Investigation Of The Influence Of Perforation On Extreme Wind Pressures And Wind-Induced Response Of Large-Span Circular Roofs

In recent years,with the continuous advancement of science and technology,the construction industry has been actively exploring and adopting new materials and techniques,leading to the widespread application of large-span structural roofing systems.These structures,characterized by their lightweight,low damping,and low natural frequencies,are highly sensitive to wind loads,which often result in severe damage to large-span roofs during wind events.Additionally,employing edge local perforation as an aerodynamic optimization strategy can effectively reduce the wind loads on the roof surface.This approach is a simple and costeffective means and holds significant importance for the development of green buildings.However,the current understanding of wind-resistant design for large-span roofs is not comprehensive.In China,the design codes and regulations do not provide specific form factors for large-span roofs and perforated roofs.Moreover,there is limited in-depth research on perforation optimization.In this regard,this study investigates the wind pressure distribution characteristics,perforation optimization measures,extreme wind pressures,and wind-induced responses of large-span circular roofs based on rigid model wind tunnel tests.The main contents and research findings are summarized as follows:(1)The average wind pressure and fluctuating wind pressure distribution for both nonperforated and perforated roofing systems were analyzed,and the variations of the average and fluctuating wind pressure coefficients at strip measurement points were studied in relation to the wind direction angle.The results indicate that the leading-edge region experiences significant negative pressures due to the combined effect of "uplift and downward push",and the distribution of fluctuating wind pressures generally follows the pattern of the average wind pressure distribution.After the roof is perforated,the vortex formed by the flow separation is disturbed,resulting in a noticeable reduction in wind pressure at the windward edge.The reduction in average wind pressure coefficient can reach around 20%,while the reduction in fluctuating wind pressure coefficient can reach approximately 25%.Wind directions at 0°,30°,and 60° are considered unfavorable for the roof,and detailed investigations will be conducted for these three wind directions.(2)A thorough investigation was conducted on the skewness and kurtosis of the roof to reveal the phenomena of flow separation and the mechanisms behind perforation optimization measures.The non-Gaussian regions of the roof were identified using the normal probability plot and the Kolmogorov-Smirnov(K-S)test,and the probability densities of the non-Gaussian measurement points were fitted using various probability models to select the optimal one.The results show that areas where vortices are formed due to flow separation exhibit high skewness and kurtosis,and perforation can mitigate the non-Gaussian characteristics in the perforated area.The boundaries of the distribution of non-Gaussian measurement points on the roof are not distinct,especially for perforated roofs where the measurement points are spaced apart.The three-parameter Gamma distribution and Lognormal distribution yield better fits to the probability densities of the non-Gaussian measurement points compared to other probability models.(3)Four methods,including the peak factor method,improved Hermite moment method,improved Gumbel method,and Sadek-Simiu method,were employed to estimate the extreme values of the roof.The study found that the Sadek-Simiu method provides high accuracy in estimating extreme wind pressures,with errors kept within 10%.The peak factors calculated using the Sadek-Simiu method for both non-perforated and perforated measurement points exceed the code-specified value of 2.5,suggesting the use of the Sadek-Simiu method or an appropriate increase in the peak factor.Perforation has the most significant effect on reducing the extreme values at measurement points with higher magnitudes,with a reduction of approximately 35%.(4)The Proper Orthogonal Decomposition(POD)technique was applied to decompose and reconstruct the roof,and modal analysis and time-history response analysis were conducted based on a finite element model.The results indicate that using the first 40 eigenmodes is sufficient to achieve the required reconstruction accuracy of the wind field.The early modes of the structure exhibit vertical vibrations,primarily concentrated at the vulnerable cantilever edges.In the time-history response analysis,the root mean square values of displacements are larger at the inner edge of the western roof,and the perforation can reduce the displacement values by up to 28.6%.The adoption of a partitioned wind response coefficient avoids the influence of singularities,and specific recommendations for wind-resistant design of large-span circular roofs are derived.