Bridge pier scour in cohesive soil: a review

Bridge failure due to local scour has stimulated the enthusiasm of many researchers to study the causes of scouring and to predict the ultimate scour depth at bridge foundation. A brief review of the state of artwork of investigation conducted on local scour at bridge pier in cohesive bed material is presented. Scour process and mechanism at bridge pier in cohesive and noncohesive soil are presented. The effects of parameters influencing local scour around bridge pier is discussed. Empirical equations for predicting ultimate scour depth at bridge pier embedded in cohesive soil are outlined. Comparisons of the equations are made considering two examples: one under laboratory condition and another under field condition.     

苏通大桥索塔深水群桩基础冲刷防护工程的设计与施工

从苏通大桥深水群桩基础结构方案出发,分析了冲刷及防护对大桥安全性的影响,进而从防护工程理念、结构设计与施工、防护效果监测等方面阐述了苏通大桥基础冲刷难题的解决方法.     

Radio-protective aprons during radiological examinations of the thorax: an optimum strategy

The current work investigates the most effective type/position of aprons for postero-anterior (PA) and lateral projections of the chest. Two apron-types were investigated: 'Mavig' half apron and Amray light plus' wrap-around apron. The half apron was positioned at the X-ray tube or image receptor side of an anthropomorphic phantom for PA and lateral projections. Radiation dose at positions corresponding to ovaries, uterus and testes was measured with thermoluminescent dosemeters. The wrap-around apron offers a higher level of protection for PA and lateral projections compared with the half apron, regardless of where the latter was positioned, with dose reductions of up to 88% compared with no apron. For the PA position, the half apron should be positioned in a gender-specific way, facing the X-ray tube for females and the image receptor for males. With all apron types/positions, gonadal dose is still clearly evident, from internal scatter, emphasising the importance of other protective practices such as collimation.     

Indian practice on estimation of scour around bridge piers—A comment

Well-laid foundation is mostly provided in road and railway bridges in India over large and medium-sized rivers. The age-old Lacey-Inglis method is used for estimation of the design scour depth around bridge elements such as pier, abutment, guide bank, spur and groyene. Codal provisions are seen to produce too large a scour depth around bridge elements resulting in bridge sub-structures that lead to increased construction costs. Limitations that exist in the codes of practice are illustrated in this paper using examples. The methods recently developed for estimation of the scour are described. New railway and road bridges are required to be built in large numbers in the near future across several rivers to strengthen such infrastructure in the country. It is strongly felt that provisions in the existing codes of practice for determination of design scour depth require immediate review. The present paper provides a critical note on the practices followed in India for estimating the design scour depth.     

高烈度软土场地桥梁地震与冲刷联合作用效应研究

冲刷会导致桥梁基础裸露,土体对桩基的约束作用减弱,使得桥梁基础在地震作用下的危险性增大,因此建立冲刷与地震联合作用下桥梁的失效概率模型,分析震区连续刚构桥冲刷作用组合分项系数具有重要的意义。以地震基本烈度Ⅷ度区某连续刚构桥为依托工程,基于Monte-Carlo法确定冲刷深度的分布函数,并采用CSIBridge有限元软件建立不同冲刷深度下全桥空间有限元动力模型,进行48条地震波下的增量动力分析(IDA),计算不同冲刷深度的地震作用效应分布函数,并采用直接积分法求得桥梁基础的失效概率及可靠度指标。研究结果表明:通过冲刷与地震的联合作用框架下失效概率分析,可建立冲刷深度与失效概率的非线性关系;该方法可合理确定冲刷与地震作用组合下荷载组合分项系数,可为桥梁在冲刷与地震联合作用下的风险评估和设计提供参考。     

The effect of circular bridge piers with different inclination angles toward downstream on scour

A fundamental principle in the safe design of bridge piers is to estimate maximum scour depth. As such, many researchers devoted their efforts to study the phenomenon of scour around bridge piers and to present relationships to estimate maximum scour depth. In the current research, scour around circular bridge piers with two different diameters and different inclination angles toward downstream has been investigated experimentally under clear water and different discharges. The obtained results revealed that increase in the inclination angle leads to a significant decrease in the scour depth, dimensions of sediment ridge and scour hole. Moreover, by comparing the data obtained from vertical bridge pier and well-known relationships, a relationship having the most agreement with the results was selected and modified to estimate equilibrium scour depth around inclined piers.     

