Lisø PhD Dissertation Manuscript - NTNU

climate change is now dominated by human influences large enough to exceed the bounds of natural
variability, the main source of global climate change being human-induced changes in atmospheric
composition. Regional changes in climate, particularly increases in temperature, have already
affected several physical and biological systems in many parts of the world, for example shrinkage of
glaciers, thawing of permafrost and lengthening of mid- to high-latitude growing seasons (McCarthy
et al. 2001). Norway’s climate is extremely varied. One of the main reasons for large local
differences in temperatures, precipitation and wind speed over short distances are the rugged
topography. The country’s long coastline and steep topography make it particularly exposed to
extreme events like coastal storms, avalanches and landslides. Regional scenarios for climate change
over the next 50 years in Norway indicate an increased risk for extreme weather. Together with a
warmer climate, especially during winter, an increased risk for intense precipitation over parts of
coastal Norway and more frequent incidents of strong winds along the coast of the two northernmost
counties and off the coast is estimated. These scenarios, emanating from the project “Regional
climate development under global warming (RegClim)” (see www.met.no), are downscaled from a
global climate model run by the Max Planck Institute for Meteorology in Hamburg. According to
these scenarios the future reliability of buildings in exposed areas could decrease.
CONCLUSIONS
The principal objective has been to obtain reliable indicators as to whether existing buildings in
Norway meet current regulatory requirements concerning safety against collapse as a result of snow
loads and/or wind actions. Some clear indications of aspects that ought to be considered as a
representative trend for the building types investigated have been found.
18 out of 20 buildings have a utilization ratio of more than 1.0 (90 % of the buildings
investigated). The design requirements for 95 % of the buildings have increased since they were built.
Nevertheless, one would assume that the buildings had built-in reserve capacities resulting in fewer
buildings experiencing a utilization ratio of more than 1.0.
It is difficult to obtain structural drawings and design calculations for existing buildings. Such
documentation is particularly important when buildings are to have alterations or reconstructions
carried out. Public authorities should therefore establish a system ensuring that such documentation is
made and maintained.
The new rules for determining wind loads that were introduced in 2002 have led to most of the
buildings investigated having greater calculated reliability against collapse owing to wind load than
the current regulations require for new buildings. For buildings in municipalities exposed to wind, for
tall buildings or in places with special topographical conditions, safety may, on the other hand,
decrease. The new rules for determining snow loads, introduced in 2001, have led to most of the
buildings investigated having lower calculated reliability against collapse owing to snow loads than
the regulations now requires.
A careless approach is often adapted to planning, or that this process is completely omitted, in the
case of alteration and additional work. This may lead to significant design capacity excess. Thus,
rebuilding, reconstruction and addition (extension) projects must also be adequately designed.
The investigation indicates too low reliability for a considerable number of buildings according to
current building regulations, when evaluating the possible consequences of the conclusions in a
national perspective. Potentially 4.5 % of the total bulk of buildings in Norway may have too low
capacity according to current regulations. Design snow loads may have increased for 4.7 % of the
total bulk of buildings.
Scenarios for future climate change indicate both increased winter precipitation and increased
temperature, and will result in changes regarding snow loads on roofs in parts of the country. An
increase in frequencies of strong winds in areas also exposed today is also estimated. According to
these scenarios the future reliability of buildings in these areas could decrease.
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