Wind Load: Everything you need to know
What is Wind Load?
Any stresses or tensions that the wind transmits to a component or structure are referred to as wind loads in this context. Essentially, there are three different kinds of wind loads that could be applied to a building. Uplift, shear and lateral wind load. Even standard building designs must take wind loads into account. Especially, if located in some areas with significant wind forces such as coastal areas. When designing structures to effectively avoid these effects, wind analysis is utilized to evaluate the dynamic effects of wind on a structure.
Wind load is the effect of wind on buildings, structures and other objects. It is caused by wind pressure, air speed and wind velocity. Wind pressure is the overall force applied upon a structure by wind. In case of it being a flat surface it includes two main elements, the primary being the energetic weight applied on the windward side of the surface referred to as wind load.
The strength of the wind load depends on the magnitude of the wind speed. Wind loads are measured in pounds per square foot (PSF) and pound per square inch (psi).
In order to prevent structural collapse, the building’s structural design must securely and efficiently absorb wind forces and convey them to the foundations.
How does Wind Load affect a building?
The size and shape of the structure determines how the wind will affect it. For the design and construction of buildings that are safer and more wind-resistant, as well as the positioning of items like antennae on top of buildings, wind load calculations are required.
The strongest forces are applied to a structure during extreme weather, such as hurricanes, tornadoes, and thunderstorms with straight-line winds. These conditions also increase the risk of implosions because of the wildly fluctuating pressure levels. The building might be affected by even “normal” gusts of wind because of the local topography and typical weather patterns.
Also, for tall, wide span and slender structures, structural dynamic analysis is essential. Wind gusts cause fluctuating forces on structures and cause large dynamic movements, including vibration.
Skyscrapers and high-rise buildings are becoming increasingly complex in their overall design and size. This increases the risk of wind effects and structurally induced forces. Architectural and design engineers must use wind engineering research to ensure safe, sustainable and cost-effective construction. These studies are now an industry standard and are conducted to first assess the dynamic effects of wind on structures and then optimize designs to mitigate those effects.
Wind load if not calculated correctly can cause further damage and lead to very dangerous accidents.
The force of the wind can cause various types of effects depending on its direction and strength. Therefore it is important for architects, builders and engineers to take into consideration these factors.
Wind load if calculated correctly may sometimes influence a change in design to ensure safety. Many architects and clients dream about designs but aren’t knowledgeable in the dangers of such designs. Which is why engineers must take wind load calculations very seriously and meticulously. Wind pressures that reach high levels can cause damage. Such as tearing down windows and doors, breaking off roofing, and destroyig walls. Busted windows, broken doors and missing roofs can become a huge issue. As t now exposes the interior of the building to wind and water from entering
Types of Wind Load Forces
The three main types of wind load forces are uplift load, shear load, and lateral load. The main difference between these loads is the direction that the wind load is enforcing on a structure, we will explain below in more depth. Wind load is a dynamic load as it is a live load, on the other hand static loads are dead loads. Dynamic loads are defined as such because they are known to make changes in direction, size or force. On the contrary, static loads are called this because they are not known to change.
Uplift Wind Load
Uplift wind load can be described as the pressure of wind currents that creates a strong lift effect, similar to that of an airplane wing. The wind flow under the roof will push you up. The wind flow on the roof is upward. Wind uplift occurs when the air pressure under the roof is greater than the air pressure above it. This can be exacerbated during high wind, as air infiltration into the building can increase pressure below the roof, whilst the speed of the wind over the roof surface can reduce air pressure above it, in much the same way it does over an aircraft wing. This can cause damage to the roof if the difference in pressure becomes too great.
All roofs are subject to wind uplift, which will vary according to location, terrain, height, size, shape, exposure and so on. For instance, this can result in problems with roofing, as the wind blows over the roof, the air pressure just above the roof is reduced. this is called negative pressure. ongoing, the wind also creates leaks of air that escape through the cracks or small openings, which forms a positive pressure. the negative pressure from above and the positive pressure from below combined form a push-pull force which rips the roofing material from the roof.
Shear Wind Load
Shear wind load expresses the quantity of horizontal force that a structure can withstand. It is the horizontal pressure or force that can cause walls or vertical structural members to tilt or fail, causing a building to lean over. This measure is crucial as this accounts for how much wind load a building/structure can hold before the structure begins inclining to either side. This eventually can lead to a building/ structure collapsing if the shear wind load is not taken into account.
Lateral Wind Load
The extent of force applied that a structure could endure before being forced off of its foundation is defined as the lateral wind load. This could lead a structure to topple over or fall off its base, by causing stress horizontally with a pushing and pulling motion. The geography, building elements, size, and the structure’s shape all influence the severity of most lateral wind loads. One structure with a construction built to withstand a significant wind load is the Eiffel Tower. Due to its height and infrastructure, this was necessary.
How to calculate Wind Load?
Although you can use a simple formula to calculate wind loads from wind speed, building designers, engineers and constructors must incorporate many additional calculations to ensure their structures won’t blow over in a high wind.
Wind load on a structure depends on several factors including wind velocity, surrounding terrain, and the size, shape, and dynamic response of the structure. Traditional theory assumes that horizontal wind load pressures act normally on the face of the structure. Computations for wind in all directions are calculated to find the most critical loading condition. Consideration of suction from pressure differential forces caused by wind is also typically estimated in the case of sidewalls and leeward walls. Typically, building codes allow for either calculated wind loads or wind loads determined by testing of models in a terrain
setting equivalent to that of the building site.
Determine the basic wind speed for the location of the structure. If no data is available for the site, use the following approximate values for basic wind speed in the United States:
Coastal and mountainous areas 110 mph Northern and central U.S. 90 mph. Other areas of the U.S. 80 mph
Select the category of terrain for the structure. Choose category “A” for city centers with other structures nearby over 70 feet. Pick “B” for wooded or urban areas with structures under 70 feet. Choose “C” for flat areas with obstructions under 30 feet in height. Select “D” for flat, unobstructed areas.
Use the following to find the coefficient of exposure (K) using the terrain category. For exposure “A” use .000307. In exposure “B” use .000940. For exposure “C” use .002046. For exposure group “D” use .003052.
Use the following calculation to estimate wind pressure on a structure: q = K x V^2 = coefficient of exposure x basic wind velocity c basic wind velocity. Multiply the wind pressure by 1.15 for important structures such as schools, hospitals, high-occupancy buildings, vital communication buildings, or tall or slender structures. Then multiply the wind pressure by 1.05 for buildings subject to hurricanes along the Gulf of Mexico or the Atlantic coast. Lastly, multiply the calculated wind pressure times the surface area, in square feet, of the structure exposed to wind in each specific direction. Use the largest surface area exposed to wind for the highest wind loading.
This section that details how to calculate wind load is strictly quoted from How to Calculate Wind load.
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