加载速率对锈蚀钢筋与混凝土粘结性能的影响

为探究加载速率对锈蚀钢筋与混凝土粘结性能的影响,开展16根RC梁(质量损失率0%～8.7%)在不同加载速率(0.5～300 mm/min)下的粘结性能测试,据此提出考虑加载速率和钢筋锈蚀影响的粘结强度计算公式,并开展锈蚀钢筋混凝土梁粘结力学行为的数值模拟,分析高加载速率(30～30 000 mm/min,应变率10^-4～10^-1s^-1)下锈蚀梁的粘结滑移力学行为。研究表明：(1)加载速率对锈蚀钢筋混凝土梁式试件的粘结应力-滑移曲线形状以及粘结强度与残余粘结强度的比值影响不大;(2)随着加载速率的增加,锈蚀钢筋与混凝土的粘结强度和残余粘结强度显著增加,粘结区应力峰值显著增加并逐渐向加载端靠近;(3)本工作提出的考虑加载速率和钢筋锈蚀影响的粘结强度计算公式在0.5～30 000 mm/min的加载速率范围内有很好的适用性。     

重复荷载下钢筋与混凝土粘结本构关系

重复荷载下粘结滑移本构关系是结构疲劳计算和有限元分析的基本关系之一。该文通过23 个试件静载和重复荷载下的拉拔试验对钢筋滑移量、粘结滑移基本关系、粘结应力形状函数、粘结疲劳破坏准则进行了全面深入的研究。首先根据加载端峰值滑移量和残余滑移量发展规律得出了计算公式;接着利用粘结滑移变化规律提出了考虑残余滑移、应力水平和循环荷载次数的幂函数形式粘结本构关系;运用沿钢筋埋长范围内应变变化得出了疲劳破坏三阶段粘结应力形状函数;最后基于重复荷载下发生粘结疲劳破坏的条件是滑移量增加到静载下的最大滑移量的基本准则,理论推导了粘结疲劳寿命方程。研究表明:当粘结疲劳没有发生时,重复荷载下极限粘结强度及最大滑移量并不受重复次数的影响。研究结果为理论分析重复荷载下受弯构件裂缝宽度、锚固长度、刚度、塑性铰转动问题等提供了依据和方便。     

往复荷载下锈蚀钢筋与混凝土粘结性能的试验研究

针对钢筋混凝土结构在服役过程中钢筋锈蚀以及承受往复荷载工况下引起的钢筋混凝土材料耐久性能劣化会对钢筋混凝土间的粘结性能产生影响，设计并制作了48根粘结区带裂缝的钢筋混凝土梁式试件，以研究在承受不同往复荷载工况(往复荷载幅度分别为极限荷载的0%、10%、20%及30%)、四种钢筋锈蚀率(0%、3%、5%及7%)以及往复荷载与钢筋锈蚀耦合工况下钢筋与混凝土粘结性能的变化情况。结果表明：钢筋锈蚀会影响试件破坏状态；施加往复荷载过程中残余滑移的增长主要发生在前六个循环，且残余滑移随着钢筋锈蚀率以及往复荷载幅度的增加而增大；耦合工况会进一步促进粘结性能的劣化，且粘结强度损失率随着钢筋锈蚀率和往复荷载幅度的增加而增大。该研究可为对应工况下钢筋混凝土构件的现状评估提供理论参考依据。     

锈蚀变形钢筋与混凝土粘结应力模型研究

研究了锈蚀对钢筋混凝土无箍筋试件粘结强度的影响,建立了锈蚀导致保护层胀裂前变形钢筋极限粘结应力的理论计算模型,定量地揭示了该阶段粘结强度增强的机理。通过对钢筋肋间混凝土在挤压力、摩擦力及锈胀力作用下的受力分析,从理论上推导了锈蚀钢筋混凝土发生劈裂破坏时的粘结应力计算表达式;给出了摩擦系数等未知参数的取值大小;详细阐述了表达式的求解思路。利用已发表文献的多个试验结果对理论模型进行验证,结果表明计算值与试验值吻合良好。     

