考虑变量相关性的桥梁时变地震易损性研究

为研究变量相关性对桥梁时变地震易损性的影响,引入Nataf变换和均匀设计,提出了一种考虑变量相关性的桥梁时变地震易损性分析方法。以一多跨连续梁桥为研究对象,基于OpenSees建立其非线性分析模型,考虑氯离子侵蚀引起的钢筋直径及面积的退化,基于OpenSees截面非线性分析及单条地震波的非线性地震响应分析,探讨了氯离子侵蚀对桥梁抗震能力和地震需求的影响。然后,考虑桥墩、铅芯橡胶支座(LRB)、板式橡胶支座(PETB)和桥台等构件的地震损伤,建立了桥梁时变地震易损性曲线;最后,针对结构参数变量相关性对桥梁抗震能力、地震需求和时变地震易损性曲线的影响进行了定性分析。研究结果表明:①氯离子侵蚀会导致桥墩截面极限抗弯承载能力下降,而截面极限曲率、延性能力却略有提升;②考虑由氯离子侵蚀引起的纵筋锈蚀后,桥梁墩底截面弯矩需求有一定程度的下降,而墩顶位移和墩底截面曲率延性需求却有所增大,桥梁在不同损伤状态下的损伤超越概率会随服役时间的增加而增大;③该方法可较好处理结构参数变量相关性,并且考虑变量相关性后,在全寿命设计基准期内,桥墩截面极限抗弯承载能力有所提升,而墩顶位移、墩底截面弯矩和曲率延性需求则有一定程度的下降;④忽略变量相关性条件的影响,可能会高估桥梁结构的时变地震易损性。     

在氯侵蚀和混凝土碳化环境下用时变可靠度和预后验决策优化桥梁检修制度

基于作者用Monte Carlo法和回归分析法开发的计算在氯侵蚀和混凝土碳化情况下混凝土梁的抗力退化随机过程的软件,用Bayes公式和桥梁检查结果更新桥梁退化状态,考虑桥梁检修的货币收益或更一般的能反映业主的财政承受能力和风险规避心理的效益函数,用预后验决策分析法给出了桥梁检查的期望效益,并以期望效益最大来优化桥梁检修制度。用北京一座混凝土梁桥为例,考虑恒载随机变量和两个Poisson随机过程活载作用下跨中抗弯承载能力极限状态,以设计基准期内任意时段的时变结构可靠度不低于桥梁设计规范的目标可靠度为条件,对这种桥梁检修制度进行优化。结果表明:用效益函数优化时,业主的财政承受能力和风险规避心理能给出明显不同的桥梁检修制度。     

考虑氯离子侵蚀的高墩桥梁时变地震易损性分析

以一高墩大跨连续刚构桥为例,基于OpenSees 程序建立其非线性分析模型。考虑氯离子侵蚀引起的钢筋直径和屈服强度退化,根据截面非线性分析结果探讨了氯离子侵蚀效应对高墩抗震能力的影响。通过单条地震波的非线性时程地震响应,定性地研究了氯离子侵蚀效应对桥梁地震需求的影响。然后输入15 条地震波进行多次增量动力分析,采用对构件能力需求比(Demand/Capacity)进行对数回归分析的方法形成了桥梁的时变地震易损性曲线,对高墩桥梁的时变抗震性能进行评估。分析结果表明:氯离子侵蚀效应会导致高墩屈服弯矩下降,而延性能力略有提高;考虑纵筋锈蚀以后,高墩的位移需求和曲率需求则会显著增加;在桥梁全寿命设计基准期内,结构在不同损伤状态的地震易损性随桥梁服役时间增加而增大。     

锈蚀钢筋混凝土结构可靠度评估

钢筋锈蚀是混凝土结构破坏最主要的原因之一,目前钢筋混凝土结构可靠度研究大多数没有考虑锈蚀的影响。提出了锈蚀钢筋混凝土结构可靠度评估方法。首先分析大气环境下和氯离子环境下钢筋锈蚀的模型,然后考虑钢筋面积和粘结强度的降低,建立锈蚀钢筋混凝土结构抗力的随机模型,最后采用一次二阶矩实用分析法计算可靠度指标,以评估大气环境下和氯离子环境下混凝土结构可靠度。两个算例表明,该方法可用于锈蚀钢筋混凝土结构可靠度评估。     

