中国海南：从经济特区到综合复合型自由贸易港的嬗变

海南自由贸易试验区与自由贸易港规划建设不仅是海南发展的需要,也是中国深化改革,扩大开放,实现经济转型以及应对国际竞争与挑战的重要措施与战略部署。相关研究就海南自由贸易试验区建设的必要性、可行性、模式与实施对策进行了初步分析。为构建自由贸易区的学术研究体系,完善海南自由贸易港规划建设的理论与实践,集中几位长期从事相关研究的地理、经济与规划学者,就海南自由贸易港的类型与功能、产业发展、空间结构、政策与监管以及风险防控等方面进行探讨,以期引起决策者与学术界的深入研究与探讨。     

基于全局弱式无单元法直流电阻率正演模拟

全局弱式无单元法是在有限单元法基础上发展起来的一种数值模拟方法,它采用局部支持域内的节点信息来构造形函数实现局部精确逼近,摆脱了单元,仅依赖于节点信息,具有预处理简单、模拟精度高、灵活性强的特点,适用于复杂地电条件下直流电阻率正演模拟.本文采用RPIM构造直流电阻率全局弱式无单元法形函数,利用RPIM形函数推导了直流电阻率全局弱式无单元法方程.然后,编制了直流电阻率全局弱式无单元法正演模拟Fortran程序,利用该程序对典型的地电模型进行了正演模拟,并将正演结果与基于线性插值的FEM正演结果及解析解进行对比,结果表明采用RPIM形函数的全局弱式无单元法用于直流电阻率正演模拟的正确性及有效性,且在同等条件下,全局弱式无单元法模拟精度高于矩形剖分的FEM,更有利于指导电法勘探的数据解译;利用该程序对复杂地电模型进行了正演模拟,结果表明全局弱式无单元法对复杂地电模型模拟效果良好,适应性强,灵活性高,可任意加密节点提高模拟精度.     

自由段先注浆对预应力锚索抗拔试验结果影响研究

为了解决无法采用已注浆锚索进行抗拔试验问题,基于界面脱黏剪切模型,利用荷载传递和弹性变形理论,考虑锚索锚固段与自由段长度比Lb /La的影响,建立了采用自由段已注浆锚索抗拔试验结果评价锚索抗拔性能的方法。结果表明：自由段注浆对锚索抗拔力有较大幅度的提高,尤其是当界面剪切阶段由弹性向脱黏过渡时,提高比例快速增加,并在脱黏后逐渐趋于稳定。其次,锚索自由段与锚固段交界面处剪切位移和轴力最大,并向两端逐渐降低。随着拉拔力的提高,界面剪切位移和轴力都不断增大,同时向锚索两端的衰减速度也加快。此外,弹性阶段时剪应力曲线为山峰型,而脱黏阶段为马鞍型,并随抗拔力的提高,马鞍开口逐渐扩大。最后,锚固段与自由段长度比Lb /La对锚索极限抗拔力的影响较小,其极限抗拔力折减系数?Q取值介于0.81～0.83之间,且Lb /La =2.5时,?Q计算值仅比实测结果小6.02%,验证了本文方法的可行性。     

基于GIS的机场多跑道三维净空管理系统的研究与开发

在研究和建立了多跑道障碍物限制面三维模型的基础上,基于G IS,开发了机场三维净空管理系统。该系统可按照相应标准自动生成单跑道特别是多跑道障碍物限制面、辅助进行净空管理,可极大地减少机场选址与规划中的超障物评定的工作量,显著提高净空管理效率,具有广阔的应用前景。     

不透水地基上均质土坝渗流自由面的有限元计算

为了保证土坝安全,水利工程中需要对土坝进行渗流计算,首先需要确定自由面。根据达西定律和渗流连续方程,以及水头和流量边界条件,建立了不透水地基上的均质土坝渗流的计算模型。利用Geoslope软件,采用有限元离散的方法计算了土坝的渗流自由面,并分析了土坝在不同的渗透系数情况下的自由面位置的差异。最后,解析解计算的自由面结果验证了有限元计算自由面方法是正确的。     

岩石膨胀性试验注意事项探讨

从室内试验的角度来探讨几类工程勘察中岩石常用膨胀性试验(自由膨胀率、膨胀力、侧向约束膨胀率、耐崩解)的注意事项,从野外取样、标准样品制取、试验操作、方法选择等方面进行了论述,力求减小试验误差,提高膨胀岩的试验水平,保证试验结果的准确性,并使膨胀岩膨胀性指标的测定方法更臻完善。     

A small-scale field check on the Fisher–Lehmann and Bakker–Le Heux cliff degradation models

