Evaluation of the influence of vertical irregularities on the seismic performance of a nine‐storey steel frame

A methodology based on incremental dynamic analysis (IDA) is presented for the evaluation of structures with vertical irregularities. Four types of storey‐irregularities are considered: stiffness, strength, combined stiffness and strength, and mass irregularities. Using the well‐known nine‐storey LA9 steel frame as a base, the objective is to quantify the effect of irregularities, both for individual and for combinations of stories, on its response. In this context a rational methodology for comparing the seismic performance of different structural configurations is proposed by means of IDA. This entails performing non‐linear time history analyses for a suite of ground motion records scaled to several intensity levels and suitably interpolating the results to calculate capacities for a number of limit‐states, from elasticity to final global instability. By expressing all limit‐state capacities with a common intensity measure, the reference and each modified structure can be naturally compared without needing to have the same period or yield base shear. Using the bootstrap method to construct appropriate confidence intervals, it becomes possible to isolate the effect of irregularities from the record‐to‐record variability. Thus, the proposed methodology enables a full‐range performance evaluation using a highly accurate analysis method that pinpoints the effect of any source of irregularity for each limit‐state. Copyright © 2006 John Wiley & Sons, Ltd.     

Adaptation of the ionospheric radio channel parameters to the current conditions using observations of the signals of reference radio stations

A method of adaptation of the ionospheric channel parameters to the current conditions is proposed. The observational data on the temporal behavior of signals of radio stations with known location and set of working frequencies (the so-called reference stations) are used as information describing the current state of the channel. A facility that makes possible to determine by simple means the moments of radio rises and declines on the reference paths has been created. A technique that relates for these instants working frequencies of the stations with maximum usable frequencies of the paths has been developed. By means of an approximate solution of the inverse problem using the method of characteristics for the calculation of radiowave propagation and the monthly average semiempirical model of the ionosphere, the height profile of electron density in a certain spatial region is refined. The efficiency of the proposed method of adaptation of the ionospheric channel parameters using the data of vertical sounding is assessed and the expediency of practical application of such adaptation is shown.     

Numerical simulation of the mutual conversion of ordinary and extraordinary waves in a magnetised plasma by artificial ionospheric turbulence

Some effects of normal mode coupling in weakly anisotropic inhomogeneous plasma are analysed on the basis of the numerical solution of transfer equations for the Stokes parameters. The numerical analysis of normal mode conversion on a set of isolated irregularities demonstrates the possibility of an effective polarisation transformation on such structures. It is shown that by the appropriate selection of discrete irregularities of the external magnetic field direction or plasma electron concentration resulting in radio-wave refraction, one can control electromagnetic radiation polarisation characteristics. Analytical expressions for mean Stokes parameters have been obtained for the rare isolated irregularities. The opportunity for the simulation of mutual wave conversion processes in the ionospheric heating experiments is discussed.     

Anisotropy of ionospheric irregularities determined from the amplitude of satellite signals at a single receiver

A new method of determining the anisotropy parameters of small-scale irregularities in the ionospheric F region is presented and experimental results are shown. The method is based on observations of amplitude fluctuations of radio waves transmitted by satellites flying above the F region. In practice, Russian navigational satellites are used and both the amplitude and the phase of the signal is measured on the ground level. The method determines both the field-aligned anisotropy and the field-perpendicular anisotropy and orientation of the spatial spectrum of the irregularities, assuming that the contours of constant power have an elliptic shape. A possibility of applying the method to amplitude tomography is also discussed. Using a chain of receivers on the ground level, one could locate the regions of small-scale irregularities as well as determine their relative intensities. Then the large-scale background structures could be mapped simultaneously by means of ordinary ray tomography using the phase observations, and therefore the relations of small-scale and large-scale structures could be investigated.     

