The different structures of the buildings

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How does wind pressure affect the different structures of the buildings?


As we know by common sense that any object at particular height in an area is subjected to be affected by the force of the wind. There is also a minimal effect on the structure that is a swinging motion is observed because of the effect of the wind. In building structures it is mainly observed that due to the collision of the wind with the structure does have a slight effect on it that is an oscillation is observed but is not felt by the dwellers. Everyone knows that with an increase in the height of a structure there is also an increase in the wind pressure and wind force. The oscillation of the building also increases with height, so there also need to be some measures which can take care of these oscillations For example a tree, due to wind in a particular area there are easy oscillation of the branches and the trunk of the tree when the wind force is very high. In the similar way the trunk is nothing but a building structure which at a greater height can be affected by the wind force. Despite having general impression about the phenomena not many people know the theory behind this process and the changes.

Since engineers do a wind tunnel testing for the change in the oscillation of the buildings my experiment is based on the similar experiment at a smaller ratio and less technological devices but will help in measuring the wind load of different structures of the buildings. Hence by determining the wind load of a structure I will be able to show the effect of wind on different structure of building in an area having a particular wind velocity.

Wind load

Buildings and structures are designed according to code specified wind loads and also the components of these structures are also hence based on it. Wind load is nothing but the amount of the wind force acting on a structure in a particular area at a particular height. The effect of the wind force and the pressure on the building is considered as a combined effect of external and internal pressures acting upon it. In most of the cases the wind load acted is perpendicular or normal to the surface of the structure.

The wind speed in a particular area increases with the height from the ground level that is level zero to a maximum level that is called the gradient height. This height is nothing but the height above the ground zero or the mean ground level where the wind blows so as a result of centrifugal force(the horizontal outward force from a circular motion of a source) and pressure gradient.Therefore observing at a particular wind speed in an area for particular years , its mean gives us the average wind speed, wind pressure in that area with an increase in a particular height.

There are actually many factors the wind load and wind pressure depend on they are altitude factor (the height of the structure), gust factor (is the departure of the wind speed in its mean value specified under interval of time), terrain factors (that includes the topography of the surrounding areas). Wind load is nothing but a drag force

Generation of pressure

When wind acts on a structure, the force of the wind is slowed down against the front face of the structure, building up pressure on the building. At this particular time only most of the pressure is deflected and accelerated around the sides of a structure (this depends on the shape, structure and design of the building). When this pressure is diverted it leads to suction taking place in the area where the pressure has been reduced. Therefore greater the speed of the wind, greater the pressure on the building thus greater is the suction taking place. The highest suction takes place near the edges of the building as the pressure is deviated through the edges of the structure. If the structure is of a smaller size than importance should be given to its edges, rooftop as most of the pressure and suction takes place there only, because as the wind is moving obliquely most of it is diverted around edges and rooftop and this is known as vortex action on the roofs. Vortex action takes place when the wind blowing to the structure is deflected around and over the building. The pressure on the walls is much less compared to that effect in taller buildings. The wind rolls up near the corner, which are edges of the roof top casing increase in pressure and force in the edges. This also leads to higher suction in that area also.

With the help of this dynamic pressure acting on the surface of the building, we can determine the wind load acting normally on the surface by multiplying the surface area of the structure affected by the pressure and the pressure coefficient. And hence with the mean of the values calculated, one can easily determine the amount of wind and its force acting in a particular direction. Also with the help of this mean we can determine the force and pressure acting on the structure in all the four different quadrants.

Dynamic pressure of the wind

When the wind is brought to rest against the windward face of the obstacle that is the surface of the building facing the wind force, all its kinetic energy (of the wind) is transferred to a pressure known as the dynamic pressure also denoted by 'q'.

'can be calculated by:

q = k.v ref2 N/m2

k = air density that is 0.613 kg/m2