屋上設置壁のある大規模建築物の屋根面に作用する風圧力の性状

Abstract

1. Introduction Recently, many large-scale factories and distribution warehouses have been constructed. In the case of these large-scale buildings, walls are often attached on the outer periphery of roofs in order to screen the drainage gradient and accommodate machinery. Previous studies have been conducted on the effect of parapets on the wind pressure. But there are a variety of factors and whose influence has not previously been well elucidated. A number of studies have investigated mitigating peak wind pressure through the use of porous parapet. 2. Models and Outline of Wind Tunnel Test and Numerical analysis Wind tunnel tests and numerical analyses are conducted by using 1/222 scale rigid models. Wind tunnel tests were intended to analyze the influence of several parameters and effect of parapets. Numerical analysis was used to make the flow around the building visible. 3. The Worst Peak Suctions effect on the Roof The definition of the worst peak suction is the ensemble average of the worst pressure from each one of 8 data records of 10 minutes duration, where wind pressure is applied as a Simple Moving Average (averaging time is 0.12 seconds based on 1m2 roofing). 4. Streamlines around the Models and Eigenmode of Wind Pressure Streamlines around the models were made visible by using numerical analysis and eigenmodes of wind pressure are derived by using Proper Orthogonal Decomposition. Then, the characteristics of the flow and 1st eigenmode of buildings with parapets were discussed. 5. The effect of each factor on the characteristic of wind pressure The effects of several parameters on the worst peak suctions affect on roofs were analyzed based on wind tunnel tests. The worst peak suctions are only slightly influenced by planar shape and roof geometry, so that those factors are negligible. But the proportional relationship between the magnitude of the worst peak suctions and the turbulence intensity of the approach flow was confirmed. 6. Reduction of Worst Peak Suction by Using Porous Parapets Porous parapets can mitigate worst peak suction on outer periphery of roof. Analyzing the worst peak suctions on corner and edge regions, it was determined that maximum reduction occurred when the openings comprised 25% of parapet's area. 7. Conclusions 1) By attaching parapets to the to the flat roofs, the magnitude of the worst peak suction affecting on the corner or edge region is decreased. But, in the central region, the magnitude is increased. 2) In the case of low-rise buildings (lower than about 20 m) without parapets, the worst peak suction is induced in wind direction θ = 0° or 90°. But as parapets become higher, the worst peak suctions are induced in wind direction θ = 45°. In the case of middle-rise buildings, the worst peak suction is induced in wind direction θ = 45° regardless of height of parapets 3) The worst peak suctions affect the roofs of square buildings and rectangular buildings with an aspect ratio is 1:2 to the same degree regardless of the height of parapets. 4) The worst peak suctions affect sloped roofs (5 % gradient) and flat roofs to the same degree if the heights of parapets are same. (The height of parapets attached to the sloped roof is defined as the maximum height of parapets.) 5) The magnitude of worst peak suction effects on the corner and edge region of roof is reduced more than 30% by using porous parapets. In this test, the magnitude of worst peak suction is lowest when the quantity of opening in parapet is 25% of parapet's area.