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31.
The non‐linear analysis of single‐degree‐of‐freedom (SDOF) systems provides the essential background information for both strength‐based design and displacement‐based evaluation/design methodologies through the development of the inelastic response spectra. The recursive solution procedure called the piecewise exact method, which is efficiently used for the response analysis of linear SDOF systems, is re‐formulated in this paper in a unified format to analyse the non‐linear SDOF systems with multi‐linear hysteresis models. The unified formulation is also capable of handling the P‐delta effect, which generally involves the negative post‐yield stiffness of the hysteresis loops. The attractiveness of the method lies in the fact that it provides the exact solution when the loading time history is composed of piecewise linear segments, a condition that is perfectly satisfied for the earthquake excitation. Based on simple recursive relationships given for positive, negative and zero effective stiffnesses, the unified form of the piecewise exact method proves to be an extremely powerful and probably the best tool for the SDOF inelastic time‐history and response spectrum analysis including the P‐delta effect. A number of examples are presented to demonstrate the implementation of the method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
32.
Several recorded motions for seven bridge systems in California during recent earthquakes were analysed using parametric and non‐parametric system identification (SI) methods. The bridges were selected considering the availability of an adequate array of accelerometers and accounting for different structural systems, materials, geometry and soil types. The results of the application of SI methods included identification of modal frequencies and damping ratios. Excellent fits of the recorded motion in the time domain were obtained using parametric methods. The multi‐input/single‐output SI method was a suitable approach considering the instrumentation layout for these bridges. Use of the constructed linear filters for prediction purposes was also demonstrated for three bridge systems. Reasonable prediction results were obtained considering the various limitations of the procedure. Finally, the study was concluded by identifying the change of the modal frequencies and damping of a particular bridge system in time using recursive filters. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
33.
闪电首次回击过程的光谱特性 总被引:3,自引:5,他引:3
用无狭缝摄谱仪,拍摄了4次云对地闪电首次回击过程390一660nm波长范围的光谱,并将原子结构的理论应用于闪电光谱的研究,用多组态Dirac—Fock方法,系统考虑相对论效应、电子关联、弛豫效应等重要贡献,对光谱的精细结构进行了计算,给出了谱线的波长、振子强度以及相应的上能级激发能量。通过与试验观测谱线的比较分析发现,大多数谱线对应的上激发能在23ev左右。首次回击过程中,闪电通道内NII离子的密度最大,并且大多数处于n=3的激发态。 相似文献
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35.
We present an overview of our recent results on utilizing small earthquakes in the earthquake engineering practice. Site-specific ground motion time-histories of large earthquakes can be successfully simulated using recordings of small earthquakes which are often referred to as 'empirical Green's functions' in seismology. Another important practical problem is whether and how these observations can be used in seismic risk studies which are based on empirical attenuation relations for ground motion parameters. We study a possibility of extrapolating attenuation relations for small earthquakes, to larger magnitudes using the data from the Garner Valley downhole array in Southern California. Finally we introduce efficient ground motion processing techniques in frequency- and time-domains and apply them to site response estimation. 相似文献
36.
Average recurrence intervals of strong earthquakes and potential risky segments along the Taiyuan-Linfen portion of the Shanxi graben system 总被引:1,自引:0,他引:1
Introduction In AD 1303, the great Hongtong, Shanxi, earthquake of magnitude 8 caused a very serious disaster, which killed over one hundred thousands people at least (Department of Earthquake Dis- *aster Prevention, State Seismological Bureau, 1995). On the occasion of commemorating this ca-tastrophe having occurred for 700 years, we have important problems that need to be answered: How long the average recurrence interval of the grea… 相似文献
37.
