低矮房屋迎风屋面局部风压特性研究

基于尺寸比为1.5:1:1(长:宽:高)的低矮房屋的风洞试验数据,分析了9类不同坡角的低矮房屋在5个不同风向的风场环境下,迎风屋面屋檐、屋脊等局部区域测点的平均、脉动及峰值风压系数.通过对比低矮房屋在不同坡角、不同风向作用下屋面的风压变化规律,总结了坡角及风向对低矮房屋屋面局部风压的影响规律.结果表明,低矮房屋在45....     

湍流积分尺度影响低矮房屋屋面风压特性风洞试验研究

采用缩尺比为1∶20的双坡屋面低矮房屋风洞试验刚性模型,以湍流积分尺度为变量,研究湍流积分尺度影响低矮房屋屋面局部区域平均、脉动、极值风压分布特征和变化规律。研究发现,湍流积分尺度的改变对平均风压系数影响不明显,对脉动、极值风压系数影响较大,且随湍流积分尺度的增大,屋面测点脉动、极值风压系数绝对值增大。当来流垂直于屋面长边时,在迎风屋面,距迎风屋檐越远,平均风压系数绝对值越小,山墙和角部区域脉动风压系数越小,而迎风屋面中心区域脉动风压系数越大。在背风屋面,远离屋脊测点的平均、脉动风压系数绝对值逐渐越小。双坡屋面低矮房屋在迎风屋檐及山墙区域风压相对较大,这些局部区域在强风作用下更易受到破坏。     

局部受损低矮房屋平均风压特性试验研究

通过风洞试验对村镇地区常见的带有硬山搁檩的双坡屋面风压规律进行研究,讨论了房屋在完全封闭、门窗洞口打开以及屋面开洞三种情况下的屋面外部、内部平均风压系数在不同方向角下的分布特性。试验结果表明:硬山搁檩双坡屋面在风向角为50°,60°时,外屋面角部易破坏;屋檐下部的风压系数随屋面坡度的改变而改变;门窗开洞时内屋面风压会加大屋面荷载;屋面开洞对降低屋面风荷载起到有利作用。     

扰流板减小低矮房屋屋面风压试验研究

近年来,我国台风灾害频繁,在历次风灾中,大量村镇低矮房屋倒塌破坏是造成生命财产损失的重要原因。在强风中,屋面是低矮房屋最薄弱部分往往最先发生破坏。目前,提高屋面抗风能力的方法主要是增加屋面本身强度和整体性,但其经济成本较高且抗风效果并不理想。针对上述问题,文中提出一种气动抗风方法,在双坡房屋屋面增设扰流板,通过改变房屋气动性能来降低屋面风压,并围绕这一方法开展了风洞试验研究工作。试验结果表明：扰流板可以有效减小双坡房屋屋面风压,尤其对屋面局部极值风压减小效果显著,最大减小幅度可达49%。山墙处扰流板对屋面风压影响最大,其次是屋檐处的扰流板,屋脊处扰流板对屋面风压无显著影响。相对于扰流板宽度与高度,扰流板角度是对屋面风压影响最为明显的几何因素,屋檐处扰流板角度建议值为0?~30?,山墙处扰流板为10?~30?。综合考虑经济与构造措施等因素,扰流板高度建议值为挑檐高度的1/70~1/12,宽度为房屋长度的1/20。最后,根据实验结果给出了安装扰流板结构屋面风压折减系数和相关的设计建议。     

强台风“黑格比”作用下低矮房屋风压特性

根据强台风"黑格比"登陆过程近地风场的实测结果及实测房屋表面测点在强台风登陆全过程监测获取的风压数据,分析了低矮房屋迎风屋面屋沿局部测点的平均、脉动及极值风压系数的变化规律,总结了其对应风场状况下的屋面体型系数。同时,利用等压线图分析了6种风场下的屋面平均、脉动及极值风压系数的分布规律。结果表明:在接近强台风"黑格比"风眼区域,由于明显交替变化的上升及下沉气流,导致低矮房屋迎风屋面屋沿及角部等局部区域形成强大的吸力及高压区,迎风屋面最小、最大体型系数值分别达到了-6.56、3.42;屋沿各测点风压谱相互吻合较好,当频率达到4Hz后,谱能急剧下降;迎风墙面测点在3/4墙高处压力最大,背风墙面各测点风压值基本一致,湍流积分尺度对平均风压系数的影响不大,但脉动风压系数和峰值风压系数随湍流积分尺度的增大而增大。     

