基于材料劣化的既有混凝土构件数值建模方法研究

基于ABAQUS,以多龄期混凝土构件为研究对象,在数值建模方面,采用三维实体线性减缩单元C3D8R和两结点三维单元T3D2模拟混凝土材料、内嵌钢筋的力学行为,将指数衰减摩擦模型用于锈蚀钢筋与混凝土间接触问题上,并将Hsich-Ting-Chen四参数强度准则作为混凝土材料的破坏准则;在材料性能退化方面,基于修正斜压场理论,以锈蚀箍筋、纵筋、受压区锈胀开裂混凝土及核心区约束混凝土为对象,综合各既有材料退化模型,预测了材料退化后的力学性能,得到了开裂混凝土、锈蚀钢筋、混凝土及其之间黏结滑移的本构模型。进而,采用多龄期混凝土构件抗震性能试验研究结果,对提出的基于ABAQUS软件平台的锈蚀混凝土构件数值建模理论进行了可靠性验证,结果表明:所建立的数值建模理论可以有效地模拟锈蚀混凝土构件的抗震性能退化规律,为既有混凝土结构的数值建模理论提供了一种有效的研究方法。     

锈蚀钢筋混凝土柱基于变形的性能指标研究

采用ABAQUS有限元软件,对按GB 50011-2010《建筑抗震设计规范》和GB 50010-2010《混凝土结构设计规范》设计的342个锈蚀钢筋混凝土柱进行有限元分析,研究钢筋的锈蚀率、轴压比、剪跨比、配箍率和纵向钢筋配筋率等参数对钢筋混凝土柱变形性能的影响。结果表明：当钢筋的锈蚀率较小时,构件的变形性能受锈蚀率影响不大;当钢筋的锈蚀率达到10%以后,构件的破坏形态发生改变,变形能力急剧退化;随着轴压比的增大,构件的变形能力降低;轴压比较小的构件变形性能受剪跨比影响比轴压比较大的构件明显;随着配箍率和纵向钢筋配筋率的增大,构件的变形能力有所提高;提出了锈蚀钢筋混凝土柱抗震性能等级和性能界限状态的划分方法,以塑性转角作为变形性能指标,对数值计算结果进行统计分析,得到了锈蚀钢筋混凝土柱各性能界限点的塑性转角统计特征值。研究成果可为钢筋混凝土结构全寿命的性能化抗震设计和抗震性能评估提供参考。     

Prediction of corrosion-induced cover cracking in reinforced concrete structures

Usually, the time of repair/replacement of reinforced concrete structures due to corrosion is controlled by cracking of the concrete cover. Thus, it is important to be able to predict with sufficient accuracy the time from corrosion initiation to crack formation in the concrete cover. The paper presents a critical overview of existing empirical, analytical and numerical models for predicting the time to corrosion-induced cover cracking. A simple nonlinear finite element (FE) is then formulated and validated. The FE model is employed to investigate inaccuracies of analytical models arising due to simplified formulation of the nonlinear behaviour of concrete and inability to account for actual location of corroding reinforcing bars. Recommendations on the applicability of analytical models are provided. Finally, the FE model is used to estimate the amount of corrosion products penetrating into concrete pores and microcracks since this amount is an essential parameter for analytical and numerical models.     

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.     

Model for cover cracking of RC beams due to partial surface steel corrosion

Cracking of the cover concrete due to steel corrosion is considered by many researchers to indicate the end-of-service life of corrosion-affected reinforced concrete (RC) structures. Numerous models have been developed to predict the time from corrosion initiation to cracking of the cover concrete. In the previous models, concrete with corroding steel bars was assumed to behave like a thick-walled cylinder under uniform internal pressure. Recent research publications have however, shown that steel corrosion is often concentrated on the surface of the steel that faces the direction of ingress of corrosion agents. This paper presents a model that relates the level of partial surface steel corrosion with the transverse and vertical strains measured on the exterior faces of corrosion-affected RC beams. The model assumes that the remaining section of the steel after corrosion is elliptical shaped. Finally, the model is calibrated with experimental data in the literature and it is shown that assuming uniform steel corrosion underestimates the internal pressure applied by the expansive corrosion products.     

