脉动风荷载时程数值模拟研究

在工程结构日趋大型化、复杂化、超高超限化的今天,建筑结构风振响应的研究受到学术界、工程界的关注和重视,数值模拟方法生成脉动风时程对于掌握结构风振特性、减少风致灾害有很好的帮助作用。介绍了近地表层风场的基本特性,阐述了实际工程应用过程中的线性滤波法和谐波叠加法模拟脉动风时程的原理,重点对谐波叠加法模拟脉动风速时程的数学形成过程进行了研究。     

结构的脉动风荷载模拟方法探讨

文章首先介绍了风荷载的基本特性,给出了人工生成随机序列的风荷载模拟方法,并讨论了它的优缺点,提出了风荷载模拟中有待解决的问题。     

塔架结构的脉动风荷载数值模拟及响应

脉动风荷载数值模拟是进行风荷载响应分析的基础。采用三角级数法对脉动风荷载进行了模拟,并借助有限元分析软件,对风荷载作用下塔架结构的动力时程响应及频谱特征进行了分析。     

高层建筑考虑脉动风荷载作用下的有限元分析

以某10层钢筋混凝土结构框架-剪力墙办公楼为例,采用有限元软件ANSYS分析了高层建筑在＂考虑脉动风荷载作用＂与＂正常设计条件＂两种情况下,对上部结构的内力及变形情况进行对比分析。分析结果表明在高层建筑结构设计时,应该充分考虑到脉动风荷载对高层建筑结构的不利影响,从而使设计更加经济、合理。     

高耸结构在脉动风荷载作用下的有限元分析

以一典型的高耸结构烟囱在脉动风荷载作用下引起的结构动力反应(主要针对内力及位移进行分析)与建筑荷载规范中的常规计算方法底部剪力法进行对比分析,通过对比得出底部剪力法与三维有限元分析方法的差异。     

高耸电视塔脉动风荷载仿真及结构风振响应分析

对合肥电视塔脉动风荷载的仿真及其结构风振响应进行了分析。首先建立了脉动风荷载的功率谱密度函数矩阵。采用频谱表示法 ,仿真得到了作用在合肥电视塔上的与塔高竖向相关的 19条脉动风荷载时程样本。在此基础上 ,采用时程分析方法计算了合肥电视塔的风振动力响应     

脉动风荷载作用下弦支穹顶结构的疲劳分析

大跨空间结构在风等交变荷载作用下,结构的应力循环交替变化,可能形成结构的疲劳损伤。通过对2008奥运羽毛球馆采用总寿命法进行疲劳分析,结合疲劳分析的基本理论,运用雨流计数法,统计出了应力循环历程,采用Miner线性累积损伤理论,得到了结构在荷载过后的疲劳损伤程度,找到了疲劳危险区域,得出了一些结论。     

巨型框架多功能减振结构脉动风振的时程分析

本文以一种结构方案为算例 ,建立了巨型框架多功能减振结构及抗振结构的分析模型 ,并随机模拟了脉动风的速度时程 ,由此研究了巨型框架多功能减振结构脉动风振的位移及加速度时程反应 ,结果表明巨型框架多功能减振结构能够显著降低结构的风振反应 ,是一种较有前途的结构形式。     

高层建筑风荷载计算要点的探讨

风荷载是高层建筑主要侧向荷载之一,在地震烈度较低地区的高层建筑,风荷载对结构的作用经常大于地震作用,高层建筑风荷载直接影响建筑的安全问题,所以结构抗风分析(包括荷载,内力,位移,顶点加速度等)是高层建筑设计计算的重要部分.     