微锈蚀钢筋混凝土高温后粘结锚固性能试验研究

为研究高温对锈蚀钢筋混凝土结构粘结锚固性能的影响,对锈蚀试件(锈蚀率为1.08%)与非锈蚀试件先进行高温试验(20℃、200℃、400℃、600℃、800℃),再进行中心拔出试验。试验结果表明:随温度的升高,锈蚀试件与非锈蚀试件粘结强度均呈下降趋势,与非锈蚀试件相比,锈蚀试件在温度不超过400℃时,其粘结强度下降趋势较为平缓。分析了高温作用后混凝土抗压强度、钢筋极限强度、钢筋与混凝土间粘结强度三者之间的关系,并建立了考虑不同温度、不同锈蚀率等因素影响下钢筋与混凝土的粘结-滑移关系式。     

钢筋锈蚀后与再生混凝土间粘结-滑移本构关系研究

为研究钢筋锈蚀后与再生混凝土间粘结-滑移本构关系,主要考虑了不同钢筋锈蚀率、不同再生粗骨料取代率、不同再生混凝土强度等因素的影响,采用加速通电锈蚀以及钢筋开槽内贴片方法,完成23组钢筋再生混凝土试件粘结-滑移性能拉拔试验,获得了再生混凝土与不同锈蚀程度螺纹钢筋间的荷载-滑移曲线以及不同锚固位置处钢筋应变。通过实测结果及理论分析,计算得到不同锈蚀率下钢筋再生混凝土间粘结应力及滑移值沿锚固长度分布规律,分析了钢筋锈蚀前后与再生混凝土间粘结应力传递及粘结锚固位置函数差异的受力机理,提出了不同锈蚀率下反映实际粘结分布规律的粘结锚固位置函数模型,最后建立钢筋锈蚀后与再生混凝土间考虑粘结-滑移位置函数的粘结-滑移本构关系,为锈蚀后钢筋再生混凝土有限元分析提供参考依据。     

高应力重复加卸载下GFRP筋与混凝土的粘结性能

对20 个GFRP 筋标准拔出试件进行了单调静力加载和高应力重复加卸载的粘结性能试验, 考察了粘结强度、加载端滑移量、粘结刚度及滞回耗能的变化规律。研究结果表明, GFRP 筋的粘结性能在等幅(Δτ=017τu ) 应力循环下表现不稳定, 在变应力幅重复加卸载下, 粘结强度衰减较为明显, 得到的包迹线和共同点曲线与单调静力加载τ s 曲线形状基本一致, 同一滑移量下共同点曲线上的粘结应力与包迹线上的粘结应力比值在0150～0. 75 变化。重复加卸载下GFRP 筋肋的损伤程度比单调静力加载下的情况更为严重, 混凝土界面没有发现劈裂裂纹。从滑移量、能量耗散和刚度衰减变化情况来看, 加载历史和损伤累积状态对这些变量的影响最为明显。      

高温后单向侧压作用下混凝土与钢筋黏结-滑移性能研究

高温后混凝土与钢筋间的黏结性能影响钢筋混凝土结构的安全评估,实际工程中钢筋混凝土常承受侧向约束作用。为此,该文以高温温度和侧压力为参数,完成了48个钢筋混凝土试件的中心拉拔试验,分析侧压力对高温后试件破坏形态、峰值黏结应力、峰值滑移、残余黏结强度的影响规律,建立了峰值黏结应力随高温温度和侧压力变化的经验公式。将侧压下钢筋-混凝土黏结应力场简化为肋前混凝土挤压力和侧压力的线性叠加,并基于微观传力模型及高温后混凝土的多轴强度破坏准则推导计算了无侧压及单向侧压下的黏结强度理论。研究结果表明:侧压作用和高温温度直接影响试件破坏形态;随着侧压力增加,高温后混凝土与钢筋间的峰值黏结应力、残余黏结强度、峰值滑移逐渐增大,但温度达到500 ℃后,有侧压试件峰值滑移较无侧压试件小;黏结强度理论计算值与实测值较为吻合,能较好地预测高温后混凝土与钢筋间的黏结强度。     