锈蚀钢筋混凝土构件粘结性能的研究进展

综述了研究锈蚀钢筋与混凝土之间粘结性能的意义,对锈蚀钢筋与混凝土之间粘结性能的退化规律以及粘结损失对钢筋混凝土构件性能的影响等方面的研究进展进行了总结．     

Extent of spatially variable corrosion damage as an indicator of strength and time-dependent reliability of RC beams

A spatial time-dependent reliability model is developed for a RC beam subject to corrosion-induced pitting corrosion. The analysis considers the spatial and time-dependent variability of pitting corrosion and its effect on cover cracking and shear and flexural resistance. The model uses extreme value theory to predict maximum pit depth as a function of bar diameter and reinforcing bar length. The effect of corrosion on the mechanical behaviour of reinforcement and associated loss of ductility is also considered. A 1D spatial model is included where concrete properties, concrete cover and the surface chloride concentration are treated as random fields. The model is then used to predict the likelihood and extent of corrosion-induced cracking (corrosion damage). The spatial time-dependent reliability model allows the loss of structural capacity and reliability to be calculated conditional to the observed extent of corrosion damage. This allows the interaction between corrosion damage and loss of structural safety to be inferred for a deteriorating RC beam. It was found that the crack width at time of structural collapse is often well in excess of 1 mm. It was also found that the extent and location of severe cover cracking is an important indicator of structural reliability.     

锈蚀钢筋混凝土保护层锈胀开裂时间的预测模型

由钢筋锈蚀引起的混凝土保护层锈胀开裂是混凝土结构耐久性极限状态的重要标志,是决定结构使用寿命的重要因素。以钢筋均匀锈蚀为前提,考虑锈蚀产物的变形特性以及锈胀裂缝开展过程中锈蚀产物进入裂缝的实际情况,借助弹性力学和Faraday腐蚀定律,建立混凝土保护层锈胀开裂时刻的钢筋锈蚀率以及锈胀开裂时间计算公式。针对影响混凝土保护层锈胀开裂时间各主要因素的分析表明,增大钢筋的混凝土保护层厚度、减小钢筋直径、提高混凝土强度以及控制锈蚀产物的体积膨胀率都有利于混凝土结构耐久性的提高。与已有试验结果的对比分析可知,对于加速锈蚀和长期锈蚀情况,计算公式的预测结果均较为理想,可用于由钢筋均匀锈蚀引起的混凝土保护层锈胀开裂时间的预测分析。     

钢筋锈蚀开裂条件的试验研究

利用电化学快速锈蚀方法,对钢筋锈蚀开裂的条件进行了试验研究。基于混凝土强度、混凝土保护层厚度、钢筋直径给出了确定开裂时钢筋锈蚀率的计算公式,并对钢筋种类和钢筋位置的影响给出了修正系数。最后,与实际工程检测结果进行了对比分析。     

Life-cycle cost analysis of reinforced concrete structures in marine environments

Chloride-induced corrosion of carbon steel reinforcement is the main cause of deterioration of reinforced concrete (RC) structures in marine environments. One of the ways to protect RC structures from corrosion is to use corrosion-resistant stainless steel reinforcing bars. However, stainless steel is between six and nine times more expensive than carbon steel. Thus, its use can only be justified on a life-cycle cost basis. In the paper a time-variant probabilistic model was presented to predict expected costs of repair and replacement which was then used to calculate life-cycle costs for RC structures in marine environments under different exposure conditions. Results of the life-cycle cost analysis can be applied to select optimal strategies improving durability of RC structures in marine environments, including the use of stainless steel reinforcement.     

无腹筋锈蚀钢筋混凝土梁承载能力的计算

锈蚀钢筋混凝土梁的承载力不仅与纵向钢筋的截面损失有关 ,而且和钢筋与混凝土之间的粘结强度的降低、混凝土保护层中出现的纵向锈胀裂缝有关。本文先考虑了由于钢筋的截面损失引起的钢筋混凝土梁的抗弯承载力的降低 ;再在梁 拱共同作用抵抗剪力的机制上 ,计算了无腹筋锈蚀钢筋混凝土梁的抗剪承载力 ,进而得到了无腹筋锈蚀钢筋混凝土梁的承载力及其相应的破坏模式。对一实例的计算结果表明 ,当混凝土保护层出现纵向锈胀裂缝后 ,钢筋与混凝土之间的极限粘结强度相应降低 ,梁的破坏模式由受弯破坏转向受剪破坏 ,承载能力有较大的降低。同时 ,锚固区的粘结强度的降低 ,导致梁也可能发生粘结锚固破坏。     

