基于风速时程的体育场挑篷结构风振响应分析

依据自回归(AR)法,确立了考虑风速时程空间相关性的模拟方法,并利用Matlab语言编制了相应的程序。基于上述方法,模拟了某体育场挑篷结构的风速时程,并对所得风速时程离散值进行数理统计分析,结果表明模拟谱与目标谱吻合较好。根据结构风振响应分析的需要,将模拟风速转变为风荷载对结构进行时程分析,获得了结构风振响应,为结构抗风设计提供依据。计算表明,基于风速时程的结构风振响应分析方法可有效分析体育场挑篷的风振响应。     

基于石沅台风谱的输电塔风场数值模拟

为了研究在台风风场下输电塔的动力特性,以广东地区某输电塔为例,采用不随高度变化的石沅台风风速谱,应用谐波叠加法生成台风风场下的风速时程,同时在模拟中采用了FFT技术,从而简化了计算过程,提高了运算效率。通过比较自功率谱和互功率谱可以看出,模拟值与目标值非常吻合,证明了该方法的有效性和可靠性。     

基于目标功率谱和包线的地震动合成

本文给出了以目标功率谱和目标包线函数为双目标函数的人工地震动合成方法,使人工地震动不仅符合目标功率谱,还基本符合目标包线函数,并对加速度基线进行了调整,使速度时程和位移时程更为合理。作者认为如果用反应谱作为目标谱,生成的人工地震动时程可能会弱化地震动的随机特性,用这样的人工地震动时程作为输入来分析建筑结构的非线性动力反应,不是理想的选择。对建筑结构进行非线性时程分析时,用基于功率谱的人工地震动作为输入,应当是一种更为合理的方法。作者认为平方和具有明确的物理意义,是随机信号的总能量参数,并通过理论分析和数值计算,对于一定持时的随机平稳信号样本,平方和(持时×平方平均值)对振幅起重要控制作用。平方和、归一化功率谱、时域包线函数是基于功率谱模型的地震动三要素。     

参数和非参数方法计算相干函数的比较

地震动空间相干函数计算主要两类方法,一是采用谱窗方法对功率谱和互功率谱进行平滑的非参数方法,另一类是采用K-T(Kainai-Tajimi)谱拟合功率谱和互功率谱的参数方法。本文选取了SMART-1台阵第5次和第45次地震的水平分量加速度记录,采用AR(Auto-Regressive)自回归模型的参数方法,计算了不同台站间距的相干系数,并选用Loh相干函数模型,对两种方法的相干系数进行拟合,分别得到了拟合参数和标准差。结果表明:(1)基于AR自回归模型方法得到的拟合标准差小于非参数法;(2)非参数法和参数法的相干系数有明显差别;(3)随着间距的增大,基于非参数法的相干系数随着频率增大而变小的程度放缓,而基于参数法的相干系数明显反映出相干系数符合随着频率增大而变小,同时也随距离的增大而减小的共识。     

近地面脉动风速时程的分形模拟研究

风荷载是不可忽略的结构设计参数,而风荷载大小是由风速决定的,所以风速时程的模拟非常重要。本文根据实测的近地面脉动风速时程,计算了其分形盒维数,进而采用具有分形特性的随机函数模拟了脉动风速时程。然后,提出了考虑空间相关性的脉动风速时程分形模拟方法,并将模拟结果与实测脉动风速进行了分形盒维数、概率分布、功率谱和互相关系数的对比,发现两者很相似。本文所提出的近地面脉动风速时程的分形模拟方法弥补了传统模拟方法的不足。     

悬索跨越管道的顺风向风振响应分析

根据渭惠渠跨越段工程中某悬索跨越管道的工程实例,利用MATLAB软件编制了悬索跨越管道的空间相关性风场的模拟程序,模拟风速的功率谱密度函数与目标功率谱均吻合较好,说明本文方法具有较高的精度。将风速转换为风荷载,并施加在悬索跨越管道的有限元模型上,进行风振响应分析,获得结构的位移和加速度时程曲线及构件的应力分布情况,结果表明该悬索跨越管道结构在风荷载作用下是安全的,为同类结构的抗风设计提供参考。     

基于平稳离散小波变换的地震动时程模拟

人工地震动时程的模拟是结构抗震分析的热点问题.基于平稳离散小波变换理论,利用小波变换的带通滤波特性,推导了各频带小波系数与功率谱密度函数的关系,从而直接采用时变功率谱密度函数,在不同频带上随机生成小波系数,进而通过小波逆变换模拟出同时具有强度非平稳和频率非平稳的地震动时程.对模拟时程的统计特性与目标值进行了比较,证明了该方法的可行性和正确性.     

