected accurately by using the method proposed in this paper,which has practical applications to the damage detection of spatial steel structures.

低温环境下基于压电陶瓷监测技术的土体强度试验研究

冻土强度对评估冻土区构筑物的稳定与安全具有重要作用。然而受制于冻土复杂的四相介质体系,目前尚无成熟的手段来实时监测土体力学性能。以东北地区某工程现场粉砂土为对象,基于压电陶瓷测试技术,结合低温三轴试验,对不同负温状态下土体的力学性态进行定量研究。结果表明:随着温度的降低,土体的破坏强度、弹性模量、黏聚力均呈现出先快后慢的增长趋势。同时,传感器接收到的压电信号时域图像呈延伸和扩展态势,且主要信号频率范围逐渐向高频方向移动,压电信号能量对土体强度变化有很强敏感性。基于小波包分析得到的分解信号能量,建立粉砂土强度强化指标,该指标能很好地反映负温与土体强度的关系。研究结果可为压电陶瓷测试技术的工程应用提供参考。

隧洞衬砌内部缺陷探地雷达正演模拟与应用

混凝土衬砌脱空等内部缺陷一直是水工隧洞的“伴生”病害,对工程的安全运行产生不利影响。探地雷达具有高效无损的特点,被广泛用于结构内部缺陷探测。受限于内部缺陷的复杂性,缺陷不同形状及类型与探测雷达图谱特征形成机制仍不明确,易引起误判。基于时域有限差分法开展规则和不规则脱空含空气、含水缺陷的正演模拟,对雷达图谱、时域、频域响应特征进行分析,并结合雷达波传过程分析其响应机制。结果表明,不规则缺陷使得雷达信号回波形态畸变,出现“多弧状”特征;脱空含水缺陷相较于含空气缺陷雷达回波出现相位反转,上下边界反射信号时间间隔延长,主频向低频偏移。将上述规律应用于某实际隧洞工程探测解译中,准确判别出了缺陷类型和尺寸。

花岗岩RHT模型部分参数确定研究

岩石RHT模型参数的确定对于简化材料参数计算及提高模拟精度具有重要意义。为准确获得花岗岩RHT模型参数B、g_(t)^(*)、ε_(0)^(c)、ε_(t)^(c)、ε^(c)、ε^(t)取值,本工作在证明借助LS-DYNA软件和采用RHT模型对SHPB冲击试验进行模拟为有效研究方法后,利用该方法设计正交模拟试验。以峰值应力为评价指标,通过多重共线性分析,证明参数B、g_(t)^(*)、ε_(0)^(c)、ε_(t)^(c)、ε^(c)、ε^(t)无交互作用。进而逐一改变以上6个参数取值,利用LS-DYNA软件模拟SHPB冲击试验,分析其取值变化对岩石破坏方式和形态以及应力-应变曲线等模拟结果的影响,并采用单因素变量法对相关参数进行敏感性定量分析。研究结果表明,峰值应力和应变率的偏移率小于3%,敏感度不大于0.21,参数B、g_(t)^(*)、ε_(0)^(c)、ε_(t)^(c)、ε^(c)、ε^(t)的取值变化对模拟结果影响较小。本工作还通过对比模拟侵彻深度与已发表文献中侵彻试验结果的误差,得到了花岗岩RHT模型参数B、g_(t)^(*)、ε_(0)^(c)、ε_(t)^(c)、ε^(c)、ε^(t)的最佳取值。

A Comprehensive Investigation on Shear Performance of Improved Perfobond Connector

This paper presents an easily installed improved perfobond connector (PBL) designed to reduce the shearconcentration of PBL. The improvement of PBL lies in changing the straight penetrating rebar to the Z-typepenetrating rebar. To study the shear performance of improved PBL, two PBL test specimens which containstraight penetrating rebar and six improved PBL test specimens which contain Z-type penetrating rebars weredesigned and fabricated, and push-out tests of these eight test specimens were carried out to investigate andcompare the shear behavior of PBL. Additionally, Finite Element Analysis (FEA) models of the PBL specimenswere established and validated against the test results. Through FEA, the effects of concrete grade, perforatedplate’s aperture, Z-type penetrating rebar’s diameter, Z-type penetrating rebar’s bending angle, and bending lengthon shear behaviors were discussed. The results indicate that (1) Compared with PBL specimens with straightpenetrating rebars, Z-type penetrating rebar can significantly improve the shear resistance and shear stiffnessof the specimens. This enhanced performance can be mainly attributed to the increased adhesion of the transverserebar. (2) By comparing the load-slip curve, the slip of PBL test specimens which contain straight penetratingrebar increases rapidly and the bearing capacity decreases rapidly after concrete craking, while the bearingcapacity of Z-type penetrating rebar specimens decreases first and then increases gradually, showing betterductility. (3) The stress of the PBL shear connector with Z-type penetrating rebar is more uniform than thePBL shear connector with straight penetrating rebar, and the overall deformation is more uniform. (4) The higherthe concrete grade, the higher the shear bearing capacity and the better ductility of the new PBL. Increasing theaperture of the perforated plate or the diameter of the rebar has a very limited effect on the improvement of theshear capacity of PBL. Through the systematic analysis of the mechanical properties of Z-type penetrating rebarPBL specimen, the experimental reference is provided for improving the structure and design of new type PBL.

