Effects of Wind-Loading on Bridges

Wind is a word that used to describe the motion of the air. It is the natural phenomenon which caused by temperature differential that is resulted from solar radiation. A moving wind that comes in contact with a solid structure will be distracted. Although the wind structure is not fully stopped, it still loses some of its velocity. This is due to the frictional force faced by the wind flow and the surface of the bridge. This phenomenon is actually called wind loading which can give big impact on the structure of the bridge.

Wind gusts that are constantly blows are strong enough to contort the bridge until it collapses. The kinetic energy of the wind is converted into the potential energy in the form of pressure. Both tangential wind loading on bridge surface and pressure can act in any directions can affects the span’s sides, top and bottom surface. This may lead the bridge to flex itself and fluctuates. The flexing alters the wind flow’s angle to the deck where the span’s lateral and torsion displacements altered by the increased wind speed, resulting in creating vibrations which grows to flutter instability.

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Each fluctuation increases the wind contact with the surface of the span which will build up the twisting motion. In the end, the cable of the suspension bridge might slip, unbalancing the bridge. The imbalance will then transferred to the deck girders, allowing them to twist and finally collapse. Bernoulli’s Equation can analyse the flow of the wind. It is basically to determine the pressure imposed by the wind to the structure of the bridge. Bernoulli’s Equation states that, 12? U2=constant along streamline . Similarly for wind loading, q=12? U2.

From this equation, it can be seen that the pressure is proportional to the square of the wind velocity. This assumes that the analysis of static wind loading at high wind velocity is a fundamental procedure in the structural analysis process. The intensity of wind pressure will be depending on the design of the bridge structural properties such as the height of the bridge which affects the wind loading as the wind loads hitting the bridge increase if the height of the bridge above waterways increases. Wind loading might sprain the strength of the ridge cable and its span elasticity when the span is too light, narrow, thin and when it is designed with too much flexibility.

The design and the materials of the span such as concrete slab and steel girder will produce unbalance lift and drag which helps in raising the torsion effects and finally resulting on the damage of the bridge. Therefore, the essentials factor in constructing bridge must be considered. Those include the wind speed of the particular location, turbulence in wind flow and the strength of the bridge where it must be designed for structural stability of flow from all directions.

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