钢筋非均匀锈蚀引发的混凝土保护层开裂细观数值研究

混凝土保护层锈裂严重影响钢筋混凝土结构的耐久性。为了研究混凝土保护层的锈裂行为,考虑到混凝土细观结构的非均质性以及钢筋锈蚀的非均匀性,将完好混凝土视为由骨料、砂浆和界面过渡区组成的三相复合材料,建立了细观随机骨料模型。在模型中,钢筋的非均匀锈蚀行为以施加非均匀径向位移的方式模拟,骨料的力学行为假定为弹性,砂浆和界面过渡区的力学特性采用塑性损伤模型来描述。在此基础上进行了中部钢筋非均匀锈蚀引发的混凝土保护层开裂行为的细观数值模拟;分析结果与已有文献中的试验结果吻合良好。另外,对比了均质模型和非均质模型中钢筋均匀锈蚀和非均匀锈蚀导致的保护层开裂模式;并探讨分析了保护层厚度和钢筋直径对保护层开裂模式、钢筋锈胀压力及保护层开裂时钢筋锈蚀率的影响。     

锈蚀钢筋混凝土柱抗震性能试验研究

为研究钢筋锈蚀对钢筋混凝土(RC)柱抗震性能的影响,设计并制作了8根RC柱试件,其中包括1根未锈蚀柱、3根纵筋锈蚀柱和4根箍筋锈蚀柱。采用5%NaCl溶液浸泡试件并通电对钢筋进行锈蚀试验,通电锈蚀完成后,分别对8根试件进行了低周往复循环荷载试验,分析得到了不同锈蚀率下各试件的破坏模式、滞回曲线、骨架曲线、刚度退化、延性及耗能能力等结果。结果表明：与未锈蚀柱相比,随着纵筋与箍筋锈蚀率的增加,滞回曲线的饱满程度均逐渐减小,同时试件的耗能能力、刚度及变形也显著降低,且箍筋锈蚀率的影响更显著。当箍筋锈蚀率达到15.19%时,试件的位移延性系数和平均耗能系数分别降低了19.9%和35.6%。同时,在柱的端部塑性铰区形成剪切破坏面,试件发生脆性破坏。箍筋锈蚀率大于15.19%这一不利影响在抗震设防区域应引起重视。     

荷载作用下开裂钢筋混凝土梁锈胀开裂模式及锈蚀分布研究

为提高混凝土结构的服役性能,对混凝土保护层的锈胀开裂过程进行研究。对荷载作用下锈蚀18个月的内掺氯盐钢筋混凝土梁的截面锈胀裂缝分析发现：环向裂缝宽度沿径向呈指数函数变化;锈胀裂缝的开裂模式、锈蚀产物与钢筋混凝土受力状态、骨料及裂缝的相对位置均密切相关;保护层破坏以层状破坏为主。通过研究提出,在对锈蚀钢筋混凝土梁进行承载力分析时,建议剪压区不考虑受压混凝土保护层的作用,对剪拉区和弯拉区钢筋与混凝土之间的黏结性能要进行折减。     

混凝土内钢筋锈蚀层发展和锈蚀量分布模型研究

从研究钢筋锈蚀物膨胀对钢筋/混凝土界面区构造的影响着手,通过对锈蚀层形成、发展及其细观构造的研究,揭示混凝土内钢筋锈蚀量分布规律;在钢筋锈胀开裂前,钢筋锈蚀量基本分布在面向混凝土保护层一侧的钢筋半圆周上,离混凝土保护层最近处锈蚀量最大,离保护层表面距离越远,锈蚀量越小;其锈蚀量在其半圆周上呈半椭圆形分布。钢筋锈胀开裂初期,钢筋锈蚀逐渐向背向混凝土保护层一侧发展,在背向保护层一侧的钢筋锈蚀量分布被假定为均匀分布,和面向混凝土保护层一侧的最小锈蚀量衔接。     

Bond strength modeling for corroded reinforcements

Bond strength of corroded reinforcements is theoretically modeled. First, corrosion pressures before and after corrosion cracking are calculated. Influence of reinforcement corrosion on concrete cover is considered and effective depth of concrete cover is introduced at different corrosion levels. Then, the frictional contact force that develops along the bar–concrete interface and interlocking force of the bar ribs in concrete are calculated by taking into account the reduction in the height of the bar ribs and reduction of cover concrete due to corrosion. As a result, bond strength of corroded bars under splitting failure is calculated. The theoretical results are compared with the experimental results and agree with those results well.     

