钢筋混凝土空心板桥荷载试验

对某钢筋混凝土空心板桥进行了荷载试验,基于有限元程序MIDAS进行了理论分析,根据理论分析结果所得控制内力进行现场加载试验,介绍了荷载试验的加载原则、测点布置、加载工况和静载试验结果,根据试验结果评价了该桥的承载能力和使用性能。     

Life-cycle reliability assessment of reinforced concrete bridges under multiple hazards

This paper proposes a novel probabilistic methodology for estimating the life-cycle reliability of existing reinforced concrete (RC) bridges under multiple hazards. The life-cycle reliability of an RC bridge pier under seismic and airborne chloride hazards is compared to that of a bridge girder under traffic and airborne chloride hazards. When conducting a life-cycle reliability assessment of existing RC bridges, observational data from inspections can provide the corrosion level in reinforcement steel. Random variables related with the prediction of time-variant steel weight loss can be updated based on the inspection results using Sequential Monte Carlo Simulation (SMCS). This paper presents a novel procedure for identifying the hazards that most threaten the structural safety of existing RC bridges, as well as the structural components with the lowest reliability when these bridges are exposed to multiple hazards. The proposed approach, using inspection results associated with steel weight loss, provides a rational reliability assessment framework that allows comparison between the life-cycle reliabilities of bridge components under multiple hazards, helping the prioritisation of maintenance actions. The effect of the number of inspection locations on the updated reliability is considered by incorporating the spatial steel corrosion distribution. An illustrative example is provided of applying the proposed life-cyle reliability assessment to a hypothetical RC bridge under multiple hazards.     

Spatial time-dependent reliability analysis of corroding pretensioned prestressed concrete bridge girders

Accelerated pitting corrosion tests have been performed to obtain spatial and temporal maximum pit-depth data for prestressing wires. This data is then used to develop probabilistic models of pitting corrosion and strength capacity of 7-wire strands. The probabilistic model of pitting corrosion for strands is then combined with a non-linear Finite Element Analysis and probabilistic models of corrosion initiation and propagation to study the spatial and temporal effects of pitting corrosion on a typical pretensioned prestressed concrete bridge girder. The limit states considered are flexural strength and serviceability. The spatial time-dependent reliability analysis takes into account the uncertainties and variabilities related to material properties, dimensions, loads and corrosion parameters as well as the spatial variability of pitting corrosion of prestressing strands. Including the spatial variability of pitting corrosion in the reliability analysis increased both the probability of strength and serviceability failure when compared with a mid-span sectional analysis.     

基于随机场理论的地基稳定性模糊可靠度分析

根据Vanmarcke提出的随机场理论描述土性参数的空间变异性,建立了考虑土性参数空间变异性的地基失稳模糊概率公式,并通过实例分析了两种情况下地基的模糊失效概率值,得出用随机场理论空间均值方差计算的模糊失效概率值比不考虑土性参数的空间变异性计算模糊失效概率值偏低的结论.     

考虑微动疲劳的斜拉桥钢绞线斜拉索时变可靠性分析

腐蚀与微动疲劳是钢绞线斜拉索退化的主要原因,与平行钢丝索相比,钢绞线斜拉索钢丝之间的相互作用力大,微动疲劳作用明显。基于时变可靠性理论,利用有限元软件ANSYS建立钢绞线钢丝接触模型求解钢丝之间的相互作用力,以此给出微动疲劳随时间发展的表达式,构造了钢绞线斜拉索抗力退化函数,进而建立同时考虑腐蚀与微动疲劳的钢绞线斜拉索时变可靠性模型。计算结果表明,以可靠指标β=4.7作为结构失效标准,与不考虑微动疲劳的钢绞线斜拉索相比,考虑微动疲劳的钢绞线斜拉索可靠性下降速度加快,寿命缩短6.3年。研究结果对探明钢绞线斜拉索退化机理,评估其使用寿命具有比较重要的理论与实际意义。     

Nonlinear analysis of multi-cell reinforced concrete box girder bridges

A numerical method of analysis is developed to determine the nonlinear response, collapse mechanisms and ultimate failure loads of multi-cell RC (reinforced concrete) box girder bridges under stepwise increasing static loads. Nonlinearities considered are material nonlinearities inherent in RC members such as cracking of the concrete, yielding of the reinforcement and formation of plastic hinges due to shear and flexure. The analytical model, based on a three-dimensional grillage, is developed for multicellular structures of arbitrary plan geometry and constant height. Realistic but simple assumptions for the interaction of internal forces due to flexure, shear and torsion in the cellular structure, as well as idealized trilinear force-deformation characteristics for the individual members comprising the grillage, result in a very economical nonlinear analytical model. The proposed analytical scheme, which is based on a mixed model formulation at the element level, is demonstrated and tested on a series of numerical examples and the analytical results indicate good agreement with experimental results obtained from large scale model tests on RC box girder bridges.     

