Wind Load on Building Structures.

 Wind is a mass of air that travels from high-pressure zones to low-pressure zones having low and high velocities which exert pressures on buildings and causes resultant loads.

                                 Figure 1.Showing Wind Pressure on Building       

An instrument for measuring wind speed is called Anemometer.       

Formula for wind-pressure is as follows

P =K.V^2

Here

P= Wind Pressure

K= Coefficient

V= Velocity of wind

Value of "K" depends on the speed of the wind and shape of the structure bearing wind pressure,

Using wind velocity in Miles per Hour (mph) wind pressures may be calculated using Coefficient of 0.00256 which will result in Pressure in Pounds per Square (psf).

Now we will calculate the intensities of pressure using various wind velocities.

World Record for Fastest Wind Speed

The fastest wind speed ever recorded comes from a hurricane gust. On April 10, 1996, Tropical Cyclone Olivia (a hurricane) passed by Barrow Island, Australia. It was the equivalent of a Category 4 hurricane at the time, 254 mph (408 km/h). So we will calculate pressures up to the wind velocity of 254 mph.

Wind applies three types of forces structures.   Description of wind is different on different velocities with units of Km/hour or Mile/Hour .

Uplift load - Wind flow pressures exerts uplift pressure as in buildings wind flow under the roof pushes upward.

Shear force load – Mostly wind flow direction remains horizontal having different angles which exert pressure and creates Shear-Forces on structures.

Lateral load – Wind Pressure results in a push and pull forces which can Slide the structure or overturn the structure , these forces are called Lateral Forces. on:

Designing Factor for against Wind Load.

The wind is a natural force that can destroy and uplift any structure which causes high losses so always consider few designing factors for the construction of structures.

1- Calculate wind loads and apply on a minimum area of 100 Sft where width will be 9 ft this will give better pressure impacts in the case of building designing.

2-Resultant pressure acts at the height of h/2 or h/3 so reinforce the building accordingly.

3-Weight of the building should be greater than wind loads a factor of safety of 2 should be adopted only for wind pressure dealing.

4-weak points in building structures are door and windows which can be sustained up to 170 mph, but if the shingle pieces or high moisture content exists in the wind air it can easily break windows even on lower velocity.

5-Buildings having steel roofs faces large intensities of uplifting pressures so the building should be designed having proper structural framing properly braced in footings, vertical members, and horizontal members.

6- In no case Resultant line created from the Center of gravity of any structure should go outside the foundation because it will overturn the building.

7-Light structures get damaged at wind velocity of 47 mph, trees are uprooted on wind velocity of 55 mph and widespread structural damages accrue on 64 mph.       

8-Building structures should be design calculating  pressures on outer sides and also inner side of buildings, make sure the weight of the building is enough to bear wind loads also ensure the stiffness of all structural elements in buildings.

9-Design outer exposed walls monolithic and with homogeneous materials to create uniform stiffness and strengthening the structure.

10-Lighting poles should be designed after calculating horizontal pressure using wind velocity of that area where light poles exist. Provide weight in foundations greater than the horizontal pressures. A Factor of safety of 1.5 to 2 may be adopted comparing wind pressure and weight of foundations.

 

CLASSIFICATION OF WIND VELOCITIES
CLASS OF WIND	WIND VELOCITIES in MPH
Strong Breez	25	28
Moderate Gale	34	49
Strong Gale	50	53
Whole Gale	54	62
Strom	63	72
Hurricane	73	78
Violent Hurricane	79	199
Tornadoes	200	311

Tornadoes may have velocities more than 200 mph.

Tornadoes are ferociously revolving columns of air that extend from a thunderstorm to the ground. Tornadoes can destroy buildings, turn over cars, and create deadly flying debris. A tornado can happen anytime and anywhere. carry strong winds, over 200 miles per Hour.

This Blog contains supporting images that are property of Google only.