低矮房屋表面平均风压的数值模拟和实测及风洞试验比较研究

基于ANSYS软件,采用Realizable k-ε,RNG k-ε和SST k-ω三种湍流模型对体型比为1.5∶1∶1低矮房屋模型迎风面、边缘及屋面的表面风压分布及变化规律进行数值模拟研究,数值模拟结果与同体型比的实测房屋及风洞试验结果对比表明,数值模拟结果与实测及风洞试验结论基本吻合,验证了三种湍流模型研究低矮房屋表面风压的可靠性,并对三种结果进行分析,研究结果能为国内低矮房屋设计提供有价值的参考。     

低矮房屋风荷载实测研究(Ⅱ)——双坡屋面风压特征分析

基于可移动的双坡屋面实验房获取的近地面台风风速和房屋表面风压同步实测数据,研究了台风作用下低矮房屋屋面风荷载。研究结果表明:在斜向风作用下,迎风屋面屋脊角部区域、屋面角部区域易形成较高的局部峰值负压并具有较大的脉动风压,风压系数概率分布为非高斯分布。在低频范围内,屋脊角部区域脉动风压预测谱与实测压力谱吻合相对较好;在高频范围内,脉动风压预测谱都低估实测谱。相对良态气候条件,在台风天气条件下,来流气流与建筑物相互作用产生的特征湍流对高频范围脉动风压功率谱影响显著,未考虑竖向风攻角和竖向脉动风速变化相对显著,在屋面角部区域现行规范计算方法相对低估其脉动风荷载。     

平面T形低矮房屋风荷载特性风洞试验与数值分析

对复杂体型的平面T形低矮双坡屋面房屋的风荷载特性进行了风洞试验研究,得到了屋面风压系数以及各屋面体型系数的变化规律;采用计算流体力学软件FLUENT建立了数值风洞模型,在数值分析结果与风洞试验结果吻合良好的基础上,对影响屋面平均风压系数及体型系数的风攻角、屋面坡角、檐口高度、房屋几何尺寸和屋面形式等参数进行了详细分析。结果表明:屋面坡角和风攻角对屋面风压系数的影响显著;在不同风攻角作用下,迎风屋面屋檐及屋脊附近形成较高负压;当屋面处于背风区域时,风压系数分布较均匀;四坡屋面坡角为30°时屋脊背风区域易形成较大负压,局部更易遭受破坏。     

檐口形状对低矮房屋屋面风压分布的影响

基于计算流体动力学（CFD）和剪切应力输运（SST）k-ω湍流模型,对带不同尺寸檐口低矮房屋的屋盖风压进行了数值模拟计算.首先,对TTU建筑模型屋盖体型系数进行数值计算,并与其他文献的结果进行对比吻合较好,验证了本文计算方法和湍流模型参数选取的合理性.然后,基于此方法研究不同尺寸檐口对低矮房屋屋面体型系数分布情况,总结出檐口尺寸对屋盖体型系数变化的规律,优化其抗风性能,研究结果可为该类建筑的工程抗风设计提供参考.     

Interpretation of full-scale strain data from wind pressures on a low-rise structure

This paper presents a study on the structural performance of a low-rise building under high-wind action, derived from the data analysis of a long-term full-scale monitoring program (1997–2000). Experimentation and full-scale measurements are critical in the study of wind-pressure-induced loading associated with complex phenomena such as three-dimensional flow fields and non-stationary winds. Recorded pressure data and corresponding deformations (strains) on selected portions of the structural frame in the proximity of the pressure transducers are evaluated and compared. The system under investigation is unique since it is located in a complex topography (coastal) environment, for which even the interpretation of basic wind and pressure data becomes challenging.The correspondence of the observed data with the United States wind load specifications (ASCE-7) is investigated both from the perspective of the loads (pressures) and of the deformation response predictions. The structural performance is evaluated through the comparison of the recorded strains with predicted deformations, derived from the application of the corresponding external wind pressure loading to a simplified structural model simulating the behavior of an instrumented region of the building.Results show good agreement between measured pressure coefficients and selected values estimated through the ASCE-7 specifications, especially in areas of positive pressures where the predictions are consistently larger than the recorded data. Reasonable and consistent correspondence was also found from the analysis of the strains in structural members.     

