Development of improved natural frequency equations for continuous span steel I-girder bridges

Field testing and analytical studies to predict natural frequencies of steel stringer bridges are reviewed in this paper. A three-dimensional (3D) finite element analysis (FEA) procedure using the commercial software ABAQUS, which efficiently captures the vibration characteristics of such bridges, is proposed. Two continuous-span composite steel bridges dynamically (field) tested by others were used to validate the proposed FEA model, which indicates excellent agreement between the analytical and field data. A natural frequency parametric study has been conducted by utilizing the FEA procedure. Based on the regression analysis of the parametric study results, practical equations are proposed to predict the natural frequencies of continuous-span composite steel bridges. The parametric study results are also compared with existing prediction methods, showing that the proposed equations represent a significant improvement over the existing prediction methods.     

斜拉索索力测量方法的比较分析

介绍常用的斜拉索索力的几种测量方法,着重介绍频率振动法的原理与影响因素。同时,结合某实际案例,介绍用有限元分析软件分析给定索力时斜拉索不同计算模型对索计算频率的影响,并与不同解析方法的计算结果对比分析,认为长索采用张拉弦模型计算结果比较精确;短索采用铰支梁模型时计算前5阶频率时可以不考虑索抗弯刚度的影响,运用固支梁模型计算的低阶频率与实测值比较接近。     

大跨度斜拉桥拉索安全性分析方法研究

斜拉桥的斜拉索在运营期间的安全是斜拉桥结构安全的最重要条件之一,对斜拉索安全性的分析显得至关重要。考虑构成平行钢丝束斜拉索的高强钢丝本构行为的不均匀性和钢丝之间的相互影响,将Matteo的钢丝延脆性模型和MonteCarlo仿真方法相结合,建立斜拉索的强度模型,并从可靠度观点出发分析了斜拉索在桥梁运营条件下安全系数的变异和演化特性,并提出断丝率随服务期演化的线性经验公式来描述拉索的退化问题。在此基础上提出了大跨度斜拉桥拉索安全性分析的工程方法,并以招宝山大桥最长索为例,详细阐述了分析过程,该方法为斜拉桥拉索的安全评估与剩余寿命估算提供了依据。     

基于定期检测与遗传算法的大跨度斜拉桥损伤识别

为了对运营中的斜拉桥进行安全性评估,首先需要根据实桥测试结果对结构损伤进行初步识别。在斜拉桥定期索力检测与主梁关键截面的应力监测结果的基础上,提出斜拉桥损伤识别的遗传算法,并编制了复杂结构损伤识别的遗传算法程序,通过各期结构检测结果之间的变化来反演检测期间结构参数的变化,据此识别结构损伤位置与程度,保证了在结构参数化有限元模型存在识别误差的情况下也能得到正确的损伤识别结果。宁波招宝山大跨度预应力混凝土独塔斜拉桥的损伤识别仿真结果表明,本文方法和程序具有较高的识别精度,并可推广应用于其它复杂结构的损伤识别。     

Time-variant reliability profiles for steel girder bridges

Evaluation of existing steel bridges becomes more important due to natural aging, increasing load spectra, deterioration caused by corrosion, and other problems. In the result, bridge structures exposed to aggressive environmental conditions are subjected to time-variant changes of resistance. Therefore, there is a need for evaluation procedures for an accurate prediction of the load carrying capacity and reliability of bridge structures, in order to make rational decisions about repair, rehabilitation, and expected life-cycle costs. The objective of this paper is to develop time-variant reliability models for steel girder bridges. Traditional methods based on deterministic analysis do not reveal the actual load carrying capacity of the structure. The proposed approach is based on reliability analysis of components and structural systems. The study involves the selection of representative structures, formulation of limit state functions, development of load models, development of resistance models for corroded steel girders, development of the reliability analysis method, reliability analysis of selected bridges, and development of the time-dependant reliability profiles including deterioration due to corrosion. The results of the study can be used for a better prediction of the service life of deteriorating steel girder bridges, and development of optimal reliability-based maintenance strategies.     

