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.     

Pressures on a surface-mounted rectangular prism under varying incident turbulence

The pressure and load coefficients obtained from two groups of eight pressure taps on the upper surface of a surface-mounted prism are characterized in terms of their mean, rms, peak, probability distribution, peak correlations and durations. The prism is a 1:50 scale model of the WERFL experimental building at Texas Tech University. Results obtained with flows generated over seven different wind tunnel floor-roughness configurations in the boundary layer wind tunnel at Clemson University cover a wide range of turbulence intensities. The results presented include the spatial variation of the peak pressure and peak load coefficients, and their variations with incident turbulence. The stochastic characteristics of the peak coefficients are also addressed here. The results reveal that the distribution of the peak coefficients is in general well established by the Extreme Value Type I (Gumbel) distribution. Conditional sampling is employed to study the duration as well as the space and space-time correlations of the peaks. Analysis of the peaks reveals that those with the larger magnitudes are generally of longer duration.     

Low-rise gable roof wind loads: Characterization and stochastic simulation

Mitigation of the damage caused by windstorms to low-rise buildings is a high priority in the wind engineering community. The development of cost-effective methods to withstand the effects of extreme winds can be advanced through improved modeling of wind loads acting on low-rise roof structures. This study explores the effects of the spatial and probabilistic characteristics of pressure fields on the aggregate uplift acting on roof panels of low-rise gable roof buildings representative of typical homes. Pressure time histories obtained at roof locations for buildings of varying roof slope at several angles of incidence in the boundary layer wind tunnel at Clemson University are used to characterize the correlation statistics between tap locations and model the marginal probability density function at individual tap locations. This information is incorporated into a multi-variate non-Gaussian simulation algorithm to study the effects of various levels of correlation on the aggregate uplift on sheathing panels. Comparisons are made between the simulated aggregate uplift and ASCE 7-98 provisions [Minimum Design Loads for Buildings and Other Structures, ASCE 7-98 Standard, American Society of Civil Engineers, New York [1]] as well as laboratory generated failure capacities for sheathing panels.     

美国输电线路风荷载计算介绍

了解《美国输电线路结构荷载指南》(ASCE74-2009)对从事涉外工程和提高工程师设计水平都有着重要意义。风荷载是输电线路设计的控制荷载,了解ASCE74-2009风荷载计算方法非常有必要。本文介绍了ASCE74-2009输电线路风荷载的计算方法,并对基本风速、风压高度变化系数、体型系数、风荷载调整系数、地形影响因子和斜向风荷载计算方法及其计算参数进行了说明。     

平屋盖围护构件设计风荷载研究

GB 50009-2012《建筑结构荷载规范》中未给出复杂体型且重要建筑物的风荷载局部体型系数,此类建筑物的风荷载需通过风洞试验确定。基于此,提出了基于风洞试验的围护构件设计风荷载计算方法,将规范中阵风系数与局部体型系数的乘积修改为局部体型系数与脉动风压系数极值之和的形式,称为风压系数极值。提出的围护构件设计风荷载计算方法不仅适用于迎风面围护构件设计风荷载的计算,也适用于气流分离区围护构件设计风荷载的计算。在脉动风压系数极值的计算中,考虑了气流分离区非正态风压时程的特性,采用非正态峰值因子的简化计算式,可简便确定非正态风压时程的峰值因子。以平屋盖围护构件设计风荷载的确定过程为例,对比了我国规范方法与文中方法的异同,提出了平屋盖围护构件风压系数极值的设计建议值。结果表明,采用文中提出的围护构件设计风荷载计算方法,基于风洞试验数据可确定气流分离区围护构件的设计风荷载,采用日本风荷载规范的屋盖风荷载分区方法是合理的;采用风洞试验得到的局部体型系数,套用GB 50009-2012规范方法确定气流分离区围护构件的设计风荷载,可能严重低估风荷载取值。     

典型拱形壳体风荷载分布规律

进行了2种典型拱形壳体结构刚性模型内外表面同步测压风洞试验,分析了拱形壳体结构体型系数与脉动风压系数的分布规律,比较了底部开口/闭口和两端封闭/开放不同状态对风压分布的影响.结果表明:底部开口与端部条件对结构风压分布影响很大,采用弧面封闭两端可以有效的降低结构端部的风压同时使得结构表面风压分布更加均匀,当底部开口较小时...     

