圆钢管混凝土柱耐火极限影响因素灰色关联分析

为分清圆钢管混凝土柱耐火极限影响因素的主次关系,基于国内外18根圆钢管混凝土柱耐火极限试验研究资料,采用灰色系统理论中的灰色关联分析方法,对影响圆钢管混凝土柱耐火极限的因素进行灰色关联度分析计算和排序.结果表明,各关联因素对圆钢管混凝土柱耐火极限影响程度的大小排序依次为:防火保护层厚度、火灾荷载比、截面尺寸、构件长细比...     

基于灰关联理论的混凝土孔结构对强度和耐久性的影响分析

通过试验和分析得出混凝土的强度和耐久性与其微观孔结构联系紧密。利用灰色关联理论得到混凝土孔结构特征参数与混凝土强度、耐久性的灰色关联度,分析了不同孔结构特征参数对混凝土强度、耐久性影响程度。结果表明:小于20 nm的孔径分布与混凝土力学性能关联度最大;100～200 nm孔径分布对混凝土耐久性有较大的影响。     

基于灰色系统理论的RAP材料颗粒组成特征分析

针对废弃沥青混凝土(RAP)颗粒组成复杂,不利于再生沥青混凝土级配准确控制的问题,利用灰色系统理论,以RAP制备的多孔沥青混凝土的孔隙率偏差值作为灰色系统的主行为,以不同虚拟系数(Kc)在合成筛分中所占的比例作为影响系统主行为的相关因素行为,对RAP材料颗粒组成进行灰色关联分析,得到代表再生沥青混凝土级配准确程度与RAP颗粒组成关系的灰色关联度序列.结果表明:不同粒径范围的RAP颗粒组成规律不同,粒径越大对再生沥青混凝土级配的影响越明显;通过关联度对比分析,可模拟出1条接近再生后RAP颗粒真实存在状态的虚拟筛分曲线,经验证,该虚拟筛分曲线能够更准确地控制再生沥青混凝土级配,从而为RAP在骨架型沥青混合料中的应用提供理论指导.     

基于灰色关联分析的钢渣沥青混凝土水稳定性研究

该文采用灰色关联法,分析了不同生产工艺的钢渣、级配、沥青以及集料粒径的水稳定性能,并通过计算它们的关联度,得出了影响钢渣沥青混凝土水稳定性能的主次因素。研究结果显示,影响钢渣沥青混凝土水稳定性的因素相对影响程度依次为沥青、集料、级配和粒径。     

凝灰岩机制砂品质对混凝土性能的影响研究

针对浙江台州地区品质波动较大的凝灰岩机制砂,探究其对混凝土性能的影响。对比研究不同批次凝灰岩机制砂、石灰岩机制砂及河沙对混凝土力学性能和耐久性的影响。结果表明相比于纯水泥混凝土,掺加20%矿物掺和料的凝灰岩机制砂混凝土性能明显改善。运用灰色关联分析计算机制砂石粉含量、泥块含量、粗糙度与混凝土7,28 d抗压强度、电通量、开裂面积间的关联度,得到两个关联度矩阵。分析得出机制砂石粉含量是影响混凝土抗氯离子渗透性主要因素,而影响机制砂混凝土抗裂性的主要因素是泥块含量。抗压强度与粗糙度的关联度最大,且石粉含量不超过一定范围时,石粉含量对混凝土的抗压强度影响很小。凝灰岩机制砂混凝土抗氯离子渗透性和抗裂性受石粉含量、泥块含量的影响要比石灰岩机制砂混凝土更加敏感,受机制砂品质波动的影响更显著。     

型钢高强混凝土界面黏结滑移推出试验及其本构关系研究

为研究型钢高强混凝土界面黏结性能,对9个型钢高强混凝土试件进行推出试验,分别考虑混凝土强度、配箍率、保护层厚度和型钢锚固长度对型钢高强混凝土界面黏结性能的影响。观察试件的加载过程和裂缝发展形态,分析了试件破坏形态,得到试件加载端荷载-滑移曲线。通过分析沿型钢锚固方向应变和界面黏结应力的分布规律,运用灰色关联理论建立了黏结应力计算式,并推导出荷载-滑移曲线关系表达式。讨论了影响界面滑移损伤变量的关系。结果表明：各试件加载端荷载-滑移曲线走势基本相同;灰色关联理论能够较好地反映黏结应力与各影响因素之间的关系,其中保护层厚度与黏结应力相关性最好;推导的黏结应力算式的计算精度能达到98%;提出的黏结应力-滑移的本构关系数学表达式拟合度较好;界面损伤发展程度与各影响因素关系紧密。     

