Lisø PhD Dissertation Manuscript - NTNU

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e in danger of collapse. Table 1 provides an overview of a number of large buildings where snow has triggered or caused significant damage or collapse (Lisø et al. 2000). The summary is not complete, but gives an idea of which types of buildings that are especially vulnerable to damage. The table is based on information from insurance companies and SINTEF Building and Infrastructure. For most buildings, defects during planning or construction have been the most likely cause of damage. In some cases, the damage has resulted from applicable building regulations not being adhered to, or construction at the location not being in accordance with the design calculations. In a few cases, the snow load assumed in the calculations has been lower than the actual loading. FIG. 1. Bardufoss Community Centre (photo: National Office of Building Technology and Administration, printed with permisssion) TABLE 1. Cases of collapse as a result of major snow loads Building Type of building County Built (year) Time of collapse/ damage Stongelandet skole Swimming pool Troms 1971 2000 Bardufoss Samfunnshus Community hall Troms 1965 2000 Lenangen Skole School Troms 1970 2000 Målselv Community hall Troms 2000 Storvoll Skole School Nordland 1990* 2000 Tromsø Tennishall Sports hall Troms 2000 Løkenås-hallen Sports hall Akershus 1978/ 1996* 1999 Lofothallen Sports hall Nordland 1999 Aukra Industrial facility Romsdal 1996 Asker Tennishall Sports hall Akershus 1994 Drammen School Buskerud 1994 Harstad Industrial facility Troms 1988 Birkenes-hallen Sports hall Aust Agder 1987 Svelvik Karosseri Industrial facility Vestfold 1987 Epokehallen Drill hall (military facility) Troms 1982 1983 Tromsø Industrial facility Troms 1975 * Year of rebuilding or reconstruction. Manuscript No. ST/2005/024694 2 of 13
The hurricane (Beaufort number 12) which occurred in northwest Norway on New Year’s Day 1992 caused damage to buildings costing somewhere in the region of $ 200 million. Wind velocities of 62 - 63 m/s were recorded, the highest wind velocities ever recorded on mainland Norway. The bulk of the damage was related to roofs and roofing, primarily due to insufficient anchoring. Most of the damage that appeared could have been avoided if the existing building regulations and Codes of Practice had been adhered to (National Office of Building Technology and Administration et al. 1993). Investigations into the damage taking place in 1992 showed that during the period 1950-1991 the likelihood of structures in new buildings having too low load carrying capacity was increasing. The investigations also demonstrated that if the safety levels in the regulations were to be conformed to, it would be necessary to update the wind action provisions. 55 % of the recorded cases of damage caused by the hurricane in northwest Norway in 1992 involved buildings erected before 1970 (National Office of Building Technology and Administration et al. 1993). The fact that a building has served well for many years is thus no guarantee that it will withstand subsequent hurricanes. Principal objectives and delimitations The principal objective of the investigation has been to obtain a reliable indicator as to whether existing buildings in Norway meet current regulatory requirements concerning safety against collapse owing to snow loads and/or wind actions, and also to establish a basis for the analysis of future climate change impacts on the Norwegian building stock. The analysis encompasses design documentation investigations and field studies of 20 existing buildings in five high-snowfall and five high-wind municipalities in Norway (Siem et al. 2003; Meløysund et al. 2004). Statistical data for e.g. building types, year of construction and geographical localization of the approximately 3.7 million registered buildings in Norway are available in the Ground Property, Address and Building Register (GAB). Special attention has been paid to exposed types of buildings, and the buildings have been randomly selected within the exposed building categories. Assessments of whether the regulations are satisfactory, and theoretical parameter studies of the regulations, are not included in the investigation. The investigation focuses on assessing the buildings’ main load-bearing structures and, to a lesser extent, their secondary load-bearing structures. BUILDING REGULATIONS AND DESIGN CODES The development of design codes for snow loads and wind actions The building regulations of 15 December 1949 (National Office of Building Technology