基于小波理论的悬臂梁裂纹定位研究

利用小波多分辨率分析,对含裂纹悬臂梁的裂纹进行定位研究,数值算例表明:多分辨率分析的高频重构部分的系数峰值清楚地指示出裂纹位置,并对不同消失矩的小波的识别效果进行了比较,发现如果只是进行裂纹定位,低阶消失矩的小波的指示效果更好。     

Crack detection of the cantilever beam using new triple hybrid algorithms based on Particle Swarm Optimization

The presence of cracks in a concrete structure reduces its performance and increases in the size of cracks result in the failure of the structure. Therefore, the accurate determination of crack characteristics, such as location and depth, is one of the key engineering issues for assessment of the reliability of structures. This paper deals with the inverse analysis of the crack detection problems using triple hybrid algorithms based on Particle Swarm Optimization (PSO); these hybrids are Particle Swarm Optimization-Genetic Algorithm-Firefly Algorithm (PSO-GA-FA), Particle Swarm Optimization-Grey Wolf Optimization-Firefly Algorithm (PSO-GWO-FA), and Particle Swarm Optimization-Genetic Algorithm-Grey Wolf Optimization (PSO-GA-GWO). A strong correlation exists between the changes in the natural frequency of a concrete beam and the crack parameters. Thus, the location and depth of a crack in a beam can be predicted by measuring its natural frequency. Hence, the measured natural frequency can be used as the input parameter of the algorithm. In this paper, this is applied to identify crack location and depth in a cantilever beam using the new hybrid algorithms. The results show that among the proposed triple hybrid algorithms, the PSO-GA-FA and PSO-GWO-FA algorithms are much more effective than PSO-GA-GWO algorithm for the crack detection.     

筒仓间框架悬挑梁施工方法

结合具体工程实例,通过筒仓间悬挑梁的施工方案的对比,经验算后选择了支撑平台形式,介绍了支撑平台的搭设和拆除方式,以完善筒仓间框架悬挑梁施工工艺,保证工程施工的质量。     

Finite element-based analyses of natural frequencies of long tapered hollow steel poles

Long tapered poles are commonly used to support Closed Circuit Television Cameras (CCTV) for security and traffic monitoring. Images received from CCTV are normally distorted due to the camera’s wind-induced vibration. To minimize the vibration experienced by the CCTV through development of a damping device to be placed at the interface between the pole and the camera, identification of the poles’ different frequencies as functions of poles’ geometric variables is essential. Thus, this study presents the development of natural frequency equations for long tapered hollow poles as functions of their geometric variables based on three-dimensional finite element model (FEM) analyses by taking into account the couplings between material, contact and geometric nonlinearities. The FEM results are compared and verified with the experimental data obtained from the instrumentation of a 60 ft pole. Sensitivity study is performed to identify the effect of different geometric parameters on the overall natural frequencies of the pole. Using the results from the parametric study, empirical formulae between the geometric parameters and the first, second and third mode natural frequencies for the long tapered hollow steel poles are obtained.     

曲线连续梁悬臂浇筑法施工技术

结合具体工程实例,详细地介绍了曲线连续梁悬臂浇筑法施工技术,提出了施工控制的目的和措施,指出该大桥施工采用的轻型斜拉式挂篮、施工控制技术、合龙技术使该桥的建设达到了较高水平。     

预应力大悬臂盖梁托架法施工技术

简要介绍了预应力大盖梁托架法施工的优点和工艺原理,着重阐述了具体施工技术,包括抱箍的验算,托架安装,模板制作及安装,钢筋及混凝土工程等内容,指出该方法可降低成本,加快施工进度,提高安全性,值得推广。     

“双控”法张拉在悬臂连续梁施工中的应用

通过跨S329省道悬臂连续梁的张拉施工实例,论述了预应力筋张拉中的应力控制技术和理论伸长值的准确实用计算方法,并对理论伸长值与实测伸长值进行比较分析,判断桥梁预加应力的准确性和可靠性。     

