建筑结构时程分析法中天然地震波的选择

要保证建筑结构时程分析结果的合理性,必须合理选择输入地震波。从工程实例出发,考虑峰值、频谱特性、地震动持时及适当的地震波数量,说明如何挑选合适的强震记录作为结构工程时程分析的输入,以此进行工程的抗震设计。     

近场强地震动合成方法研究及地震动模拟

本文通过对近场强地震动合成方法的研究,采用随机有限断层法合成了沈阳地区近场强地震动,将得到的断层附近加速度时程结果与已有的采用混合有限元法计算结果进行对比。认为这一合成地震动的方法在重大工程选址以及缺乏强震记录地区开展抗震设防工作具有重要意义。     

用人工地震波研究三峡地区地面地震动衰减特征

利用长江三峡工程坝区及外围深部构造的人工地震波记录资料,进行了相对速度幅值、速度反应谱和加速度反应谱衰减特征分析,同时利用历史地震资料经转换命同的地震动衰减规律进行对比,反映出由人工地震记录地震动参数衰减特征与由历史资料转换确定的地震动衰减特征是有差异的,在不同地质条件的局部地区,这一差异更为明显,这些结果中为缺乏强震记录的地区的地震动估计提供参考。     

地震动的小波分析技术在高层结构抗震设计中的应用研究

利用具有良好时频局部化性质的小波基函数时频分析真实地震动,提出一种可行的基于小波分析法调整地震动的方法。实际地震波(El Centro波和TH2TG055波)经过调幅、小波变换和标准反应谱拟合得到调整后的地震波,将其输入到拟建结构模型中进行地震反应分析,对比层间剪力、层间位移及层间位移角等几方面的计算结果,表明选取小波分析后的地震波作为结构时程分析输入能够得到比较准确的数值,满足结构抗震设计的需要,在工程应用方面具有一定的应用参考价值。     

工程结构地震反应与地震动输入关系研究

工程结构地震动输入是结构抗震设计研究中的重要问题,输入的合理与否直接影响着结构抗震能力。本文以框架结构为分析对象,将结构振动周期作为结构动力参数,地震记录加速度反应谱的特征周期作为地震动特征参数,通过计算对比发现:场地条件相同、峰值加速度相同、震中距相近的情况下,反应谱特征周期与结构基本周期接近的地震记录会让结构产生较大的地震反应。     

基于水工设计反应谱的人工地震波合成及应用

在研究和评估水工建筑物的抗震性能时,人工模拟地震波是一种常用的输入荷载。为此本文建立了地震动的随机数学模型,确定了白噪声平稳过程的基本参数,根据设计反应谱和功率谱,功率谱与幅值谱之间的关系,并以随机相位角和强度包络线为参数,建立了频谱曲线。利用MATLAB编制相应程序,以FFT变换和FFT逆变换建立时域和频域之间的关系,调试反应谱与设计反应谱之间的误码差,实现了人工地震动的生成。为了消除人工波中残余长周期分量的影响,本文利用最小二乘法拟合原始加速度均值,利用加速度均值对人工地震动加速度进行校正,纠正了位移时程的漂移。结果表明该方法计算精度高和收敛快。最后以生成的人工地震动为输入,计算工程结构的动力响应,以期对工程抗震设计提供参考和依据。     

《强震观测与分析原理》一书评介

强震仪的出现和强震记录的获得,使结构抗震理论和抗震措施得以从宏观经验的定性描述,逐步转向以强震观测资料为依据的定量方面发展。当代地震工程学的发展,在一定程度上是以强震观测为基础的。地震学家也应用强震观测资料于震源机制、地震能量和地震波传播等的研究。     

缺乏强震观测资料地区地震动参数的估算方法

本文提出了一个在缺乏强震观测资料的地区估算地震动参数的新方法。建议方法的基点是:(1)缺乏强震观测资料的地区有烈度衰减资料,参考地区则既有地震动衰减资料又有烈度衰减资料;(2)在震级相同的条件下,利用烈度与地震动参数的换算关系求得所需要的地震动衰减规律。文中利用几个地区已知的地震动和烈度衰减资料对建议的方法作了比较验证。使用本文建议的方法可直接估算重点工程抗震设计所需要的场地地震动参数,也可供修改我国抗震规范规定设计地震动时参考。     

地震动演变功率谱模型参数的统计建模

工程上常将规范反应谱拟合的确定性取值作为地震动演变功率谱参数,这虽然便于工程应用,但同时存在明显弊端:一方面,参数并非从实测强震记录中获得,具有较强的经验性;另一方面,确定性参数生成的地震动样本过于规则,且工程特性单一,无法全面地反映地震动的随机性。为了克服上述难题,从PEER的NGAGWest2地震动数据库中筛选1 766条主轴方向的实测强震记录,并根据《中国地震动参数区划图》建议的场地类别和聚类方法划分为15组;随后,识别实测强震记录的演变功率谱参数,并结合K-S检验和BIC信息准则,确定每个参数最优概率模型;最后,根据演变功率谱参数统计建模结果,结合降维方法,生成了Ⅱ类场地与Ⅲ类场地的代表性时程。与《建筑抗震设计规范》中建议取值不同,研究参数来源于实测地震动,且具有随机性,避免地震动样本工程特性的单一化和规则化。     