基于OpenSees的钢筋混凝土梁粘结滑移数值分析

粘结滑移性能的数值分析是钢筋混凝土结构研究的热点,该文在总结现有粘结滑移本构关系的基础上,采用分离式思想在OpenSees中建立粘结滑移精细化分析模型,并通过拉拔试件与RC梁构件的数值分析研究梁中钢筋与混凝土的粘结滑移作用,同时考虑箍筋量对构件滑移分布的影响。经过该文分析可知,该数值分析模型具有一定的合理性,能较准确的反映出粘结应力、滑移等分布的规律;通过梁构件数值分析可知,其整体性能受到粘结性能、钢筋滑移量大小及箍筋配置等的影响,箍筋的配置对构件局部滑移会产生一定的影响,但对滑移的整体分布影响并不显著。     

海洋环境下混凝土中钢筋锈蚀机理及监测技术概述

2014年我国由于腐蚀产生的损失约为21 278亿元,占国家GDP的3.34%。海洋环境中氯离子渗透至混凝土内部导致钢筋锈蚀是海洋环境下混凝土结构损伤的重要原因。海洋不同腐蚀区域的离子浓度、氧气浓度及海水干湿循环作用时间各不相同,这使得海洋不同腐蚀区域中暴露混凝土的氯离子传输速度和分布规律、钢筋锈蚀产物及锈蚀模式、钢筋锈蚀速率存在显著差异。其中海洋浪溅区和高潮位区域因氧气充足、海水干湿循环作用剧烈及浪溅作用导致钢筋混凝土更易破坏。钢筋锈蚀产物体积是原始体积的2~6倍,持续增加的锈蚀产物将导致混凝土开裂、保护层剥落并进一步加速钢筋锈蚀;考虑钢筋非均匀锈蚀、锈蚀产物填充效应、钢筋及混凝土性能的钢筋混凝土锈胀开裂模型将更加精确。根据海洋不同腐蚀区带特点、钢筋混凝土性能及受荷情况,建立不同腐蚀区域中混凝土的氯离子传输模型,钢筋锈蚀速率模型和混凝土锈胀开裂模型有助于准确预测海洋环境下钢筋混凝土的服役寿命。 通过对混凝土中钢筋锈蚀的检测与监测有助于实时了解混凝土的服役状态。采用线性极化、电化学噪声和电化学阻抗谱等电化学方法可以较好地检测钢筋锈蚀状态、获得混凝土中钢筋的锈蚀速率。基于电化学原理开发的阳极梯和环形电极、基于钢筋锈胀应力测试的光纤监测技术以及基于数字图像技术获得混凝土中钢筋锈蚀应力应变场,有助于实现对混凝土中钢筋锈蚀的监测,并且部分已应用于海洋工程。相比于普通钢筋,锈蚀钢筋的导电率和导磁率均显著降低,采用电磁感应原理开发钢筋锈蚀装置实现了暴露在海水中的普通钢筋和耐蚀钢筋磁通量变化值与钢筋质量损失线性关系的建立。这也为更精确监测混凝土中钢筋锈蚀全过程、实现混凝土中钢筋锈蚀源定位及损伤程度识别提供可能。因此,综合利用氯离子、pH微电极等实现混凝土内部微环境监测,开发先进的钢筋锈蚀监测传感器实现混凝土中钢筋锈蚀源和锈蚀速率监测,通过图像监测技术实现钢筋锈蚀诱导混凝土开裂过程监测。综合上述措施将实现对钢筋混凝土结构腐蚀的全过程监测,并为海洋钢筋混凝土服役寿命预测模型的验证与修正提供依据,同时为海洋环境混凝土的耐久性评估系统提供预警机制。     

Impact of crack width on bond: confined and unconfined rebar

This paper reports the results of a research project comparing the effect of surface crack width and degree of corrosion on the bond strength of confined and unconfined deformed 12 and 16 mm mild steel reinforcing bars. The corrosion was induced by chloride contamination of the concrete and an applied DC current. The principal parameters investigated were confinement of the reinforcement, the cover depth, bar diameter, degree of corrosion and the surface crack width. The results indicated that potential relationship between the crack width and the bond strength. The results also showed an increase in bond strength at the point where initial surface cracking was observed for bars with confining stirrups. No such increase was observed with unconfined specimens.     

