Field Study Of Wind Characteristics During Tropical Cyclone And Their Effects On Roof Pressures Of Low-rise Buildings

Post-typhoon damage survey revealed that the buildings damaged or destroyed in typhoons are mostly low-rise buildings. Therefore, a comprehensive understanding of the wind-induced damage mechanisms of low-rise buildings is of great significance. Since the approaching wind plays an important role in the generations of wind loads, it is prerequisite to well understand the wind characteristics of typhoons. In this study, two important turbulence parameters, gust factor and power spectral density(PSD), were firstly investigated with the field measured wind data. Then, the influence of vertical wind angle on the roof pressures was investigated using the wind and pressure data recorded synchronously by a monitor system installed on a full-scale low-rise building.Based on the high resolution wind data recorded during 10 tropical cyclones, the characteristics of gust factor were investigated in detail. The nonlinear relationship between gust factors and roughness lengths was observed. In order to characterize the terrain effects on the gust factors, the upstream exposure is classified to four types, namely, Sea Terrain, Smooth Terrain, Open Terrain and Rough Open Terrain. For the same terrain, it is found that the mean values of gust factors change hardly with the increasing of the mean wind speed for the mean wind speed above 10 m/s. The mean values of 3s gust factors with respect to 10-minute averaged wind speeds are 1.26, 1.35, 1.52 and 1.65 for Sea Terrain, Smooth Terrain, Open Terrain and Roughly Open Terrain, respectively. Meanwhile, those of the 1-minute gust factors are 1.11, 1.15, 1.18 and 1.27, respectively. Over Sea Terrain, the probability distribution of 3s gust factors matches well with the Gaussian distribution, while the distribution skews slightly to left in Smooth Terrain, and that skews to right in both Open and Roughly Open Terrain. Furthermore, the relationships among gust factors, fluctuating wind directions and turbulence intensities were discussed and presented. The results indicate that gust factors are linearly dependent on fluctuating wind directions and increase with the increase of turbulence intensities.From field measurements accumulated in several landfalls of typhoons, we selected 96 samples with the time duration of 1 hour to analyze the wind spectrum. The non-linear trend terms in each sample were eliminated with Empirical Mode Decomposition(EMD) method, which can provide favorable results. In addition, through the comparison between the on-site PSDs and empirical model, Von Karman Spectral model shows the best correspondence in both low frequency range and inertial subrange and Davenport Spectral model matches the field measurements in inertial subrange, while underestimates the values in low frequency range. Meanwhile, Kaimal Spectral model agrees with the field data in low frequency range and overestimates the values in inertial subrange. In addition, the PSDs of u, v and w components at eyewall contain more energy than those in peripheral regions in inertial subrange, while it is opposite in the low frequency range. The spectra of velocity component at both eyewall and peripheral zone fit well with the Kolmogorov-5/3 law in inertial subrange.Based on the simultaneously recorded data of wind velocity and roof pressures on low-rise building during landfalls of tropical storms Mujigea and Soudelor, the effects of vertical wind angle on the roof pressures were investigated. A positively linear correlation was found between roof pressures and the incident vertical wind angle. For the approaching wind normal to the roof ridge, the pressures on windward region were affected by vertical wind angles most seriously. The effects of vertical wind angle were reduced with the increase of distance away from the windward roof weave. However, pressures on the leeward region close to the ridge were strengthened. In oblique wind,pressures on windward region of gable roof was also affected by vertical wind angle.Since the traditional wind tunnel cannot simulate the approaching wind in the vertical direction, this may be the major reason for discrepancies between wind tunnel testing results and field measurements.