桥梁施工高程控制网精度及跨河水准观测设计

分析了水中桥墩施工允许误差,推导了桥梁施工高程控制网的必要精度,研究并设计了不同跨河长度下的桥梁高程控制测量等级和跨河水准测量的测回数及组数,研究成果可供相关规范修订时借鉴。     

桥梁基础挖方计算方法探讨

本文针对山区铁路桥梁,利用墩台纵横向的实际勘测数据,通过假设墩台附近范围内地形纵横向变化的连续性建立斗形空间几何体计算模型,根据简单多边形面积公式及拟台体体积公式,提出了墩台基础挖方量的计算方法并通过程序实现。     

How are large western hemisphere warm pools formed?

During the boreal summer the Western Hemisphere warm pool (WHWP) stretches from the eastern North Pacific to the tropical North Atlantic and is a key feature of the climate of the Americas and Africa. In the summers following nine El Niño events during 1950–2000, there have been five instances of extraordinarily large warm pools averaging about twice the climatological annual size. These large warm pools have induced a strengthened divergent circulation aloft and have been associated with rainfall anomalies throughout the western hemisphere tropics and subtropics and with more frequent hurricanes. However, following four other El Niño events large warm pools did not develop, such that the mere existence of El Niño during the boreal winter does not provide the basis for predicting an anomalously large warm pool the following summer.In this paper, we find consistency with the hypothesis that large warm pools result from an anomalous divergent circulation forced by sea surface temperature (SST) anomalies in the Pacific, the so-called atmospheric bridge. We also find significant explanations for why large warm pools do not always develop. If the El Niño event ends early in the eastern Pacific, the Pacific warm anomaly lacks the persistence needed to force the atmospheric bridge and the Atlantic portion of the warm pool remains normal. If SST anomalies in the eastern Pacific do not last much beyond February of the following year, then the eastern North Pacific portion of the warm pool remains normal. The overall strength of the Pacific El Niño does not appear to be a critical factor. We also find that when conditions favor a developing atmospheric bridge and the winter atmosphere over the North Atlantic conforms to a negative North Atlantic Oscillation (NAO) pattern (as in 1957–58 and 1968–69), the forcing is reinforced and the warm pool is stronger. On the other hand, if a positive NAO pattern develops the warm pool may remain normal even if other circumstances favor the atmospheric bridge, as in 1991–92. Finally, we could find little evidence that interactions internal to the tropical Atlantic are likely to mitigate for or against the formation of the largest warm pools, although they may affect smaller warm pool fluctuations or the warm pool persistence.     

可替换式桥梁横向防落梁限位装置抗震性能研究

针对目前桥梁结构横向防落梁限位装置损毁后修复困难的问题,提出一种新型的带可更换耗能段的桥梁横向防落梁限位装置。分别以可更换耗能段的腹板厚度、腹板高度及安装位置等为参数,采用有限元软件ABAQUS建立了10个不同参数的装置模型并对其开展拟静力仿真试验,探讨其工作机理,验证其可更换的设计思想并剖析其破坏机理,研究各参数对装置滞回曲线、承载力、延性和耗能能力的影响规律。结果表明:该装置可通过先可更换耗能段破坏再竖板破坏达到多道设防和分级耗能的目的,且整个加载过程中装置的滞回曲线饱满、稳定、无明显捏拢,表现出良好的耗能能力;随着可更换耗能段腹板厚度的增加,装置屈服承载力、极限承载力、屈服位移、极限位移以及延性系数逐渐增大,耗能能力逐渐增强;可更换耗能段高度对装置屈服承载力影响不显著;随着可更换耗能段高度的增加,装置极限承载力逐渐增大,装置屈服位移先增大后减小,装置极限位移整体呈下降趋势,装置的延性系数和耗能能力逐渐减小;可更换耗能段的安装高度对装置屈服承载力和耗能能力的影响无统一规律,但与装置的屈服位移、极限位移及延性系数成负相关。基于本析结果,建议装置在满足承载力要求的前提下,应尽量选取可更换耗能段腹板厚度较厚、高度较小和安装位置较低的参数进行设计。     

顾及地形特征的机载LiDAR数据桥梁提取算法研究

提出了一种从机载LiDAR点云数据中提取水陆桥梁的新算法,采用先滤波分类再识别桥梁的策略用于桥梁主体及其与地面连接处脚点的提取。首先对机载LiDAR点云数据进行严格滤波,在此基础上利用多个阈值对非地面脚点进行初步提取;然后引入Alpha-shapes算法对初步提取结果进行分割,并辅以面积阈值提取出属于桥梁主体部分的脚点;最后提出一种顾及地形特征的点云区域生长算法,用于准确提取桥梁主体与地面连接部分的脚点。实验证明,本文算法对水面和陆地桥梁提取均有很好的效果。     

