低层坡屋面房屋风荷载特性风洞试验研究

对低层双坡屋面和四坡屋面建筑进行了风洞试验研究,考虑了屋面形式、屋面坡度、来流方向和挑檐长度等不同因素对屋面风压分布的影响,分析了屋面平均和脉动风压系数的分布特性。结果表明,0°风向角（来流垂直吹向屋脊）、屋面坡度为30°时,迎风屋面屋檐及屋脊附近形成较高负压,迎风屋面风压系数呈环状分布;屋面坡度为15°时,迎风屋面风压系数呈阶梯状分布。屋面体型系数受风向角、屋面坡度和屋面形式的影响较大：0°风向角、双坡屋面模型中,15°屋面坡度迎风屋面体型系数为30°屋面坡度的2.76倍;四坡屋面模型中,15°屋面坡度迎风屋面体型系数为30°屋面坡度的228倍;背风屋面体型系数受屋面坡度的影响较小;0°和45°风向角下,对于15°和30°屋面坡度,当屋面坡度相同,屋面形式由双坡改为四坡时,迎风屋面的体型系数绝对值有所增大,屋面更容易受力破坏,但对背风屋面的影响较小。     

Interference effects on wind loads on low-rise hip roof buildings

The Natural wind in the wind tunnel was simulated at the University of Roorkee (India) on the basis of full/model-scale comparison. For this, the Texas Tech University (TTU) building model was fabricated on a geometric scale of 1:50 and tested in the simulated wind for comparison of the pressures with full-scale values. A hip roof building model (geometric scale 1:50) of plan dimensions 280 mm×140 mm×58 mm (eave height) with 30° roof slope was selected as the test building (T.B.) so as to examine interference with a similar building as well as three similar buildings placed on the upstream side at fifteen different locations (Fig. 2). A quadrant portion of the model roof was divided into ten different zones to see the effect of interference at critical roof positions. Significant effects have been observed.     

相邻低层四坡屋面房屋在风荷载下的相互干扰作用

采用数值模拟方法,结合风洞模型试验对两栋低层四坡屋面房屋周围的风场及表面风压进行了计算和分析,数值模拟基于Reynolds时均方程和可实现k-ε湍流模型,采用了具有良好拓扑性能的非结构四面体网格,FLUENT软件实现了流场的数值求解.在单体计算结果和风洞试验结果有较好吻合的前提下,获得了有相邻建筑干扰的情况下,低层四坡屋面房屋的表面风压的变化规律,结论可直接供工程设计参考.     

周边建筑对低矮建筑平屋面风荷载的干扰因子

低矮建筑通常都是成群出现的,周边建筑对被包围建筑的风荷载存在干扰效应。通过刚性模型表面测压风洞试验对被同类周边建筑所包围的平屋面低矮建筑表面风压系数进行测量,分析周边建筑的建筑面积密度、相对高度及排列方式对被包围建筑平屋面上的最大局部负风压及最大屋面升力的干扰因子的影响。试验结果显示,最大局部负风压的干扰因子除少数周边建筑面积密度很低或相对高度较矮时大于1.0外,多数情况下都小于1.0;所有存在周边建筑的试验工况中最大屋面升力的干扰因子总是小于1.0;两个干扰因子都随周边建筑面积密度的增大而减小;当周边建筑的相对高度小于1.0时,两个干扰因子都随周边建筑相对高度的增大而减小,但当周边建筑的相对高度大于1.0时,两个干扰因子对周边建筑相对高度的变化不敏感。基于上述试验结果,将两个干扰因子拟合成周边建筑面积密度及相对高度的函数形式,为低矮建筑的设计提供依据,为建筑结构荷载规范的修订提供参考。     

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。     

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。     

低层双坡房屋屋面平均风压影响因素的数值模拟研究

采用Fluent6.0软件平台和雷诺应力模型(RSM),对我国沿海地区常见的一类带挑檐的低层双坡房屋屋面风压进行了数值模拟,研究了各影响因素对屋面平均风压的影响。首先,将数值模拟结果和模型风洞试验结果进行对比,以说明文中采用的湍流模型和计算参数的适用性。然后,采用数值模拟方法,研究带挑檐的低层双坡房屋屋顶具有不同外形参数(坡角、挑檐长度、檐口高度)时,屋面的局部平均风压分布特性和变化规律。结果表明,各参数对屋面风压的影响程度不一,且与风向角的影响有关。坡角对屋面风压分布的影响是整体性的,挑檐长度则只有局部性的影响,而檐口高度对整体屋面风压的影响较小。研究结果可供我国沿海地区低层房屋抗风设计参考。     

