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基于氯离子扩散传输机理,利用有限体积法(FVM)推导了二维矩形和圆形截面混凝土氯离子扩散传输离散方程。根据FVM的数值模拟计算结果,研究了暴露条件及混凝土组成材料对具有不同截面形状的混凝土构件中氯离子含量及使用寿命的影响。数值模拟计算表明,不仅暴露条件、混凝土组成材料等对海工混凝土结构的耐久性有重要影响,而且其影响程度与混凝土构件截面的几何形状有关,有比较明显的几何形状效应。圆形截面由于有近似的一维扩散传输特征,在相同条件下,混凝土中的氯离子含量小于矩形截面,其使用寿命比矩形截面的大,但两种截面的差别在不同暴露条件和混凝土组成材料时又有显著的不同,大气区以及掺矿渣时更为明显。 相似文献
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海洋浪溅区的混凝土结构,由于长期受到氯盐的侵蚀和海浪冲刷作用,导致混凝土结构发生钢筋锈蚀、保护层胀裂剥落等耐久性破坏,无法满足长期服役要求。本工作选取3种不同矿渣掺量的高性能矿渣混凝土进行实验室自然扩散和海洋浪溅区现场暴露试验,基于可靠度理论和修正氯离子扩散理论的ChaDuraLife V1. 0寿命分析软件,对海洋浪溅区的高性能矿渣混凝土结构进行寿命分析与研究。结果表明:随着服役时间的延长,海洋环境下高性能矿渣混凝土结构的失效概率逐渐增大,可靠度指标逐渐降低。随着矿渣掺量和保护层厚度的增大,高性能矿渣混凝土结构的服役寿命呈增长趋势。海洋浪溅区环境下,矿渣含量为35%、粉煤灰含量为15%、强度等级为C50的高性能矿渣混凝土在保护层厚度取7 cm、8 cm和9 cm的情况下,其服役寿命分别可以满足50 a、100 a和120 a的使用寿命要求。同时,建议将GBT50476-2008《混凝土结构耐久性设计规范》中规定的浪溅区混凝土最小保护层厚度和28 d氯离子侵入指标DRCM最大值进行修正,以满足其规定的设计使用年限要求。 相似文献
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在桥梁耦合抖振谱分析的基础上,采用谐波合成技术,依据Monte Carlo思想大量模拟位移谱时程,由此便可以方便、快捷地计算桥梁抖振响应首次超越失效概率,克服传统Monte Carlo方法时域内再现桥梁抖振首次超越小失效概率事件效率偏低的问题。采用江阴长江大桥和上海杨浦大桥作为算例,比较了抖振首次超越响应谱Monte Carlo模拟结果与目前广泛使用的基于Poisson、Poisson包络、Markov过程三种假定的近似解析算法结果差异,表明由于考虑大气紊流环境下桥梁抖振背景分量,在较高阈值情况下,近似解析算法不再适用,而本文方法具有更高的精度。 相似文献
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考虑氯离子侵蚀与混凝土碳化的公路桥梁时变可靠度分析 总被引:1,自引:1,他引:1
基于国内外对氯离子侵蚀和混凝土碳化环境下钢筋锈蚀速率的最新研究成果,建立了混凝土构件在氯离子侵蚀下考虑坑蚀和在混凝土碳化下考虑平均锈蚀的弯曲抗力退化模型,用Monte Carlo方法和统计回归法编制了退化钢筋混凝土构件及系统的时变可靠度计算程序。以北京地区一座公路桥为算例,结果表明:在氯离子侵蚀下考虑坑蚀的桥梁承载能力时变可靠度在30年左右即下降到设计目标可靠度,在混凝土碳化下考虑平均锈蚀的桥梁承载能力时变可靠度在50年左右即下降到设计目标可靠度,从而需要补强,这表明考虑主筋锈蚀后我国钢筋混凝土公路桥一般达不到100年设计使用期;对因主筋锈蚀导致混凝土保护层胀裂而言,构件达到抗裂正常使用极限状态远远早于达到承载能力极限状态,建议将混凝土保护层开裂时间作为桥梁检查/维修参考点。 相似文献
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当前在进行海工混凝土结构受氯盐侵蚀的耐久性研究时往往忽略了混凝土力学损伤的影响,这可能会导致高估结构的耐久性能。该文提出了在数值分析中引入损伤因子实现综合考虑结构损伤影响及氯盐侵蚀共同作用的分析方法,通过干湿循环的氯盐侵蚀试验与数值模拟分析,研究遭受氯盐腐蚀且受到长期荷载作用的预应力混凝土梁的耐久性能。结果表明,数值分析结果和试验结果吻合良好。参数分析结果表明:0.2mm宏观裂缝的出现对氯离子浓度有着较为显著的影响,未出现宏观裂缝时,拉应力对氯离子输运的影响较为有限;荷载比的大小影响结构的损伤范围和程度,进而影响氯离子在混凝土内的传输;梁构件施加预应力后,在15%和30%两种低荷载比状态下延缓其力学损伤(裂缝)的开展,减小荷载作用对氯离子扩散系数的增大效应,有效提高构件的抗氯盐侵蚀性能,当荷载比增加到45%以上,普通钢筋混凝土梁相对于预应力梁的氯离子浓度增比降至10%以内,这表明较高应力比下预应力对梁抗氯盐侵蚀能力的影响减弱。 相似文献
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为研究荷载对钢筋锈蚀速率及结构耐久性的影响,在潮汐区与盐雾区开展不同荷载条件下氯离子扩散试验,荷载大小分别为无荷载、0.3倍和0.5倍混凝土抗折强度.在混凝土中掺入氯盐,开展不同浓度氯盐条件下的钢筋锈蚀试验.通过氯离子扩散试验得到荷载对氯离子扩散影响系数与荷载大小的关系,修正菲克第二定律中的氯离子扩散系数.钢筋锈蚀试验中测试不同时间下混凝土构件中钢筋的锈蚀电流密度,拟合出钢筋锈蚀电流密度与氯盐浓度和锈蚀时间之间的关系.结合混凝土中考虑荷载影响的氯离子扩散模型与钢筋锈蚀模型,给出荷载作用下混凝土中钢筋锈蚀速率的计算方法.该方法对于海洋环境中荷载作用下钢筋混凝土结构耐久性寿命计算具有重要意义. 相似文献
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考虑海底隧道承受侵蚀性高压力海水的服役环境特点以及高性能混凝土的非饱和特性,建立了海底混凝土隧道氯离子扩散-对流传输模型和耐久寿命预测模型。以舟山沈家门海底隧道为工程背景,通过室内实验确定计算参数,采用TOUGH2软件数值模拟了环境中氯离子侵入隧道的传输过程,得到了氯离子经时传输规律,以及水头、混凝土初始饱和度、环境氯离子质量分数的作用规律,比较了扩散、饱和扩散-对流、非饱和扩散-对流预测模型的计算差异。结果表明:海底隧道腋角位置的氯离子质量分数累积最高;水头和环境氯离子质量分数与氯离子质量分数增长呈正相关,混凝土初始饱和度与氯离子质量分数增长呈负相关;按照扩散模型预测得到的隧道耐久寿命最长,按照非饱和扩散-对流模型预测得到的耐久寿命最短。 相似文献
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氯离子引起的腐蚀严重影响到混凝土结构的持久性,为了提高钢筋混凝土构筑物的持久性,需掌握和了解氯离子在混凝土中的扩散行为及其规律,以便根据这些规律进行混凝土结构耐久性设计和服役寿命预测。混凝土氯离子扩散系数测定仪可定量评价混凝土抵抗氯离子扩散的能力.为氯离子侵蚀环境中的混凝土结构耐久性设计与施工以及使用寿命的评估与预测提供基本参数。 相似文献