连续梁桥变截面桥墩自振频率计算的合成法

采用瑞利法和Southwell频率合成法,将基频表示成各惯性元与复位元所组成的子系统的频率合成,导出了变截面桥墩自振频率下限的计算公式,然后用有限元模型验证该公式的正确性,并分析了不同变截面系数及不同类型的弹簧约束刚度对变截面桥墩自振频率的影响,对桥墩结构状态的评定具有一定的参考作用。     

某大厦改造后挑梁构件的加固

本文以某大厦原设计使用功能为宾馆,改造为自助KTV包厢,导致二层局部挑梁构件承栽力不足,针对现场情况和工程特点,提出一种加固处理挑梁的新方法.     

悬臂梁结构损伤检测方法研究

提出了一种基于模态应变能的损伤诊断指标,并用于悬臂梁结构损伤检测。验证结果表明该损伤诊断指标能够有效地对结构的损伤进行精确定位,对构件损伤程度的评估也能得到令人满意的结果。     

带挑梁剪力墙结构局部强度破坏

采用ANSYS程序,建立三维有限元模型,对带挑梁剪力墙结构进行数值模拟计算.深入分析了主体结构剪力墙在强配筋挑梁处局部区域的复杂应力状态,包括混凝土局部区域的应力变化规律及主应力的分布、伸入钢筋的应力分布以及钢筋与混凝土之间的粘结应力的变化规律,同时也详细论述了混凝土中裂缝的分布及开展规律.在此基础上进一步研究了混凝土的局部强度破坏模式,总结归纳出了混凝土的锥形破坏模式,并对该破坏模式的形状通过数值模拟计算进行了参数分析.     

左挑臂盖梁的分析及计算

通过大型有限元程序Midas civil及平面杆件程序桥梁博士分别计算了左挑臂盖梁,并对结果进行了比较,得出了一些有益的结论。     

菱形挂篮悬臂浇筑箱形连续梁工法

以永定新河特大桥跨公路连续梁施工为例,详细介绍了菱形挂篮悬臂浇筑箱形连续梁工法,分别阐述了菱形挂篮的工作原理和施工工艺流程及操作要点,并提出了裂缝控制措施和安全措施,为类似工程积累了施工经验。     

Crack identification using electrical impedance tomography and transfer learning

Sensing skins and electrical impedance tomography constitute a convenient and inexpensive alternative to dense sensor networks for distributed sensing in civil structures. However, their performance can deteriorate with the aging of the sensing film. Guaranteeing high identification performance after minor lesions is crucial to improving their ability to identify structural damage. In this paper, electrical resistance tomography is used to identify the crack locations in nanocomposite paint sprayed onto structural components. The main novelty consists of using crack annotations collected during visual inspections to improve the crack identification performance of deep neural networks trained using simulated datasets through transfer learning. Transfer component analysis is employed for simulation-to-real information transfer and applied at a population level, extracting low-dimensional domain-invariant features shared by simulated models and structures with similar geometry. The results show that the proposed method outperforms traditional approaches for crack localization in complex damage patterns.     

Span ratios in bridges constructed using a balanced cantilever method

This paper introduces a relation to determine the span ratio between exterior and interior spans, which is required in the preliminary design stage of bridges constructed by balanced cantilever method. On the basis of the numerical results obtained by rigorous time-dependent analyses and by the simple equations introduced in the companion paper, the moment distribution along the spans and its variation with the construction sequence are reviewed, and a recommendation for a rational design is suggested. First, a relation for the initial tendon force is derived on the basis of an assumption that no vertical drift occurs at the far end of a cantilever beam due to the balanced condition between the self-weight and the cantilever tendons. In advance, the determination of an effective span ratio is followed with an assumption that the magnitude of maximum negative moment must be the same as that of the maximum positive moment along all of the spans. Finally, many rigorous time-dependent analyses are conducted to establish the validity of the introduced relations, and this paper shows that an effective span length ratio of the exterior span to the interior span ranges between 0.75 and 0.8.     

