大跨度平屋盖表面风荷载体型系数研究

Study of shape factors for large-span flat roofs

通过平屋盖刚性模型风洞测压试验,基于分离泡作用机理,以顺风向及横风向风压为研究对象,对屋盖表面的风压特征进行分析,进而提出合理的分区体型系数。①基于顺风向平均、脉动风压变化曲线和脉动风压谱,发现分离泡作用下的平屋盖表面可以分为主涡作用区、次级涡作用区以及旋涡脱落区;②提出风压相关长度的概念,计算横风向互相关长度,结果表明在旋涡作用范围内,各相关长度相差无几,超出旋涡区后风压相关长度出现衰减;③基于面积平均压力的概念计算刚性平屋盖表面的分区体型系数。通过面积平均压力的累积概率曲线对准定常理论和我国《建筑结构荷载规范》(GB 50009—2001)中的规定系数-0.6进行验证,发现在分离泡作用下准定常理论是适用的,我国规范在迎风前缘附近的强吸力区和屋盖中后部分别低估和高估了实际体型系数;将本文的体型系数取值与美国规范(ASCE7-98)、加拿大规范(NBC-1995)以及日本规范(AIJ-2004)进行对比,发现本文的体型系数计算结果与美国规范较为接近。

Based on the mechanism of separation bubble, the characteristics of wind pressure distribution on flat roofs are investigated through wind tunnel test, taking along-stream and along-span pressures as the subjects of study. The shape factors for the subregions of a flat-roof are proposed. The roof surface is divided into main vortex area, secondary vortex area and vortex shedding area according to the along-stream wind pressures and their spectra. The suggested correlation length is calculated for pressures of along-span rows. It is revealed that the correlation lengths are roughly equivalent in the main vortex area, and decreases beyond the main vortex area. The sectional shape factors are obtained based on area- averaged pressures. Using the cumulative probability of the area-averaged pressure, the quasi-steady theory and the specified shape factor of - 0.6 for flat roofs in the Loading Code for Design of Building Structure is verified. The results indicate that the quasi-steady theory is applicable on flat roofs under the influence of the separation bubble and that the specified shape factor of - 0.6 underestimates the actual shape factor for the severe suction region and overestimates for the middle and rear part of the roof, respectively. The proposed shape factor is compared with that from the ASCE7-98, NBC-1995 and AIJ-2004. It is demonstrated that the suggested shape factor is close to the rule of ASCE7-98.