基于广义位势理论的土的数值弹塑性模型及其初步应用研究

广义位势理论从数学角度出发建立土的本构模型,可克服传统本构理论的不足,而又同时包含了传统理论作为其特例,从而为土的本构模型研究提供新的和适用性更广的理论。以广义虎克定律为基础的邓肯-张模型以其简单方便、参数确定容易且有明确的物理意义而得到广泛的应用,而其最大缺点则是不能反映土的剪胀性;此外,邓肯-张模型采用双曲线函数拟合试验曲线也有一定的局限性。为保留其参数确定简便的优点,并弥补其不足,基于广义位势理论建立了数值弹塑性模型。该模型保留了邓肯-张模型在参数确定方面的简单性,同时由于采用了广义位势理论来建模,不再受广义虎克定律的限制,因而可弥补邓肯-张模型在反映土体剪胀性方面的缺陷。此外,该模型采用数值手段来表示试验曲线的建模方法,可以克服邓肯-张模型采用双曲线函数表示试验曲线方法的局限性,具有更为广泛的适应性。通过对一碎石桩复合土体三轴试验结果的数值模拟表明：基于广义位势理论的数值弹塑性模型计算与试验结果吻合良好,且在反映碎石的剪胀特性方面优于邓肯-张模型,从而初步证明了该模型的合理性及优越性。     

高速铁路穿透型CFG桩复合地基沉降计算修正系数分析

为掌握铁路工程CFG桩复合地基在路堤荷载作用下的沉降计算修正系数变化特点,基于武汉－广州高速铁路24个路堤断面的地基沉降测试数据,结合地勘和设计参数,分析了地基沉降计算修正系数的变化规律及工后沉降的时间效应特征,结果表明,软弱土层浅薄的穿透型CFG桩复合地基具有优良的沉降控制效果,对应的地基沉降计算修正系数在0.63～0.17之间,较当量压缩模量相当的《铁路工程地基处理技术规范》推荐值偏低约1/3;地基沉降表现出显著的时间效应特征,地基工后沉降占最终沉降的比值有随时间逐渐降低的趋势;路堤填筑速率加快和地基布桩间距加大,对穿透型CFG桩复合地基工后沉降占最终沉降的比值有明显增大作用,地基沉降稳定所需的时间更长。     

刚性桩复合地基桩体抗震性能分析

建立三维有限模型,分别采用振型分解反应谱法和时程分析法研究刚性桩复合地基的抗震性能,并根据相似理论,建立刚性桩复合地基群桩模型,采用模型拟动力试验,对其进行了地震作用下桩体响应规律试验研究,并对其在不同方法下的结果进行了对比分析,结果表明：无论是弯矩值还是剪力值,都是角桩最大,其次是边桩,再次是中心桩;不同分析方法所得的位移值相差不大,位移分布比较均匀;而且通过观察试验现象、分析试验和理论数据可见刚性桩复合地基具有良好的抗震性能;模型动力试验方法用于研究刚性桩复合地基的抗震性能是可行的,并且可推广应用到类似性的其他复合地基的抗震性能试验研究。     

基于分式析因及最佳子集回归的多种污染物复合污染特征——阿特拉津与多种污染物在松花江沉积物上的吸附效应

为揭示农药（晶体乐果、甲霜灵、阿特拉津、马拉硫磷、扑草净）与重金属（铜、锌、铅、镉、镍）10种污染物共存时的复合污染规律,以阿特拉津为目标污染物,采用分辨度为Ⅲ的2^10-6分式析因实验设计,并用完全折叠实验和区组设计进行辅助,通过多元线性回归的建模方法筛选并建立了以阿特拉津为因变量、10种污染物因子主效应和二阶交互效应为自变量的多元线性回归吸附模型。研究表明：共存体系中因子主效应项铅、铜、锌、镉、镍和农药晶体乐果显著抑制（显著性水平α=0.05）阿特拉津在沉积物上的吸附,与阿特拉津产生竞争吸附效应,因重金属主效应产生的拮抗作用占总拮抗作用的63.5%,其拮抗作用从大到小为镍、镉、晶体乐果、锌、铅、铜;在以镍为关键自变量的二阶交互效应项中,因二阶交互效应项产生的协同或拮抗作用占阿特拉津吸附能力的35.3%,其中,铅、镉和晶体乐果抑制镍与阿特拉津的竞争吸附,与阿特拉津在沉积物上的吸附发生协同作用,协同作用从大到小为镉×镍、铅×镍、镍×晶体乐果;而镍作为调节自变量的二阶交互效应项镍阿特拉津会促进阿特拉津的吸附,说明多种污染物共存体系中重金属镍对阿特拉津在沉积物上吸附影响作用的复杂性和重要性。     

干旱区不同土壤和作物灌溉量的无机碳淋溶特征实验研究

为探讨干旱区作物灌溉对盐碱土无机碳传输的影响,通过选择不同含盐量的土壤,即耕地土（F）、混合土（C）和原生荒漠土（D）,分别种植水稻（R）和棉花（C）,进行了一个生长季的淋溶实验,并定期收取且分析土壤淋溶液中的可溶性无机碳（DIC）含量。结果表明：（1）水稻处理无机碳的淋溶主要集中在秧苗分蘖期和幼穗发育期,而棉花处理则集中在花铃期和吐絮期;（2）不同含盐量土壤在同一灌溉量下,土壤含盐量越高,其淋溶过程得到的无机碳总量越大,最高约为8.4 g·m^-2·a^-1,最低仅约0.7 g·m^-2·a^-1;（3）同种土壤不同灌溉量,其水稻高于棉花,高出值范围为2.9～4.1 g·m^-2·a^-1;种植作物处理得到的无机碳总量均大于其相应对照处理的量（p＜0.05）。研究结果表明,土壤的盐含量及作物灌溉量对土壤无机碳淋溶有重要影响。     

