Force transfer mechanism on fastener section of mechanically anchored waterproofing membrane roofs under wind pressure during typhoons

The wind pressure, billow of a PVC sheet, and fastener load of a mechanically anchored waterproofing membrane system on a building rooftop were measured during a typhoon. The results showed that the waterproof sheet billowed upward, and the height of the billow was greater on the windward side that was under higher negative pressure. The axial and lateral forces acting on the fastener of the waterproof sheet were measured by a six-component force transducer, and it was found that the lateral force acting on the windward side of the fastener was larger. The tensile force acting on the fastener section was calculated using an equation for rooftop wind pressure. Finally, the method used to determine the fastener's position and the types of materials best-suited to cope with wind pressure on the roof were proposed, and the safety of this waterproof system was evaluated.     

Wind effects on a long-span beam string roof structure: Wind tunnel test, field measurement and numerical analysis

The Guangzhou International Convention & Exhibition Center (GICEC) with roof dimensions of 210 m wide and 457 m long is the largest exhibition center in Asia and the 2nd largest of this kind in the world. This paper presents results from a combined study of wind tunnel test, full-scale measurement, and numerical analysis of wind effects on the long-span beam string roof structure. In the wind tunnel test, wind-induced pressures including mean and fluctuating components were measured from the roof of a 1:300 scale GICEC model under suburban boundary layer wind flow configuration. The Proper Orthogonal Decomposition (POD) method and the quasi-steady approach as well as probability analysis were adopted to estimate the characteristics of the fluctuating wind pressures on the roof. On the other hand, full-scale measurements of wind actions and wind-induced structural responses of the roof were conducted during the passage of Typhoon Nuri. The field data such as wind speed, wind direction, and acceleration responses, etc., were continuously and simultaneously monitored from a wind and structural response monitoring system installed on the roof structure during the typhoon. Detailed analysis of the field data was performed to investigate the characteristics of the typhoon-generated wind and the wind-induced vibration of the long-span roof structure under typhoon condition. The dynamic characteristics of the roof were determined from the field measurements and comparisons with those calculated from the finite element model (FEM) of the structure were made. The damping ratios of the roof structure were estimated by means of the random decrement method and the amplitude-dependent damping characteristics were presented and discussed. Finally, the full-scale measurements were compared with the model test results to examine the accuracy of the wind tunnel test results and to identify possible modelling errors in the numerical study. The results presented in this paper are expected to be of considerable interest and of use to researchers and professionals involved in designing long-span roof structures.     

Wind effects on the world’s longest spatial lattice structure: Loading characteristics and numerical prediction

The 486-m long roof structure of Shenzhen Citizens’ Centre is the world’s longest spatial lattice structure. This paper presents some selected results from a combined wind tunnel and numerical simulation study of wind effects on the extra-long-span roof structure. In this study, simultaneous pressure measurements on its entire roof are made in a boundary layer wind tunnel, and the measured wind pressures, such as mean, root-mean-square (rms) and peak pressure coefficient distributions on the roof are presented and discussed. Based on the measured data from a number of pressure taps, a numerical simulation approach using backpropagation neural networks (BPNN) is developed for the predictions of wind-induced pressure time series at other roof locations which are not covered in the wind tunnel measurements. The BPNN is trained with the pressure data time series measured from adjacent pressure taps. The good performance of the developed neural network is demonstrated by comparing the predictions with the model test results, illustrating that the BPNN approach can serve as an effective tool for the design and analysis of wind effects on large roof structures in conjunction with wind tunnel tests.     

上海铁路南站平均风荷载的风洞试验和数值模拟

介绍了上海铁路南站模型风洞试验和风荷载数值模拟的主要结果。通过风洞试验,给出了这一大跨度屋盖结构在无周边建筑和有周边建筑情况下屋面的风压分布特性。总的来说,挑篷迎风前缘有较大的负压,且梯度较大;前缘中部压力系数接近零;屋盖顶部又呈现负压状态;屋盖背风处一般是正压。同时,基于CFX5.5软件平台,利用RSM湍流模型,对屋盖上的平均风压进行了数值模拟,并将计算结果与测压模型风洞试验数据进行了对比。对比结果显示两者较为吻合。此外,通过降低悬挑部分的高度以研究几何参数变化对平均风荷载的影响。数值模拟表明,降低悬挑高度可以显著减小悬挑部分的平均风荷载。     