Continuous modal parameter identification of cable-stayed bridges based on a novel improved ensemble empirical mode decomposition

The objective of this paper was to perform an effective and meticulous continuous modal parameter identification. Since the data obtained from the cable-stayed bridge was non-linear and time varying, and also there exists a phenomenon of mode mixing in the current decomposition techniques, such as empirical mode decomposition (EMD), which further complicates the extraction of accurate structural information, therefore, a novel improved Ensemble EMD method was proposed. This method can effectively deal with the non-linear and time varying structural behaviour and eliminate the phenomenon of mode mixing effectively, specially for cable-stayed bridges, because in this method the added white noise was selected by a pre-defined process and also the intrinsic mode function (IMF) selection was made self-adaptively, then finally Pareto technique was adopted to reconstruct the IMF. After the signal decomposition and reconstruction, Recursive Stochastic Subspace Identification was employed to carry out the continuous modal parameter identification. Sutong Yangtze Bridge, a long-span cable-stayed bridge, with main span of 1088 m was taken as a case study and the proposed method was applied. The result showed that the proposed method was effective in attaining its goals and can endows better results in real life bridge health monitoring.     

斜拉桥拉索磁流变阻尼器减振技术的参数优化研究

针对应用磁流变阻尼器控制斜拉桥拉索振动中参数优化这一关键问题,通过试验研究,建立了目前常用的RD-1005型磁流变阻尼器非线性双黏性模型,得到了基于输入电压、激振频率、振动幅值等参数的磁流变阻尼器等效黏性阻尼系数计算公式;然后提出了考虑拉索垂度、弯曲刚度和倾角等因素影响的黏性阻尼器拉索减振设计方法,修正了Pacheco的设计曲线;最后提出了磁流变阻尼器拉索减振的优化设计方法,并通过实桥试验得到验证。     

基于数据融合的张弦桁架多位置损伤识别与抗噪性分析

为提高张弦桁架多位置损伤识别的准确性,将数据融合方法与损伤识别指标相结合,采用D-S证据矩阵理论融合叠加曲率模态改变率和模态柔度差曲率两项指标的损伤识别结果,提出了张弦桁架多损伤的单次融合和两阶段融合识别方法。以某实际工程缩尺简化得到的张弦桁架作为研究对象,设计了两种不同的多损伤工况,通过有限元分析获取了结构损伤前后的前三阶模态数据,并进行了损伤识别分析。结果表明：基于数据融合的多损伤识别方法能够准确地识别张弦桁架多损伤,其能够综合两种单指标的识别结果,降低甚至消除非损伤位置的干扰,有效解决了单指标识别精度低、不能全面反映损伤位置的问题;两阶段融合方法通过两次融合逐步降低了非损伤位置的干扰,识别效果优于单次融合方法。此外,分析中考虑了不同水平噪声对张弦桁架多损伤识别的影响,结果表明：基于数据融合的多损伤识别方法具有较好的抗噪能力,能够降低噪声和非损伤位置的干扰,且两阶段融合方法的抗噪能力优于单次融合方法。     

ANN and ANFIS performance prediction models for hydraulic impact hammers

Hydraulic impact hammers are mechanical excavators that can be used in tunneling projects economically under geologic conditions suitable for rock breakage by indentation. However, there is relatively less published material in the literature in relation to predicting the performance of that equipment employing rock properties and machine parameters. In tunnel excavation projects, there is often a need for accurate prediction the performance of such machinery. The poor prediction of machine performance can lead to very costly contractual claims. In this study, the application of soft computing methods for data analysis called artificial neural network (ANN) and adaptive neuro-fuzzy inference system (ANFIS) to predict the net breaking rate of an impact hammer is demonstrated. The prediction capabilities offered by ANN and ANFIS were shown by using field data of obtained from metro tunnel project in Istanbul, Turkey. For this purpose, two prediction models based on ANN and ANFIS were developed and the results obtained from those models were then compared to those of multiple regression-based predictions. Various statistical performance indexes were used to compare the performance of those prediction models. The results suggest that the proposed ANFIS-based prediction model outperforms both ANN model and the classical multiple regression-based prediction model, and thus can be used to produce a more accurate and reliable estimate of impact hammer performance from Schmidt hammer rebound hardness (SHRH) and rock quality designation (RQD) values obtained from the field tests.     

基于外海环境预报的近岸岛礁桥址区波高ANN推算模型

中国跨海桥梁多建于近岸岛礁海域,桥址区的波浪要素随时空演变复杂。桥址区波高的准确推算对于桥梁结构设计和施工组织具有十分重要的意义。提出一种基于外海环境预报数据的近岸岛礁桥址区波高人工神经网络（ANN）推算模型,并以平潭海峡公铁两用大桥桥址海域为研究对象,运用ANN算法中常用的BP神经网络对外海海洋预报台提供的波高、风速数据以及在桥址区实测波高数据进行训练,建立二者之间的映射关系及ANN推算模型。为验证推算模型的可行性和有效性,运用上述模型对桥址区连续80 d的海浪波高进行推算,通过对比前人模型和实测数据发现,推算波高和实测波高的变化趋势基本吻合,均方根误差满足预测要求,获得了理想的预测效果。研究表明,提出的波高ANN推算模型可以利用外海预报信息进行近岸岛礁桥址区的波高推算,且建模过程较为简单。     