考虑钢筋锈蚀的复合受扭混凝土箱梁时变承载力研究

对考虑钢筋锈蚀的复合受扭钢筋混凝土箱梁时变承载力进行研究。针对复合受扭混凝土箱梁中混凝土开裂面与钢筋斜交的情况,推导了综合考虑钢筋混凝土粘结滑移效应及正交配筋效应的钢筋修正本构模型。引入钢筋和混凝土材料的时变劣化模型,结合复合受扭钢筋混凝土箱梁的修正板-桁架模型,编制了复合受扭钢筋混凝土箱梁时变承载力的计算程序。与纯扭锈蚀构件和复合受扭构件的试验对比,验证了所提出钢筋修正本构模型的适用性较好。算例结果表明:在假定的一般大气环境和受力条件下,考虑钢筋锈蚀的复合受扭钢筋混凝土箱梁构件100年后抗扭强度降低约15%。     

控制钢筋保护层厚度的有效措施

在桥梁结构中,钢筋不断锈蚀,宵效截面不断减小,桥梁结构承载力不断下降,钢筋混凝土构件丧失基本承载能力。控制好钢筋保护层厚度有利于防止钢筋锈蚀,保证混凝土结构耐久性和使用寿命。本文结合工程实际,通过四控一检,在钢筋保护层厚度控制方面作如下简述。     

考虑氯离子腐蚀作用的近海桥梁结构全寿命抗震性能评价

基于全寿命理念的桥梁结构全寿命抗震性能设计与评价方法,是近年来国内外桥梁工程领域普遍关注的热点课题。主要研究了氯离子腐蚀作用在全寿命周期内对钢筋混凝土近海桥梁结构抗震性能的影响,结合氯离子对钢筋混凝土结构的腐蚀作用模型,提出了基于时变腐蚀电流密度的钢筋混凝土结构在氯离子腐蚀作用下钢筋腐蚀程度公式。取某一长期受海洋潮汐环境中氯离子腐蚀作用影响的近海桥梁工程结构为算例,考虑桥梁墩柱内纵筋直径、力学性能以及混凝土性能在全寿命周期内的退化效应,对各个寿命周期阶段内的算例桥梁进行Pushover分析和增量动力分析,并通过易损性分析方法对全寿命周期内桥梁的抗震性能进行了评价。研究结果表明,随着氯离子腐蚀作用的进行,桥梁结构在全寿命周期内的抗震能力不断降低,地震动作用下的抗震需求不断增加,到达极限破坏状态的概率不断增加。该桥梁结构全寿命抗震性能评价方法可为桥梁结构全寿命抗震性能设计提供参考。     

考虑氯离子侵蚀维度的钢筋混凝土码头服役寿命预测

合理评估和预测海洋环境下考虑氯盐侵蚀的钢筋混凝土(RC)码头结构服役寿命,对港口正常、安全运营意义重大.根据混凝土多相复合材料的细观组成结构,建立考虑粗骨料为凸多边形的混凝土细观数值模型.基于氯离子侵蚀混凝土的有限元数值模拟仿真方法,评估得到混凝土细观模型中氯离子一维、二维侵蚀的浓度分布,并建立氯离子一维、二维侵蚀模型.以沿海某RC高桩码头工程中方桩构件为例,根据建立的氯离子侵蚀模型并结合钢筋锈蚀速率模型,预测RC方桩构件的服役寿命.结果表明:在氯离子二维侵蚀下RC方桩的服役寿命预测值较一维侵蚀提前了约34％,RC结构的服役寿命大幅缩短.建议在RC码头耐久性设计过程中充分考虑氯离子侵蚀维度对结构物服役寿命的影响,以保障RC码头结构的运营安全.     

海工结构服役寿命及保护层开裂模式细观数值模拟

通过在钢筋与混凝土交界面处施加时变边界位移建立非均匀锈蚀钢筋锈胀模型,其中混凝土损伤本构采用指数应力软化模型,时变边界位移采用Faraday定律对氯离子浓度积分计算得到.参数化分析保护层厚度、钢筋位置、钢筋直径等因素对服役寿命及保护层开裂模式的影响.研究结果表明,服役寿命随保护层厚度增加而增长,而且增加幅度逐步增大,而钢筋直径变化对服役寿命影响较小,角部钢筋锈蚀则导致结构服役寿命缩短;中部钢筋的锈蚀使得保护层出现三条主裂缝,当保护层较小,保护层破坏模式为凸起式破坏,保护层较大时则将出现层裂;同时,角部钢筋锈蚀将在保护层内形成两条主裂纹,最终导致角部保护层脱落.     