玖龙纸业(天津)有限公司厂房屋面防锈蚀、冷凝技术

玖龙纸业(天津)有限公司厂房防水、保温屋面采用双层PE膜隔汽层作为XPS保温层的辅助层,上设PVC卷材防水层,同时采用奥氏体防锈蚀冷凝专用紧固件系统,最大限度地避免屋面出现冷凝结露、锈蚀现象;同时屋面细部节点都采用了PVC卷材包覆等处理,延长了屋面系统的寿命。     

单层屋面系统抗风揭试验及其应用

概述了单层屋面系统的基本组成和在欧美的发展现状,重点阐述了单层屋面系统的抗风揭试验方法,包括美国ANSI/FM4474方法和欧洲ETAG006方法,简要介绍了抗风揭试验结果在屋面设计中的应用。     

Response of pierced fixed corrugated steel roofing systems subjected to wind loads

The low-cycle fatigue response of corrugated metal roof cladding to fluctuating wind loads was studied by subjecting cladding specimens to a series of static, cyclic and simulated “real” cyclonic wind loads using a Pressure Loading Actuator (PLA), and measuring fastener response using a x–y–z load cell. The overall performance of cladding including crack initiation, propagation and patterns, and cycles to failure was found to be similar to previous tests that used line-loads to simulate wind pressure. The reaction at a fastener to spatially varying pressures was assessed by analysing the influence coefficients, to show that it is predominantly influenced by local loads acting along the screwed crest. In addition, the response of roofing specimens subjected to fluctuating cyclonic wind pressures replicated failures observed in the field. The fastener response varied with the load level and the response spectrum followed the wind load spectrum up to 5 Hz even with deformation and cracking of the cladding showing that these higher frequency wind “load cycles” were transferred into the supporting structure via the fastener.     

Large eddy simulation of wind effects on a long-span complex roof structure

This paper presents a combined study of numerical simulations and wind tunnel tests for the determinations of wind effects on a long-span complex roof of the Shenzhen New Railway Station Building. The main objective of this study is to present an effective approach for the estimations of wind effects on a complex roof by computational fluid dynamics (CFD) techniques. A new inflow turbulence generator called the discretizing and synthesizing random flow generation (DSRFG) approach was applied to simulate inflow boundary conditions of a turbulent flow field. A new one-equation dynamic subgrid scale (SGS) model was adopted for the large eddy simulations (LES) of wind effects on the station building. The wind-induced pressures on the roof and turbulent flow fields around the station building were thus calculated based upon the DSRFG approach and the new SGS model integrated with the FLUENT software. In parallel with the numerical investigation, simultaneous pressure measurements on the entire station building were made in a boundary layer wind tunnel to determine the mean, fluctuating, and peak pressure coefficient distributions. The numerically predicted results were found to be consistent with the wind tunnel test data. The comparative study demonstrated that the recommended inflow turbulence generation technique and the new SGS model as well as the associated numerical treatments are useful tools for structural engineers to assess wind effects on long-span complex roofs and irregularly shaped buildings at the design stage.     

Mechanics and test study of flexible membranes ballooning in three dimensions

Numerous enclosure wall systems employ membranes that are not fully adhered, common examples being mechanically attached housewraps in screen-type exterior wall systems. Many roofing systems also incorporate membranes that are not fully adhered such as mechanically fastened single-ply membranes. Under a negative air pressure differential caused by wind suction, these wall and roof membranes can deform or balloon. Ballooning of the membrane affects many aspects of its performance. For instance, it changes the volume of the air chamber in screen-type wall systems and therefore, affects both the extent of screen pressure moderation and the nature of ventilation within the wall. In case of the single-ply roofing membrane, excessive ballooning can tear or rupture the membrane at the mechanical fastener location and therefore fail the membrane as the primary waterproofing component in the roofing system. This paper develops the structural mechanics for flexible membranes ballooning in three dimensions under a negative air pressure differential. The governing differential equation is derived and solved numerically. A second-order paraboloid of revolution is assumed to describe the ballooning shape. A series of physical tests were conducted to confirm that the ballooning shape follows the second-order paraboloid of revolution and compare the model predict with the test data.     

