Seismic fragility analysis of highway bridges considering multi-dimensional performance limit state

Fragility analysis for highway bridges has become increasingly important in the risk assessment of highway transportation networks exposed to seismic hazards. This study introduces a methodology to calculate fragility that considers multi-dimensional performance limit state parameters and makes a first attempt to develop fragility curves for a multi-span continuous (MSC) concrete girder bridge considering two performance limit state parameters: column ductility and transverse deformation in the abutments. The main purpose of this paper is to show that the performance limit states, which are compared with the seismic response parameters in the calculation of fragility, should be properly modeled as randomly interdependent variables instead of deterministic quantities. The sensitivity of fragility curves is also investigated when the dependency between the limit states is different. The results indicate that the proposed method can be used to describe the vulnerable behavior of bridges which are sensitive to multiple response parameters and that the fragility information generated by this method will be more reliable and likely to be implemented into transportation network loss estimation.

CHAOTIC MOTIONS AND LIMIT CYCLE FLUTTER OF TWO-DIMENSIONAL WING IN SUPERSONIC FLOW

Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.

Tubular limiting stream surface: “tornado” in three-dimensional vortical flow

A new physical structure of vortical flow, i.e., tubular limiting stream surface(TLSS), is reported. It is defined as a general mathematical structure for the physical flow field in the neighborhood of a singularity, and has a close relationship with limit cycles.The TLSS is a tornado-like structure, which separates a vortex into two regions, i.e., the inner region near the vortex axis and the outer region further away from the vortex axis.The flow particles in these two regions can approach to(or leave) the TLSS, but never could reach it.

基于极限平衡法的危岩倾覆稳定性三维计算方法

目前危岩防治工作中,危岩稳定性评价主要以简化后的二维剖面作为计算模型。由于自然界中的危岩形态极不规则,采用二维剖面计算模型并不能真实反映危岩受力情况。为了研究危岩稳定性三维计算方法,在前人研究基础上,基于极限平衡理论,提出了由后缘裂缝抗拉强度控制的危岩倾覆稳定性三维计算公式,采用数值积分和空间几何方法给出了在危岩单体三维模型基础上求解危岩后缘岩体抗拉力、水压力及其力矩计算公式和实现流程。以三峡库区瞿塘峡吊嘴危岩为实例开展了应用,并通过数值分析进行了验证。通过不同形态危岩的三维稳定性分析,讨论了三维与二维稳定性计算结果的关系,对比发现危岩形态对稳定性计算结果有明显影响,三维计算较二维计算更准确和实用。

GENERALIZED FATIGUE CONSTANT LIFE CURVE AND TWO-DIMENSIONAL PROBABILITY DISTRIBUTION OF FATIGUE LIMIT

According to the traditional fatigue constant life curve, the concept and the universal expression of the generalized fatigue constant life curve were proposed. Then, on the basis of the optimization method of the correlation coefficient, the parameter estimation formulas were induced and the generalized fatigue constant life curve with the reliability level p was given. From P-S-a-S-m curve, the two-dimensional probability distribution of the fatigue limit was derived. After then, three se, of tests of LY11 CZ corresponding to the different average stress were carried out in terms of the two-dimensional up-down method. Finally, the methods are used to analyze the test results, and it is found that the analyzed results with the high precision may be obtained.

考虑基质吸力影响的非饱和路堤三维稳定性上限分析

采用极限上限分析定理构建了路堤失稳的三维旋转破坏机构,继而根据Bishop非饱和土抗剪强度理论,考虑非饱路堤内部基质吸力的空间分布及其随地下水位的变化,建立了路堤破坏土体外力功率与内部能量耗散功率的能量守恒方程,并利用遗传算法编写了非饱和路堤最小上限解的高效搜索算法。通过将非饱和土路堤基底破坏模式退化为边坡破坏模式,并与现有非饱和土边坡稳定性计算结果对比,验证了所提上限解的正确性和遗传搜寻算法的准确性。进一步地,对路堤三维稳定性的关键影响因素展开了系统分析,研究了路堤填土孔径分布、基质吸力、进气值倒数、路堤倾角以及有效内摩擦角等因素对路堤三维稳定性的影响规律。研究表明,非饱和土质路堤的稳定性不仅取决于路堤填土性质,而且依赖于影响土体吸力大小与分布的填土孔径参数和进气值等因素。地下水位升降引起的基质吸力变化对路堤稳定性存在显著影响。研究结果为路堤稳定性精细化分析提供了重要的理论依据。

