纎维状晶体

改善结构材料的最终目的是使材料获得十足的强度,而此一强度又取决于原子间结合力的大小。目前,增加结构材料的强度方法大多数是采用冶金方法,例如合金化的方式求实现的。然而,现今的冶金方法所能达到的最大强度仅仅是金属中原子完全结合时之理论强度     

既有隧道结构混凝土材料性能研究

混凝土材料性能劣化是当前隧道结构维护中面临的主要问题,从既有隧道结构维护的角度出发,总结归纳了混凝土碳化和氯离子侵蚀这两种能够影响混凝土材料性能的关键因素的作用机理,并依据工程实践过程,给出了既有隧道结构中混凝土材料性能的鉴定方法.     

考虑可靠度可信区间的结构可靠性优化设计

 在贝叶斯统计理论和结构可靠性优化设计方法的基础上,研究了结构在小样本情况下考虑可靠度可信区间的结构可靠性优化设计问题.将结构可靠度作为随机变量,根据先验信息和样本信息,采用贝叶斯推断技术获得结构可靠度的概率分布,给出了可靠度的点估计及区间估计.建立了考虑可靠度可信区间的结构可靠性优化设计模型,提出了考虑可靠度可信区间的结构可靠性优化设计方法.所提出的方法为解决小样本情况下的结构可靠性优化设计问题提供了新的解决方案.数值算例验证了所提出的结构可靠性优化设计方法的有效性和正确性.     

混凝土灌注桩承载力的可靠性分析

本文就混凝土灌注桩承载力，用可靠度理论从单桩强度设计值到单桩轴向受压容许承载力计算各各方面影响因素作了系统全面地分析，采用数字推导方法和以数理统计为基础的概率分布模型统计推断的方法，对桩基承载力进行可靠性分析。并对沉管灌注桩的极限承载力，作了统计推断，利用拟合优度检验得桩基极限承载力概率分服从布尔分布。     

硫铝酸盐基高水材料强度与微观结构研究

研究了20℃和5℃时硫铝酸盐基高水填充材料的强度发展规律及微观结构,通过XRD、孔结构测试等方法研究了高水充填材料的微观结构与强度的关系,并重点研究了亚硝酸钠对高水充填材料水化产物微观结构及强度的影响.研究表明:高水充填材料的水化产物主要是以钙矾石为主的胶凝材料;亚硝酸钠具有促进硫铝酸盐水泥熟料水化和改善高水充填材料硬化体孔结构的双重作用,在5℃时这种作用更加明显.以硫铝酸盐基填充材料代替木材、钢材作为可泵性支护材料,具有凝结硬化速度快、施工方便、价廉等优点,但施工温度低于20℃时材料的性能研究报道甚少.     

包覆成孔剂法制备高性能多孔氮化硅陶瓷工艺

为了制备高强度且分布均匀的氮化硅陶瓷,采用包覆成孔剂法改进普通添加成孔剂的方法,常压烧结氮化硅多孔陶瓷,采用阿基米德法、三点弯曲法分别测试材料的孔隙率及抗弯强度,用扫描电镜和光学放大镜对氮化硅多孔陶瓷显微结构和表观结构进行研究.结果表明,添加包覆过的成孔剂强度比添加未包覆的成孔剂强度高,孔隙率为50%时,强度增加近一倍.强度的提高归因于特殊的微观结构,即气孔的均匀分布和孔与孔之间相间隔分布.     

Logistic 组稀疏回归模型的 Bayes 建模及变分推断

在工程应用中,如数据挖掘、成本预测以及风险预测等,Logistic 回归是一类十分重要的预测方法．当前,大部分 Logistic 回归方法都是基于优化准则而设计,这类回归方法具有参数调试过程繁琐、模型解释性差、估计子没有置信区间等缺点．本文从 Bayes 概率角度研究 Logistic 组稀疏性回归的建模与推断问题．具体来说,首先利用高斯-方差混合公式提出 Logistic 组稀疏回归的 Bayes 概率模型;其次,通过变分 Bayes 方法设计出一个高效的推断算法．在模拟数据上的实验结果表明,本文所提出的方法具有较好的预测性能．     

复合材料点阵夹芯结构平压性能不确定分析与优化

考虑一体化成型工艺制备的复合材料点阵夹芯结构及其不确定性,采用区间向量实现不确定参数定量化,建立复合材料点阵夹芯结构平压性能区间分析模型.考虑结构功能状态判断的模糊性,分别在不考虑设计容差与考虑设计容差情形下,建立了不确定平压载荷作用下含区间参数模糊可靠性分析与优化模型.研究结果表明:材料参数及结构参数不确定性,特别是设计容差对复合材料点阵夹芯结构平压性能影响明显,因此在工程优化中不仅需要充分考虑材料参数与外部载荷等不确定性,而且需要充分重视传统不确定设计方法中未计及的设计容差的影响.本研究实现了理论成果与工程应用的有机结合,为工程领域复合材料点阵夹芯结构平压性能分析与优化提供有效理论方法.     