Failure analysis of masonry arch bridges subject to local pier scour

In European roadway and railway networks, many multi-span unreinforced arch bridges were built in the last century. These structures are often characterized by piers with shallow foundations placed in the riverbed, which can be subject to hydrodynamic turbulences in case of river floods and further localized scour phenomena. The lack of adequate monitoring can cause scour-induced settlements over time, potentially causing bridge structural failure. This work investigates the structural behavior of existing masonry bridges subject to local pier scour. A case study is used to carry out the failure analysis, simulating the evolution of the structural behavior of a six-span masonry arch bridge with a finite element model, correlated with the local scour profile.     

A comparison of dose savings of lead and lightweight aprons for shielding of 99m-Technetium radiation

Nuclear medicine technologists (NMTs) have the highest effective doses of radiation among medical workers. With increase in the use of lightweight materials in diagnostic radiography, the aim was to compare the effectiveness of lead and lightweight aprons in shielding from 99m-Technetium ((99m)Tc) gamma rays. The doses received from a scattering phantom to the entrance, 9cm depth and exit of a phantom were measured with LiF:Mg, Cu, P thermoluminescent dosemeters (TLDs). Doses and spectra were assessed without no shielding, with 0.5-mm lead and lightweight aprons. The lead and lightweight aprons decreased entrance surface doses by 76 and 59%, respectively. The spectral analysis showed that the lightweight apron provided better dose reduction at energies <95 keV, though lead was 35% more efficient at higher energies. While lead apron demonstrated better shielding, the additional savings should be considered with the weight differential. It is concluded that the lightweight apron is suitable to be worn by NMTs interacting with patients injected with a (99m)Tc labelled radiopharmaceutical.     

弹塑性Winkler地基上双柱式桥墩的地震反应

浅平基桥墩在承受强震作用时,其基础与地基之间会发生提离,地基土会进入塑性状态。要精确模拟上述两个问题是非常复杂的。分析中地基采用了能考虑基础提离及地基塑性的弹塑性Winkler地基模型,钢筋混凝土墩柱采用了武田三线型滞回模型。采用1940ElCentro地震记录作为输入,对双柱式浅平基桥墩进行了非线性时程分析。研究结果表明,基础提离和地基塑性对双柱式桥墩的地震反应具有重要影响。与线性分析相比,考虑基础提离和地基塑性后,双柱式桥墩的位移增大,内力减小。在设计中允许地基发生提离和屈服对于保护桥墩是有利的。     

允许提离的弹塑性 Winkler 地基上桥墩的地震反应

钱平基桥墩在承受强震作用时,其基础与地基之间会发生提离,地基上会进入塑性状态。要精确模拟上述两个问题是非常复杂的。本文分析中采用了能考虑基础提离及地基塑性的弹塑性 Winkler 地基模型,采用 1940 EI Centro 地震记录作为输入,对法平基桥墩进行了非线性时程分析。研究结果表明,基础提高和地基塑性所产生的非线性行为是非常明显的。考虑基础提离和地基塑性后,桥墩—地基系统的刚度不断退化,基础转角明显增大,而基底弯矩明显减小。     

大曲率非对称匝道桥爆破拆除

为提高大曲率非对称匝道桥爆破拆除的成功率,针对大曲率非对称匝道桥的特点,以南京市汉中门匝道桥爆破拆除为工程实例,重点介绍了桥台预处理、预留0.5~1.5 m桥墩立柱、修筑1.5~2.5 m沙袋轮胎缓冲墙及重要管线上方铺设16 mm钢板等预处理技术措施和防止滑移的保护措施。在此基础上,为控制桥体塌落过程的姿态,防止侧翻,桥墩起爆顺序选择50 ms及310 ms两个延期时间,再辅以直接防护、桥墩近距离防护和桥墩远距离防护等爆破飞石防护措施。结果表明,预处理及选择的爆破方案能使上部桥体平稳塌落,未出现侧翻及滑移,选择的飞石防护措施和地下管线保护措施安全有效。     

露天煤矿预裂爆破的设计施工与评价

露天矿生产要求通过预裂爆破保护到界边坡岩石的完整性和稳定性,安家岭煤矿长期以来进行此项工作效果并不明显。为此组织相关技术人员对预裂爆破重新设计、优化施工并进行试验与评价,提高了爆破效果与质量。本文对成功经验进行总结,供同类矿山企业技术参考。     