GFRP筋—混凝土粘结性能影响参数的灰色关联分析

灰色系统具有“少数据建模”的特点,着重研究概率统计、模糊数学所不能解决的“小样本、贫信息”的不确定问题.基于已有玻璃纤维(GFRP)筋—混凝土粘结性能试验研究的资料,运用灰色系统理论的关联度分析方法研究GFRP筋—混凝土粘结性能影响参数关联计算的技术.考虑的影响参数包括GFRP筋直径、肋高度、肋间距.灰色关联分析结果表明,对GFRP筋—混凝土粘结强度的影响程度从大到小排序依次为GFRP筋肋高度、直径、肋间距;对滑移的影响程度从大到小排序依次为GFRP筋直径、肋高度、肋间距.在关联分析基础上,构建了考虑各影响参数组合权系数的滑移计算模型,并回归出系数向量,公式计算值与试验值吻合良好.     

FRP筋黏结性能影响因素灰色关联度分析

利用灰色关联度分析理论,对FRP筋黏结性能与混凝土强度、黏结长度和筋材直径三个因素的关联程度进行了分析。得出各因素对FRP筋黏结性能的影响与FRP筋种类有关,GFRP筋和BFRP筋黏结性能关联度依次为:黏结长度、筋材直径和混凝土强度,CFRP筋为筋材直径、黏结长度和混凝土强度。此外还发现,提高混凝土强度等级能有效提高普通钢筋黏结性能,但对BFRP筋、CFRP筋和GFRP筋并不适用。     

再生微粉掺量对再生透水混凝土性能的影响研究

基于灰色关联分析法构建以再生骨料透水混凝土抗压强度、劈拉强度、孔隙率、透水系数及质量损失率为评价指标的优选模型,计算得到再生微粉掺量与最优指标集的关联程度。结果表明,0、10%和20%三种再生微粉掺量的灰色关联度较高;掺量为0时,再生骨料透水混凝土的强度最高,10%掺量能够改善其耐磨性能;20%掺量能够显著提高其透水性能。     

基于灰色关联的多因素耦合作用下混凝土材料耐久性评估

为探明碳化-硫酸盐侵蚀-干湿循环等多因素耦合作用下的混凝土材料耐久性评估问题,通过开展室内加速试验,以所测混凝土试件的抗压强度、质量损失率及相对动弹性模量3个耐久性评价指标为依据,应用层次分析法与熵权法确定复合权重,构建了灰色关联理论的混凝土材料耐久性评估模型,确定了各组试件不同时段下的灰色关联度向量。研究表明:碳化-硫酸盐侵蚀-干湿循环等多因素耦合作用下不同配合比混凝土试件的关联度值均呈现先增强后下降的现象且最大值约出现在干湿循环30次处,即混凝土综合耐久性整体上呈先增强后下降趋势,与试验结果相符,验证了该方法的合理适用性,相关研究可为混凝土构件的配合比优化及耐久性评估问题提供有益参考。     

高层建筑框架、框-剪结构分析的传递矩阵法

本文介绍的传递矩阵法以单根竖杆为计算单元,楼层为循环单元,杆底端的内力和变形为未知量.用逐层传递的方式,反映了结构刚度、几何约束以及荷载等沿高度不连续的变化。用它分析高层建筑框架和框-剪结构,建筑层数增加只是增加计算过程中的传递次数,未知量数始终保持不变。从而提高了计算机的分析能力。     