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Chloride-induced corrosion is the main factor in determining the durability and service life of the reinforced concrete structures exposed to marine environments. Recognition of chloride diffusion phenomenon in concrete and developing a prediction model that can estimate the service life of the concrete structures subject to long-term exposure is vital for aggressive marine environments. The present study focuses on developing such a prediction model of chloride diffusion coefficient for silica fume concrete under long-term exposure to a durability site located in the southern region of Iran. All investigations are based on 16 concrete mix designs containing silica fume with variable water-to-binder ratios exposed to sea water for maximum period of 60 months. This empirical model is developed by applying regression analysis based on Fick’s second law on the experimental results and is compared with previous studies in this area. This comparison indicates that the predicted chloride diffusion coefficient level is within a ±25% error margin in the specimens. The results indicate that reducing the water-to-binder ratio and adding the silica fume to a dosage of 10% reduces the chloride diffusion coefficient in concrete. This study also confirms that the chloride diffusion coefficient increases with temperature and decreases over time. 相似文献
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This paper addresses the analysis of probabilistic corrosion time initiation in reinforced concrete structures exposed to chloride penetration. Structural durability is an important criterion that must be evaluated for every type of structure. Considering reinforced concrete members, chloride diffusion process is widely used to evaluate durability, especially when these structures are constructed in aggressive atmospheres. The chloride ingress triggers the corrosion of reinforcements; therefore, by modelling this phenomenon, the corrosion process can be better evaluated as well as the structural durability. The corrosion begins when a threshold level of chloride concentration is reached at the steel bars of reinforcements. Despite the robustness of several models proposed in the literature, deterministic approaches fail to predict accurately the corrosion time initiation due the inherent randomness observed in this process. In this regard, structural durability can be more realistically represented using probabilistic approaches. A probabilistic model capable to model chloride ingress is presented in this paper. The chloride ingress is modelled using the Fick’s diffusion law. This law simulates the chloride diffusion process considering time-dependent effects. The probability of failure is calculated using Monte Carlo simulation and the first order reliability method with a direct coupling approach. Some examples are considered in order to study these phenomena. Moreover, a simplified method is proposed to determine optimal values for concrete cover. 相似文献
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To show the application of the chloride conductivity index test in service life prediction (SLP) using both the deemed-to-satisfy and probabilistic approaches to performance-based durability design. It is desirable to adopt a performance-based approach with respect to durability design of reinforced concrete (RC) structures. This is based on the perception that the durability of RC is achieved when the limiting value from an established test method is met. In South Africa, the durability index (DI) approach has been developed, which permits performance-based specifications for durability of RC. This approach involves the application of a test method together with a SLP model. This integrated approach links material properties directly with the expected service life of RC structures and environmental