Determining the parameters of the layer of scattering irregularities,forming coherent echo,according to the Irkutsk IS Radar data

The method for determining the parameters of the layer of scattering irregularities, form coherent echo, based on the Irkutsk Incoherent Scatter (IS) Radar data is presented. It has been indicted that the method has the necessary accuracy. The processing of experimental data for the periods of September 25–26, 1998, and July 15–16, 2000, indicated that our results are in good agreement with the data obtained by other researchers. The analysis of the experiments with a high time resolution made it possible to reveal the time variation in the determined parameters. The time variations in the layer thickness and height do not contradict the data obtained by other researchers, and the time variations in the angular sensitivity of irregularities has been observed for the first time and requires further studies.     

Atmospheric parameters measured using artificial periodic irregularities with different spatial scales

The parameters of the neutral atmosphere have been studied using artificial periodic irregularities of the ionospheric plasma. A few measurement cycles were carried out in 2006–2007 using the new method, in particular: irregularities were created by powerful radiowaves at two separated frequencies. The possibilities of the method have been demonstrated. Based on the relaxation times of artificial periodic irregularities measured at two frequencies, the N(z) electron density profiles in the 95–115 km height interval have been determined and have been used to estimate the parameters of the neutral atmosphere. The results of determining the temperature and density of the neutral atmosphere are presented and compared with the data obtained earlier.     

Comparison of the orientation of small-scale electron density irregularities and F region plasma flow direction

Results are shown from an experimental campaign where satellite scintillation was observed at three sites at high latitudes and, simultaneously, the F region plasma flow was measured by the nearby EISCAT incoherent scatter radar. The anisotropy parameters of field-aligned irregularities are determined from amplitude scintillation using a method based on the variance of the relative logarithmic amplitude. The orientation of the anisotropy in a plane perpendicular to the geomagnetic field is compared with the direction of F region plasma flow. The results indicate that in most cases a good agreement between the two directions is obtained.     

基于最佳摄动量法的桩基承载力反演

通过高应变动力试桩法来获得桩土参数是目前比较流行的试桩方法,其原理主要是通过以桩顶的实测信息来反演桩土参数,其中比较成熟的CAPW APC法主要用试凑法来反演桩土模型参数,其反演结果呈现一定的随机性且正确性过于依赖操作者经验。本文尝试以CAPW APC法所采用比较成熟的桩土模型为基础,引入基于最佳摄动量法的局部优化方法来反演桩土参数。在弹性波波动方程隐式差分的基础上,对反演参数采用摄动展开并推导出参数反演的递推公式,最后给出合适的反演算法。考虑到初始参数对局部优化方法的影响,根据场地的实际情况选取合适的初始模型,计算显示可以获得比较理想的结果,说明本法是对桩基动测方法的一种有效的新尝试。     

The inversion of incoherent scatter spectra with a non-Maxwellian electron distribution

With the action of powerful, high-frequency (HF) radio waves, the ionosphere plasma will depart from the equilibrium state and the non-Maxwellian distribution function can be produced. An artificial field-aligned irregularities (AFAI) model is introduced to describe the distortion from the normal shape, and the measured data are analyzed with this model during ionosphere heating at a 186-km height on August 15th, 2006. The electron temperature and density deduced from the AFAI model are compared with the results obtained from a standard procedure. The inversion of the electron temperature is evidently affected, and the overestimation is up to 22.9%. Owing to the introduction of the AFAI model, the new irregularities’ parameters can be obtained, which implies that incoherent scatter radar is feasible as a ground-based instrument to diagnose information on irregularities.     

Effect of ionospheric irregularities on accuracy of dual-frequency GPS systems

The residual error of the ionospheric correction of signals from dual frequency GPS systems, related to a ray deviation in random ionospheric irregularities, is studied. The formulas taking into account ray deviation from a straight line in an inhomogeneous ionosphere have been obtained based on the disturbance theory when solving the ray equations. These formulas have been used to estimate the extreme accuracy of a dual frequency GPS method. The algorithm for correcting this ionospheric error of the second order using three-frequency reception has been proposed.     

