A full-scale study of wind loads on agricultural ridged canopy roof structures and proposals for design

Full-scale measurements have been made under natural wind conditions to ascertain the wind loads on the canopy roofs of two modern ridged roof Dutch barns. The two barns were of different geometries and representative of those currently produced in the UK. Measurements were made with the barns in the empty state, and with various arrangements of material stored internally. Detailed results are given in the form of pressure coefficients describing the wind loads generated over the two canopy roofs and the internal blockages by winds approaching from various directions. Comparisons with the results show that the pressure coefficients given in the British Standard Code of Practice CP3 “Code of basic data for the design of buildings, Chap. V, Part 2, 1972, Wind loads” are unsatisfactory for the design of ridged canopy roof structures.Simplifications of the detailed experimental data are proposed which may be used with the existing procedures of the Code of Practice CP3 for the design of canopy roof structures of a size and geometry which fall within those of the two Dutch barns employed in the experiments.     

体育场主看台悬挑屋盖的风荷载计算

采用数值模拟方法并结合风洞模型试验数据,对一平屋面和一斜屋面的体育场主看台悬挑屋盖的表面风压进行了计算和分析,对屋盖上下表面的风压分布规律进行了总结和归纳。在此基础上,提出了两种屋面情况的屋盖风荷载简化分布图线和计算方法,并与国外相关规范建议的公式作了比较。该简化计算方法可直接供同类结构的抗风设计参考和应用。     

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。     

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.     

外形几何参数对低矮建筑双坡屋盖升力系数极值的影响

对一系列低矮建筑双坡屋盖的刚性模型测压风洞试验数据进行了处理,研究了屋盖升力系数极值的特征,讨论了最不利屋盖升力系数随建筑外形几何参数的变化规律。研究结果表明,屋盖坡角的变化对最不利屋盖升力系数有重要影响：对高宽比相同的低矮建筑,屋面最大升力系数随屋盖坡角增大而减小,且建筑的厚宽比越大,这种趋势越剧烈;最不利屋盖升力系数随着建筑高宽比的增大而增大,但这种增大的趋势随着屋盖坡角的增大而减小。基于这些数据,用多参数最小二乘法将最不利屋盖升力系数拟合成了屋盖坡角、建筑高宽比和厚宽比的函数形式,并对拟合函数进行了误差分析。所得结论及拟合公式可为低矮建筑的结构设计及相关荷载规范的制订和修改提供参考。     

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.     

大跨度屋盖结构等效静力风荷载方法及应用

结构风致振动是控制大跨度屋盖结构设计的主要因素。大跨屋盖结构模态密集,风致振动有多模态参与并受模态交叉项影响的特性,这给建立大跨度屋盖结构等效静力风荷载的计算方法带来了很大的困难。本文基于计算共振分量的修正SRSS法,将LRC法和考虑模态耦合系数的惯性风荷载法相组合来表示等效静力风荷载。本文的方法能考虑模态之间相互耦合的情况,给出的等效静力风荷载具有明确的物理意义。最后将该方法运用于一个实际工程,检验了计算方法的精度。计算结果表明,本文方法和CQC法得到的响应值非常接近,最大误差约为3%,相对而言SRSS法的计算误差较大。     

Wind loads on attached canopies and their effect on the pressure distribution over arch-roof industrial buildings

Arch-roof industrial buildings are very wind sensitive. The current aerodynamic coefficients in wind codes do not contemplate the possibility of existence of canopies attached to the buildings. This paper presents the results of an investigation on the influence exerted by canopies on the static wind actions on arch-roof industrial buildings. Six scale models of these arch-roof buildings were tested, with five types of canopies attached. Three of these canopies were instrumented and the static wind pressures were measured. The tests were done at the boundary layer wind tunnel of the Universidade Federal do Rio Grande do Sul. The results show that the aerodynamic coefficients for the roof are not affected by the canopies, in the case of axial incidence. However, the influence on the pressure distribution is noticeable for wind incidence perpendicular to the main axis of the arch roofs and for other incidences as well. This influence is discussed in the paper. The aerodynamic coefficients for the design of the arch-roofs, with and without the attached canopies are given. Aerodynamic coefficients for design of the canopies are also suggested. Furthermore, the paper discusses the relation between the magnitude of the canopy design forces and the canopy width, as well as the relation between the canopy height location and the height of the building wall. The results were compared with design recommendations from previous work of Jancauskas and Holmes (in: US National Conference on Wind Engineering, Proceedings, Texas Tech University, Lubbock, 1985) and Jancauskas and Eddleston (in: International Conference on Wind Engineering, Fotodruck J. Mainz, Aachen, 1987).     

