Developing a predictive model for fine particulate matter concentrations in low socio‐economic households in Durban,South Africa

In low‐resource settings, there is a need to develop models that can address contributions of household and outdoor sources to population exposures. The aim of the study was to model indoor PM_2.5 using household characteristics, activities, and outdoor sources. Households belonging to participants in the Mother and Child in the Environment (MACE) birth cohort, in Durban, South Africa, were randomly selected. A structured walk‐through identified variables likely to generate PM_2.5. MiniVol samplers were used to monitor PM_2.5 for a period of 24 hours, followed by a post‐activity questionnaire. Factor analysis was used as a variable reduction tool. Levels of PM_2.5 in the south were higher than in the north of the city (P < .05); crowding and dwelling type, household emissions (incense, candles, cooking), and household smoking practices were factors associated with an increase in PM_2.5 levels (P < .05), while room magnitude and natural ventilation factors were associated with a decrease in the PM_2.5 levels (P < .05). A reasonably robust PM_2.5 predictive model was obtained with model R² of 50%. Recognizing the challenges in characterizing exposure in environmental epidemiological studies, particularly in resource‐constrained settings, modeling provides an opportunity to reasonably estimate indoor pollutant levels in unmeasured homes.     

框筒结构的层模型简化分析方法

将分析平面框架结构的D值法简化,并推广应用于框筒结构在侧向荷载作用下的内力和位移分析上。将楼层变形划分为剪切变形和弯曲变形;结构的整体剪切变形及内力直接用D值法进行分析,考虑了翼缘框架的剪切刚度的影响;结构的整体弯曲变形及内力通过假定轴向位移模式的简化方法进行分析,考虑了正剪力滞的影响,分析了影响结构位移的因素。通过与空间框架分析程序的比较表明,本文方法简单,实用,可直接进行手算,因而可供初步设计阶段使用。     

Parameter prediction for cash flow forecasting models

The paper describes the application of the DHSS formula to 27 completed construction projects comprising four types - steel-framed low rise buildings, new build housing developments, housing refurbishment projects, and multi-house ‘pre-paint’ maintenance contracts. Application of the formula to individual projects indicates that the ‘best’ parameter values offer a ten-fold improvement over the published values based on project size. Similar results occur when using the best parameter values for other two parameter models.

Various approaches are considered in attempting to predict the best parameter values of the models based on known characteristics of the project. A multiple linear regression with project value, duration, and type independent variables is shown not to produce any significant improvement on standard DHSS formula predictions. However, a reduction in the number of independent variables by cross validation produces an approximately 25% improvement on standard DHSS formula forecasts outside the data base. Examination of the models derived from this analysis indicate the type of project to be of major importance.     

楼层施工进度与工序交叉引起的荷载叠加研究分析

作为国民经济的支柱产业,房地产业发展迅速,要求施工速度不断加快,由于施工过程中混凝土楼面的施工作业面和垂直运输机械的运输能力有限,各个工序的作业时间短,这样就不可避免地产生了工序交叉的现象.每个工序的施工都产生施工荷载,工序交叉就引起了施工荷载的叠加.在住宅的主体施工过程中,施工速度快,混凝土养护时间短,强度低,楼面混凝土在叠加荷载作用下承载力不足,出现开裂现象,裂缝影响建筑物的美观和使用功能.混凝土结构在设计过程中没有考虑施工荷载叠加,通过对施工现场的施工荷载调研,对施工过程划分工况,提出结构设计需要考虑的合理的施工荷载.     

基于灵敏度矩阵分析的钢桁架桥模型修正

基于灵敏度矩阵分析的模型修正方法是目前最常用的模型修正方法之一.而在模型修正过程中,不可避免地存在求解过程的不适定性.不适定问题的求解中,正则化参数的选取对结果精度和效率都有重要影响.研究了基于灵敏度矩阵分析的钢桁架桥有限元模型修正工作,并对目前较常用的正则化参数选取方法——广义交叉验证(generalized cro...     