Amplification of earthquake ground motion by steep topographic irregularities

The problem of amplification of seismic waves by surface topographic irregularities is addressed through analytical and numerical investigations. First, a closed‐form expression for estimating the fundamental vibration frequency of homogeneous triangular mountains is obtained, using Rayleigh's method. Subsequently, numerical modelling based on the spectral element approximation is used to study the 3D seismic response of several real steep topographic irregularities excited by vertically propagating plane S‐waves. A topographic amplification factor is obtained for each case, by a suitable average of the ratio of acceleration response spectra of output vs input motion. The 3D amplification factors are then compared with those derived by 2D analyses as well as with the topographic factors recommended in Eurocode 8 for seismic design. Copyright © 2002 John Wiley & Sons, Ltd.     

Response uncertainty and time-variant reliability analysis for hysteretic MDF structures

Response uncertainty evaluation and dynamic reliability analysis corresponding to classical stochastic dynamic analysis are usually restricted to the uncertainties of the excitation. The inclusion of the parameter uncertainties contained in structural properties and excitation characteristics has become an increasingly important problem in many areas of dynamics. In the present paper, a point estimate procedure is proposed for the evaluation of stochastic response uncertainty, and a response surface approach procedure in standard normal space is proposed for analysis of time-variant reliability analysis for hysteretic MDF structures having parameter uncertainties. Using the proposed procedures, the response uncertainties and time-variant reliability can be easily obtained by several repetitions of stochastic response analysis under given parameters without conducting sensitivity analysis, which is considered to be one of the primary difficulties associated with conventional methods. In the time-variant reliability analysis, the failure probability can be readily obtained by improving the accuracy of the first-order reliability method using the empirical second-order reliability index. The random variables are divided into two groups, those with CDF and those without CDF. The latter are included via the high-order moment standardization technique. A numerical example of a 15F hysteretic MDF structure that takes into account uncertainties of four structural parameters and three excitation characteristics is performed, based on which the proposed procedures are investigated and the effects of parameter uncertainties are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Three-dimensional dynamic soil–structure interaction analysis in the time domain

A new numerical procedure is proposed for the analysis of three-dimensional dynamic soil–structure interaction in the time domain. In this study, the soil is modelled as a linear elastic solid, however, the methods developed can be adapted to include the effects of soil non-linearities and hysteretic damping in the soil. A substructure method, in which the unbounded soil is modelled by the scaled boundary finite-element method, is used and the structure is modelled by 8–21 variable-number-node three-dimensional isoparametric or subparametric hexahedral curvilinear elements. Approximations in both time and space, which lead to efficient schemes for calculation of the acceleration unit-impulse response matrix, are proposed for the scaled boundary finite-element method resulting in significant reduction in computational effort with little loss of accuracy. The approximations also lead to a very efficient scheme for evaluation of convolution integrals in the calculation of soil–structure interaction forces. The approximations proposed in this paper are also applicable to the boundary element method. These approximations result in an improvement over current methods. A three-dimensional Dynamic Soil–Structure Interaction Analysis program (DSSIA-3D) is developed, and seismic excitations (S-waves, P-waves, and surface waves) and externally applied transient loadings can be considered in analysis. The computer program developed can be used in the analysis of three-dimensional dynamic soil–structure interaction as well as in the analysis of wave scattering and diffraction by three-dimensional surface irregularities. The scattering and diffraction of seismic waves (P-, S-, and Rayleigh waves) by various three-dimensional surface irregularities are studied in detail, and the numerical results obtained are in good agreement with those given by other authors. Numerical studies show that the new procedure is suitable and very efficient for problems which involve low frequencies of interest for earthquake engineering. Copyright © 1999 John Wiley & Sons Ltd     

Rapid assessment for seismic vulnerability of low and medium rise infilled RC frame buildings

