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.     

基于GA－RS的规则钢筋混凝土桥梁圆形单柱桥墩延性抗震优化设计

提出抗震结构集成优化设计的新方法,将多目标遗传优化算法与反应谱分析很好地结合起来,建立规则钢筋混凝土圆形单柱桥墩多目标抗震优化设计的通用框架,以圆形单柱桥墩的截面半径、纵向钢筋配筋率和横向箍筋配筋率为设计变量,以结构的初始材料造价、抗震强度需求能力比、抗震延性需求能力比为优化目标函数。通过把延性抗震设计问题转化为多目标优化问题,从而使设计者可以很好地平衡抗震设计的各种关键因素,并以可控的方式处理多个优化目标而获得Pareto意义上的最优设计参数。     

桥梁单墩不同侧向力分布模式Pushover分析方法

Pushover分析使用一定分布模式的递增水平侧向力代表地震作用下结构惯性力的分布,分布模式的不同会直接影响Pushover分析的结果, 尤其是结构高阶振型影响显著时,因此侧向力分布的选取是Pushover分析中的一个关键问题。本文通过选取7条强震地震波,对比了典型地震波下非线性时程分析（IDA）和采用4种不同侧向力分布模式的Pushover分析的15m、30m和60m墩的地震反应。并从总体、构件和截面三个层面对各种模式Pushover分析进行评价,分析其适用性。研究表明结构进入非线性和高阶振型影响显著时,自适应侧向力模式较其他模式Pushover分析结果更接近IDA分析结果。     

Photoluminescence investigations on alumina ceramic bearing couples tested under different angles of inclination in a Hip joint simulator

Aseptic loosening due to wear and dislocation of the implant represents the main complication after total hip arthroplasty. To gain more insight into the influence of the implant position on wear, commercial alumina couplings have been tested in a hip joint simulator under three different angles of cup inclination (23°, 45°, 63°) with respect to a horizontal plane. The planned length of the test was ten million cycles. However, the test was stopped at 5.5 million cycles due to the fracture of one of the femoral heads, tested with at angle of 63°. The residual stress state in the worn acetabular cups and in the fractured femoral head were evaluated by the frequency shift and broadening of the R₁ and R₂ fluorescence bands due to the Cr³⁺ ions naturally present in alumina ceramics as trace impurities. The gravimetric measurements did not show significant differences among the three different inclinations tested, in agreement with previous simulator studies, but in disagreement with in vivo findings. The fluorescence measurements allowed to affirm that an angle of 63° represents a worsened mechanical condition for the prosthetic component, with a consequently higher probability of fracture and/or damage potentially conducive to massive wear. In the light of the fluorescence results, it did not appear surprising that the femoral head that fractured was the one being tested at 63°.     

Finite element analyses on transverse impact behaviors of 3-D circular braided composite tubes with different braiding angles

This paper presents finite element analyses (FEA) on the transverse impact responses of 3-D circular braided composite tubes with the braiding angles of 15°, 30° and 45°. A finite element model of the braided composite tube was established at microstructure level to analyze the transverse impact behaviors. From the FEA results, the impact damage, deformation and stress distribution were obtained to analyze the damage mechanism. Stress propagation in lower braiding angle tubes was faster than that of the higher braiding angle. The impact responses of the braided composite tubes were also tested to obtain load–displacement curves and energy absorption for the comparisons with the FEA results. The impact damage and fracture morphology obtained from the FEA were in good agreement with the experimental results, which demonstrated the feasibility of the FEA model for the design of the braided tube.     

非规则高墩曲线桥梁振动台试验研究

据模型相似原理及多点激励理论,对缩尺比1:20的钢筋混凝土高墩曲线桥梁进行地震模拟振动台试验。研究高墩曲线桥梁结构在不同频谱地震波、不同峰值加速度及局部场地效应作用下高柔桥墩损伤模式及结构动力响应规律。结果表明,高柔桥墩损伤有明显的分布柔性特点,墩高差对桥墩裂缝开展及桥梁动力响应影响显著;不同频谱地震波作用下曲线桥梁结构动力响应规律各异;曲线桥梁结构动力响应峰值与地震波加速度峰值基本呈线性增长;局部地形效应使结构动力响应增大,导致曲线桥梁结构动力响应呈非线性增长;高墩曲线桥梁地震响应有明显空间性,首尾桥墩顶径向动力响应较大,易发生横桥向落梁破坏。     

