Influence of total charge in a blast on the intensity of ground vibrations—field experiment and computer simulation

A number of factors influence the generation, propagation and intensity of ground vibrations. However, there are conflicting opinions with regard to the influence of the blast size on the intensity of ground vibrations. This paper discusses the experiments conducted in an opencast coal mine in India and a simulation study carried out to establish the influence of total charge in a blast on the intensity of ground vibrations. Studies clearly indicate that the total explosive charge in a blast has insignificant influence on the intensity of ground vibrations for distances between 100 m and 3000 m.     

In situ experiments and seismic analysis of existing buildings. Part II: Seismic integrity threshold

The interest of in situ measurements (presented in Part I paper) for a seismic assessment of existing buildings is analysed in this paper. It is shown that the experimental modal characteristics obtained on regular concrete structures are described successfully by suited Timoshenko beam modelling. For a given structure, taking into account the experimental data, the corresponding beam model, and choosing the maximum tensile strain of concrete as damage criterion for key structural elements, a maximum level of the ground acceleration can be determined. This so‐called seismic integrity threshold is directly related to the onset of structural damages. This new approach is illustrated on one of the studied buildings. The advantages of using ambient vibrations survey for the vulnerability assessment of existing buildings are discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

A method for the transfer function matrix of combined primary–secondary systems using classical modal decomposition

An iterative method is presented to compute the transfer function matrix of combined primary–secondary systems for seismic response analysis. It accounts for non‐proportional damping and dynamic interaction of the combined system. A closed form sequence is developed for the iterative computation of the transfer function matrix. Such sequence is assembled using independently the real classical mode frequencies, shapes and damping ratios of the primary system, and the natural frequency and critical damping ratio of the SDOF secondary system. The necessary and sufficient condition for convergence of the sequence is given in the paper. The method is illustrated through a couple of examples, including one of an appendix connected to a multi‐storey shear building. Convergence of the method is thoroughly analysed and peak responses are obtained using a spectral density function approach. Copyright © 2005 John Wiley & Sons, Ltd.     

Efficiency of trenches along railways for trains moving at sub- or supersonic speeds

A full 3D analytical approach is adopted to account for trenches on one or both sides close to a railroad. Low-frequency ground vibrations are investigated due to the passing of trains, and open trenches are used as wave barriers. The modelling technique is based on Fourier transforms and Fourier series. The ground is modelled as a layered semi-infinite domain and the embankment with finite layers. The trenches are obtained by simulating the upper surface layer with two or three finite rectangular regions with appropriate widths. A particular boundary condition is adopted at the vertical sides of all finite regions to enable the solution procedure. Rails and sleepers are accounted for with Euler–Bernoulli beams and an anisotropic Kirchhoff plate with transversal isotropy. The wheel loads from the boogie wheel pairs of the train are simulated as moving forces. Hence, no irregularities in rails or wheels are accounted for.     

Assessment of the frequency domain decomposition technique by forced‐vibration tests of a full‐scale structure

Dynamic characteristics of buildings are of utmost importance in earthquake engineering. The vibration periods are required to determine design loads, and damping is necessary in time‐history analysis. These parameters are generally obtained through forced‐vibration tests (FVTs) or after a seismic event in the case of permanently instrumented structures. However, for large civil engineering structures, FVTs are often too costly or practically difficult, and ambient or output‐only methods are used. This paper describes a comparison between ambient and FVTs carried out on a two‐story building. Results from both testing methods are compared and discussed in order to assess the vibration properties estimates obtained with the frequency domain decomposition technique. Copyright © 2007 John Wiley & Sons, Ltd.     

Gaussian mixture–based equivalent linearization method (GM-ELM) for fragility analysis of structures under nonstationary excitations

Gaussian mixture–based equivalent linearization method (GM-ELM) is a recently developed stochastic dynamic analysis approach which approximates the random response of a nonlinear structure by collective responses of equivalent linear oscillators. The Gaussian mixture model is employed to achieve an equivalence in terms of the probability density function (PDF) through the superposition of the response PDFs of the equivalent linear system. This new concept of linearization helps achieve a high level of estimation accuracy for nonlinear responses, but has revealed some limitations: (1) dependency of the equivalent linear systems on ground motion intensity and (2) requirements for stationary condition. To overcome these technical challenges and promote applications of GM-ELM to earthquake engineering practice, an efficient GM-ELM-based fragility analysis method is proposed for nonstationary excitations. To this end, this paper develops the concept of universal equivalent linear system that can estimate the stochastic responses for a range of seismic intensities through an intensity-augmented version of GM-ELM. Moreover, the GM-ELM framework is extended to identify equivalent linear oscillators that could capture the temporal average behavior of nonstationary responses. The proposed extensions generalize expressions and philosophies of the existing response combination formulations of GM-ELM to facilitate efficient fragility analysis for nonstationary excitations. The proposed methods are demonstrated by numerical examples using realistic ground motions, including design code–conforming nonstationary ground motions.     

多维耦合振动复合压电振子的设计

运用表观弹性法,采用二次径向谐振频率计算表观弹模量,设计高度与直径可比拟,谐振频率不满足压电晶片和金属圆片最低径向谐振频率方程的多维耦合振动复合电振子。用本方法设计垂直探鱼仪的换能器和提高优质单胞藻饲料多不饱和脂肪酸含量的超声辐射仪换能器。计算结果表明,理论与值与实验值相符合。这种方法简单,方地压电晶片的径向谐振频率低于换能器揩能器谐振频率的多维耦合振动复合压电振的设计。     

Modal analysis of a fast patrol boat made of composite material

The structural dynamic behaviour of a fast patrol boat is studied with two- and three-dimensional idealizations for dry-hull analysis. A preliminary two-dimensional beam analysis is conducted by means of the Prohl-Myklestad method to derive a first estimate of the first four symmetric mode shapes. A more complex three-dimensional finite element model is developed in order to evaluate the modal characteristics for both symmetric and coupled anti-symmetric distortions, with the emphasis placed on the former.     

Analysis of disturbances in the Planetary Fourier Spectrometer through numerical modeling

Fourier transform spectrometers are instruments with high sensitivity to many kinds of disturbances. This study started from the analysis of the disturbances related to mechanical vibrations on the PFS FTIR spectrometer to show how the measured spectra can differ from the actual ones. The complete study, more in general, accounts for the characteristics of a real instrument and its operating environment to show, which can be the effects of many sources of disturbances on realistic measurements. The analysis is especially relevant when the spectra are used for the determination of parameters through “best fitting techniques” by matching with synthetic ones because it shows how spectral features used in these studies can be modified by disturbances. A previous work addressed the theoretical treatment of vibrations borne effects on FTIR spectrometers and is the ground work for the present; however, that study, being based on an analytical approach could only show examples of single effects on simplified input signals such as emission lines. This study conversely is based on a numerical model, developed in order to include altogether the effects addressed in the theoretical work to show combined effects on complex spectra like those expected from Mars. This allows not only to evaluate the linked effects of many kinds of disturbances but also to account for the real spectrometer characteristics. The use of synthetic spectra as input allows the comparison between expected spectra and measured ones. The simulation is tailored on the Planetary Fourier Spectrometer (PFS), onboard the ESA Mars Express spacecraft, from 2003 orbiting around Mars and in particular on its short wavelength (SW) channel, where many disturbances are more evident.