and Administration 1949) referred to a general snow load on roofs corresponding to 1.5 kN/m 2 . This value could be reduced or increased by the individual building authority with the Ministry’s approval. The importance of the shape of the roof for the size of the snow load on the roof was calculated in a simple way. Structures should normally be designed for a wind pressure equal to 1.0 kN/m 2 , while a wind pressure equal to 1.5 kN/m 2 should be used in exposed areas. In heavily exposed areas, building authorities could increase these basic values with the Ministry’s approval. The sum of the wind shape factors for lee and windward walls for a closed building was 1.2 (i.e. 1 + 0.2). In NS 3052 (Standards Norway 1970) snow maps were introduced showing zones with roof snow loads with values of up to 1.5 kN/m 2 , between 1.5 and 2.5 kN/m 2 and above 2.5 kN/m 2 . Four curves for the wind pressure were introduced: the curves A, B, C and D as seen in Figure 2. The code quoted many more detailed rules for the wind shape factors than the building regulations of 1949. The sum of the shape factors for the lee and windward walls was in the code also set to 1.2 (i.e. 0.7 + 0.5). Compared to the building regulations of 1949, the changes in NS 3052 largely implied a reduction in the wind velocity pressures in exposed areas. In NS 3052 the partial factor method was introduced. The partial factor for snow loads was set to 1.6 while the partial factor for wind actions was set to 1.5. Manuscript No. ST/2005/024694 3 of 13
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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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Page 75 and 76: cost of repairing process-induced b
Page 77 and 78: change in quality (Mehus et al., 20
Page 79 and 80: on the impacts of different climati
Page 81 and 82: different strategies: risk-based, p
Page 83 and 84: Lisø, K.R./ Building envelope perf
Page 85 and 86: Learning from experience - an analy
Page 87 and 88: An important aspect of the programm
Page 89 and 90: Concrete walls 32 % LECA masonry 10
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Page 93 and 94: BUILDING RESEARCH &INFORMATION (JAN
Page 95 and 96: greater variations (Lisø et al., 2
Page 97 and 98: Typical problem areas and recommend
Page 99 and 100: Figure 3b Recommended design of win
Page 101 and 102: Figure 7 Example showing the recomm
Page 103 and 104: Figure 11a Poor solution for a £as
Page 105 and 106: Acknowledgements This paper was wri
Page 107 and 108: Climate adapted design of masonry s
Page 109 and 110: 2. Masonry defects in Norway 2.1. S
Page 111 and 112: Fig. 2. Example illustrations of th
Page 113 and 114: The presented results are in good a
Page 115 and 116: appropriate in a more severe type o
Page 117 and 118: screen in a two-stage weatherproofi
Page 119: INCREASED SNOW LOADS AND WIND ACTIO
Page 123 and 124: The extensive revisions of the code
Page 125 and 126: The number of buildings investigate
Page 127 and 128: As is apparent from the values in t
Page 129 and 130: climate change is now dominated by
Page 131: TABLE 3. Summary of findings Struct
Page 134 and 135: Lisø, K.R./ Building envelope perf
Page 136 and 137: temperature of -4°C or less. See F
Page 138 and 139: Today, frost resistance of brick, c
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Page 142 and 143: accelerated frost damage or frost d
Page 144 and 145: A possible objection to the present
Page 146 and 147: [17] Dührkop H., Saretok V., Sneck
Page 149 and 150: Decay potential in wood structures
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Page 155: Acknowledgements This paper has bee
Page 158 and 159: (a driving rain gauge), however, is
Page 160 and 161: Fig. 1. Map of Norwayshowing the lo
Page 162 and 163: Frequency 25 20 15 10 5 0 highest p
Page 164 and 165: interesting to compare those result
Page 167 and 168: Effects of wind exposure on roof sn
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variety of roofs and wind exposures
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Li and Pomeroy [13] evaluated hourl
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Fig. 5. Exposure coefficients for 3
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meteorological stations are expecte
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Many of the meteorological stations
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the ground with return period of 30
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References [1] Standards Norway. De
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