桩筏基础共同作用分析方法研究

计算桩筏基础的方法很多,如弹性理论法、荷载传递法、混合法、有限元法和有限元有限压缩层法等等。但是这些方法计算复杂,计算机容量大,计算时间长,因而采用能量变分原理来分析桩筏基础。即先假定筏板的位移模式,用能量变分的方法计算位移模式中的一系列未知参数,建立桩筏系统方程,它不需要对桩、筏进行单元离散,减少了计算的复杂性,可方便的应用于大型群桩筏计算。     

用变分法解群桩-承台(筏)系统

分别将群桩、承台(筏)选用各自合适的位移模式,并将能量变分方法应用于群桩-承台(筏)系统,用最小势能原理求解各参数.应用本文方法,可以很方便地得到群桩-承台(筏)系统中各桩所受荷载及沉降,承台各任意位置的弯矩、扭矩、正应力和剪应力.本文方法极大地减少了计算量,在工程应用方面有较大的优越性.     

土-桩-筏共同作用的混合分析法

提出了一种土-桩-筏共同作用的混合分析法.将桩和桩间土简化为弹簧作用于筏板下,桩土相互作用系数基于Mindlin解和Boussinesq解,为避免桩端应力集中,在桩端面上进行应力积分,并引入修正参数来考虑桩挤开土的实际情况.筏板采用无剪切闭锁的四边形厚薄板通用单元进行有限元分析.根据桩土柔度系数得到桩土柔度矩阵,求逆后与筏板刚度矩阵耦合,形成土-桩-筏体系的刚度矩阵.桩的沉降计算和土层参数的确定与规范法一致,适用于成层地基上变桩长、变桩径情况,板单元适用于平面形状不规则的薄板及中厚板.通过计算Poulos提出的经典桩筏基础模型并与其它几种典型方法对比,表明该法合理、实用.     

群桩-厚筏板基础的设计与分析

提出了一种群桩中单桩非线性刚度的计算模型.即将筏板下的桩、土看成弹簧作用在筏板上,在对厚筏板有限元计算时采用三维退化层合单元,得到了桩-土-筏共同作用的有限元简化计算方法,对群桩-厚筏板基础进行了计算和分析,可用以指导设计.     

桩筏基础抗拔变形的简化分析方法

提出一个预测抗拔桩筏基础非线性变形的简化分析方法,方法将桩假定为相互作用的非线性弹簧,使用双曲线函数拟合抗拔单桩的荷载-位移曲线,并将其用于桩筏基础的变形分析中,使用相互作用系数方法分析桩-桩的相互作用。与室内群桩模型试验和现场群桩试验结果的比较说明,方法不但可以节省计算时间,而且计算结果与实测结果也比较吻合。     

考虑固结过程的桩-土-筏三维相互作用分析

针对存在较厚软弱下卧层的桩土筏结构体系 ,本文建立了桩端下卧层固结沉降计算的半透水边界模型。应用半透水地基固结解得到任一时刻桩端下卧层的沉降 ,进而得到任一时刻群桩中每根单桩的刚度。与筏板有限元分析结合 ,构成桩 -土 -筏共同作用有限元分析模型 ,并研制开发了相应的分析软件 ,可以分析筏板内力、筏板挠度和桩顶反力随时间的变化规律。工程分析表明 ,此方法有一定的实用价值     

基于共同作用的桩筏基础分析及设计

以宏达国际酒店高层建筑桩筏基础为工程背景,采用Poulos位移解计算桩土刚度,Reissner厚板理论分析桩基筏板,并利用该方法对桩筏体系的总体沉降、差异沉降、桩顶反力、筏板内力等结果进行了计算.此法较现有的桩基设计规范中基于筏板绝对刚性假定的计算具有一定的优越性.通过分析计算结果总结变化规律,认为荷载密度对此类基础的局部沉降、桩顶反力影响较大.分析结果能够为高层桩筏基础工程的设计提供有益参考.     

桩-筏(梁)基础设计中地基反力的确定方法

桩 -筏 (梁 )基础设计时 ,筏板 (梁 )底部的地基反力的确定是十分关键的 ,它不仅受到上部结构的刚度影响 ,还受到地基土的固结度随着时间的增长而不断变化及地基刚度的时效性等的影响 .设计时其计算模型的建立又和桩 -筏 (梁 )的刚度有关 .根据地基土在桩 -筏 (梁 )基础的作用下的实际受力状况 ,结合工程实例 ,提出桩 -筏 (梁 )基础设计时简化计算的 3种模型及 3种型使用时的注意事项 .     

