【作者】 侯宁；

【导师】 孙利民；

【作者基本信息】 同济大学 ， 土木工程， 2022， 博士

【摘要】 目前我国在役公路桥梁结构技术状况评定规范和标准,如《公路桥涵养护规范》(JTG 5120-2021)和《公路桥梁技术状况评定标准》(JTG/T H21-2011)等所采用的评定方法还是以经验性方法为主,与设计阶段采用的概率设计法并不匹配。相对于设计阶段的拟建桥梁,在役桥梁使用环境和结构响应都是真实存在且可以被测量记录,但如何基于这些记录数据,准确、高效地提取出影响结构安全的信息、建立在役桥梁的概率评估法,从而对结构的安全状态进行评估,是一项挑战性的研究课题。本论文针对在役桥梁结构的安全状态评估开展概率性方法研究,采用了理论分析、数值统计、有限元模拟和模型试验等研究手段,从桥梁结构健康长期监测数据中识别出桥梁结构实际经受的荷载和真实抗力水平的统计特征,进而对在役桥梁结构安全进行可靠性评估。主要研究内容和成果如下:1)基于车辆动态称重数据,采用极值理论,建立了包含虚拟集中力和车距的两参数车道荷载模型。汽车荷载是在役桥梁受到的最重要活荷载之一。本文以上海长江大桥主航道斜拉桥的车辆动态称重(WIM)数据为基础,从数据驱动的角度分析了车重、车速、轴距等的数学统计特征,建立了车道荷载模型。整体计算时,多参数的单车模型可以简化为单参数的虚拟集中力;由轴重、轴距、车辆间净距等多变量组成的车队模型,可以简化为仅包含虚拟集中力和车距两变量的车道荷载模型。虚拟集中力可以用车重乘以一个与荷载效应影响线加载长度相关的比例系数来表示。车重的模型可以通过基于广义帕累托分布(GPD)的超阈值(POT)模型来确定。2)基于桥址环境和结构响应监测数据,分析了温度和风的作用特性,建立了桥梁结构关键构件(区域)的整体温度场模型、钢箱梁竖向温差作用模型,以及桥面处的风荷载模型。环境和结构温度是影响在役桥梁性能的又一主要因素。研究表明,桥梁不同构件(区域)整体温度场差别较大。“箱室效应”和材料共同影响着温度场的分布,会使钢箱梁内最高温度远高于外界环境温度,也高于设计值;同时也导致塔内大气温度变化值小于外界环境温度变化。对于没有混凝土桥面板的钢箱梁竖向温度梯度,本文提出了三角形分布温差荷载。有限元的计算表明,这种三角形竖向温差荷载下的结构响应大于设计值。对于桥面处分风场的分析可知:桥面处的风速值、纵向和横向的紊流强度值均小于设计值。3)以实测索力作为验证荷载,采用Bayesian法建立斜拉桥抗力模型,并引入抗力退化函数修正方法。在役桥梁经受多种荷载(验证荷载)的作用,这些验证荷载综合作用的结果表现为结构响应,可以用结构响应的分布函数来代替荷载综合作用的分布函数。研究表明仅采用Bayesian法建立的考虑验证荷载的结构抗力会随时间(验证荷载)的增长而提高,这与实际情况并不相符。引入抗力退化函数对Bayesian模型进行修正,得到的抗力更贴合实际。4)对比分析了影响结构设计和在役结构技术状况评估的不确定性因素,提出了在役桥梁结构运营期的目标可靠指标建议值,建议了结构安全评估的两种概率方法--可靠指标法和极限状态法。在分析影响在役结构可靠性的不确定因素以及建筑结构和桥梁结构设计阶段的目标可靠指标的基础上,结合在役建筑结构评估的目标可靠指标,本文建议在役桥梁结构运营期的目标可靠指标选定为比设计阶段的目标值低一个数量级(0.5)。分别采用可靠指标法和极限状态法对典型拉索进行了安全评估,以斜拉桥为例的计算结果表明:两种方法得到的结果基本一致,拉索的使用寿命均大于规范要求的使用年限(20年);且在斜拉索服役前期,长拉索比短拉索具有更高的冗余度。更多还原