An indexing method for rapid evaluation of the seismic vulnerability of infi lled RC frame buildings in Jordan is proposed. The method aims at identifying low and medium rise residential buildings as safe or in need of further detailed evaluation. Following a rapid visual screening, the building is assigned a Basic Capacity Index(BCI); fi ve performance modifi ers are identifi ed and multiplied by the BCI to arrive at the Capacity Index(CI) of the building. A Capacity Index lower than a limit CI value indicates that the screened building could experience moderate earthquake damage whereas a higher value implies that minor damage, if any, would take place. To establish the basic evaluation parameters; forty RC frame buildings were selected, designed and analyzed using static nonlinear analysis and incorporating the effect of infi ll walls. Effects of seismicity, local site conditions, horizontal irregularities(setbacks and re-entrant corners), vertical irregularities(soft story at ground fl oor level) and overhangs on the seismic performance of local buildings were examined. Assessment forms were designed and used to evaluate and rank 112 sample buildings. About 40% of the surveyed buildings were found to be in need of detailed evaluation to better defi ne their seismic vulnerabilities.     

Fair function minimization for interpretation of magnetic anomalies due to thin dikes, spheres and faults

A new method is proposed to interpret magnetic anomalies due to a thin dike, a sphere, and a fault like structure, where depth, horizontal location, effective magnetization intensity and effective magnetization inclination of a buried structure are simultaneously obtained. The proposed method is based on Fair function minimization and also on stochastic optimization modeling. This new technique was firstly tested on a theoretical synthetic data randomly generated by a chosen statistical distribution from a known model with different random noises components. This mathematical simulation shows a very close agreement between the assumed and the estimated parameters. The applicability and validity of this method are thereafter applied to magnetic anomaly data taken from United States, Australia, India, and Brazil. The agreement between the results obtained by the new method and those obtained by other interpretative methods is good and comparable. Moreover, the depth obtained by such a method is found to be in high accordance with that obtained from drilling information.     

Application of Multi-Criteria Decision Analysis to Geoelectric and Geologic Parameters for Spatial Prediction of Groundwater Resources Potential and Aquifer Evaluation

Prediction of groundwater resources potential is a spatial decision problem that involves a set of multiple evaluation parameters. In order to produce a groundwater resources potential prediction model of higher reliability and precision in a given study area, the effects of all the important parameters that can contribute to the groundwater occurrence in the area must be integrated. However, the methodology of integrating these parameters such that the relative importance of each is reflected is still a challenge that has not been efficiently handled. In this study, the principle of multi-criteria decision analysis in the context of the analytical hierarchy process is proposed as a technique that can yield a prediction model of higher reliability and precision. The proposed technique was applied to geoelectric and geologic parameters, derived from the results of the interpretation of 2D resistivity imaging data acquired from the study area. The advantage of the proposed technique is that it reduces bias in decision making. The main objective of the study is to produce groundwater potential map for the area. Furthermore, an attempt was also made in the study to characterize the aquifer of the area by estimating the Dar-Zarrouk parameters, using the integration of borehole and 2D resistivity data. The success rate (accuracy) of the prediction was established to be 80 %. Furthermore, the regression line fitted to the aquifer transmissivity and transverse resistance data shows linear relationship with a high regression coefficient of 0.79. The prediction success rate obtained showed that the method proposed in this study is reliable, accurate, and an improved technique of integrating multiple parameters for holistic evaluation of groundwater resources.     

电离层不规则结构漂移的GPS测量及其初步结果

本文阐述了利用GPS接收机台阵测量到的闪烁和TEC变化率ROT快速起伏图样估计F层不规则结构漂移的原理和方法,并利用实测数据估计了静日和暴时电离层不规则结构的水平漂移速度.短间距台网和超短间距台链观测实例的计算结果表明,暴时武汉地区引起TEC快速起伏的电离层不规则结构沿纬圈向西漂移,21∶30至03∶00 LT,西向漂移速度在约40 m/s至130 m/s的范围内变化;在桂林地区,磁静日午夜前后引起L波段电波闪烁的电离层不规则结构沿纬圈向东漂移,漂移速度从约70 m/s下降到约55 m/s,磁扰日午夜前不规则结构向西漂移,速度从约150 m/s下降到约50 m/s,午夜后转为向东漂移,速度从约25 m/s上升到约65 m/s.文中还提出了由单站多卫星观测估计F层不规则结构漂移的设想.实例分析与计算结果表明,利用单站多卫星观测估计电离层不规则结构漂移是一种合理可行的方法.     

