GPS in dynamic monitoring of long-period structures

Global Positioning System (GPS) technology with high sampling rates (10 samples per second) allows scientifically justified and economically feasible dynamic measurements of relative displacements of long-period structures—otherwise difficult to measure directly by other means, such as the most commonly used accelerometers that require post-processing including double integration. We describe an experiment whereby the displacement responses of a simulated tall building are measured clearly and accurately in real-time. Such measurements can be used to assess average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the building performance during extreme motions caused by earthquakes and strong winds. By establishing threshold displacements or drift ratios and identifying changing dynamic characteristics, procedures can be developed to use such information to secure public safety and/or take steps to improve the performance of the building.     

挤密砂桩加固水下软土大型原位载荷试验研究

港珠澳大桥岛隧工程水下深厚软土采用挤密砂桩进行加固,设计了一套大型原位载荷试验系统对水下挤密砂桩 （sand compaction pile,SCP）复合地基的力学和变形特性进行研究,通过在水下设置高精度静力水准系统获得了良好的沉降观测结果。试验结果表明,水下挤密砂桩复合地基在同一置换率下的应力分担比与载荷水平以及时间效应密切相关;应力分担比比值随荷载级别的升高表现出先减小后增大的趋势,在同一荷载级别下比值随着时间逐步衰减,并最终趋于某一定值。对比分析了几种散体材料桩复合地基承载力理论的计算结果,表明按被动土压力法得到的复合地基承载力与载荷试验结果较为接近。对于高置换率的挤密砂桩复合地基,采用建筑地基处理技术规范提出的沉降折减系数计算得到的复合地基沉降与实测值最为接近,采用日本经验公式计算得到的沉降量偏大。研究结果对于水下挤密砂桩复合地基的设计计算和深水原位测试具有一定的参考意义。     

Behavior of a seismically isolated bridge crossing a fault rupture zone

The effect of the fault rupture zone traversing a seismically isolated bridge is investigated utilizing a finite element model of a section of the Bolu Viaduct and a set of synthetic broadband strong ground motions simulated for the Bolu Viaduct site due to the 1999 Duzce earthquake. Both the original and a potential retrofit seismic isolation system designs are considered in the analyses. The results show double isolation system demands when fault crossing is considered, as compared to the case where fault crossing is ignored. The pier drift demands, however, remain comparable in both cases. Furthermore, the location of fault crossing along the bridge length, as well as the fault orientation with respect to the bridge longitudinal direction are shown to influence substantially the response of the seismically isolated bridge. Isolation system permanent displacements are greatly influenced by the restoring force capability of the isolation system when fault crossing effects in the excitations are ignored. In the case of fault crossing, the permanent displacements of the isolation system are dominated by the substantial permanent tectonic displacement along the fault trace which is imposed upon the structure. The results of this study contribute to developing a better understanding of how seismically isolated bridges respond when traversed by fault rupture zones. The lack of analyses and design guidelines for bridges crossing faults in international standards renders this study a useful reference for the profession.     

深圳―中山跨珠江通道对珠江三角洲地区可达性的空间效应

借助可达性分析模型,以深圳―中山跨珠江通道（简称“深中通道”）为案例,采用加权平均旅行时间、覆盖度指数、经济潜能指数分析深中通道建设后对珠江两岸地区可达性的影响和空间分布,并采用可达性变化均衡指数分析深中通道建设对区域可达性公平性变化的影响。结果表明：深中通道建设将显著提升珠三角区域南部的可达性,珠江口西岸地区的可达性提升高于东岸地区。中山市、珠海市 1 h 等时圈内的人口增加最大。珠江口东岸的深圳市、香港特别行政区和西岸的中山市和江门市的经济潜能得到较大的增长。中山市、东莞市和佛山市内部可达性呈现均衡化趋势,可达性公平性得到提升。最后,提出了完善深中通道周边交通运输网络布局和推进珠江口两岸产城互动融合等有针对性的政策建议。     

动水压力作用下深水桥墩非线性地震响应分析

为研究动水压力作用对深水桥墩地震响应的影响,本文分别采用Morison方程和辐射波浪理论建立了动水压力计算方法,分析了动水压力作用对桥墩地震响应的影响;同时分析了考虑材料非线性时动水压力作用对桥墩地震响应的影响。研究表明:动水压力作用增大了桥墩的地震响应,其影响随着相对水深的增加而增强;考虑材料非线性时动水压力对桥墩地震响应的影响,相对线性材料而言有所变化。     

