Finite element model for arch bridge vibration dynamics considering effect of suspender length adjustment on geometry stiffness matrix

1 Introduction When librating with small amplitude, the discrete linearization freedom vibration equation of a structure is [1]: [m ] {x } [k ]{ x } = {0 } (1) The relevant vibration characteristic question is ([ k ] ? p 2[ m] ){φ } = {0} (2) where [m]…     

建筑垃圾资源化利用新技术及产业链构思

本文从建筑垃圾的基本概念入手,阐明了建筑垃圾的资源化利用的重大意义、国内外建筑垃圾的处理利用现状,以及从现有处理利用产品系列到房屋和道路的地基基础工程应用的新技术,并对建筑垃圾处理产业链问题加以深入思考,展现了建筑垃圾的资源化利用的广阔前景。     

H型钢梁柱外伸端板螺栓连接节点的性能研究

根据H型钢梁柱外伸端板螺栓连接节点的简化力学模型，提出用节点尺寸来计算节点初始转动刚度Ri的计算公式，通过与试验结果比较，验证了初始转动刚度Ri的计算公式的正确性；并对节点的破坏形式、抗震性能及影响节点初始转动刚度的因素进行了分析讨论。     

Time-course of running treadmill adaptation in novice treadmill runners

ABSTRACT

Studies on running biomechanics and energetics are usually conducted on a treadmill. To ensure that locomotion on a treadmill is comparable to locomotion overground, participants need to be expert in the use of the device. This study aimed to identify the number and duration of sessions needed to obtain stable measurements for spatiotemporal and metabolic parameters in unexperienced treadmill runners. Fourteen male recreational runners performed three 15-min treadmill running trials in different days at a submaximal speed. Spatiotemporal and metabolic parameters were registered at minutes: 5, 10, 15 and their within-trial and between-trial changes were analysed using a two-way repeated measures ANOVA and Bonferroni post-hoc test. Within-trial differences were found in step frequency (decreased over time), Step Length and Contact Time (increased), reaching stability at different time points. Ventilator parameters increased, reaching stability after 5–10 min, while heart rate increased progressively over time. The only between-trial differences were an increase in step length and a decrease in step frequency at min 1, between trials 1 and 3. In conclusion, at least three running trials of 15 min are required to familiarize with the device. The last 5 min of the third trial can be regarded as stable measurements.     

车削螺纹时发生“啃刀”现象的分析

车削螺纹时发生的＂啃刀＂现象,其主要原因是：刀架部件刚度变化;加工硬化和小滑板产生了爬行。防止产生此现象的方法是：调整中、小滑板的塞铁间隙;保持车刀刃口的锋利以减小加工硬化程度,同时可在车刀前刀面上磨出圆弧和预防＂爬行＂产生。     

基于刚度的框架结构抗震能力评估简化方法(英文)

针对结构物在地震作用下的灾害评估问题,提出了一种基于刚度退化概念的框架结构整体与层间损伤指标.该指标通过结构静力弹塑性分析方法进行计算,利用塑性铰考虑结构的地震损伤.同时,根据能力谱方法建立了该损伤指标与抗震设防等级的关系.然后,将建议指标应用于2个3层钢筋混凝土框架结构,并与其他损伤指标进行了对比.结果表明:建议的损伤指标偏于安全,且对静力弹塑性分析的水平荷载模式不敏感;层间损伤指标能够清晰地反映各楼层的损伤情况,从而判断薄弱层的位置.最后,通过统计分析给出了结构不同性能水准与损伤指标的对应关系,为基于性能的框架结构抗震评估提供参考.     

道岔竖向刚度不均匀分析及在线检测研究

轨道竖向刚度不均匀是道岔的主要缺陷之一。文章通过应用有限元方法对道岔区轨道竖向刚度不均匀进行分析,探讨道岔区轨道竖向刚度不均匀对列车运行舒适性和安全运营的影响,研究控制平顺的必要性,进一步探讨提出相应的在线检测方法。     

Dynamic stiffness for thin-walled structures by power series

INTRODUCTION Thin-walled structures have considerable tech-nological importance in many situations of engi-neering practice. The rotary and warping inertia terms should be considered in the analyses of thin-walled structures (Alwis and Wang, 1996), although it is difficult to obtain the analytical solutions of govern-ing differential equations, especially of thin-walled frame and spatial twisted structure. The finite element method (FEM) is widely used for vibration and sta-bility analy…     

Perception of self-selected running speed is influenced by the treadmill but not footwear

In this study, we examined whether self-selected overground running speed was consistent (1) with perceived overground speed on the treadmill and (2) among barefoot and three footwear conditions. Participants ran across a 20-m runway 10 times for each overground condition, with running speed calculated from kinematic data. For the treadmill condition, the participants were instructed to run at a speed that felt similar to their overground speed. This treadmill speed was chosen upon perception, with the display covered from the participant's view. Repeated-measures analysis of variance was used to detect differences in speed between overground and treadmill running, and also among barefoot and footwear conditions. Coefficient alpha (α) was calculated to determine repeatability of observations in each overground condition. The speed was higher during overground (3.65 ± 0.40 m/s) than treadmill (2.25 ± 0.75 m/s) running but did not differ among the barefoot and the three footwear conditions. Overall, overground speed was highly repeatable within an individual (α = 0.96–0.98). Researchers might consider using self-selected speed when investigating overground running mechanics with different foot–ground interface conditions. The influence of treadmill on the perception of speed may be related to shear force, running duration, joint load control, and/or other psychological factors.     

基于边界摩擦的碟簧隔振器力学性能(英文)

为研究边界摩擦对碟簧隔振器力学性能的影响,基于能量守恒定律推导了在考虑边界摩擦时碟簧隔振器的载荷位移迟滞曲线公式.通过有限元分析与静载试验验证了该公式的正确性.在此基础上研究了边界摩擦对碟簧隔振器承载能力的影响,并通过动载试验研究了边界摩擦对碟簧隔振器的动态性能的影响.试验结果表明:边界摩擦可提供较大的阻尼,使得碟簧隔振器具有良好的阻尼特性,其阻尼比可达0.23;隔振器的耗能、动刚度和阻尼特性对加载幅值更为敏感,而对加载频率敏感度较小.该研究成果对碟簧隔振器设计具有重要的指导意义.