钢筋混凝土框架结构阻尼性能的研究

阻尼比是一个重要的结构动力特性参数,它对结构的动力响应有重要影响。目前结构抗震计算通常取阻尼比为常数,这不能真实反映建筑物的阻尼机理,与阻尼比的实测结果也有很大的差距。本文以选取的混凝土框架现场脉动实测阻尼数据、混凝土框架模型振动台试验实测阻尼数据、由地震记录识别的混凝土框架阻尼数据及自行完成的混凝土悬臂试件自由振动实测阻尼数据为依据,对混凝土强度、实验方法、结构方位、结构自振频率和结构变形大小等对混凝土框架阻尼性能的影响进行了分析,在此基础上,统计得到了混凝土框架弹性阻尼比、弹塑性阻尼比与频率或变形相关的计算公式。通过与国内外已有公式的比较,论证了本文建立的阻尼比计算公式的合理性和有效性。     

抗震结构的阻尼减振效果分析

研究了抗震结构的阻尼减振效果。首先，考虑了单自由度体系在不同频率简谐干扰作用下阻尼比对结构反应的减小效果；然后，考虑了阻尼比对结构地震反应谱的影响，分析了我国现行建筑抗震设计规范反应谱，并讨论了不同阻尼比对水平地震影响系数的修正公式。     

罕遇地震弹塑性静、动力分析方法中结构阻尼问题探讨

本文针对罕遇地震弹塑性静、动力分析方法中结构的阻尼问题进行了一些算例和理论方面的探讨.总结了现有"规范"对于结构阻尼方面的规定;针对实际的高层混凝土和高层钢结构算例,探讨了各性能设计阶段结构等效阻尼比的变化情况,以及弹塑性阻尼对于结构静力推覆分析和能力谱方法计算结果的影响;探讨了不同的阻尼比对于罕遇地震弹性和弹塑性动力时程分析结果的影响;指出了将Rayleigh阻尼自然推广到弹塑性动力时程分析中所存在的问题;本文提出了实时阻尼比概念,通过算例分析表明可以较好地改进罕遇地震弹塑性动力时程分析中的阻尼问题.     

黏性阻尼与复阻尼对钢筋混凝土框架结构地震响应影响的分析

本文讨论了利用黏性阻尼和复阻尼模型求解结构动力响应的方法;按相同的阻尼比,分别采用复阻尼模型和黏性阻尼模型计算了两个框架结构在不同地震波作用下的响应,并将结果进行对比,分析了两种不同的阻尼模型对结构动力响应的影响。结果表明,采用不同类型的阻尼对结构响应影响很大。     

结构阻尼与材料阻尼的关系

针对固体材料在弹性阶段的内阻尼,采用材料粘弹性本构关系,通过有限单元法建立了考虑剪切变形影响的杆单元阻尼矩阵,得到了材料拉压粘滞系数和剪切粘滞系数之间的关系。我们可以通过实验测试材料的损耗因子或粘滞阻尼系数(材料阻尼),像结构质量矩阵、刚度矩阵一样通过比较确切的计算得到弹性阶段结构内阻尼的阻尼矩阵(结构阻尼),而且此阻尼矩阵既基于材料阻尼实验测试,又便于数学处理,且物理意义明确。其次,本文分析了材料阻尼对结构阻尼比影响,得到了材料损耗因子与结构模态阻尼比间的关系,并通过10层钢筋混凝土剪切型框架结构进一步给出了具体的数值结果。     

形状记忆合金超弹性阻尼性能的试验研究

本文分析了形状记忆合金（SMA）超弹性阻尼减振的机理，通过试验研究了温度、加载频率、循环次数及预变形等因素对SMA超弹性阻尼的影响。研究结果表明，利用SMA的超弹性阻尼特性可以研制出性能良好的耗能减振装置，在工程结构振动控制方面具有比较好的应用前景。     

