Traditional methods of identifying bridge mode shapes often have limitations such as time-consuming,labor-intensive,and weak anti-noise ability.To change the weaknesses of previous identification methods,this paper proposes a new bridge mode identification method based on statistical moment theory.Theoretical and numerical experimental analyses are conducted.Two test vehicles installed with accelerometers were used to synchronously collect signals at the preset measuring points on the bridge deck at a fixed distance.After about 30 s of acquisition,the test vehicle moved to the next position to continue the test until the signal acquisition of all bridge deck measuring points was completed.Subsequently,the collected acceleration signal was used to calculate the statistical moment value of each measuring point of the entire span bridge,and finally,the fundamental mode curve of the whole span bridge was constructed by calculating the corresponding relationship between the statistical moment and fundamental mode.The equivalent relationship between the statistical moment ratio and fundamental mode value is theoretically expounded for the first time,and numerical simulations were conducted to analyze the effects of different factors.Furthermore,the distinctions between the proposed and existing mode shape identification methods were compared.Finally,the new method in this article was further proved using an actual bridge test.The results show that,compared with traditional mode-shape identification methods such as stochastic subspace identification and transmissibility,the first mode-shape error of the bridge obtained using the proposed method is smaller,the time efficiency is higher,resistance to noise is better,and no human factors such as preset parameters are involved in the identification process.It can effectively compensate for the limitations of traditional mode shape identification methods in direct measurement technology.

提出一种时域内的高耸类结构抗侧刚度突变位置快速检测方法.首先在高耸类结构同一竖直线上等高度间距布设测点,获取结构各高度测点在水平方向的同步动力响应;其次计算出响应信号二阶统计矩,并将相邻测点响应二阶统计矩作比,绘出该比值随测点高度变化的关系曲线;最后根据曲线突变位置判断结构抗侧刚度突变节段所在位置.本文基于单自由度结构统计矩理论,推导了多自由度结构体系响应统计矩与结构节段抗侧刚度的映射关系,首次结合矩阵摄动法论证了利用结构响应二阶统计矩比值曲线判段结构抗侧刚度突变节段位置的可行性,考虑实际工程应用中存在的诸多影响因素,利用数值模拟论证分析不同高耸结构在不同激励形式及30、40 dB噪音影响下所提方法的适用性,最后结合现场风电塔筒的实测响应数据进行分析研究.研究结果表明利用结构位移响应二阶统计矩作为检测指标,通过高耸结构相邻测点响应统计矩比值曲线,能够初步判断高耸类结构抗侧刚度突变位置,无需进行高耸结构抗侧刚度突变前后数据指标对比,有助于在实际高耸类结构检测工程中得到应用.

基于移动车辆在桥梁上运行来测试桥梁基频的间接量测法已经获得实桥的验证,提出一种新型间接量测法,该方法有别于牵引车拖动测试车辆一直运行并同步采集信号的传统间接量测方式,需牵引车同时拖动固定间距的前、后2辆测试车辆前行,并在固定点静止采集少许时间后,继续重复操作至测试车辆通行整跨桥梁,利用测试车辆上采集的信号,计算整跨桥梁的传递率矩阵,然后利用奇异值分解识别出桥梁的第1阶模态,进而利用改进的直接刚度法计算桥梁单元弯曲刚度,并进行损伤识别.首先从理论上说明该方法的可行性,然后在各类影响因素下进行数值模拟分析,最后通过某实桥试验进行初步验证.研究结果表明:相比于常规在桥梁上直接测试的方法,提出方法耗时短,机动性好,适用于大面积大区域桥梁集群快速测试;相比于传统间接量测方式,提出方法通行时间虽有少量增加,但能较好解决桥梁阻尼比、测试车阻尼、外激励变化、噪音、桥面粗糙度等传统间接量测方法中存在的问题.

基于单自由度体系推导的统计矩理论,针对无模型方法识别结构损伤距离实际应用差距较大等问题,结合融入广义模式搜索算法,提出一种以融合位移四阶矩和加速度八阶矩为指标的全新框架结构两步层递式快速损伤检测方法.所提广义搜索模式算法结合无模型快速损伤定位理论形成的全新损伤诊断方法,利用融合位移四阶矩和加速度八阶矩作为指标,对12层框架结构数值模型有无噪声工况进行数值模拟,与标准结果偏差均在3％以内,证明了该方法的精确性及抗噪性效果.并与相同指标下的统计矩二范数优化方法和类贝叶斯思想方法进行对比,验证了该新方法相较其他方法在损伤检测精度、稳定程度及快速检测计算时间上的优越性.通过12层标准框架振动台试验数据,选取3个典型工况分别进行损伤诊断,并与实测报告分析对比,其结果表明该方法相对于其他方法更能反映试验工况累积而表现出来的单元损伤程度变化,凸显了新方法在工程检测中的可靠性.