考虑锈蚀黏结退化的钢筋混凝土桥墩抗震性能分析

受氯离子腐蚀作用影响,钢筋混凝土结构的抗震性能在其服役期内会发生退化。以钢筋混凝土桥墩为例,采用OpenSees有限元软件模拟了非锈蚀足尺桥墩的振动台试验以及锈蚀缩尺桥墩的拟静力试验结果,后者引入了氯离子腐蚀作用模型,同时考虑了桥墩的纵筋力学性能衰减以及粘结退化问题。随后基于概率地震需求模型对足尺桥墩的三种纵筋腐蚀工况进行了易损性分析。研究结果表明:采用非线性梁柱单元与零长度截面单元串联方式建立的数值模型能够有效模拟钢筋混凝土桥墩的足尺振动台试验结果和缩尺锈蚀拟静力试验结果;当纵筋腐蚀率较小时,纵筋的性能退化对墩顶最大位移影响不大,但基底剪力和基底弯矩下降明显;轻微破坏状态下,桥墩的抗震性能受纵筋锈蚀的影响不明显,随着破坏程度的加深,纵筋锈蚀对桥墩抗震性能的影响逐渐显著,较小的腐蚀率能导致桥墩的破坏概率发生较为明显的提高。研究内容可为考虑全寿命周期内性能退化的钢筋混凝土结构抗震设计提供参考。     

Performance evaluation of corrosion-affected reinforced concrete bridge girders using Markov chains with fuzzy states

A methodology for performance evaluation of reinforced concrete bridge girders in corrosive environments is proposed. The methodology uses the concept of performability and considers both serviceability- and ultimate-limit states. The serviceability limit states are defined based on the degree of cracking (characterized by crack width) in the girder due to chloride induced corrosion of reinforcement, and the ultimate limit states are defined based on the flexural load carrying capacity of the girder (characterized in terms of rating factor using the load and resistance factor rating method). The condition of the bridge girder is specified by the assignment of a condition state from a set of predefined condition states. Generally, the classification of condition states is linguistic, while the condition states are considered to be mutually exclusive and collectively exhaustive. In the present study, the condition states of the bridge girder are also represented by fuzzy sets to consider the ambiguities arising due to the linguistic classification of condition states. A non-homogeneous Markov chain (MC) model is used for modeling the condition state evolution of the bridge girder with time. The usefulness of the proposed methodology is demonstrated through a case study of a severely distressed beam of the Rocky Point Viaduct. The results obtained using the proposed approach are compared with those obtained using conventional MC model. It is noted that the use of MC with fuzzy states leads to conservative decision making for the problem considered in the case study.     

Chloride redistribution and reinforcement corrosion in the interfacial region between substrate and repair concrete—a laboratory study

One of the most common deterioration mechanisms in concrete structures is reinforcement corrosion caused by chlorides. An often used repair strategy is to remove the damaged concrete and sometimes also undamaged concrete and replace with a repair concrete. The chloride contaminated undamaged concrete and the repair concrete have to be compatible in order to achieve a durable system. This laboratory study has investigated 13-year-old reinforced concrete specimens with both substrate concrete with mixed-in chlorides and an initially chloride free repair concrete. The main objective was to study chloride transport from the contaminated substrate concrete into the repair concrete and establish chloride profiles across the interfacial region and interfacial zone between the two materials. Another objective was to evaluate the location of reinforcement corrosion in the interfacial zone, in the substrate concrete and in the repair concrete. The main results from this laboratory investigation show that reinforcement corrosion occurs in and near the interfacial zone between chloride contaminated and repair concrete. It was found that the corrosion occurs in local areas with passive steel areas between, i.e. macrocell corrosion. The chlorides are transported from the contaminated substrate concrete into the repair concrete. This investigation indicates that there is a risk for reinforcement corrosion around a patch repair when the substrate concrete has chloride contents exceeding 1.0 wt% by weight of cement.     

体外预应力桥梁锚固结构的受力性能与配筋研究

通过两座不同截面类型的体外预应力桥梁锚固结构的空间应力分析,获得了其应力分布特点,指出了其薄弱环节。探讨了角钢、锚垫板、体外预应力钢管对锚固结构受力性能的影响。根据力流传递形式结合拉压杆模型方法,建立了锚固结构拉压杆配筋计算模型,提出了配筋建议。分析表明:在锚固结构与梁交接部位设置角钢,能有效地降低该位置混凝土的应力集中;按弹性材料分析得到的锚固结构附近区域混凝土的各应力值均不同程度地超出设计强度的若干倍,但考虑材料的非线性,考虑角钢、锚垫板、体外预应力钢管、钢筋网以及分布钢筋的作用,锚固结构混凝土的局部应力大为降低,满足规范限值要求。     

Repair method and residual bearing strength evaluation of a locally corroded plate girder at support