西辽河通辽段河床沉积物渗透系数的现场测定

采用不同方法对西辽河通辽段河床沉积物渗透系数进行现场测定,获取各点位的垂向渗透系数。并分别在探坑、土样坑、渗透仪渗水试验、竖管试验、渗坑法渗水试验、双环渗水试验位置处及其附近,先从河底表面取沉积物样,再从岩性明显变化的不同深度取样,带回实验室,进行颗粒分析,探讨河床沉积物渗透系数与颗粒级配之间的关系。结果表明:随着河床沉积物中砂石含量的增加其渗透系数也增大;反之,河床沉积物中黏土含量增加其渗透系数减小。沉积物的颗粒级配是影响渗透系数的重要因素,颗粒级配对于沉积物的孔隙尺寸、孔隙的形状及大小都有很大的影响。研究结果可为计算地表水与地下水的交换量提供可靠的水文地质参数,进而提高地下水资源评价结果的精度。

装配式桥梁下部结构的抗震性能

为研究装配式桥梁的抗震性能,制备12组灌浆套筒试件进行单向拉伸试验,根据现浇结构钢筋混凝土黏结应力-滑移本构关系式拟合套筒黏结滑移曲线,拟合黏结滑移曲线与试验黏结滑移曲线基本相同;采用软件ABAQUS建立2组装配式桥梁下部结构有限元模型和1组现浇桥梁下部结构有限元模型,设定参数,对装配式桥梁下部结构进行数值模拟,从破坏形态、滞回曲线、骨架曲线、累积耗能、刚度和延性多角度对比分析装配式桥梁下部结构的抗震性能。结果表明:灌浆套筒连接的装配式桥梁下部结构的破坏形式主要为弯曲破坏,3组模型的滞回环形状为梭形或弓形,骨架曲线下降段斜率相差较小,刚度退化和延性系数基本一致,表明灌浆套筒连接的装配式桥梁下部结构具备良好的抗震性能。

基于聚类分析理论的CPTU土分类方法研究

采用孔压静力触探(CPTU)测试资料进行土的工程分类时,在土成分和力学性状等相关性方面会产生很多不确定性。根据已有的CPTU土分类系统划分土类时,这种不确定性经常会导致不同土类的重叠。聚类分析是一个对相似数据进行分组归类的数学统计方法,基于CPTU测试资料将其应用于地质土层的划分。根据5条高速公路场地的现场CPTU试验和钻孔柱状图资料,阐述了已有聚类分析方法在划分土层界面的应用。结果表明:聚类分析方法不仅能够描绘出土层中主要的变化,而且能够探测到薄土夹层。因此,基于聚类分析理论的CPTU方法可以可靠有效地提供地质土层的初步划分。

基于小波包能量谱的结构损伤预警方法研究

基于小波包分析推导了结构动力系统在不同分析尺度上的状态方程和观测方程,在此基础上研究了结构动力响应在不同分析尺度上的时-频特性以及系统矩阵和测量噪声在各个分析尺度上的递推性。理论分析证明,采用结构动力响应的小波包能量谱进行结构损伤预警具有较好的损伤敏感性和噪声鲁棒性。根据瞬态激励的特性提出对激励和响应的时域互相关序列进行小波包分解得到小波包能量谱,并在此基础上计算结构损伤预警指标。通过一钢筋混凝土板静力承载力的振动试验分析,对板不同受力阶段的损伤状态进行了判别,并与实际损伤程度进行了比较。

基于振动测试与小波包分析的结构损伤预警

将结构振动测试技术与小波包分析相结合,提出对振动激励信号与响应信号分别进行小波包分解并在此基础上计算结构的小波包脉冲响应函数及其小波包能量谱,用以表征结构动力系统的损伤状态．通过一钢筋混凝土板静力承载力的振动试验分析,计算该板在不同受力阶段的小波包脉冲响应函数及其小波包能量谱,在此基础上对板不同受力阶段的损伤状态进行了判别．该方法克服了结构动力响应的小波包能量谱不能反映结构损伤状态的缺点,试验表明所采用的方法是可行的．

我院624例抗菌药物ADR回顾分析

目的分析我院抗菌药物致药品不良反应(ADR)及皮试阳性的特点,为临床安全合理使用抗菌药物提供参考依据。方法收集我院2014年1月—2020年2月上报的624份抗菌药物ADR报告,按照患者基本情况、药物种类、给药途径、临床表现、发生时间、恢复时间等情况进行回顾性分析。结果624例中有196例为皮试阳性,196例皮试阳性报告中女性(56.12%)多于男性(43.88%),其中≤10岁的患者最多(38.78%);皮试阳性的症状以皮丘隆起、有伪足、红晕、瘙痒为主,皮丘的直径平均为1.88cm;发生时间及恢复时间在16~30min多见。428例为使用药品过程发生ADR的患者,其中也是女性(58.18%)多于男性(41.82%),男女性别比为1:1.39,以21~30岁年龄段的患者最多;以粉针剂静脉滴注发生ADR数量最多;品种头孢菌素最常见,其次为喹诺酮类药物;累及的系统以皮肤及其附件最多,其次为消化系统和循环系统。发生不良反应的时间0~30min占绝大多数(60.18%),恢复时间多以16~30min。结论进一步重视和加强抗菌药物ADR的监测及详细上报工作,详细询问,确保患者用药安全。