广义位移法在土-结构相互作用问题分析中的应用

对目前土 -结构相互作用的有限元法数值建模中的若干不足进行了评述。通过深入分析土 -结构相互作用的力学机制 ,指出 :在相互作用体系中 ,由于两者之间悬殊的刚度 ,接触界面上公共节点的位移将受到结构本身变形性态的影响 ,在假设接触界面变形协调的前提下即是要求这些点的位移都应服从结构体变形的位移模式 ;因此 ,土 -结构相互作用整体有限元数值模拟的关键在于如何较好地反映由于土中结构体刚度条件而导致的、对周围土体变形所施加的一种约束条件。针对桩 /板筏与地基土的两类土结构相互作用问题 ,根据梁、板的工程弹性理论分别建议了桩 /筏基础结构的广义位移模拟方法。     

群桩-厚筏板基础的简化计算方法

提出了一种群桩-土-筏板基础共同作用的有限元简化计算方法,计算时将筏板下的桩、土根据各自的非线性刚度简化成弹簧作用在筏板上,对厚筏板采用三维退化层合单元进行有限元计算,在保证精度要求下有效地减少了单元数和节点数。对一实际桩筏基础进行了计算和分析,用以指导优化设计,并把计算结果与等刚度法计算结果及实测值进行了比较,计算结果与实测比较吻合。     

Monopolistic competition, increasing returns, agglomeration, and transport costs

This paper presents a model where production concentrated in one place is compared with dispersed production. Concentrated production can attain a higher level of productivity but must incur transport costs. Dispersed production, on the other hand, has a lower productivity level but need no transportation. In order to avoid unnecessary complications, output per capita is used as an objective function. Transport cost is measured in units of output and will therefore affect the objective function directly. The model uses a linkage approach where a final output is produced under constant returns to scale. This production has increasing returns to the number of differentiated inputs. The differentiated intermediate inputs are produced subject to increasing returns to scale in a framework of Chamberlinian monopolistic competition. The size of the market determines the number of intermediate inputs that the local economy can accommodate. In this way the model formalises Adam Smith's theorem on the division of labour being limited by the extent of the market. The paper examines how the break-even point between the two ways of organising production is affected by (i) changes in transport cost and market density and (ii) shifts in technology for producers of intermediaries and the final output. Received: December 1999/Accepted: January 2001     

巴纳德学院黛安娜中心,纽约,美国

本文介绍了巴纳德学院黛安娜中心的工程概况、设计理念和设计手法以及采用的节能环保新技术。     

The Thiel–Zsutty earthquake damage model,reformulated and extended

The Thiel–Zsutty (TZ) model predicts mean and the probability distribution function for earthquake damageability of building as a function of peak ground acceleration. ATC‐13‐1 provides an alternate damageability model based on modified Mercalli intensity characterization of ground motion and a beta distribution function for selected building types. This paper provides a reconciliation of the TZ and Applied Technology Council (ATC) methods. It is shown that the beta distribution can provide a continuous representation of the step‐wise TZ Markov distribution function. When the TZ model uses a compression factor for the standard deviation to represent the degree of uncertainty in the parameters, then the TZ results are found to be consistent with the ATC‐13‐1 distribution function for a specific compression factor of 0.40. This paper provides a new, simply applicable method to determine the damage distribution function for a given site, building type, and site conditions; using a beta distribution and allowing inclusion of the degree of confidence the assessor has in the determination of the parameters. New equations are provided to estimate the mean, standard deviation, and upper confidence limit of the damage ratio.     

杭州萧山钱江世纪城亚运村片区地下空间规划

结合杭州亚运村片区的开发建设,全面介绍了基于RBD功能的CAZ城市片区地下空间总体布局方案。同时,依托上位规划的功能定位及开发条件,重点分析了地下空间规划的关键技术问题并提出针对性解决途径,论述了片区地下空间开发的必要性和紧迫性,归纳了亚运村片区地下空间开发的目标原则及总体思路。在对地下空间的功能、规模进行全面研究的基础上,打造了城市CAZ高品质片区立体化交通集约型地下空间的典范布局。探索了界定地下空间要素的控规编制原则,并对地下空间开发及管理模式提出了建议。本专项规划具有中国新时代城市建设特色,可为地下空间开发类似工程提供参考。     

