Wind shakes the building.
Many people think of earthquakes as a cause of building sway, but wind can also cause buildings to sway. Especially the taller the building, the more
- Stronger force received from the wind,
- Slow, loud shaking tends to last longer on higher floors.
In addition, various winds blow around the building in complex directions, not only in the direction in which the wind blows, but also perpendicular to the wind and the building may sway in a twisting manner.
For these reasons, the Building Standard Law stipulates that the structural safety of super high-rise buildings be verified by taking into account the effects of wind, and wind sway countermeasures are commonly used in super high-rise buildings.
Wind sway occurs even in mid- and high-rise buildings.
The taller the building, the more likely it is to sway in the wind, but wind sway can be a problem even in mid- to high-rise buildings of up to about 15 stories.
Wind sway is often not considered for such mid- to high-rise buildings because the effect of earthquakes is more significant than wind sway. However, buildings built on narrow lots in urban areas are often slender and slender, and are susceptible to wind sway in the same way that skyscrapers are.
Effects of building wind sway
Unlike earthquakes, wind is characterized by shaking that lasts for tens of minutes or hours. Although the shaking is small compared to that of an earthquake, feeling the shaking for a long time can have adverse effects such as anxiety and motion sickness-like symptoms.
In fact, when we examine posts on social networking sites during typhoons, we can see posts about anxiety and feeling sick due to the shaking of buildings caused by the storm.
Livability and comfort required for hotels and offices
In recent years, buildings are required not only to maintain a high level of safety and functionality against earthquakes, but also to provide a more comfortable living environment.
In addition, high-grade, medium- and high-rise office buildings and hotels with high livability, comfort, and design quality are attracting attention these days. In such buildings, where habitability in addition to safety determines a major part of the building performance, this type of demand is strong.
Hotels, in particular, can suffer a great deal of damage if they receive low ratings in reviews on social networking and word-of-mouth sites because of wind shaking.
Therefore, more and more mid- and high-rise buildings are considering occupant comfort due to wind sway and implementing countermeasures.
Wind sway control for buildings
Here are some of the main wind sway countermeasures. The first basic method is to increase rigidity. The first basic method is to increase the rigidity of the structure by thickening the pillars and other parts of the structure.
Next is (2) countermeasures using vibration control (seismic) dampers. Bracing materials incorporating oil dampers, etc., are installed on walls and other surfaces to absorb the shaking of the shaft assembly by the damping force of the dampers.
Finally, (3) measures by mass damper. The reaction force of the weight is used to absorb building sway. There are two types of mass dampers: TMDs, which use weights adjusted to the natural period of the building to absorb sway, and AMDs, which use weights that are powered to actively absorb sway.
See also here for the features of each of the vibration control devices.Introduction to Vibration Damping (3) - Vibration Damping (Seismic) Devices This and That
When trying to prevent wind sway in a long, narrow pencil building on a narrow site, methods (1) and (2) may result in a decrease in the effective floor space inside the building. The mass damper in (3) is simply installed on the roof, so it has the advantage of effectively utilizing the space inside the building. In addition, the compact size of AMDs makes it possible to address problems that arise after building construction is completed.
Actual examples of building wind sway countermeasures using vibration control devices
Here is an actual example of Yacmo's use of a vibration control system to prevent wind sway.
The building was designed to accommodate guest rooms for hotel use, so occupant performance was required. The building is long and narrow, and wind swaying was a concern.
First, wind speeds for a reproduction period of one year (the maximum wind speed that can occur in one year) were set based on the Building Load Guidelines, simulations were performed, and preliminary evaluations were conducted using the Building Research Institute of Japan's “Occupant Performance Guidelines.
As a result, the evaluation was H-V level “most people perceive and do not feel much anxiety or discomfort,” and the vibration control device TMD was examined with the target value set at the H-III level, which is not perceived by most people.
Two 7.5-ton TMDs were installed on the rooftop, and a vibration test was conducted using human-powered excitation (horizontal step). Vibration acceleration was reduced to about 1/2~1/3, indicating that the TMDs are fully effective.
Please see more examples of wind sway countermeasures on the Construction Results page. Please take a look at them as well!