基于电阻率静力触探的海相黏土成因特性分析

土的电阻率是表征土体导电性的基本参数,也是反映土体固有物性的一个综合性指标。众所周知,土的电阻率影响因素较多,因此电阻率随深度的变化可以反映出土体的许多性状。电阻率静力触探(RCPT)作为一种新型的原位测试技术,除可测锥尖阻力、侧壁摩阻力和孔隙水压力以外,还可以同时测试土的电阻率。首先简要介绍了RCPT测试技术,采用电阻率静力触探(RCPT)在连云港海相黏土场地进行了试验,得到土的原位电阻率测试值。结合连云港海相黏土的室内物理化学分析试验,研究了其矿物成分、沉积化学特征,分析了该海相软黏土的电阻率指标与矿物成分、离子含量、胶结特性和氧化环境间的关系。分析表明:基于RCPT测试成果是可以充分反映出连云港海相黏土的成因特性的。

基于小波包分析的肋拱桥结构损伤状态研究

针对某服役四十余年的钢筋混凝土旧拱桥制作了有机玻璃缩尺模型,通过对拱肋截面发生不同程度损伤以及损伤修补后拱桥模型的动力试验研究,得到了各种损伤情况下结构的自振频率;利用小波包分析方法对不同损伤情况下拱桥结构的观测信号进行分析,通过对小波包分量能量的灵敏度分析,确定了结构异常状态的敏感特征。研究结果表明:小波包分量能量对拱桥结构拱肋的异常状态较为敏感,可以作为拱肋的损伤敏感特征对拱桥进行健康诊断。

基于小波包分析的声发射源定位方法

利用小波包分析技术 ,先对信号进行分解 ,再对衰减的信号在不同频率段内进行有效的补偿 ,然后对分解的信号进行小波包重构 ,利用互相关技术计算出时差 ,进而进行声发射源定位。此定位方法能有效地减小声发射源定位的误差 ,提高定位精度。

基于CPTU测试的桩基承载力可靠性分析

通过连盐高速(连云港—盐城)和宁常(南京—常州)高速公路PTC、CFG和PHC桩基场地进行的CPTU试验资料,提出了一个预测桩基承载力的CPTU新方法。桩单位侧阻力由CPTU超孔压和侧壁摩阻力得出,而桩单位端阻力则由有效锥尖阻力获得。以静载荷和高应变试验得到的桩基承载力作为参考值评估了各种方法预测桩基承载力的有效性。基于可靠度理论,分别分析了承载力极限状态、正常使用极限状态与联合承载力极限状态和正常使用极限状态的可靠度指数。针对几种CPTU桩基预测方法,分别进行了可靠性分析。结果表明:提出的CPTU方法比其余3个方法具有更高的可靠度。CPTU方法具有简单、快速、多参数的优点,并且不依赖于操作者主观性的影响,在桩基工程中值得推广应用。

青藏公路路面病害成因分析

青藏公路多年冻土段路面大范围出现波浪沉陷和开裂等病害 ,在综合病害调查、钻探取芯分析、动力触探、路面弯沉检测和面层材料试验等基础上 ,讨论了病害与青藏高原特殊自然条件 ,路基下多年冻土变化 ,路基及地基密实程度 ,路面基层性状和面层材料的关系 .分析了路面病害的分布规律和影响因素 ,认为恶劣的气候条件和多年冻土的变化是路面病害发生的主要原因 ,面层和基层材料质量达不到要求也是重要影响因素 .

4LL-1.5Y型履带式油菜联合收获机割台振动分析

针对油菜联合收获机振动剧烈,整机稳定性、工作可靠性和驾驶舒适性较差等问题,以4LL-1.5Y型履带式油菜联合收获机的割台为研究对象,在道路运输(仅发动机工作)、道路运输(发动机与工作部件同时工作)以及田间收获作业3种典型工况下,在割台上选择3个测点,利用DHDAS动态信号采集分析系统对油菜联合收获机割台振动进行了测试,并基于时域分析、小波分析和频域分析对试验数据进行了处理。研究表明:发动机、拨禾轮、割刀的振动是整机主要激振源,但作物喂入割台后,吸收了部分振动,使得拨禾轮和割刀的振动总量分别下降了23.5%和68.7%;振动信号主要集中在0~125 Hz内,油菜联合收获机割台上各激振力的激振频率以低频为主;油菜联合收获机工作时发动机引起的一阶惯性振动频率为29.18Hz;研究结果对提高油菜联合收获机工作的可靠性、降低收获损失、减轻驾驶员的疲劳具有重要意义。