Measurement of deflections and of oscillation frequencies of engineering structures using Robotic Theodolites (RTS)

The Robotic Theodolite or Robotic Total Station (RTS) is a new generation geodetic instrument that can automatically record the changing coordinates of a moving target (reflector). RTS was so far used for monitoring of static and very slow displacements. This limitation was imposed by some characteristics of these instruments (real sampling rate <2 Hz and non-constant, noisy results in high frequency sampling, etc.). A study of a new generation of RTS based on: (1) systematic experiments using an apparatus producing oscillations of known, computer-determined characteristics (frequency and amplitude of oscillation) which were compared with those recorded by the RTS; (2) upgrading of the instrument’s built-in software to display measurements with a 0.01 s resolution; and (3) spectral analysis of the obtained non-equidistant data with a least-squares based software without prior interpolations, permitted us to show that the range of application of RTS may be safely extended to higher frequency oscillations.

In particular, it was shown that: (1) the maximum real sampling rate of RTS is 6–7 Hz, but since sampling rate is variable, aliasing-free results can be obtained above the Nyquist frequency. (2) The potential to record oscillations depends on the maximum angular velocity of the instrument and on the maximum velocity of the moving target; for velocities up to about 10 cm/s in field studies, results are very precise. On the contrary, for targets moving with maximum velocities > 15 cm/s, some displacements cycles are not well-defined or are lost, and hence, the accuracy of the oscillation amplitude and frequency are lower. (3) RTS can be used to measure small (on the order of a few mm) amplitudes of oscillation, and to some degree of frequencies of oscillation of various relatively stiff engineering structures (modal frequencies > 1 Hz, up to 3–4 Hz). This potential is demonstrated on the basis of several field examples, including the monitoring of two bridges with dominant modal frequencies > 1.5 Hz.

Obviously, these limits reflect the most unfavorable cases of application of RTS, and higher period/larger amplitude oscillations or other deflections can be successfully measured if the main requirement for this type of instrument is satisfied: an unobstructed view of a reflector at a maximum distance of a few hundred meters from an RTS set on stable ground.     

Measurement of the dynamic displacements and of the modal frequencies of a short-span pedestrian bridge using GPS and an accelerometer

Signal analysis techniques (supervised-type learning filter in combination with a Chebyshev filter) constrained and tested by independent accelerometer data were used to process noisy GPS measurements of oscillations of 40 m long steel footbridge excited by coordinated jumps of a group of people. This approach permitted to de-noise the geodetic displacement record and reconstruct a minimum bias waveform for the dynamic displacement of this stiff bridge (4.3 Hz modal frequency, ∼6 mm oscillation amplitude). This result indicates that properly processed high-frequency satellite geodetic data may be used to measure dynamic displacements not only of high-rise buildings, cable-stayed bridges and other flexible structures, but of stiff civil engineering structures as well and may be useful for the Structural Health Monitoring, analysis and design of a large range of engineering structures. It was also found that although currently used 10 Hz sampling rate GPS receivers may underestimate certain high-frequency peak displacements, this will not be a problem for the recently introduced 50-100 Hz receivers.     

GPS monitoring of a steel box girder viaduct

Structural performance monitoring of bridges has increased as major infrastructure ages and is required to sustain loads that are significantly greater than those predicted during design. Structural stiffness and/or mass distribution can change over the lifespan of a bridge structure. Resulting changes in profile or resonant frequency provide key indicators of change, and may identify structural defects. Field tests using GPS for monitoring relatively small deformations were carried out on a steel box girder viaduct bridge in the UK. The configuration consisted of five GPS receivers located at key locations on the viaduct and two reference GPS receivers. GPS data was collected at either 10 Hz or 20 Hz and post-processed using proprietary software, along with appropriate filtering and spectral analysis. Three main frequencies were clearly detected by the GPS in the vertical component. A previously reported frequency of approximately 0.56 Hz was identified along with two other frequencies. The peak vertical deflections lie in the range of ± 50 mm, while lateral and longitudinal deflections of much smaller magnitude – in the order of a few mm – are also measured. The use of GPS leads to readily obtained and useful engineering data for continued monitoring of structures.     

Global Positioning System aided autonomous construction plant control and guidance

The advent of Real Time Kinematic (RTK) Global Positioning System (GPS) positioning means that this technology can now be used for dynamic control and guidance applications. The paper outlines the recent advances in GPS technology, which have enabled RTK GPS to become a reality. Tests have been carried out in construction plant control and monitoring applications with a demonstrated precision of the order of a few millimeters. The results are compared with those achieved using a laser level and a digital automatic level.     