The UWO contribution to the NIST aerodynamic database for wind loads on low buildings: Part 2. Comparison of data with wind load provisions

Wind tunnel test data on generic low buildings have been obtained at the University of Western Ontario (UWO) to contribute to the NIST aerodynamic database. In Part 1 the basic data and archiving format are presented. In the present paper, data from two models of different roof slope (1:12 and 3:12) at four eave heights each (4.9 m (16 ft), 7.3 m (24 ft), 9.8 m (32 ft), and 12.2 m (40 ft)), in open and suburban terrain conditions, were examined in detail. The data were compared to the historical data obtained by Stathopoulos in the late 1970s from which current North American code provisions were developed. Structural response coefficients were calculated on an assumed structural system and these data were compared with the current wind load provisions for low buildings in the ASCE 7-02 (ASCE Standard, Minimum Design Loads for Building and other Structures, ASCE 7-02, ASCE, New York, USA, 2002), the AS/NZS 1170.2 (Australian/New Zealand Standard Structural Design Actions, Part 2: 2002—AS/NZS 1170.2:2002, Standards Australia International Ltd., Sydney, AS and Standards New Zealand, Wellington, NZ, 2002), the Eurocode (Eurocode 1: Basis of Design and Actions on Structures. Part 2-4: Wind Actions, ENV-1991-2-4-1, CFN, Brussels, 1995), and the NBCC (National Building Code for Canada 1995 (NBCC(1995)); Includes User's Guide—NBC 1995 Structural Commentaries (Part 4), NRCC, Ottawa, Canada, 1995. The peak response coefficients from the current data set were found to increase with eave height. The ASCE 7-02 and the NBCC (1995) underestimated the peak response coefficients calculated for the current data set by ∼15% for the lowest eave height; and were worse for larger eave heights. Generally, the Eurocode (ENV, 1995) wind load provisions match the peak response coefficients from the data set at all eave heights. The response coefficients calculated using the AS/NZS (2002) provisions were generally a good match for the interior region only, however they significantly underestimated the wind tunnel response coefficients for the end bays.     

四面坡顶轻钢空旷结构表面风压数值模拟

采用基于CFD的数值模拟技术和RNG k-ε湍流模型对一四面坡顶轻钢空旷结构进行了静力风荷载数值模拟,主要考虑了风向角的变化,得到了结构表面的风压分布,并进行了对比分析.该结构表面风压分布不均匀,局部风压较大;风向角对结构表面风压分布具有一定影响.最后,根据分析结果提出了该类结构表面风压的分区方法.     

Windlasten für Standsicherheitsnachweise der Dachtragwerke von Stadiondächern

Wind loads for the ultimate limit state design of the roof structures of stadiums. Wind effects are usually the dominant loading on roofs of stadia, however, on the basis of actual wind loading codes they cannot be determined with the required accuracy in each case. Often, wind tunnel investigations provide more precise wind loads. Herewith, the aerodynamic coefficients are determined individually for each particular case and they are transferred to wind loads for the design. Load assumption are focused on an optimum modelling of the aerodynamic effects on the structures under consideration. By means of wind loads for realized stadia the potential of improved load investigations are introduced. The size effect of the loading area, which significantly reduces the load magnitude is pointed out. On the other hand, buffeting resonance effects may set particular requirements. Wind loads on stadia during erection are addressed.     

高层建筑标准模型脉动风压特性大涡模拟适用方法研究

为提高钝体建筑结构绕流模拟结果的精度,基于两种大涡模拟(large eddy simulation, LES)入口湍流生成方法,分别为NSRFG（narrow band synthesis random flow generation）方法和CDRFG（consistent discretizing random flow generation）方法,进行CAARC(commonwealth advisory aeronautical research concil)高层建筑标准模型绕流的数值模拟比较研究。以风洞试验结果为参照,在对大气边界层湍流风场进行模拟验证的基础上,详细对比分析采用上述两种方法模拟得到的建筑表面平均和脉动风压系数、绕流场湍流结构、风压系数概率密度分布特性等的差异,并着重从脉动风压非高斯特性角度进行探讨,检验采用上述两种方法模拟钝体建筑结构绕流的适用性和准确性。结果显示：在受来流直接作用的建筑迎风面,采用两种方法模拟的脉动风压基本都符合高斯特性;而在受分离流和尾流作用的侧风面和背风面,采用NSRFG方法能更好地反映建筑表面脉动风压的非高斯特性。极值风压分析表明,为了满足99.38%的保证率,CAARC标准模型迎风面极大与极小峰值因子需分别取为3.0和2.5,侧风面和背风面极大和极小峰值因子需分别取为2.5和4.0。     