关于随机场理论在土工可靠度计算中应用的研究

应用随机场理论进行可靠度分析时,关键在于随机场理论求得的参数,尤其是方差折减函数如何同可靠度理论结合起来。在土工可靠度计算中正确选取并且合理应用方差折减函数是一个非常关键但又很容易被忽略的问题。本文从随机场的基本理论出发,对这一问题进行探讨和研究,提出方差折减函数的确定原则;并通过一个工程算例,说明此折减原则较为合理,且在实际工程中偏于安全。     

腐蚀疲劳钢筋混凝土梁正截面应变分析

通过钢筋混凝土梁的腐蚀疲劳试验和对比试验,根据实测的试验梁在循环荷载作用下正截面上钢筋和混凝土的动态应变,分析了正截面钢筋和混凝土的应变发展过程。结果表明,在腐蚀环境中,钢筋的拉应变由于腐蚀介质的作用增长率加大,而且是一种不间断的连续增长。不同腐蚀环境中的应变发展过程相似,但应变增长率不同,随着腐蚀环境的不同而变化。在腐蚀环境相同的情况下,受疲劳荷载水平控制;在疲劳荷载水平相同的情况下,受不同的腐蚀环境作用控制。正截面上的应变发展过程同样有三个不同的阶段,即初始阶段、发展阶段和破坏阶段。其结果可以为腐蚀疲劳钢筋混凝土构件的耐久性设计提供参考。     

Seismic fragility analysis of reinforced concrete continuous span bridges with irregular configuration

A set of fragility curves of a class of reinforced concrete bridges with different degrees of irregularity has been generated. Eighteen bridge configurations have been identified, from regular to so-called highly irregular models. The geometric irregularity in this class of bridges is assumed to vary with the height of the piers. Using non-linear analytical models and an appropriate suite of 60 ground motions, analytical fragility curves have been generated for the individual piers of each of these 18 bridge models. Discussions have been made about the imposition of the displacement ductility demand of the piers versus the earthquake intensity as well as the bridge regularity. Comparison of the fragility curves shows that the most vulnerable bridges are the irregular bridges and high damage probability is expected for the short piers of this class of bridges. It was found that the fragility curves may be used for categorisation of regular and irregular bridges.     

基于高斯过程回归的响应面法及边坡可靠度分析

提出了一种新型高斯过程响应面法(GPRSM),通过高斯过程回归算法构建随机变量与功能函数响应值之间的关系。该方法相较多项式响应面法对于功能函数为高维和高度非线性的可靠度问题,具有更高的精度和计算效率。此方法可以通过新增加训练点以动态更新响应面函数。与此同时,为了模拟岩土参数的空间变异性,通过KL展开构建随机场,并与极限平衡法结合进行边坡稳定性分析。使用提出的GPRSM构建替代模型并用于蒙特卡洛模拟求解边坡失稳概率,在保障计算精度的同时减少了对边坡稳定性分析程序的调用。最后将所提出的方法分别应用于功能函数为显式和隐式两个案例,并与其他论文中的方法对比,证明了该方法的有效性和适用性。     

中承式钢筋混凝土肋拱桥动静载试验分析

通过对某地震灾区一座中承式钢筋混凝土肋拱桥的静动载试验,了解和掌握了地震后该桥的总体技术状况及实际承载能力状态,及时发现该桥主要病害和严重程度,分析了其产生机理和发展趋势,为管理部门今后对该桥进行维修加固或改造决策提供科学的技术资料和依据。     

System reliability evaluation of in-service cable-stayed bridges subjected to cable degradation

Abstract

The cables in a cable-stayed bridge are critical components supporting the long-span girders and ensuring their functionality. However, cables are prone to fatigue damage and atmospheric corrosion, which directly affect the bridge safety. This study presents a framework for system reliability evaluation of in-service cable-stayed bridges subjected to cable degradation. The effect of cable strength degradation on the system reliability is demonstrated through simulation on a parallel-series system representation. Learning machines are utilised to approximate the non-linear and dynamic response functions of critical components due to cable rupture, and the system reliability is finally evaluated from the event tree established by the β-unzipping method. Both short-span and long-span cable-stayed bridges are selected as prototypes to investigate the influence of cable degradation on the system reliability. On this basis it is revealed that cable degradation can significantly influence the collapse mechanism of a cable-stayed bridge and thereby lead to a significant reduction in the system reliability. This phenomenon is associated with cable spacing, where a spare cable system seems more sensitive to cable gradation. It is demonstrated that the consideration of cable corrosion and correlation is essential for lifetime safety evaluation of in-service cable-stayed bridges.     