基于半经验的UHPC配合比设计方法

超高性能混凝土(UHPC)是国内外学者当下关注的热点,但对于UHPC配合比设计目前没有明确的规范.采用理论分析和试验相结合的方法提出一种基于半经验的UHPC配合比设计,首先按照参考文献胶凝材料配合比配制胶砂试件并测出其28 d抗压强度,其次使用Matlab拟合工具箱拟合UHPC 28 d抗压强度与水胶比、胶凝材料28 d强度的定量关系;再采用Mathematica拟合胶凝材料强度与水泥胶砂强度的关系,通过拟合公式确定水胶比,依据最大密实理论确定骨料的掺加比例,最后通过全体积计算方法确定UHPC配合比.在这之后对基于半经验的UHPC配合比设计方法进行了验证,测试了蒸养条件下的抗压强度与抗折强度.结果表明:根据拟合公式计算的理论配制强度与实际测试的抗压强度接近,其差值在抗压强度测量误差范围内,该配合比设计方法具有较好的可靠性,此方法为广大工作者设计UHPC提供了一种新思路.     

针对老年社区文化设施设计的色彩偏好预测研究

目的针对老年人,提出色彩偏好值的预测方法。方法根据样本数据,运用回归分析法,得出年度变量与色彩偏好均值的函数关系,由预测时间变量得出预测色彩偏好均值;采用区间估计法,得出预测色彩偏好均值区间。结果基于180位老年人连续6年的调研样本,得出2018年老年人色彩的偏好均值区间,并应用于社区文化设施的色彩搭配设计。结论样本均值回归分析与区间估计法,能够解决大样本数据的区间预测问题,适用于色彩趋势预测与配色设计。     

A univariate Chebyshev polynomials method for structural systems with interval uncertainty

This paper presents an effective univariate Chebyshev polynomials method (UCM) for interval bounds estimation of uncertain structures with unknown-but-bounded parameters. The interpolation points required by the conventional collocation methods to generate the surrogate model are the tensor product of each one-dimensional (1D) interpolating point. Therefore, the computational cost is expensive for uncertain structures containing more interval parameters. To deal with this issue, the univariate decomposition is derived through the higher-order Taylor expansion. The structural system is decomposed into a sum of several univariate subsystems, where each subsystem only involves one uncertain parameter and replaces the other parameters with their midpoint value. Then the Chebyshev polynomials are utilized to fit the subsystems, in which the coefficients of these subsystems are confirmed only using the linear combination of 1D interpolation points. Next, a surrogate model of the actual structural system composed of explicit univariate Chebyshev functions is established. Finally, the extremum of each univariate function that is obtained by the scanning method is substituted into the surrogate model to determine the interval ranges of the uncertain structures. Numerical analysis is conducted to validate the accuracy and effectiveness of the proposed method.     

基于非概率集合理论的屋面板风致疲劳寿命估计

现有疲劳分析中,通常将结构材料参数、几何尺寸等定义为确定性参数;实际结构中,相关参数均为有界但不确定变量,如按确定性参数估计结构的疲劳寿命是偏于不安全的。该文将结构体系中不确定参数定义为区间变量,在线性疲劳损伤累积理论基础上,提出一种仅需一次动力响应分析即可计算不确定结构在动力荷载作用下疲劳损伤的新方法。该方法将金属屋面板弹性模量和屋面板板厚等由于施工误差等因素引起的不确定参数定义为区间变量,通过摄动法和区间动力响应分析,计算屋面板在脉动风荷载作用下的应力响应区间;结合屋面板材料的S-N曲线,采用修正Miner疲劳线性累积准则对屋面板的疲劳损伤和寿命区间进行估计。结果表明:该文方法可有效计算考虑结构参数不确定条件下金属屋面板的疲劳损伤和寿命区间;与顶点法比较,该文方法仅需一次动力响应分析就可计算金属屋面板风致疲劳损伤和寿命区间。     

Component reliability assessment using quantitative and qualitative data

The estimation of a component failure rate depends on the availability of plant specific numerical data. The purpose of this study was development of a new method that explicitly includes numerical and linguistic information into the assessment of a specific failure rate. The basis of the method is the Bayesian updating approach. A prior distribution is selected from a generic database, whereas likelihood is assessed using the principles of fuzzy set theory. The influence of component operating conditions on component failure rate is modeled using a fuzzy inference system. Results of fuzzy reasoning are then used for building an appropriate likelihood function for the Bayesian inference.The method was applied on a high voltage transformer. Results show that with the proposed method, one can estimate the specific failure rate and analyze possible measures to improve component reliability. The method can be used for specific applications including components for which there is not enough numerical data for specific evaluation.     

梁结构刚度动态非概率可靠性分析

 为了定量分析在疲劳载荷作用下梁在不同寿命期内刚度的可靠性,建立梁结构物理性能退化的精确公式就十分重要.依据疲劳载荷造成的累积损伤对材料极限应力的影响,基于材料剩余强度模型,利用材料强度与弹性模量之间的关系,推导出结构弹性模量的退化表达式,并在此基础上,提出梁弹性模量退化系数的递推表达式,推导出圆截面梁剩余抗弯刚度的表达式.在对结构可靠性分析时,概率可靠性模型和模糊可靠性模型对于原始数据信息要求较高.为了充分利用结构的不确定性信息弥补原始数据的不足,将梁的初始弹性模量及所受的疲劳载荷等看作区间变量,利用区间模型建立基于刚度退化的梁刚度动态非概率可靠性模型.最后,结合工程实例的计算表明了该方法对梁的刚度退化分析及其刚度动态可靠性分析是可行、有效和合理的.     

