Application of the structural articulation method to dynamic impact loading of railway bridges – a case study

This article demonstrates a practical application of the structural articulation method. An existing prototype railway bridge was selected to compare our new method with the industry codes of practice. The response history and dynamic increment of the bridge were investigated through a variety of methods: lump sum mass analysis (LSMA) and suspension system analysis (SSA) for a single-axle force, and SSA for multi-axle forces. We considered both a local irregularity and a global sinusoidal irregularity. The dynamic impact load induced by either form of track irregularity increases approximately linearly with the vehicle speed up to a certain point, then tends to decrease gradually. This behaviour reveals that the dynamic impact load induced by track irregularities is dominated by the resonance of the bridge. If a bridge must support multiple axles, or if an especially accurate dynamic impact factor is required for safety reasons, then multi-axle SSA is recommended because this approach is the most accurate and likely to produce a weaker response than single-axle analysis. The random irregularity is generated by the stochastic track irregularity process. It is found that the dynamic impact load induced by the random irregularity is negligible, compared with the deterministic irregularity.     

Structural analysis of 3D high-speed train–bridge interactions for simple train load models

Three-dimensional models are developed for analysing the dynamic interaction that occurs between high-speed trains and bridges. The reliability and accuracy of developed models are verified by comparing the results from analysing field tests on high-speed trains. A number of train load models are proposed and their performances are compared in order to identify possible models that would reduce the computational and modelling efforts while maintaining suitable accuracy. The results show that at least 16 cars out of a 20-car train should be modelled to achieve results that are comparable to those obtained using the highly detailed 20-car model. Regarding the simplified train load model, more accurate results are obtained employing the 3D moving vehicle model for power cars, the heaviest cars of a high-speed trainset, and a moving force model for other cars, power passenger cars, and passenger cars, compared with highly detailed 20-car model.     

气动载荷下高速列车车体焊接结构疲劳寿命预测

随着列车速度的不断提高,列车与空气的相互作用成为一个备受关注的问题.从可靠性的要求出发,将数值模拟计算结果与试验结果进行了对比,验证了模拟计算的可靠性.在此基础上采用流固耦合技术实现了实际计算载荷与有限元模型的耦合.并对耦合后的某车体焊接结构应用焊缝疲劳寿命预测的新方法——主S-N曲线法,对关键焊缝进行了焊缝疲劳寿命预测.为车体焊接结构的进一步设计提供参考.     

大跨度钢桁斜拉桥上无缝线路制动力的计算

为探讨大跨度钢桁斜拉桥上无缝线路制动力的传力机制,基于有限元法和梁轨相互作用理论,建立了反映斜拉索、主塔、半漂浮体系等桥梁特征的梁轨纵向相互作用平面模型,分析了斜拉索刚度、主塔刚度以及半漂浮体系中粘滞阻尼器对制动力的影响,并提出了制动力的简化算法.研究结果表明:制动力满足斜拉桥上铺设无缝线路的要求,且其分布规律与普通桥上相同;粘滞阻尼器对制动荷载下斜拉桥上无缝线路梁轨相互作用的改善较明显,有效降低了梁轨相对位移,减小了制动力;与主塔刚度相比,斜拉索刚度对桥上无缝线路制动力的影响较大,因此,设计桥上无缝线路时,可只考虑斜拉索刚度的影响.     

埋置波纹钢板管涵刚度对其受力性能的影响

为了分析埋置波纹钢板管涵结构的刚柔性及对整体受力性能的影响,建立了考虑土-结相互作用的有限元模型,在其他参数不变的条件下,改变波纹钢板的波形和厚度,分别计算和对比管涵内力、变形及土体变形,分析各种截面类型下波纹钢管涵的刚柔性,并研究各种情况下管涵内力、变形和土体变形分布的特点.结果表明：波纹钢板的截面特性参数改变会导致管涵结构刚柔性的改变;波纹钢板截面刚度的增大,使管涵的变形减小,导致管涵结构受到的土压力增大和管涵的应力增大;应平衡结构的应力和变形,合理选择波纹钢板的截面形式.     