基于环境振动测试的高层钢筋混凝土结构模态参数识别

根据高层钢筋混凝土结构环境振动测试数据,采用随机信号的频域分析方法,确定了高层结构的自振频率;基于不同测点在固有频率处的响应比及零迟时互相关函数确定了结构的振型;运用自功率谱和互功率谱,采用半功率点法计算了各阶振型的阻尼比.结果表明,环境振动测试能够较好地识别高层结构的1～3阶振型.对实测自振周期与<建筑结构荷载规范>的公式和数值模拟结果进行比较,发现:结构的层数小于20层时,实测值与<规范>规定的值最接近;结构超过20层时,实测值小于<规范>规定的值和数值模拟的结果.     

超随机特性对地震动谱特性和时间历程的影响

本文从单个地震动样本的角度分析了超随机部分对地震动波形的影响,认为自相关函数噪声部分或功率谱的随机波动部分对地震动波形的影响不大,对地震动的波形起主要控制作用的是地震动的相位谱或相位差谱,而自相关函数的噪声部分（或功率谱的随机波动成分）只对地震动波形起一定程度的调整作用。文中基于平稳随机过程的理论,用蒙特卡罗方法分析了自相关函数噪声项对人工合成地震动振幅和反应谱的影响：由于自相关函数的随机噪声项对地震动总功率或平方和的贡献为零,因此随机噪声项对合成地震动幅值的影响不大,但是由于自相关函数随机噪声项明显改变了地震动功率谱的形状和分布特征,使其出现了明显的波动,也在一定程度上提高了平均反应谱的峰值,从而对平均反应谱也产生一些影响。考虑地震动自相关函数中的随机噪声部分有助于更真实地模拟和反映地震动的真实特性。     

去除交通环境振动观测记录中本底振动的自互功率谱法

去除环境振动观测记录中的本底振动是提高信噪比、揭示交通环境振动特征的一个重要环节.本文在分析现有从交通环境振动观测记录中去除本底振动方法不足的基础上,从考虑本底振动与观测振动互相关性出发,提出了采用自互功率谱法去除本底振动的新方法,推导了计算公式,并通过实际算例论证了方法的可靠性.分析结果表明,本文提出的自互功率谱法能够更有效地去除观测数据中的本底干扰,获得更贴近实际的交通环境振动的功率谱、时程、振动级以及加权振级.在本底振动占优势的低频段,本文提出的方法较现有方法计算精度有明显的提高.     

节点刚度变化下角钢塔静力和风振响应分析

使用有限元分析软件ANSYS,研究节点刚度对自立式角钢塔结构静力性能和风振响应的影响,主要研究内容有:采用线性滤波法中自回归AR模型和MATLAB编程模拟了脉动风速时程;建立考虑节点刚度的角钢塔模型,研究了静力和风振作用下节点刚度对结构内力和位移的影响。分析结果表明:节点刚度对角钢塔的静力性能和风振响应影响显著。     

地震和风耦合作用下上海中心大厦结构易损性研究

随着城市人口的增加,越来越多的超高层建筑在中国各大城市涌现,在其全寿命周期内不可避免的会遭受风甚至地震等多灾害的作用。以上海中心大厦为分析模型,根据其场地条件,采用Benowitez在2015年提出的1种基于随机波的模型方法模拟不同高度处具有空间相关性的脉动风荷载时程。通过对Perform 3D有限元软件建立的上海中心大厦模型进行非线性动力时程分析,研究地震和风耦合作用下对于结构性能的影响,并基于多灾害需求生成结构在地震和风耦合作用下的易损性曲面来研究结构的抗振可靠度。结果表明:结构的响应和易损性随着风速和PGA的增大而显著增大;随着风速的增大结构的响应和易损性均有增大的趋势,但随着地震动的增大,风荷载对结构响应和易损性影响逐步减小。     

