Lisø PhD Dissertation Manuscript - NTNU

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Year of construction, loads and geographical location Design loads on buildings have changed considerably in the period from 1949 till today. The year of construction may therefore tell something about the building’s safety level. In general, older buildings in high-snowfall areas may have a lower safety with respect to snow loads than newer buildings. The difference in safety level with respect to wind action is probably somewhat less. The safety level is probably affected mostly in areas that are heavily exposed to the environmental loads, when snow loads and wind actions in the regulations are increased from general loads that have applied to the entire country to differentiated loads that are adjusted to the actual environmental load variation in Norway. Increased wind actions therefore probably have the greatest consequences for coastal areas from northwest Norway northward. Locally, roughness of terrain and topography may be of great significance for the wind actions that the buildings experience. Inland areas high above sea level are most vulnerable to increased snow loads. Locally, topography and wind action is also important for the snow loads that the building experiences. The construction process Questions may be raised as to whether buildings erected by way of voluntary communal work or that are self-built, are more vulnerable to collapse than other buildings. It has been claimed that savings on design costs and technical expertise in the construction phase are often made for such buildings. Such savings can lead to little or no documentation of the structures being produced, and there may be a lack of people with the necessary technical competence to take overall responsibility for the execution of the work. This can lead to unfortunate improvisations on site that is assessed by the person implementing the project as “good enough”. It is therefore reasonable to believe that there is a greater probability of weak points that can result in the sudden collapse of such buildings. Prefabricated structures are often imported. It has been claimed that the design calculations do not always meet the design rules set out in Norwegian codes and that many structures have been designed for relatively small snow loads compared to Norwegian requirements. Structures have been imported from countries such as Denmark that are designed for snow loads well below those required in Norway. The history of buildings Reconstruction or rebuilding may lead to significant changes in both design loads and load-bearing capacity. Columns and beams in outer walls (for example) may be centrally arranged during rebuilding, and thus assume greater loads. The need to strengthen structural elements, including foundations, may be extensive and is not always met. When walls are removed or new openings established, the stabilising elements of columns can change, or the anchoring may change, resulting in reduced load-bearing capacity. Modifying the construction of roof structures may result in load change. For example, roofs that are changed from e.g. roofing membranes to tiles acquire an additional load of about 0.5 kN/m 2 . Additional insulation of roofs in older buildings may lead to reduced snow melting. Assuming the same precipitation pattern, this may result in larger quantities of snow remaining on the roof than before the additional insulation. Changing the use of buildings, which may lead to greater consequences in the event of collapse, makes it necessary to reassess the capacity of the structures. In the case of a change of use from for example a storage building to a building for public use, the requirement concerning maximum annual probability of failure becomes more stringent, and there may be a need to strengthen the building. Selection criteria It would be desirable to identify a selection of buildings that could at large be characterised as communal halls, sports halls, buildings used by many people, lightweight structures, prefabricated buildings, buildings with large spans, buildings supplied as package solutions, buildings with modified applications, buildings erected via communal voluntary work, temporary structures and converted buildings. These are building types all of which are regarded as being especially exposed to increasing snow loads and wind actions. <strong>Manuscript</strong> No. ST/2005/024694 6 of 13
The number of buildings investigated has for economical reasons been limited to 20. This number of buildings is too small to render possible valid statistical analyses of the reliability of the building stock in Norway as a whole, but importance has been attached to the sample being random and having a geographical spread. The results may in this way be assessed as a representative trend for the parts of Norway that have experienced significant changes in the rules governing snow loads and wind actions. It was therefore decided that the buildings should represent ten municipalities in six counties. The municipalities have been chosen in such a way that half be in an area exposed to high wind actions and the other half in a high-snowfall area. The municipalities are Andøy, Bardu, Fræna, Grane, Kristiansund, Nittedal, Røyrvik, Tromsø, Trondheim and Ørland (see Fig. 3). Tromsø, Bardu, Grane, Røyrvik and Nittedal are situated in high-snowfall areas. Andøy, Ørland, Trondheim, Kristiansund and Fræna are in areas exposed to high wind actions. FIG. 3. Geographical localisation of the investigated buildings In light of the fact that the regulations governing snow loads and wind actions have changed over three periods of time, it was decided that the sample should represent these periods. The periods can briefly be characterised as: Before 1970, when the 1949 building regulations were in force. Between 1970 and 1979, when NS 3052 was in force. After 1979, when NS 3479 was in force. The buildings are all compared with today’s design rules, including the current reliability code, NS 3490 (Standards Norway 1999), the current rules for determining snow loads, NS 3491-3 (Standards Norway 2001), and the current rules for determining wind actions, NS 3491-4 (Standards Norway 2002a). To fulfil the requirement for randomness in the sample of buildings, the Norwegian Mapping Authority was asked for permission to search the GAB Register. However, the search criteria available proved to be limited. For buildings older than 1983, the data in the register is normally <strong>Manuscript</strong> No. ST/2005/024694 7 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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774 Nordvik and Lisø probably to a
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Page 75 and 76: cost of repairing process-induced b
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Page 81 and 82: different strategies: risk-based, p
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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
Page 91 and 92: construction industry, and academic
Page 93 and 94: BUILDING RESEARCH &INFORMATION (JAN
Page 95 and 96: greater variations (Lisø et al., 2
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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 and 120: INCREASED SNOW LOADS AND WIND ACTIO
Page 121 and 122: The hurricane (Beaufort number 12)
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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
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Page 146 and 147: [17] Dührkop H., Saretok V., Sneck
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Page 155: Acknowledgements This paper has bee
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Page 160 and 161: Fig. 1. Map of Norwayshowing the lo
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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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