Assessment of wind load factors for hurricane-prone regions

We study the issue of whether the wind load factors specified in the ASCE 7–95 Standard for hurricane- prone regions on the one hand and extratropical storm regions on the other are mutually consistent with respect to risk. We consider structures or elements whose design is governed by wind loads and for which wind directionality effects are not significant. We present estimates according to which ASCE 7–95 Standard provisions for wind loads inducing the design strength result in (1) safety levels that are considerably lower for hurricane-prone than for extratropical storm regions, and (2) estimates of mean recurrence intervals of hurricane wind loads inducing the design strength of about 500 y if epistemic uncertainties are neglected, and significantly lower than 500 years otherwise.     

Wind force coefficients for designing free-standing canopy roofs

Wind loads on free-standing canopy roofs have been studied experimentally. Three types of roof geometries, i.e. gable, troughed and mono-sloped roofs were tested. Wind pressures were measured simultaneously at many points both on the top and bottom surfaces of the roof model for various wind directions. Based on the results for the most critical positive and negative peak pressure coefficients irrespective of wind direction, the wind force coefficients for the design of cladding and its immediately supporting structures are proposed. Correlation between the wind force and moment coefficients is investigated, and appropriate wind force coefficients for the design of main wind force resisting systems are proposed. Axial forces in the columns supporting the roof are regarded as the most important load effect. Two loading patterns causing maximum tension and compression of columns are considered.     

Study on suitable method to simulate fluctuating wind pressurecharacteristics of standard high-rise building model based on LES

为提高钝体建筑结构绕流模拟结果的精度，基于两种大涡模拟(large eddy simulation, LES)入口湍流生成方法，分别为NSRFG（narrow band synthesis random flow generation）方法和CDRFG（consistent discretizing random flow generation）方法，进行CAARC(commonwealth advisory aeronautical research concil)高层建筑标准模型绕流的数值模拟比较研究。以风洞试验结果为参照，在对大气边界层湍流风场进行模拟验证的基础上，详细对比分析采用上述两种方法模拟得到的建筑表面平均和脉动风压系数、绕流场湍流结构、风压系数概率密度分布特性等的差异，并着重从脉动风压非高斯特性角度进行探讨，检验采用上述两种方法模拟钝体建筑结构绕流的适用性和准确性。结果显示：在受来流直接作用的建筑迎风面，采用两种方法模拟的脉动风压基本都符合高斯特性；而在受分离流和尾流作用的侧风面和背风面，采用NSRFG方法能更好地反映建筑表面脉动风压的非高斯特性。极值风压分析表明，为了满足99.38%的保证率，CAARC标准模型迎风面极大与极小峰值因子需分别取为3.0和2.5，侧风面和背风面极大和极小峰值因子需分别取为2.5和4.0。     

一种非高斯风压峰值因子快速求解算法

为了计算非高斯风压峰值因子,基于双边保证率模型提出了计算非高斯风压时程峰值因子的快速快速搜索法和用于峰值提取的逐级分段法。通过某超高层建筑刚性模型测压风洞试验对常用的几种建筑覆面非高斯风压的峰值因子计算方法进行比较分析,对比各种方法得到峰值因子的大小及其与观察平均峰值的误差率。基于算法结果,研究了脉动风压概率特性,分析了偏度、峰度和峰值因子间的变化关系及其内在变化机理。结果表明:基于可靠度理论,用数值手段无限接近风压时程真实分布的快速搜索法总体精确性和适用性比经典的Sadek-Simiu法有所提高; 极大值序列的峰值因子及其误差率随风向角变化而变化的总趋势和极小值序列是一致的; 侧风面的前缘气流分离区、背风面及迎风面切角区、方形截面45°风向角下两背风面交接处是强非高斯区; 风压时程概率密度分布是否具有绝对值较大的超越峰度与样本对称出现在均值线附近的集中程度相关。     

Performance of toe-nail connections under realistic wind loading

Using recently developed pressure loading actuators (PLA), ramp and realistic fluctuating wind loads are applied to toe-nail connections which are typically used in wood-frame residential construction. The failure capacity from the ramp and fluctuating wind load tests are found to be similar, and are comparable to capacities reported in the literature. However, under realistic wind loading, the toe-nail connections are found to fail in increments with the majority of the damage to the connection occurring intermittently at the peak pressures so that it takes many peaks for a connection to fail. In addition, the effects of construction defects, in this case missing nails, were also examined in order to determine the reduction in capacity. Considering the wind loads on a typical house, estimates for failure wind speeds were obtained, assuming a factor of safety, and compared to ASCE 7-05 wind regions.     

