Various "vibrations" occur around us and affect the comfort and livability of our lives. This trivia will explain the classification of vibration sources and their characteristics.
Classification of vibration sources
The causes of vibrations that occur around us fall into two main categories.
- Natural Vibration SourceVibration caused by natural phenomena such as strong winds and long-period seismic motions.
- Artificial Vibration SourceVibration: Vibration caused by human activity, divided into "internal artificial vibration sources" and "external artificial vibration sources".
Natural Vibration Source
- unsewn part of a hanging sleeve on a traditional Japanese woman's garment: A phenomenon that is particularly problematic in high-rise buildings. Fluctuations in wind speed and direction and the generation of vortices cause slow, large shaking that lasts for a long time.(Wind shakes the building? How to achieve comfortable occupancy?)
- Earthquake (long-period seismic motion)The characteristics of the shaking are different depending on the periodic component. In earthquakes occurring in remote areas, the short-period component (short and small tremors) weakens and the tremors become smaller, while the long-period component does not weaken and travels through the ground, causing high-rise buildings (especially high-rise floors) to shake slowly and significantly.
Artificial Vibration Source
Internal Artificial Vibration Source
[human movement].
It is caused by human movement, such as walking or exercise.
The excitation force (stepping force) when walking is not that great. However, the excitation force has a rhythm (period) of walking. When the periodic component of 1 to 5 times the walking tempo approaches the period at which the floor tends to sway, the floor will sway greatly (resonance) There are times when the
Resonance is likely to occur under the following conditions
- Floor with long span (distance between floor supports)
- Lightweight floor structure
- Steel-framed buildings (it takes longer for the shaking to subside than RC or wooden buildings)
When these conditions combine, even small forces can cause significant shaking and affect occupant comfort.
In aerobics, fitness, and other situations where multiple people are jumping and bending to a tempo, the excitation force itself also increases. As a result, when the period of excitation matches the period of the floor, resonance increases, and the shaking can be transmitted to the floor above, below, or even several floors away, which can be problematic.
Equipment
Equipment in buildings includes elevators, mechanical parking garages, air conditioning equipment, water supply and drainage equipment, and boiler equipment. Vibration is generated by the rotation and reciprocating motion of these equipment. Vibrations may also be caused by water flow or air currents inside machinery.
These vibrations are not only felt as shaking, but can also be heard as sound (solid sound) transmitted through walls, ceilings, floors, etc., and can become a noise problem.
External artificial vibration source
- road traffic: Vehicle type, speed, traffic volume, pavement condition, and other factors cause ground vibration.
- railroadThe following factors affect the performance of the rail: the weight and speed of the train and passengers, the wear condition of the wheels, and the condition of the rails. There are also many impact vibrations generated by rail joints, which are transmitted to the ground and building frame,solid soundgenerates a
- plant: Production machinery such as metalworking machines, compressors, and cranes generate impact and rotational vibrations from presses and motors. It affects not only the inside of the building but also the surrounding area through the ground.
References
Guidance for Environmental Vibration Design to Ensure Occupant Performance 2020.6 Architectural Institute of Japan