氯盐环境下锈蚀预应力混凝土梁抗弯性能试验

为探讨氯盐环境下锈蚀预应力混凝土梁的抗弯性能,制作了5根先张预应力混凝土梁,采用电化学法分别对其进行了0 d、7 d、14 d、28 d及42 d的快速腐蚀,随后进行了四点弯曲试验。研究了不同锈蚀程度对预应力混凝土梁自振频率、钢绞线滑移、结构变形、弯曲开裂、破坏模式及极限承载力等性能的影响。结果表明:氯盐环境下锈蚀对预应力混凝土梁高阶频率影响较小,导致一阶频率逐渐增大,28 d后锈蚀裂缝较大且局部混凝土脱落,一阶频率迅速减小;轻微腐蚀对预应力混凝土梁的抗弯性能影响较小,腐蚀程度增大,抗弯性能明显降低,腐蚀42 d后,极限挠度减小了18.7%,抗弯承载力减小了17.3%,延性降低了19%;锈蚀钢绞线与混凝土间滑移速率增大,极限滑移值由5 μm增加至11.4 μm;钢筋锈蚀对弯曲裂缝高度发展的影响不大,但促进了裂缝宽度的扩展,结构屈服后,底部裂缝开裂速率由0.0062 mm/kN增加至0.0252 mm/kN。在试验研究基础上,采用有限元软件ANSYS对各锈蚀梁的受载全过程进行了有限元模拟计算,极限荷载和钢绞线滑移量的模拟值与实测值误差分别小于5%和10%,吻合较好。      

酸雨环境下腐蚀RC剪力墙抗震性能试验研究

为研究酸雨环境中RC剪力墙的抗震性能,设计了6榀剪跨比为2.14的RC剪力墙试件,采用人工气候环境模拟技术对其进行酸雨环境加速腐蚀试验,进而进行拟静力试验,分析轴压比和腐蚀程度对RC剪力墙抗震性能的影响。结果表明:在酸雨溶液中的H+和SO₄2+共同侵蚀作用下,试件表面出现析出晶体、侵蚀孔洞、骨料外露等现象,且随酸雨侵蚀循环次数增加腐蚀现象不断加重;随腐蚀程度增加,墙底水平裂缝出现时间提前且裂缝之间间距增加,裂缝宽度变宽,试件承载能力、变形能力和耗能能力均有不同程度的退化,峰值点剪切变形及其占总变形比例减小;随轴压比增加,墙体开裂、屈服和峰值荷载增大,裂缝发展速度减慢,但各试件的变形能力和耗能能力不断降低,峰值点剪切变形及其占总变形比例减小。     

Nondestructive Corrosion Detection in RC Through Integrated Heat Induction and IR Thermography

A novel integrated system of electromagnetic heat induction and infrared (IR) thermography is proposed for nondestructive detection of steel corrosion in reinforced concrete (RC) structures, by taking advantage of the difference in thermal characteristics of corroded and non-corroded steel. This paper presents a proof-of-concept experimental study. An inductive heater was employed to remotely heat the steel rebar from concrete surface, and an IR camera was applied to measure IR intensity at the concrete surface. Bare rebar and concrete specimens with different cover depths were fabricated, and induced with different levels of corrosion through an accelerated corrosion process. IR thermography was recorded during the specimen heating and cooling periods. The test results reveal a clear correlation between the extent of corrosion and the IR thermal characteristics. More corroded specimens exhibit higher peak IR intensities and faster rates of heating than those of less corroded specimens. As the concrete cover depth increases, however, it becomes less efficient to heat the rebar and more difficult to identify the difference between corroded and non-corroded specimens using the IR camera. This study demonstrates a potential application of the integration of heat induction and IR thermography for nondestructive detection of rebar corrosion in concrete structure.     