双坡低矮建筑风压系数的概率统计特性分析

基于低矮建筑表面风压测量风洞试验数据,分析了低矮建筑各部位风压系数的概率统计特征。分析结果显示,在迎风墙、屋盖上风区和侧墙上风区以及斜风时屋盖某些关键测点上,风压系数的偏度系数和峰度系数都严重偏离高斯过程对应值,表现出很强的非高斯性;在背风墙、屋盖下风区和侧墙下风区,尽管风压系数的偏度系数接近高斯过程对应值,但峰度系数仍然偏大,风压系数仍然是非高斯性的。将利用峰值因子法得到的模型各测点上的最不利正、负风压系数与直接观察法得到的结果进行了对比,结果表明,峰值因子法低估了墙面上的最不利正、负风压系数,低估了屋盖上的最不利负风压系数,但高估了屋盖上的正风压系数,估计误差率在-37%～+120%之间。     

强风作用下低矮民居受力分析

受台风影响的中国东南沿海地区,低矮房屋的损坏最为普遍也最为严重。基于此,本文对低矮民居的表面风压进行了模拟并对其抗风性能进行了研究,并指出了后续的低矮民居结构抗风研究侧重点。     

楼群风效应对高层建筑的影响研究

基于完全非结构化网格的有限体积法,研究了轻质高强材料建筑群和风之间的综合影响关系,解决了现有规范和实际设计中只重视考虑单独的高层建筑而忽略周围建筑群和风之间相互作用的问题,得出了楼群效应较大的影响着楼群风压分布和风流线的结论。     

洞口设置对高层建筑静力风荷载的影响研究

本文对涉及两种开洞率、三种不同开洞位置和全封闭(无洞口)的八个高层建筑刚性模型的表面平均风压分布进行了风洞试验研究,并与计算流体动力学(CFD)大型商业软件Fluent6.0的计算结果进行了对比分析。结果表明,开洞建筑平均风压的减少主要是受荷面积减少引起的,但其减少的比率大于开洞率。此外,借助Fluent6.0对不同开洞率情况下的建筑模型进行了大量算例分析,得到了中部开洞建筑模型的平均风压系数相对值和基底弯矩系数相对值与开洞率之间的相关方程;探讨了底部开洞建筑模型洞内平均风速的增大效应与洞口大小、来流方向之间的关系。分析表明,在最不利来流风向角情况下,洞中最大平均风速可超过建筑模型顶部的远处来流风速,应引起建筑风环境设计者的关注。     

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.     

罩棚式低矮房屋屋面风荷载特性及气动抗风措施研究

采用模型的风洞试验详细研究了矩形和圆形罩棚屋面结构的平均风压和峰值风压分布特征,分析了屋面风致破坏的主要原因,在此基础上实施了7种不同的屋面局部修改方案的对比试验,从中筛选出可以有效消减屋面风荷载的抗风措施。两种平顶矩形和圆形罩棚屋面结构均以负压为主,试验测得两结构屋面的最高平均负压系数分别为-1.83和-0.97,相应最高极值负压系数为-5.41和-3.11,结果远高于GB 50009-2001《建筑荷载规范》推荐的平均风压乘以阵风系数的方法,这显示规范中的阵风系数方法并不适合于计算该类屋面结构的风压值。根据分析结果给出了平顶矩形和圆形罩棚屋面结构风压体型系数取值的建议值,采用斜切角形式的屋檐或在屋面板和侧面围板交界处开贯通透风槽方式可以使屋面风敏感区域的极值负压削减25%~35%。     

A hybrid RANS and kinematic simulation of wind load effects on full-scale tall buildings

