How to Apply Climate Data to Structural Design
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Recently, I’ve been aiding a customer in transitioning a proprietary building material approved for use in Canada into the United States construction industry. While working with local engineers, this has allowed me to delve into the International Building Code, the International Residential Code, ASCE 7, and select state codes and amendments. It has piqued my interest in how different jurisdictions apply climatic data in structural design.
Climatic Data and the National Building Code
The following climatic data is documented in the National Building Code of Canada 2015 (NBC):
Design temperatures, including the January 1% and 2.5% design
temperatures, the July 2.5% wet-bulb and dry-bulb temperatures, and the heating degree-days below 18oC;
Rain data, including the 15 minute rain, One day rain, 1 in 50 year rain, annual rain, moisture index, annual total precipitation, and 1 in 5 year driving rain wind pressure;
The 1 in 50 year ground snow load and the 1 in 50 year associated rain load;
Hourly wind pressures, including 1 in 10 year hourly wind and the 1 in 50 year hourly wind; and
Seismic design data, including the 5% damped spectral response acceleration value over a specified period of time, the peak ground acceleration, and the peak ground velocity.
Climatic data is used for various purposes in the NBC including structural design, mechanical design, and building envelope design. The intent of this article is to address the applications to structural design.
Snow and Rain Data
Snow and rain data are typically used for roof design, and design of structural elements responsible for transferring the roof load down to the foundation.
Snow and rain data can be found in “Table C2 – Climatic Design Data for Selected Locations in Canada” in Appendix C, Division B of the NBC. Data is provided for over 600 locations across Canada. Generally, these locations are determined based on larger regional towns and cities, and infilled with some smaller communities to create a more representative map. In some instances such as mountainous and coastal regions, additional data points have been added based on an identified need for that additional information.
In most provinces and territories, there are provincial or territorial amendments to the NBC. In some instances, additional data points and/or slightly modified data points are provided. In such instances, the provincial data will supersede the NBC data.
Further, some municipalities and planning districts may amend the provincial or territorial climatic data to provide a more representative data set for the communities comprising their area. Such information may be written into bylaws or available from the Authority Having Jurisdiction.
The climatic data provided is not intended to be interpolated without thorough consideration of elevation, topography, and other potential constraints. Specifically, interpolation within mountainous regions is advised against. In mountainous areas, data points tend to be applicable to the valleys or bases of such mountains, and not to the slopes or higher passes.
Where climatic data is not provided, it may be obtained by contacting the Meteorological Service of Canada (formerly the Atmospheric Environment Service, referred to in the NBC).
Rain Data
Rain data is typically used in roof drainage systems to carry the weight of rainfall when considering the intensity of the rainfall and the duration of time for the rain to travel to the gutter. This impacts the roof design and design of structural elements responsible for transferring the roof load down to the foundation. Rain data may also be used to design structural components for the driving rain wind pressure
Rain data can be found in “Table C2 – Climatic Design Data for Selected Locations in Canada” in Appendix C, Division B of the NBC.
It is necessary to confirm that there is not more stringent provincial, territorial, or municipal data that supersedes the NBC.
Caution should be taken in interpolating rain data, especially in mountainous or coastal areas. Where climatic data is not provided, it may be obtained by contacting the Meteorological Service of Canada.
Wind Data
Wind data is typically used for the design of primary and secondary members of walls and roof. It is also used in the design of lateral load resisting systems. Similar to the impacts of snow and rain, the impacts of wind loads will also be carried through to all structural elements responsible for transferring the load down to the foundation.
Wind data can be found in “Table C2 – Climatic Design Data for Selected Locations in Canada” in Appendix C, Division B of the NBC.
Just as with snow and rain data, it is necessary to confirm that there is not more stringent provincial, territorial, or municipal data that supersedes the NBC.
Caution must be taken if interpolating the data. Wind speed is sensitive to many conditions including but not limited to elevation, hills or valleys, and proximity to large bodies of water.
Where climatic data is not provided, it may be obtained by contacting the Meteorological Service of Canada (formerly the Atmospheric Environment Service, referred to in the NBC).
Seismic Data
Seismic data is used in the seismic design of buildings. The NBC provides data for firstly determining if seismic design applies, and secondly performing the seismic design for the building.
Seismic data can be found in “Table 3 – Seismic Design Data for Selected Locations in Canada” in Appendix C, Division B of the NBC.
It is necessary to confirm that there is not more stringent provincial, territorial, or municipal data that supersedes the NBC.
Seismic information for locations not listed can be obtained by contacting Earthquakes Canada or the Geological Survey of Canada .
