锈蚀钢箱梁桥的极限强度分析

结构可靠性理论可有效地评估结构老化的程度。通过研究给出一个程序,用于评估存在部分腐蚀板构件的钢箱梁桥的极限强度的可靠性。基于腐蚀和强度衰减的解析式,提出一种确定钢箱梁极限强度的概率模型。研究内容包括典型结构选型、极限状态方程、腐蚀钢箱梁抵抗模型的发展、可靠性分析法的发展、选定桥梁的可靠性分析和可靠性时程曲线的发展,以及腐蚀引起的结构退化。研究结果较好地预测退化钢箱型梁桥的使用年限和可靠性设计优化方案的发展。     

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.     

Ultimate strength of cracked plate elements under axial compression or tension

In addition to corrosion, fatigue cracking is another important factor of age related structural degradation, which has been a primary source of costly repair work of aging steel structures. Cracking damage has been found in welded joints and local areas of stress concentrations such as at the weld intersections of longitudinals, frames and girders. Fatigue cracking has usually been dealt with as a matter under cyclic loading, but it is also important for residual strength assessment under monotonic extreme loading, because fatigue cracking reduces the ultimate strength significantly under certain circumstances.In this paper, an experimental and numerical study on the ultimate strength of cracked steel plate elements subjected to axial compressive or tensile loads is carried out. The ultimate strength reduction characteristics of plate elements due to cracking damage are investigated with varying size and location of the cracking damage, both experimentally and numerically. Ultimate strength tests on cracked steel plates under axial tension and cracked box type steel structure models under axial compression are undertaken. A series of ANSYS nonlinear finite element analyses for cracked plate elements are performed. Based on the experimental and numerical results obtained from the present study, theoretical models for predicting the ultimate strength of cracked plate elements under axial compression or tension are developed. The results of the experiments and numerical computations obtained are documented. The insights developed will be very useful for the ultimate limit state based risk or reliability assessment of aging steel plated structures with cracking damage.     

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.     

Analytical demonstrations to assess residual bearing capacities of steel plate girder ends with stiffeners damaged by corrosion

Many field surveys depict that steel plate girder ends tend to corrode due to the leakage of water from construction joints and/or detention of rain water near bearing regions. In many cases, buckling failures of plate girders were observed due to the excessive loss of material at the bottom portion of bearing stiffeners. In this study, the effect on the buckling strength of steel plate girder due to the corrosion damage at bearing stiffeners was investigated. Full-scale experimental tests were performed on two plate girder ends to determine the bearing capacity. Bearing capacity and failure modes were also verified by numerical analyses. Initial imperfections and welding residual stresses were also taken into account in analytical models. The simulation of the model was extended to the various corrosion damages, considering different damaged heights and thicknesses of the bearing stiffener near weld seam. All results were plotted in terms of remaining bearing capacity versus damage thickness ratio keeping the damage height of the stiffener constant. In this study, a damage parameter Reduced Thickness Ratio was used to assess the ultimate capacity and buckling of steel plate girder end with various corrosion levels.     

九圩港大桥工程连续钢箱梁设计

九圩港大桥主桥跨越南通市九圩港河,采用了三跨变高度连续钢箱梁方案,跨度布置为（50＋80＋50）m。介绍变高度连续钢箱梁的设计思路、构造特点、铺装、防腐涂装要求以及架设方法。此类型的连续钢箱梁桥具有可工厂化制造、吊装重量轻、施工时间短以及对交通和航道影响小等优越性,特别适用于跨越较窄的河道、城市跨线以及工期要求紧张的桥梁。设计方法对类似桥梁的设计有一定的借鉴意义。     

Ultimate shear strength of plate elements with pit corrosion wastage

The aim of the present paper is to investigate the ultimate strength characteristics of steel plate elements with pit corrosion wastage and under in-plane shear loads. A series of the ANSYS nonlinear finite element analyses for plate elements under in-plane shear loads are carried out, varying the degree of pit corrosion intensity and the plate geometric properties. Closed-form design formulae for the ultimate strength of pitted plates under edge shear, which are essentially needed for the ultimate limit state based risk or reliability assessment of corroded structures, are derived by the regression analysis of the computed results. The insights developed from the present study will be very useful for damage tolerant design of plated structures with pit corrosion wastage.     