平面拱形桁架等效静风荷载研究

对矢跨比分别为1/4、1/6、1/8的3个拱形屋面进行了同步测压风洞试验,分析风荷载和结构参数对平面拱形桁架风振响应和等效静风荷载的影响规律。风洞试验结果表明, 0°风向时,高矢跨比屋面的最大负压幅值出现在屋顶,而低矢跨比的出现在迎风前缘。从方便工程应用的角度,采用简化振型函数表达针对结构多个位移和杆件应力响应的多目标等效静风荷载。在工程常用范围内,分析结构矢跨比、跨度、屋面质量、设计风速和风向等参数对中部和端部平面拱形桁架多目标等效静风荷载的影响,得到可用于指导该类结构抗风设计的等效静风荷载风压系数建议值,且经校核,在该等效静风荷载作用下的结构响应与实际动力响应极值吻合较好。     

大尺度高低跨柱面屋盖的风压系数分区研究

针对大尺度高低跨柱面屋盖体系风压分布变化梯度较大、跨间相互干扰以及此类屋盖风压分区无相关规范可查阅等问题,在得到各种风向下最不利极值风压的基础上,采用K-means聚类的风压系数快速分区方法将高低跨柱面屋盖表面划分为多个区域,并计算了各区域的分区风压系数。同时,在高低跨柱面屋盖风压系数分区研究过程中,对K-means方法的k值取值范围和最佳k值确定方法进行针对性改进。结果表明,高低跨柱面屋盖的边缘属于风敏感部位,而中间部分风压变化较小,因而在进行大尺度平屋盖抗风设计时,采用聚类方法进行风压分区更为合理。     

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。     

大跨度屋面风压分布的插值计算方法

大跨度结构由于跨度大、体型复杂等特点,风流经过时会产生复杂的气流分离和再附着,因而其表面上的风压分布较为复杂．刚性模型试验是测量大跨度屋面结构风压分布较有效的方法,但是刚性模型试验只能布置有限的测点,得出有限测点的风压系数．本利用二元函数和多元函数的分段低次插值方法,求出风压系数分布的插值函数,进而反映整个屋面的风压分布情况,此方法能避免高阶插值方法带来的“龙格”现象;利用外插技术可以处理边缘部位和不规则的平面形状;并且通过坐标变换或投影平面代替曲面等方法可以处理球壳及曲面屋盖的风压分布插值计算。     

单个周边建筑对工业厂房屋面平均风压的气动干扰效应

工业厂房通常处于工业厂区内,受周边建筑的干扰,其表面风压分布与单个独立厂房不同,相邻建筑会对风荷载产生影响。基于单个厂房与两个串列厂房刚性模型风洞试验,给出了不同工况下屋面的平均风压,分析了屋盖横向、纵向端部与中部测点的平均风压分布规律,对比了不同串列距离条件下受扰厂房与独立厂房屋盖表面平均风压分布,探讨了平均风压系数干扰因子随风向角及干扰距离的变化规律。试验结果表明：不同风向角时,干扰效应截然不同;干扰效应存在临界风向角。临界风向角一般保持在 30°~50°范围内,小于临界风向角时,干扰起放大效应;大于临界风向角时,干扰为遮挡效应。此外,运用最小二乘法拟合了干扰因子设计值实用计算式,为受扰厂房建筑屋盖表面风压的修正提供依据。     

大连市贝壳博物馆表面风压分布特性风洞试验研究

为了满足大连市贝壳博物馆的抗风安全需要,进行了刚性模型表面风压分布特性风洞试验研究。详细介绍了试验所采用的主要技术参数与基本的数据处理方法,给出了典型风向角下结构表面风压分布的等值线图和结构典型测点在不同风向角下的风压变化规律;分析了各风向角下绝对值最大的局部体型系数及其出现的位置,并将屋盖的局部体型系数与现行《建筑结构荷载规范》(GB 5009—2001)进行了对比。结果表明:屋面上表面的风荷载主要表现为负压,顶部迎风挑檐边缘较大,屋面的尾流区域较小或为正压。屋面两侧的悬挑部分及主入口处迎风时分布有大面积正压,以靠近拐角部分最大,且这部分屋面对风作用反应敏感,设计时应考虑体型系数的变号情况。     

周边高层建筑对大跨度曲面屋盖的气动干扰

结合无锡新区科技交流中心的风洞试验,分析了有无周边建筑两种情况下的风压分布,并对梅花形屋盖的花蕊、花瓣凹弧面和花瓣凸弧面3个典型部位的风荷载体型系数进行了研究,获得周边高层建筑对大跨度曲面屋盖气动干扰的相关结论:虽然受扰建筑的最不利风向角和风压发生很大变化,但是最危险部位始终处于檐口附近,而且是负风压为主;在"兜风效应"的作用下,受扰建筑的风压会急剧增大;在"阻挡效应"的作用下,受扰建筑的风压存在由负压向正压变化的趋势;屋盖凹弧面的槽向与风向角一致时,存在涡流作用与"兜风效应"叠加的现象,受"吸"破坏力极大,在曲面屋盖设计中应予以重视。     