基于密实核理论的TBM盘形滚刀磨损预测模型研究

CCS(Constant Cross Section)盘形滚刀磨损是影响硬岩隧道掘进工作效率和成本预算的关键问题。根据CCS型滚刀的工作特点和岩石切割破碎原理,分析研究滚刀破碎岩石的复杂应力状态,建立了考虑密实核效应的滚刀破岩机理。通过推导密实核长度的理论解析式,获得了基于塑性去除磨粒磨损机制的滚刀磨损量与法向荷载之间的数学关系式,进而提出了滚刀磨损速率及切削寿命预测模型。基于此,分析计算了深圳地铁12号线某区间共757环的正面滚刀实测磨损数据,发现预测值与实测值的相对差异率值均小于10%,验证了预测模型的有效性。此外,通过与现有滚刀磨损预测模型对比分析,结果表明本文提出的预测模型计算结果更接近于现场实测值,说明了滚刀磨损速率和切削寿命指标可作为评价滚刀磨损特性的可靠指标,为TBM工程现场刀具更换方案设计提供更为合理可行的理论依据。     

城市供水水量预测模型研究及案例分析

从分析城市用水量的变化规律着手,给出了城市用水量预测的常用模型,并以此为基础分析了选择用水量预测模型时所需考虑的影响因素,然后以铜陵市日用水量预测为例,建立了三阶自回归预测模型,最后分析了铜陵节假日用水量预测模型,为供水系统管理的良好调度提供了数据依据。     

Grouping methods for MPS soot transport model and its application in large-scale enclosure fires

A soot transport model called Multi-Particle-Size model (MPS model) was developed to improve the prediction of soot movement by considering the uneven mass size distribution of soot particles and the influence of particle size on the gravitational settling. The model requires a sophisticated grouping method to divide the soot particles into several groups and determine the representative size for each group. In this paper, several soot particle grouping methods and the approach to calculate the representative sizes are developed with the aim of balancing the computational efficiency and the prediction accuracy of the model. The performance of the MPS model when different grouping methods are applied is investigated through the comparison of the predicted movement of soot particles generated from several materials. Based on this analysis a grouping method that results in the identification of three groups is shown to be sufficient to represent the influence of particle size on the gravitational settling for a variety of combustible materials and the computational cost of the extra governing equations for the transport of soot particles in the groups is acceptable. Furthermore, the efficiency of the model is demonstrated by simulating soot movement in a large-scale industrial building with a high ceiling.     

基于模型确认的结构概率损伤识别方法研究进展

基于静动力特性改变的结构损伤识别方法在过去几十年中得到了长足发展。相对于确定性的损伤识别,基于概率统计理论框架的损伤识别方法能够更好地反应损伤问题的不确定性本质,是一种非常有发展潜力的损伤识别方法,有望解决当前大多数损伤识别方法对于测量误差和噪声敏感的问题,从统计意义上实现复杂工程结构健康监测早期损伤的诊断。在回顾结构确定性损伤识别方法的基础上,主要介绍不确定性损伤识别方法和有限元模型确认的研究进展,分析比较各种方法的优点和不足之处;最后对有待进一步研究的问题和基于模型确认的概率损伤识别方法发展趋势进行展望。     

Some tools for fire model validation

General ideas are offered for describing fire model validity prior to starting product design. Validation of independent test results is part of this phase. Differences between comparable results, graphical methods, and distinctions between random and systematic errors are discussed. Reference: Alan D. Davies, Some Tools for Fire Model Validation,Fire Technology, Vol. 23, No. 2, May 1987, pp. 95–114.     

地下水水质预测的多克线性回归分析模型研究

运用回归分析理论和方法,建立了一个基于多元线性回归分析法的地下水水质动态预测模型,并将该模型用于遵义市海龙坝地下水水质的动态预测。结果表明预测精度较高,建立的模型较符合本研究区的实际情况。     

堆石料广义塑性模型研究

通过分析试验资料和以往研究成果,修正了堆石料不同围压下剪切过程峰值应力比表达式,论述了塑性模量对平均应力的依赖性。基于广义塑性理论框架,借鉴Lade-Duncan单屈服面模型中引入塑性功定义硬化规律的思路,对塑性模量进行了修正,提出了一种改进的广义塑性模型。为了验证改进方法的合理性,塑性模量改进方法被应用于刘恩龙模型,同时使用提出的修正广义塑性模型预测了另外两种堆石料试验。不同围压下模型的预测结果与试验结果吻合较好,表明修正的模型可以较好地预测堆石料的应力–应变特性。     

一个改进的堆石料广义塑性模型

在广义塑性理论框架下,通过引入两个修正系数修正塑性模量,增强了广义塑性模型在高围压条件下的适应性,成功地将砂土广义塑性模型改造成堆石料广义塑性模型。提出的修正广义塑性模型参数较少,容易确定,具有一定的实用性,并且可以推广至状态相关情况。模型中塑性模量公式简洁,可以退化成等向压缩塑性模量。模型可以很好地预测堆石料常规三轴加载应力应变关系,对等P以及等应力比路径也具有一定适应性。     

Above-floor tube-and-plate radiant floor model development and validation

While some building energy simulation tools include dedicated models to represent thermally massive embedded-tubes radiant floor systems, there are no models available for lightweight above-floor tube-and-plate (AFTP) systems. AFTP systems consist of a grooved wooden subfloor (or high density insulation layer), and conductive fin. This paper discusses the development of a transient AFTP radiant floor model and its implementation into ESP-r. This AFTP radiant floor model uses the general approach of the existing embedded-tube model in ESP-r and combines an analytical model of the tube with a two-dimensional finite difference model of the top layers of the floor construction. The new AFTP radiant floor model was found to compare closely with a transient two-dimensional finite element analysis model. Additionally, a full-scale transient experiment was conducted to empirically validate the model. The new model's predictions were found to be in close agreement with the measurements from this experiment.     