基于网格自适应加密策略的隧道稳定性三维极限分析下限有限元法研究

网格分布形式对三维极限分析下限有限元法的计算精度影响较大,为获取精确下限解,通常需对破坏区域进行密集网格划分,从而极易导致计算规模过大,求解效率低下。针对上述问题,提出一种基于单元应力的三维极限分析下限有限元“后验”网格自适应加密策略。首先,构建基于Mohr-Coulomb(M-C)准则和半定规划技术的三维极限分析下限有限元模型,避免了屈服准则的近似处理。其次,引入基于M-C准则的网格自适应加密策略,通过判断各个单元应力接近屈服的程度,确定加密点的坐标。然后,将加密点与原先节点组合构成新的点集,并重新划分网格,建立新的下限有限元计算模型。最后,利用所提方法研究隧道稳定性问题,表明利用所提网格自适应加密策略能够以较少单元精确模拟破坏区域应力分布,从而获取高精度下限解。

地震荷载作用下非饱和土边坡三维极限承载力研究

研究旨在对地震荷载作用下非饱和土边坡稳定性进行分析。为了考虑地震荷载时间效应、边坡放大效应及土体阻尼特性的影响,采用修正拟动力法对边坡动力响应进行描述。采用考虑基质吸力影响下非饱和土广义黏聚力和饱和土摩擦角定义非饱和土剪切强度参数。基于三维离散破坏模型,采用极限分析上限法构建了地震荷载作用下非饱和土边坡三维极限承载力分析模型,通过已发表文献结果验证了所提出模型的有效性。最后,提供了非饱和土边坡三维极限承载力设计图表。研究结果表明:①与二维破坏模型相比较,所提出三维破坏模型能实现对边坡稳定性更为准确的评估;②忽略非饱和土剪切强度参数影响往往导致边坡稳定性评估结果偏于保守。

含挖填界面边坡三维稳定性上限分析

针对工程实践中挖填交界面与边坡坡面走向线斜交的高边坡空间三维稳定分析问题,基于极限分析上限定理,构建拓展的三维牛角状破坏机构,通过引入机构参数挖填界面倾角α突出边坡特性,建立与之对应的功能平衡方程,采用序列二次规划优化算法求解强度折减后的边坡安全系数上限解。在此基础上,计算了宁夏黄土丘陵地区妙岭750kV变电站高边坡以及相关文献中极限状态下边坡稳定性系数γH/c工程案例,并将计算结果与有限元极限分析软件模拟值进行对比分析。结果表明:随着挖填界面倾角α的增大,边坡安全系数Fs上限解和模拟值均减小,两种方法的计算结果相对误差在5.9%以内,且拓展的破坏机构与数值模拟的剪切耗散变形模式基本一致;在极限状态下,拓展机构的上限解和数值模拟结果都十分接近于1.0,二者相对误差未超过8.3%。研究工作为此类高边坡空间稳定分析问题提供了一种简便实用的计算方法。

粒子群自进化算法求解物流装箱问题

为了解决当今物流行业中装载货物类型为强异构的情况,提高装载填充率和效率,提出了一种求解三维装箱问题的元启发式算法——粒子群自进化算法。算法包含两部分:极限点构造启发式算法和粒子群自进化规则。极限点构造启发式算法引入了极限点的概念,利用新的极值点思想推导出了三维装箱问题的启发式算法。粒子群自进化规则提出了在货物装载序列中表示粒子的方法,推导了粒子间交叉、变异算子,在极限点构造启发式算法的基础上不断迭代进化完成货物的装载。通过不同结果的比对,证明该算法显著提高了物流装载的空间利用率,强异构货物的平均装载率达到了85%,验证了算法在强异构货物下的有效性与优越性,并给出了货物装载的三维模型。由于实际测试集的缺少,分别为机腹仓装载类和集装板类模型提出了实例生成器,通过生成器的测试集验证了算法在实际应用中的紧凑性、实用性和快捷性。

塔尔煤田Ⅱ区块露天煤矿南帮边坡空间形态优化

为解决巴基斯坦塔尔煤田Ⅱ区块露天煤矿南帮原设计到界边坡形态不合理问题,采用二维与三维相结合的分析方法来进行边坡稳定性分析,基于简化Bishop法、剩余推力法以及数值模拟分析方法对巴基斯坦塔尔煤田Ⅱ区块露天煤矿南帮边坡空间形态进行优化,确定了到界边坡的最优空间形态。研究结果表明:塔尔煤田Ⅱ区块露天煤矿南帮横采内排追踪距离应控制在100 m以内,优化设计后的边坡空间形态与原设计对比,整体边坡角增大2°,回采煤炭资源增加8.858×10^(6)t,剥采比为0.5,有利于实现煤炭资源的最大限度回采。