Study on semi-active control of mega-sub controlled structure by MR damper subject to random wind loads

The recently proposed mega-sub controlled structure （MSCS）, a new type of structure associated with the design and construction of super-tall buildings, has attracted the attention of designers for use in enhancing the control effectiveness in mega-frame buildings. In this paper, a dynamic equation and method to assemble parameter matrixes for a mega-sub controlled structure under random wind loads is presented. Semi-active control using magnetorheological dampers for the MSCS under random wind loads is investigated, and is compared with a corresponding system without dampers. A parametric study of the relative stiffness ratio and relative mass ratio between the mega-frame and the substructures, as well as the additional column stiffness ratio that influences the response control effectiveness of the MSCS, is discussed. The studies reveal, for the first time, that different control mechanisms exist. The results indicate that the proposed structure employing semi-active control can offer an effective control mechanism. Guidelines for selecting parameters are provided based on the analytical study.     

基于改进的OBV模型的下击暴流风荷载模拟

下击暴流是雷暴天气产生的近地面短时强风,具有和大气边界层近地风显著不同的风场特征,其风荷载数值模拟方法也和常规风荷载模拟方法不同。在将下击暴流风速表达为时变的平均风速和调制的非平稳脉动风速之和的前提下,本文采用基于改进的OBV模型（Oseguera and Bowles／Vicroy（OBV））的方法来模拟平均风速,其平均风速直接由改进的OBV模型表达,而不同于已往研究中将平均风速表达为竖向风剖面与时间函数的乘积,并采用结合快速傅里叶变化的谐波叠加法来模拟调制的非平稳脉动风速。改进的OBV模型考虑了下击暴流的风暴中心移动和强度演化的影响,更准确地描述了下击暴流的实际物理过程。通过实例仿真,说明结果准确合理。     

Effects of high modes on the wind-induced response of super high-rise buildings

For super high-rise buildings,the vibration period of the basic mode is several seconds,and it is very close to the period of the fluctuating wind.The damping of super high-rise buildings is low,so super high-rise buildings are very sensitive to fluctuating wind.The wind load is one of the key loads in the design of super high-rise buildings.It is known that only the basic mode is needed in the wind-response analysis of tall buildings.However,for super high-rise buildings,especially for the acceleration response,because of the frequency amplification of the high modes,the high modes and the mode coupling may need to be considered.Three typical super high-rise projects with the SMPSS in wind tunnel tests and the random vibration theory method were used to analyze the effect of high modes on the wind-induced response.The conclusions can be drawn as follows.First,for the displacement response,the basic mode is dominant,and the high modes can be neglected.Second,for the acceleration response,the high modes and the mode coupling should be considered.Lastly,the strain energy of modes can only give the vibration energy distribution of the high-rise building,and it cannot describe the local wind-induced vibration of high-rise buildings,especially for the top acceleration response.     

超高层建筑周围风场特性实测研究

为探究超高层建筑周围风场特性,以天津高银117大厦为例,通过DZZ2型采集系统进行现场实测,对该大厦周围的平均风速、脉动风速、湍流强度、湍流积分尺度、Von Karman谱等风场特性进行分析。结果表明:顺风向及横风向脉动风速变化规律不服从标准高斯分布;顺风向及横风向湍流强度与平均风速呈负相关,且其变化程度与平均风速范围有关;顺风向及横风向湍流积分尺度均随平均风速的增加而增大;Von Karman谱对低频范围内超高层周围风场特性描述较为准确。     

Control of the earthquake and wind dynamic response of steel‐framed buildings by using additional braces and/or viscoelastic dampers

