【作者】 王俊；

【导师】 李加武； 王峰；

【作者基本信息】 长安大学 ， 桥梁与隧道工程， 2022， 博士

【摘要】 从21世纪初开始,山区峡谷大跨径桥梁的建设与日俱增。同时,峡谷中强烈的紊流是诱发桥梁抖振的充分条件。目前,国内外学者针对峡谷风场特征及其对桥梁抖振影响的研究,取得了丰硕的成果。但峡谷地区风参数分布规律尚不明确,抗风规范中风参数难以适用于山区峡谷桥梁抗风设计。据此,本文开展的主要工作有:(1)对U形峡谷开展实测研究。研究发现:峡谷内风速剖面严重偏离规范的幂指数律或对数律,平均风速沿主梁展向呈均匀分布和抛物线分布,实测风攻角远超规范推荐的取值范围,阵风因子和紊流强度呈线性关系,脉动风卓越频率随高度增加而增加,实测功率谱与规范谱模型差距显著。研究定义了描述风向随高度变化的风向偏转率的概念,提出了更接近实测谱的3参数功率谱模型,明确了其3个参数的概率分布及与高度的关系,验证了Hui模型的相干函数的适用性,提出了桥址处风观测塔合理高度的建议。(2)对U形峡谷进行模型数值模拟和风洞试验,研究了来流特征及峡谷特征对风参数的影响。结果表明:来流风速增加,风参数空间分布趋于稳定;当来流风向与峡谷走向存在夹角时,相同位置处风速减小,风攻角和紊流强度增加,来流风向对风攻角和风偏角的影响最明显;峡谷内粗糙度分布模式对风速影响不明显;宽深比减小,风速加速效应、风攻角和紊流强度均减小。研究给出了模拟峡谷内粗糙度的方法,探明了峡谷宽深比与功率谱模型系数的关系,建立了来流特征对风参数影响程度的评价模型。(3)基于Navier-Stokes方程,分析了Couette流动和Poiseuille流动的特征,发现可从压力梯度、壁面摩擦和峡谷特征尺寸等角度阐释峡谷中的风速分布机理;推导并验证了U形峡谷中风速的空间抛物面模型;给出了风速展向分布的折线函数。(4)以来流风速分布模式、来流风速大小及桥梁位置为切入点,分析了U形峡谷中大跨径桥梁的抖振响应。研究发现:采用均匀分布来流,将高估抖振响应;抖振位移响应与来流风速呈非线性关系;不同位置处,斜拉桥抖振位移小于规范推荐值;相对高度增加,减小了悬索桥的抖振响应。研究给出了在开展峡谷中桥梁抖振响应研究时选取合理风参数的建议。更多还原

【Abstract】 The designs and constructions of long span bridges for crossing valleys and rivers in the mountainous areas are increasing dramatically since the 21 st century in China.At the same time,the strong turbulent flow in the valley area is a sufficient condition for bridge buffeting.At present,scholars have focused on the on-site wind field characteristics of several mountainous areas,as well as the influence on bridge buffeting responses.However,the distribution law of wind characteristics in the valley area is still unclear,and the wind parameters of the Specification are difficult to be applied to the wind resistance design of mountainous valley bridges.Therefore,the main work carried out in the present study is as follows:(1)The field measurement was carried out in a U-shapped valley.It is found that the wind speed profile deviates seriously from the power exponent and logarithm law in the Specification.The average wind speed along the deck exhibits uniform and parabolic distributions.The measured wind attack angle is out of the range recommended by the current design Specification.The gust factor and turbulence intensity show a linear correlation.The preeminent frequency of fluctuating wind increases with the increase of height.The difference between the measured power spectrum and the power spectrum models in the Specification is significant.A concept,deflection rate of wind direction,is defined to describe the variation of wind direction with the elevation.A three-parameter power spectrum model which is closer to the measured spectrum is proposed,and the probability distributions of the three parameters and their relationship with elevation are also clarified.The applicability of the coherence function defined by Hui is verified.The reasonable elevation of the meteorological mast instrument at the bridge site is suggested.(2)Numerical simulation and wind tunnel test were carried out to study the influence of oncoming flow characteristics and valley characteristics on wind parameters.The results show that the spatial distribution of wind characteristics tends to be stable with the increase of oncoming wind speed.When there is an angle between the oncoming wind direction and the valley strike,at the same position,the wind speed decreases,the wind attack angle and turbulence intensity increase.The oncoming wind direction has the most obvious effect on the wind attack angle and wind deflection angle.The surface roughness distribution pattern in the valley has no obvious effect on the wind speed.When the ratio of width to depth decreases,wind speed acceleration effect,wind attack angle and turbulence intensity all decrease.A method to simulate the roughness in the valley is given,the relationship between the ratio of width to deep and the power spectrum model coefficient is proved,and the evaluation model of the influence degree of the oncoming flow characteristics on the wind parameters is established.(3)Based on Navier-Stokes equations,the characteristics of Couette flow and Poiseuille flow are analyzed,the distribution mechanism of wind speed in the U-shaped valley from the perspectives of pressure gradient,wall friction and U-shaped valley characteristic size can be explained.The spatial wind speed distribution in the U-shaped valley is deduced and verified,the simplified envelope function of spanwise distribution of wind speed is put forward.(4)The buffeting response of a long-span bridge in a U-shaped valley is analyzed based on the speed distribution model of oncoming flow,the oncoming wind speed and the location of the bridge.The results show that the buffeting response will be overestimated when the flow is uniformly distributed.The buffeting displacement response has a nonlinear relationship with the oncoming wind speed.At different positions,the buffeting displacement of the cable-stayed bridge is smaller than the recommended value.The buffeting response of the suspension bridge is reduced with the increase of relative height.Some suggestions are given for selecting reasonable wind characteristics when studying buffeting response of bridges in valleys.更多还原