应用高光谱遥感数据估算土壤表层水分的研究 总被引:8,自引:0,他引:8
土壤水分是土壤的重要组成部分,它在陆地表层和大气之间的物质和能量交换方面扮演着重要角色,寻求快速而准确的方法估算土壤水分具有重要意义。通常,从可见光一近红外对土壤表层水分的估计多是建立在土壤水分与反射率的关系之上的。而在土壤水分含量不高时,土壤水分的增加使土壤光谱反射率在整个波长范围内降低,尤其在760nm,970nm,1190nm,1450nm,1940nm和2950nm等水分吸收波段,而在土壤水分含量较高时,土壤水分的增加会使土壤光谱反射率在某些光谱波段升高。而土壤水分的估计往往是基于土壤水分与土壤水分吸收波段的吸收强度之间的线性关系上,虽然这些经验的方法对于估算某些土壤的表层水分含量是有效的,但这些关系应用于其它条件(如不同种类土壤、土壤湿度变化范围很大的情况)时却面临很多困难,这与土壤的光谱反射率是由土壤的组成成分(土壤水分、有机质、氧化铁和粘土矿物等)的含量和它们在土壤中的分布密切相关。微分技术处理“连续”的光谱是遥感中常用的数学方法,微分技术能部分消除低频光谱成分的影响。现在微分光谱已广泛地应用于研究植被的生物物理参数、矿物和有机质等。然而利用微分光谱对土壤水分反演的研究却鲜见报道。本文通过对实验室中多种不同类型的土壤进行光谱与土壤表层水分含量进行观测,探讨了通过土壤反射率与微分光谱对土壤表层水分的反演方法。4种类型的土壤光谱数据(反射率(R),反射率倒数的对数(log(1/R)),反射率的一阶微分光谱(dR/dλ),反射率倒数的对数的一阶微分光谱(d(log(1/R))/dλ))与土壤表层水分之间的关系在本文中得到分析,R与log(1/R)对于不同土壤类型与土壤表层水分都很敏感,说明通过R与log(1/R)反演土壤表层水分受土壤类型的影响很大,而dR/dλ,d(log(1/R))/dλ)对土壤类型却不敏感,对土壤表层水分较为敏感,说明dR/dλ和d(log(1/R))/dλ)对于反演不同类型土壤具有很大的潜力,微分光谱与土壤水分在某些波段具有显著的相关性。通过随机对9种土壤(各具有4个土壤水分)的数据建立反演土壤水分的模型,并其他9种土壤(各具有4个土壤水分)的数据进行验证模型,结果表明,dR/dλ和d(log(1/R))/dλ)能够显著提高R与log(1/R)对于不同土壤类型土壤表层水分的反演精度,由于吸收过程是非线性的,在四种类型的土壤光谱数据中,总体来说,d(log(1/R))/dλ)具有最好的能力预测不同类型土壤的表层水分含量。 相似文献
38.
基于灰关联分析的GPS高程拟合加权平均函数模型权函数优选 总被引:6,自引:0,他引:6
基于灰色系统理论的灰关联分析方法,提出了权函数的优选方法,实例分析表明其具有较好的实用价值. 相似文献
39.
Underground coal and copper ore exploitation in two Polish mining regions causes mining tremors and a series of other negative phenomena in the environment. Although these tremors are strictly connected with human activity, they differ considerably from other paraseismic vibrations. The moment of their occurrence is not to be foreseen likewise for earthquakes. The main problem discussed in the paper was formulated as the neural network evaluation of a relation between mining tremor energies, epicentral distances and acceleration response spectra. Back-propagation neural networks with Resilient back-propagation learning method were used. Each input vector included information about the mining tremor energy and the epicentral distance. Values of acceleration response spectrum were expected as the outputs of neural networks. Neurally evaluated spectra were compared with spectra computed on the basis of experimental data. After the network is trained and tested, it can be used for mapping of new data of mining tremor energies and epicentral distances into the spectra. Then, what is the substantial advantage of neural approach, the prediction of acceleration response spectra can be performed without recording of surface vibrations. In the light of the results, it is visible that the presented way of computation of acceleration response spectra can be peculiarly applied to prognosis of mining tremors influences on structures. 相似文献
40.
Introduction Estimation of an attenuation relationship for strong ground motion parameters has been an interesting research subject in the field of engineering seismology and has played a very important role in seismic safety evaluation, seismic zoning, seismic hazard evaluation of major constructions, etc. At present, the generally used parameters include peak acceleration, peak velocity and elastic response spectrum. Such parameters mentioned above are essentially independent of the duration… 相似文献