一种免标靶桥梁挠度仪校准方法

采用自行研制的桥梁挠度仪自动校准装置对一种新型免标靶视频桥梁挠度仪竖向、横向挠度误差进行校准,并对校准结果进行分析,为桥梁挠度仪计量校准提供参考,具有很强的现实指导意义。     

桥梁应变与挠度动力放大系数的大小关系研究

比较了简支梁桥和连续梁桥的应变和挠度动力放大系数的大小关系。首先对作用有移动常量力的简支梁和连续梁进行理论推导,分别得到了应变和挠度动力放大系数并进行了比较。为考虑动力车辆荷载影响,采用移动弹簧质量作为车辆模型建立了车桥耦合振动模型进行数值模拟。理论推导和数值模拟的结果均表明:应变动力放大系数基本小于挠度动力放大系数;两者比值受很多因素影响,其中计算桥梁响应所用的桥梁模态阶数对比值的影响较大。     

桥梁动态挠度测量与实测曲线分析

桥梁动态挠度是评价桥梁综合性能的重要参数。《桥梁动态位移测量系统》直接测出军用桥梁的竖向,横向动态挠度,从而能够对整桥梁的质量进行评价。     

浅析对预应力混凝土连续箱梁桥裂缝控制

预应力混凝土箱梁桥因其具有更多优点而在桥梁建设中得到广泛应用,但由于各种因素影响,预应力连续箱梁桥出现了不同病害,其中裂缝是其中最重要一种。加强对预应力连续箱梁桥裂缝的控制,对提高桥梁使用安全和使用寿命具有重要意义。本文首先分析了预应力混凝土连续箱梁桥的特点,随后对影响梁桥裂缝成因进行分析,最后提出了对梁桥裂缝修补策略。     

预应力混凝土梁变幅疲劳性能试验研究

对后张法预应力混凝土梁进行多级疲劳荷载循环试验,分析预应力混凝土梁在疲劳荷载下的裂缝开展情况及梁体刚度退化情况,推导预应力混凝土梁疲劳刚度退化方程,编制疲劳挠度计算程序。结果表明：未达开裂荷载水平时,预应力混凝土梁在疲劳循环荷载下亦出现裂缝,且裂缝出现时间与应力水平有关;梁体刚度在疲劳荷载循环的前15万次中降低幅度较大,之后呈稳定降低趋势;疲劳试验梁静载挠度在静载破坏试验开裂前较静载梁大;但随荷载增大,静载梁裂缝发展较完全;后两者挠度较接近,疲劳梁破坏时挠度较静载梁大20%;基于刚度退化方程的疲劳挠度计算程序结果与实验值吻合较好,可用于计算、预测疲劳挠度。     

变速移动荷载作用下简支梁桥的动力响应及共振分析

基于振型叠加原理,采用广义坐标变换的方式建立了移动荷载匀变速通过简支梁桥时系统的动力平衡微分方程并编写了分析程序。以某3×32 m铁路多跨简支箱梁桥为例,计算得到车辆匀速运行时桥梁最大挠度随车速的变化曲线,选取曲线上的代表值点进一步计算,并从车桥共振的角度详细分析了桥梁最大挠度的变化趋势以及车辆变速运行对桥梁最大挠度的影响。     

基于附加质量块的桥梁模态挠度预测方法研究EI北大核心CSCD

以16 m跨径空心板单梁为研究对象,研究基于附加质量块的质量归一化方法和模态柔度法测试预测桥梁模态挠度的准确性和工程可行性。基于环境激励测试16 m单梁在施加质量块前后的模态参数,提出包含相对频率改变平方项的振型质量归一化计算方法,预测单梁在多级竖向静力荷载作用下的模态挠度,将模态挠度与实测静挠度进行比较,研究8种附加质量工况下单梁模态挠度的测试预测精度,分析附加质量占比以及质量块的数量对预测精度的影响,分析传感器数量对模态挠度预测精度的影响。结果表明,在环境激励下,5个传感器与8个传感器模态挠度预测精度基本一致,满足工程精度要求;基于附加质量块预测的模态挠度可代替实测弹性静挠度,进而评估桥梁的实际刚度状态;附加质量块质量占梁体总质量约10%时,模态挠度的预测相对误差小于8%,预测精度较高。在实际工程应用中,可适用于其他跨径桥梁;在附加质量块占比相同的情况下,多个小质量快的模态挠度预测精度优于大质量块;仅利用单梁前两阶竖向模态即可获得较精确的模态挠度。     

