Wind effects on low rise structures

Wind effects on low rise structures

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  Wind Effects on LowRise Structures M Gokul (19MCD1016)
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  Introduction:  Normally windis one of the criteria for the design of the structure.  Due to the effect of the wind on structure, it may lead to the failure of the structure.
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  Nature of Windand Pressure • The variation with height depends primarily on the terrain conditions. • The magnitude of fluctuating components of the wind speed which is called gust depends on the average time.
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  Wind Effect onStructures  It was found that destruction of the cladding is often the beginning of structure failure and inhabitant injury during an extreme wind event.  Thus, for the structure’s design, along with other loads, wind load must also be considered.  When a building is subjected to wind load, then wind load has mainly two components: 1. drag force 2. lift force (both may be positive or negative wind pressures)
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  Wind Effect onHigh Structures (Cont..) Geometry of building has a significant effect on distribution of wind pressure on surface of roof and walls of building.
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  Wind Effect onLow Rise Structures (Cont..)
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  Geometry of Buildingand Significant Effect on Low Rise Building:  Low-rise is a building that is only a few stories tall or any building that is -shorter than a high- structure, i.e. structure is below 18 - 20 meters.  Height is based on American wind code and Indian wind code, respectively(ASCE/SEI: 7-10 2010; IS 875(Part 3) : 2015 2015).  Strength requirement is a dominant factor.
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  Forces Acting onBuilding: • Lift Force: An lift force is any upward pressure applied to a structure that has the potential to raise it relative to its surroundings. Uplift forces can be a consequence of pressure from the ground below, wind, surface water, and so on. • Drag Force: 1. Drag force used to increase in surge and heave reactions. 2. The influence of the current drag is determined by the extent of the wave energy spectrum.
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  Basic Flow Direction 1.Windward: The face of the building which is located in the direction of blowing wind is called windward 2. Leeward: The face of the building which is located on the opposite side of windward side in the building is called leeward side.
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  Flow Pattern aroundBuilding: Roof Pitch at 15 degree Roof Pitch at 15 degree Roof Pitch at 15 degree
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  Pressures on Building: Positive Pressure: The positive pressure acts on the windward direction and therefore the positive pressure is pushing the building.  Negative Pressure: I. The leeward pressure is assumed as negative, as it is opposite in action in windward side. II. Hence, the negative pressure in the leeward side pulls the building.
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  Conclusion: • Wind Engineeringhas increasingly focused on the modest low rise structure, since much of the damage and financial loss associated with extreme wind events happens to these minimally engineered buildings. • A face perpendicular to the wind direction will have the higher pressure coefficients as compared to the pressure coefficients on parallel faces. • It is also noticeable that when the joint of two faces is perpendicular to the wind direction, then the whole roof surface will have low wind pressure. • When there are openings in a building, the wind pressure distribution on walls and roof are significantly affected.
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  Future Scope:
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  Thank You