海水环境下钢筋混凝土人工鱼礁的耐久性寿命预测

根据人工模拟的流动海水环境(流速约为0.15m/s)下的混凝土侵蚀试验测得的混凝土中氯离子质量分数,分别测定了腐蚀350,380,400d后混凝土的氯离子扩散系数,并计算和预测了混凝土人工鱼礁的耐久性寿命。研究结果表明:氯离子在混凝土人工鱼礁中的扩散规律基本上遵循Fick第二定律;钢筋混凝土人工鱼礁的耐久性寿命与保护层厚度的平方成正比;海水盐度对混凝土人工鱼礁的耐久性寿命影响较大。     

A practice‐oriented estimation of the failure probability of building structures

In the presented practice‐oriented probabilistic approach for the seismic performance assessment of building structures, the SAC‐FEMA method, which is a part of the broader PEER probabilistic framework and permits probability assessment in closed form, is combined with the pushover‐based N2 method. The most demanding part of the PEER probabilistic framework, that is incremental dynamic analysis, is replaced by the much simpler N2 method, which requires considerably less input data and much less computational time, but which can, nevertheless, often provide: acceptable estimates for the mean values of the structural response. Using some additional simplifying assumptions that are consistent with seismic code procedures, an explicit equation for a quick estimation of the annual probability of “failure” (i.e. the probability of exceeding the near collapse limit state) of a structure can be derived, which is appropriate for practical applications, provided that predetermined default values for the dispersion measures are available. In the paper, this simplified approach is summarized and applied to the estimation of the “failure” probability of reinforced concrete frame buildings representing both old structures, not designed for earthquake resistance, and new structures designed according to Eurocode 8. The results of the analyses indicate a high probability of the “failure” of buildings, which have not been designed for seismic loads. For a building designed according to a modern code, the conservatively determined probability of “failure” is about 30 times less but still significant (about 1% over the lifetime of the structure). Copyright © 2011 John Wiley & Sons, Ltd.     

Cyclic performance of large‐scale corroded reinforced concrete beams

Nine large‐scale beam specimens were constructed. Of which, one was used as the control, whereas the other eight ones were divided into four sets. Each set had two specimens and was subjected to accelerated corrosion using an imposed current for the same time interval. Following the corrosion, a specimen in each set was tested using cyclic loading to examine the seismic performance, whereas the other one was demolished to examine the extent of corrosion. Cyclic loading results indicated that with an increasing corrosion level, the ultimate drift, ductility, plastic rotation capacity, and energy dissipation of the beams initially increased and later decreased. The failure mode switched from flexural failure, largely owing to buckling of the longitudinal reinforcement to flexural‐shear failure, which is mainly caused by fracturing of the transverse reinforcement. Corrosion increased shear deformation and the spread of plasticity of the plastic hinge region. The residual flexural strength, as estimated by an empirical equation based on the maximum pit depth in the longitudinal reinforcement, closely corresponds to experimental values. Furthermore, the residual shear strength estimated based on the minimum reduced cross‐sectional area of transverse reinforcement correlates better with the experimental observations than that based on the weight loss. Copyright © 2011 John Wiley & Sons, Ltd.     

An efficient performance‐based seismic design method for reinforced concrete frames

In this paper, a practical method is developed for performance‐based design of RC structures subjected to seismic excitations. More efficient design is obtained by redistributing material from strong to weak parts of a structure until a state of uniform deformation or damage prevails. By applying the design algorithm on 5, 10 and 15‐storey RC frames, the efficiency of the proposed method is initially demonstrated for specific synthetic and real seismic excitations. The results indicate that, for similar structural weight, designed structures experience up to 30% less global damage compared with code‐based design frames. The method is then developed to consider multiple performance objectives and deal with seismic design of RC structures for a design spectrum. The results show that the proposed method is very efficient at controlling performance parameters and improving structural behaviour of RC frames. Copyright © 2011 John Wiley & Sons, Ltd.     

The reinforcement contribution to the cyclic behaviour of reinforced concrete beam hinges

The cyclic behaviour of plastic hinges is an essential component in tracking the behaviour of RC frames to failure, not only for monotonically increasing force/pressure loads such as under extreme wind loads but also for dynamic displacement-driven loads such as under earthquake ground motions. To describe member deformations at ultimate loading, traditional moment–curvature techniques have required the use of an empirical hinge length to predict rotations, and despite much research a definitive generic expression for this empirical hinge length is yet to be defined. To overcome this problem, a discrete rotation approach, which directly quantifies the rotation between crack faces using mechanics, has been developed for beams and been shown to be accurate under monotonic loading. In this paper, the discrete rotation approach for monotonic loads is extended to cope with cyclic loads for dynamic analyses, and this has led to the development of a new partial interaction numerical simulation capable of allowing for reversals of slip of the reinforcing bars. This numerical tool should be very useful for the nonlinear analysis of reinforced concrete beams and reinforced concrete columns with small axial loads under severe dynamic loads. Copyright © 2011 John Wiley & Sons, Ltd.