Development of an Accurate Positioning System Using Low-Cost L1 GPS Receivers

Abstract:   The present article reports the development of an accurate positioning system based on GPS technology. This system employs an inexpensive L1 GPS receiver and a small patch antenna. As these devices are very inexpensive and small, they can be attached to an array of sensor nodes of a wireless network sensing system. In the present study, we first develop a program that can be used to estimate the relative positions of receivers and evaluate its performance. Next, a number of experiments were conducted to assess the performance of the inexpensive L1 GPS receiver with a patch antenna. Compared to the results obtained using a sophisticated antenna, the present measurement system, which uses a patch antenna, is less accurate. However, the present system achieves an accuracy of 1–2 cm. This system can be used as a localization system for the sensor nodes or, because of its accuracy, as a displacement monitoring system.     

以江西省上犹县为例谈数字化地籍测量的实现

介绍了数字化成图系统,结合江西省上犹县数字化地籍的实施过程,说明了如何使用先进的数字化测量仪器和技术,如GPS接收仪、全站仪、电子手簿以及控制测量平差软件等来实现数字化地籍测量。     

Fatigue properties of intact sandstone samples subjected to dynamic uniaxial cyclical loading

In this paper, the fatigue behaviour of intact sandstone samples obtained from a rockburst prone coal mine and studied under dynamic uniaxial cyclic loading in the laboratory is presented. Tests were conducted on dry and saturated samples with loading frequencies ranging from 0.1, 1 and 10 Hz and amplitudes of 0.05, 0.1 and 0.15 mm. From the laboratory investigations, it was found that the loading frequency, as well as the amplitude, was of great significance and influenced the rock behaviour in dynamic cyclic loading conditions. The dynamic fatigue strength and the dynamic axial stiffness of the rock reduced with loading frequencies and amplitude. The dynamic modulus was found to increase with the loading frequency but decrease with the amplitude. In the case of the saturated samples, it was found that the dynamic fatigue strength reduced by approximately 30 per cent, while the dynamic Young's modulus reduced by about 20 per cent. From the presented study, the dynamic energy was found to be independent of the testing conditions while other rock properties were found to be dependent on these. Finally, it was concluded that rock would more readily succumb at low frequencies and amplitude than at high frequencies and amplitude for a given energy availability.     

Road Infrastructure Data Acquisition Using a Vehicle-Based Mobile Mapping System

Abstract:   This study presents the technology of a vehicle-based mobile mapping system to maintain an updated transportation database. The mobile mapping system that integrates the global positioning system (GPS), the inertial navigation system (INS), and digital cameras has been developed to collect data on position and attributes of road infrastructure. The vehicle-based mobile mapping system works by having the GPS and INS record the position and attitude data, and digital cameras take road images. The stereovision system can determine the position of objects that are visible on the image pair in the global coordinate system with GPS and INS data. As field data acquisition is a very expensive task, a mobile mapping system offers a greatly improved solution. In this study, we successfully created a road infrastructure map with mobile mapping technology and proposed automatic algorithms for detecting and identifying road signs from road images. The proposed detection algorithm includes line and color region extraction processes and uses the Hopfield neural networks. The identification algorithm uses seven invariant moments and parameters that present geometric characteristics. With this combined method, we could successfully detect and identify road signs.     

精密仪器隔减振平台振动控制效应分析

为解决宽频激励(0～100Hz)对精密仪器设备正常工作带来的振动问题,采用研制的磁流变弹性体(magnetorheological elastomers,简称MRE)隔减振装置和高耗能隔振支座对精密平台实施振动控制。提出半主动控制装置与被动控制装置相结合的混合控制方案,结合各减振装置力学模型及平台运动姿态分析,建立“七自由度”的隔减振平台模型及其运动方程;设计与平台振动控制方案相适应的模糊控制器,并利用SIMULINK仿真软件对所建立的精密仪器隔减振平台进行动力仿真分析。结果表明：平台质心处竖向Z、绕X轴向及绕Y轴向的加速度与功率谱幅值显著降低,加速度峰值与均方根控制效果可达80%,控制效果显著。     

Computational modelling of geometric imperfections and buckling strength of cold-formed steel

Computational modelling of the buckling strength of cold-formed steel members as influenced by initial geometric imperfections is studied. The geometric imperfections are represented by the member eigenmode shapes. Along with the classical measure — the amplitude of imperfections, an energy measure defined by the square root of the elastic strain energy hypothetically required to distort the originally perfect structural element into the considered imperfect shape is used. Based on the measures, two approaches for the choice of the most unfavourable imperfections are suggested. Normalising imperfections by the amplitude, the energy measure is calculated as indicative parameter of imperfection significance. Vice versa, when adopting normalisation by the energy measure, the amplitude is used as a supporting parameter. The suggestions are illustrated on calculating the strength of an axially compressed steel lipped channel column with eigenmodes exhibiting local-distortional interactions. For eigenvalue and geometrically and materially non-linear strength calculations, the FEM codes MSC.NASTRAN and COSMOS/M are employed.     