基于连续损伤理论的巷道围岩弹脆性损伤分析

考虑岩石的脆性损伤特性,引入非线性的岩石脆性损伤本构模型,将损伤演化方程从一维推广到三维,建立岩石损伤变量与脆性参数的关系。将圆形巷道围岩划分为损伤残余区、渐进损伤区和弹性区,采用弹脆性连续损伤理论,对巷道围岩损伤范围及应力进行求解。当巷道周边围岩只出现渐进损伤区时,推导出巷道围岩发生不同程度损伤的极限地应力及损伤半径;当巷道出现损伤残余区时,考虑围岩破坏后仍然具有残余承载能力的特点,推导出巷道围岩损伤区半径及围岩应力的表达式。通过算例分析了岩石损伤程度和脆性强弱对巷道围岩损伤半径及围岩应力场分布的影响,研究结果表明:岩石的脆性对损伤半径的影响跟损伤程度有关,岩石脆性越强,围岩切向应力的峰值越大;岩石损伤程度越大、损伤半径越大,切向应力峰值离巷道壁面越远。     

Fatigue tests on steel-concrete-steel sandwich components and beams

In Bi-Steel steel-concrete-steel sandwich members, the friction welded bar-plate connections are subject to plate tension, bar tension and bar shear with associated bar bending. The relative magnitude of these force components depends on the beam geometry and the type of loading. The force components interact, so component fatigue tests were performed under single and combined loads, each with a sufficient number of stress ranges to enable stress vs. fatigue life (S/N) curves and equations to be defined. Fatigue tests were also conducted on eighteen beams, and the experimental fatigue lives are compared with the values estimated by means of a proposed interaction equation based on the experimental S/N equations derived from the component tests.     

Experimental study on compaction-induced anisotropic mechanical property of rockfill material

The anisotropy of rockfill materials has a significant influence on the performance of engineering structures. However, relevant research data are very limited, because of the difficulty with preparing specimens with different inclination angles using traditional methods. Furthermore, the anisotropy test of rockfill materials is complex and complicated, especially for triaxial tests, in which the major principal stress plane intersects with the compaction plane at different angles. In this study, the geometric characteristics of a typical particle fraction consisting of a specific rockfill material were statistically investigated, and the distribution characteristics of particle orientation in specimens prepared via different compaction methods were examined. For high-density rockfill materials, a set of specimen preparation devices for inclined compaction planes was developed, and a series of conventional triaxial compression tests with different principal stress direction angles were conducted. The results reveal that the principal stress direction angle has a significant effect on the modulus, shear strength, and dilatancy of the compacted rockfill materials. Analysis of the relationship between the principal stress direction angles, change in the stress state, and change in the corresponding dominant shear plane shows that the angle between the compacted surface and dominant shear plane is closely related to interlocking resistance associated with the particle orientation. In addition, different principal stress direction angles can change the extent of the particle interlocking effect, causing the specimen to exhibit different degrees of anisotropy.     

Mining-induced stress change and consequences of stress path on excavation stability — a case study

For stability assessments as well as for support design, it is important to understand the factors leading to detrimental stress changes. Stress changes not only influence the demand on the rock support, they also change the support capacity of frictional support components such as plain cablebolts. Stress and stress changes are commonly predicted by numerical models but it is rarely possible to verify these predictions. This study presents a practical example illustrating the usefulness of stress change measurements in providing an accurate picture of the mining-induced stress changes and their value for numerical model calibration. Stress changes, associated with mining of the 565#6 stope at Winston Lake Mine, were measured by four CSIRO HI stress cells, two in the hangingwall and two in the back of a sill drift. In order to obtain the full stress history of the hangingwall, stresses at the installation time were calculated by use of a three-dimensional boundary element program — MAP3D. Two types of rockmass failure were observed at this mine: hangingwall delamination and collapse leading to ore dilution, and wedge-like failures in the backs of sill drifts. All stress cells were located such that they were affected by these failure mechanisms. Using measured and predicted stress paths, this study explains the nature of these two failure modes, as experienced at Winston Lake Mine. Excellent correspondence between measured and predicted stresses is achieved for both the hangingwall and the back of the sill drifts. Modelled stress rotations in the hangingwall follow closely the stress rotations determined in the field, except at the end of the monitoring campaign when the stress cells were affected by inelastic straining of the host rock. These measurements assist in understanding the failure processes and in defining the limitations of the adopted numerical models.     

