土-桩-结构相互作用对大跨悬索桥动力特性的影响研究

本文以国内第一大跨桥梁———润扬长江公路大桥南汊悬索桥为研究对象,基于大型有限元分析软件ANSYS建立了该桥的三维有限元模型,其中采用质量-弹簧体系模拟了土-桩-结构的相互作用。以此为基础对润扬悬索桥的自振特性进行了分析,重点研究了土-桩-结构相互作用因素对大跨悬索桥动力特性的影响,与现场动力测试结果的良好吻合表明了有限元分析结果的可靠性。研究结果为大桥的损伤预警和状态评估奠定了研究基础。     

大跨悬索桥损伤预警方法

本文在基于小波包能量谱的结构损伤预警理论基础上,建立了大跨悬索桥损伤预警方法,并以润扬大桥悬索桥为例,详细研究了损伤预警指标的损伤适用性和损伤敏感性.分析结果表明,采用基于小波包能量谱的结构损伤预警指标能有效地发现大跨悬索桥桥面结构的损伤,并且不同预警指标的损伤敏感性不同.     

蒙特卡罗数值模拟技术在桥梁状态评估中的应用

介绍了蒙特卡罗数值模拟的基本原理及方法。以润扬大桥状态评估系统为例 ,对大桥在正常运营和损伤状态下的结构可靠度进行分析 ,对超过限值的结果进行预警 ,其分析结果形象直观 ,提高了评估的效率 ,使维护决策的制定更加客观准确。     

润扬大桥:科技伟力气贯长江

润扬长江公路大桥工程，北起扬州南绕城公路．跨经长江世业洲．南迄沪宁高速公路镇江丹徒枢纽，联通京沪、宁通、沪宁、宁杭四条高速公路．全长3566公里。主桥由南汉悬索桥和北汉斜拉桥等部分组成，悬索桥主跨1490米．为目前中国第一、世界第三的大跨径悬索桥．斜拉桥主跨406米。润扬大桥是国内第一座由悬索桥和斜拉桥两座特大跨径桥梁组合而成的特大型现代化桥梁。     

深基坑施工过程多支撑挡土墙动态可靠度计算

提出了支护结构多支撑挡土墙施工过程“动态强度可靠度”和“动态刚度可靠度”的概念 ,研究了基于Monte Carlo法的多支撑挡土墙动态可靠度计算方法 ,并详细分析计算了润扬长江公路大桥南汊悬索桥北锚碇基坑施工过程中嵌岩地下连续墙的可靠度变化。     

基于小波分析大跨度悬索桥的结构健康监测

在土木结构,如大跨度桥梁,在关键岗位局部损坏的使用寿命可能会不断累积,并可能最终导致他们的突然失效。全球基于振动健康的一个核心问题监测方法是寻求一些对结构性损坏敏感的伤害指标。论文提出了一种针对大跨度悬索桥的在线结构健康监测方法,即利用小波变换的方法。该基于利用小波变换的方法是基于结构的环境振动反应的能量变化烂掉的小波分析。这种方法的主要特点是,所提出的小波能量谱有能力检测出由大跨度悬索桥的环境振动测试造成的结构损伤。作为一个示例,小波能量谱为基础的健康监测系统被用于日常环境条件下的润扬大桥悬索桥。该分析表明,环境温度变化对小波能量谱长期影响,而流量的效果在测量桥的小波能量谱载荷呈现出由于非平稳性质的负荷引起的瞬时变化。该状态指示指数性病反映环境温度对动态特性的润扬大桥悬索桥的影响。现场测试表明,该波包能量谱为基础的状态指示指数对于处于激励环境下的大跨度悬索桥的健康监测是一个很好的候选指数。     