配置竖向无粘结预应力筋的RC桥墩残余变形研究

为进一步讨论采用竖向无粘结预应力筋减少钢筋混凝土(Reinforced Concrete,RC)桥墩震后残余位移的可行性,建立了竖向配置预应力筋的RC桥墩动力分析模型,结合拟静力和振动台试验结果,对数值分析模型的准确性进行了验证。在此基础上讨论了无粘结预应力筋对RC桥墩震后残余位移的影响。结果表明,RC桥墩中配置竖向无粘结预应力筋能够明显减小桥墩震后残余位移;随预应力筋配筋率的增加,墩顶残余位移值明显减少;预应力筋初始应力和预应力筋位置对桥墩震后残余位移影响不大。近断层地震动是引起桥墩震后残余位移过大的主因,远场地震动下,桥墩震后残余位移与墩顶最大位移的比值在10%内;而近断层地震动下,桥墩震后残余位移与墩顶最大位移的比值可达30%以上。预应力筋最大应力值随墩顶最大变形基本呈线性增加的趋势。     

扩容角对圆形巷道岩爆过程的影响

利用FLAC模拟了不同扩容角时圆形巷道的岩爆过程。为了模拟巷道开挖,利用编写的FISH函数删除巷道内部的单元。岩石服从莫尔库仑剪破坏与拉破坏复合的破坏准则,破坏之后呈现应变软化—理想塑性行为。文章的模拟分为3步:首先,将静水压力施加在模型上,直到达到静力平衡状态;然后,利用编写的FISH函数,开挖巷道;最后,计算重新开始,直到达到静力平衡状态。模拟结果表明,随着扩容角的增加,剪切带变宽,岩爆坑变深,破坏单元数目增多,破坏区变大。当扩容角较低时,高剪切应变集中于"狗耳"形岩爆坑位置,剪切带与巷道周边切线之间的夹角较大;当扩容角较高时,高剪切应变集中于巷道周边的一些位置上,剪切带与巷道周边切线之间的夹角较小。该研究结果与Roscoe,Arthur理论相符。     

钢纤维混凝土局部增强桥墩抗震性能试验研究

为分析钢纤维体积率、钢纤维混凝土增强区域长度以及配箍率等因素对钢纤维混凝土桥墩抗震性能的影响,对考虑以上三个设计参量的八个桥墩试件进行了低周反复荷载作用下的拟静力试验,并探讨了钢纤维混凝土桥墩试件破坏形态、滞回特性、骨架曲线、延性性能和耗能能力等抗震性能。结果表明：钢纤维体积率为1.0%的桥墩试件较其他体积率的试件承载力更大,滞回曲线相对更加饱满,延性性能更好;钢纤维可以代替部分箍筋作用,在较低配箍率下保持良好的抗震能力;在桥墩潜在塑性铰区域局部合理地采用钢纤维混凝土,可达到与桥墩整体采用钢纤维混凝土相近的极限承载力、刚度、延性和耗能能力。最后提出了简化计算公式用以估算在单柱式桥墩中局部使用钢纤维混凝土的合理长度,并通过试验结果验证了其精度。     

高墩大跨径连续刚构桥抗震性能评估

高墩大跨径连续刚构桥的抗震性能评估既是桥梁抗震研究的热点又是抗震研究的难点。本文根据其特点提出了一种适合于其弹塑性地震响应的分析方法,利用提出的塑性铰单元和已有的有限元程序,实现了对罕遇地震作用下桥梁结构的地震响应模拟。使地震波峰值逐渐增大直至结构破坏,对西部某高墩大跨径连续刚构桥进行了弹塑性地震响应分析,得到了该种桥型的破坏形式、能够承受的最大地震等级等结论,为抗震设计提供参考。     

桥墩不均匀沉降对高速列车运行安全影响研究

针对运营阶段列车循环加载导致软土地基桥梁产生附加不均匀沉降威胁行车安全性问题,分别建立车辆-桥梁动力相互作用模型、桩基础-地基沉降模型。将用动力模型获得列车过桥时支反力时程作为外部激励,利用沉降模型研究列车荷载作用下桩基础的累积沉降规律;将由桥墩沉降产生的附加线形变化叠加到原始轨道不平顺中,考虑由其引起的竖向类离心力影响,用动力模型研究桥墩不均匀沉降对列车行车安全影响。以德国ICE3高速列车及三跨32 m简支梁桥为研究对象进行实例分析,结果表明,软土累积沉降主要发生在桩底约10 m厚土层范围内;相邻桥墩沉降引起的桥梁相对上拱对行车安全更不利。     

高阶振型对高墩桥梁抗震性能的影响及其识别

针对墩高60m、90m 的典型高墩桥梁,运用增量动力分析方法（IDA）和基于基阶振型的非线性静力推倒方法（MPA）     

车辆撞击作用下泡沫铝防撞桥墩的动态响应特性

针对车辆撞击桥墩问题,设计了一种采用泡沫铝材料的桥墩防撞装置.采用LS-DYNA软件分别建立有无防撞装置的桥墩三维实体单元模型,分析了车辆撞击作用下各桥墩的动态时程响应.对比了两种情况下车辆对桥墩的撞击力、桥墩位移和应力等特征参量,并从能量传递的角度分析了泡沫铝防撞装置的耗能能力和撞击车辆损伤.结果表明:采用泡沫铝防撞...     

