Optimum multiple tuned mass dampers for structures under the ground acceleration based on the uniform distribution of system parameters     

Chunxiang Li  Yanxia Liu 《地震工程与结构动力学》2003,32(5):671-690

The five MTMD models, with natural frequencies being uniformly distributed around their mean frequency, have been recently presented by the first author. They are shown to have the near‐zero optimum average damping ratio (more precisely, for a given mass ratio there is an upper limit on the total number, beyond which the near‐zero optimum average damping ratio occurs). In this paper, the eight new MTMD models (i.e. the UM‐MTMD1～UM‐MTMD3, US‐MTMD1～US‐MTMD3, UD‐MTMD1 and UD‐MTMD2), with the system parameters (mass, stiffness and damping coefficient) being, respectively, uniformly distributed around their average values, have been, for the first time here, proposed to seek for the MTMD models without the near‐zero optimum average damping ratio. The structure is represented by the mode‐generalized system corresponding to the specific vibration mode that needs to be controlled. Through minimization of the minimum values of the maximum dynamic magnification factors (DMF) of the structure with the eight MTMD models (i.e. through the implementation of Min.Min.Max.DMF), the optimum parameters and values of Min.Min.Max.DMF for these eight MTMD models are investigated to evaluate and compare their control performance. The optimum parameters include the optimum mass spacing, stiffness spacing, damping coefficient spacing, frequency spacing, average damping ratio and tuning frequency ratio. The six MTMD models without the near‐zero optimum average damping ratio (i.e. the UM‐MTMD1～UM‐MTMD3, US‐MTMD1, US‐MTMD2 and UD‐MTMD2) are found through extensive numerical analyses. Likewise, the optimum UM‐MTMD3 offers the higher effectiveness and robustness and requires the smaller damping with respect to the rest of the MTMD models in reducing the responses of structures subjected to earthquakes. Additionally, it is interesting to note, by comparing the optimum UM‐MTMD3 with the optimum MTMD‐1 recently investigated by the first author, that the effectiveness and robustness for the optimum UM‐MTMD3 is almost identical to that for the optimum MTMD‐1 (without inclusion of the optimum MTMD‐1 with the near‐zero optimum average damping ratio). Recognizing these performance benefits, it is preferable to employ the optimum UM‐MTMD3 or the optimum MTMD‐1 without the near‐zero optimum average damping ratio, when installing the MTMD for the suppression of undesirable oscillations of structures under earthquakes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

高填方路堤互锚式薄壁挡土墙土压力试验研究   总被引：1，自引：0，他引：1  

窦斌  梅利芳  范瑛  余天庆  杨凯华 《地质科技情报》2003,22(3):109-112

在山区修建高等级公路工程中，挡土墙结构广泛应用于高填方路堤工程。在提出一种新型互锚式薄壁挡土墙结构的基础上，通过埋设土压力盒的方法对该种挡土墙的结构型式进行了力学模型试验，并进行了模型土压力强度特性分析。试验及分析表明，该挡土墙结构成本低廉，施工方便，结构合理，可以应用于高填方路堤实际工程。  相似文献   

Simplified vibratory characterization of alluvial basins     

Jean-François Semblat  Roberto Paolucci  Anne-Marie Duval 《Comptes Rendus Geoscience》2003,335(4):365-370

For the analysis of seismic wave amplification, modal methods are interesting tools to study the modal properties of geological structures. Modal approaches mainly lead to information on such parameters as fundamental frequencies and eigenmodes of alluvial basins. For a specific alluvial deposit in Nice (France), a simplified modal approach involving the Rayleigh method is considered. This approach assumes a set of admissible shape functions for the eigenmodes and allows a fast estimation of the fundamental frequency of the basin. The agreement with other numerical results (Boundary Element Method) and experimental ones is fully satisfactory. The simplified modal method then appears as an efficient mean for the global vibratory characterization of geological structures towards resonance. To cite this article: J.-F. Semblat et al., C. R. Geoscience 335 (2003).  相似文献   

A simple test and predictive models for assessing swell potential of Ankara (Turkey) Clay     

