水力冲击内蕴初始裂纹混凝土致裂机理

为研究水力冲击内蕴初始裂纹混凝土破碎机理,采用光滑粒子流体动力学(SPH)方法建立了水力冲击含竖向裂纹混凝土数值模型,并基于图像处理技术,量化表征了混凝土致裂区破碎规律。研究表明:在初始裂纹弱作用区,水锤效应导致液固接触边界出现剪切断裂,贯通后形成近似"碗状"破碎坑;在初始裂纹强作用区,液固接触边界压剪应力和初始裂纹上部应力集中共同作用引发了初始裂纹上尖端裂纹;"水楔+砼楔"效应与初始裂纹下部应力集中导致了初始裂纹下尖端裂纹;水力冲击激发的应力波在自由边界和初始裂纹反射后相互叠加,引发了锥形裂纹;混凝土破碎度沿射流轴向呈非线性阶跃衰减,表明初始裂纹对混凝土破碎演化有明显阻断及强干扰作用。     

运营桥梁结构间接辨识的统计估计方法

建立了运营桥梁结构系统辨识的数学模型,以及对于运营桥梁结构参数实现间接辨识的点估计及区间估计的方法.引入系统辨识理论,定义了运营桥梁结构的数据、模型类、准则要素;基于车辆响应,通过对准则优化的实现,实现了基于车辆响应对结构参数的间接辨识;分别基于半解析解、数值解、加入白噪声的半解析解以及数值解对结构的频率和刚度,进行了...     

Fatigue-induced in-situ strength deterioration of micro-polyvinyl alcohol (PVA) fiber in cement matrix

For soft fiber and brittle matrix system such as polymeric fiber-reinforced cementitious composites, the fiber strength deterioration dominates the performance of composites subject to fatigue loading. The fatigue-induced in-situ fiber strength deterioration in brittle matrix, however, has rarely been studied. In this paper, fatigue-induced in-situ strength deterioration of micro-polyvinyl alcohol (PVA) fiber in cement matrix was experimentally investigated. The effects of fiber embedment, fiber inclination, and fiber surface treatment on the in-situ strength of micro-PVA fibers are reported. The results show that fiber embedment into cement matrix not only reduces the in-situ strength of fiber but also changes the fatigue stress-cycle (S-N) curve and failure mode of fiber. Fiber inclination further decreases the in-situ strength of embedded fiber due to local stress concentration of bent fibers. Oil-treatment on fiber surface can effectively delay fatigue-induced in-situ strength deterioration of micro-PVA fiber.     

Soil freezing point as obtained on melting

The method of numerical analysis of the differential scanning calorimetry (DSC) thermogram obtained during warming makes it possible to obtain a complete curve of the unfrozen water content in frozen soil, including the highest temperature at which last ice crystals melt and the unfrozen water content becomes equal to the total water content. This is referred to as the freezing point of the soil–water system obtained on melting. Statistical analysis of 137 results obtained for 6 monomineral and homoionic model soils implies that, similarly to the freezing point obtained from the cooling curves, the soil freezing point obtained on melting strongly depends on the water content. An empirical equation, found basing on the reported results, has proved to be useful as a predicting tool with reference to 33 foreign data points obtained in the typical way (i.e., from the cooling curve).     

大跨径拱桥缆索吊装主缆垂度计算

基于三跨计算模型,考虑主塔塔顶偏位的影响,利用力学关系和几何关系得到了新的主缆垂度计算公式。针对不同的情况,提出了各自简化公式,并探讨了塔顶偏位对主索垂度影响的规律。工程应用表明,该公式具有相当的精度,可为以后缆索吊装施工提供参考。     

Solving fuzzy capacitated location routing problem using hybrid variable neighborhood search and evolutionary local search

A fuzzy capacitated location routing problem (FCLRP) is solved by using a heuristic method that combines variable neighborhood search (VNS) and evolutionary local search (ELS). Demands of the customer and travel times between customers and depots are considered as fuzzy and deterministic variables, respectively in FCLRP. Heterogeneous and homogeneous fleet sizes are performed together to reach the least multi-objective cost in a case study. The multi-objective cost consists of transportation cost, additional cost, vehicle waiting cost and delay cost. A fuzzy chance constrained programming model is added by using credibility theory. The proposed method reaches the solution by performing four stages. In the first stage, initial solutions are obtained by using a greedy heuristic method, and then VNS heuristic, which consists of seven different neighborhood structures, is performed to improve the solution quality in the second stage. In the third stage, a perturbation procedure is applied to the improved solution using ELS algorithm, and then VNS heuristic is applied again in the last stage. The combination of VNS and ELS is called VNSxELS algorithm and applied to a case study, which has fifty-seven customers and five distributing points, effectively in a reasonable time.     

Strength and chemical resistance of mortars containing brick manufacturing clays subjected to different treatments

This paper presents the results of an investigation of the properties of mortar in which a calcined clay was employed as a pozzolan. Mortars were prepared using either heat treated clay or ground waste clay bricks (from the same clay subjected to 1000 °C calcining) as a pozzolanic partial replacement for cement at replacement levels of 10%, 20% and 30%. The compressive strengths of the mortars were monitored up to 90 days and the resistance to sodium sulphate solution and synthetic seawater was monitored up to 300 days. The specimens were also monitored for weight changes. Partially replacing cement by ground brick or heat-treated brick clay gives early strengths that are lower than that of the control. At 90 days, however, the strengths are the same as or are greater than that of the control. Heat-treated clay is effective in reducing expansion during exposure of the mortar to sulphate solution and synthetic seawater. The rapidly cooled clay gives better performance, in terms of strength development and resistance to harmful solutions, than the slow cooled clay.     

强度储备安全系数不同定义对稳定系数的影响

在极限平衡的双安全系数分析中,安全系数有c、tanφ的安全储备（定义1）和岩土参数a、k的安全储备（定义2）2种定义,分析了在应用有限元强度双折减系数法计算边（滑）坡安全系数时,强度储备的不同定义对计算结果的影响。2种安全系数定义得到的安全系数是不一样的,但是,强度参数c,tanφ按一定比例折减的同时,岩土参数a,k同时也在按相同的比例进行折减。Drucker-Prager准则与参数a和k的选取直接相关,若采用外接D—P准则,对于各种土体定义1和定义2得到的边（滑）坡的安全系数比较接近;若采用平面应变匹配D—P准则及等面积圆D—P准则,对于结构性黏土,定义2得到的安全系数略小于定义1,但对于滑体和滑带土为很粗的碎石土时,定义2得到的安全系数与定义1得到的安全系数要小得多。     

应用ANSYS的轻轨道岔梁有限元分析

以川东船舶制造的轻轨道岔梁为例,应用ANSYS软件对其在直线状态和曲线状态时进行局部受力分析。通过建立轨道梁的力学模型和数学模型,采用三维有限单元法精确计算出轨道梁各个部位的应力情况,分析轨道梁结构的变形,并找出应力最大的地方。     

Effects of freestream turbulence on streamwise pressure measured on a square-section cylinder

Wind tunnel experiments were performed to study the effects of freestream turbulence on the flow around a square cylinder. The results indicate that the pressure fluctuations on streamwise surfaces are produced mainly by periodic vortex shedding when turbulence intensity, σ_u/U, is less than 12%. As σ_u/U approaches 20%, vortex shedding weakens significantly and pressure fluctuations occur over a broad range of frequency. Flow visualization experiments show that extreme negative pressure peaks in highly turbulent flow are associated with intermittent reattachment of separated shear layers. The results also show that an increase in turbulence scale causes peak pressure coefficients to increase.