高耸结构广义人造脉动风时程模拟研究

高耸结构的风振响应要考虑非线性就必须在时域内进行,这就要发展顺风向脉动风的模拟方法。本文在了解风的基本特性基础上,利用互谱密度矩阵分解,并考虑了随高度变化的风谱,为提高计算机效率和计算精度,引入了快速FFT变换技术,数值算例表明该方法切实有效可行。     

风速时程AR模型及其快速实现

随着工程结构日趋多样化、大型化、复杂化,结构风振响应研究受到学术界、工程界的关注和重视,基于数值模拟方法得到的风速时程曲线在结构风振分析中被采用,自回归(AR)模型具有一系列优异性能,在时间系列分析中被广泛应用,本文基于自然风特性,通过考虑结构节点间的风速时程相关性,采用AR模型模拟节点随机脉动风速时程,并提出VC与Matlab混合编程模拟的快速实现方法．对模拟所得的网壳节点风速时程统计分析表明,AR模型可有效地模拟具有时间相关性、空间相关性的节点脉动风速时程,采用VC与Matlab混合编程快速实现方法,可较好解决模拟精度、模拟速度和计算稳定性的问题。     

Synthesis of non-Gaussian wind pressure time series on low building roofs

This paper presents an efficient and practical method for the digital generation of univariate non-Gaussian wind pressure time series on low building roofs. The method, based on the Fast Fourier Transform (FFT) approach, essentially inverts the Fourier coefficients which are a linear combination of Fourier amplitude and phase. In this study, the Fourier amplitude part is assumed to be known. The Fourier phase capable of inducing non-normality to the time series is carefully modelled and a simple stochastic model with a single parameter is suggested for its simulation. The computation of this single parameter is accomplished by minimizing the sum of the squared errors in higher order statistics such as skewness and kurtosis. The simplicity and effectiveness of this methodology have been demonstrated using several measured non-Gaussian pressure data from various low building roofs under different conditions.     

Theoretically estimated peak wind loads

Current estimation of peak pressure coefficients and peak wind loads on structures in the ASCE 7 Standard [American Society of Civil Engineers, ASCE Standard, Minimum Design Loads for Buildings and Structures, ASCE 7-02, ASCE, Reston, VA, USA, 2002] is based on the assumption that they are distributed normally. However, this assumption is erroneous in the case of low-rise structures because the time varying pressures and loads along roof edges and ridges have been observed to be generally non-Gaussian [H.W. Tieleman, Z. Ge, M.R. Hajj, T.A. Reinhold, Pressures on a surface-mounted rectangular prism under varying incident turbulence, J. Wind Eng. Ind. Aerodyn. 91 (2003) 1095-1115]. In this article, a new procedure is used to evaluate from one individual non-Gaussian sample record statistics of peak pressure or peak load coefficients. The initial step for the analysis requires the identification and evaluation of the appropriate marginal probability distribution. The results reveal that the distribution of the time histories of surface pressure and load coefficients is well represented by the gamma distribution, whose parameters can be adequately evaluated from the theoretical moment estimators. The corresponding distribution of the peaks of the sample records that represents either the pressure coefficients or the load coefficients, can then be obtained using a standard translation process approach. This information yields the mean and the standard deviation of the sample peaks, which are then used to determine the extreme coefficients associated at any selected probability level of non-exceedence. This latter step can be made by assuming that the distribution of the peaks follows the Extreme Value Type I (Gumbel) distribution. The analysis is applied to pressure measurements on the 1:50 scale model of the experimental building at the Wind Engineering Research Field Laboratory (WERFL), and executed in the Clemson boundary-layer wind tunnel over a range of incident turbulence intensities.     