Finite element analysis of structure-borne vibration from high-speed train

Finite element analyses were used to investigate the behavior of the building vibration induced by high-speed trains moving on bridges. The model includes the bridge, nearby building, soil and train. Finite element results indicate that trainload frequencies are more important than the natural frequencies of bridges and trains for building vibrations. If the building natural frequencies approach to the trainload frequencies, which equal an integer times the train speed over the compartment length, the resonance occurs and the building vibration will be large. Moreover, the vibration shape is similar to the mode shape of the resonance building frequency. To isolate the building vibration induced by moving trains, this paper investigates three common types of foundations, which include the extension of retaining walls, pile foundation and soil improvement around the building. Soil improvement around the building is the best way to reduce the building vibration both in horizontal and vertical directions.     

考虑高程系统差的桥梁GPS高程拟合模型

本文研究利用GPS和两岸水准观测资料统一大跨度桥梁工程高程系统的方法,通过引入两岸高程系统差参数,改进了经典的多项式拟合模型,并且对解算的高程系统差参数进行了显著性检验。文中以苏通大桥GPS控制网与水准测量数据为例进行了验算,说明了该方法的可行性。     

港珠澳大桥西人工岛桥结合段波浪演变数值模拟

近年来海洋极端天气频发,港珠澳大桥西人工岛地处外海,与其相连接的桥梁非通航跨的桥面高程较低,容易受到海浪侵袭,威胁到岛桥功能的正常发挥和结构自身安全。针对西人工岛桥结合部周围的复杂地形条件,采用OpenFOAM^®开源程序,分别对S、SSW和SW三个方向的极端波浪进行了数值模拟。通过数值计算结果与物理模型试验测量值的比较验证了的模型的准确性。分析了不同方向入射波的波高和沿岛体斜坡爬高的变化规律。随着波浪入射角的增大,人工岛南侧斜坡的波浪爬高呈逐渐减小,但在岛体西端靠近桥梁的位置处,波浪爬高逐渐增大;同时也反映了越浪和桥面上水风险的大小。研究旨在为实际工程的管理和设计提供参考。     

Clear water scour around a finite array of cylinders

This experimental study presents clear-water scour and deposition patterns around hexagonal arrays of circular cylinders in steady flow conditions. Understanding the scour processes around such configurations could facilitate the design of several hydraulic and marine engineering structures, such as bridge piers and piles. The flow alteration caused by the examined porous obstacles depends on the solid volume fraction of the obstacles and on the angle of attack of the incoming flow, due to the limited number of cylinders constituting the array. Flume experiments with erodible bed were carried out for four array densities (solid volume fractions: 0.14, 0.20, 0.32 and 0.56) under three different orientations (regular, angled and staggered configurations). The scour/deposition characteristics were obtained by means of laser scanner and the results were compared to solid cylinders of equal circumambient diameter. Different angles of attack of the incoming flow lead to different blockage ratios, which have direct impact on the scour characteristics and deposition patterns. The arrays with the higher solid volume fraction generated scour/deposition patterns similar to solid cylinder, while in the arrays with the lower solid volume fractions, local scour around the individual small cylinders became evident. Finally, considering that the load bearing capacity of a pier basically depends on the area of its cross-section, a comparison of the maximum induced scour depth and volume by the cylinder arrays and the solid cylinder with equal solid cross-sectional area is presented, in order to introduce an alternative pier configuration that induces less scour. The results showed that the array of cylinders could generate 27% less scour volume and 22% less scour depth compared to its single solid cylinder counterpart.     

天兴洲公铁两用斜拉桥主梁纵向列车制动振动反应分析

本文对天兴洲公铁两用斜拉桥主梁纵向列车制动的振动反应进行了研究。天兴洲大桥是目前在建的世界上跨度最大的公铁两用斜拉桥,由于具有四线铁路,其主梁在列车制动及行车移动荷载作用下会沿纵向产生大幅振动,因此对其列车制动及行车移动荷载反应进行研究尤为必要。文中,首先根据车辆动力学的原理建立了列车制动动力学模型,获得了列车制动力纵向荷载及在制动过程中列车行走所产生的竖向荷载,并建立制动力传递有限元模型,应用有限元分析软件来获取钢轨上制动力及列车行走时引起的桥梁结构节点上的作用力时程。最后对天兴洲公铁两用斜拉桥主梁纵向列车制动及行车移动荷载的振动反应进行了仿真分析,发现了其主梁纵向列车制动反应具有位移大且速度极小的特点。