Reliability-based optimisation design of post-tensioned concrete box girder bridges considering pitting corrosion attack

Since the mid-twentieth century, prestressed concrete (PC) bridges have been significantly developed to become the most important type of bridge in the world. However, only a few studies have dealt with the reliability-based design optimisation (RBDO) of PC bridges despite the fact that RBDO demonstrates the real behaviour of structures. Moreover, the corrosion of post-tensioned tendon in PC bridges seriously caused sudden failures which have been recorded in the world. Since then, this study presents the probabilistic model and approach to formulate and analyse the RBDO of PC box girder bridges which consider the pitting corrosion phenomenon of shear, torsion reinforcements and post-tensioned tendon. A practical example of a typical PC box girder bridge is presented and discussed. Sensitive analyses are performed to evaluate the influence of ultimate target reliability index on the optimal solution. For the simple support PC box girder bridge, the ultimate target reliability index should be in the range of β_ult: 3.5–5 in order to produce the optimal design.     

Modeling of Chloride Concentration Effect on Reinforcement Corrosion

Abstract:   The corrosion of reinforcement is one of the major causes of deterioration of reinforced concrete (RC) structures, considerably affecting their durability and reliability. The rate of reinforcement corrosion is governed by, among other factors, the presence of chlorides on the surface of the steel. The assessment of such deteriorating effects necessitates the development of relevant models and the utilization of advanced simulation techniques to enable the probabilistic analysis of concrete structures. In this article an approach for the assessment of the durability and reliability of RC structures under attack from chlorides is introduced. The field of chloride concentration at different locations in the structure (represented in 2D space by chosen longitudinal or cross sections) is modeled as a function of time by a cellular automata (CA) technique. The results of this simulation are then utilized for the assessment of a steel corrosion prognosis using a probabilistic 1D model at chosen points, although the rate of corrosion is based on experimental results. The concentrations of chlorides and pH levels are reflected in this way. The described approach is applied to an illustrative example showing the feasibility of capturing the effect of chloride concentration on the steel corrosion rate and consequently on the assessment of the service life and/or reliability of the structure.     

Reliability-based condition assessment of deteriorating concrete bridges considering load redistribution

A wide variety of models have been proposed for estimating the reliability of highway bridges. For reinforced concrete bridges subjected to environmental attack, time-variant reliability methods have to be used. In this study, the condition of reinforced concrete girder bridges is assessed using a time-variant system reliability approach in which both load and resistance are time-variant quantities. Several system models are considered, including failure of any girder (series system) and failure of a specified number of adjacent girders (series-parallel system). Adaptive importance sampling is used to determine the cumulative-time system failure probability. An existing reinforced concrete T-beam bridge located near Pueblo, Colorado, is investigated. The influence of resistance degradation and post-failure load redistribution is included. A comparison of reliability estimates for several system models is given, including the influence of correlation among initial girder strengths. The results can be used as a guide for the selection of system models for bridge reliability analysis, identification of critical girders in a bridge system, and for the development of optimal reliability-based maintenance strategies for reinforced concrete highway bridges.     

Deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion

A three-dimensional reinforced concrete (RC) deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion is presented in this study. The finite element formulation accounts for both material and geometrical nonlinearity. Damage modelling considers uniform and pitting corrosion and includes the reduction of cross-sectional area of corroded bars, the reduction of ductility of reinforcing steel and the deterioration of concrete strength due to splitting cracks, delamination and spalling of the concrete cover. The beam finite element is validated with reference to the results of experimental tests carried out on RC beams with corroded reinforcement. The application potentialities of the proposed formulation are shown through the finite element analysis of a statically indeterminate RC beam and a three-dimensional RC arch bridge under different damage scenarios and corrosion penetration levels. The results indicate that the design for durability of concrete structures exposed to corrosion needs to rely on structural analysis methods capable to account for the global effects of local damage phenomena on the overall system performance.     