Statistical analysis of the fluctuating counts of fecal bacteria in the water of Lake Kinneret

Counts of E. coli, Enteroccoci and fecal coliforms in four sites around Lake Kinneret (The Sea of Galilee), collected every 2-4 weeks for about 5 years during 1995-2002 showed irregular fluctuations punctuated by aperiodic outbursts of variable magnitude. Because of the haphazard nature of fecal contamination and large intervals between successive counts, these patterns were described by probabilistic models, based on the truncated Laplace or Extreme Value distribution. Their applicability was tested by comparing the predicted frequencies of counts exceeding different levels calculated from the first half of each record with those actually observed in its second half. Despite the records imperfections and minor violations of the underlying models' assumptions, there was a reasonable agreement between the estimated and actual frequencies. This demonstrated that it is possible to translate the irregular fluctuation pattern into a set of probabilities of future high counts. In principle, such probabilities can be used to quantify the water's fecal contamination pattern and as a tool to assess the efficacy of preventive measures to reduce it.     

循环荷载下冻结兰州黄土变形性质的实验研究

对温度为-1 ℃的冻结兰州黄土在围压为0.6 MPa和不同动荷载振动频率条件下进行动三轴试验,试验采用分级加载,每一级荷载振动十次,加载波形为正弦波。实验结果表明:冻结兰州黄土的累积应变在整个加载过程中逐渐增大;当动荷载加载级数增加时,累积应变率逐渐变大。动应变幅随加载频率和振次的增加而减小;当频率小于或等于1 Hz时,动应变幅随加载级数的增加而增大;当频率大于1 Hz时,动应变幅随加载级数变化不大。随着加载级数的增加,滞回曲线的面积和密集程度越来越小,整体斜率和不闭合程度越来越大。用动模量来描述滞回曲线的整体倾斜程度。当频率小于或等于7 Hz时,动模量随加载级数的增加而增大;当频率大于7 Hz时,动模量随加载级数没有明显的规律。     

The effect of geometric imperfections on the vibrations of anisotropic cylindrical shells

Analytical–numerical models to analyse the flexural vibration behaviour of anisotropic cylindrical shells are presented. The two models (denoted as Level-1 and Level-2 Analysis) have different levels of complexity and can be used to study the influence of important parameters, such as geometric imperfections, static loading, and boundary conditions. A specific anisotropic shell is used in the calculations in this paper. The influence of the imperfection shape and amplitude on the natural frequency is investigated for this shell via both the Level-1 and the Level-2 Analysis. Imperfections with the shape of the “lowest vibration mode” give a decrease of the natural frequency with increasing imperfection amplitude. The results of the Level-2 Analysis for the effect of imperfections on the natural frequency are in reasonable agreement with Finite Element calculations.     

高精度三维GPS控制网的建立与数据处理

全面介绍了南宁市城市高精度三维GPS控制网的概况,然后讨论了利GAMIT/GLOBK软件处理控制网的基线处理方案和网平差方案,计算出各个测站在ITRF2005框架下的三维直角坐标,得出南宁市三维GPS控制网不论从布网,还是精度上均达到甚至优于国家B级GPS网的结论.     

分级加载下冻土动弹性模量的试验研究

基于黏弹性理论,将动态弹性模量的最大值定义为冻土的动模量,通过计算滞回曲线中直线斜率的方法来计算冻土的动模量。通过动三轴试验,对不同频率、围压和负温条件下冻土的动模量随动应变幅的变化规律进行了试验研究,结果表明：在不同频率(0.1～20 Hz)、围压(0.3～2 MPa)和负温(-0.2～-2℃)条件下,青藏黏土的动模量取值范围为393～1749 MPa,兰州黄土的动模量取值范围为101～713 MPa;同一级加载下,动模量随着振次的增加基本不变,可以采用平均值来表征该级加载下的动模量;对于青藏黏土和兰州黄土,不同频率条件下,动模量随动应变幅的增加最终趋于一稳定值,该稳定值随加载频率的增加而增大;不同温度和围压条件下,随着动应变幅的增加,动模量先减小再趋于一个稳定值,该稳定值随围压的变化较复杂,随温度的降低而增大。     

