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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A strain-consistent approach for determination of bounds of ductility damage index for different performance levels for seismic design of RC frame members
The aspects of a robust and practical damage-based deterministic seismic design approach for reinforced concrete (RC) buildings have been discussed. The proposed performance-based design approach can be used for different structural systems by using fundamentals of reinforced concrete behavior and practical analyses. Several aspects of the proposed design approach need to be tuned including the selection of the damage measure and its quantification for a required performance level. Ductility damage index is a suitable damage measure for performance-based design of RC frame members. Currently, there is no systematic approach for selecting the bounds for a damage index according to the required performance level. The preset values provided in literature are based on engineering judgment and cannot be extended to RC members with all kinds of geometries and detailing. In this article, the correlation of damage level to concrete core and rebar strains is used to establish a procedure for determination of damage index intervals for different performance levels of RC plastic hinges. Then, the developed procedure is illustrated through numerical simulations for square and circular columns. The strain consistent curvature ductility damage index values are determined for operational, immediate occupancy, life-safety, and collapse prevention performance levels used for seismic design of new columns.
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Quote:The Industrial Police on Tuesday had instructed the garment owners to keep their factories closed after a big crack appeared in the building. They wanted to bring in an engineer from BUET to decide if the structure was safe for use, Mustafizur Rahman, Director for Industrial Police told reporters at the site of the collapse.
The people responsible acted very wrong.
Quote:The Rana Plaza is owned by Md Sohel Rana. He had apparently said the cracks were nothing serious.
Quote:None of us wanted to go in. The bosses came after us with beating sticks. At the end we were forced to get in.
A data base on cyclical soil strength would be of significant assistance in many phases of site evaluation where detailed complete cyclical soil testing is not available or could not economically be obtained. The objective of this study was to develop a partial data base for determining the seismic strength of saturated cohesionless materials, and, by using this data base, to broaden understanding of the mechanism of soil liquefaction induced in the laboratory.
The study is in support of efforts to mitigate the effects of earth-quakes through improved methods for determining the seismic strength of soils. To assist in this problem, cyclic triaxial test data were compiled from published literature and from commercial and research laboratories involved in cyclic testing of cohesionless soils; the data were organized, reviewed, and evaluated. Results were grouped by soil type (Unified Classification System). This data may assist geotechnical engineers to evaluate the seismic strength of cohesionless materials.
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How the strength properties of gravel soils depend on the type and state of the sand filling the pores
Author: A. A. Vasil'eva, V. V. Mikheev, G. L. Lobanova | Size: 502 KB | Format:PDF | Quality:Unspecified | Publisher: Soil Mechanics and Foundation Engineering | Year: 1971 | pages: 5
Little information is available on the shear parameters of coarse detrital soils. Because these conrain
large fragments, it is very difficult to determine their shear resistances. Apparatus and methods (of
laboratory and field types) for investigation of coarse detrital soils have not yet been perfected. Construction
Specification SNiP II-B.I-62 states that the normative pressures on bases of coarse detrital soils
should depend on the type and state of the filler. But in determining the shear parameters of the pore fillers
of such soils we meet almost insuperable difficulties owing to the need to prepare the filler while conserving
the natural state of density and wetness.
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Article/eBook Full Name: How the strength properties of gravel soils depend on the type and state of the sand filling the pores
Author(s): A. A. Vasil'eva, V. V. Mikheev, G. L. Lobanova
Edition: 8(3)
Publish Date: 1971
Published By: Soil Mechanics and Foundation Engineering
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