Limit equilibrium method for slope stability based on assumed stress on slip surface

In the limit equilibrium framework, two- and three-dimensional slope stabilities can be solved according to the overall force and moment equilibrium conditions of a sliding body. In this work, based on Mohr-Coulomb(M-C) strength criterion and the initial normal stress without considering the inter-slice(or inter-column) forces, the normal and shear stresses on the slip surface are assumed using some dimensionless variables, and these variables have the same numbers with the force and moment equilibrium equations of a sliding body to establish easily the linear equation groups for solving them. After these variables are determined, the normal stresses, shear stresses, and slope safety factor are also obtained using the stresses assumptions and M-C strength criterion. In the case of a three-dimensional slope stability analysis, three calculation methods, namely, a non-strict method, quasi-strict method, and strict method, can be obtained by satisfying different force and moment equilibrium conditions. Results of the comparison in the classic two- and three-dimensional slope examples show that the slope safety factors calculated using the current method and the other limit equilibrium methods are approximately equal to each other, indicating the feasibility of the current method; further, the following conclusions are obtained: 1) The current method better amends the initial normal and shear stresses acting on the slip surface, and has the identical results with using simplified Bishop method, Spencer method, and Morgenstern-Price(M-P) method; however, the stress curve of the current method is smoother than that obtained using the three abovementioned methods. 2) The current method is suitable for analyzing the two- and three-dimensional slope stability. 3) In the three-dimensional asymmetric sliding body, the non-strict method yields safer solutions, and the results of the quasi-strict method are relatively reasonable and close to those of the strict method, indicating that the quasi-strict method can be used to obtain a reliable slope safety factor.

GIS-based 3D limit equilibrium analysis for design optimization of a 600 m high slope in an open pit mine

Combining the GIS （geographic information systems） grid-based data with four proposed column-based 3D slope stability analysis models, a comprehensive solution of a high-steep open-pit slope has been obtained. For six searching ranges, 19 critical slip surfaces of different sizes have been studied, in which the minimum 3D safety factor is 1.33. Comparison of 3D safety factors of designed and proposed slope plans shows for all the critical slip surfaces for the proposed plan, the smallest 3D safety factor is 1.33 under the most unfavorable condition. This means that the proposed plan of the high slopes, about 600 m, of an open pit （2-5° steeper than designed plan） is feasible.

Three-dimensional analysis of slopes reinforced with piles

Based on the upper bound of limit analysis, the plane-strain analysis of the slopes reinforced with a row of piles to the 3D case was extended. A 3D rotational failure mechanism was adopted to yield the upper bound of the factor of safety. Parametric studies were carried out to explore the end effects of the slope failures and the effects of the pile location and diameter on the safety of the reinforced slopes. The results demonstrate that the end effects nearly have no effects on the most suitable location of the installed piles but have significant influence on the safety of the slopes. For a slope constrained to a narrow width, the slope becomes more stable owing to the contribution of the end effects. When the slope is reinforced with a row of piles in small space between piles, the effects of group piles are significant for evaluating the safety of slopes. The presented method is more appropriate for assessing the stability of slopes reinforced with piles and can be also utilized in the design of plies stabilizing the unstable slopes.

Three-dimensional critical slip surface locating and slope stability assessment for lava lobe of Unzen volcano

Even Unzen volcano has been declared to be in a state of relative dormancy,the latest formed lava lobe No.11 now represents a potential slope failure mass based on the latest research.This paper concentrates on the stability of the lava lobe No.11 and its possible critical sliding mass.It proposes geographic information systems (GIS) based three-dimensional (3D) slope stability analysis models.It uses a 3D locating approach to identify the 3D critical slip surface and to analyze the 3D stability of the lava lobe No.11.At the same time,the new 3D approach shows the effectiveness in selecting the range of the Monte Carlo random variables and locating the critical slip surface in different parts of the lava lobe No.11.The results are very valuable for judging the stability of the lava lobe and assigning the monitoring equipments.

