【作者】 李涛；

【导师】 黄海云； 周军勇；

【作者基本信息】 广州大学 ， 建筑与土木工程（专业学位）， 2021， 硕士

【摘要】 基于实测车流荷载数据进行在役桥梁结构响应分析与可靠性评估,是真实掌握桥梁运营荷载状态及结构安全性的重要手段,目前这一研究主要针对桥梁单一力学状态的可靠性分析(弯曲、剪切、轴拉等)。然而,桥梁在外部荷载作用下通常会出现复杂的力学行为,如弯剪复合、压弯复合、弯剪扭复合等,复合受力往往会成为控制结构安全的重要失效模式。目前针对结构复合受力主要关注抗力层面,通过试验手段研究给定构造设计的抗复合受力的需求;然而,随机交通荷载作用下桥梁的内力效应也呈现复合特征,这一规律未引起足够重视,在当前我国超载重载非常严重的情势下,这一问题对在役桥梁的结构安全尤为关键。为此,本文主要开展了如下研究:(1)建立了梁桥弯剪复合受力的概率可靠性评估方法,形成了基本评估框架。首先,给出了弯剪复合受力的桥梁可靠性评估主要内容及关键技术;其次,本研究针对复合受力的可靠性评估方法归纳了两种策略:一是基于失效路径推导出最不利可靠度计算平面的路径法,二是采用Lamé曲线模型建立弯-剪复合失效的功能函数方法;最后,针对构建功能函数所对应的多变量非线性极限状态方程,通过基于梯度直接微分的非线性计算方法(i-HLRF)求解桥梁的弯-剪复合的可靠度指标,并通过算例验证了这种可靠度计算方法的精确度在0.1%内并且具有良好的收敛性。(2)针对量大面广中小跨径桥梁承受超载车作用的安全性问题,研究了超重车作用下桥梁复合受力行为的可靠性评估。首先,基于AASHTO推荐的MCFT理论建立弯剪耦合抗力的概率模型;其次,结合实际地点的车辆荷载WIM数据,建立了超载车荷载模型,并分析了超载车作用下弯剪复合荷载效应的分布规律;最后,分别采用路径法和Lamé曲线功能函数法,结合某一工程案例详细说明了关键控制截面的弯剪复合受力的结构可靠性。研究结果表明:在这些弯、剪效应都较为显著的截面,弯剪复合作用的失效概率要大于纯弯或者纯剪等单一作用。(3)为准确反映桥梁实际服役中复合受力行为的时间演变特性,开展了随机车流作用下的概率可靠性评估。首先,以我国某单向两车道高速公路的WIM数据为基础,借助极值理论构建了复合荷载效应模型,并按论文建立的复合受力行为的基本评估框架对上述工程案例进行可靠度指标计算比对;然后根据现有掌握的桥梁运营荷载信息及结构性能退化情况,结合修正压力场理论建立弯剪抗力退化时变模型,分析桥梁在弯剪复合受力状态下的时变可靠性。结果表明在实际日常运营过程中,考虑弯剪复合受力的状态下比单一受力状态更不利且随运营时间增长影响更大。论文分别建立了重载车辆及随机车流作用下复合受力行为的概率可靠性评估体系,通过某一工程案例详细说明了该评估体系的实施过程与效果。虽然研究对象集中于梁桥的弯剪复合受力问题,但相关研究思路可以推广于任意复合受力失效模式的桥梁结构在随机荷载作用下的安全评估分析,这为改进现有规范的设计理论和方法,厘清桥梁结构在复合受力行为下的概率可靠性评估提供了参考。更多还原

【Abstract】 Structural response analysis and reliability assessment of in-service bridges based on measured traffic load data is an important means of obtaining a true picture of the operational load state and structural safety of bridges,and this research currently focuses on the reliability analysis of single mechanical states of bridges,such as moment,shear and axial tension.However,bridges are often subject to complex mechanical behaviour under external loads,such as moment-shear,compression-moment,moment-shear-torsion,etc.,and the composite forces often become an important failure mode in controlling the safety of the structure.At present,the main focus on composite forces is on the resistance level,and the need to resist composite forces for a given structural design is investigated by means of tests;however,the internal force effects of bridges under random traffic loading also show composite characteristics,and this law has not received sufficient attention,which is particularly critical for the structural safety of bridges in service under the current situation of very serious overloading and heavy loading in China.The main research content and results of this paper include:(1)A probabilistic reliability assessment method for moment and shear composite forces on girder bridges was developed,and a basic assessment framework was formed.Firstly,based on the reliability assessment of a single failure mode,two methodological strategies are summarised in this study for the reliability assessment of composite forces:firstly,the path method based on the failure path to derive the most unfavourable reliability calculation plane,and secondly,the Lamé curve model is used to establish the functional function method for the combined moment-shear failure;subsequently,for the multivariate non-linear limit state equations corresponding to the constructed functional functions,the reliability of the moment-shear composite is solved by a The reliability index of the moment-shear composite bridge is then solved for the multivariate non-linear limit state equation based on gradient direct differentiation(i-HLRF),and the accuracy of this reliability calculation method is verified to be within 0.001 with excellent convergence by means of an example.(2)The reliability assessment of the composite force behaviour of bridges under the action of overloaded vehicles is particularly investigated for the safety of a large number of small and medium span bridges subjected to the action of overloaded vehicles.Firstly,a probabilistic model of the moment-shear coupled resistance is established based on the MCFT theory recommended by AASHTO;secondly,a model of the overloaded vehicle loads is established by combining the WIM data of vehicle loads at actual locations and the distribution law of the moment-shear composite load effects under the action of overloaded vehicles is analysed;finally,the path method and the Lamé curve functional function method are used respectively to illustrate in detail the critical control in conjunction with an engineering case Finally,the structural reliability of the moment-shear composite forces at critical control sections is illustrated in detail by using the path method and the Lamé curve functional method respectively,combined with an engineering case.The results of the study show that in these sections where both moment and shear effects are significant,the probability of failure of the moment-shear composite action is greater than that of the pure moment or shear damage modes.(3)In order to accurately reflect the characteristics of the composite force behaviour of the bridge in actual service,a probabilistic reliability assessment under the action of random traffic flow was carried out.Firstly,based on the vehicle load WIM data of a one-way two-lane motorway in China,a realistic composite load effect model was constructed with the aid of extreme value theory,and the reliability indexes were calculated and compared for the above engineering case according to the basic assessment framework of composite force behaviour established in the thesis;then,based on the available information on bridge operational loads and structural performance degradation,a modified pressure field theory was combined to establish The time-varying model of moment-shear force degradation is then combined with the modified pressure field theory to analyse the time-varying reliability of the bridge under the moment-shear composite stress condition.It is shown that in daily operation,the moment-shear composite stresses are less favourable than the single stresses and have a greater impact on the bridge as service time increases.The paper establishes a probabilistic reliability assessment system for composite force behaviour under heavy vehicles and random traffic respectively.Although the study is focused on the composite moment and shear stresses of girder bridges,the research idea can be extended to the safety assessment of bridge structures under random loads with any composite stress failure mode,which provides a reference for improving the design theory and methodology of existing codes and clarifying the probabilistic reliability assessment of bridge structures under composite stress behaviour.更多还原