Simplified discrete systems for dynamic analysis of structures on footings and piles

A simplified discrete system in the form of a simple oscillator is developed to simulate the dynamic behavior of a structure founded through footings or piles on compliant ground, under harmonic excitation. Exact analytical expressions for the fundamental natural period and the corresponding damping coefficients of the above system are derived, as function of geometry and the frequency-dependent foundation impedances. In an effort to quantify the coupling between swaying and rocking oscillations in embedded foundations such as piles, the reference system is translated from the footing–soil interface to the depth where the resultant soil reaction is applied, to ensure a diagonal impedance matrix. The resulting eccentricity is a measure of the coupling effect between the two oscillation modes. The amounts of radiation damping generated from a single pile and a surface footing are evaluated. In order to compare the damping of a structure on a surface footing and a pile, the notion of static and geometric equivalence is introduced. It is shown that a pile may generate significantly higher radiation damping than an equivalent footing, thus acting as an elementary protective system against seismic action.     

Quantifying the epistemic uncertainty in ground motion models and prediction

The aim of this paper is to compute the ground-motion prediction equation (GMPE)-specific components of epistemic uncertainty, so that they may be better understood and the model standard deviation potentially reduced. The reduced estimate of the model standard deviation may also be more representative of the true aleatory uncertainty in the ground-motion predictions.The epistemic uncertainty due to input variable uncertainty and uncertainty in the estimation of the GMPE coefficients are examined. An enhanced methodology is presented that may be used to analyse their impacts on GMPEs and GMPE predictions. The impacts of accounting for the input variable uncertainty in GMPEs are demonstrated using example values from the literature and by applying the methodology to the GMPE for Arias Intensity. This uncertainty is found to have a significant effect on the estimated coefficients of the model and a small effect on the value of the model standard deviation.The impacts of uncertainty in the GMPE coefficients are demonstrated by quantifying the uncertainty in hazard maps. This paper provides a consistent approach to quantifying the epistemic uncertainty in hazard maps using Monte Carlo simulations and a logic tree framework. The ability to quantify this component of epistemic uncertainty offers significant enhancements over methods currently used in the creation of hazard maps as it is both theoretically consistent and can be used for any magnitude–distance scenario.     

云南鲁甸6.5级地震灾害特点浅析

通过对2014年8月3日云南鲁甸6.5级地震震害开展实地调查,对灾区破坏情况进行总体介绍,并就各烈度区特征和建筑物震害、地震地质灾害、工程结构震害进行分析,初步得出本次地震的一些震害特点.一是灾区人口密度大,人员死亡较集中.人员死亡主要集中在Ⅷ和Ⅸ度区.二是地震振动强,灾区破坏严重.本次地震震源深度12km,极震区烈度高达Ⅸ度,震源破裂在11s内集中释放.三是抗震能力弱,房屋破坏严重.灾区属国家级贫困区,农村民居抗震能力弱,且多数民房坐落在河谷陡坡上,边坡效应加重房屋震害,重灾区砖木和土木房屋成片损毁、倒塌.四是灾区条件恶劣,救灾难度大.震区活动断裂密集发育、地质破碎疏松、地形崎岖不平,又恰值雨季,诱发极其严重次生地质灾害,导致人员伤亡,造成灾区大面积交通、通信、电力中断,救援物资与救援力量无法及时发挥作用.     

ShakeMap在2014年于田7.3级地震快速损失评估中的应用

本文介绍了2014年2月12日新疆于田Ms7.3级地震的震害特征,将改进的ShakeMap烈度图成功地运用到了于田7.3级地震的快速损失评估中.结果表明,考虑了场地效应的ShakeMap烈度图明显优于当前“十五”应急指挥系统的衰减关系模型的烈度图,能更好地为地震灾害损失评估服务,其快速评估的结果更接近官方公布的数据.因此,应用ShakeMap技术在震害损失快速评估中,能显著地提高评估结果的准确性.     

Modifying the intensity distribution by assessing the reliability

This article presents an application of a procedure to modify the intensity distribution by assessing the reliability. There are two potential possibilities that may influence the intensity distribution: (1) For the interpolation error, we generate a measured grid across the calculation region. When the point to station spacing is <5 km, we consider the results precise; however, some points have less precision because these are farther from the corresponding stations. When the spacing is between 5 and 50 km, we consider the results imprecise and define a reliability factor that correlates with the distance. (2) Some records may have errors that result from local site conditions, equipment problems, or some disturbance such as lightning stroke, which will lead to some grid points having an incorrect intensity. We regress the attenuation relation for sites with abnormal intensities and consider the results to be accurate when the standard deviation (STD) is <σ and inaccurate when the STD is > 2σ. We then define a reliability factor to correlate with STD between σ and 2σ, such that the intensity distribution is in accord with both wave propagation theory and the investigation intensity.     