Optimization for Roads' Construction: Selection,Prioritization, and Scheduling

Limited resources (budget, labor, machinery) have a significant toll on the roads' construction. The question of interest is: given variations of resources over a lengthy construction time, what would be the best construction scheduling plan, or how to optimize the Gantt chart while considering two highly challenging features (1) prerequisite conditions and (2) the interdependency of the benefit of the projects’ completions. We formulate it as a bilevel problem where the objective function is to minimize generalized costs and the lower level accounts for the drivers’ route choice. We employ a solution algorithm based on a supervised learning technique (a linear regression model of machine‐learning) and an integer programming problem and it is applied to the datasets of Winnipeg and Chicago. The regression model was found to be a tight approximation which resulted in an efficient algorithm (the CPU time is almost a linear function of the number of iterations). Moreover, the proposed methodology can render promising results (at least locally optimal solutions). This article is the first to formulate the Gantt chart using linear binary constraints and optimize it tailored to real‐life case studies.     

Demand,location, and the theory of production

This paper presents a profit-maximizing location model to investigate the impact of demand on the optimum location decision of a firm in the Weberian triangle. It will be shown that:(1) When the distance of the firm's location from the product market is held constant, the optimum location for the firm would be independent of the demand function if and only if the expansion path in input space is linear through the origin as demand varies;(2) When the distance of the firm's location from the product market is a decision variable, the optimum location for the firm would be independent of the demand function if and only if the production function is linearly homogeneous.I am grateful to Professor Bob Logan for helpful discussions, and especially Professor T.R. Lakshmanan for very valuable suggestions and comments. This work was partially supported by a 1987 Summer grant from the School of Management, University of Alaska Fairbanks     

基于“大事件”驱动的城市空间效应研究--以江苏省南通市为例

从大事件营销的角度对南通市新城区的发展进行分析，指出南通市通过省运会这一大事件，激活周边地块的价值提升并产生连锁反应，从而对地区发展形成显著的触媒作用。这一过程为南通新市级中心周边地区带来发展机遇，同时也通过促进地区功能完善和城市结构整合，为城市长期发展提供持续强大的推动力。实证研究表明，不仅仅是大城市，二、三线城市也可以通过大事件的机遇实现地区腾飞，大事件营销正成为一种日益普遍的推动城市发展的政府手段。     

Network structure,complexity, and adaptation in water resource systems

Infrastructure systems are often complex. Many have both natural and built components. For such systems, including water resource networks, resilience is a common policy goal. In the formalised study of complex systems, the structure and function of networks can contribute directly to system resilience. One branch of complex systems studies, network science, describes how connectivity between individual components can explain some system-wide properties of growth and reliability. Water resource systems analysis has only begun to apply techniques from network theory and complexity science to assess adaptability and resilience. We present an analysis of connectivity in a network model of California's water infrastructure system using several network science techniques. Results indicate that nodes in California's water system are clustered but without scale-free properties. The network originates from a mixture of top-down (centralised) and bottom-up (dispersed interactions of parties) planning. This structure provides managers greater flexibility to use local and distant water sources. We use the analysis to illustrate how several disciplinary notions of resilience apply to civil infrastructure planning. We also explore how adaptability, not just complexity, influences resilience in planning. Creating systems that can respond to future changes must be an important policy goal in planning civil infrastructure.     

德国疗养地(Kurort)与疗养公园(Kurpark)：形成、发展、空间模式与景观设计特点

德国疗养地具有典型性的公共绿地类型:疗养公园(德文:Kurpark;英文:spapark),从德国疗养地的历史出发,对疗养地与疗养公园的形成和发展阶段进行论述。选择德国40处疗养地的疗养公园作为研究对象,结合地图与文献资料,通过应用制图方法和数据分析方法就公园与城镇、公园与疗养功能建筑的空间关系分别进行分析并归纳总结其特征,公园-城镇空间共有3种模式即城镇边界型、城镇内部型与城镇近郊型,以边界型最常见;公园-疗养建筑的空间模式以建筑分布于公园外侧为主,建筑按照功能可细分为医疗类、娱乐休憩类与住宿类。采用案例分析法,以典型的克奈普疗养地——巴特沃利斯霍芬的疗养公园为例,探讨其景观设计要点,包括重视自然要素、步行空间体系建设、植物专类园设计及疗愈设施建设。最后总结德国疗养公园的建设经验对于当前中国小城镇建设及"康养小镇"在规划设计方面具有的借鉴意义。