Posted by: pelelo - 04-25-2013, 01:03 AM - Forum: Archive
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Thomas, H.G., 2011, Slope stability prism monitoring: A guide for practising mine surveyors. Unpublished M.Sc dissertation, University of the Witwatersrand, Johannesburg, South Africa.
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Posted by: pelelo - 04-25-2013, 12:58 AM - Forum: Archive
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Afeni, T.B. and Cawood, F.T., 2010, ‘Do the properties of glass matter when taking total station distance measurements through an observation window?’ Proceedings of International Society for Mine Surveying (ISM) XIV international Congress held in Sun City, South Africa, pp. 109 – 120
A necessary modification for the finite element analysis of cracked members detection, construction, and justification
Author: A. Ranjbaran, H. Rousta, M. O. Ranjbaran, M. A. Ranjbaran, M. Hashemi, M. T. Moravej | Size: 362 KB | Format:PDF | Quality:Unspecified | Publisher: Springer | Year: 2013 | pages: 10
The finite element analysis of cracked beam-like members is investigated. Through concise formulation,
computer implementation, and numerical experiment, the necessity for a paramount modification in
the governing differential equation is detected. In the course of numerical analysis, physical consideration,
and mathematical theory, the structure of the modification and its relation with the member geometry and
crack parameters is constructed and justified. Several new chain rules for use in the application of the method
of weighted residual to differential equations containing the derivatives of the Dirac’s delta distribution is
proposed. Through analysis of typical examples and comparison of the results with that of the others, the
accuracy, efficiency and robustness of the work are verified.
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A structural damage detection method based on the change of strain energy in each element before and after the occurrence of damage is presented. The proposed method can localize and quantify both single and multiple damages. The algorithm requires only the stiffness and mass matrices of the baseline structure and a few measured mode shapes of the current structure to find the location and severity of damage. The proposed method is applied to a benchmark problem sponsored by the IASC-ASCE Task Group on Structural Health Monitoring, which was developed in order to facilitate the comparison of various damage identification methods.
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This note utilizes the analog models of forced vibration to express the mass of foundation block in terms of damping ratio and
thereafter obtains the expression for the minimum foundation mass required to limit vertical machine vibration amplitude to a prescribed
limit. The resulting formula, which accounts for internal damping, is constrained by the limitations of the original analog solutions.
Moreover, formulas are derived for determining the damping ratio for conditions different from optimum that enable the evaluation of the
nonoptimum foundation mass required to limit vibration. Since the ideal optimum solution may not be practical, an expression has been
derived for the best nonoptimum foundation mass. The method presented in this note is believed to be easier to implement and to yield
smaller foundation blocks than the existing traditional method, and thus will enable cheaper machine foundations to be constructed. It is
believed that the proposed optimal solution may lead to the near elimination of machine vibration nuisance produced by high-frequency
machines during operation
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Material degradation due to corrosion significantly alters the seismic response of ground-based cylindrical steel storage tanks. A numerical study is conducted to investigate the effects of internal shell corrosion on the dynamic buckling of three cone roof ground-based, steel cylindrical tanks with height to diameter ratios (H/D) of 0.40, 0.63 and 0.95, subjected to horizontal seismic base excitations. Internal corrosion is considered as a time dependent uniform thinning of the wall at the upper and the lower parts of the tank being in contact with, respectively, atmospheric oxygen and acid gases and residual water. Detailed numerical models of the tank–liquid systems at different stages of corrosion degradation are subjected to two representing accelerograms and for each model the critical peak ground acceleration (PGA) for dynamic buckling of the shell and its associated mode of failure are evaluated. It is found that in all three tanks, the critical PGA is markedly reduced with thinning of the shell, irrespective of the type of ground input. The buckling mode of failure of the tanks also changed from an elastic diamond-shaped failure at the top of the shell to an elasto-plastic elephant foot type failure near the base, after 10 years for the shorter tanks (H/D=0.4 and 0.63) and after 15 years for the tallest tank. The effects of uniform corrosion degradation on the critical buckling load of the tanks were found to be such that after 20 years of thinning due to corrosion, the static loading alone was responsible for the elephant foot buckling of the shell.
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Spectral analysis of ambient ground-motion—Noise reduction techniques and a methodology for mapping horizontal inhomogeneity
Author: Marc-André Lambert; Tung Nguyen; Erik H. Saenger; Stefan M. Schmalholz | Size: 4 MB | Format:PDF | Quality:Unspecified | Publisher: Elsevier | Year: 2011 | pages: 13 | ISBN: --
Inhomogeneities in the subsurface can interact with and modify seismic waves. As a consequence, the quasistationary, ambient ground-motion response at the Earth's surface carries valuable information about underground inhomogeneities. Extracting and interpreting such information by analyzing low-frequency passive measurements is not an easy task because distinct events in the time traces are usually absent in ambient ground-motion recordings and the signal-to-noise ratio is low. This paper presents four processing techniques to reduce different types of anthropogenic noise effects and proposes a methodology for extracting and mapping passive seismic characteristics that help image horizontal inhomogeneity. The methodology uses Fourier amplitude spectra to calculate four independent spectral attributes that quantify signatures of interest in the data. The methodology is applied to a noisy data-set acquired at an oil and gas field in Austria. Two horizontally separated hydrocarbon reservoirs are considered as possible inhomogeneities in the subsurface. Results show that anthropogenic noise is successfully removed from the data, enhancing the signal-to-noise ratio. Attribute profiles are extracted and show stable spatial patterns that are apparently related to stationary site properties. Correlation between attribute patterns at the Earth's surface and the horizontal location of the reservoirs is discussed. Although this paper addresses an application for hydrocarbon reservoir characterization, the proposed methodology is suitable to quantify and map signatures related to any subsurface inhomogeneity of interest (e.g. underground cavities) that has a measurable impact on the ambient ground-motion at the Earth's surface.
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A considerable number of numerical and experimental studies, carried out to-date to investigate the behaviour of masonry walls under seismic loading, have considered the in-plane or the out-of-plane response of the wall separately without due consideration for any possible interaction between the two responses. In this paper, the results of a series of tests with different levels of simultaneous in-plane shear and out-of-plane bending actions on small brick walls are presented. The tests results indicate noticeable interaction between the in-plane shear and out-of-plane bending strengths of brick walls. Test results are also used to validate representing numerical models of wall panels. The combined in-plane/out-of-plane capacity interaction in full-scale walls having different aspect ratios is then investigated using these numerical models. It is found that the wall aspect ratio highly influences the interaction level, which must be considered in masonry design.
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Motivated by one of the concepts in the field of health monitoring for structural systems, a damage detection procedure
is developed. In order to perform the system health monitoring, structural health along with sensor and actuator
malfunction must be continuously checked. As a step toward developing a system health-monitoring scheme, this paper
investigated structural damage detection, using a constrained eigenstructure assignment. The proposed damage detection
method is constructed based on a concept of control theory and subspace rotation for two-dimensional (2D)-structural
systems. To demonstrate the capabilities of the developed damage detection algorithm, the behavior of a simulated
degraded braced-frame structure is studied. Using Monte Carlo simulation, the performance of the approach is evaluated.
It shows that the proposed algorithm is potentially promising for application to real cases.
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