高职学生英语课堂互动心理障碍及应对策略

运用心理学相关理论,从教师和学生两个方面分析了高职学生在英语课堂互动中产生心理障碍的因素,并针对这些因素提出了应对策略,指出应在以下几方面对高职英语课堂教学进行进一步的改革：教师应转变教学理念、为学生创造表现空间、调动学生的积极性、激发学生的学习动机以及增加小组合作的机会,以期消除学生心理障碍,使学生在真正意义上获得用英语进行交际的能力,从而培养具备实际英语应用能力的高职高专人才。     

CXCL12/CXCR4轴在胰腺癌-神经交互作用中的研究

目的本研究旨在阐述CXCLl2/CXCR4轴对胰腺癌神经相互作用的影响,探讨CXCLl2/CXCR4在胰腺癌嗜神经过程中的相关分子机制。方法体外培养胰腺癌Panc-1、Miapaca-2细胞,实验分为空白对照组、外源性CXCLl2组及CXCR4受体特异性阻断剂AMD3100组。采用RT-PCR检测胰腺癌细胞CXCR4及CXCL12mRNA的表达,检测基质金属蛋白酶-2(matrix metalloproteinase-2,MMP-2)、基质金属蛋白酶-9(matrix metalloproteinase-9,MMP-9)及人尿激酶型纤溶酶原激活物(human urokinase plasminogen activator,uPA)mRNA的表达;采用Transwell侵袭实验观察各实验组中细胞侵袭性的变化;提取大乳鼠脊髓背根神经节,建立胰腺癌细胞Miapaca-2与脊髓背根神经节(DRG)共培养模型,倒置显微镜成像系统动态观察不同实验组中神经轴突生长差异。结果胰腺癌细胞Panc-1、Miapaca-2细胞存在CXCR4mRNA的表达,而CXCL12mRNA无表达;两种胰腺癌细胞之MMP-2、MMP-9及uPAmRNA在AMD3100组、对照组、CXCLl2组中的表达差异具有统计学意义(P<0.01);Transwell细胞侵袭性实验中,外源性CXCLl2明显增强Panc-1、Miapaca-2细胞的侵袭性,而AMD3100有效抑制肿瘤细胞的侵袭能力,组间存在显著差异(P<0.05)。胰腺癌细胞与脊髓背根神经节共培养模型中,外源性CXCLl2明显增强神经轴突的生长,促使胰腺癌细胞与神经轴突接触,而AMD3100有效抑制神经轴突生长及与肿瘤细胞接触;细胞共培养144h后各组神经生长轴突数差异有统计学意义(P<0.01)。结论 CXCLl2/CXCR4一方面增强胰腺癌细胞的侵袭能力,促进胰腺癌细胞神经浸润;另一方面,神经元与施万细胞等构成神经纤维分泌CXCL12并通过化学趋化作用,诱导表达CXCR4的胰腺癌细胞向神经迁移,导致神经浸润的发生。     

基于空间引力模型的选址问题研究

由于空间的相互作用对人流量的影响,引入引力模型来估计用户流量的大小。与传统选址不同,考虑了两种类型的需求,一类是产生于固定点的需求,另一类是产生于交通网络上的需求,分析了这两类需求对设施的不同的影响程度时的选址决策。结合最大覆盖模型和截流模型,建立了0-1整数规划模型,给出了启发式算法,同时给出了该算法在最差情况下的界限,并通过实例,将启发式算法与精确解进行比较。     

由单桩载荷试验预测水平受荷群桩的非线性变形

将桩假定为相互作用的非线性弹簧,使用双曲线函数或幂函数拟合试桩的荷载-位移曲线,并用来模拟桩和土的非线性关系。使用相互作用系数的方法分析桩-桩之间的相互作用,并且给出了计算桩-桩相互作用系数的理论公式,从而简化了相互作用系数的计算过程。与现场水平受荷群桩的试验结果进行对比,结果表明,该简化分析方法可以较好地预测水平受荷群桩的非线性变形,理论预测结果与实测结果较为吻合。由于将桩假定为相互作用的非线性弹簧,避免了对桩进行单元划分,从而大大减少了群桩变形的分析时间。该简化方法特别适用于大规模水平受荷群桩的变形分析。