Net pressures on the roof of a low-rise building with wall openings

This paper deals with an investigation of the characteristics of net pressures on two significant roof areas of a low-rise building with two different dominant wall openings. Wind tunnel boundary layer studies were conducted on a corner and a gable-end roof area of a 1:50 geometric scale model of the Texas Tech University (TTU) test building with a corner and a central wall opening. Mean and peak pressure coefficients, RMS values for the pressure coefficient fluctuations about their mean, as well as roof external pressure—internal pressure correlation coefficients were obtained for the entire 360° wind azimuth range. Frequency domain studies were also conducted for a few selected point roof pressure situations from which the frequency-dependent roof external pressure—internal pressure phase difference functions, root coherence functions and the spectral density functions were obtained. The results show that the mean, RMS and peak net pressure coefficients are particularly enhanced relative to the coefficients for the roof external pressure in the ±50° wind range. Zero-time-lag correlation coefficients of up to −0.64 were obtained in agreement with results from past studies, while root coherence values of up to 0.7 were also recorded. It is demonstrated that the provisions of both the Australian/New Zealand wind loading code—the AS/NZS1170.2:2002, and the American wind loading code—the ASCE7-02, are sometimes non-conservative in the prediction of mean and peak net roof pressure coefficients. These are believed to be due to non-conservative internal pressure coefficients allowed for in these codes.     

Analysis of full-scale wind and pressure measurements on a low-rise building

Significance of full-scale experiments, analyzing wind and pressure fields in the proximity or on low-rise buildings, is evident from the attention that has been dedicated by researchers to these programs in the recent past. In the south and southeastern regions of US this problem is of particular relevance due to the presence of hurricanes and high-speed winds. This paper presents some recent results derived from a three-year monitoring of a structure located near the coast of North Carolina.In the first part of this study, attention is devoted to the characterization of the wind field around an instrumented house; a comprehensive investigation on wind velocity and turbulence characteristics during the passage of three tropical storms and other significant events is summarized. In the second part, results associated with the meteorological studies are used to assist the interpretation of pressure time histories related to such extreme events.Analyses associated with the derivation of normalized pressure coefficients were concentrated on the identification of direction-dependent pressure characteristics, correlation among consecutive taps and potential effects of the wind unsteadiness on the maximum and minimum values. Building geometry and local topography effects had an important and direct influence on these analyses.     

The influence of Helmholtz resonance on internal pressures in a low-rise building

This paper deals with an investigation of the phenomenon of Helmholtz resonance under oblique wind flow, and an examination of the applicability of the quasi-steady approach to internal pressures in buildings with a dominant opening. Studies on a 1:50 scale model of the Texas Tech University (TTU) test building in a boundary layer simulation show that ‘Helmholtz resonance under oblique wind flow’ produces an extremely strong response in internal pressure fluctuations, in comparison with that obtained under normal onset flow. It is verified that ‘eddy dynamics over the opening’ rather than ‘freestream turbulence’ is responsible for the intense excitation at oblique flow angles, implying that even if the Helmholtz resonance frequency were to be in the tail of the freestream turbulence spectrum, severe excitation would still be possible.Experimental measurements of internal pressures for a range of opening situations also reveal that the quasi-steady approach is inapplicable in the prediction of peak internal pressures. Furthermore, it is demonstrated that while the provisions of the Australian/New Zealand wind loading code—AS/NZS1170.2:2002, which is based upon the quasi-steady method, is adequate as far as mean internal pressures are concerned, it however underpredicts peak internal pressures in some situations. In particular, for the range of situations studied, measurements indicated that peak pressures were up to 25% higher than the AS/NZS1170.2:2002 provisions, in the case of openings in the positive pressure and sidewall regions. It is also shown that for openings located in the sidewall region, peak internal pressures could be just as extremely positive as it can be negative. It is suggested that in the calculation of internal pressures, the AS/NZS1170.2:2002 provide for the use of local pressure factors K_l, that are at present applied only to external pressure calculations. Secondly, the code should provide for internal pressure coefficients to be both negative and positive, when openings are located in sidewall regions. Finally, in order to account for the effects of additional fluctuations arising from Helmholtz resonance oscillations, the possibility of the use of an internal pressure factor K_i should be explored.     