基于小田原试验场地数据的不同基岩输入模型对预测地震动特征的影响研究

随着强震台网的密布及观测记录的增加,为研究各类局部场地地震反应预测模型的合理性提供了有效的参考依据,也使利用强震记录及场地条件研究地震动特征成为可能。选取场地地质参数资料和地震记录数据齐全的日本小田原（Ashigara Valley）盲测试验场地,通过对比不同地震动输入方式及场地反应分析模型,研究地震动特征,分析现有模型的优劣。基于1990年8月5日M5.1强震事件的地表基岩记录和地下基岩地震记录,采用地下台强震记录直接输入、地表基岩台强震记录减半为基底地震动输入、地表基岩台强震记录反演为基底地震动输入作为3种基岩地震动输入。基于局部场地条件分别建立一维等效线性模型、二维黏弹性模型及二维时域等效线性化模型等工程中常用的场地数值分析模型,进行局部场地地震反应分析,预测该盲测场地的地表地震动特征,并与对应的实测强震记录结果进行对比,分析不同基岩地震动输入方式对预测地震动特征及地表土层反应谱特征的影响,重点分析地震动输入、土体非线性、场地横向不均匀性及几何与非线性特征共同作用等因素对地表地震动特征的影响,以期为地表地震动的合理预测提供参考。     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Foreword

Destructive earthquakes have caused great damage in China and the United States and collapsing buildings havecaused many deaths and injuries. The field of earthquake engineering studies earthquake hazards, the occurrence ofearthquakes of various magnitudes, the nature of the ground shaking during an earthquake, the vibration of structuresduring earthquakes, the strengthening of existing structures and the design of new structures to be earthquake resistant,and finally, how to cope with earthquake damage and restore a city to normal functioning. Such efforts are in progressin both countries, but unfortunately, the language barrier interferes with the free flow of information between China andthe Untied States. It would be mutually beneficial if some means could be developed to promote the exchangeof information across the Pacific Ocean. This new journal has been established for this purpose and its success willbe an important step in promoting earthquake engineering in China and the United States.     

WORLD ASSOCIATION FOR SEDIMENTATION AND EROSION RESEARCH(WASER)

正President:Giampaolo Di Silvio,Italy Vice Presidents:Ulrich C.E.Zanke,Germany Zhao-yin Wang,China The World Association for Sedimentation and Erosion Research(WASER),inaugurated on Oct.19,2004,is an independent non-governmental,non-profit organization.The mission of WASER is to promote international co-operation on the study     

Enhancing remote sensing research on global change to improve our understanding on Earth system processes

正Global Change includes climate change and other environmental changes caused by the joint interaction among various layers of Earth. From the positive side, global change provides new opportunities to human and other living forms on Earth. In the meantime, it creates tremendous challenges and negative impact. At present, the negative impacts have reached all primary processes of the global ecosystem and every aspect of human society, especially causing degradation of the ecosystem. For instance, intensive deforestation causes decline of biodiversity; global warming causes sea level rise and increases     

Dissolved Carbohydrate Concentration,Composition, and Bioavailability to Microbial Heterotrophs in Stream Water

Dissolved total carbohydrates (DTCH), dissolved free monosaccharides (DFMS), dissolved organic carbon (DOC), biodegradable DOC (BDOC), and humic substances (HS) were measured in White Clay Creek (WCC), a stream in southeastern Pennsylvania Piedmont, USA. Samples were collected over different seasons and under baseflow and stormflow conditions. DOC concentrations ranged from 1.0 to 12.8 mg/L C with the highest concentrations associated with stormflows. Carbohydrates ranged from 0.42 to 12.4 μM and accounted for 2.9 to 12.7% of the DOC. Humic substances represented the major DOC fraction, accounting for 55 to 72% of the DOC pool under all flow conditions. The humic fraction had a lower carbohydrate content (4.4%) than the non-humic fraction of DOC (7.2%). Stormflow DOC was enriched in carbohydrates relative to baseflow DOC, but the percentage of humic-C changed little. Carbohydrates were primarily present as dissolved polysaccharides (55%), but a significant fraction was bound to humic substances (40%), while a small proportion was present as monosaccharides (5%). The major monosaccharides in stream water, listed in order of decreasing concentration, included glucose, galactose, rhamnose, xylose, arabinose, mannose, and fucose. On average (30.6 ± 7.4)% (n = 44) of the stream water DOC was biodegradable, and carbohydrates accounted for 9.9 to 17.7% of the BDOC.