高层建筑顺风向脉动荷载相干性研究

在确定高层建筑顺风向风致响应及等效静力风荷载时,顺风向荷载的竖向相干函数是非常重要的因素之一。目前的大多数研究均是以风速的相干函数来代替风压的相干函数,导致计算结果的误差较大。根据多个高层建筑模型表面测压风洞试验结果,详细分析高层建筑脉动阻力在B、D两类风场中的竖向相干特性,给出顺风向阻力竖向相干函数衰减指数CDz的公式,并与有关文献中提出的Davenport、Shiotani、ECCS等三种风速相干函数的表达公式进行比较,指出阻力相干性要明显大于风速相干性。结合准定常理论,计算一栋实际高层建筑的顺风向风致响应。结果表明:利用给出的阻力竖向相干函数得到的结果与根据风洞试验数据计算的结果相吻合,而其他几种表达公式导致的响应误差则较大,最大可达30%。     

Frequency response requirements for fluctuating wind pressure measurements

The frequency response requirements for measuring fluctuating wind pressures were examined by analysing full scale data collected at the Texas Tech Wind Engineering Field Research Laboratory It was found that mean peak pressures adjacent to separation and reattachment points were attenuated when the instrumentation frequency response was below 10 Hz for mean wind speeds of 10 m/s. This corresponds to a full scale wavelength of 1 m. For pressures away from these regions and for area-averaged pressures, the cut-off wavelength was higher. A reasonable collapse of the available data for response ratios under separated flow was obtained indicating that attenuation of mean peak pressures could be expected for V/n_cB>0.1 (mean reference velocity V, cut-off frequency n_c and smallest building plan dimennsion B). These findings have implications for the frequency response of wind tunnel model studies investigating peak pressure distributions.     

Safety of glass panels against wind loads

Safety of glass panels under wind loads is investigated. Noting that strength of glass displays significant size dependent scatter, the theory of brittle fracture statistics is applied to find the probability of failure of brittle rectangular plates under uniform lateral loads. The effects of plate size, plate thickness, intensity of lateral load and strength of glass on probability of failure are studied. The results are presented graphically and a specific example is studied in detail.     

Effects of wind exposure on roof snow loads

This paper presents results from an investigation of the suitability of the exposure coefficient as defined in ISO 4355 “Bases for design of structures—Determination of snow loads on roofs”, based on thorough analyses of weather data from 389 weather stations in Norway for the reference 30-year period 1961–1990. First, the background of the exposure coefficient is examined. Historical field investigations of snow loads on roofs are also evaluated. Next, values for the exposure coefficients in Norway are calculated according to ISO 4355. Finally, possible approaches aiming at improving calculations of wind exposure on roof snow loads are suggested. It is shown that the exposure coefficient as defined in ISO 4355 does not reflect the actual effects of wind exposure on roof snow loads in Norway, the main reasons being oversimplifications in the definition of the coefficient and the extreme variations of the climate in Norway. The definition is based on coarse simplifications of snow transport theories, and must be revised and improved to serve as an applicable tool for calculations of design snow loads on roofs in Norway.     

广州西塔风荷载研究

广州西塔是广州双塔的西塔楼,目前为华南地区第一高楼,高宽比超过6.5,主塔楼结构采用钢管混凝土斜交网格外筒+钢筋混凝土内筒的筒中筒体系。由于广州为台风多发地区,风荷载为其结构设计的控制荷载,故对其抗风设计进行了详尽的介绍。通过风气候分析确定了区域风况和设计风参数,以及与风响应有关的结构参数,并通过模型风洞试验确定了大楼的等效风荷载取值,并对大楼舒适度进行了判别。     

Analysis of hurricane wind loads on low-rise structures

Time series of pressure coefficients collected on the roof of a house by the Florida Coastal Monitoring Program during landfall of Hurricane Ivan on the Florida panhandle in 2004 are analyzed. Rather than using peak values, which could vary due to the stochastic nature of the data, a probabilistic analysis is performed to characterize extreme values of pressure coefficients and associated wind loads. It is shown that the pressure coefficient time series follows a three parameter Gamma distribution, while the peak pressure follows a two-parameter Gumbel distribution. The analysis yields a probability of non-exceedance of a given threshold of the pressure or load coefficients. For this specific house and specific storm, the 80 percentile load coefficient value of the probability of non-exceedance is −1.7. This is discussed in the context of ASCE 7 GCp values.