黄河口有机质疏浚土压缩特性及改良利用研究

疏浚土是一种性质复杂和分布不均的材料,为研究含有机质疏浚土的压缩特性及相应的改良方案,通过试验确定了0%~11%有机质含量下天然疏浚土的工程指标,采用扫描电镜(SEM)和X射线荧光光谱分析(XRF)对疏浚土的微观结构及矿物成分进行了分析,并通过一维固结试验,分析了添加石灰、粉煤灰、火山灰等改良材料的疏浚土的压缩特性,探讨了有机质含量对改良效果的影响。研究表明:随着有机质含量的增大,天然疏浚土的界限含水率增大,密度减小,碱性由中碱性变为微碱性,天然疏浚土的压缩指数范围在0.10~0.32之间,压缩性和膨胀性越来越高;添加石灰和粉煤灰都可以有效提高疏浚土的抗压缩性,其中粉煤灰对各有机质含量的疏浚土均有明显改良效果,当其含量在15%以上时,可以大大降低疏浚土压缩性;火山灰添加后体积压缩系数、压缩指数反而增大,说明其对抗压缩产生了不利的影响。研究结果可为水运工程中疏浚土的建材化利用提供参考。

基于改进跳蛛算法的二维OTSU限重标志识别算法

针对交通标志识别中限重标志和限速标志相似程度大、容易造成误检等问题,结合抗噪能力强的二维OTSU自动阈值分割法与寻优能力强的跳蛛优化算法,提出了一种基于跳蛛优化的二维OTSU限重标志识别算法。该算法通过统计交通标志牌感兴趣区域的二维灰度直方图,采用改进跳蛛算法求解二维OTSU分割阈值,快速地实现交通标志图像的二值化,再利用DBSCAN对二值化图像边缘点聚类,最后根据聚类结果的相对位置正确识别限重标志。实验结果表明:在不降低识别率的条件下,运算时间降低了34.16%,并能够正确区别限重标志和限速标志。

基于极限平衡法高边坡稳定性分析方法

岩石高边坡是山区水电站工程建设中的主要地质环境,尤其在我国西部地区,高边坡问题作为重大工程的关键技术问题之一,控制着工程建设的可行性和经济效益,因此有必要对其进行分析研究。以如美水电站中坝址高陡边坡稳定性分析为目标,基于二维极限平衡法,结合现场勘查、理论分析和Geo-Studio数值模拟,考虑如美水电站中坝址高陡边坡的三种不同节理组合形式,在降雨工况和地震工况下对边坡整体稳定性进行分析评估。研究结果表明,降雨工况对边坡稳定性影响远大于地震工况,产生塑性区的范围相较于地震工况更大,在开挖卸荷工况下,边坡受到较大扰动产生卸荷区,发生失稳破坏。基于数值模拟结果,得到满足工程实际的结构面选取方式。

非线性光学碳点的调控及应用研究进展

碳点(Carbon dots,CDs)作为一种新型零维碳纳米材料,具有优良的荧光和磷光等光学特性。随着对CDs光学性能的不断探索,学者们发现其不仅在弱光下表现出优异的线性光学特性,在强光下也表现出良好的非线性光学特性,如非线性极化率较高、非线性吸收方式可变、光限幅阈值较低以及对飞秒等超快激光具有较快的响应等,在军事、通信和医疗等领域中展现出巨大潜力。据此,本文对CDs非线性光学性质的调控及应用进行综述。首先,总结出CDs本体(CDs尺寸、掺杂元素和表面官能团等)及其外部环境(液态分散基质、固态分散基质和入射激光能量等)对其非线性光学性质的影响;其次,介绍其在光限幅、光开关、生物应用和物质检测等非线性光学方面的应用研究进展;最后,提出目前CDs在非线性光学领域中面临的问题,并对其进行展望。

基于同步共轴结构的辐射层析测温仪设计

光学辐射测温技术因时空分辨率高、测温范围宽等优势在燃烧场温度时空演化特性表征领域具有重要应用价值。固体火箭发动机燃烧室内可测试空间受限,基于多视线投影的三维温度场重构方法因光线遮挡而失效。针对该问题,在傅里叶光学理论基础上,建立了燃烧断面与像靶平面之间的物像空间映射关系模型,设计加工了光机电一体化的动态辐射层析测温仪,实现了多个像探测器共光轴且能够同步聚焦于不同空间位置的燃烧断面。试验结果表明,通过对某型号开窗燃烧室内固体推进剂药条燃烧辐射采样数据的卷积与反卷积处理,堆栈的燃烧断面在沿着仪器光轴方向上能够相互分离,在光电信号关系标定基础上利用普朗克辐射定律对已分离的燃烧断面温度分布进行测量过程中,测温的相对误差小于8%。该仪器能够在单向投影光路上以层析方式实现对动态三维燃烧温度场的解析。