Bond strength of hot-dip galvanized reinforcement in normal strength concrete structures

Hot-dip galvanizing is one of the methods used to solve the problem of corrosion of reinforcement in concrete structures. The few research reported in the literature on the effect of galvanizing on bond strength of reinforcing bars anchored in pullout specimens, indicates contradictory results. The primary objective of this paper is to evaluate experimentally the effect of hot dip galvanizing on the bond capacity of tension lap splices. The test results may have an implication on the development length and splice length design provisions of galvanized bars in building design codes. To achieve the objective, six concrete beam specimens were tested in positive bending. For each of three bar sizes 20, 25, and 32 mm, two companion beams identical except for whether the bars were black or galvanized, were tested. Each beam was designed with bars spliced at midspan in a constant moment region. The nominal concrete strength was 28 MPa. The mode of failure was splitting of the concrete cover in the splice region. The test results indicated that the use of galvanized bars has a negligible negative effect on bond strength of reinforcement in normal strength concrete.     

Effect of transverse reinforcement spacing on fire resistance of high strength concrete columns

The confinement effect due to the congested transverse reinforcement is a very important feature for reinforced concrete columns subjected to accidental load conditions. The influence of transverse reinforcement spacings on load bearing capacity of high strength concrete (HSC) columns at ambient temperature has been the subject of many research projects, both experimental and theoretical. However, at high temperature the results of research into this subject are scarce and do not provide unambiguous evidence as to the effect of spacing of transverse reinforcement on fire load capacity and fire resistance.The first part of this paper presents an experimental study of the influence of transverse reinforcement spacing on fire resistance of axially loaded, HSC columns with circular cross-section. The results of full-scale tests indicate that columns with spacing of ties recommended by the code provisions for design of concrete structures could suffer a premature failure as a consequence of inelastic buckling of main reinforcing bars between adjacent ties.The next part of the paper concerns the supplementary numerical analysis of tested columns. The columns were modelled in axisymmetry with embedded reinforcement. The applied material model took into account the influence of transient temperature on mechanical properties of concrete and steel. The effect of cracking, development of transient creep strains and plastic strains for concrete were also included in the analysis. The inelastic buckling of main reinforcement was modelled using average stress–strain relationships for steel in compression. The comparison of numerical simulations and experiments shows reasonable agreement. The assessment of failure modes using the numerical simulation is also presented in the paper. The results of calculations indicate that during the whole heating period high thermal gradients generated tensile stresses in the plane of cross-section of the columns. Due to this fact the confinement effect was not observed for the columns with congested spacing of transverse reinforcement.     

混凝土保护层锈胀开裂条件的弹性力学分析

混凝土中钢筋锈蚀是混凝土结构耐久性研究的重要内容,研究混凝土中的钢筋锈蚀,并建立混凝土保护层锈胀开裂时钢筋锈蚀量估计模型,是分析现有结构性能退化及耐久性评估的关键工作,对于准确预测结构的使用寿命与剩余寿命具有十分重要的意义.采用弹性力学分析方法,对混凝土保护层锈胀开裂全过程进行了建模,借助一些合理的假设,得到了混凝土保护层锈胀开裂条件的理论计算公式,该公式不仅可以应用普通混凝土结构,也可应用于其他类型混凝土结构.最后并对公式进行了验证,表明理论计算公式具有较好的实用性.     

锈蚀钢筋与混凝土粘结应力模型研究

研究了混凝土保护层胀裂时及胀裂前锈蚀对无横向约束光圆钢筋混凝土试件粘结性能的影响机理。应用弹性力学理论,建立了锈胀力计算模型,推导出了保护层胀裂时刻钢筋锈蚀深度的计算表达式;结合已有研究成果,建立了钢筋表面摩擦系数计算公式;在综合考虑锈胀力作用及钢筋表面状况变化对粘结强度影响的基础上,提出了光圆钢筋粘结应力计算模型,并通过多个试验结果对理论模型进行了验证,结果表明计算值与试验值吻合良好,从而定量阐明了保护层锈胀裂前光圆钢筋粘结应力随锈胀力增长及钢筋表面摩擦系数增大而增长的内在机理。