润扬长江公路大桥

国家重点工程——连接镇江、扬州两座古城的润扬长江公路大桥,是我国第一座由悬索桥和斜拉桥两座大跨径桥梁构成的组合型特大桥梁。南汊悬索桥主跨径1490米,是目前中国第一、世界第三的大跨径悬索桥。北汊斜拉桥长758米。全桥采用双向六车道高速公路标准,设计使用寿命为100年。润扬大桥总投资57.8亿元,于2000年10月开工建设,2005年4月30日正式通车。原交通部长张春贤称赞:润扬大桥“代表了当前我国桥梁建设的最高水平。”润扬大桥建设者们瞄准国际一流水平,克服重重困难,先后取得了25项科技创新成果,部分成果在国际上处于领先水平,创造出8项…     

润扬长江大桥工程创多项国内第一

连接江苏扬州和镇江的润扬长江大桥将于今年5月正式通车。润扬大桥是目前长江上首座由斜拉桥和悬索桥两种桥型组合而成的大型桥梁．其南汉桥为跨径1490米的单孔双铰钢箱梁悬索桥．是目前“中国第一．世界第三”的大跨径悬索桥。     

超深开挖面地下连续墙受力机理和基于可靠度的优化设计

通过对超深开挖面地下连续墙受力机理的理论研究，提出深基坑支护开挖施工过程的确定性有限元数值模拟和随机有限元可靠性模拟的方法，并成功在润扬长江公路大桥南汉悬索桥北锚碇基础工程中实施应用。     

钢箱梁焊接细节基于长期监测数据的疲劳可靠性评估:疲劳可靠度指标

提出基于长期监测数据的钢箱梁焊接细节疲劳可靠度的评估方法,并以润扬大桥悬索桥和斜拉桥钢箱梁顶板-U型肋焊接细节为对象开展应用研究。首先,建立疲劳损伤极限状态方程并讨论方程中各个参数的概率分布特性,在此基础上,采用最优化方法进行疲劳可靠度的求解,得到疲劳可靠度指标随服役时间增长的变化规律和日循环次数Nd的随机性对可靠度的影响。最后重点研究疲劳荷载效应增长对可靠度的影响,并据此提出对大桥日常运营管理的建议。结果表明:①将Nd作为随机变量处理是偏安全的,且Nd的随机性对斜拉桥焊接细节可靠度影响要较悬索桥更为显著;②悬索桥焊接细节的疲劳可靠度明显低于斜拉桥;③考虑疲劳荷载效应的增长会显著减小两桥焊接细节的疲劳可靠度;④为了得到钢箱梁焊接细节在服役期内的疲劳可靠度的准确评估,对其进行长期的应变监测是必要的。     

Reliability analysis of long span steel arch bridges against wind-induced stability failure

An efficient method for reliability assessment of long span steel arch bridges against wind-induced stability failure is presented in this paper. The prediction of wind-induced stability of such bridge structures is performed by an eigenvalue method and the reliability estimates are determined by a generalized first-order reliability algorithm. A software strategy for interfacing the present method with ANSYS is developed via a freely available MATLAB software tool (FERUM). A numerical example involving a detailed computational model of a long span steel arch bridge with a main span of 550 m is presented to demonstrate the applicability and merits of the present method and the software strategy. Finally, the most influential random variables on the reliability of long span steel bridges against wind-induced stability failure are identified by a sensitivity analysis.     

基于改进一次二阶矩法的桥梁颤振可靠性评价

随着以悬索桥和斜拉桥为代表的大跨度柔性桥梁的发展,由风与桥梁的相互作用而引起桥梁颤振稳定问题倍受关注,而在各种随机因素作用下的桥梁颤振可靠性评价也受到了人们的重视.在对传统的一次二阶矩可靠度计算方法改进的基础上,对国内14座大跨度桥梁进行了颤振可靠性评价.通过与Monte Carlo数值模拟结果的对比表明,所提出的改进一次二阶矩方法能够有效提高小失效概率条件下的可靠度计算精度.     

