Loads for which awning and canopies may need to be designed can be categorized as follows:
Dead Load
This is the self-weight of the awning or canopy frame, fabric and hardware. This load must always be included with other design loads since it is always acting on the structure
Wind Load
This load, as well as snow load, is usually the most critical load on awnings and canopies. Important aspects of wind loads are:
- Speed or velocity- Basic wind pressure is a function of its speed. Basic wind pressure(psf) can be computed as the product of 0.00256 times the square of the wind speed (mph). Design wind speeds are generally shown on maps published in the building code. Local codes may require higher design wind speeds.
- Exposure – This is a general category for the amount of protection from wind that is afforded by the surrounding environment.
- Gusts- These are short- term excursions of velocity above the steady design velocity, which must be accounted for in its design
- Drag, Lift- Drag is the wind-induced pressure toward the fabric surface, and lift is the pressure away from the fabric surface. Wind forces on an awning system act in different directions. When designing an awning frame, all of these factors must be taken into account.
- Return period- This is used to describe the time interval, which is the basis for establishing the required design wind speed. For most applications the return period is 50 years. This simply means that the required design wind speed is that which has a 0.02 statistical probability of occurring once in 50 years. Loss and safety experts have determined that it is an acceptable level of risk and have based code design requirements on it.
Snow Load
Required design snow loads are established by maps published in the building code. As in the case for wind, sometimes local requirements are more stringent. On the other hand, in many localities there is no requirement for snow load design. Some considerations about designing for snow are:
- Ground snow- The beginning point for snow design, this is the pressure of the designed snow load occurring at ground level.
- Exposure- This is a general catefory for the amount of protection from the wind that is afforded by the surrounding environment.
- Flat roof snow load- This is the design load occurring at the actual roof level, and results from factoring the ground snow load by a coefficient accounting for exposure and height. Many times the flat roof snow load can be as little as 0.6 or 0.7 times the ground snow load.
- Drifting- Building codes require that the phenomenon of drifting snow be accounted for in the design of roofs; this includes awnings and canopies.
Live Load
These are loads that are associated with the forces related to human occupants, furniture, equipments, etc. Since these loads are movable, the live load stipulation is an allowance for the most sever anticipated condition or case. Some codes do not require a live load design and others greatly reduce the requirement.
Ponding
This is a potential load on an awning or canopy and must be addressed in one of several ways.
- Design for ponding must be taken structurally
- Keeping the fabric properly supported and taut will avoid the problem
- Remove snow before it melts and ponds water
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