鄂尔多斯韩土2号桥钢箱梁拼装架设施工

根据鄂尔多斯韩土2号桥桥位工况和结构特点,介绍内陆地区钢箱梁现场拼装架设施工工艺;钢箱梁采用单元件形式出厂、龙门吊机吊装的施工方案。同时介绍了支架的设计和设置、焊接变形控制、测量控制方法;采用该方法施工的钢箱梁各项指标均符合设计及规范要求,可供类似钢箱梁高架桥的施工参考。     

Finite element investigation of shear capacity of locally corroded end panel of steel plate girder

This study discusses the effect of local corrosion damages nearby the bearing region including the bearing stiffener and adjacent web damage on the ultimate shear and post-buckling strength of steel plate girder bridges. A computer package ABAQUS is utilized for the verification and extension of the numerical study. Various corrosion damage cases, specifically the bearing stiffener are studied considering different damage thickness and damage heights. The study concludes that local damage on bearing stiffener damage is more fatal than the local web damage for the shear resistance of the plate girder. Further, some empirical relationships are also derived to assess the residual shear capacity of the locally corroded plate girder at the bearing region.     

Effects of in‐cycle strength degradation on collapse capacity of steel moment frames

In this study, the effects of in‐cycle strength degradation of steel moment connections are investigated on global behavior of multiple degree‐of‐freedom structures. Two types of degrading connection models are defined and compared with a bilinear non‐degrading model. Due to dispersion of the experimental test results on connections performance, two models are considered for each type. A probability assessment is carried out by implementation of incremental dynamic analysis to find the capacity of the structures for various performance levels. A sensitivity study is conducted on hysteresis parameters of connection models to investigate the effect of these parameters on global behavior of the structures. Due to increased dispersion of displacement demands observed in degrading cases, a reliability analysis is carried out to consider the effect of uncertainty on confidence level of the structures. Results show that in‐cycle strength degradation can lead to abrupt dynamic instability and as a consequence decrease in reliability of the system against collapse. Copyright © 2013 John Wiley & Sons, Ltd.     

Reliability evaluation in nonlinear analysis of reinforced concrete structures

Modern building codes provide a basis for development of advanced nonlinear models for analysis and design of reinforced concrete (RC) structures. Application of nonlinear models permits direct evaluation of reliability of the whole structure at the stage of a structural analysis. In this paper a probabilistic method for reliability evaluation of plane frame structures with respect to ultimate limit states is proposed. The method is based on a combination of the nonlinear finite element structural model and the first-order reliability method (FORM). Implementation of the FORM for nonlinear analysis of RC structures is considered. Uncertainties associated with the structural model are taken into account and their influence on structural reliability is examined via sensitivity analysis.     

Effect of secondary elements on bridge structural system reliability considering moment capacity

Secondary elements such as barriers, sidewalks, and diaphragms may increase the load carrying capacity of girder bridges. This in turn affects reliability. The objective of this study is to evaluate the potential benefit of secondary elements on the system reliability of girder bridges, if these elements are designed with the structural system to participate resisting vehicular live loads. Simple span, two lane structures are considered, with composite steel girders supporting a reinforced concrete deck. For structural analysis, a finite element procedure is developed that combines a grillage model of the bridge deck with solid elements for edge-stiffening effects. Random variables considered are composite girder, barrier, and sidewalk flexural strengths (each in turn composed of many random variables), load magnitude (dead load and truck traffic live load), and live load position. System resistance parameters are estimated with a point integration method. System resistance is evaluated in terms of maximum load carried at ultimate capacity. It was found that the interaction of typical secondary element combinations has a varying effect on system reliability, depending on element stiffness, bridge span, and girder spacing.     