The insertion of steel braces equipped with viscoelastic dampers (VEDs) (‘dissipative braces’) is a very effective technique to improve the seismic or wind behaviour of framed buildings. The main purpose of this work is to compare the earthquake and wind dynamic response of steel‐framed buildings with VEDs and achieve optimal properties of dampers and supporting braces. To this end, a numerical investigation is carried out with reference to the steel K‐braced framed structure of a 15‐storey office building, which is designed according to the provisions of Eurocodes 1 and 3, and to four structures derived from the first one by the insertion of additional diagonal braces and/or VEDs. With regard to the VEDs, the following cases are examined: absence of dampers; insertion of dampers supported by the existing K‐braces in each of the structures with or without additional diagonal braces; insertion of dampers supported by additional diagonal braces. Dynamic analyses are carried out in the time domain using a step‐by‐step initial stress‐like iterative procedure. For this purpose, the frame members and the VEDs are idealized, respectively, by a bilinear model, which allows the simulation of the nonlinear behaviour under seismic loads, and a six‐element generalized model, which can be considered as an in‐parallel‐combination of two Maxwell models and one Kelvin model. Artificially generated accelerograms, whose response spectra match those adopted by Eurocode 8 for a medium subsoil class and for different levels of peak ground acceleration, are considered to simulate seismic loads. Along‐wind loads are considered assuming, at each storey, time histories of the wind velocity for a return period T_r=5 years, according to an equivalent spectrum technique. Copyright © 2010 John Wiley & Sons, Ltd.     

矩形高层建筑扭转动力风荷载解析模型

本文通过研究不同长宽比、高宽比的矩形棱柱体在边界层风洞中典型攻角下的扭矩，提出了矩形高层建筑扭矩功率谱密度、均方根扭矩系数和Strouhal数的经验公式，并对相干函数作了一定的探讨，建立了完整的扭转动力风荷载解析模型。该模型和试验结果吻合较好，证明它是合理有效的，可在此基础上建立高层建筑扭转动力响应频域计算方法。     

Running safety analysis of a train on the Tsing Ma Bridge under turbulent winds

The dynamic responses of the Tsing Ma suspension bridge and the running behaviors of trains on the bridge under turbulent wind actions are analyzed by a three-dimensional wind-train-bridge interaction model. This model consists of a spatial finite element bridge model, a train model composed of eight 4-axle identical coaches of 27 degrees-of-freedom, and a turbulent wind model. The fluctuating wind forces, including the buffeting forces and the self-excited forces, act on the bridge only, since the train runs inside the bridge deck. The dynamic responses of the bridge are calculated and some results are compared with data measured from Typhoon York. The runnability of the train passing through the Tsing Ma suspension bridge at different speeds is researched under turbulent winds with different wind velocities. Then, the threshold curve of wind velocity for ensuring the running safety of the train in the bridge deck is proposed, from which the allowable train speed at different wind velocities can be determined. The numerical results show that rail traffic on the Tsing Ma suspension bridge should be closed as the mean wind velocity reaches 30 m/s.     

Aeolian processes across transverse dunes. I: Modelling the air flow

This paper discusses a two-dimensional second-order closure model simulating air flow and turbulence across transverse dunes. Input parameters are upwind wind speed, topography of the dune ridge and surface roughness distribution over the ridge. The most important output is the distribution of the friction velocity over the surface. This model is dynamically linked to a model that calculates sand transport rates and the resulting changes in elevation. The sand transport model is discussed in a separate paper. The simulated wind speeds resemble patterns observed during field experiments. Despite the increased wind speed over the crest, the friction velocity at the crest of a bare dune is reduced compared to the upstream value, because of the effect of stream line curvature on turbulence. These curvature effects explain why desert dunes can grow in height. In order to obtain realistic predictions of friction velocity it was essential to include equations for the turbulent variables in the model. In these equations streamline curvature is an important parameter. The main flaw of the model is that it cannot deal with flow separation and the resulting recirculation vortex. As a result, the increase of the wind speed and friction velocity after a steep dune or a slipface will be too close to the dune foot. In the sand transport model this was overcome by defining a separation zone. Copyright © 1999 John Wiley & Sons, Ltd.