Model and parameter uncertainty in IDF relationships under climate change

Quantifying distributional behavior of extreme events is crucial in hydrologic designs. Intensity Duration Frequency (IDF) relationships are used extensively in engineering especially in urban hydrology, to obtain return level of extreme rainfall event for a specified return period and duration. Major sources of uncertainty in the IDF relationships are due to insufficient quantity and quality of data leading to parameter uncertainty due to the distribution fitted to the data and uncertainty as a result of using multiple GCMs. It is important to study these uncertainties and propagate them to future for accurate assessment of return levels for future. The objective of this study is to quantify the uncertainties arising from parameters of the distribution fitted to data and the multiple GCM models using Bayesian approach. Posterior distribution of parameters is obtained from Bayes rule and the parameters are transformed to obtain return levels for a specified return period. Markov Chain Monte Carlo (MCMC) method using Metropolis Hastings algorithm is used to obtain the posterior distribution of parameters. Twenty six CMIP5 GCMs along with four RCP scenarios are considered for studying the effects of climate change and to obtain projected IDF relationships for the case study of Bangalore city in India. GCM uncertainty due to the use of multiple GCMs is treated using Reliability Ensemble Averaging (REA) technique along with the parameter uncertainty. Scale invariance theory is employed for obtaining short duration return levels from daily data. It is observed that the uncertainty in short duration rainfall return levels is high when compared to the longer durations. Further it is observed that parameter uncertainty is large compared to the model uncertainty.     

Precise Synchrotron Radiation Spectrum of Fast-cooling Electrons and the Prompt GRB Emission

It is generally believed that the synchrotron radiation of electrons from the internal shock is the main radiation mechanism of the prompt GRB (gamma-ray burst) emission. However, what this model predicts can not explain observations well. In this paper, we confirm that electrons are quickly cooled due to radiation losses and also point out that the synchrotron radiation spectrum presented in previous papers is a relatively rough estimation. We get the precise synchrotron radiation spectrum of fast-cooling electrons by carrying out a numerical calculation, and thereby reasonably explain the observed distribution of low-energy spectral index (α) of long GRBs based on a unified model. In addition, we fit the correlation between α and the peak energy of the νFν spectrum (E_p).     

近50 年中国光合有效辐射的时空变化特征

基于中国陆地区域1961-2007 年逐年/季节平均光合有效辐射(PAR) 的空间化数据(10km×10km),结合GIS 空间分析技术与Mann-Kendall 趋势分析方法对近50 年年/季节平均PAR进行时空变化特征分析。结果表明：① 全国PAR的空间分布差异明显,总体上呈现东南低、西部高的特点,年均PAR在17.7~39.5 mol m^-2 d^-1之间。② 全国像元平均的年/季节平均PAR表现出一个较明显的波动下降过程,年均PAR降幅为0.138 mol m^-2 d^-1/10a,不同季节下降幅度存在差异,夏季降幅最大。③ 逐像元分析显示全国大部分地区PAR呈现显著下降趋势(α = 0.05),东部趋势变化较西部明显,夏冬两季在PAR年际变化中的贡献最大。华北地区在不同季节都是下降区域,而青藏高原西北地区在不同季节都表现为上升趋势。④ PAR年际变化率空间分布在不同时段差异明显,同一地区PAR年际变化率不仅在不同季节存在差异,而且在不同时段也不相同,总体上1990年代之前PAR下降较快,之后下降趋势变缓。     

Map errors that could account for deviations from a uniform intensity of land change

Intensity Analysis is a mathematical framework that compares a uniform intensity to observed intensities of temporal changes among categories. Our article summarizes Intensity Analysis and presents a new method to compute the minimum hypothetical error in the data that could account for each observed deviation from a uniform intensity. A larger hypothetical error gives stronger evidence against a hypothesis that a change is uniform. The method produces results for five groups of measurements, which are organized into three levels of analysis: interval, category, and transition. The method applies generally to analysis of changes among categories during time intervals, because the input is a standard contingency table for each time interval. We illustrate the method with a case study concerning change during three time intervals among four land categories in northeastern Massachusetts, USA. Modelers can perform the analysis using our computer program, which is free.     

历史强震烈度点数量的统计特征及其对历史地震参数的影响

以1995 年出版的《中国历史强震目录(公元前23 世纪～ 公元1911 年)》为基础,首先统计了中国历史强震烈度点数量的总体分布情况,然后对历史强震烈度点数量在时间、空间和强度上的分布进行了分析,结果表明中国历史强震的烈度点资料普遍偏少。在时间和强度上,公元1500 年以前,受条件所限很多历史大震没有记载或者有些记载没能流传至今,而流传下来的历史地震也仅有少数烈度点;公元元年以前,史料记载过于简单且有缺漏,导致估定的最大震级记录不超过7 级;公元1500 年以后才开始出现8 级以上大震记录。在空间上,中国东部地区地震记载点明显较西部地区更为翔实。本文对单烈度记载点历史强震情况进行了重点分析,并将既有仪器记录又有宏观考察的现代地震按照历史地震参数获取方法进行处理,以讨论烈度点稀缺对确定历史地震参数的影响。