Construction of Benten Viaduct,rigid-frame bridge with seismic isolators at the foot of piers

`Benten Viaduct' is one of the reconstructed bridges of Hanshin Expressway Route 3, which suffered a significant damage during the Hanshin/Awaji Earthquake in 1995. This section had consisted of 8 bridges before the earthquake, but revived as an innovative structure, 19-span continuous rigid-frame bridge with seismic isolators installed underneath the steel piers. This paper reports the seismic isolation design and construction techniques of this innovative bridge structure, comparing the result of analysis with that of the vibration test using the actual bridge structure.     

基于结构响应极值前四阶矩的桥墩抗震可靠度

为研究桥墩非线性地震响应下的抗震可靠度,引入随机函数-谱表示模型与高阶矩法,提出了基于结构响应极值前四阶矩的桥墩抗震可靠度分析方法。考虑三线型恢复力模型,建立了桥墩的单墩模型;利用随机函数-谱表示模型生成非平稳地震加速度时程样本并对桥墩进行非线性时程分析,在此基础上,建立了结构响应极值前四阶矩(均值,标准差,偏度和峰度)的计算框架;最后,考虑桥墩位移界限,给出了桥墩位移的功能函数,进而利用高阶矩法计算桥墩抗震可靠指标。通过对桥墩结构分析,验证了该方法的高效性与精确性;计算结果表明:与Monte Carlo模拟结果相比,该方法计算的前四阶矩、抗震可靠指标(失效概率)的最大相对误差分别为0.28%,1.92%(4.92%),该方法为桥墩抗震可靠度评估提供了一种有效的途径。     

TFT光刻平面倾斜对光刻图形的影响及改善

薄膜晶体管光刻制程中,光刻胶光刻平面位置是决定光刻图形质量的关键因素。为了在光刻机最小分辨率条件下改善光刻图形质量,本文从光刻胶内反射光线的反射特点出发,以减小光刻胶内反射光线对非光刻区域的光刻光强及增加光刻区域的光刻胶底部光刻光强为基础,推导出光刻光线倾斜入射光刻胶平面时,光刻胶光刻平面位置调整量的计算公式,并以该公式计算出的调整量对光刻胶光刻平面进行调整。结果表明：对于最小分辨率为3.0 μm的投影光刻机,进行线间距为2.2 μm的产品光刻时,以该公式计算出的调整量对光刻胶光刻平面调整后,较未调整前,光刻图形坡度角提升了13.3%,光刻胶线宽或线间距宽度(DICD)均一性改善了14.7%,光刻图形光刻胶残留得到解决。     

春季河冰流凌对桥墩撞击作用计算模型的研究

采用LS-DYNA显示动力分析软件就流冰对桥墩撞击力的计算机仿真模型进行了研究。提出了河冰的简化本构关系模型;建立了桥墩与流冰接触撞击的有限元分析模型。探讨了接触类型与算法、冰排网格密度、接触区域桥墩网格密度对桥墩撞击力计算结果的影响,并与实测结果进行了对比。得出如下结论：流冰及接触区域的桥墩可采用solid164单元;河冰材料可采用线弹性模型,最大拉应力失效准则;ASTS自动面面接触类型及对称罚函数接触算法就流冰对桥墩撞击力模型是适合的;与桥墩接触的近区冰排单元大小及接触区域桥墩网格密度对撞击力均有较大影响,应注意单元尺寸的合理选择。研究结果为流冰对桥墩撞击力的计算提供了新的方法,对完善流冰撞击力的计算方法具有理论价值及现实意义     

Effectiveness of combinations of raft foundation with aprons as a protection measure against bridge pier scour

Scour around bridge pier is the main reason for the failure of bridges. The local scour around the pier causes exposure of the foundation and may lead to undermining of the structure. Different types of protection measures such as the provision of raft, apron, sheet piles, etc. can be used as scour protection measures. One of the possible effective bridge scour protection measures is to provide a raft foundation with cut-off walls and provision of flexible stone aprons towards upstream (u/s) and downstream (d/s) sides of the pier. In this study, the effectiveness of various bridge pier scour protection measures using raft and aprons is investigated through hydraulic model studies in the laboratory. The results are compared for various cases, such as a simple pier, pier with raft and extended raft, pier resting on a raft with stone aprons at u/s and d/s of the raft and pier resting on an extended raft with stone aprons on u/s and d/s of it. The comparison of various cases showed that rigid raft with stone aprons on u/s and d/s and extended raft with apron are found to be more effective in reducing immediate scour beyond the rigid raft, thereby giving protection to the bridge piers.