通过对单自由度体系的统计矩理论分析,提出一种融合位移四阶矩和加速度八阶矩的特征指标,并结合L1正则化优化准则进行模型修正的框架结构损伤识别新方法.基于理论分析构建3种典型统计矩特征指标,考虑无噪音和信噪比40 dB下的不同损伤工况,对某12层标准框架模型进行损伤识别对比研究.在此基础上对常规残差优化准则和基于L1正则化优化准则进一步分析,结合12层标准框架振动台试验数据,选取3个典型振动工况中所有梁柱单元的损伤识别结果进行研究.结果 表明:新方法下融合位移四阶矩和加速度八阶矩的特征指标较单一统计矩指标具有更高的敏感性和抗噪性,结合L1正则化优化准则的模型修正方法较常规残差优化准则的传统模型修正方法具有更高的稳定性及有效性.

利用检测车在桥梁上运行可进行桥梁结构损伤识别,针对该间接测量技术的诸多局限性问题,基于车桥耦合模型,提出了通过检测车在桥梁上运行,利用安装在检测车辆上的传感器所得的动力响应信号来识别梁单元弯曲刚度,进而进行结构损伤识别的间接测量方法.在此基础上,考虑了路面粗糙度等因素对间接量测方法的影响,以均匀设计法和控制变量法为研究工具,通过数值模拟对检测车速度、检测车质量、检测车阻尼、桥梁模态阻尼比等4个参数进行研究分析.研究结果表明,检测车质量、检测车阻尼,以及桥梁阻尼比等相关参数在适当的范围,可以大幅度提高该方法的使用效果,进而有助于推动间接量测技术在桥梁结构损伤识别中的实际应用.

基于间接测量技术,采用国际标准化组织建议的功率谱密度函数(PSD)模拟路面粗糙度等实际因素在车桥耦合模型中的影响,提出一种通过检测车辆在桥梁上运行,并利用安装在检测车辆上的传感器所得的动力响应信号来识别梁弯曲刚度,进而进行结构损伤识别的间接测量新方法.考虑到应用该新方法过程中路面粗糙度等实际因素易产生不利影响,提出利用车频及车辆阻尼比相同的2辆检测车位移信号相减的方法来消除路面粗糙度产生的影响.首先通过理论推导对该方法进行理论验证,接着采用数值模拟的方法分别对采用该方法消除路面粗糙度影响的可行性、桥梁损伤位置识别的可行性以及损伤程度识别的可行性进行验证,最后采用该方法进行实桥实测试验.研究结果表明:所提方法可以有效消除路面粗糙度等实际因素对间接测量技术的不利影响,可以有效地识别梁弯曲刚度,进而达到桥梁损伤识别的目的,有助于推动基于动力测试的间接测量技术在桥梁结构损伤识别工作中的实际应用.

Deriving from the single free system, structural damage detection basing on fusion index of fourth-order displacement and eighth-order acceleration statistical moment by using updated model method is proposed. In this study, damage detection results of numerical simulation and shaking table test of a 12-story frame structure was analyzed and contrasted. Two different damage indice were compared with consideration of environment noise. And the recoded data of shaking table test was used to validate the establishment of the theoretical model. Three typical cases were selected for damage detection analysis. It is demonstrated that the fusion method by using displacement and acceleration statistical moment theory to conduct damage detection of frame structure is feasible and effective.

Video-based displacement measurement is a cost-effective way for remote monitoring the health of conditions of civil structures, especially for situations where accessibility is restricted and does not allow installation of conventional monitoring devices. The technical basis of video-based remote displacement measurement system is digital image analyses. Comparison of the images allow the field of motion to be accurately delineated. Such information are important to understand the structural behaviours including the motion and strain distribution. This paper presents system architecture and utilizes frame difference method to analyse the image sequences to extract the feature of motion. Firstly, the measurement spot is calibrated using a dark panel with known geometry. Then the system captures the full picture of structure with high image resolution using a commercial digital video camera. Meanwhile, the motion of the target is calculated using image processing techniques, which requires target tracking algorithms, calculation of the actual displacement using target geometry and the central point coordinates of moved pixels. The performance is demonstrated on a testbed of large scale burr arch-truss under dynamic loading process and validated using displacement sensor data. The results indicate that the proposed method can estimate the displacement of the bridge with sensitivity of 2.04 mm. With further refinement of system hardware and image processing software, it will be developed into a remote video based monitoring system for structural health monitoring of civil infrastructure to assist the diagnoses of its health conditions.