Zeynal Abiddin Erguler  Resat Ulusay   《Engineering Geology》2003,67(3-4):331-352

During the past three decades, damage due to swelling action of Ankara Clay has been observed more clearly in some parts of Ankara where rapid expansion of the city led to the construction of various kinds of structures. In this study, a comprehensive research program has been conducted (i) to investigate the effect of remoulding and desiccation on the swelling behavior of Ankara Clay and its swelling anisotropy, (ii) to estimate depth of active zone, (iii) to develop a simple technique in determining the magnitude of swelling based on water content of the soaked specimen after 24 and 72 h (w_max24,72), and (iv) to produce predictive models which could be used to estimate the swelling potential of Ankara Clay from its mineralogical and simply measured engineering characteristics. A laboratory testing program was carried out using both undisturbed, and remoulded and desiccated samples selected from 20 different locations. Montmorillonite was identified as being the main clay mineral present. Based on the moisture content variation with depth, the active expansive zone was considered to be about 2 m. The test results suggest that swelling pressure of the clay considerably decreases and/or dies out when the water content is greater than 30%. It is also noted that the measured lateral swelling is significantly in excess of the vertical equivalent indicating an anisotropy with respect to swelling. Statistical assessments indicate that a new parameter (w_max24,72) from a simple test, suggested in this study, is a very strong parameter for predicting swelling parameters of Ankara Clay. Based on 60 empirical predictive equations with coefficients of correlation between 0.96 and 0.66 from multiple regression analyses, w_max24,72, methylene blue value, liquid limit, dry unit weight and smectite content are the most important index and mineralogical properties to predict the swelling parameters of Ankara clay with small deviations from the measured values.  相似文献   

A statistical approach to evaluating distance metrics and analog assignments for pollen records     

Daniel G. Gavin  W. Wyatt Oswald  Eugene R. Wahl  John W. Williams 《Quaternary Research》2003,60(3):356-367

The modern analog technique typically uses a distance metric to determine the dissimilarity between fossil and modern biological assemblages. Despite this quantitative approach, interpretation of distance metrics is usually qualitative and rules for selection of analogs tend to be ad hoc. We present a statistical tool, the receiver operating characteristic (ROC) curve, which provides a framework for identifying analogs from distance metrics. If modern assemblages are placed into groups (e.g., biomes), this method can (1) evaluate the ability of different distance metrics to distinguish among groups, (2) objectively identify thresholds of the distance metric for determining analogs, and (3) compute a likelihood ratio and a Bayesian probability that a modern group is an analog for an unknown (fossil) assemblage. Applied to a set of 1689 modern pollen assemblages from eastern North America classified into eight biomes, ROC analysis confirmed that the squared-chord distance (SCD) outperforms most other distance metrics. The optimal threshold increased when more dissimilar biomes were compared. The probability of an analog vs no-analog result (a likelihood ratio) increased sharply when SCD decreased below the optimal threshold, indicating a nonlinear relationship between SCD and the probability of analog. Probabilities of analog computed for a postglacial pollen record at Tannersville Bog (Pennsylvania, USA) identified transitions between biomes and periods of no analog.  相似文献   

岩体变形模量的尺寸效应   总被引：2，自引：0，他引：2  

喻勇  肖国强  王法刚 《岩土力学》2003,(Z1)

岩土工程中,现场岩体的承压板试验和变形试验可看作是不同尺寸岩体的变形试验。在某工程的现场岩石力学试验中,对同一组试点的岩体先后进行了承压板变形试验和承载力试验,研究了岩体变形模量的尺寸效应,结果表明,岩体变形模量主要受岩体中的裂隙发育状况控制,当岩体质量较好时,可以由承载力试验曲线来确定岩体的变形特性,这一做法具有一举两得的效果。  相似文献   

锤击沉管碎石桩处理液化地基的工程实践     

李兴武  宋任平  罗旭辉 《岩土力学》2003,(Z1)

结合实际工程,对锤击沉管碎石桩加固处理液化地基的设计、施工控制及处理效果进行了系统论述,对碎石桩设计、施工中遇到的若干问题提出了建议。  相似文献   

岩体工程质量分级应用研究   总被引：1，自引：0，他引：1  

任重阳  唐爱松 《岩土力学》2003,(Z1)

岩体质量评价采用的测试技术包括地质勘察、弹性波检测和室内岩石力学试验。结合水布垭水利枢纽大坝建基岩体工程质量评价实例,对岩体工程质量分级的应用进行了研究。  相似文献   

平板载荷试验应思考的几个问题   总被引：3，自引：0，他引：3  

肖兵  张敏勇 《岩土力学》2003,(Z1)

提出了平板载荷试验中的几个问题:(1)复合地基平板载荷试验垫层的重要性;(2)复合地基平板载荷试验存在尺寸效应;(3)单墩或单桩平板载荷试验不完善。重点对目前广泛使用的复合地基荷载试验进行了讨论,以引起检测人员注意。  相似文献   

横山水库除险加固工程的安全论证——土工膜与结构面摩擦试验     

王琦  臧光文 《岩土力学》2003,(Z1)

土工膜是工程防渗处理的一种主要材料[1]。斜坡面上土工膜与结构面的抗滑稳定直接影响到工程的安全运行。摩擦试验模拟了现场施工和运行情况,得到土工膜与结构面的抗滑剪力和摩擦系数,对工程的安全进行了论证。  相似文献