Frontier of continuous structural health monitoring system for short & medium span bridges and condition assessment

It is becoming an important social problem to make maintenance and rehabilitation of existing short and medium span(10-20 m) bridges because there are a huge amount of short and medium span bridges in service in the world. The kernel of such bridge management is to develop a method of safety(condition) assessment on items which include remaining life and load carrying capacity. Bridge health monitoring using information technology and sensors is capable of providing more accurate knowledge of bridge performance than traditional strategies. The aim of this paper is to introduce a state-of-the-art on not only a rational bridge health monitoring system incorporating with the information and communication technologies for lifetime management of existing short and medium span bridges but also a continuous data collecting system designed for bridge health monitoring of mainly short and medium span bridges. In this paper, although there are some useful monitoring methods for short and medium span bridges based on the qualitative or quantitative information, mainly two advanced structural health monitoring systems are described to review and analyse the potential of utilizing the long term health monitoring in safety assessment and management issues for short and medium span bridge. The first is a special designed mobile in-situ loading device(vehicle) for short and medium span road bridges to assess the structural safety(performance) and derive optimal strategies for maintenance using reliability based method. The second is a long term health monitoring method by using the public buses as part of a public transit system (called bus monitoring system) to be applied mainly to short and medium span bridges, along with safety indices, namely, “characteristic deflection” which is relatively free from the influence of dynamic disturbances due to such factors as the roughness of the road surface, and a structural anomaly parameter.     

Stochastic seismic analysis of Kömürhan Highway Bridge with varying material properties

Stochastic seismic finite element analyses of the Kömürhan Bridge, the material properties of which are described by random fields, are presented in this paper. The stochastic perturbation technique and Monte Carlo simulation (MCS) method are used in the analyses. A summary of MCS and perturbation-based stochastic finite element dynamic analysis formulation of the structural system is given. The Kömürhan Bridge, located on the 51st km of Elaz??-Malatya highway in the east of Turkey, was chosen as a numerical example. The Erzincan earthquake in 1992 was considered a ground motion, since it took place in the vicinity of the bridge. The material properties were considered to be random variables. During the stochastic analysis, displacements and internal forces of the bridge under consideration were obtained using the perturbation-based stochastic finite element method (SFEM), as well as the MCS method. The selected random variables were elastic modulus and mass density. The efficiency and accuracy of the proposed SFEM algorithm were validated through comparison with results of the MCS method.     

Risk assessments of long-span bridges considering life-cycle cost concept and near-fault ground motion effect

The influence of the near-fault ground motion on the response of long-span bridges must be considered as a critical factor for seismic design because the response indicates different aspects from existing earthquake characteristics. Also, it is important to note that the safety index for the risk assessment of long-span bridges is determined based on the minimum expected life-cycle cost E(LCC). In this study, earthquake characteristics are analyzed by creating elastic and inelastic response spectrums with actual measurement records (Chi-Chi earthquake records) and then the numerical analysis of the long-span bridge in Namhae, Korea is performed according to the increase and reduction of the member stiffness based on the standard design., the reliability evaluation of the long-span bridge considering aleatory uncertainties is performed on the basis of the combined results of static analysis and seismic response analysis. Also, the minimum LCC is estimated based on failure probabilities by the different alternative design. Because of epistemic uncertainties, the results of reliability evaluation and the LCC of optimal design are selected as random variables; the safety index, failure probability and expected minimum LCC are re-evaluated with regard to critical percentage values for a risk-averse design of the long-span bridge, and are presented graphically using cumulative percentages. It is, therefore, expected that this study will provide the basic information for the risk assessment and optimal design method in performing seismic design of the long-span bridge considering earthquake characteristics.     

Flutter reliability analysis of suspension bridges

A reliability analysis method is proposed in this paper through a combination of the advantages of the response surface method (RSM), finite element method (FEM), first-order reliability method (FORM) and the importance sampling updating method. The method is especially applicable for the reliability evaluation of complex structures of which the limit state surfaces are not known explicitly. After the accuracy and efficiency of the method are demonstrated through numerical examples, the method is used to estimate the flutter reliability of a suspension bridge. The uncertainties such as material properties, geometric parameters, structural damping ratio, flutter derivatives and extreme wind velocity at the bridge site are considered. The example suspension bridge is the Jiang Yin Bridge with a main span length of 1385 m built in China. The results show that the proposed method based on an empirical formula in which the limit state function is explicitly represented as a function of variables overestimates the flutter reliability of suspension bridges. The actual flutter reliability should be more accurately analyzed using the proposed method based on the deterministic finite element method in which the limit state function is implicitly represented as a function of variables. Finally, the most influential random variables on flutter reliability of suspension bridges are identified by using a sensitivity analysis.     

