Comparison of web plate numerical models for self‐centering steel plate shear walls

Previous research has shown that self‐centering steel plate shear walls (SC‐SPSWs) are capable of achieving enhanced seismic performance at multiple hazard levels, including recentering following design‐level earthquakes. When modeling SC‐SPSWs numerically, these studies considered an idealized tension‐only steel plate shear wall (SPSW) web plate behavior. Research has shown that web plate behavior is more complex than predicted by the idealized model, and web plates can provide more strength, stiffness, and energy dissipation than predicted by the idealized model. The idealized model of web plate behavior is used widely in SPSW numerical models where the moment‐resisting boundary frame provides supplemental hysteretic damping and stiffness; however, in SC‐SPSWs, where the post‐tensioned boundary frame is designed to remain elastic during an earthquake, accounting for the more complex web plate behavior can have a significant impact on seismic performance estimates from numerical simulation. This paper presents different methods for modeling SC‐SPSWs. Responses from these models are compared with experimental results. A simple modification of the tension‐only model, referred to as the tension‐compression strip model, is shown to provide a reasonable approximation of SC‐SPSW behavior. Results from nonlinear response history analyses of SC‐SPSWs with the tension‐only and tension‐compression web plate models are compared to assess how the approximation of web plate behavior affects SC‐SPSW seismic performance. Copyright © 2015 John Wiley & Sons, Ltd.     

长江经济带新型城镇化协调性的趋同与差异研究

近10年来,城镇化进程中暴露的很多问题可以归结为城镇化的协调性问题,本文以“人地关系”理论为基础,从城乡、产城、城镇化区域和城镇化与资源环境协调发展4个方面来衡量新型城镇化的协调性。并以长江经济带为研究区域,运用空间杜宾面板模型(spatial Durbin panel data model, SDPDM)从经验上考察新型城镇化协调性的俱乐部与条件趋同现象,发现制约长江经济带东、中、西部新型城镇化协调性的因素并不一致：东部城市应进一步加强城镇化同资源环境的协调,促进区域间的协同发展;中部城市应改变大拆大建的城市建设模式,着重发展服务业和增强城市间的合作;西部城市应进一步推进市场开放进程,减少政府对市场的干预和城市建设中的攀比,发展服务业和促进本地经济增长。同时,限制城市人口增长的政策对于新型城镇化协调性不存在显著影响,而放开户籍管制,则会促进人口向城市集聚;无论从促进第三产业发展、产城融合或是城乡协调发展,均会对新型城镇化协调性起到正向作用。     

Seismic design and testing of the bottom vertical boundary elements in steel plate shear walls. Part 1: design methodology

This research investigates the seismic design method and the cyclic inelastic behavior of the bottom column, also called the vertical boundary element (VBE), in steel plate shear walls (SPSWs). This study consists of two parts. This Part 1 paper discusses the anticipated pushover responses for properly designed SPSWs and the possible inelastic responses of the bottom VBE at various levels of inter‐story drift. Considering both the tension field action of the infill panel and the sway action of the boundary frame, this study develops a simplified method to compute the flexural and shear demands in the bottom VBE. Based on the superposition method, this approach considers various plastic hinge forming locations at different levels of inter‐story drift. One of the key performance‐based design objectives is to ensure that the top ends of the bottom VBEs remain elastic when the SPSWs are subjected to the maximum considered earthquake. This paper presents the comprehensive design procedures for the bottom VBE. Furthermore, this study conducted cyclic performance evaluation tests of three full‐scale two‐story SPSWs at the Taiwan National Center for Research on Earthquake Engineering in 2011 to validate the effectiveness of the proposed design methods. The experimental program, cyclic inelastic responses of the SPSWs and bottom VBEs, and numerical simulations are presented in Part 2. Copyright © 2014 John Wiley & Sons, Ltd.     

Oblique wave scattering by undulating porous bottom in a two-layer fluid: Fourier transform approach

The problem involving scattering of oblique waves by small undulation on the porous ocean bed in a two-layer fluid is investigated within the framework of linearised theory of water waves where the upper layer is free to the atmosphere. In such a two-layer fluid, there exist waves with two different wave numbers (modes): wave with lower wave number propagates along the free surface whilst that with higher wave number propagates along the interface. When an oblique incident wave of a particular mode encounters the undulating bottom, it gets reflected and transmitted into waves of both modes so that some of the wave energy transferred from one mode to another mode. Perturbation analysis in conjunction with Fourier transform technique is used to derive the first-order corrections of velocity potentials, reflection and transmission coefficients at both modes due to oblique incident waves of both modes. One special type of undulating bottom topography is considered as an example to evaluate the related coefficients in detail. These coefficients are shown in graphical forms to demonstrate the transformation of water wave energy between the two modes. Comparisons between the present results with those in the literature are made for particular cases and the agreements are found to be satisfactory. In addition, energy identity, an important relation in the study of water wave theory, is derived with the help of the Green’s integral theorem.     