阻尼修正条件均值谱及其在时程分析地震波选择中的应用

目前时程分析选波常采用目标谱法,即选择反应谱与目标谱有较好匹配的地震波,条件均值谱(CMS)已成为目前国内外广受关注及认可的目标谱。通常的CMS是基于5%阻尼比建立的,当结构阻尼比并非5%时,则需要对CMS进行阻尼修正。本文旨在建立1种CMS阻尼修正方法和计算公式,以便于不同阻尼比结构抗震时程分析的选波工作。以美国SAC Steel Project计划提出的针对洛杉矶地区设计的9层抗弯钢框架为场地和结构实例,建立了3种地震危险性水平(50年超越概率50%、10%和2%)下2%阻尼比的CMS目标谱,并进行了时程分析地震波选择及结构反应的计算。研究表明:提出的CMS的阻尼修正方法可不受衰减关系影响,适用的阻尼比范围(0.5%~30%)及周期范围(0.01s^10s)均较广泛,可用于各种类型的结构的抗震分析。     

钢筋混凝土建筑物振动特性的高度效应研究

建筑物振动特性对于结构抗震设计有重要的理论价值,其中自振周期和阻尼比是2个主要的动力参数。对福州地区129栋不同高度钢筋混凝土建筑物进行振动测试,并统计建筑物的基本特征,研究了高度在21~99m范围内建筑物的自振周期和阻尼比随建筑物高度变化的规律。结果表明:建筑物自振周期随高度增加而增大,有良好的相关性,自振周期约是高度的0.018 63倍;长短轴向自振周期也随高度的增加而增大,长轴向自振周期约是高度的0.014 56倍,短轴向自振周期约是高度的0.018 46倍;随着建筑物高度的增大,阻尼比、长轴向阻尼比和短轴向阻尼比这三者在一定的范围内近似均匀分布,对高度的敏感性低,其中建筑物阻尼比的平均值为4.44%,与建筑抗震设计规范所取的定值5%是比较接近的。研究结论:可为蓬勃发展的高层钢筋混凝土建筑物的初期设计提供科学依据。     

耗能减振结构的抗震设计方法

本文基于国内外耗能减振装置的性能试验和耗能减振结构的计算研究并结合我国正在修订的建筑结构抗震规范。提出了耗能减震结构抗震设计的统一方法。首先,提出了速度相关型线性耗能器和滞变型耗能器等效阻尼和刚度的计算方法;其次,通过大量的计算比较,研究了耗能减振结构非交阻尼阵强行解耦的精度和实际应用的可行性,提出了在结构地震反应分析了振型分解反应谱法中耗能器可统一归结为结构附加振型阻尼比的方法;第三,通过耗能减     

框架-阻尼框筒结构附加阻尼比简化计算方法

针对框架-阻尼框筒新型减震结构体系,考虑钢板阻尼墙屈服后强化和框架弹塑性,推导了结构附加阻尼比简化计算公式。以某框架-阻尼框筒结构为例,采用试验和有限元分析方法确定公式的参数取值,以此得到结构附加阻尼比的公式计算值,通过与结构动力弹塑性分析值进行对比,论证了简化计算公式的可用性。进一步基于参数分析给出了不同因素对公式计算值的影响。该简化计算方法为框架-阻尼框筒结构方案的快速设计提供了有效途径。     

Empirical estimate of fundamental frequencies and damping for Italian buildings

The aim of this work is to estimate the fundamental translational frequencies and relative damping of a large number of existing buildings, performing ambient vibration measurements. The first part of the work is devoted to the comparison of the results obtained with microtremor measurements with those obtained from earthquake recordings using four different techniques: horizontal‐to‐vertical spectral ratio, standard spectral ratio, non‐parametric damping analysis (NonPaDAn) and half bandwidth method. We recorded local earthquakes on a five floors reinforced concrete building with a pair of accelerometers located on the ground and on top floor, and then collected microtremors at the same location of the accelerometers. The agreement between the results obtained with microtremors and earthquakes has encouraged extending ambient noise measurements to a large number of buildings. We analysed the data with the above‐mentioned methods to obtain the two main translational frequencies in orthogonal directions and their relative damping for 80 buildings in the urban areas of Potenza and Senigallia (Italy). The frequencies determined with different techniques are in good agreement. We do not have the same satisfactory results for the estimates of damping: the NonPaDAn provides estimates that are less dispersed and grouped around values that appear to be more realistic. Finally, we have compared the measured frequencies with other experimental results and theoretical models. Our results confirm, as reported by previous authors, that the theoretical period–height relationships overestimate the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Evaluation of Rayleigh damping and its influence on engineering demand parameter estimates