There is growing interest in the maintenance and repair of bridges according to the increase in their service time. Many corrosion problems have especially been reported in plate girder bridges in support regions because of their high moisture level due to the bad air circulation, sediments, deposition, rain water, and antifreeze penetration in the drainage-type expansion joint. In this study, CFRP repair of a plate girder with localized corrosion at its support was proposed, and this method was used to repair the locally corroded plate girder around its support to examine the applicability and effectiveness of the corrosion repair method using CFRP. FE analysis of the corroded plate girder model was carried out to clarify the residual bearing strength and failure mode due to the localized plate girder corrosion in the web and stiffener at the support region. The application of the CFRP repair method to the plate girder bridge with local corrosion at its support showed that such method can be useful for corroded bridges due to its rapid and simple application and the stress level improvement on the repaired corroded surface on account of the sectional reinforcement effect of the CFRP repair and the prevention of the corrosion progress in the plate girder. The evaluation of the residual bearing strength of the plate girder with local corrosion at its support showed that such strength was affected more by the corrosion related to the stiffener than by the local web corrosion at the support. Therefore, to prevent local corrosion of a plate girder at its support, the corrosion ratio of the stiffener must be considered more than that of the web, and a corroded stiffener must be repaired or reinforced ahead of a corroded web.     

Corrosion of reinforcement induced by environment containing chloride and carbon dioxide

Reinforced concrete structures during their exploitation may be exposed to the common action of carbonation and chlorides causing corrosion of steel reinforcement. Therefore, the related data seem to be interesting and important when the evaluation of the service life of the structures is the object of interest. This fact was a motivation for the present experimental study on the sequence of action of chloride solutions and carbonation of the embedding concrete. The results obtained show that carbonation of concrete foregoing the action of chloride solutions may intensify the process of corrosion of steel reinforcement in comparison to the converse sequence of the action of mentioned media. At the same time the natrium chloride solution has been shown as a more aggressive medium opposite to the calcium and magnesium chloride solutions.     

Impact of mechanical loading on the corrosion of steel reinforcement in concrete structures

This paper presents results of an experimental investigation on the effect of mechanical loading on the corrosion of steel reinforcement in concrete. Reinforced concrete beams were cast, subjected to mechanical loadings and then exposed to corrosive environment. Successive drying and wetting cycles using 3% sodium chloride salt solution were used to accelerate the corrosion attack. Electrochemical techniques such as macrocell corrosion current, linear polarization resistance (LPR), corrosion potential (E _corr ) and electrochemical impedance spectroscopic (EIS), were used to evaluate the corrosion behavior of the reinforcement. Also, chloride penetration profile and visual inspection of the beam rebars were obtained. The results shows that the pre-exposure mechanical load has no influence on the corrosion initiation or corrosion rate thereafter, unless it reaches to some limit where it develops connected cracks through which the chloride ions flow and depassivate the rebars. The load of 25% of the ultimate capacity seems to be the critical load limit where some microcracks onset to be connected, facilitate the chloride ions flow, and initiate the rebar corrosion.     

Structural performance of corroded RC beams repaired with CFRP sheets

Corrosion of reinforcement is a serious problem and is the main cause of concrete structures deterioration costing millions of dollars even though the majority of such structures are at the early age of their expected service life. This paper presents the experimental results of damaged/repaired reinforced concrete beams. The experimental program consisted of reinforced concrete rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied between 5% and 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Corroded beams were repaired by bonding carbon fiber reinforced polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. Different strengthening schemes were used to repair the damaged beams. Test results showed detrimental effect of corrosion on strength as well as the bond between steel reinforcement and the surrounding concrete. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. However, strength of damaged beams due to corrosion was restored to the undamaged state when strengthened with CFRP sheets. On the other hand, the ultimate deflection of strengthened beams was less than ultimate deflection of un-strengthened beams.     

锈蚀和疲劳耦合作用下梁桥时变承载力评估

钢筋混凝土桥梁在环境和荷载双重作用下将出现锈蚀、粘结退化和疲劳损伤,现有承载力计算方法不能同时考虑三者的综合影响。根据已有成果系统阐述锈蚀、粘结退化和疲劳损伤对承载力的影响,分析锈蚀和疲劳耦合作用下的钢筋面积退化情况。根据锈蚀钢筋与混凝土界面间的变形协调关系推导多因素影响下截面协同工作系数的表达式,提出同时考虑锈蚀、粘结退化和疲劳损伤的承载力计算方法。以钢筋混凝土简支梁为例,对其承载力退化过程进行理论分析和数值模拟。结果表明:所提出的承载力评估方法可以合理准确地反映桥梁在疲劳和锈蚀耦合作用下的承载力退化过程,可为计算锈蚀和疲劳耦合作用下桥梁承载力评估提供参考。