Planar rocking response and stability analysis of an array of free‐standing columns capped with a freely supported rigid beam

This paper investigates the planar rocking response of an array of free‐standing columns capped with a freely supported rigid beam in an effort to explain the appreciable seismic stability of ancient free‐standing columns that support heavy epistyles together with the even heavier frieze atop. Following a variational formulation, the paper concludes to the remarkable result that the dynamic rocking response of an array of free‐standing columns capped with a rigid beam is identical to the rocking response of a single free‐standing column with the same slenderness yet with larger size, that is a more stable configuration. Most importantly, the study shows that the heavier the freely supported cap beam is (epistyles with frieze atop), the more stable is the rocking frame regardless of the rise of the center of gravity of the cap beam, concluding that top‐heavy rocking frames are more stable than when they are top light. This ‘counter intuitive’ finding renders rocking isolation a most attractive alternative for the seismic protection of bridges with tall piers, whereas its potential implementation shall remove several of the concerns associated with the seismic connections of prefabricated bridges. Copyright © 2012 John Wiley & Sons, Ltd.     

桥梁沉降观测布网方案浅析

从变形监测理论入手,结合多年实践经验介绍了桥梁监测中涉及的一些基本概念,包括桥梁监测中基准点,工作基点和变形观测点介绍、监测网的布设原则、一般网形示例介绍、引起桥梁不均匀沉降的原因以及监测网点位置安排等内容。     

城市高架桥合理抗震体系选择与经济性对比

探讨了基于两水准设防的城市高架桥的合理抗震设防标准与相应的结构性能目标.选取两座典型的城市高架桥结构,包括一座正线桥和一座匝道桥,分别采用延性抗震体系和减、隔震体系进行结构抗震设计.对比了不同结构抗震体系所对应的结构在各水准地震作用下具体抗震性能表现,结果表明减、隔震体系具有更优的抗震性能.在此基础上,进一步从经济性的...     

打桩引起的基坑开挖问题及处理

通过某电厂桩基处理工程实例,介绍了打桩引起的预制桩偏位及开挖问题。在不加外荷载情况下,采用塑料排水板方法消散打桩引起的超静孔隙水压力的处理措施,解决了高孔隙水压力下主厂房的开挖问题。分析了塑料排水板消散孔隙水压力的影响因素。观测结果及工程实践表明,塑料排水板处理桩基工程快速经济,可不需加载,但处理效果与水平排水系统有关。     

非平稳地震激励下隔震曲线梁桥振动控制研究

曲线梁桥由于其平面不规则性导致结构在地震激励下产生弯扭耦合效应,使得隔震曲线梁桥的地震响应更加复杂。目前常用的控制方法是将隔震技术与附加减震装置相结合对曲线梁桥进行控制。本文将地震动考虑为一均匀调制非平稳随机过程,针对隔震曲线梁桥长周期、低频率的特点,选取Clough-Pension平稳地震动功率谱模型作为随机地震动输入模型,对无控(NON-C)、经典线性最优控制(COC)以及序列最优控制算法(SOC)三种状态下的曲线桥梁进行随机响应分析。通过建立曲线梁桥在随机地震动作用下的运动方程,求出减震控制结构的位移谱密度、加速度谱密度响应及时变方差。分析结果表明:序列最优控制算法(SOC)在使隔震层位移得到减小的同时,可以更有效地控制上部结构的地震响应,具有更好的控制效果。     

漂浮体系悬索桥拟静态纵向运动特性及其控制

营运状况下漂浮体系悬索桥加劲梁纵向运动产生的过大累积行程会引起伸缩缝和塔梁纵向阻尼器等连接构件的性能退化和疲劳损坏.探索加劲梁纵向运动过大累积行程的成因,并找出降低累积行程的控制措施是确保悬索桥健康运营的关键.首先,以江阴长江大桥实测位移时程数据为基础,对不同频谱特性的位移成分进行分解,并统计了不同位移成分的循环次数和...     

基于随机森林的中小跨径公路梁桥双柱墩地震易损性模型

为准确建立线路中小跨径梁桥桥墩的地震易损性模型,采用统计工具得到某山区高速公路桥梁双柱墩的结构、几何和材料特性的概率分布,由拉丁超立方体抽样生成桥墩属性数据集,建立了参数化的有限元模型.通过Pushover分析和基于非弹性需求谱的能力谱方法获取双柱墩的地震需求和抗震性能数据点,提出由随机森林(RF)模型建立桥墩地震易损...     

深水连续刚构桥地震响应分析

本文探讨连续刚构桥在深水中地震响应的特性.首先建立了地震作用下深水桥梁的运动方程,简要阐述了该运动方程的求解方法,应用该运动方程,对一座桥墩淹没水深168m的连续刚构桥进行了地震响应分析,考察了在纵向、横向激励作用下桥墩的内力响应和位移响应特征,探讨了矩形空心截面桥墩内域水、外域水对桥墩地震响应的影响,结果表明,由于墩-水相互作用,桥墩的位移和内力响应均有明显增大,对于矩形空心墩,内域水和外域水的影响应同时计入.     

Pseudo-fractal interpolation for risk analysis

This paper describes a new method of analyzing the risk incurred when the outcome of a decision depends on interpolated values, for example, on the flow through an aquifer sparsely sampled for permeability or on the ratio of waste to ore in a mineral deposit sparsely sampled for grade. The method uses large families of interpolations constructed between sample values using adaptations of the well-known midpoint displacement method for generating pseudo-fractional Brownian motion trajectories. The parameters defining each family are chosen interactively by specialists to incorporate their expert knowledge. Each family, or ensemble, then defines a population of values for any global characteristic (functional) such as flow rate or waste ratio. The probabilities of various outcomes are estimated by counting them and calculating their ratios. For example, if 900 out of 1000 are acceptable the chance of success is estimated to be 90%.     

Probabilistic analyses of soil consolidation by prefabricated vertical drains for single‐drain and multi‐drain systems

Natural soils are one of the most inherently variables in the ground. Although the significance of inherent soil variability in relation to reliable predictions of consolidation rates of soil deposits has long been realized, there have been few studies that addressed the issue of soil variability for the problem of ground improvement by prefabricated vertical drains. Despite showing valuable insights into the impact of soil spatial variability on soil consolidation by prefabricated vertical drains, available stochastic works on this subject are based on a single‐drain (or unit cell) analyses. However, how the idealized unit cell solution can be a supplement to the complex multi‐drain systems for spatially variable soils has never been addressed in the literature. In this study, a rigorous stochastic finite elements modeling approach that allows the true nature of soil spatial variability to be considered in a reliable and quantifiable manner, both for the single‐drain and multi‐drain systems, is presented. The feasibility of performing an analysis based on the unit cell concept as compared with the multi‐drain analysis is assessed in a probabilistic context. It is shown that with proper input statistics representative of a particular domain of interest, both the single‐drain and multi‐drain analyses yield almost identical results. Copyright © 2016 John Wiley & Sons, Ltd.