The use of Artificial Neural Networks to estimate seismic damage and derive vulnerability functions for traditional masonry

This paper discusses the adoption of Artificial Intelligence-based techniques to estimate seismic damage, not with the goal of replacing existing approaches, but as a mean to improve the precision of empirical methods. For such, damage data collected in the aftermath of the 1998 Azores earthquake (Portugal) is used to develop a comparative analysis between damage grades obtained resorting to a classic damage formulation and an innovative approach based on Artificial Neural Networks (ANNs). The analysis is carried out on the basis of a vulnerability index computed with a hybrid seismic vulnerability assessment methodology, which is subsequently used as input to both approaches. The results obtained are then compared with real post-earthquake damage observation and critically discussed taking into account the level of adjustment achieved by each approach. Finally, a computer routine that uses the ANN as an approximation function is developed and applied to derive a new vulnerability curve expression. In general terms, the ANN developed in this study allowed to obtain much better approximations than those achieved with the original vulnerability approach, which has revealed to be quite non-conservative. Similarly, the proposed vulnerability curve expression was found to provide a more accurate damage prediction than the traditional analytical expressions.     

曲线桥梁在多向地震作用下的动力分析方法

由于曲线桥梁具有由其平面不规则性导致的弯扭组合效应,地震分量的输入角度对最大反应有较大影响.本文研究了多向地震作用下曲线桥梁的地震反应,系统分析和对比了多种计算方法.通过对CQC3方法和SRSS3方法进行推导,界定了SRSS3方法,并指出了该方法的缺陷和适用范围,同时对两种国内外抗震规范采用的简化计算方法的原理和参数进行了详细分析.本文中用多种方法计算了曲线桥梁在相应于实际地震反应谱的结构反应,并与采用地震记录进行的时程分析作了对比.文中的计算结果不仅验证了CQC3方法的正确性同时文中也分析了SRSS3的局限性,研究结果还表明在未来的桥梁抗震规范中可以在最不利的地震作用输入角度下采用比较准确的CQC3方法计算多向地震反应的设计值.不过为方便起见也可采用SRSS方法和百分比方法的保守值作为多向地震作用下的设计值是必要的.     

斜拉桥悬臂施工阶段自振频率简化计算方法

本文采用双质点法建立了斜拉桥施工阶段动力分析模型,推导了斜拉桥施工阶段自振频率的计算公式,并对公式进行了合理简化,得到斜拉桥施工阶段自振频率的估算公式.基于实桥工程,将双质点振动模型、自振频率估算公式、有限元法分析和现场的模态测试结果进行了对比分析.结果表明,估算值与有限元法很接近,估算公式为自振频率的计算提供了较为准...     

Tension force estimation of extradosed bridge cables oscillating nonlinearly under gravity effects

Extradosed bridges have loose and sagged cables that are different from those used in cable-stayed bridges. The total tension force of an extradosed bridge cable estimated using the existing formulas is not accurate. Although the existing formulas are widely used in the field, they do not consider the exact deflection curve, features of nonlinear oscillation, and stretching force due to self-weight. In this study, a new method was developed to calculate the total tension force of the cable. In the new method, the total tension force of the cable includes the applied axial load and the stretching force due to self-weight. For the exact estimation of the applied axial load to the cable, the vibration of the cable was treated as a conservative nonlinear oscillation system, and a new formula was derived using the perturbation technique. The new formula was used to clearly explain the hardening effect due to the initial amplitude of the initial excitation, the presence of imaginary number of frequencies, the correlation with the stretching force due to self-weight, and the softening effect of the slenderness ratio on nonlinear natural frequency. For calculating the stretching force due to self-weight, the stretching of the cable for the static deformation was considered. A field test showed that it is necessary to add the stretching force due to self-weight to the estimated axial load for extradosed bridge cables and that the new method can be used to calculate the total tension force of loose and sagged cables.     

Simplified probabilistic non-linear assessment of existing railway bridges

An objective of the European Commission's Sixth Framework Research Project, Sustainable Bridges, is to advance understanding of the behaviour of existing railway bridges and develop tools to assess their ability to safely handle future traffic demands and extend their service lives. This paper presents the findings of a study that reviews structural safety models applicable to the assessment of existing bridges. The study proposes the use of simplified probabilistic non-linear structural analysis methods to provide more accurate assessments of the load capacity of bridge systems than traditional methods. The simplified methods use the results of a limited number of deterministic non-linear structural analyses and apply these results into a reliability framework. The application of the proposed methods is illustrated by assessing the safety of an existing bridge. The accuracy and efficiency of the simplified methods are verified by comparing the results of the simplified methods to those obtained from full probabilistic non-linear analysis procedures.     