The effects of Rayleigh damping model on the engineering demand parameters of two steel moment‐resisting frame buildings were evaluated. Two‐dimensional models of the buildings were created and response history analysis were conducted for three different hazard levels. The response history analysis results indicate that mass‐proportional damping leads to high damping forces compared with restoring forces and may lead to overestimation of floor acceleration demands for both buildings. Stiffness‐proportional damping, on the other hand, is observed to suppress the higher‐mode effects in the nine‐story building resulting in lower story drift demands in the upper floors compared with other damping models. Rayleigh damping models, which combine mass‐proportional and stiffness‐proportional components, that are anchored at reduced modal frequencies lead to reasonable damping forces and floor acceleration demands for both buildings and does not suppress higher‐mode effects in the nine‐story building. Copyright © 2012 John Wiley & Sons, Ltd.     

Appropriate viscous damping for nonlinear time‐history analysis of base‐isolated reinforced concrete buildings

There is no consensus at the present time regarding an appropriate approach to model viscous damping in nonlinear time‐history analysis of base‐isolated buildings because of uncertainties associated with quantification of energy dissipation. Therefore, in this study, the effects of modeling viscous damping on the response of base‐isolated reinforced concrete buildings subjected to earthquake ground motions are investigated. The test results of a reduced‐scale three‐story building previously tested on a shaking table are compared with three‐dimensional finite element simulation results. The study is primarily focused on nonlinear direct‐integration time‐history analysis, where many different approaches of modeling viscous damping, developed within the framework of Rayleigh damping are considered. Nonlinear direct‐integration time‐history analysis results reveal that the damping ratio as well as the approach used to model damping has significant effects on the response, and quite importantly, a damping ratio of 1% is more appropriate in simulating the response than a damping ratio of 5%. It is shown that stiffness‐proportional damping, where the coefficient multiplying the stiffness matrix is calculated from the frequency of the base‐isolated building with the post‐elastic stiffness of the isolation system, provides reasonable estimates of the peak response indicators, in addition to being able to capture the frequency content of the response very well. Furthermore, nonlinear modal time‐history analyses using constant as well as frequency‐dependent modal damping are also performed for comparison purposes. It was found that for nonlinear modal time‐history analysis, frequency‐dependent damping, where zero damping is assigned to the frequencies below the fundamental frequency of the superstructure for a fixed‐base condition and 5% damping is assigned to all other frequencies, is more appropriate, than 5% constant damping. Copyright © 2013 John Wiley & Sons, Ltd.     

Damping estimation of high-rise buildings considering structural modal directions

One widespread problem in damping estimation of high-rise buildings is the neglect of structural modal directions, which may induce beating in measured dynamic responses along building geometric axes and thereby induce errors in damping estimations to some extent. Based on a proposed two degrees of freedom (2-DOF) simulation model, the effects of neglecting the modal directions on damping estimate are systematically investigated. The results show that the angular differences between the modal directions and the building geometric axes, as well as the frequency difference between the involved modes, both have significant effects on the damping estimate of high-rise buildings. This paper proposes a spectral method to determine the modal directions of high-rise buildings and further validate this method by an analysis of full-scale measurements from four skyscrapers. The damping ratios estimated based on the responses along the identified modal directions are more accurate than those based on those measured along the building geometric axes. Furthermore, an empirical prediction model for damping ratio of high-rise buildings with heights over 200 m is proposed based on the field measured damping results of several buildings with consideration of the modal directions. The objective of this study is to improve the accuracy of damping estimation of high-rise buildings and therefore provide useful information for the structural design of future skyscrapers.     