复杂环境下桥墩与桥台基坑深孔控制爆破开挖

叙述了高压线下和电塔旁桥墩与桥台基坑深孔控制爆破的设计与施工,重点介绍了有效地控制爆破飞石、爆破振动的相关技术措施,为今后类似爆破工程提供成功经验。     

刚性桩复合地基竖向承载特性分析

为研究刚性桩复合地基的承载机理,利用有限元程序,对刚性桩复合地基在竖向荷载下的轴力、沉降特性进行了计算分析,着重讨论了桩身轴力、基础沉降等随垫层厚度、垫层模量、桩长、土体模量及桩间距等因素变化的规律,并在此基础上对刚性桩复合地基设计参数的选取原则进行了讨论。     

The collapse of the Schoharie Creek Bridge: a case study in concrete fracture mechanics

On April 5, 1987, the New York State Thruway bridge over Schoharie Creek collapsed without warning. The primary cause of failure was scour beneath a plain concrete pier footing. However, a necessary secondary cause was unstable propagation of a single crack in the pier. Conditions for initiation of the curvilinear crack are first evaluated. It is concluded that about 28 feet of scour had to occur to initiate stable process zone formation at the point of initiation, but that at least 44 feet was required to cause unstable cracking. Simulation of propagation was studied using discrete representation in a finite element model and nonlinear fracture mechanics. About 5 feet of propagation was necessary to transition from nonlinear to LEFM. Good agreement was found between observed and predicted final crack trajectories, and load redistribution in the bridge structure was determined to have been a necessary part of the failure process. Discussions concerning the application of the finite element method to crack initiation problems and the use of the size effect to estimate failure conditions in large, plain concrete structures are also presented.     

考虑水底柔性反射边界的深水桥墩地震动水压力分析

在深水桥墩地震动水压力分析中一般假定水底为完全反射边界,而忽略水底柔性介质对动水压力波的吸收作用。该文考虑水底柔性反射边界,基于辐射波浪理论,建立了深水桥墩地震动水压力的计算公式,深入分析了水底柔性反射边界对动水压力的影响。研究表明:水底柔性反射边界会在特定的荷载激励频率范围内对深水桥墩动水压力产生影响,且动水压力随水底反射系数的减小而减小,深水桥墩地震动水压力分析可以忽略水底柔性边界的影响。从而为长大桥梁地震灾变过程精细化模拟提供了理论依据。     

580 m长钢筋混凝土箱型拱桥爆破拆除

580 m长钢筋混凝拱桥需爆破拆除。大桥是钢筋混凝土建造,拱肋采用箱型截面的砼箱形拱桥,经多次加固,桥墩最大体积1200 m~3,桥面到墩角最高33 m,拱箱壁为薄壁结构。因传统钻爆方式无法有效破坏大桥结构,采用水压、深孔和浅孔爆破相结合的方式,将药包置于注满水的箱型拱肋内的设计位置上,以水作为传爆介质传播爆炸压力使拱肋破坏,从而达到破坏拱轴解除支撑的目的;对桥墩采用大孔径深孔,由桥面垂直钻孔一次性爆破解除;桥面、拱上结构等用浅孔爆破。大桥解体充分,空气冲击波、飞石及噪声等得到有效控制,也减少了后续出渣工作量。     

可提离式桩基础规则连续梁桥的地震响应分析

以上海嘉闵高架桥为依托,利用OpenSees软件构建有限元分析模型进行非线性时程分析,对两种不同基础体系下的规则连续梁桥的主梁、墩柱、基础等的地震响应进行对比分析,并考虑墩高变化的影响。结果表明：基础提离设计,相较常规基础设计,会显著降低墩柱的纵、横向弯矩响应,改善墩柱的受力性能,纵向降幅为20.4%~32.0%,横向降幅为2.5%~23.8%;单桩的纵向弯矩响应减小,降幅达16.2%~40.0%;桩基最大拉力受到有效控制。基于新规范体系,评估了墩柱和基础在E2地震下的抗震性能,结果表明采用提离式桩基础的规则梁桥可有效降低墩柱、基础的地震需求。在E2地震下,墩柱均处于弹性状态,单桩配筋率相较常规基础体系梁桥可随墩高增加适当降低。     

复杂耦合隔振系统的实用解研究

针对工程实际中的复杂柔性耦合系统 ,本文对建立在柔性基础 弹性浮筏上的隔振系统应用子系统导纳法进行分析 ,推导了耦合系统动态功率流传递计算公式。在研究中 ,将浮筏和基础的基频与被隔振机组固有频率之比作为特性参数 ,对系统在不同频率比下的传递特性进行了计算研究 ;针对计算结果 ,分析了浮筏的弹性和基础的柔性对耦合系统的传递功率流的影响 ,给出了可以将基础或浮筏当作刚体来处理的弹性变化范围。