Excessive deflection in a building can affect building use and can even cause problems opening doors and windows. An example of this is a building with a bridge crane and the amount the building will deflect when that crane is carrying its maximum load, or the possibility of damage or vibrations in the building.
SLS, or serviceability limit states factors building deflection during use and ensures required deflection performance from the building while in use. The limit states on safety are called ultimate limit states (ULS) and design for maximum capacity, fractures, overturning, etc. Limit states design ensures building safety from collapse during construction and safety after completion. Introduced in 1975 into the National building code, limit states design was initially designed for steel building but now is incorporated into the design of all major structures. The collateral load included in the design of a pre-engineered steel building is a dead load to cover the additional loading requirements for mechanical, electrical, or any other services or equipment the building requires. The site class (A,B,C,D,E,F) classify the ground type, soft soil, hard soil, rock, etc and this value must be confirmed by a Soils engineer through a geotechnical report. Like the other climatic design loads, an importance factor is applied to these loads based on the steel buildings end use. As well the peak ground acceleration is considered in the same mean factor. The National Building Code, NBC 2005, lists median values for design ground motion, a mean of 2% in 50 year probability, of acceleration for periods 0.1 seconds, 0.5, 1.0 and 2.0. The other earthquake factors are considered in other areas of the design. This part of the design only considers ground shaking. Earthquakes can cause damage through ground shaking, soil failures, or surface fault ruptures. Like all structures, the earthquake loads on a pre-engineered steel building is a major factor in the design. Wind loads are calculated considering environmental data on winds for each area, mean pressures that will act on the building, gust factors, terrain type (exposure class), building openings and importance factors related to the building type (or end use). Pre-engineered steel buildings need to be designed to ensure that the main structural system and all secondary components, such as cladding will withstand the pressures and suctions the wind put on a building. These loads are factored under guidelines set out in the building code, an importance factor is applied based on the buildings end use and an overall roof design load is determined.
The unit weight of snow (generally 2-5 kn/m3) converts snow depth to load Ss and for rain failing on the snow the same procedure is used to get Sr. The roof of a pre-engineered steel building has to support the greatest weight of snow that is likely to accumulate on it in 1-50 years. Here is a very brief description of what climatic loads are considered in the pre-engineered steel building’s design and how they are considered in the British Columbia Building code.
Interpolation from the values in the Table to other locations is not acceptable and local municipalities, failing that Environment Canada, must be contacted to provide climatic design loads for locations not listed.
The British Columbia Building code lists loading criteria for over 600 major cities. In British Columbia it also must conform to Part 4 of the BCBC—using loads, and deflection and vibration limits from either Part 4 or Part 9.