屋根面上の雨水の流下性状に関する基礎的研究

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Knowledge about behavior of rainwater on roof surfaces is essential for the proper design of pitched roofs, enpecially to insure their waterproofing and drainage performance. However, little is known so far about rainwater flow patterns and their characteristic values on roof surfaces. In this study, continuous rainwater flow over flat and smooth roof surface under steady rainfall condition was examined in order to collect fundamental data for waterproofing and drainage design of pitched roofs. Coated galvanized steel sheet specimen (size : 5.02m by 0.48m) of two different coating materials, i.e., polyvinylidene fluoride and modified polyester were used as roof surface. Specimens of both of the steel sheet were tested either as manufactured or after being exposed to outdoor climate for four months. Specimens were fitted onto the deck of a model roof which pitch could be changed from 3/10 to horizontal. An artificial rain apparatus which utilized full cone pattern spray nozzles was fitted over the roof model, and gave artificial rain of intensity of 0.4 to 4.0 mm per minute, evenly over the specimen surface. It was found that flow patterns of rainwater are not always the same on such a flat and smooth surface. Three different flow patterns were observed throughout the tests. They were (1) scattered flow, in which accumulated raindrops fall down the roof surface separately, (2) concentrated flow, in which rainwater flows continuously in the shape of narrow and heaped stream, and (3) spread flow, in which the roof surface get wet evenly by lighty rippling thin film of rainwater. Scattered and concentrated flow were peculiar to the newly used specimens, and also seen only under lighter rain conditions, while spread flow were observed for all the test conditions on the surface of exposed specimens and also under heavier rain conditions on newly used specimens surfaces. The depth of flows was measured by using ultrasonic displacement gauge. It was found that with spread flows, measured mean flow depth almost agreed with calculated values for steady and uniform laminar flows over a flat surface. As for scattered and concentrated flows, the flow depths were several times larger than the calculated values. Flow speed of water drops in scattered flow or the front edges of the stream in concentrated flow were also measured by using two sets of laser detectors and a speedometer, The flow speed varied considerably within the same test condition, but it was found that the maximum flow speed ranged from 4 to 20 times higher than the mean flow speed of spread flow in the same flow rate and the same roof pitch. It was also found that there is a certain combination of flow rate and roof pitch conditions in which flow speed of rainwater become the fastest.
東海大学の論文

屋根面上の雨水の流下性状に関する基礎的研究

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