低矮建筑表面破坏性旋涡及其诱导的风压特性研究综述

柱状涡和锥形涡是低矮建筑表面常见的两种破坏性旋涡。这两种旋涡将在屋盖表面局部诱导产生强风吸力,会使结构整体失效。因此,为减少低矮建筑的风致破坏,应对其表面旋涡及诱导的风压特性进行研究。通过调研相关文献,对旋涡形态特征、旋涡诱导的风压分布特性以及旋涡作用下强风吸力产生机理三个方面的研究现状进行了总结。结果表明：柱状涡和锥形涡在低矮建筑屋面诱导的风压分布可分别采用相应的拟合公式进行统一表达;其诱导下的风压脉动特性大多通过幅值分析（时域）和能量分析（频域）获得。为了探讨旋涡诱导下强风吸力的产生机理,基于风洞试验所测得的风压数据,研究其时域及频域特征;并结合旋涡理论,对旋涡作用机理给出间接的理论推测。此外,亦有学者通过测量旋涡截面流速,对现有旋涡模型进行改进,据此分析旋涡作用与涡下吸力的量化关系。     

Experimental study of wind loads on gable roofs of low-rise buildings with overhangs

Gable roofs with overhangs (eaves) are the common constructions of low-rise buildings on the southeastern coast of China, and they were vulnerable to typhoons from experience. The wind pressure distributions on gable roofs of low-rise buildings are investigated by a series of wind tunnel tests which consist of 99 test cases with various roof pitches, height-depth ratios and width-depth ratios. The block pressure coefficients and worst negative (block) pressure coefficients on different roof regions of low-rise buildings are proposed for the main structure and building envelope, respectively. The effects of roof pitch, height-depth ratio, and width-depth ratio on the pressure coefficients of each region are analyzed in detail. In addition, the pressure coefficients on the roofs for the main structure and building envelope are fitted according to roof pitch, height-depth ratio and width-depth ratio of the low-rise building. Meanwhile, the rationality of the fitting formulas is verified by comparing the fitting results with the codes of different countries. Lastly, the block pressure coefficients and worst negative pressure coefficients are recommended to guide the design of low-rise buildings in typhoon area and act as references for the future’s modification of wind load codes.     

女儿墙对平屋面低矮建筑风荷载特性的影响

对平屋面低矮建筑进行1∶25缩尺刚性模型测压风洞试验,研究了无女儿墙工况和4种不同高度女儿墙的平屋面低矮建筑的风荷载分布规律。无女儿墙的平屋面主要承受风吸力作用,斜风向锥形涡诱导的最不利吸力区域为屋面迎风边缘角部区域,为全风向下最不利区域。女儿墙的存在可明显减小屋面的平均风吸力和极值风吸力,平均风吸力减小幅度可达150%,同时最不利平均风压系数和极小值风压系数的出现位置逐渐远离了屋面角部区域;随着女儿墙高度的增加,极值风吸力进一步减小,极值风压力增大,最大的极大值风压系数出现在尾流区;采取分区的方式给出了不同女儿墙高度的屋面体型系数建议取值。     

Effect of building length on wind loads on low-rise buildings with a steep roof pitch

A wind tunnel model study was carried out on long, low-rise buildings with a steep roof pitch to determine the effect of the length-to-span aspect ratio on the external wind pressure distributions. The study showed a significant increase in the magnitude of the negative pressure coefficients on the leeward roof and wall, with an increase in aspect ratio, for oblique approach winds. These large suction pressures also generate large design wind load effects on the frames near the gable-end. The 1989 edition of the Australian standard for wind loads, AS 1170.2-1989 was found to underestimate the wind loads on steep pitch gable-roof buildings of aspect ratio greater than 3, on areas near the windward gable-end, and hence the critical bending moments in the supporting structural frames. The current Australian/New Zealand wind load standard, AS/NZS 1170.2-2002 specifies increased negative pressure coefficients on the leeward half of high pitch roof buildings, and critical bending moments in the supporting frames calculated from these distributions agree quite well with values obtained from the wind tunnel study. However, other major standards severely underestimate the critical bending moments, and the effective pressure coefficients producing those bending moments, especially on the leeward roof slope.     

Experimental and numerical study of wind pressures on irregular-plan shapes

This paper presents the results of a program of wind tunnel model tests on pressure distributions for irregular-plan shapes (L- and U-shaped models). The experiments were carried out in a closed-circuit wind tunnel and a multi-channel pressure measurement system was used to measure mean values of loads on 1:100 scale models. The same tests were carried out on a cube-shaped model as an experimental validation. The effectiveness of the model shape in changing the surface pressure distributions is assessed over an extended range of wind directions. The experimental data for the L- and U-shaped models showed different wall pressure distributions from those expected for single rectangular blocks. Furthermore, a Computational Fluid Dynamics (CFD) code was used to illustrate some particular cases and to provide a better understanding of the flow patterns around these irregular-plan models and of the pressure distributions induced on their faces. Computed pressure coefficients have also been compared with wind tunnel results for normal and oblique wind incidence. A general good agreement has been found for normal wind incidence whereas some differences have occurred for other directions.