Chapter 4 Wind Load 4.1 Background information of wind 4.2 Wind pressure 4.3 Height variation factor of wind pressure 4.4 Shape factor of wind load 4.5 Along-wind effect on structure 4.6 Cross-wind effect on structure 4.7 Wind load for bridge 归东理王大军 SHANDONG UNIVERSITY OF TECHNOLOGY
Chapter 4 Wind Load 4.1 Background information of wind 4.2 Wind pressure 4.3 Height variation factor of wind pressure 4.4 Shape factor of wind load 4.5 Along-wind effect on structure 4.6 Cross-wind effect on structure 4.7 Wind load for bridge
4.1 Background information of wind风的有关知识 Cause of wind风的形成 Wind is caused by differences in the atmospheric pressure.When a difference in atmospheric pressure exists,air moves from the higher to the lower pressure area,resulting in winds of various speeds.On a rotating planet,air will also be deflected by the Coriolis effect(柯氏效应)，except exactly on the equator.Globally,the two major driving factors of large-scale wind patterns (the atmospheric circulation)are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces)and the rotation of the planet. 北极 图3.1大气热力学环流模型 赤道 的东理王大军 SHANDONG UNIVERSITY OF TECHNOLOGY
4.1 Background information of wind 风的有关知识 • Cause of wind 风的形成 ▫ Wind is caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds. On a rotating planet, air will also be deflected by the Coriolis effect(柯氏效应), except exactly on the equator. Globally, the two major driving factors of large-scale wind patterns (the atmospheric circulation) are the differential heating between the equator and the poles (difference in absorption of solar energy leading to buoyancy forces) and the rotation of the planet. 图3.1 大气热力学环流模型
4.1 Background information of wind风的有关知识 ·Three major types of wind三类性质的大风 Typhoon台风 A typhoon is a mature tropical cyclone that develops between 180 and 100E in the Northern Hemisphere.This region is referred to as the Northwestern Pacific Basin,and is the most active tropical cyclone basin on Earth,accounting for almost one-third of the world's annual tropical cyclones. In the Atlantic,Caribbean and eastern North Pacific,Hurricanes is used while in the Western Pacific and the South China Sea,typhoon is called. 归东理王大军 SHANDONG UNIVERSITY OF TECHNOLOGY
4.1 Background information of wind 风的有关知识 • Three major types of wind 三类性质的大风 ▫ Typhoon 台风 A typhoon is a mature tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere. This region is referred to as the Northwestern Pacific Basin, and is the most active tropical cyclone basin on Earth, accounting for almost one-third of the world's annual tropical cyclones. In the Atlantic, Caribbean and eastern North Pacific, Hurricanes is used while in the Western Pacific and the South China Sea, typhoon is called