基于转角数据的梁式桥挠度响应重构方法

挠度是评估桥梁安全性能的重要参数,对桥梁挠度的精确测量是桥梁健康监测领域的研究热点。提出一种基于桥梁转角进行响应重构的挠度测试方法,可利用桥跨合适测点位置处转角数据准确重构邻近梁段截面的挠度响应。根据桥梁几何参数和荷载位置信息建立挠度响应与转角响应之间关联,结合实测转角响应识别中间变量,以此计算桥梁挠度响应信息,实现由转角测点数据重构桥梁挠度响应。开展数值仿真和模型试验,研究表明基于转角数据重构的挠度响应与实际挠度响应高度一致;另一方面该方法结合荷载信息和桥梁几何参数,基于单个转角响应即可重构挠度响应,具有较好的实用性。     

一种便携式桥梁挠度检测复用系统的研制

针对桥梁挠度检测的特点,提出了一种基于嵌入式仪器技术的可以采用两种传感器件采集不同信号实现复用桥梁挠度检测系统的实现方案。介绍了系统传感器的选型原则和所选择信号采集器件的特性,以高速ARM9芯片为核心实现了硬件电路设计。并具体介绍了最小平方卷积反演对挠度信号进行恢复的数据算法原理和其快速嵌入式程序软件的实现。     

浅谈现浇箱梁施工支架设计

AKO+224驷马互通A匝道桥桥梁总长:208m,桥梁宽:8.5m,本桥最高墩柱高度为24.6米,梁高为1.4m,上部结构采用(29+22+3×20)+(5×20)m钢筋混凝土现浇箱梁。本文介绍了现浇箱梁满堂支架的设计,并对支架底模、横梁、纵梁强度、立杆受力、支架压缩变形及地基承载力等进行了验算。     

发动机热端部件电子束焊修复接头的高温疲劳裂纹扩展行为

研究了力学不均匀性对电子束焊接修复接头疲劳裂纹扩展行为的影响规律，结果表明，由于力学不均匀性的影响，位于修复法接头焊缝和热潮影响区的疲劳裂纹垧母材偏转扩展，力学不均匀性与裂纹偏转导致裂纹扩展的驱动力下降，使得焊接区的表现疲劳裂纹扩展速率低于母材。     

Fatigue and fracture paths in cold drawn pearlitic steel

This paper analyses the influence of microstructural anisotropy of a progressively drawn pearlitic steel (orientation of pearlitic lamellae in the drawing direction) on the microscopic and macroscopic evolution of cracking paths produced by fatigue and fracture. The fatigue crack path is always contained in the transverse section of the wires, i.e., the subcritical propagation develops under a global mode I, so that the main crack path is associated with mode I and some very local deflections take place to produce a roughness in the fatigue crack path depending on the drawing level. The fracture crack path evolves from a global mode I propagation following the transverse plane in slightly drawn steels (including the hot rolled bar that is not cold drawn at all) to a global mixed-mode propagation associated with crack deflection in intermediate and heavily drawn steels (the latter with a strong mode II component), the deviation angle being an increasing function of the drawing degree in the steel.     

Monitoring and analysis of cast-in-place concrete bored piles adjacent to deep excavation by using BOTDA sensing technology

In order to monitor the deflection of bored piles, BOTDA sensing technology is employed to measure the strain and temperature profiles along three bored piles adjacent to a deep excavation. Based on the measured strain, the deflections can be calculated according to the mechanics of materials. Comparison between the deflections measured by traditional inclinometer and strain based measurement method has been fully conducted. A two-dimensional FEM model was constructed to simulate the interaction between excavation and subway tunnel and examine the deflection of the three bored piles during progressive excavation. Finally, the deflection profiles calculated from measured strains and simulated by FEM are comprehensively summarized and analysed. It can be found that the deflection changing trend at the top of the bored piles are consistent with the simulation results with acceptable errors while the deflection calculated from the measure strains has a significant discrepancy with the simulation results.     

基于倾角仪测试铁路桥梁静态挠度

桥梁挠度测量是桥梁检测的重要组成部分和安全性评价的一项重要指标。随着铁路桥梁设计跨度逐步增大、桥梁主跨下面为江流等因素,传统的静态挠度测试法如水准仪等不再适合测试大跨度桥梁的静态挠度,该文利用QY倾角仪测量了焦柳铁路线上的融水大桥第3跨的静态挠度。测试结果表明:倾角仪测得的静态挠度值与水准仪测得值相差较小,其挠度曲线也相似于有限元分析所得挠度曲线,可适用于大跨度铁路桥梁的静态挠度测试。     

Crack deflection in ceramic composites and fiber coating design criteria

It is widely understood that the remarkable toughnesses demonstrated by some ceramic composites are dependent upon deflection of matrix cracks into fiber/matrix interfacial cracks. Carbon and BN fiber coatings are ideally suited for promotion of such crack deflection, but have the unfortunate weakness of limited oxidation resistance. The rational design of oxidation-resistant alternative fiber coatings is facilitated by consideration of the details of crack deflection, growth of interfacial cracks, and subsequent sliding along the interfacial crack surface. This work discusses some of these details and the implications regarding the design and testing of alternative fiber coating systems.     