基于ZH-1卫星探测的太阳活动低年顶部电离层不规则结构的时空特征

利用ZH-1卫星2019、2020年的原位电子密度观测数据,对卫星观测范围,即地理纬度南北65°之间午夜后顶部电离层的不规则结构进行研究,得到如下结果.(1)午夜后顶部电离层不规则结构集中区主要分布在地磁赤道、中纬度以及较高纬度区,白天赤道异常峰值区为不规则结构的谷值区.(2)不同纬度区不规则结构随地理经度分布呈现出明...     

An overview and synthesis of plasma irregularities in equatorial spread F

A unified picture of plasma irregularities in equatorial spread F is developed from the analysis of satellite, sounding rocket, and coherent scatter radar observations. The coherent scatter data are analyzed using a new in-beam radar imaging technique that permits direct comparison between radar data, in situ data, and computer simulations of the irregularities. Three varieties of irregularities, all produced by ionospheric interchange instabilities, are found to occur. Thin bottom-type layers are composed of waves with primary transverse wavelengths less than about 1 km and with significant parallel wavenumbers. These exist on magnetic flux tubes controlled by the E region dynamo and drift westward in the postsunset ionosphere. A nonlocal analysis is used to calculate their linear growth rate. When the F region dynamo takes control of the flux tube, bottomside irregularities can emerge. These are more robust irregularities with longer primary wavelengths and which exhibit greater vertical development. Nonlinear analyses explain the appearance of steepened structures in rocket observations and solitary waves in satellite observations of bottomside layers. The one-dimensional spectra of these irregularities obey power laws but are anisotropic and have variable spectral indices and spectral breaks. Very strong polarization electric fields can eject large regions of deeply depleted plasma through the F peak and form topside irregularities. Theoretical calculations supported by satellite data show that ion inertia may become important for topside irregularities. The one-dimensional spectra of irregularities in the inertial regime obey a k^−5/3 power law, but strong plasma inhomogeneity implies that Kolmogorov weak turbulence is not the explanation. Topside depletions are shown to bifurcate and also to pinch off from the bottomside.     

Equatorial plasma bubbles at altitudes of the topside ionosphere

A consistent patter, indicating that subtroughs in the He⁺ density and plasma bubbles can be considered as phenomena of the same origin, has been obtained within the scope of the existent model of equatorial plasma bubbles. The study has been performed based on the measurements of the ISS-b satellite, which flew during the period of high solar activity. The conclusion has been made based on a comparative analysis of the characteristics of subtroughs with the parameters of the known equatorial phenomena. (1) The similarity of the LT variations in the latitude of the minimums of subtroughs in the He⁺ density has been revealed. (2) It has been displayed that the variations in the averaged depth of subtroughs change from season to season similarly to the LT variations in the average velocity of the equatorial vertical plasma drift. (3) Good correlation (R = 0.67) between the occurrence probability of subtroughs and equatorial spread F statistics, constructed as the functions of LT and month, has been obtained. (4) The obtained velocity of the possible rise of plasma irregularities (observed as regions depleted in He⁺) is in good agreement with the ionosonde, satellite, and radar measurements of the equatorial plasma bubble velocities of the same period. (5) It has been indicated that plasma irregularities, reaching the altitudes of the topside ionosphere in the low-latitude and midlatitude regions during high solar activity, are most observable as depleted regions (subtroughs) of He⁺ density.