Lisø PhD Dissertation Manuscript - NTNU

the ground with return period of 30 years are used when calculating the roof-to-ground
ratio. Similar evaluation should be performed also for other measurement data, for instance
the data of Høibø [5].
In Norway the meteorological data needed are not easily accessible for structural
engineers. The data basis can be bought at the Norwegian Meteorological Institute, but the
wind category (according to ISO 4355 [2]) has to be calculated either by meteorologists or
by consultants in structural engineering. After deciding the mean temperature and wind
category for the nearest meteorological station delivering such data, the structural engineer
has to evaluate if these values are reasonable for the temperature and wind climate at the
specific building site. Local topography including altitude, surrounding buildings and trees
has to be evaluated in order to decide the wind category. High-resolution maps are
required. This evaluation is time-consuming and demands high qualifications.
The investigation presented will be used as an important basis for ongoing studies
within the ongoing Norwegian research & development programme “Climate 2000” [17],
e.g. the relationship between snow loads on roofs and wind exposure will be further
investigated [18]. In this article the suitability of the exposure coefficient as defined in ISO
4355 is analysed. Further work should focus on developing a definition reflecting the
physical processes more correctly. There is for instance a need for taking into account the
length of the snow accumulation. The definition of wind categories should also be looked
into, and a more detailed method specifying wind exposure should be developed. The
authors are now addressing these issues.
When using the exposure coefficient, the snow load on a sheltered roof becomes
twice as large as the snow load on a windswept roof. The significance of this coefficient
according to total building costs will be studied. To what degree could the society profit by
an entirely use of this exposure coefficient? The advantage of built-in security accounting
for future change in wind exposure or climatic impact could be desirable.
Methods are in the recent years being developed making it possible detailing the
design processes according to design loads. In this work advanced tools and data
processing are required. These tools are for many cases not available for structural
engineers. Using these methods also requires high qualifications and the risk of engineers
using it in an erroneous way are present. Further work should focus on developing tools for
structural engineers making it possible differentiating design loads and thereby taking into
account local topography and climate.
The “robustness” of the Norwegian building stock will also be addressed as part of
the "Climate 2000" programme, e.g. through analysis of statistical data from the Ground
Property, Address and Building Register along with knowledge on process induced
building defects [19]. The lifetime of the built environment depends closely on the severity
of local climate conditions, and a sensible way of ensuring high-performance building
enclosures in a country with extreme variations could be to develop more sophisticated
climate classifications or exposure indexes for different building materials and building
enclosures. This work is now concentrated on issues related to building technology or
building physics, and include development of methods for classifying different climate
parameters and their impact on building enclosure performance (e.g. [20], [19]).
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