Ermüdungsrißausbreitung bei gleichphasiger Mixed-Mode I+II Belastung

Fatigue crack propagation under in phase mixed mode I+II loading Stress intensity factors of kinked cracks are calculated by using the boundary-element-method (BEM). The results are compared to some analytical solutions. Referred to the crack deflection angles. The results of BEM calculation agree well with NUISMER's criterion and in addition with the experimental results. The growth rates of kinked cracks are compared to purely mode I loaded cracks. At R = 0.6 the crack growth rates don't show any difference. At R = 0.1 the angled cracks show slower growth rates. The reason is a significant -induced crack closure. When referring the crack growth rates to ΔK_eff, there is almost no difference between the propagation rates of angled cracks and straight cracks. This is in good agreement with the results, achieved at R = 0.6.     

颗粒和微观结构对Cu/WCp复合材料疲劳裂纹萌生和扩展行为的影响

通过原位扫描电子显微镜(SEM)研究了粉末冶金制备的Cu/WCp复合材料的疲劳裂纹萌生和扩展行为,分析了颗粒和微观结构对Cu/WCp复合材料疲劳裂纹萌生和早期扩展行为的影响。结果表明:疲劳微裂纹萌生于WCp颗粒和基体Cu的界面;微裂纹之间相互连接并形成主裂纹,当主裂纹和颗粒相遇时裂纹沿着颗粒界面扩展。在低应力强度因子幅ΔK区域疲劳小裂纹具有明显的"异常现象",并占据了全寿命的71%左右。疲劳小裂纹的早期扩展阶段易受局部微观结构和颗粒WCp的影响,扩展速率波动性较大,随机性较强;当小裂纹长度超过150μm时,裂纹扩展加快直至试样快速断裂。裂纹偏折、分叉和塑性尾迹降低了疲劳裂纹扩展速率,而颗粒界面脱粘则提高了复合材料的疲劳裂纹扩展速率。通过数值模拟也可以发现颗粒脱粘增大了材料的疲劳扩展驱动力,从而提高了疲劳裂纹扩展速率。     

Aspects of rapid crack propagation in silicon

Fracture experiments with silicon specimens in recent years have shown the need for a new approach to the analysis of rapidly propagating cracks in single crystals. Behaviour and phenomena have been revealed that fracture in these materials is rather different from the fracture of both amorphous and polycrystalline materials. We show that continuum mechanics is insufficient for analyzing crack propagation in single crystals since it is unable to consider atomistic‐scale phenomena. Accordingly, we describe basic phenomena associated with rapid crack propagation in silicon : (i) anisotropic velocity‐dependent R‐curve behaviour, as a key phenomenon dictating atomistic scale behaviour, (ii) crack deflection from one cleavage plane to another as a mesoscopic scale phenomenon in single‐crystal fracture, (iii) the Rayleigh surface wave speed as the limiting crack tip velocity is re‐examined, (vi) the lowest crack velocity in brittle crystals is examined, and finally (v) the interaction between crack path and preferred cleavage planes in single crystals is depicted.     

Precise 3D crack growth simulations

The continuous growth of 3D cracks under cyclic loading conditions is considered within a discrete simulation procedure. It is performed within the framework of linear elastic fracture mechanics. An incremental procedure is applied to consider the non-linear behavior of crack growth within the simulation. In each increment the direction and magnitude of the crack propagation for each point along the crack front are needed to define the new crack front. Within the present context the crack deflection results from the maximum tangential stress criterion and the crack extension is obtained by the evaluation of a crack propagation rate. To simulate the crack propagation as exactly as possible the evolution of the stress field between two consecutive crack fronts is taken into account. The analysis of the changing stress field is utilized for optimization of the predicted crack fronts. The whole procedure is realized in terms of a predictor–corrector scheme. Numerical examples are presented to demonstrate the benefits of this concept.     

1年持续载荷下GFRP-混凝土组合梁长期性能试验

玻璃纤维增强树脂(GFRP)-混凝土组合梁由上部混凝土板和下部GFRP型材以及连接二者的抗剪连接件组成。开展了2根GFRP-混凝土组合梁(非预应力及施加体外预应力组合梁各1根)在1年持续载荷下行为的试验研究。考虑混凝土收缩徐变及GFRP型材蠕变耦合的影响,开展了50年的24根GFRP-混凝土组合梁时随有限元参数分析。结果表明:在1年持续载荷下,非预应力与施加体外预应力组合梁长期挠度分别为其初始挠度的1.42倍及2.91倍;非预应力与预应力组合梁中连接件的长期滑移分别为0.230 mm及0.164 mm,相比初始滑移2种组合梁的最终滑移分别增加了53.3%和58.2%;50年后,非预应力组合梁长期挠度与初始挠度的比值在1.50~1.56之间;而施加体外预应力组合梁长期挠度与初始挠度的比值在3.03~6.08之间。基于以上研究提出了GFRP-混凝土组合梁长期挠度的计算建议。