The preliminary damage assessments for simply supported beams and shaking table tests of a 12-story RC frame model were conducted with the improved direct stiffness calculation (DSC)method and the measured data.Through comparing the assessment results with the damage descriptions under different operating conditions in the test reports,it was demonstrated that the improved DSC method used to assess preliminarily cumulative damages of bending type structures is feasible and effective.

This work investigates the correlation between a large number of widely used ground motion intensity measures (IMs) and the corresponding liquefaction potential of a soil deposit during earthquake loading. In order to accomplish this purpose the seismic responses of 32 sloping liquefiable site models consisting of layered cohesionless soil were subjected to 139 earthquake ground motions. Two sets of ground motions, consisting of 80 ordinary records and 59 pulse-like near-fault records are used in the dynamic analyses. The liquefaction potential of the site is expressed in terms of the the mean pore pressure ratio, the maximum ground settlement, the maximum ground horizontal displacement and the maximum ground horizontal acceleration. For each individual accelerogram, the values of the aforementioned liquefaction potential measures are determined. Then, the correlation between the liquefaction potential measures and the IMs is evaluated. The results reveal that the velocity spectrum intensity (VSI) shows the strongest correlation with the liquefaction potential of sloping site. VSI is also proven to be a sufficient intensity measure with respect to earthquake magnitude and source-to-site distance, and has a good predictability, thus making it a prime candidate for the seismic liquefaction hazard evaluation.

In order to improve the anti-seismic performance of a building with plane abnormity steel frame structure which was not constructed according to the design drawing, the anti-seismic strengthening for the building was carded out with locally adding the steel support. The SAP2000 software was used to establish a spatial model, and then the dynamic time-history analysis for the steel frame structure under both existing and strengthed conditions was performed. In addition, the anti-seismic performance of the structure under various seismic conditions was investigated, and the influence concerning the displacement response of top floor, displacement distribution between floors and shear force distribution of base for the structure was studied. The analysis results show that the anti-seismic deformation of the structure system can be controlled by the optimized strenthening scheme, the torsion effect decreases evidently. And the strengthening scheme can provide the references for the anti-seismic strengthening in similar engineering.

An improvement to the direct stiffness calculation(DSC) method for bending-type frame structures was proposed here,it could be used to conduct damage assessment.The corresponding system identification toolbox in the platform of OpenSees was expected to be used in engineering.The proposed improvement was simple,but apparently quite effective,the modification of the DSC method for damage detection and the system identification toolbox were applicable to practical bending-type frame structures.Aiming at the benchmark test of a 12-story reinforced concrete frame model performed on a shaking table in Tongji University,a simulation model for this benchmark test under excitation of several seismic waves was evaluated to verify the modified DSC technique and the system identification toolbox.The results showed that the preliminary assessment using the improved direct stiffness method and the corresponding system identification toolbox is feasible and efficient for damage detection of bending-type structures.

A SHM toolbox namely SystemID toolbox using OpenSees,developed by OpenSees Navigator(Version 2.5) allows users to build models using elastic elements for bridge and frame structure,and then input a certain frequency and mode shape of the corresponding structure,for instance i-th frequency and i-th mode shape after suffering an earthquake excitation signal and so on(obtained from separate nonlinear simulation,experimentation or measurements from instrumented structures),then flexural rigidities at nodes are determined.By comparing the results with those from the section stiffness extracted from the undamaged model,a measure of the damage index in terms of the stiffness change namely Stiffness Variation Index(SVI) can be estimated for evaluating the health state of the structure.Researched on the OpenSees standard example under excitation of seismic waves,the simulation model using the developed system identification toolbox was evaluated to verify the feasibility of assessment with the bending-type structures after earthquake or other loads.

Abstract:The numerical simulations for the benchmark test of a 12-story reinforced concrete frame model carried out in Tongji University in 2003 were conducted in consideration of cumulative effect caused by series of earthquake events in platform of OpenSees. Meanwhile the damage status of the model was evaluated by using the System Identification toolbox of OpenSees formed by the principle of the improved direct stiffness method. Through comparison with the damaging description in several cases during the test, it is demonstrated that the preliminary assessment by using the System Identification Toolbox to conduct damage detection of 3-D frame structures in different direction are feasible and effective.

An improvement to the Direct Stiffness Calculation (DSC) method and corresponding new damage index, Stiffness Variation Index (SVI), is proposed in this paper. SVI is a parameter related to modal curvature and bending moment calculated, respectively, by central difference scheme to displacement and integral method to load. The proposed improvement makes the DSC technique applicable to damage detection of practical bending-type structures. Research on the effect of measurement errors was performed through numerical simulation. Moreover, a continuous steel beam was tested to verify the modified DSC technique in the condition of concentrated damages. The limitation of measurement points and number of modes are discussed. The results show that the improved direct stiffness method is feasible and efficient in the damage detection of bending-type structures.