Models of reinforced concrete structures for reliability analysis

The semi-probabilistic design approach to reinforced concrete structures may be substantially improved through probabilistic analysis of the systems or their members. Models are proposed for this purpose, covering all possible failures, the deformability characteristics of the failure zones, and the variability of the general factors.Members in compression (columns and walls) and the cracking resistance of beams are considered. It is shown that, in important specific cases, the analysis may be reduced in practice to use of constants.     

Fatigue-safety assessment of reinforced concrete (RC) bridges: application to the Brazilian highway network

During the assessment programme of Brazilian roadway bridges, it was noticed that two girder-slab reinforced concrete bridges, with cantilever girders on extremity spans, were a common structural solution adopted 40 years ago in Brazil. Particularities intrinsic to these systems like significant displacements expected on cantilevers associated with soil embankment settlement in bridge entrance can take to a sudden change in slope grades near its ends, provoking sometimes high impact factors. Besides that, traffic and axle load increase has been of concern because these bridges were designed with different scenarios 40 years ago. Therefore, these facts can affect the structural performance of these structures in face of 100 years life required on most current codes for new bridges. So, in this article, a safety assessment to this assembly of bridges is performed. For this study, a simulation model has been developed, which includes the most significant sources of uncertainty in the definition of traffic action and structural response of bridges. Database provided by dynamic tests of these bridges were used for this performance-based assessment. As a result, reliability indexes to fatigue and ultimate limit state of bending are calculated and compared with target values as specified by codes.     

Computer modeling and reliability evaluation of steel through truss bridges

The need for determining an effective means for modeling and evaluating existing bridges, particularly for those exceeding their design life, is apparent in the United States infrastructure. In this study a representative through truss bridge is chosen for analysis and modeling comparison. Interpretation of the AASHTO loading for this bridge is presented. Bridge models are identified and both deterministic and probabilistic evaluation methods are used. Results for two two-dimensional models, one composed entirely of truss elements and one containing beam and truss elements, are presented and discussed.     

交通荷载作用下加筋土路基残余变形减小的机理分析

应用有限单元法对交通荷载作用下加筋土路基进行隐式动力分析,并基于累积塑性变形的计算和影响因素分析,揭示加筋减小路基土残余变形的机理。分析结果表明:对于级配碎石基层沥青混凝土路面,加筋改善路基表面的压应力分布,减小传递到路基表面的剪应力,加筋后路基土上部80cm范围内动偏应力大大减小,而动偏应力是引起路基残余变形的重要因素之一;另一方面,交通荷载作用下,路基土的累积塑性变形主要发生在路基上部100cm范围内。因此,加筋后路基土累积塑性变形的减小,主要是由于加筋减小交通荷载作用下路基土上部的动偏应力;土工格栅刚度越大,动偏应力减小越显著。     

Dynamic response and reliability analysis of tall buildings subject to wind loading

This paper explores the wind stochastic field from a new viewpoint of stochastic Fourier spectrum (SFS). The basic random parameters of the wind stochastic field, the roughness length z₀ and the mean wind velocity at 10 m height U₁₀, as well as their probability density functions (PDF), are obtained. It provides opportunities to use probability density evolution method (PDEM), which had been proved to be of high accuracy and efficiency, in computing the dynamic response and reliability of tall buildings subject to the wind loading. Principals and corresponding numerical solving algorithm of the PDEM are first presented. Then, the adopted model of the wind stochastic field is described briefly. The simulation method of the fluctuating wind velocity based on the SFS is introduced. Finally, as an example of the application of the PDEM, a 20-storey frame subject to wind loading is investigated in detail. The responses, including the mean value and the standard deviation, and the reliabilities of the frame are evaluated by the PDEM. The results demonstrate that the PDEM is applicable and efficient in the dynamic response and reliability analysis of wind-excited tall building.     

任意施工荷载作用下天然结构性软粘土的一维非线性固结分析

考虑固结过程中结构性土体的非线性压缩特性、渗透系数的变化以及施工荷载随时间任意变化规律因素,推导了天然结构性土体的一维非线性固结方程。利用Crank-Nicolson差分格式离散非线性固结方程以方便求解。分析表明:不考虑土体结构效应的非线性固结和线性固结分析所得的超孔压明显大于考虑土体结构效应的非线性固结结果;当时间因数较小时,考虑土体结构性的非线性固结分析的固结度明显大于不考虑土体结构性的非线性固结分析和线性固结结果;同时表明不考虑土体结构效应的非线性固结和线性固结分析的结果相差不大。