略论工程量清单计价模式的造价管理

首先介绍了工程量清单计价的概念及其合理性和可行性,并提出实行工程量清单计价的优点,针对工程量清单计价中容易出现的问题提出了相应对策,以顺应市场经济发展的要求。     

考虑围压效应的修正软岩热弹黏塑性本构模型

 大量的软岩三轴剪切试验表明,不同的围压下,软岩力学特性变化非常大。随着围压的增加,软岩的应变软化和剪胀性变弱;当围压足够大时,甚至表现为应变硬化和剪缩。已有软岩热弹黏塑性本构模型针对不同的围压大小,需要设定不一样的参数,使其应用到数值分析上带来一定困难。为了能用统一参数来描述软岩受围压影响的力学性质,对已有的软岩热黏弹塑性本构模型进行修正。修正模型中所有参数都具有明确的物理意义且都可通过常规三轴试验确定。通过实验数据与计算结果对比,验证了修正本构模型的正确性。     

考虑钢筋与混凝土相对滑移的修正钢筋本构模型

为了研究钢筋滑移对钢筋混凝土柱抗震性能的影响,在材料层次上建立了考虑钢筋与混凝土相对滑移的修正钢筋本构模型。采用等效三段阶梯函数描述黏结应力沿黏结长度的非线性分布规律,结合钢筋双线性应力-应变关系,推导了锚固钢筋滑移和平均滑移应变的理论计算式。锚固钢筋的总应变定义为理想黏结的钢筋应变与平均滑移应变之和。分别通过屈服和极限应力对应的钢筋总应变修正弹性模量和硬化模量,进而得到间接考虑钢筋滑移的简化分段线性应力-应变关系。非锚固钢筋的滑移采用降低屈服应力和屈服应变的方法加以考虑。对于钢筋的滞回规则,采用Sakayi等修正的Menegotto-Pinto模型。将本构模型通过子程序嵌入ABAQUS软件中,基于纤维梁单元,对往复荷载作用下钢筋混凝土柱的非线性响应进行了数值模拟,并与试验结果对比,验证了该模型的有效性。结果表明,所建议的钢筋本构模型,数学表达形式简单且计算效率高,能够模拟地震作用下钢筋混凝土柱的承载力和变形特性,达到满足工程需要的精度。     

基于矩阵模式热经济学的(火用)成本分析

以基本的空调系统制冷循环为基础,提出了利用矩阵模式热经济学原理对(火用)成本进行分析的思路,并叙述了建立事件矩阵A及其补充方程的方法.冷水机组 燃气锅炉方案的冷量(火用)成本和热量(火用)成本的计算结果与用其他方法计算的结果接近,并叙述了产生差异的主要原因.     

浅析灰色预测模型在建筑工程造价中的应用

针对建筑工程造价预测问题,提出了灰色模型方法,以工程造价历史资料为依据,建立了建筑工程造价的灰色预测模型,为建筑工程的工程招投标提供了依据,从而使工程投资达到预期目标。     

A modified deformation coordination model for calculating the internal force of anchored piles

Anchored piles are an important combined supporting structure and widely used in landslide prevention and control. The calculation of the internal force of a pile-anchor is highly significant. In this paper, we propose a modified deformation coordination model to more accurately calculate the internal force of anchored piles based on a simple analysis model originally developed by (Qu et al. 2016). In the modified deformation coordination model, the pile-anchor interaction is divided into two stages: (1) prestressed anchor cable application stage; and (2) landslide thrust action stage. The anchor cable deformation is taken as the sum of the free section and anchorage section. A deformation coordination equation is established based on the unification of the horizontal pile displacement and anchor cable deformation at the junction of the pile and anchor cable. The anchor cable tensile stress calculation formula is then obtained by combining the virtual work principle and graph multiplication theory in structural mechanics. An engineering case study of a pile with double-row anchor cables is tested to compare the results obtained using the traditional model and Chinese codes, which demonstrates the capability of the proposed model to calculate the internal force of anchored piles.