悬臂法施工连续梁临时固结体系的设计与优化

结合客运专线连续梁悬灌施工实例,详细介绍了临时固结体系的设计、检算、优化及拆除方案,并对临时固结体系作了进一步说明,以确保梁体结构的稳定和安全。     

组合加固混凝土悬挑梁力学性能研究

基于某工程悬挑结构的加长方案,提出了增大截面、屋面吊挂、增设拉杆以及增设型钢支撑这几种加固方案,对比分析各加固方案后,最终选择增设型钢支撑这一组合加固方案.为研究加固节点的受力性能,采用ABAQUS软件对节点进行模拟加载,分析节点在设计荷载(1.3恒载+1.5活载)及1.2倍设计荷载作用下的材料应力及塑性应变开展过程....     

A simplified method for calculation of the natural frequencies of wall–frame buildings

A simple hand method is presented for the three-dimensional frequency analysis of buildings braced by frameworks, coupled shear walls, shear walls and cores. Lateral vibration is characterised by three types of deformation: the full-height ‘local’ bending of the individual columns/wall sections/shear walls/cores, the full-height ‘global’ bending of the frameworks/coupled shear walls, which is associated with the axial deformations of the columns/wall sections, and the shear deformation of the frameworks/coupled shear walls. Based on the stiffnesses associated with these three types of deformation, a closed formula is derived for calculation of the lateral frequencies. An analogy between bending and torsion is used to carry out the pure torsional frequency analysis. The coupling of the lateral and pure torsional modes is taken into account. The results of a comprehensive accuracy analysis covering 144 multi-storey structures demonstrate good agreement with the finite element solution, the maximum difference being 7%. A worked example with step-by-step instructions shows the easy use of the method.     

Design moment variations in bridges constructed using a balanced cantilever method

This paper introduces simple, but effective, equations to calculate the dead load and cantilever tendon moments in reinforced concrete (RC) bridges constructed using the balanced cantilever method (FCM). Through time-dependent analyses of RC bridges considering the construction sequence and creep deformation of concrete, structural responses related to the member forces are reviewed. On the basis of the compatibility condition and equilibrium equation at every construction stage, basic equations which can describe the moment variation with time in balanced cantilever construction are derived. These are then extended to take into account the moment variation according to changes in the construction steps. By using the introduced relations, the design moment and its variation over time can easily be obtained with only the elastic analysis results, and without additional time-dependent analyses considering the construction sequences. In addition, the design moments determined by the introduced equations are compared with the results from a rigorous numerical analysis with the objective of establishing the relative efficiencies of the introduced equations.     

变刚度悬臂式双排抗滑桩水平推桩模型试验研究

双排抗滑桩常用于加固大型滑坡,其中悬臂式双排抗滑桩由于施工便利,受到工程界广泛重视。已有研究表明,后排桩承受的滑坡推力大于前排桩,是困扰设计的重要问题。文章借鉴变刚度调平设计原理,通过改变前后排桩间距实现前后排桩刚度的调整,设计了变刚度悬臂式双排抗滑桩支护形式,并进行了室内水平推桩模型试验,得到桩顶及坡顶位移、桩身弯矩以及滑体内土压力分布。结果表明：水平推桩模式下,桩顶位移和桩身弯矩随荷载增大而增大,模型边坡沿着滑动面破坏,根据桩顶的荷载-位移曲线,双排桩在推力作用下的发展过程被划分为三个阶段;适度增大前排桩的桩间距并不会明显降低双排抗滑桩的临界荷载;采用变刚度调平设计悬臂式双排抗滑桩,前排作用被充分调动,前后排最大弯矩差值变小;双排抗滑桩存在明显的三维土拱效应,在推力方向上被划分为后排桩后土拱效应、桩排间土拱效应、前排桩前土拱效应,在深度方向上,滑体中部土拱效应与滑体下部有所不同;适度扩大前排桩的间距,桩排间土体保持稳定,未见土体绕流现象,桩排间土拱效应作用明显。