Stiffness‐damping simultaneous identification using limited earthquake records

A new method of stiffness‐damping simultaneous identification of building structures is proposed using limited earthquake records. It is shown that when horizontal accelerations are recorded at the floors just above and below a specific storey in a shear building model, the storey stiffness and the damping ratio can be identified uniquely. The viscous damping coefficient and the linear hysteretic damping ratio can also be identified simultaneously in a numerical model structure. The accuracy of the present identification method is investigated through the actual limited earthquake records in a base‐isolated building. It is further shown that an advanced identification technique for mechanical properties of a Maxwell‐type model can be developed by combining the present method with a perturbation technique. Copyright © 2000 John Wiley & Sons, Ltd.     

A design procedure for buildings equipped with energy dissipation devices using nonclassical damping and iso-performance curves

This article describes a design procedure for elastic buildings equipped with linear and nonlinear energy dissipating devices. The objective is to achieve a design that responds to a target building performance following a simple and robust step-by-step algorithm. The proposed procedure identifies first the modal significance of key design performance indicators and controls the modal properties by solving a singular two-parameter eigenvalue problem. For that purpose, a new modal significance metric is proposed, and a target frequency shift and damping ratio for the complete structure are obtained from the so-called iso-performance design curves. The design algorithm employs linear-equivalent stiffness and damping properties, which are then transformed into parameters characterizing inelastic force-deformation constitutive models corresponding to physical devices. The design algorithm leads to an optimal damper distribution corresponding to the minimum global amount of supplemental equivalent damping needed to achieve a maximum modal perturbation. The design procedure is first demonstrated using a five-story building example and then a real and complex 22-story free-plan building with two towers of rhomboid-shape plan with a very singular dynamic behavior.     

Seismic behaviour of asymmetric buildings with supplemental damping

This paper investigates the response of asymmetric‐plan buildings with supplemental viscous damping to harmonic ground motion using modal analysis techniques. It is shown that most modal parameters, except dynamic amplification factors (DAFs), are affected very little by the plan‐wise distribution of supplemental damping in the practical range of system parameters. Plan‐wise distribution of supplemental damping significantly influences the DAFs, which, in turn, influence the modal deformations. These trends are directly related to the apparent modal damping ratios; the first modal damping ratio increases while the second decreases as CSD moves from right to left of the system plan, and their values increase with larger plan‐wise spread of the supplemental damping. The largest reduction in the flexible edge deformation occurs when damping in the first mode is maximized by distributing the supplemental damping such that the damping eccentricity takes on the largest value with algebraic sign opposite to the structural eccentricity. Copyright © 2000 John Wiley & Sons, Ltd.     

Damped resonant appendages to increase inherent damping in buildings

It is demonstrated that the addition of a tuned mass-spring-dashpot system with a relatively small mass and a high damping ratio can be an effective way to increase the inherent damping characteristics of buildings and reduce, thus, their response to earthquake excitations. The demonstration is based on a theoretical formulation and on numerical and experimental studies that confirm this formulation. In the theoretical formulation, it is shown first that, if certain conditions are satisfied, the damping ratios in two of the modes of the system that is formed by a building and an appendage in resonance are approximately equal to the average of the corresponding damping ratios of the building and the appendage. Based on this finding, it is then shown that an attached appendage with a high damping ratio and tuned to the fundamental frequency of a building may increase the damping ratio in the fundamental mode of the building to a value close to half the damping ratio of the appendage. In the numerical study, the response of a ten-storey shear building is analysed under two different earthquake ground motions with and without the proposed resonant appendages. Appendages with damping ratios of 20 and 30 per cent are considered. In this study, it is found that under one of the ground motions the maximum displacement of the building's roof is reduced 30 per cent with the appendage with 20 per cent damping and 39 per cent with the one with 30 per cent damping. Similarly, with these two appendages the building's base shear is reduced 31 and 41 per cent, respectively. In the experimental study, a wooden three-storey structural model is tested in a shaking table with and without an appendage designed and constructed to have a damping ratio of 53-5 per cent. The test is conducted under random and sinusoidal base excitations. In the shaking table test under random excitation, the attached appendage reduces the response of the model 38-6 per cent, while in that under sinusoidal vibration 45-2 per cent.