A STUDY ON THE TYPES OF SNOWDRIFTS IN DOMED STADIUM USING SNOW WIND TUNNEL

Transcription

1 The Eighth Asia-Pacific Conference on Wind Engineering, December 10 14, 2013, Chennai, India A STUDY ON THE TYPES OF SNOWDRIFTS IN DOMED STADIUM USING SNOW WIND TUNNEL Byung-Hee NAM 1, Jang-Youl YOU 2, Ki-Pyo YOU 3 and Young-Moon KIM 4 1 Master`s Course, Architectural Engineering, Chonbuk National University, Jeonju, Korea, lucknbh@naver.com 2 Senior Researcher, KOCED Wind Tunnel Center, Chonbuk National University, Jeonju, , Korea, wmjlove1877@jbnu.ac.kr 3 Associate Professor, Architectural Engineering, Chonbuk National University, Long-span Steel Frame System Research Center, Jeonju, , Korea, youkp@jbnu.ac.kr 4 Professor, Architectural Engineering, Chonbuk National University, Jeonju, , Korea, kym@jbnu.ac.kr ABSTRACT The necessity of a dome stadium is increasing with the continued increase in sport interests. In tune with such trend, southwestern region baseball stadium, the first domed stadium in the nation, is being constructed. The roof is composed of membrane structure, which is significantly affected by snow loads. The Metrodome of Minnesota, which had a roof designed as a membrane structure had its roof collapse due to heavy snowdrift in For this reason, snow load is increasingly important. Nevertheless, studies on snowdrift experiment, which is considered important in estimating snow load, are insufficient in reality. This paper focused on snowdrift experiment that was performed on southwestern region baseball stadium that happens to be the first domed stadium in the nation. Snow wind tunnel, the use of the measured result, the maximum depth of fresh snowdrift, and the maximum depth of snowdrift were predicted in the experiment. As result, it is anticipated that snow will heap up on the roof of the stadium in 2.9cm to 32.2cm range if maximum depth of fresh snowdrift is applied and in 3.4cm to 37cm range. Keywords: Snow drift, Wind-Tunnel, Snowdrift, Dome-Stadium Introduction In modern times, the improvement of living standard and shortening of work hours have contributed to an increase in leisure time. Conversely, sports is growing rapidly as an industry with high economic impacts that includes the creation of employment and valueadded and improvement of national image along with the harmonizing of nationals beyond the degree of simply enjoying exercise. In particular, baseball has risen dramatically in popularity as the national representative team accomplishes outstanding score in Beijing Olympic and WBC tournament. In 2012, professional baseball drew high popularity by attracting an audience of 7 million in total. However, as baseball is a sports event, which is significantly affected by weather, the game cannot be conducted if it rains or snows. Based on these characteristics, this sporting event came to require domed stadium where they can enjoy the game without being affected by weather. Currently, southwestern region baseball stadium, the first domed stadium in the nation, is being constructed. Collapse of the building is anticipated due to the building lateral pressure or unbalanced distribution weights. This can be attributed to the snow-accumulating phenomenon that occurs intensively on the side the building or on the roof. Therefore, it is more desirable to identify snow accumulation occurrences in advance in the planning stage. The roof of the southwestern region domed stadium is composed as Proc. of the 8th Asia-Pacific Conference on Wind Engineering Nagesh R. Iyer, Prem Krishna, S. Selvi Rajan and P. Harikrishna (eds) Copyright c 2013 APCWE-VIII. All rights reserved. Published by Research Publishing, Singapore. ISBN: doi: /

2 framework membrane structure of an atypical shape, where membrane structure is significantly affected by snow load. As a method to identify snow accumulation occurrences, an outdoor experiment that uses the accumulation model or blizzard wind tunnel experiment and numerical value simulation is applied. Estimation of snowdrift requires simulation of snowdrift amount. For this reason, this paper focused on the execution of a snowdrift experiment of the southwestern region baseball stadium. With the use of the maximum depth of fresh snowdrift and the maximum depth of snowdrift, baseball stadium roof and low story part snowdrift amount were examined. [Kim J. S (2011)] Experiment condition and wind tunnel experiment Experiment condition In this paper, experiment was conducted on the baseball stadium, a domed stadium being constructed in Gocheok dong, Guro-gu, Seoul presently. Because it had a different shape from Gwangmyeong bicycle race dome arena, which is the first dome and standard shape arena, snowdrift experiments were conducted to forecast the snowdrifts on the roof and lower floors. For estimation of snowdrift amount on the roof and low story parts, snowdrift experiment was conducted, and the conditions where the snow turns into ice, the cases where the snow repeats melting, and heaping up were not considered. Main wind angle was defined as percentages by converting the occurrence frequencies of 16 wind directions, which were measured in the winter from 1986 to 2007 at Seoul Weather Station. Fig 1 represents the occurrence frequencies of winter wind directions in Seoul city in each season. From 1986 to 1995, main wind angles are west (W) and west/north/west (WNW), but from 1996 to 2007, west winds much decreased and west/north/west winds much occurred. Therefore, west/north/west wind, which has the highest occurrence frequencies, was determined as a main wind angle WNW W WSW NW SW NNW SSW N NNE SSE NE SE ENE E ESE S S (a) (b) Fig. 1. Occurrence frequencies of winter wind directions in Seoul city WNW W WSW NW SW NNW SSW N NNE SSE NE SE ENE E ESE In addition, when the recycled period of 100 years was predicted with Gumbel random model applied to 20 years snowdrift data of Seoul city, the maximum depth of fresh snowdrift was estimated as 29.3cm and the maximum depth of snowdrift as 33.6cm. Here, fresh snow cover means the depth of the snowdrift, which was accumulated for a specified period and it is often referred as the depth of the snow, which is accumulated for a day. Snowdrift means the depth of the snow, which is physically accumulated on the ground during the measurement, regardless of the accumulating periods, and it could be the depth of the snow, 282