4.1 Background information of wind风的有关知识 ·Three major types of wind两类性质的大风 ·Monsoon季风 Seasonal wind between land and sea. Fundamental reason:thermal characteristics of earth surface Thunderstorm雷暴 ·Thermal Convective thunderstorm热对流雷暴 ·topographical thunderstorm地形性雷暴 ·frontal thunderstorm锋面雷暴 的东理王大军 SHANDONG UNIVERSITY OF TECHNOLOGY
4.1 Background information of wind 风的有关知识 • Three major types of wind 两类性质的大风 ▫ Monsoon 季风 Seasonal wind between land and sea. Fundamental reason: thermal characteristics of earth surface ▫ Thunderstorm 雷暴 Thermal Convective thunderstorm 热对流雷暴 topographical thunderstorm 地形性雷暴 frontal thunderstorm 锋面雷暴
4.1 Background information of wind风的有关知识 General conditions of wind climate in China我国风气候总况 1. 台湾、海南和南海诸岛由于地处海洋，常年受台风的直接影响，是我国最大的风 2. 东南沿海地区由于受台风影响，是我国太陆的大风区。，风速梯度由沿海指向内陆。 台风登陆后，受地面摩擦的影响，风速削弱很快。统计表明，在离海岸100k处， 风速药减小一半。 3. 东北、华北和西北地区是我国的次大风区，风速梯度由北向南，与寒潮入侵路线 致。 北地区夏季受季风影响，风速有可能超过寒潮风速。黑龙江西北部处于 我国纬度最北地区，它不在蒙古高压的正前方，因此那里的风速不大。 4. 青藏高原地势高，平均海拔在4~5km,属较大风区。 5. 长江中下游、黄河中下游是小风区，一般台风到此已大为减弱，寒潮风到此也是 强骜之末。 6. 云贵高愿处于东亚大气环流的死角，空气经常处于静止状态，加之地形闭塞，形 成了我国的最小风区。 归东罪子大军 SHANDONG UNIVERSITY OF TECHNOLOGY
4.1 Background information of wind 风的有关知识 • General conditions of wind climate in China 我国风气候总况 1. 台湾、海南和南海诸岛由于地处海洋，常年受台风的直接影响，是我国最大的风 区。 2. 东南沿海地区由于受台风影响，是我国大陆的大风区。风速梯度由沿海指向内陆。 台风登陆后，受地面摩擦的影响，风速削弱很快。统计表明，在离海岸100km处， 风速约减小一半。 3. 东北、华北和西北地区是我国的次大风区，风速梯度由北向南，与寒潮入侵路线 一致。华北地区夏季受季风影响，风速有可能超过寒潮风速。黑龙江西北部处于 我国纬度最北地区，它不在蒙古高压的正前方，因此那里的风速不大。 4. 青藏高原地势高，平均海拔在4～5 km，属较大风区。 5. 长江中下游、黄河中下游是小风区，一般台风到此已大为减弱，寒潮风到此也是 强弩之末。 6. 云贵高原处于东亚大气环流的死角，空气经常处于静止状态，加之地形闭塞，形 成了我国的最小风区
大气运动与地球运动、维度、地形地貌等因素密切相关 ,所以风气候往往也与所在地区的地理位置、地形条件等因 素有关。 风力 大 台湾、海南、南海诸岛（最大风区） 东南沿海地区（大风区） 东北、华北、西北地区（次大风区） 青藏高原（较大风区） 长江、黄河中下游地区（小风区） 云贵高原（最小风区） 小
（最大风区） （大风区） （次大风区） （较大风区） （小风区） （最小风区） 大气运动与地球运动、维度、地形地貌等因素密切相关 ，所以风气候往往也与所在地区的地理位置、地形条件等因 素有关
风速 风级 名称 平地满地0米就战国 陆地地面物探 无风 0.0-0.2 鞋，烟直上 软风 03-15 烟示风向 4.1 Background information of wind 轻网 16.33 感觉有风 微风 3.4-5.4 应族服开 和风 5,5-7.9 欢起尘士 ·Wind force scale风力等级 砂风网 8.0-107 小树提摆 10.8-13.8 Historically,the Beaufort wind 强风 电线有声 疾风 13.9-17.1 步行困难 force scale(created by Beaufort) 大风 17.2-20.7 析毁树技 蒲福风力等级provides an 烈风 20.8.24.4 小损房屋 empirical description of wind 狂风 24.5-28.4 拔起树太 28.5-32.6 speed based on observed sea 分 风 损毁质大 恩风 32.7-36.9 推股极大 conditions.Originally it was a 13- 37.041.4 level (0-12)scale,since 2001 14 415-46.1 《台风业务和服务规定》，t 15 462-50.9 51.056.0 was expanded to 18-level (0-17). 256.1 策划制作：王若嘉 中国气象网
4.1 Background information of wind 风的有关知识 • Wind force scale 风力等级 ▫ Historically, the Beaufort wind force scale (created by Beaufort) 蒲福风力等级 provides an empirical description of wind speed based on observed sea conditions. Originally it was a 13- level （0-12）scale，since 2001 《台风业务和服务规定》，it was expanded to 18-level (0-17)
