Wind sway is a phenomenon that occurs in high-rise and pencil buildings in which wind causes the building to slowly sway sideways. This trivia explains how wind sway affects the building. In addition, examples of effective countermeasures using TMDs and AMDs will be introduced.
What is wind sway?
Many people think of earthquakes as a cause of building swaying, but wind can also cause swaying. In particular, the higher the building is, the stronger the force received from the wind, and the higher the floors, the slower and louder the shaking tends to be for a longer period of time.
In addition, there are a variety of winds blowing around the building in complex ways. As a result, the building may sway not only in the direction the wind blows, but also in a direction perpendicular to the wind or as the building twists and turns.
For this reason, the Building Standard Law stipulates that the structural safety of super high-rise buildings be verified by considering the effects of wind. It is common for skyscrapers to have wind sway countermeasures.
Does wind sway occur even in mid- to high-rise buildings?
The taller the building, the more likely it is to sway in the wind. However, wind sway can be a problem even in mid- to high-rise buildings up to about 15 stories.
Wind sway is often not considered for such mid- to high-rise buildings because of the large seismic impact. However, buildings that are built on narrow lots in urban areas need to be careful.
Effects of building wind sway
Unlike earthquakes, wind-induced shaking lasts longer. Characteristic of wind-induced shaking is that it lasts for tens of minutes to several hours.
Although the shaking is small compared to that of an earthquake, feeling the shaking for a long time can lead to anxiety and discomfort. Some people may experience symptoms similar to motion sickness.
During storms, social networking sites show posts about buildings shaking and anxiety.
Livability and comfort required for hotels and offices
In recent years, in addition to basic performance such as seismic safety and functional maintenance, buildings are also required to be comfortable and habitable.
Especially in high-grade, medium- and high-rise office buildings and hotels, "safety" is a natural prerequisite. On top of that, how well the building can provide a space where people can feel safe and secure without feeling any shaking will greatly affect the evaluation of the building.
In fact, if word of mouth or social networking posts spread from hotel guests that they were shaken and anxious or could not sleep, it would seriously affect the brand image and attract customers.
As a result, more and more mid- and high-rise buildings are actively introducing habitability measures to reduce wind sway.
Wind sway control for buildings
Here are some of the main wind sway measures.
First of all, the basic(1) How to increase rigidityIt is. Make pillars and other structures thicker and sturdier to prevent swaying.
next(2) Countermeasures with vibration (seismic) dampersThe following is a list of the types of bracing materials that are used. Bracing materials incorporating oil dampers, etc., are installed on walls and other surfaces to absorb the swaying of the shaft assembly by the damping force of the dampers.
Finally.(iii) Measures to be taken by mass damperIt is. Available in TMD and AMD. For more information on the features of each type of vibration control device, please click here.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 area inside the building. The mass damper in (3) is simply installed on the roof, so it has the advantage of making effective use of the space inside the building. In addition, the compact size of AMDs makes it possible to address problems that arise after the building is completed.
Example of wind sway countermeasure
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. However, the building is long and narrow, and wind sway was a concern.
First, wind speeds for a reproduction period of one year (the maximum wind speed that can occur in one year) are set based on the Building Load Guidelines. Next, simulations were performed, and a preliminary evaluation was conducted using the "Occupant Performance Evaluation Criteria" of the Architectural Institute of Japan.
The result was an evaluation at the H-V level: "Most people perceive it and do not feel much anxiety or discomfort. Therefore, we set the target value at the H-III level, "Most people do not perceive it, and do not feel uneasy or uncomfortable at all," and studied the TMD vibration control device.
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 effective.
Please see more examples of wind sway countermeasures on the Construction Results page. Please take a look at them as well!