conditions. Two DIs are relevant to degradation processes in RC: the chloride conductivity index which is related to chloride ingress, and the oxygen permeability index related to carbonation. The study presented here focuses on the application of the chloride conductivity index as the main input parameter of a SLP model concerned with chloride-induced reinforcement corrosion. The methodology and output of the SLP model as applied in the deemed-to-satisfy approach are compared with those of the probabilistic approach. Both approaches are exemplified using a concrete pier cast in situ in a marine environment. The performance-based durability specifications from the deemed-to-satisfy approach are found to be more conservative compared to those of the probabilistic approach. 相似文献
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Chloride penetration into concrete in marine environment-Part II: Prediction of long term chloride penetration 总被引:3,自引:0,他引:3
The development of chloride penetration models is essential for the assessment of the service life of concrete structures exposed to marine environment. Simple models derived from Fick's second law of diffusion are at present the best way to predict the chloride penetration in practical situations. However these models need to be calibrated with experimental results. This paper presents an experimental study where the parameters used in the penetration model were calibrated to allow the prediction of long term chloride content in concrete. The results showed that both the concrete cover and concrete quality requirements stated in the present codes need to be increased so that an acceptable service life can be achieved. 相似文献
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With an increasing concern about long-term durability, chloride transport and service-life prediction of cracked concrete are now a hot area in concrete research. However, only few researches up to now investigated the effect of crack density on chloride transport in cracked concrete. Nevertheless, in real concrete structures, multiple cracks instead of a single crack are most commonly observed. The present study investigates non-steady state chloride diffusion in concrete samples with different crack densities prepared by a non-destructive notch method. The relationship between diffusion coefficient and crack density is discussed. Water and acid soluble chloride contents increase significantly with increasing crack density up to a certain value. A linear function is found for the relationship between diffusion coefficient determined by acid soluble chloride and crack density. A piecewise function including linear and exponential function is proposed to describe the relationship between diffusion coefficient determined by water soluble chloride and the crack density. 相似文献
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本文分别研究了大连港服役11年和50年的某码头大气区、浪贱区和潮汐区混凝土的外观破坏情况和物理力学性能,测定了不同深度混凝土的氯离子含量分布以及混凝土电阻率和RCM氯离子扩散系数(DRCM)等耐久性参数,探讨了部分耐久性参数之间的相关关系。结果表明,两个年代海洋码头的潮汐区混凝土都存在剥落现象,其中服役50年码头的大气区和浪溅区混凝土还存在裂缝现象。综合文献数据研究发现,海洋混凝土结构的表面自由氯离子含量随着暴露时间的延长呈指数函数或幂函数的增长关系,且服役早期增长较快,服役后期增长速度减缓。海洋混凝土结构的表观氯离子扩散系数随暴露时间的延长呈现经典的幂函数衰减关系。 相似文献
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碳化环境下的混凝土结构耐久性模型,是基于扩散理论、快速试验、自然暴露试验以及工程经验建立的。由于结构固有的不确定性和服役环境的复杂性,理论模型的预测结果与实际结构检测的耐久状况存在较大偏差。该文利用工程耐久性检测获得的碳化深度、检测钢筋锈蚀比例、检测混凝土开裂比例,综合先验知识,基于贝叶斯理论,提出碳化环境下的耐久性模型更新方法。结合结构实际的检测结果,经过更新的耐久性预测模型与待评估结构实际耐久状况更相符。依此模型进行相应剩余耐久寿命的概率预测和耐久性评级,为既有结构耐久性评估提供参考。 相似文献