风致屋面积雪分布风洞试验研究

为了预测屋面积雪分布,对一典型阶梯形屋面和两种双坡屋面进行了积雪分布风洞试验研究。首先对流场进行了测量,然后进行屋面积雪分布试验,测量了不同时间内屋面雪深分布,考察了风速、风向对屋面积雪分布的影响,并对屋面上粒子质量流率进行了分析。结果表明,运动粒子使表面附近的流场湍流度降低,流场有效气动粗糙长度与摩擦速度平方成正比;阶梯形屋面在风向角为0°时,雪深分布与观测结果基本一致,斜向风时,雪深分布严重不均匀,特别在风向角135°时,最小雪深系数为0,最大雪深系数达1.7;双坡屋面在风向角0°时背风屋面局部产生较多沉积,坡度10°的双坡屋面最大雪深系数达1.6,坡度20°的双坡屋面最大雪深系数为1.2;屋面上平均质量流率与风速呈线性关系,表明屋面上粒子质量输运率按摩擦速度三次方增加。     

大跨度屋盖结构的多级抗风设计

结合风灾破坏的实地调查结果,对我国荷载规范中基本风压的取值规定进行了探讨;借鉴建筑抗震设计标准和规范,提出适合于大跨度屋盖的多级抗风设防标准和设计方法,并结合北京奥运乒乓球馆屋盖结构进行了抗风分析,得到的主要结论是:基本风压的取值决定了建筑物抗风设防的标准;现行规范中我国部分地区的基本风压取值有所偏低;对于大跨度屋盖结构而言,可以引入抗震设计思想和方法,进行多级抗风分析与设计。最后探讨了一些适合大跨度屋盖的抗风概念设计方法,以供设计和建造时参考。     

开合屋盖体育场风荷载特性试验研究

建筑立墙迎风面开孔时内部风压随开口处外压变化显著,使得屋盖所受净压显著增大,其测量值往往大于规范取值。而对于屋盖顶部开孔的建筑,其内部风荷载我国规范没有相应取值。为了进行开合屋盖结构设计和探讨屋盖顶部开孔对屋盖风荷载变化的影响,以1∶300的几何缩尺比制作了一个开合屋顶体育场的刚性模型,在B类地貌中对该体育场固定、活动屋盖的上、下表面进行了风洞测压试验,得到了屋盖上、下表面的体型系数、平均风压系数、脉动风压系数和极值风压系数。试验结果表明：活动屋盖的开启,可有效减小固定屋盖和活动屋盖的平均风荷载,引发整个结构承受向下的风荷载;活动屋盖开启将增大固定屋盖和活动屋盖的净脉动风荷载;活动屋盖开启将减小固定屋盖和活动屋盖的极小值风荷载,且固定屋盖上的最大极小值风压系数的位置往屋顶开口方向移动。     

Full-scale validation of vortex suppression techniques for mitigation of roof uplift

Widespread damage to roofs in hurricanes and other high wind events has highlighted the need for improving the wind performance of roofs, including both new construction and retrofit on existing buildings. Effective and economical methods to mitigate wind effects on roof components are sought to reduce accumulated losses from frequently recurring low- and moderate-intensity events. An experimental study was carried out in the 6-fan Wall of Wind (WoW) testing apparatus to assess the effectiveness of aerodynamic edge devices at full scale in reducing wind effects over the roof corner and edge regions. Two sets of tests, roof gravel scour testing and pressure testing, were carried out to visualize the development of edge vortices and compare roof uplift pressures with and without aerodynamic edge shapes, thus allowing the estimation of the effects of such shapes in alleviating wind damage of roofing material as well as high uplift pressures on roofs. Probabilistic estimates of peak pressures indicated that the use of such mitigation devices resulted in significant reductions in uplift within the instrumented area, which according to the US wind load specifications (ASCE 7-05) represents a corner section of the roof that will experience the highest suction. The largest reduction was achieved with the Flat Roof AeroEdge Guard (FRAG1). This research demonstrates the potential for substantial reduction of roof uplift pressures through the development and application of mitigation techniques to lessen or prevent hurricane-induced damage to new and existing roofs.     

复杂型体悬挑屋盖风荷载风洞试验与数值模拟

基于Fluent 6.1软件平台,将Realizablek-ε模型与非平衡壁面函数搭配使用,对位于海岛强台风地区的某海洋文化中心屋盖风压分布进行了计算流体动力学(CFD)数值模拟,同时也对该建筑进行了风洞试验。模拟结果与风洞试验数据的对比显示数值模拟可较准确地反映实际风压。风洞试验和数值模拟均显示悬挑屋盖受到了很大的吸力,对屋盖结构极为不利,对此问题采取在屋盖悬挑部分开洞的减压措施,以改善屋盖悬挑部分的受风特性。对开洞后的建筑进行了CFD建模与计算,结果表明在屋面前缘开洞可有效降低屋盖悬挑部分的最大风压和所受的竖向升力,大大改善屋盖结构的受力状态。