桩基低应变完整性测试的双速度分析

传统的低应变测试是将一个加速度传感器安装在桩的自由表面 ,从信号的反射特性来判读桩中变截面及桩端。这种情况下 ,要正确判读速度信号 ,需考虑两个因素 :首先 ,混凝土的应力波波速是未知的 ,这是一个非常重要的量 ,它直接影响桩长的确定。其次 ,桩基测试时 ,由于桩与上部结构物相连或桩不均匀 ,桩中的应力波不仅只有下行波还有由于上部结构反射的上行波。这些二次反射必须区分出来 ,以免与桩阻抗变化和桩端反射混淆起来。因此 ,沿着桩身同时测量两个加速度信号可得到精确的应力波波速。本文给出了由理论模型导出的相应分析过程。     

桩锚支护结构在深基坑中的应用

近年来随着我国城市建设的迅速发展,高层建筑物越来越多,由于城市用地的有限性,使得高层建筑不断向地下空间发展,需要进行基坑的开挖,随着基坑开挖深度的增大就要求对基坑进行支护。本文结合工程实例,根据桩锚支护结构的特点,以及该工程的地质条件和周围环境,对本工程基坑开挖进行了可行性和稳定性分析,并对桩锚在工程中的应用进行了探讨。     

Metallurgical analysis of a corrosion failure

A Nicrofer 6025 HT alloy 602 tube in a furnace, used for the recovery of steel pickling liquors, failed during operation at 1100°C. Metallographic investigations—microstructural and energy dispersive X-ray spectrometry (EDS)—of the failed tube showed evidence of corrosion and the presence of chlorine and sulfur in the corrosion products. The failure of the furnace tube was due to the presence of sulfur dioxide in combination with chlorine.     

Forensic analysis of buildings affected by mining subsidence

This work presents a forensic analysis of ground subsidence occurred in Lo Tacón industrial area, which is located at the outskirts of La Unión (Murcia, SE Spain). Subsidence was triggered by the collapse of abandoned underground mining labours occurred in 1998. Coinciding in time with this event, it was detected a seismic movement, whose epicentre was located close to the study area.In the first part the affected area is analysed and delimited, as well as the spatial and temporal evolution of the damages attributed to the collapse of 1998. Then the causes of ground failure are also determined, as well as their possible temporal and spatial relationship with the seismic movement detected. Through this analysis it is presented a methodology to determine the effects of this phenomenon. It consists on extending field work radially to all existing buildings within the affected area, considering the centre around the zone where the greatest damage was produced. Finally it is analysed the temporal and spatial evolution of the cracks inventoried in buildings to determine active areas where certain subsidence persists. According to the results presented in this work, it may be concluded that damages are the consequence of buildings constructed in a potentially dangerous area where ground settlement occurs due to mining subsidence.     

地铁区间施工对近接既有桩基及周围土体影响的研究现状及其思考

随着地铁建设的的发展,新建隧道近接既有桩基础的情况越来越多,并且与之相关的工程问题成为一项亟待解决的课题。通过桩基础承载力、变形规律及新建地铁对既有桩基础承载力影响等方面的分析研究,本文提出了真实反映新建地铁施工对既有桩基础影响,应全面考虑“空间—时间—工法”效应印工程的近接情况、施工进度、施工方法等具体的条件因素。     

Stability analysis of a tangentially loaded column with a maxwell type viscoelastic foundation

Summary The stability of a uniform cantilever column supported by a Maxwell type viscoelastic foundation and subjected to a constant tangential force is investigated. Stability conditions are obtained for the entire range of system parameters through an application of Routh-Hurwitz criteria. Unlike the case of conservative loading, the Maxwell foundation is shown to produce a stabilizing effect on this nonconservative problem. Furthermore, an optimum combination of foundation parameters exist to yield the maximum flutter load. An approximate analysis is also presented through an application of the Galerkin's method. It is shown that a two-term approximation may not be adequate to yield meaning-ful results in a certain range of system parameters.With 6 Figures     

Preparing and writing a failure analysis report

Afailure analysis report is the summation of all of the tests and analyses performed during the course of an investigation. The report coalesces the results and presents them in a concise and logical format that describes the particulars of the subject being studied, conveys pertinent information gathered from testing and analysis, and logically and accurately interprets and explains the data and results.     