4.2 Wind pressure Reference wind pressure(velocity)基本风压（风速） Definition ·The wind pressure determined by the wind speed measured at prescript terrain地s貌， heighti高度，time framel时距，Sampling period样本时间，Return period重现期. Factors ·Reference height标准高度：I0mfor《建筑结构荷载规范》 ·Reference terrain标准地貌：clear and level,far away from city ·Nominal time frame公称时距：10 mins for《建筑结构荷载规范》 ·Sampling period样本时间：yearly maximum wind speed ·Return period重现期：50 yrs for normal buildings;.more for high-rise building and wind-sensitive buildings 归东理子大军 SHANDONG UNIVERSITY OF TECHNOLOGY
4.2 Wind pressure • Reference wind pressure (velocity) 基本风压(风速) ▫ Definition The wind pressure determined by the wind speed measured at prescript terrain地貌, height高度，time frame时距， Sampling period样本时间，Return period重现期. ▫ Factors Reference height标准高度: 10m for 《建筑结构荷载规范》 Reference terrain标准地貌: clear and level, far away from city Nominal time frame公称时距: 10 mins for 《建筑结构荷载规范》 Sampling period样本时间: yearly maximum wind speed Return period重现期: 50 yrs for normal buildings; more for high-rise building and wind-sensitive buildings
4.2 Wind pressure Relationship between wind speed and wind pressure风速和风压关系 Wind load is one of the main lateral loads in engineering structure.Not only horizontal wind pressure水平风压but also types of vibrations多种风 振are caused by wind load.Therefore,both statici静态and dynamicz动态 actions are imposed on structures due to wind. The relationship between wind speed and pressure could be obtained by Bernoulli equation =i0听=6 1 2g @o-Wind pressure on unit area P-Air density y-Bulk unit weight of air 归东理王大军 vo-Average wind speed SHANDONG UNIVERSITY OF TECHNOLOGY
4.2 Wind pressure • Relationship between wind speed and wind pressure风速和风压关系 ▫ Wind load is one of the main lateral loads in engineering structure. Not only horizontal wind pressure 水平风压 but also types of vibrations 多种风 振 are caused by wind load. Therefore, both static静态 and dynamic动态 actions are imposed on structures due to wind. ▫ The relationship between wind speed and pressure could be obtained by Bernoulli equation 𝜔𝜔0 = 1 2 𝜌𝜌𝑣𝑣0 2 = 𝛾𝛾 2𝑔𝑔 𝑣𝑣0 2 𝜔𝜔0-Wind pressure on unit area 𝜌𝜌 -Air density 𝛾𝛾 -Bulk unit weight of air 𝑣𝑣0-Average wind speed
4.2 Wind pressure风压 ·Relationship between wind speed and wind pressure.风速和风压关系 At standard atmosphere condition:y=0.012018k N/m3,g=9.80 m/s2 Therefore, (kN/m) 01630 However,the atmosphere condition varies with place.In order to compare the wind pressures of different places,the difference in terrain and measurement height:测量高度should be considered. 归东理子大军 SHANDONG UNIVERSITY OF TECHNOLOGY
4.2 Wind pressure 风压 • Relationship between wind speed and wind pressure风速和风压关系 ▫ At standard atmosphere condition: Therefore, However, the atmosphere condition varies with place. In order to compare the wind pressures of different places, the difference in terrain地形 and measurement height测量高度 should be considered. 𝛾𝛾 = 0.012018𝑘𝑘 𝑁𝑁⁄𝑚𝑚3 , 𝑔𝑔 = 9.80 𝑚𝑚⁄𝑠𝑠2 𝜔𝜔0 = 𝑣𝑣0 2 1630 𝑘𝑘 𝑁𝑁⁄𝑚𝑚2