液化场地桥梁群桩基抗震分析简化方法

基于已完成的液化场地土—桩—桥梁结构地震相互作用振动台试验,利用两步法、等效单桩法,建立了液化场地群桩基础抗震分析的动力非线性文克尔地基梁模型。该模型考虑了桩—土相互作用的影响。首先,按照等刚度原则将群桩简化为等效单桩;其次,选用弹簧元件和阻尼原件并联的宏单元模拟桩—土动力相互作用;然后,计算地震作用下自由场地的土体位移和孔压比;最后,将地震作用下自由场地土体位移和孔压比作为模型的外部激励,计算桩的动力反应规律。将简化方法计算结果与液化场地桥梁桩基振动台试验结果进行对比发现,两者吻合较好,验证了简化方法的正确性。     

Experimental study of a highway bridge with shape memory alloy restrainers focusing on the mitigation of unseating and pounding

This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechanical property tests of the SMA wire used in the restrainers are conducted first to understand the pseudo-elastic characteristics of the material.Then,a series of shaking table tests are carried out on a highway bridge model.The structural responses of the highway bridge model equipped with SMA restrainers,installed in the form of deck-deck and deck-pile connections,are analyzed and compared with the uncontrolled structures.The test results of this study indicate that the SMA restrainers are not only effective in preventing unseating but also in suppressing the seismic-induced pounding of the highway bridge model used in this study.     

直剪条件下非贯通节理岩体岩桥力学性质弱化机制及贯通模型初步研究

通过非贯通节理岩体直剪试验的力学特点和理论分析,修正了Lajtai岩桥张拉破坏理论。通过非贯通节理岩体直剪试验中岩桥的应力状态,提出岩桥内部的张拉破坏使岩桥力学性质发生弱化,并进一步分析研究了力学性质可能弱化的区域。分析非贯通节理岩体扩展贯通过程,提出了非贯通节理岩体的贯通破坏模式。通过非贯通节理岩体直剪试验初步验证了修正的岩桥张拉破坏理论和贯通破坏模式。     

软土地区小桥涵桥台路基沉降拟合处理方法

软土地区桥台与桥涵之间产生较大的差异沉降, 影响使用.提出采用沉降拟合方法, 即根据复合地基的设计思想, 通过在桥台与桥涵部位采用不同置换率, 调整沉降量, 使其相近, 以达到减少沉降差的目的.      

中日规范中关于液化和侧向扩流场地桥梁桩基抗震设计考虑之比较

评述了我国液化场地和侧向扩流场地桥梁桩基抗震设计规范。总结了中日两国液化场地和侧向扩流场地桥梁桩基的抗震设计方法与技术细节,阐述了日本规范中液化场地和侧向扩流场地桥梁桩基抗震设计中的液化地基土反力折减系数的确定方法,以及土体液化侧向扩流对桩作用力的计算模式。指出我国规范中在液化和侧向扩流场地桩的抗震分析方法、不同土层分界处桩的抗震措施、桩的竖向承载力及桩的屈曲稳定性分析等方面存在的主要问题,据此给出了亟待改进的初步建议。这对我国桥梁工程的抗震安全性具有重要意义,可供我国工程技术人员参考借鉴。     

Effects of engineering geological condition on response of suspension bridges

The geological condition may vary largely from one support to another for a long span bridge. The effect of geological variability and spatial variation produced by propagation and coherence loss of seismic ground motion on the response of long span suspension bridges is investigated in this article. The case of Jiangyin Yangtse River Bridge, a suspension bridge with a main span of 1385 m, is studied in detail. Numerical results show that the geological difference at the supports has a significant effect on the seismic response of long span suspension bridges and, that it is unacceptable to neglect the difference. The effect of the propagation of seismic ground motion on the response of long span suspension bridges is far more important than that of the coherence loss. The response of bridges varies greatly with the horizontal apparent velocity in a very complex way, and there is a critical horizontal velocity for a given response quantity.     

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。     

山西吕梁山北段中生代构造特征及对成矿的制约

为进一步研究山西吕梁山北段中生代构造特征及对成矿的制约,利用数字化填图方法,在偏关县一带开展1:25万区域地质调查。发现几条中生代大型构造带,查明了这些大型构造带的空间展布、性质、断裂组合及运动学特征; 证实了中生代为该区重要的多金属成矿期,成矿作用尽管与中生代岩浆活动关系密切,但在空间上分布受NE向隐伏构造的制约; 大型挠褶构造是地壳强烈隆升的标志,区内大型构造带多数是在挠褶构造的基础上叠加断层而形成的。该研究对于探讨山西中—新生代构造的演化发展具有重要意义。     

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.