Loan Modifications and Foreclosure Sales during the Financial Crisis: Consequences for Health and Stress

Loan modifications and foreclosure sales are two ways mortgage servicers can respond when homeowners fall behind on house payments. We investigate the consequences of these events for health and stress by linking longitudinal survey data with administrative mortgage performance data that identify those survey participants who experienced a foreclosure sale, a loan modification, or neither. We find that between 2008 and 2013, loan modifications and foreclosure sales were both associated with a reduction in the stress of house payments, while foreclosure sales alone were associated with a reduction in the stress of home maintenance. Beyond these property-related stressors, the changes in survey participants' self-reported sense-of-control and mental, physical, and general health are most associated with transitions in employment, income, marital status, and residential quality rather than with loan modifications or foreclosure sales. These findings run counter to prevailing research, yet they inform the debate over how to address problems that arise when homeowners become delinquent on mortgages.     

Numerical modelling of in situ stress calculation using borehole slotter test

Accurate determination of in situ stress magnitude and orientation is an essential element of the design process of all underground openings. A stress calculation method was proposed for the new stress measurement technique using the borehole slotter device. Two major objectives were the focus of this research work. The first goal was to simulate the slotter test process numerically and delve into the mechanisms involved in this test. A precise 3D numerical model of a typical slotter test condition was constructed using the FLAC3D code. The effects of variations in rock mass deformation modulus on the strain/stress relieve, and thus borehole slotter test results, were investigated numerically. The second objective of the work was to employ 3D modelling in the interpretation of slotter field tests conducted at Bakhtiari dam site. These tests were aimed at determining the stress magnitude and orientation to be used in the design of underground chambers and tunnels associated with Bakhtiari dam. The stress regimes measured in field were applied as boundary condition on the constructed 3D model and a backward analysis was conducted. For each case the actual strain field measured was compared against strain field calculated numerically. Accordingly, the boundary condition (stress magnitude and orientation) associated with the model results that provided the best fit to the measured data was determined as the governing stress regime. A good agreement was achieved between numerical and field test results. The obtained numerical results provided valuable insights in selecting the governing in situ stress condition from a set of recorded field data.     

Ageing Effects on the Yielding Characteristics of Cement-Mixed Granular Materials

Ageing effects on the elasto-viscoplastic property of compacted moist cement-mixed granular material (GM) were evaluated by performing a series of non-standard drained triaxial compression (TC) tests. Two types of GM, crushed gravelly soil from a quarry and crushed concrete aggregate (i.e., a recycled material), were used. The specimens were produced by moist-compaction and then cured at constant water content under unstressed conditions for seven days. They were re-cured basically for two days under different stress states during otherwise drained TC loading at a constant strain rate. Yielding characteristics upon the restart of drained monotonic loading (ML) at a constant strain rate toward ultimate failure at the same or increased or decreased confining pressure were evaluated. The stress-strain behaviour before the stress state reaches the current yield locus is very stiff and highly reversible. Unlike elasto-plastic materials exhibiting no ageing effects, the yield locus expands during sustained loading at a fixed effective stress state due to not only yielding associated with creep deformation, controlled basically by the viscous property, but also ageing, controlled basically by time-elapsing. The shape and location of current yield locus depends on the location of the current stress state relative to the current ultimate failure envelope. The observed yield characteristics were analyzed based on a newly introduced interactive double-yield concept while in the framework of the non-linear three-component elasto-viscoplastic model that takes into account ageing effects as well as an interaction between ageing and inviscid yielding (and its potential decay by irreversible straining). The trends of stress-strain-time behaviour observed with the two types of cement-mixed GMs are essentially the same.     

动态荷载作用下混凝土破裂的数值模拟

简单介绍了材料破裂过程分析(MFPA)程序模拟混凝土动态破裂过程的基本原理.用MFPA程序模拟了非均质混凝土在静态和动态应力作用下的破裂过程,给出了不同应力波幅值时试样的破裂模式,并探讨了应力波幅值和应力波作用时间对混凝土破裂模式的影响.数值模拟结果表明,动态荷载作用下混凝土的破裂过程受控于应力波传播及其诱发损伤的过程,混凝土材料力学性能的非均质性是造成其动态强度提高的原因之一.     

地下水位对基底土颗粒压应力的影响

根据土力学有效应力理论,结合浮力学基本原理,对地下水作用下基底土颗粒压应力与地基承载力的关系进行分析,对有效应力理论加以改进,引入土颗粒压应力的概念,研究地下水位对其有效应力的影响,采用数学方法对相关公式进行推导,并得出初步的结论。