硫酸盐腐蚀锚索结构锚固性能退化规律试验研究

 硫酸盐腐蚀是锚索结构长期锚固性能退化的原因之一。为模拟围岩约束条件下硫酸盐对锚索浆体的腐蚀及腐蚀后的锚固受力过程,设计外包钢管圆柱形素水泥浆中置钢绞线短黏结试件并进行长期硫酸盐干湿循环腐蚀,然后通过静力拔出试验观察黏结受力过程,获取黏结滑移曲线,定义锚固特征参数。结果表明：围岩约束作用对腐蚀过程及拔出受力过程产生显著影响,腐蚀引起的物理损伤得以阻止,化学损伤成为主要腐蚀损伤方式;拔出破坏特征为：浆体螺旋肋逐渐被磨平,索体最终被抽出;全程黏结滑移曲线由初期极速上升段、中后期锯齿形上升段及末期快速下降段组成;当围岩变形模量增大时,设计允许滑移、设计强度、极限滑移以及极限强度均随之增大;当浆体腐蚀程度增大时,设计强度、极限滑移以及极限强度随之降低,而设计允许滑移则因浆体模量的退化而随之增大。     

受拉侧锈蚀钢纤维-钢筋混凝土管片承载力退化模型研究

近年来,国内外新建盾构隧道与管道工程中采用钢纤维-钢筋混凝土管片愈来愈多,在侵蚀环境下管片钢筋锈蚀的问题突出,提出适用于锈蚀后钢纤维-钢筋混凝土管片的残余承载力计算的方法十分重要。鉴于此,文章根据服役期盾构隧道管片所处环境及受力特征,结合钢筋混凝土结构正截面承载力计算理论,提出受拉侧锈蚀钢纤维 钢筋混凝土管片承载力退化模型,并给出相应的求解流程。同时,分析不同锈蚀率与不同钢纤维掺量下受拉侧锈蚀钢纤维-钢筋混凝土管片承载力曲线,并将该模型理论解与压弯荷载作用下钢纤维-钢筋混凝土管片的同步加速锈蚀室内试验结果进行比较,验证了该模型的适用性和可靠性。主要结论有：①随着钢纤维的掺量增加,混凝土的立方体抗压强度会先增大后减小;②偏心受压管片构件极限弯矩最大值随主筋锈蚀率的增大而不断减小,随钢纤维掺量的增大而不断增大,但增大幅度逐渐减小;极限轴力最大值受主筋锈蚀率的影响不大,但随钢纤维掺量先增大后减小。③主筋锈蚀率与钢纤维掺量对大偏心受压构件的影响均大于小偏心受压构件;界限偏心距随主筋锈蚀率的增大而减小,随钢纤维掺量的增大而增大。     

Research on reasonable value of target reliability index for steel main girder of cable-stayed bridge considering durability

Abstract

This article studies the relationship between the target reliability index and the design life of the main girder of a long-span cable-stayed bridge to provide a theoretical basis for the design of steel girders for such an application. The changes of the bending section modulus under atmospheric corrosion and the residual ultimate stress of the section of a steel box girder under alternating loads are discussed. A resistance attenuation function for a steel girder of a cable-stayed bridge to predict the resistance change of a steel box girder over the service period is proposed, and the change characteristics of the time-varying reliability index of a steel box girder of a cable-stayed bridge are studied. By analysing the relationship between the time-varying reliability index and the evaluating benchmark value of the reliability index, the time point of maintenance and reinforcement is predicted. Based on the change over time of the difference between the time-varying reliability index and the evaluating benchmark value of the reliability index, the relation function between the target reliability index and the service lifetime of a bridge considering resistance attenuation are provided.     

Bending strength of concrete-filled narrow-width steel box girder

A new type of partially concrete filled steel box girder is proposed. The distance between the two webs is narrower than that of a conventional steel box girder, and concrete is filled inside the box girder at the intermediate supports of the continuous girder. Static bending loading tests were conducted with these new type girders, showing that the ultimate bending strength of the concrete filled steel box girder model was 40% larger than that of the steel box girder model. The ductility also increased about 8 times. The tests with the half concrete filled steel box girder model showed that the ultimate bending strength was 25% larger than the steel box girder model and the ductility was about 6.5 times larger. The half concrete filled steel box girder model without vertical stiffeners had the same ultimate bending strength of that of the girder with vertical stiffeners but the ductility was about half. The simple calculation method was developed using fibre models. The calculated results agreed with the test results and the calculation method has been verified.