Tribological failure analysis of a magnetic drive pump

The failures of a magnetic drive pump are investigated to determine the root cause. The journal bearing design was verified and compared to a similar application that has experienced no operating problems. Also, an investigation of the materials and the product used for lubrication were performed. The root cause was found to be an insufficient fluid film thickness being developed for hydrodynamic lubrication. This occurs as a result of low viscosity of the product and high dynamic loads. It is suggested that care should be taken with bearing selection and design for specific magnetic drive pump applications as inadequate design can lead to catastrophic failures.     

Material-based failure analysis of a helicopter rotor hub

A Lynx helicopter from the Royal Netherlands Navy lost a rotor blade during preparation for take-off. The blade loss was due to failure of a rotor hub arm by fatigue. The arm was integral to the titanium alloy rotor hub. An extensive material-based failure analysis covered the hub manufacture, service damage, and estimates of service stresses. There was no evidence for failure due to poor material properties. However, fractographic and fracture mechanics analyses of the service failure, a full-scale test failure, and specimen test failures indicated that the service fatigue stress history could have been more severe than anticipated. This possibility was subsequently supported by a separate investigation of the assumed and actual fatigue loads and stresses.     

Fatigue failure analysis of a spring for elevator doors

The present work details a study performed for the determination of the causes of the premature rupture of a spring from an elevator door control mechanism. The study is based on the general methodology applicable to failure analysis. The results obtained in the experimental analysis and the analytical calculations lead to the conclusion that the fracture of the spring was caused by a mechanical fatigue mechanism whose origin is related to the presence in the periphery of the material of inclusions and superficial folds (stress concentrators), probably aggravated by the tensional state derived from the lack of alignment in the application of the load on the spring with respect to its axial axis.     

Metallurgical failure analysis of cold cracking in a structural steel weldment: Revisiting a classic failure mechanism

Cold cracking of structural steel weldments is a well-characterized, well-documented, and well-understood failure mechanism. Extensive effort has been put forth to recognize the welding and materials selection parameters that are conducive to cold cracking; however, these engineering efforts have not fully eliminated the occurrence of such failures. This article describes cold cracking failure specifically related to the construction industry. This particular failure was successfully identified prior to final erection of the structural member, and the weld was successfully reworked. These actions potentially prevented a serious catastrophic event that could have occurred have occurred either later in the construction process or possibly during the use of the building. Individual welding parameters, such as electrode/wire selection, joint design, and pre/postheating, played a role in the failure, and a number of human factors relating to the actual fabrication practices also contributed to the failure process.     

Early failure analysis of machining centers: a case study

To eliminate the early failures and improve the reliability, nine ex-factory machining centers are traced under field conditions in workshops. Their early failure information throughout the ex-factory run-in test is collected. The field early failure database is constructed based on the collection of field early failure data and the codification of data. Early failure mode and effects analysis is performed to indicate the weak subsystem of a machining center or the troublemaker. The distribution of the time between early failures is analyzed and the optimal ex-factory run-in test time for machining center that may expose sufficiently the early failures and cost minimum is discussed. Suggestions how to arrange ex-factory run-in test and how to take actions to reduce early failures for machining center is proposed.     

Bayesian analysis of repairable systems showing a bounded failure intensity

The failure pattern of repairable mechanical equipment subject to deterioration phenomena sometimes shows a finite bound for the increasing failure intensity. A non-homogeneous Poisson process with bounded increasing failure intensity is then illustrated and its characteristics are discussed. A Bayesian procedure, based on prior information on model-free quantities, is developed in order to allow technical information on the failure process to be incorporated into the inferential procedure and to improve the inference accuracy. Posterior estimation of the model-free quantities and of other quantities of interest (such as the optimal replacement interval) is provided, as well as prediction on the waiting time to the next failure and on the number of failures in a future time interval is given. Finally, numerical examples are given to illustrate the proposed inferential procedure.