Time-dependent reliability assessment for mass concrete structures

Under the influences of random thermal creep stresses, the safety of mass concrete structures could be described by time-dependent reliability. In this paper, based on probabilistic finite element method (PFEM), numerical methods for the time-dependent reliability assessment are presented. By using the presented methods, various kinds of random variability including non-stationary temperature of concrete, modulus of elasticity, creep compliance and strength parameters of concrete can be conveniently taken into account. The suggested method is useful for the mass concrete structural design and safety evaluation when random factors should be taken into account.     

大跨度桥梁的抗风强健性及颤振评价

国际学术界公认的结构强健性,是指结构系统抵抗未曾遇见或超乎正常的环境作用的能力。为了突出风灾的未曾遇见性和超乎正常性,文章率先将结构强健性的理念引入桥梁抗风设计与颤振评价中,定义桥梁抗风强健性包括强度、刚度和稳定3个方面,并提出采用桥梁可以抵抗的设计风速的重现时间来表示抗风强健性。针对桥梁抗风稳定中的颤振强健性评价问题,建立用4个随机变量表示的颤振安全域度随机模型,提出采用等效中心点法来计算颤振强健性的可靠指标、失效概率和重现时间。基于提出的颤振强健性评价方法,对4座已经建成的大跨度桥梁和4座将要建设的大跨度桥梁进行颤振强健性分析。     

城市供水管网抗震可靠性评估的随机模拟方法

在进行管网抗震可靠性评估时,现有方法大多采用相同方式进行管道的渗漏与爆管水力模拟,这会导致管网水力模拟及可靠性评估结果的不准确。考虑到地震时管道破损具有很大的随机性,对城市供水管网抗震可靠性评估的随机模拟方法进行研究。应用蒙特卡洛模拟产生管网震损场景,用泊松随机数与均匀随机数判定管道工作状态,用正态随机数确定管道渗漏系数;利用EPANET软件中喷嘴及管道关闭功能实现管道渗漏及爆管等效模拟,提出将长管道分段并应用"分步迭代"法求解低压管网水力方程,提高震损管网水力模拟精度。以震损场景下节点流量统计平均值与正常时节点流量的比值作为可靠度指标,分别采用所提出算法及GIRAFFE软件对云南某古镇供水管网在VIII、IV烈度时抗震可靠性进行评估,评估结果证明了所提出算法的可行性。评估结果还表明,除地震烈度外,管网本身水力条件对供水可靠性影响较大,管网末端、支管服务区域及地势较高区域供水可靠性远低于干管服务区。     

Reliability of composite steel bridge beams designed following AASHTO''s LFD and LRFD specifications

Composite steel beam bridges designed following AASHTO's Load Factor Design (LFD) method and the newly developed Load and Resistance Factor Design method (LRFD) are proportioned for different loading conditions. They need to satisfy these conditions at maximum design load, an overloading condition, and fatigue load. The ultimate strength of compact composite steel beams is based on the fully plastic stress distribution. The capacity of non-compact beams is based on the yield or partially-plastic moment, depending on whether the beam violates all or few of the compactness or ductility requirements. In this paper, the reliability for the ultimate flexural capacity limit state of composite steel beams is investigated. The structural reliability is measured in terms of the reliability index. The statistical data on strength are generated starting from statistics on material properties and using the Monte Carlo simulation method. Statistical data on load components are compiled from the available literature. The scope of the study covers a wide range of rolled beams, span lengths, beam spacings, and two yield strengths. The deterministic study showed that the design of composite steel beams is usually not governed by the maximum design load combination, but rather by the overloading condition. The results of the reliability study indicate non-uniformity in the safety of steel bridges that are designed by the AASHTO LFD code. This is also true for AASHTO's LRFD code since it is not calibrated for the overloading condition. The value of the reliability index is a function of the compactness classification, method of design, beam spacing, span length, and section size.