Lisø PhD Dissertation Manuscript - NTNU

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6. Conclusions It is shown that the exposure coefficient as defined in an informative annex of ISO 4355 does not reflect the actual effects of wind exposure on roof snow loads in Norway, the main reasons being oversimplifications in the definition of the coefficient and the extreme variations of the climate in Norway. The definition is based on coarse simplifications of snow transport theories. It must be revised and improved to serve as an applicable tool for calculating design snow loads on roofs, using the best available data from meteorological stations in Norway. As documented in this paper, Norway has areas with high snow loads and high frequency of wind. In these areas the wind affects roof snow loads, and the exposure coefficient is expected to achieve its lowest value. The definition of the exposure coefficient as given in ISO 4355 does not point out these areas as areas where wind blows snow away from roofs. Acknowledgements This paper has been written within the ongoing SINTEF research & development programme “Climate 2000 - Building Constructions in a More Severe Climate” (2000 - 2006), strategic institute project “Impact of Climate Change on the Built Environment”. The authors gratefully acknowledge all construction industry partners and the Research Council of Norway. A special thanks to Dr. Kristoffer Apeland for valuable comments on the text. Page 16 of 17
References [1] Standards Norway. Design of structures - Design actions - Part 3: Snow loads (in Norwegian). Oslo, Norway: Standards Norway; 2001. [2] International Organization for Standardization. Bases for design on structures - Determination of snow loads on roofs. Genève, Switzerland: International Organization for Standardization; 1998. [3] Lutes DA. Snow loads for the design of roofs in Canada. In: Proceedings of the Western Snow Conference. Victoria, British Colombia, Canada: 1970, p. 61 - 67. [4] Otstavnov VA, Rosenberg LS. Consideration of Wind Effect in Standardization of Snow Load. In: A multidisciplinary approach to snow engineering: 1 st International Engineering Foundation. US Army Corps of Engineers Cold Regions 8387.500 SR 89-6, 1989, p. 256 - 263. [5] Høibø H. Snow Load on Gable Roofs - Results from Snow Load Measurements on Farm Buildings in Norway. In: the First International Conference on Snow Engineering. Santa Barbara, California, USA: CRREL Special Report, 1988, p. 95-104. [6] Løberg PA. Snølaster på tak (in Norwegian). Arbeidsrapport nr. 5. Oslo, Norway: Norwegian Building Research Institute; 1976. [7] Taylor DA. A survey of snow loads on the roofs of arena-type buildings in Canada. Canadian Journal of Civil Engineering 1979; Vol. 6 1979: 85 - 96. [8] O'Rourke M, Koch P, Redfield R. Analysis of roof snow load case studies - Uniform Loads. CRREL Report 83-1. Cold Regions Research & Engineering Laboratory; 1983. [9] Commission of the European Communities. Scientific support activity in the field of structural stability of civil engineering works - Snow loads. Final report. Pisa, Italy: University of Pisa, Dep. of Structural Engineering, Prof. Luca Sanpaolesi; 1999. [10] Irwin PA, Gamble SL, Taylor DA. Effects of roof size, heat transfer, and climate on snow loads: studies for the 1995 NBC. Canadian Journal of Civil Engineering 1995; Vol. 22: 770 - 784. [11] Mellor M. Cold Regions Science and Engineering, Part III, Section A3c, Blowing snow. Hanover, New Hampshire, U.S.A.: U.S. Army Material Command, Cold Regions Research & Engineering Laboratory; 1965. [12] Kind RJ. Snow drifting. In: Gray DM, Male DH editors. Handbook of snow: Principles, Processes, Management & use. Pergamon Press; 1981, 338 - 359. [13] Li L, Pomeroy JW. Estimates of Threshold Wind Speeds for Snow Transport Using Meteorological Data. Journal of Applied Meteorology 1997; Vol. 36 March: 205 -213. [14] Nordli Ø. Fjellet i snø, vind, sol og tåke - Dannevigs Fjellbok (in Norwegian). Oslo, Norway: Det Norske Samlaget; 2000. [15] Isyumov N, Mikitiuk M. Climatology of snowfalls and related meteorological variables with application to roof snow load specifications. Canadian Journal of Civil Engineering 1977; 4, 1977: 240 - 256. [16] Taylor DA. Snow loads on sloping roofs: two pilot studies in the Ottawa area. Canadian Journal of Civil Engineering 1985; Vol. 12: 334 -343. [17] Lisø KR, Kvande T, Thue JV. Climate 2000 - Building Enclosure Performance in a More Severe Climate. In: the 7th Symposium on Building Physics in the Nordic Countries. Reykjavik, Iceland: the Icelandic Building Research Institute, 2005, p. 1195 - 1202. [18] Meløysund V, Lisø KR, Siem J, Apeland K. Increased Snow Loads and Wind Actions on Existing Buildings: Reliability of the Norwegian Building Stock. Journal of Structural Engineering 2005. [19] Lisø KR, Kvande T, Thue JV, Harstveit K. A frost decay exposure index for porous, mineral building materials. 2005. [20] Rydock JP, Lisø KR, Førland EJ, Nore K, Thue JV. A driving rain exposure index for Norway. Building and Environment 2005; Vol. 40(11): 1450 - 1458. Page 17 of 17
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Building envelope performance asses
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Lisø, K.R./ Building envelope perf
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BUILDING RESEARCH &INFORMATION (200
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LisÖ et al. on how to cope with an
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LisÖ et al. the exposure to contin
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LisÖ et al. business premises. The
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LisÖ et al. construction industry
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Research in Building Physics, Carme
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4 CLIMATE CHANGE SCENARIOS FOR NORW
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with large amounts of precipitation
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will most likely be worse, even wit
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Graves, H.M. & Phillipson, M.C. 200
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766 Nordvik and Lisø The topic of
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768 Nordvik and Lisø into the futu
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770 Nordvik and Lisø climate chang
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772 Nordvik and Lisø 0 Â Â = p d
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774 Nordvik and Lisø probably to a
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BUILDING RESEARCH &INFORMATION (200
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cost of repairing process-induced b
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change in quality (Mehus et al., 20
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on the impacts of different climati
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different strategies: risk-based, p
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Learning from experience - an analy
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An important aspect of the programm
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Concrete walls 32 % LECA masonry 10
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construction industry, and academic
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BUILDING RESEARCH &INFORMATION (JAN
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greater variations (Lisø et al., 2
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Typical problem areas and recommend
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Figure 3b Recommended design of win
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Figure 7 Example showing the recomm
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Figure 11a Poor solution for a £as
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Acknowledgements This paper was wri
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Climate adapted design of masonry s
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2. Masonry defects in Norway 2.1. S
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Fig. 2. Example illustrations of th
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The presented results are in good a
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appropriate in a more severe type o
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screen in a two-stage weatherproofi
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INCREASED SNOW LOADS AND WIND ACTIO
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The hurricane (Beaufort number 12)
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The extensive revisions of the code
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The number of buildings investigate
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As is apparent from the values in t
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climate change is now dominated by
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