Up till recent years, predicting wind loads on full-scale tall buildings using Large Eddy Simulation (LES) is still impractical due to a prohibitively large amount of meshes required, especially in the vicinity of the near-wall layers of the turbulent flow. A hybrid approach is proposed for solving pressure fluctuations of wind flows around tall buildings based on the Reynolds Averaged Navier-Stokes (RANS) simulation, which requires coarse meshes, and the mesh-free Kinematic Simulation (KS). While RANS is commonly used to provide mean flow characteristics of turbulent airflows, KS is able to generate an artificial fluctuating velocity field that satisfies both the flow continuity condition and the specific energy spectra of atmospheric turbulence. The kinetic energy is split along three orthogonal directions to account for anisotropic effects in atmospheric boundary layer. The periodic vortex shedding effects can partially be incorporated by the use of an energy density function peaked at a Strouhal wave number. The pressure fluctuations can then be obtained by solving the Poisson equation corresponding to the generated velocity fluctuation field by the KS. An example of the CAARC building demonstrates the efficiency of the synthesized approach and shows good agreements with the results of LES and wind tunnel measurements.     

Computational evaluation of wind effects on buildings

A computer simulation of wind flow around a block-shaped building has been attempted by using 3-D turbulent flow conditions. The Control Volume Method is used for numerical discretisation. The SIMPLE algorithm inter alia fulfils the continuity condition. Results have been compared with previous computational attempts and also with data obtained in boundary layer wind tunnel tests. The inclusion of modifications in the standard k-ε model improves the prediction of pressures on the building envelope.     

Distribution of background equivalent static wind load on high-rise buildings

In this paper, the along-wind and cross-wind fluctuating load distributions along the height of high-rise buildings and their correlations are obtained through simultaneous pressure measurements in a wind tunnel. Some typical methods proposed in some relative literatures, i.e., load-response correlation (LRC), and quasi-mean load (QML) and gust load envelope (GLE) methods, are verified in terms of their accuracy in describing the background equivalent static wind load distribution on high-rise buildings. Based on the results, formulae of the distribution of background equivalent static load on high-rise buildings with typical shapes are put forward. It is shown that these formulae are of high accuracy and practical use.     

On the wind-tunnel simulation of the atmospheric surface layer for the study of wind loads on low-rise buildings

Mean velocity and turbulence measurements are made in a shear layer generated in a short test-section wind tunnel. This shear layer is developed by the spire-roughness technique and simulates as closely as possible the lower part of the neutral atmospheric surface layer for the study of pressures on 1:70 scale models of low-rise buildings. In Ref. [1] and in a companion paper [2], to be published at a later date, the statistical quantities describing the fluctuating pressures acting on a low-rise building in model and in full scale are compared.Comparison of the generated shear flow with measurements obtained in the atmospheric surface layer indicates that simultaneous simulation of mean-velocity power index, surface-roughness length, turbulence intensity and turbulence integral scale is extremely difficult to achieve. On the basis of results obtained to date, it is tentatively concluded that close simulation of the turbulence intensity and development of a turbulence integral scale at least as large as the largest model dimension are required for proper simulation of the fluctuating wind pressures. In order to satisfy these requirements, the scaling of the upstream roughness elements must be exaggerated.     

Distribution of background equivalent static wind load on high-rise buildings

In this paper, the along-wind and cross-wind fluctuating load distributions along the height of high-rise buildings and their correlations are obtained through simultaneous pressure measurements in a wind tunnel. Some typical methods proposed in some relative literatures, i.e., load-response correlation (LRC), and quasi-mean load (QML) and gust load envelope (GLE) methods, are verified in terms of their accuracy in describing the background equivalent static wind load distribution on high-rise buildings. Based on the results, formulae of the distribution of background equivalent static load on high-rise buildings with typical shapes are put forward. It is shown that these formulae are of high accuracy and practical use. __________ Translated from Journal of Tongji University (Natural Science), 2008, 36(3): 285–290 [译自: 同济大学学报(自然科学版)]     

X形超高层建筑层风激励谱计算模型研究

通过X形超高层建筑刚性模型多点同步测压风洞试验,研究高层建筑风荷载阻力系数和升力系数平均值、均方根值沿高度的变化规律,并与矩形高层建筑均方根升力系数进行比较.提出X形高层建筑顺风向与横风向动力风荷载功率谱密度函数、相干函数的计算模型,并根据风洞试验数据进行拟合计算,结果表明该计算模型与风洞试验结果吻合较好,可以以此为基础进行类似高层建筑顺风向与横风向动力响应的频域计算.     

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.