【Abstract】 In our country,the condition assessment for the technical condition of in-service bridge structures is still based on experience,with low probability level.It does not match with the probability design method adopted in the design stage.Compared with the proposed bridge in the design stage,the service environment and structural response of the in-service bridge are real and can be measured and recorded.However,how to accurately and efficiently extract information that affects structural safety based on these recorded data,establish a probabilistic evaluation method for in-service bridges and evaluate the safety status of the structure is a challenging research topic.This paper conducts research on the state assessment of in-service bridge structures using theoretical analysis,numerical statistics,finite element simulation and model tests,etc.In order to assess the in-service bridge structure,this paper identifies the actual load and resistance of the bridge structure from the data recorded by the structural health monitoring system.The main research content and results are as follows:1)Based on WIM data and extreme value theory,a lane load evaluation model containing only two parameters of virtual concentration and vehicle distance is established.Based on the WIM data of the cable-stayed bridge in the main channel of the Shanghai Yangtze River Bridge,the mathematical statistical characteristics of vehicle weight,vehicle speed,and wheelbase are analyzed from the perspective of data driving.Through the measured data,model tests and finite element analysis,it can be known that in the overall calculation,the multi-parameter single-vehicle model can be simplified to a single-parameter virtual concentrated force.A fleet model composed of multiple variables such as axle load,wheelbase,and clear distance between vehicles can be simplified to a fleet load model that only contains two random variables,virtual concentration and distance between vehicles.The virtual concentrated force can be expressed by multiplying the weight of the vehicle by a proportional coefficient related to the length of the load effect influence line.The vehicle weight model can be established through the POT model based on the GPD distribution.2)Based on the natural environment and structural response data obtained by monitoring,this paper established the overall temperature field model of different components(regions)of the bridge and the structural temperature load model of the steel box girder without concrete deck.This paper also analyzed the characteristics of the wind field at the bridge site.The overall temperature field of different components(regions)of the bridge is quite different.The "box effect" and the material together affect the distribution of the temperature field.The "box effect" causes the atmospheric temperature in the steel box girder to be much higher than the ambient temperature and higher than the design value.And it is also the "box effect" that causes the atmospheric temperature in the tower to be lower than the ambient temperature and lower than the design value.For the structural temperature of the steel box girder without concrete deck,it is proposed that the triangular distribution of the structural temperature load is more suitable.Finite element calculations show that the stress under this triangular temperature load is greater than the response under the design load.For the analysis of the wind field at the bridge site,it can be seen that the wind speed and the longitudinal and transverse turbulence intensity values at the bridge deck are all less than the design value.3)The cable force obtained from the monitoring is used as the verification load,t,the Bayesian method is used to establish the resistance model,and the resistance degradation function is introduced to modify the resistance model.The in-service bridges experience the effects of various loads(verification loads)during bridge operation.The results of these verification loads are shown as structural responses,so the distribution function of the structural response can be substituted for the distribution function of the comprehensive verification loads.Studies have shown that the structural resistance established only by Bayesian method considering the verification loads will increase with time(verification loads),which is not consistent with the actual situation.Introducing the resistance degradation function to modify the Bayesian model,the resistance obtained is more practical and convenient for application.4)Comparative analysis of the uncertain factors affecting the structural design and the existing structure evaluation,the recommended values of the target reliability index of the existing bridge structure are given.Two methods for structural safety assessment are given—reliability index method and limit state method.Based on the analysis of the uncertain factors that affect the reliability of the existing structure,as well as the target reliability index of the building structure and bridge structure design stage,combined with the target reliability index of the existing building structure evaluation,this paper recommends that the target reliability index of the in-service bridge structure be selected to be one order of magnitude(0.5)lower than the target value in the design stage.The reliability index method and the limit state method are used to evaluate the safety of the key cables.The calculation results show that the results obtained by the two methods are basically the same,and the service life of the cables is greater than the service life required by the specification(20 years).The calculation results also show that the long stay cable has a higher degree of redundancy than the short stay cable in the early stage of the stay cable service.更多还原