The paper considers the development of initially straight, steep rock cliffs, bounded above and below by horizontal surfaces, in which basal debris removal is zero and degradation occurs by the weathering away of fine debris from the cliff face to form a scree at its foot. Of the slope degradation models available, the two earliest and simplest, namely the Fisher–Lehmann and the Bakker–Le Heux models, are regarded as most relevant and are briefly summarized. The main purpose of the paper is to check the predictions of these models, particularly with regard to the shape of the rock surface buried beneath the scree, against field data. Such data are sparse. It is concluded that the best field case currently available, despite its small scale, is that provided by the 1·75 m deep ditch which forms part of the experimental earthwork in the chalk on Overton Down, Wiltshire. The predictions of the two models are checked against field measurements made of the stage of degradation reached on each face of the ditch by July 1968, eight years after its excavation. These stages were influenced to different degrees by the presence of a surface turf layer. For the NE face, where this influence was least, the agreement of the predictions of the Fisher–Lehmann model with the actual rock profile is excellent and that of the Bakker–Le Heux model only marginally less so. For the SW face, as expected, the agreements are somewhat less close. These results may be to some extent fortuitous because of the influence of the turves and because the scree slopes tend to be concave rather than rectilinear, as assumed. Also, the free faces decline with time in a manner intermediate between those assumed in the two models. Larger scale field checks are clearly desirable before firm general conclusions can be drawn. Rates of crest recession for the Overton Down ditch are logarithmic with time after a very rapid initial phase. Extrapolation from the early phase of this logarithmic behaviour leads to a close estimate of the time needed for the slope to develop fully. The associated ultimate crest recession is also closely predicted by equations derived from both models. © 1998 John Wiley & Sons, Ltd.     

Identification of modal parameters of a 600-m-high skyscraper from field vibration tests

Accurate prediction of the dynamic responses of a high-rise building subjected to dynamic loads such as earthquake and wind excitations requires the information of its structural dynamic properties such as modal parameters including natural frequencies and damping ratios. This paper presents the identification results of the modal parameters based on field vibration tests on a 600-m high skyscraper. A set of tests, including ambient vibration test (AVT) and free vibration test (FVT), were conducted on the skyscraper to identify its modal parameters. Firstly, this paper presents and discusses the modal parameters of the skyscraper assessed by several identification methods applied to the AVT measurements. These methods include the wavelet transform (WT) method, the stochastic subspace identification (SSI) method, and the random decrement technique (RDT). Secondly, an active mass damper (AMD) system with total mass 1000 tons equipped into the skyscraper was used to excite the building for estimation of the modal parameters by FVT. Thirdly, this paper presents observations on the structural dynamic behavior of the skyscraper with the operation of the AMD system during a typhoon event. The field measurement results show that the AMD system functioned efficiently for suppression of the wind-induced vibrations of the skyscraper during the typhoon. This paper aims to further understand the structural dynamic properties of super-tall buildings and provide useful information for structural design and vibration control of future skyscrapers.     

饱和软土自由场地地震反应特性振动台试验

为了解软土自由场地地震反应特性,开展饱和软土自由场地地震反应特性大型振动台模型试验。分别从模型体系自振特性、震陷位移及不同土层深度测点的加速度、动孔压比等动力响应指标方面,较为深入和全面地分析饱和软土自由场地地震反应规律、破坏机理。同时还分析模型箱的"边界效应"以验证试验土箱的合理性、有效性和测试仪器性能,并由此进一步确定模型地基有效工作区域。研究表明:(1)地震动作用下,饱和软土自由场地特征频率降低,阻尼增大;(2)饱和软土自由场地对水平输入地震波具有短周期滤波、长周期放大效应,且强震作用下地基失效并表现为减隔震作用;(3)饱和软土自由场地动孔压比优势区域位于浅埋土层,并随着输入地震动强度的增大,该区域动孔压比优势逐渐减弱。该研究可为非自由软土场地试验研究提供必要的技术经验。     

双向地震作用下锯末混合土场地动力特性分析

在北京工业大学振动台台阵系统上开展了一系列锯末混合土地基自由场振动台模型试验,试验中模型箱采用装配式连续体刚性模型箱,试验中输入地震动时程采用El Centro地震动记录、Taft地震动记录和天津地震动记录,地震动输入方向分为水平单向和水平双向。文中,重点考察了双向地震动输入下锯末混合土模型场地的动力特性及其变化规律,主要指标包括模型场地地震动反应的峰值加速度及其动力放大系数、加速度时程及其傅氏谱。试验结果表明:随着输入地震动强度的增大,同一测点反应的峰值加速度总体上在增大,而其加速度动力放大系数总体上呈现减小的趋势,反应的频谱组成从较高频率向较低频率移动;双向地震作用下锯末混合土模型场地的动力变化规律与单向地震作用下较为一致。