What are wind exposure categories?
ASCE 7 (26.7 of ASCE 7-16) describes the process to which wind speed is converted into wind pressure to design such structures. One of which is called ‘Exposure Category’ and reflects the characteristics of ground surface irregularities at a site which the building or structure is to be constructed.
What is an exposure category?
Exposure category is based upon ground surface roughness, which is determined from the topography, vegetation, and existing structures. ASCE 7 defines three exposure categories: B, C and D.
What is wind exposure category D?
Exposure D: Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance greater than 5,000 ft (1,524 m) or 20 times the building or structure height, whichever is greater.
How do you calculate wind exposure?
Armed with pressure and drag data, you can find the wind load using the following formula: force = area x pressure x Cd. Using the example of a flat section of a structure, the area – or length x width – can be set to 1 square foot, resulting in a wind load of 1 x 25.6 x 2 = 51.2 psf for a 100-mph wind.
What is basic wind speed?
The wind speed that is used in determining wind load on a structure before other factors (such as height above the ground and the effects of shielding) are taken into account.
What is Risk Category II?
Risk Category II: These buildings represent a lesser hazard to life because of fewer building occupants and smaller building size compared to those that are considered Risk Category III. Most buildings and structures are considered to be Risk Category II.
Which exposure will allow the most wind to hit the structure?
Exposure D is the highest standard of wind exposure and are required when a building is within one mile of an open body of water.
How are buildings classified?
According to the Building Owners and Managers Association (BOMA), there are three classifications a building can be given. These classifications are Class A, Class B, and Class C. Let’s explore the lowest classified buildings to the highest classified buildings.
IS 875 1987 is used for?
IS: 875-1987(Part-4)- Snow Loads: This standard deals with the snow loads on roofs of buildings. Roofs should be designed for the actual snow load due to snow or for the imposed loads specified in Part 2 Imposed Loads.
Is 875 a wind zone?
IS-875 is the standard in India for design loads (other than earthquake) for buildings and structures. Basic wind speed as applicable to 10 m height above mean ground level for different zones in the country can be directly calculated if the proper value is defined in the Wind Zone Number box.
What is a risk category 4?
Risk Category IV: These are buildings that are considered to be essential in that their continuous use is needed, particularly in response to disasters. Hospitals, fire stations, police stations and emergency vehicle garages must remain operational during and after major disaster type events.
How are exposure categories determined for wind direction?
For each wind direction considered, an exposure category that adequately reflects the characteristics of ground surface irregularities shall be determined for the site at which the building or structure is to be constructed.
What do the wind speeds represent in the weather data?
The wind speeds correspond to 3-second gust speeds at 33 ft above ground for exposure C category. The wind speeds represent 50-year return period. Change from ASCE 7-98 to 02 & 05. Exposure A is deleted. A distinction was made surface roughness categories and exposure categories.
What is windwind exposure B?
Wind Exposure B is a site protected from the wind in all four directions, within ¼ mile, by trees, hills or other buildings. This would include building sites in residential neighborhoods and wooded areas.
Which exposure should be used for wind loading?
The exposure to be adopted should be the one that will yield the highest wind load from the said direction. The description of each exposure classification is detailed in Section 26.7.2 and 26.7.3 of ASCE 7-10.