型钢混凝土结构粘结滑移性能试验研究

进行了20榀试件的实腹式型钢混凝土粘结滑移性能的拉拔试验,分析了型钢与混凝土的粘结滑移机理、影响粘结滑移性能的主要因素以及沿锚固长度粘结应力和滑移量的分布规律,建立了型钢混凝土粘结强度和滑移量的计算公式,提出了型钢混凝土局部粘结破坏和整体粘结破坏极限荷载的计算原理与方法,根据混凝土板的冲切破坏理论,提出了确定临界保护层厚度的方法。研究成果为改进型钢混凝土结构的强度、刚度、变形、裂缝宽度计算理论以及进行这种结构的有限元分析提供了试验依据。     

Cover cracking as a function of bar corrosion: Part I-Experimental test

The appraisal of concrete structures suffering rebar corrosion is one of the most urgent needs regarding the selection of the technical and economical optimum time for repair. Up to now this appraisal has been mainly based on empirical and subjective considerations. Among the different distressing consequences of rebar corrosion the best known is the cracking of concrete cover. However, very few data have been reported in the literature on the amount of corrosion needed to induce this cracking. In the present paper, some preliminary experiments are reported in which small reinforced beams are artificially corroded by an impressed current, and the amount of current (and loss of bar cross-section) needed to induce the crack at the surface are monitored, together with the evolution of crack width, by the use of strain gauges applied to the surface of the specimens. In a companion paper, a numerical model to relate the decrease in rebar cross-section to the cover cracking will be developed. That model is based on the orderly imposition of corrosion to finite elements of the rebar by a fictitious temperature increment that produces analogous effects, while concrete cracking is introduced by a standard smeared-crack model. The experimental results indicate that only a few micrometres of loss in rebar cross-section are needed to induce visible cover cracks (0.1 mm width) in the conditions of the test.     

Towards incorporating the influence of cover cracking on steel corrosion in RC design codes: the concept of performance-based crack width limits

This paper advocates for the adoption of performance-based limiting crack widths with respect to steel corrosion in reinforced concrete structures. The authors argue that, from both durability and sustainability viewpoints, the practice of adopting a universal limiting crack width for a wide range of in-service exposure conditions and concrete cover conditions and quality is not valid. As new performance-based concrete design codes are being developed and/or improved, the influence of cover cracking on steel corrosion needs to be incorporated in these codes. An experimental set-up was designed to investigate the influence of cover cracking, cover depth and concrete quality on chloride-induced corrosion. Beam specimens (120?×?130?×?375?mm) were cast using five concretes made using two w/b ratios (0.40 and 0.55) and three binders (100?% CEM I 42.5?N (PC), 50/50 PC/GGBS and 70/30 PC/FA). Other variables in the experiments included cover depth (20 and 40?mm), crack width (0, 0.4 and 0.7?mm). A total of 105 beam specimens were cast and exposed to cyclic 3-days wetting (with 5?% NaCl solution) and 4-days air-drying in the laboratory (23?°C, 50?% relative humidity). Corrosion rate was monitored bi-weekly in the specimens. The results relevant to this paper are presented and discussed. For a given concrete quality and cover depth, corrosion rate increased with increasing crack width. If crack width and cover depth are kept constant, corrosion rate increases with decreasing concrete quality, and vice versa. A model framework that can be used to objectively select cover depth, concrete quality and crack width is proposed. Such a model can be improved into, for example, a nomograph and used in the design process for RC structures prone to corrosion. Performance-based crack width limits should be adopted in the design of RC structures prone to steel corrosion. These crack width limits should be dependent on a complex interaction of, inter alia, concrete quality, cover depth, crack characteristics and prevailing exposure conditions. This study showed the inter-relationship between crack width, cover depth and concrete quality in affecting chloride-induced corrosion rate. Accurate corrosion rate prediction models incorporating the influence of cover cracking on corrosion are a pre-requisite to implementing the influence of cover cracking in future concrete design codes.     

Q690D高强钢基于连续损伤模型的断裂破坏预测分析

高强钢材在实际钢结构中已经开始逐步得到应用,该文针对Q690D高强度结构钢材,进行了钢材圆棒试样在单调加载和超低周循环加载下的断裂破坏试验,研究了试样裂纹的起始位置,分析了加载制度对试样承载能力和变形能力的影响,并采用扫描电镜观察了试样断口的微观形貌,断口呈现韧窝形式的延性断裂特征。基于Q690D钢材缺口圆棒试样的单调拉伸试验结果,结合有限元分析,标定了钢材的连续损伤模型参数。最后,应用钢材的连续损伤模型,对圆棒试样和带初始间隙试样在不同加载制度下的断裂破坏进行预测分析,得到试样的裂纹起始位置、荷载-位移曲线、断裂位移和疲劳寿命均与试验结果吻合良好。