3 which was accumulated today, yesterday or those accumulated since couple of days ago. Based on this, highest fresh snow cover for a day means the deepest snowdrift for a day (from 0 to 24 o clock), after one day, snow is removed, and newly accumulated snow is measured again. Amount of highest fresh snow cover for a day means the amount of snowdrift when the snowdrift has the highest accumulation and when the snow continues to be accumulated without changing snow conditions, snowdrift continues to increase, but if the snow melts or is blown off by the wind, amount of snowdrift could decrease. Years Maximum depth of fresh snowdrift (cm) Table years snowdrift data of Seoul city (unit: cm) Maximum Depth of snowdrift Years Maximum depth of fresh snowdrift Maximum depth of snowdrift Surface roughness test subject for the upwind side of the building based on the area of 45 degrees to 40 times the height H of less than 3km and within the scope of analysis of the surface state of the middle class buildings scattered over a surface roughness B (=0.22), the wind speed a 1.2m/s decided. Actual size of the building is 243m(W) 239m(L) 60m(H) big but it was reduced as 1/400 scale for the experiment, and the experiment was conducted. Wind tunnel experiment The experiment in this paper was performed with the use of a small wind tunnel device owned in the wind tunnel laboratory of Chonbuk National University. This small wind tunnel experiment device, a closed type, maintains constant velocity by using D/C motor, and has the specification shown in Table 2. As for devices used in the experiment, dust generator, nozzle, and compressor, etc. were used. Dust generator plays the role to supply sodium bicarbonate at constant speed during snowdrift experiment, and compressor serves to spray the sodium bicarbonate supplied at 2cc per second during the snowdrift experiment to the nozzle installed at the wind tunnel by supplying pressure to it. Figure 2 shows the appearance of the small wind tunnel and Figure 3-4 the appearance before and after the snowdrift experiment. In order to identify the accumulation types, which are accumulated near the building, selection of the snow should be considered first. Actually, even though various researches are much being conducted in existing overseas papers in order to simulate various snow, identical snowdrift types are not acquired according to actual wind tunnel sizes and conditions. Through the reference papers, simulated snow was selected based on Sapporo snow and Nagaoka snow. However, because the characteristics of the snow vary according to the topology and climate environments, it cannot be considered exactly same with the snow in Korea, which will require the further studies about the characteristics of Korean snow in the future. Mellor is suggesting the average snow particle size to be 150m in his theoretical 283

4 Proc. of the 8th Asia-Pacific Conference on Wind Engineering (APCWE-VIII) interpretation and insisted that the proximal size factor is useful for snow wind tunnel experiment. In this paper, sodium bicarbonate, which has 70m of average particle size, was used as a material of snow. [You K.P (2012)] Table 2: Specifications of small wind tunnel Type Closed Type Measuring Part B(90Cm) H(60Cm) L(13.5m) Fig 2. The appearance of wind tunnel Wind-tunnel Length 18.3m Velocity m/sec Turbulence intensity Below 0.5% Velocity deviation Below ±1% Fig 3. Before Snowdrift Experiment Fig 4. After Snowdrift Experiment Measuring the experiment date To measure the depth of snow heaped on the roof of the domed stadium, 3D-scanner was used. The scanning method is a 3 dimensional shape measuring method using slit beam. Specifically slit beam deformed by shape was obtained by projecting slit beam to measured object, and after deformed slit beam is obtained with CCD camera, 3 dimensional coordinate of the shape is calculated from the geometric correlation. Figure 5 shows the appearance of measuring using 3D-scanner, and Figure 6 the 3 dimensional shape displacement. Fig 5. Measuring Using 3D-scanner Fig 6. The 3 Dimensional shape displacement 284