基于混合遗传算法的斜测电离图参数反演

斜向探测是获取电离层状态信息的重要手段之一,对斜测电离图的反演可以得到电离层的相关结构参数.遗传算法是一种有效的并得到普遍应用的反演方法,该算法的求解不依赖于初值的选择,可以有效地减少反演问题解的非唯一性,但也存在“过早收敛”和局部搜索能力差等缺陷,从而导致反演精度下降,影响反演结果的可靠性.本文提出将基于模拟退火的混合遗传算法应用到斜测电离图的参数反演中,该算法不仅把握总体能力强,且具有较强的局部搜索能力,是遗传算法和模拟退火算法的优势互补.为了验证该算法反演结果的可靠性和稳定性,首先分别采用遗传算法、模拟退火算法和混合遗传算法对合成的电离图进行反演,反演参数包括临界频率,最大电子浓度和半厚度.通过对三种算法反演结果的对比,得出混合遗传算法的反演结果最接近真实值,需要的迭代次数也远远小于其他两种算法;通过改变种群大小和总迭代次数来判断参数值的改变对三种算法反演结果的影响,得出混合遗传算法有效地降低了参数的选取对反演结果的影响.然后用这三种反演算法对实测电离图进行反演,并将它们的反演结果与斜测链路中点的实际垂测数据进行比较,结果显示混合遗传算法84.62%的反演结果可以控制在误差范围之内,高于遗传算法（76.93%）和模拟退火算法（65.38%）.这些都表明了混合遗传算法的反演结果具有较强的可靠性,在反演的寻优能力和稳定性上要明显优于遗传算法和模拟退火算法,对实测电离层图的反演具有很强的借鉴意义和应用价值.     

黑龙江及邻区地壳应力场初步研究

采用综合震源机制方法,利用5 002条P波极性数据反演黑龙江地区二维应力结构,求得该区0.5°×0.5°综合震源机制解.初步研究表明：21世纪以来,构造应力场总特征基本一致,具有明显的继承性,主压应力和主张应力的优势方向明显,与板块运动关系具有成因上的联系.     

土-水特征曲线测定过程中潜在影响因素与异常现象研究

基于压力板仪对相同制样参数的4个环刀试样与12个三轴试样进行土-水特征曲线（SWCC）试验,研究影响试验的各种潜在因素以及相关的异常现象。试验结果表明：即便是相同条件制备的试样,其SWCC之间也会存在差异性,这种差异与土的颗粒级配不良有直接关系,而与平衡时间无关;蒸发效应在SWCC试验中持续存在,并在平衡后期成为失水的主要因素,因此,对平衡条件应适当修正;试样的侧面防护对试样的SWCC影响显著,特别对于大高径比试样,蒸发效应将因其侧面防护脱离而成为失水的主要因素,严重影响SWCC的试验结果;横向裂纹这一异常现象并未影响SWCC测量结果,但其产生机制却可能反应了轴平移技术的不足,值得进一步研究。根据上述研究结果和其他相关试验成果,对SWCC试验提出建议和改进方法。     

一种激光收敛测量方法及其精度评估

结合传统收敛测量和全站仪测量两种测量方法的优势,提出了一种新的收敛测量方法。传统收敛测量方法存在着操作要求高,施工干扰多,不易长期监测等缺点;全站仪测量方法由于采用间接测量策略,测点间的距离需要进行解算,施测精度较低。新方法延用了全站仪测量方法所采用的激光测距技术,同时也延用了传统收敛测量方法采用的直接测量距离策略。借助于目前市场上成熟的激光测距产品,研制和加工了新方法所需的测量装置。它由5个部分组成,依次为激光测距仪、测距仪底座、测量基点连杆、连接套筒、测量基座。按照一定的实施步骤,在程潮铁矿采空区的地面隧道进行了测量精度在现场工程环境下的试验评估。试验结果表明,新方法的成本低廉、操作简捷、稳定性好,施测精度可达到0.7 mm,有利于收敛监测在地下工程建设过程中的普及应用。     

辽宁省环境效率及其时空分异

环境问题已经成为辽宁省经济发展的瓶颈。基于随机前沿分析SFA与非期望产出的数据包络SBM的研究方法,选取2005年到2011年为研究时间,对辽宁省14个地级市环境效率进行测算,并利用聚类分析、基尼系数与β趋同等研究方法对环境效率进行时空分析。在此基础上,利用Tobit模型建立多元回归,以分析辽宁省环境效率的影响因素。结果表明：大连、沈阳、鞍山的环境绝对效率水平较高,朝阳市绝对效率水平最低;大连、盘锦、沈阳处于生产有效单元,朝阳相对效率属强无效单元;在空间与时间的分析上大连、沈阳等是效率水平高的地区,朝阳为最低地区,空间呈“山脊状”分布;绝对效率值差距在不断缩小,相对效率差距在拉大后趋于稳定;回归结果显示产业结构与经济发展水平对环境经济效率及企业资本深化与生产技术水平起正向作用;财政支持与外商直接投资没有通过模型检验,未对环境效率起作用。     

Sequential city growth: Theory and evidence from the US

City growth patterns are attracting more attention in urban geography studies. This paper examines how cities develop and grow in the upper tail of size distribution in a large-scale economy based on a theoretical model under new economic geography framework and the empirical evidence from the US. The results show that cities grow in a sequential pattern. Cities with the best economic conditions are the first to grow fastest until they reach a critical size, then their growth rates slow down and the smaller cities farther down in the urban hierarchy become the fastest-growing ones in sequence. This paper also reveals three related features of urban system. First, the city size distribution evolves from low-level balanced to primate and finally high-level balanced pattern in an inverted U-shaped path. Second, there exist persistent discontinuities, or gaps, between city size classes. Third, city size in the upper tail exhibits conditional convergence characteristics. This paper could not only contribute to enhancing the understanding of urbanization process and city size distribution dynamics, but also be widely used in making effective policies and scientific urban planning.