连续基准网GPS数据质量检测与分析

利用TEQC软件对中国地壳运动观测网络基准站1999年至2007年的原始观测数据进行质量检测,给出了各站Mp1、Mp2和CSR的月变化趋势图及年平均值;参照IGS的GPS观测数据质量标准对其进行统计分析,得出结论：网络工程基准站大部分站点观测数据质量优于IGS标准;数据质量较差的站为：shao、wuhn和yong。     

关于圆柱壳几何缺陷分析中傅立叶级数选取的探讨

圆柱壳屈曲一般对壳壁上微小几何缺陷的型式和幅值均十分敏感.为了能将缺陷的不同分量和圆柱壳的结构特征联系起来以及研究缺陷各分量对壳屈曲强度的影响,缺陷通常采用傅立叶级数分解.然而,大多数先前的研究选取不适当的傅立叶级数得到不正确的结果.本文首先考察傅立叶级数的数学描述基础,进而讨论不同傅立叶级数在描述不同型式几何缺陷的表现,从而得出如何选取适当的傅立叶级数用来描述圆柱壳几何缺陷的结论.采用这些适当的傅立叶级数,能更好地了解圆柱壳几何缺陷的特征分量以及这些分量对壳体屈曲强度的影响.     

结合实例对污水提升泵站结构的地震响应分析

为了研究污水泵站在水平地震动作用下结构的安全可靠性,采用快速拉格朗日时域有限差分法进行时程分析,并利用大型岩土软件FLAG3D对某地下式污水提升泵站结构进行数值模拟计算.结果表明:水平地震荷载作用下,泵站结构水平残余位移为13.0mm,泵站结构顶板和底板之间的水平相对位移较小;泵站结构整体应力变化较小,应力幅度最大波动18％;结构自振频率约为6.20Hz.总体上,泵站结构产生剪切破坏的概率较小,泵站结构抗震性能较好,结构安全可靠,但仍需做好抗震构造措施.本文的结论可为同类泵站结构的抗震设计提供参考.     

Imperfections in steel girder webs with and without perforations under patch loading

In this paper, the problem of stability of web plates with imperfections, subjected to patch load, is studied. The aim is to give some insights about the best way to take into account real imperfections in non-linear stability analyses of plates with and without perforations. In this context, the study is developed on the basis of the measured imperfections or numerically deriving the deformed model (theoretical imperfections). The influence of the patch load length, out-of-plane imperfection amplitude, dimension and position of the hole on stability behaviour and buckling strength are studied comparing some theoretical deformed configurations corresponding to different modal shapes. The results obtained with a three-dimensional model of the whole real beam with stiffeners, with experimentally measured imperfections, and each corresponding single web panel are compared and discussed obtaining some insights about the accuracy of the simplified (and conservative) model of the single panel.The main insights of this work are as follows. The deformed shape, corresponding to the first buckling mode, can be assumed as the initial configuration of the panels with and without holes to study post-critical behaviour until ultimate condition. The shape of the imperfection does not severely change the critical buckling stress. A longer patch load reduces the ultimate stress in the panel. An initial imperfection amplitude of less than 1% of the height of the panel does not reduce the ultimate load by more than about 5%.     

Blast vibration damage to underground coal mines from adjacent open-pit blasting

A study was conducted to evaluate the effect of heavy blasting in open-pit coal mines on the stability of adjoining underground coal mine workings. Investigations were carried out at seven coal mines in India. Strata monitoring instruments, viz. borehole extensometers, convergence indicators, strain bars, stress capsules and load cells were installed in the roof and pillar. Monitoring of strata behaviour was carried out before and after the blasts. Arrangements were made to mount the transducers of seismographs in the roof and pillars to monitor vibration. Altogether, 202 production blasts were conducted and 622 vibration data were recorded.

The maximum peak particle velocity (PPV) recorded was 372.8 mm/s with the associated frequency of 78 Hz. At this magnitude of vibration, a coal block of 0.38 m³ detached from the roof. Minor damage in the form of loosened coal chips falling from the roof and the pillars was noticed at PPV level of 113 mm/s. Major damage was observed when the magnitude of PPV exceeded 181.9 mm/s. The damage is classified into three groups, viz. major damage, minor damage and no damage. The vibration levels in no damage zone are taken as safe level of vibration, The threshold value of vibration for the safety of underground workings is recommended based on the RMR of the roof rock.

It was also observed that the roof of underground roadways vibrated with 1.1–2.58 times higher amplitude of vibration compared to the pillars, The amplification was further higher at junctions. Monitoring of underground strata behaviour indicated, in all the mines, some amount of divergence between the roof and floor just after the blast, but, later on it was followed by convergence and most of the divergence that occurred was restored.