屋面风荷载及风致破坏机理

随着建筑科技和施工工艺的进步,大量形式新颖、质量轻、柔度大的大跨度屋面结构不断涌现,风荷载成为这类结构的重要荷载。本文通过综合大量风洞试验成果和灾后实地调查结果,研究了平屋面、坡屋面、弧状屋面、柱壳和球壳屋面等各种屋面形式的风压分布特征,给出了可供设计和研究参考的屋面风压系数,并对屋面风压分布及屋面结构的风致破坏机理作了较为详细的论述,得出对屋面抗风设计颇有指导意义的结论。     

The effect of non-Gaussian local wind pressures on a side face of a square building

An accurate probabilistic representation of input forces and structural response in the extreme region is essential for the assurance of the safety and reliability of structures subjected to environmental loads. When the loads differ significantly from the Gaussian, they may increase expected damage. The design loads of a cladding glass subjected to the local wind pressures must not exceed the allowable load of a glass panel. The design loads of a cladding glass can be dependent on whether the local wind pressures have a non-Gaussian or Gaussian distribution. In this study, comparing non-Gaussian local wind pressures with Gaussian local wind pressures, and comparing the equivalent 1-min loads of cladding glass subjected to the simulated non-Gaussian local wind pressures with those of cladding glass subjected to the simulated Gaussian local wind pressures are performed to investigate the effect of non-Gaussian local wind pressures on a side face of a square building.     

弦弓式预应力柱面网壳结构风洞试验及风致效应研究

弦弓式预应力柱面网壳结构是一种新颖的结构形式,通过对网壳下部拉索施加预应力使结构成为自平衡体系,某火电厂干煤棚为弦弓式预应力柱面网壳结构在干煤棚结构中的首次应用,风荷载是其主要荷载之一,目前规范对该类网壳结构的体型系数未作明确规定,因此需要进行风洞试验来确定其体型系数,试验考虑了网壳周边环境的作用,严格模拟了规范规定的大气边界层风场,分析研究了网壳表面风压分布规律及其影响因素,给出了可供设计采用的体型系数,同时进行了风致效应的研究,研究表明,周边环境对网壳表面风压分布的影响较大而煤堆的影响较小,大气边界层风场中风速脉动导致的风压改变在设计时已不容忽视,风荷载对网壳下部预应力拉索应力起着卸载作用,各索的最大应力减少比例在20％左右。     

《屋盖围护结构风荷载标准》的制订依据及相关规定

为配合新编行业标准JGJ/T 481—2019《屋盖结构风荷载标准》的推广、应用,对屋盖围护结构风荷载的制订依据及相关规定进行了介绍。在对比国内外规范风荷载条文规定的基础上,以围护结构风荷载全风向最小值和最大值作为确定其标准值的依据,引入围护结构风压系数极值表达围护结构的风压标准值;根据风压系数时程样本的不同数量规定了风压系数极值的估计方法,对比了各国规范中封闭式低矮双坡屋盖的风压系数极值。新编标准以风荷载理论为依据制订了屋盖围护结构风荷载条文,完善和发展了我国标准的相关规定,提供了相对简单、合理的风压系数极值计算方法。     

Sample-specific linearization in reliability analysis of off-shore structures

The reliability analysis of off-shore structures under dynamic non-Gaussian wave, wind and water current loading is considered using an outcrossing approach and directional simulation in the space of the load processes. To circumvent the non-Gaussianity of the load processes for which results for mean outcrossing rate are not generally available, the “sample-specific linearization method” is proposed. This method is based on well-known results for Gaussian processes and uses the functional relationships between the non-Gaussian wave, wind and water current loads and the corresponding velocities. The proposed method is applied to a simple model off-shore structure. The structure is analyzed also to obtain probability of failure by means of Monte Carlo simulation and using time domain simulation of the load processes. This was found to be extremely expensive of computer time. The results were found to compare very favourably with those obtained by the proposed method, both in terms of accuracy and computation required.