湍流边界层中低矮建筑绕流大涡模拟

通过对平板湍流边界层进行大涡模拟,采用拟周期边界条件维持湍流边界层厚度稳定,提取速度和压力时程作为低矮建筑绕流模拟之脉动入流边界条件,研究脉动入流下的低矮建筑绕流特性。研究结果表明：入流边界特性对网格变化适应性良好,其平均速度剖面、湍流强度、流速频谱特性基本符合空旷地貌风场特性;脉动入流下,建筑表面的平均风压系数、脉动风压系数的计算结果与风洞试验结果基本吻合。受雷诺数及湍流强度的影响,流动分离区负压与试验值存在一定差别;屋盖上分离区风压时程具有非高斯概率特性,尤以气流分离较剧烈的屋盖迎风边缘及屋盖两侧风压的非高斯特性明显,该特征与风洞试验基本一致;受非高斯特性的影响,建议峰值因子g取4.5~5.5。     

Reliability analysis of roof sheathing panels exposed to a hurricane wind

Light-frame wood roofs are frequently used in the US for residential and commercial construction. High wind events, such as hurricanes, may cause severe damage to these structures by breaking the roof envelope and allowing penetration of wind-driven rain. Most previous wood panel reliability studies have used static, uniform wind pressure load models and code-specified load distribution rules for analysis. This study re-estimates the reliability of roof sheathing panels exposed to a specific hurricane event using actual wind pressure data and a more refined structural analysis model. The objective is to examine the adequacy of the simplified wind load and structural analysis models used for roof panel reliability analysis. In the procedure here, panel failure behavior is modeled by individual fastener extraction from the panel as dynamic wind pressure is increased. For reliability analysis, the limit state is based on panel pull-off. The results show that the use of a refined model provides some significant differences in panel reliability found from simplified techniques.     

A venturi-shaped roof for wind-induced natural ventilation of buildings: Wind tunnel and CFD evaluation of different design configurations

Wind tunnel experiments and Computational Fluid Dynamics (CFD) are used to analyse the flow conditions in a venturi-shaped roof, with focus on the underpressure in the narrowest roof section (contraction). This underpressure can be used to partly or completely drive the natural ventilation of the building zones. The wind tunnel experiments are performed in an atmospheric boundary layer wind tunnel at scale 1:100. The 3D CFD simulations are performed with steady RANS and the RNG k-? model. The purpose of this study is twofold: (1) to evaluate the accuracy of steady RANS and the RNG k-? model for this application and (2) to assess the magnitude of the underpressures generated with different design configurations of the venturi-shaped roof. The CFD simulations of mean wind speed and surface pressures inside the roof are generally in good agreement (10–20%) with the wind tunnel measurements. The study shows that for the configuration without guiding vanes, large negative pressure coefficients are obtained, down to −1.35, with reference to the free-stream wind speed at roof height. The comparison of design configurations with and without guiding vanes shows an – at least at first sight – counter-intuitive result: adding guiding vanes strongly decreases the absolute value of the underpressure. The reason is that the presence of the guiding vanes increases the flow resistance inside the roof and causes more wind to flow over and around the roof, and less wind through it (wind-blocking). As a result, the optimum configuration is the one without guiding vanes.     

西卡渗耐PVC防水系统在虹桥机场西航站楼的应用

虹桥机场西航站楼屋面形式有混凝土和轻钢两种,设计分别选用了西卡渗耐的PVC卷材满粘系统和机械固定系统。本文从材料选择、系统理论依据、节点处理等方面分别介绍了这两种单层屋面系统技术,指出整个屋面防水系统使用效果良好。     

A method to assess peak storm wind speeds using detailed damage surveys

A detailed damage survey of a single, wood-framed, structure, which had a complete roof failure during the passage of a gust front in southern Ontario, was performed. Radar data was used to estimate upper level wind speeds associated with the gust front. Details pertaining to the structural failure, including the debris field, were obtained. Wind tunnel pressure time histories, in a simulated atmospheric boundary layer, were used to establish the roof height, gust wind speed at failure. This speed was smaller than the upper level speed found from the analysis of the radar. The flight of the roof was also examined, and confirmed the wind speeds obtained from the structural analysis of the failure. The study illustrates that detailed damage surveys, which incorporate the use of wind tunnel test data and debris flight in the analysis, can shed considerable light on the details of the wind speeds at failure, reducing the uncertainty caused by the many assumptions in such analyses.     