粗颗粒间液桥毛细力演化规律的动态计算方法

水力特性是非饱和土力学理论与工程的重要课题之一,土样水力特性的变化过程本质上可反映为土颗粒间毛细力的演化规律。为此,以粗颗粒为研究对象,将其简化为一对不等径球体颗粒,而其间的水分形态可视为形如圆环的液桥,不考虑颗粒重力和浮力的影响。以Young-Laplace方程为基础,先推得计算液桥毛细力的控制方程组,再结合液桥的无量纲体积最大、最小值及其外曲率半径的割线迭代算法提出求解毛细力的动态计算方法,进而研究毛细力与颗粒间距、颗粒半径比和液桥体积的无量纲关系,结果表明：当颗粒间距一定时,液桥的毛细力随其体积和颗粒半径比增大均呈递增趋势;当液桥体积一定时,其抗拉刚度随颗粒间距增大呈递减趋势。最后,利用已有文献中液桥毛细力与颗粒间距的实测关系,验证了该动态计算方法在表征液桥从形成至断裂时毛细力演化规律的有效性。     

新型FMCW地基合成孔径雷达在大桥变形监测中的应用

地基合成孔径雷达（GB-SAR）是一种新型的建筑变形监测技术,相较于传统的监测手段,该方法拥有高精度,覆盖面大等优点。基于FMCW技术的Fast-GBSAR系统采用调频连续波技术,相较于国内已有的基于步进连续波技术的类似系统,该系统处理速度提高30倍,并拥有更高的可靠性。Fast-GBSAR在国内已对多座大桥进行了公开测试,监测结果表明Fast-GBSAR测量精度能达到0.01 mm,在变形监测领域极具潜力。     

Nonsmooth dynamics prediction of measured bridge response involving deck‐abutment pounding

Earthquake‐induced deck‐abutment contact alters the boundary conditions at the deck level and might activate a different mechanical system than the one assumed during the design of the bridge. Occasionally this discrepancy between the assumed and the actual seismic behavior has detrimental consequences, for example, pier damage, deck unseating, or even collapse. Recently, an insightful shake‐table testing of a scaled deck‐abutment bridge model 1 , showed unexpected in‐plane rotations even though the deck was straight. These contact‐induced rotations produced significant residual displacements and damage to the piers and the bents. The present paper utilizes that experimental data to examine the validity and the limitations of a proposed nonsmooth dynamic analysis framework. The results show that the proposed approach satisfactorily captures the planar rigid‐body dynamics of the deck which is characterized by deck‐abutment contact. The analysis brings forward the role of friction on the physical mechanism behind the rotation of the deck, and underlines the importance of considering the frictional contact forces during deck‐abutment interaction even for straight bridges, which typically are neglected. Finally, the paper investigates the sensitivity of the rotation with respect to macroscopic contact parameters (i.e., the coefficient of friction and the coefficient of restitution). Copyright © 2017 John Wiley & Sons, Ltd.     

Experimental investigation of spatially varying effect of ground motions on bridge pounding

Pounding between adjacent bridge structures with insufficient separation distance has been identified as one of the primary causes of damage in many major earthquakes. It takes place because the closing relative movement is larger than the structural gap provided between the structures. This relative structural response is controlled not only by the dynamic properties of the participating structures but also by the characteristics of the ground excitations. The consequence of the spatial variation of ground motions has been studied by researchers; however, most of these studies were performed numerically. The objective of the present research is to experimentally evaluate the influence of spatial variation of ground motions on the pounding behaviour of three adjacent bridge segments. The investigation is performed using three shake tables. The input spatially varying ground excitations are simulated based on the New Zealand design spectra for soft soil, shallow soil and strong rock using an empirical coherency loss function. Results confirm that the spatially nonniform ground motions increase the relative displacement of adjacent bridge girders and pounding forces. Copyright © 2012 John Wiley & Sons, Ltd.     

强潮流作用下桥墩不对称“双肾型”冲刷地貌特征与机理

本文在海图地形资料分析桥轴线附近的海床自然冲刷的基础上,利用多波束测深技术研究大桥主墩附近局部冲刷地形。结果表明,该大桥桥位附近地形冲刷较显著,且大桥主墩位置有持续冲刷的趋势;主墩上、下游群桩最大冲刷深度呈上游最深、中部淤积、下游渐深的不对称形态,最大局部冲刷深度为4 m;桥墩整体冲刷坑形态呈南北“双肾型”;潮流流向与桥墩迎流面存在偏南的入射角,使得各桥墩南侧的最大冲深和冲刷范围均大于北侧。