5 Experiment result and analysis If sodium bicarbonates are supplied at 2cc/sec time based on the characteristics of this wind tunnel, the snowdrift depth on the experiment model ground plate. For this reason, the correlation of velocity and rooftop snowdrift depth cannot be compared as snowdrift depth, and thus the correlation was compared and reviewed by obtaining expression (1) [Accumulation coefficient(r)]. [You K.P (2011)] The measuring point on the ground plywood was set in the same method as model. Accumulation coefficient is a value, which is acquired by measuring the depth of the accumulated snow on the plate where the model is put and subsequently by dividing with the depth of accumulated snow, which was accumulated at the same time and it, is acquired by the wind tunnel experiment. With this accumulation coefficient and using the highest fresh snow cover for a day, which are actual data values, measured in Weather Station, the amount of snowdrift, which is to be accumulated on the dome arena, was forecasted. Accumulation coefficient (R) = The snowdrift depth of roof The snowdrift depth on the ground plate (1) Figure 7 shows the accumulation coefficients of the roof of the southwestern region baseball stadium obtained in the experiment whose wind direction angle is WNW by sizes. maximum depth of fresh snowdrift = Accumulation coefficient recycled period of 100 years maximum depth of fresh snowdrift (2) maximum depth of snowdrift = Accumulation coefficient recycled period of 100 years maximum depth of snowdrift (3) Figures 8 and 9 show the anticipated amounts of the maximum depth of fresh snowdrift and the maximum depth of snowdrift of 100 years recycled period of Seoul city with the use of accumulation coefficients. The snowdrift depth of the ground plate obtained in the experiment was measured as 5.8cm. As shown in Figure 6, accumulation coefficient grows higher in WNW direction the main direction in which wind blows, and this means that snowdrift is heavy and toward the opposite side of main wind direction, snowdrift decreases. The reason snowdrift is heavy on the front face of main wind direction is judged to be because the snow heaped up as the flow of snow is blocked due to the protrusion at the center of the roof of the domed stadium. When accumulation coefficients are distributed between 0.2 and 1.1, maximum depth of fresh snowdrift and maximum depth of snowdrift were predicted with the use of accumulation coefficient. As a result, it is anticipated that snow will be heaped on the roof face of domed stadium with the maximum depth of fresh snowdrift in 2.92cm to 32.3cm range and the maximum depth of snowdrift in 3.4cm to 37cm range. Figure 10 shows the measured result values of displacement by locations where snowdrifts are measured with 3D camera. 285

6 Proc. of the 8th Asia-Pacific Conference on Wind Engineering (APCWE-VIII) Fig 7. Sedimentation coefficients of the roof Fig 8. The anticipated amounts of the maximum depth of fresh snowdrift Fig 9. The anticipated amounts of the maximum depth of snowdrift 286

7 Fig 10. Measured result values of displacement by locations (unit:mm) Conclusion 1) The occurrence frequencies by 16 wind direction angles measured in winter from 1986 to 2007 by Seoul Weather Station were converted to percentage, and as a result, WNW wind occurred the most, and thus was determined as the experiment wind direction angle. 2) The 100 years recycled period was applied to the experiment with the use of the 20 years (1990 to 2010) snowdrift data of Seoul city and Gumbel random model, and as a result, the maximum depth of fresh snowdrift was estimated as 29.3cm and the maximum depth of snowdrift as 33.6cm. 3) The examination of the accumulation coefficients of the stadium roof indicated the accumulation coefficients were distributed between 0.2 and 1.1. It is anticipated that snow will heap up on the roof of the stadium in 2.9cm to 32.2cm range if maximum depth of fresh snowdrift is applied and in 3.4cm to 37cm, range if maximum depth of snowdrift is applied based on 100 years recycled period. References Kim Jong-Soo, The Necessity of Building a Large Dome Stadium, Journal of Architectural institute of Korea, Vol.11, no.2, pp 30-33, 2011 Report, Seonam-Gwon(South-West Region) Baseball park Snowdrift experiment,

8 You Ki-Pyo, Evaluation of Snow Load Using a Snow Simulation Wind Tunnel, Journal of Architectural Institute of Korea, Vol.28, no.7, pp , 2012 You Ki-Pyo, Lee Hoo-Ryoung, A Study on the Simulation of Snow Particle and Snowdrift Patterns on Buildings Using a Wind Tunnel System, Journal of Architectural Institute of Korea, Vol.27, no.4, pp , 2011 Taylor D.A, Schriver W.R. "Unbalanced snow distributions for the design of Arch-Shaped roofs in Canada", Canadian Journal of Civil Engineering Vol. 7, No. 4, pp , 1980 Isyumov N, Davenpord AG. "A probailistic to the prediction of snow loads", Candion Journal of Civil Engineering, Vol. 1, pp ,