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Barbara G. Simpson Ph.D. 《地震工程与结构动力学》2020,49(14):1406-1427
Strongback-braced frames employ an essentially elastic steel truss, or strongback, that distributes demands more uniformly to delay or prevent story mechanisms. Because inertial forces are no longer limited by the formation of a story mechanism, strongback-braced frames can exhibit large elastic force demands, particularly in the higher modes. This paper characterizes the higher-mode force response of strongback-braced frames. Four-story archetypes were designed using nonlinear dynamic analyses to incorporate higher-mode force demands into the design process. The response of the archetypes was compared with that of reference buckling-restrained braced frames that were allowed to form story mechanisms. The force demands in the strongback were then described using equivalent-static forces to represent the inertial forces induced by the higher modes. Force demands in the strongback arise from a yielding first-mode ‘pivoting’ and elastic higher-mode ‘bending’ response. These higher-mode force demands are elastic, ill-constrained by the strength of the yield mechanism, and depend significantly on the choice of ground motion record used for the analysis. In remaining elastic in the higher modes, the strongback distributes demands more uniformly and mitigates the formation of story mechanisms. Consequently, design and analysis methods for strongback-braced frames need to include estimates for these near-elastic higher-mode force demands. 相似文献
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珊瑚礁破碎带附近波浪演化和波生流实验研究 总被引:2,自引:0,他引:2
为了研究珊瑚岸礁破碎带附近波浪演化和波生流特性,通过水槽实验对规则波浪作用下珊瑚岸礁上沿礁分布的水位和流速进行了详细的测量。在典型卷破波条件下,测试了礁冠存在与不存在的两种情况。实验结果表明,多重波浪反射作用引起岸礁上形成不完全驻波,而破碎带附近的浅化作用则产生高次谐波,波浪破碎所耗散的波能主要来源于主频波,礁坪上透射波成分中二次谐波与主频波的能量相当;礁冠的存在引起破碎带宽度减小、礁坪上增水变大以及礁坪上各次谐波变小;礁冠不存在时,岸礁上波生流的沿礁分布与平直海岸相似,而礁冠的存在一定程度上阻碍了礁坪上水体向外海的回流。研究成果将丰富和发展珊瑚礁水动力学理论,并为岛礁工程的建设和维护提供一定的理论参考。 相似文献
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关于大地电磁信号非最小相位性的讨论 总被引:7,自引:1,他引:6
由于信号的功率谱仅包含振幅信息而不包含相位信息,因此传统功率谱方法仅能处理最小相位信号,难于适用于非最小相位信号.本文对不同地区的实际大地电磁(MT)信号作了分析,结果表明,不同测点MT信号在Z平面上的零点分布并不全部位于单位圆之内,可以判定MT信号一般具有非最小相位的特点,因此有必要改进传统处理方法,发展新的资料处理方式.实际信号分析,理论和数值模型实验证明,信号的高阶统计量包含其相位信息,因此,高阶统计量方法能够有效处理具有非最小相位特征的MT信号. 相似文献
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张雪莲 《广东海洋大学学报》2013,(2)
高职声乐教学多年沿袭高等专业音乐院校的指导思想和教学模式,造成高职学生不能较好胜任基层音乐教育工作。高职声乐教学应以培养合格基础音乐人才为目标,精选合适的教学内容,培养学生一专多能的音乐素养。 相似文献
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高等地理教育对地理学基础教育人才和科研创新人才培养起着重要作用,本文通过对我国地理学本专科专业设置与招生状况、二级学科研究生培养机构的统计,分析我国地理学高等教育与人才培养的现状。研究发现:我国地理学高等教育学校或机构的数量有了明显增加,学科发展明显增强,各级各类人才的培养规模取得较大发展,但同时也存在地区发展不平衡、培养机构的背景比较单一、生源质量和地理院系冠名多样化等问题。 相似文献
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Palynological analyses were completed for the A and B horizons of a forested Mollic Hapludalf to determine type, amount, and distribution of pollen and spores within the soil solum. Hypotheses regarding the origin of pollen and the mechanisms of its movement within soil bodies are also advanced. Pollen downwash within the mineral soil seems to be very slow and confined to the uppermost porous and most homogenized part of the solum. The predominance of non-arboreal pollen at depth was believed to be a result of deposition with the loess parent material. High arboreal pollen frequencies in the upper horizons coupled with increases in non-arboreal types at depth indicate gradual ongoing mixing from the present vegetation into the soil. 相似文献
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The N2 method has been extended in order to take into account higher mode effects in elevation. The extension is based on the assumption that the structure remains in the elastic range when vibrating in higher modes. The seismic demand in terms of displacements and storey drifts can be obtained by enveloping the results of basic pushover analysis and the results of standard elastic modal analysis. The approach is consistent with the extended N2 method used for plan‐asymmetric buildings. The proposed procedure was applied to three variants of three steel frame buildings used in the SAC project. The structural response was investigated for two sets of ground motions. Different ground motion intensities were used in order to investigate the influence of the magnitude of plastic deformations. The N2 results were compared with the results of nonlinear response‐history analysis, two other pushover‐based methods (modal pushover analysis (MPA) and modified MPA (MMPA)), and pushover analysis without consideration of higher modes. It was found that a considerable influence of higher modes on storey drifts is present at the upper part of medium‐and high‐rise structures. This effect is the largest in the case of elastic behaviour and decreases with ground motion intensity. The higher mode effects also depend on the spectral shape. The approximate methods (extended N2, MPA and MMPA) are able to provide fair estimates of response in the case of the test examples. Accuracy decreases with the height of the building, and with the intensity of ground motion. The N2 results are generally conservative. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献