Interference effects on wind loading of a row of closely spaced tall buildings

Interference effects on a row of square-plan tall buildings arranged in close proximity are investigated with wind tunnel experiments. Wind forces and moments on each building in the row are measured with the base balance under different wind incidence angles and different separation distances between buildings. As a result of sheltering, inner buildings inside the row are found to experience much reduced wind load components acting along direction of the row (x) at most wind angles, as compared to the isolated building situation. However, these load components may exhibit phenomena of upwind-acting force and even negative drag force. Increase in x-direction wind loads is observed on the upwind edge building when wind blows at an oblique angle to the row. Other interference effects on y-direction wind loads and torsion are described. Pressure measurements on building walls and numerical computation of wind flow are carried out at some flow cases to explore the interference mechanisms. At wind angle around 30° to the row, wind is visualized to flow through the narrow building gaps at high speeds, resulting in highly negative pressure on associated building walls. This negative pressure and the single-wake behavior of flow over the row of buildings provide explanations for the observed interference effects. Interference on fluctuating wind loads is also investigated. Across-wind load fluctuations are much smaller than the isolated building case with the disappearance of vortex shedding peak in the load spectra. Buildings in a row thus do not exhibit resonant across-wind response at reduced velocities around 10 as an isolated square-plan tall building.     

Assessment of pollutant dispersion from rooftop stacks: ASHRAE,ADMS and wind tunnel simulation

The prediction of downwind concentration of effluents from stack located on top of buildings is important. Most current dispersion models assess the pollutant concentration at distances away from the building. It is important to study pollutant dispersion within the recirculation zone of the building, since studies have shown that effluents released from rooftop stacks have a tendency to re-enter the building through intakes located on the roof. These effects get more pronounced with the influence of RoofTop Structures (RTS). This paper presents a comparative study of the Atmospheric Dispersion Modelling System (ADMS), American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE 2003 and 2007 versions) and wind tunnel results. Four different cases involving a low-rise and high-rise building for stack heights (h_s) ranging from 1 m to 7 m, exhaust momentum ratios (M) ranging from 1 to 5 and wind direction (θ) of 0° and 45°, have been studied for neutral atmospheric stability conditions. In this regard the effect of RTS has also been examined by using wind tunnel, ADMS and ASHRAE models. ADMS yields higher dilutions near the stack at θ = 0° and cannot model the effect of RTS. Wind tunnel data compare well with ASHRAE 2003 at M = 5 for the low-rise building, but generally predict higher dilutions for the high-rise building. ASHRAE 2003 predicts lower dilutions than ADMS for the high-rise building, while ASHRAE 2007 yields very low dilutions for all cases, suggesting a need to reassess its suitability for practical design.     

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。     

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.     

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.     

单跨双坡工业厂房平均风压试验研究

通过一系列不同外形尺寸的单跨双坡厂房刚性模型风洞测压试验,研究不同风向角下结构表面的平均风压系数,重点讨论建筑结构外形参数和风场条件对单跨厂房主体承重结构风压系数的影响。研究发现,主体结构框架梁屋面平均风压系数受高跨比和风向角影响很大,而基本不受纵跨比和风场类型的影响。框架梁屋面的负风压随着高跨比的增大而增大,但中部和端部框架梁屋面的风压特性有很大差异;中部框架梁屋面的负风压随着风向角的增大不断增大,端部框架梁屋面的风压随着风向角的变化也很显著,但缺乏很好的规律性。主体承重结构框架柱墙面的平均风压分布较为均匀,风压系数可直接按美国金属建筑结构手册选取。根据试验数据采用阻尼最小二乘算法拟合框架梁屋面风压分布公式。经验证,公式计算出的风压系数能良好地反映分布规律,且具有较好的精度,可以为荷载规范的修订和补充提供参考。