海上风机部分埋入群桩水平-摇摆振动与结构共振分析

对于海上风机部分埋入群桩基础,风机结构的高度将导致基础承受较大的倾覆力矩,因而在风机振动分析中需要考虑到基础的摇摆特性。为避免发生共振,风机结构第一阶自振频率应避开风轮转动频率（1P频率）和叶片通过频率（3P或2P频率）。目前关于风机结构动力特性的研究常常以底部刚性固定为假定,忽略了地基基础的影响,因而可能带来误差。结合既有研究成果,推导简化解析方法研究了部分埋入群桩基础的水平-摇摆耦合振动特性以及基础阻抗对风机结构共振特性的影响。首先,推导了采用动力Winkler地基模型的部分埋入群桩基础水平-摇摆动力阻抗,与精确解进行对比,验证了方法的正确性;其次,考虑基础阻抗的作用,推导了风机结构水平-摇摆振动方程;最后,通过简化方法和频域有限元方法对不同地基条件下某风机结构的共振特性及基础阻抗进行了计算和对比,研究了基础阻抗对结构共振特性的影响,并验证了简化方法的正确性。     

Three-dimensional finite element modelling of long-span cable-stayed bridges

Finite element (FE) modelling is a prominent way to simulate both static and dynamic characteristics of cable-stayed bridges to understand their structural complexities. Many initial FE models have not been successful in the analysis of the structural behaviour of cable-stayed bridges. This paper presents the details of an updated FE modelling procedure for long-span cable-stayed bridges. The design information of Tatara Bridge with an 850-m main span is considered for numerical studies. The dynamic properties of the FE model, including mode shapes and natural frequencies, are compared with field vibration test results to validate the presented modelling process. Sensitivity analysis of structural parameters is also applied to update effective parameters and understand the structural behaviour of the bridge. The new and beneficial aspects presented in this paper regarding FE modelling procedure and finding effective material and structural parameters will be useful for future design and analysis of cable-stayed bridges.     

大跨斜拉桥拉索频率识别的环境变异性研究

为了研究大跨斜拉桥拉索振动频率的环境时变特征,本文对苏通大桥斜拉桥的拉索振动响应进行了模态频率识别,并详细地考察了日常运营条件下实测模态频率的环境变异性。分析结果表明,温度的变化对斜拉桥拉索各阶振动频率的影响很小,相反,交通荷载与拉索实测模态频率存在较为明显的相关关系,即拉索各阶振动频率基本随车流量增大而线性增大。在此基础上,本文建立了基于模糊模式识别的拉索异常状态预警方法,实现了对拉索振动频率异常的在线监测与预警。     

遗传算法和人工神经网络在斜拉桥可靠度分析中的应用

将遗传算法(GAs)和人工神经网络(ANN)这一类智能方法引入斜拉桥可靠度分析领域,分别对斜拉桥主梁和索塔在多种失效模式下的可靠度进行计算和分析.实例数值结果表明,遗传算法和人工神经网络为结构可靠度研究提供了新的有效的思路和手段.     

Stability evaluation of steel girder members in long-span cable-stayed bridges by member-based stability concept

The member-based design concept utilizing the buckling length of each structural member has been widely used to assess the buckling instability of steel structures. Since steel girder members in conventional cable-stayed bridges are generally exposed to large axial forces, the buckling instability of these members should be carefully investigated in the design stage. However, analytical approaches for obtaining the buckling lengths of steel members, such as the alignment chart, story-buckling and story-stiffness methods, may not be adopted to cable-stayed bridges because these approaches imply some theoretical assumptions that are adequate only for steel framed-structures. Furthermore, the boundary conditions of steel girder members supporting by cables are obscure to be prescribed in general terms. Numerical eigenvalue analysis may be one of the most excellent candidates for determining the buckling lengths of steel girder members in that this method can handle the interactions among members implicitly without any irrelevant assumptions for cable-stayed bridges. This paper discusses detailed procedures for obtaining buckling lengths of steel girder members in cable-stayed bridges by numerical eigenvalue analysis. In order to avoid the problem of generating excessively large buckling lengths in some girder members having small axial forces, a modified eigenvalue analysis is proposed by introducing the concept of a fictitious axial force. Practical application example for a real cable-stayed bridge is illustrated with some discussions on the effect of the proposed modification and stability evaluation by member-based stability concept.