基于类桁架材料模型的不确定荷载下结构拓扑优化

用区间分析方法研究了不确定荷载下结构拓扑优化方法。采用类桁架材料模型建立拓扑优化类桁架连续体结构。根据区间变量运算法则推导出不确定荷载下应力约束体积最小类桁架结构的拓扑优化方法。首先采用区间分析方法得到任一点的最不利荷载工况下应变状态。在此应变状态下,利用满应力准则优化类桁架材料中杆件的方向和密度。如此反复分析和优化,直至迭代收敛。最后由类桁架中杆件分布场可以近似离散得到桁架结构。通过几个数值算例验证了方法的有效性。数值算例显示了不确定荷载下的结构拓扑优化布局更合理。     

A graphical method for assessing the concrete strength class in existing RC structures

This paper aims to provide the reader a simple graphical method for the estimation of the concrete strength class (CSC) in existing reinforced concrete structures, which may be adopted even using limited concrete core drillings (less than three per test region) when compared to actual practice (European standards). The method is based on a combined probabilistic/empirical model for material properties of in situ concrete compressive strength and age-hardening effects. Assumptions are according to Eurocodes. The procedure has been subjected to a rigorous validation process. The principle of this approach is to use two graphs to mimic the role that in situ compressive strength test results play in determining the CSC of existing structures at the ages of the core drilling and of the construction time (28 days). Basis for the method are few considerations on: (a) age of concrete; (b) exposure environment; and (c) type of cement. Information from the two graphs is combined allowing valid and reliable estimates to be drawn. The proposed method is intended to be used as a clear alternative to classic methodologies and will be useful for professionals working in the field of structural rehabilitation. It reduces invasiveness, time expenditure and labour cost while maintaining high accuracy in estimations. Furthermore, it provides extra information about the concrete strength development that may be used to explore alternative scenarios in safety analyses.     

Managing demand uncertainty through fuzzy inference in supply chain planning

In this paper, we investigate methods for managing the irregular and uncertain demands involved in supply chain planning. We first build a supply chain planning model based on fuzzy linear programming, which defines demand as a fuzzy parameter. Next, we propose a fuzzy inference approach for converting fuzzy demand into crisp demand. In the proposed fuzzy inference-based approach, judgments of upcoming demand from both internal and external experts are used as input variables to reflect the expected demand irregularity. By adopting fuzzy inference, we can compensate for the limitations of the existing demand treatment approaches, which usually demonstrate poor forecasting performance in cases of irregular demand and thus reduce the accuracy of supply chain planning. To verify the feasibility of the proposed approach, we present an illustrative example of a Korean electronics company.     

Robust stability analysis of structures with uncertain parameters using mathematical programming approach

This paper presents a novel mathematical programming approach for the static stability analysis of structures with uncertainties within the framework of FEM. The considered uncertain parameters are material properties, geometry of element cross section, and loading conditions, all of which are described by an interval model. The proposed method formulates the two cases of interest, namely, worst and best buckling load calculation, into a pair of mathematical programming problems. Two straightforward advantages are exhibited by such formulations. The first advantage is that the proposed formulation can overcome the interference on the sharpness of bounds of the buckling load due to the interval dependence issue. The second benefit is that the information of uncertain parameters causing the extremities of buckling load can always be retrieved as by‐products of the uncertain stability analysis. Some numerical examples are presented to illustrate the capability of the proposed method on various structures and the sharpness of the bounds of the buckling load factors. The efficiency and effectiveness of the proposed method are also demonstrated through comparison with the classical Monte Carlo simulation method. Copyright © 2014 John Wiley & Sons, Ltd.     

Prediction of High-Temperature Long-Term Strength for Damaged Structures

A method is proposed for analytical estimation of the high-temperature long-term strength of structures with material discontinuities, which are stress raisers. We consider the processes involving the formation of diffusion pores. Diffusion processes in metals are strongly enhanced with increasing temperature and stresses.     

随机荷载作用下参数不确定结构的疲劳损伤估计

基于改进区间分析和频域疲劳计算方法,对参数不确定结构在平稳高斯荷载作用下的疲劳损伤进行研究,提出完全混合和简化计算两种方法。采用区间变量模型定义结构的不确定参数,功率谱密度描述外荷载的随机性;利用有理级数显式表示结构区间频响函数及在平稳高斯荷载作用下不确定结构的应力响应区间。通过数值方法验证疲劳损伤期望率关于不确定参数的单调性后,将应力响应中不确定参数的界限完全组合提出完全混合方法,准确估计参数不确定结构的疲劳损伤期望率区间;简化计算方法则将不确定参数的界限适当组合,由显式表达式近似计算结构的疲劳损伤期望率区间。算例表明,两种方法均具有较高计算精度,且大幅减少计算量。