Simplified identification of building anomalies with a single sensor

Assistant Professor Daiki Tajiri and Professor Shozo Kawamura of the Machine Dynamics Laboratory, Technology Department of Mechanical Engineering, Toyohashi University have developed a simple method that identifies the rigidity deterioration of a building’s columns based on only the frequency response of force measured using an inertial shaker installed on the top floor of the building. This method enables the diagnosis of abnormalities in the entire building without requiring acceleration sensors and other equipment on multiple floors, as in the case of conventional methods; in fact, it requires only force sensors. The research results are published in the international academic journal Mechanical Systems and Signal Processing.

　An important aspect in achieving Sustainable Development Goals (SDGs) Goal 11, “sustainable cities and communities” is the early identification of abnormalities in buildings. In this regard, researchers from various fields have performed assessments on the soundness of buildings.

The frequency at which a building shakes the most (resonant frequency ≈ natural frequency) is known to be associated with physical properties such as the mass of the building’s floors and the rigidity of its columns. Researchers have performed studies to identify methods for diagnosing abnormalities based on such associations. Many of these studies involve the application of forces to buildings through vibrations from the environment or actuators, as well as reading the resonant frequency from the frequency response of acceleration measured using acceleration sensors installed on multiple floors to identify the floor on which the abnormality occurred and its severity. Additionally, researchers recently proposed methods that use machine learning to identify abnormalities from the frequency response of acceleration sensors installed on a single floor. The floor on which a single acceleration sensor should be installed has been investigated both in Japan and overseas.

　Therefore, this study aimed to overcome the challenge of determining the optimal number and placement of sensors by developing a method that does not require installing acceleration sensors on every floor. This method involves shaking a building using an inertial shaker installed on the top floor of the building and identifying abnormalities using only the frequency response of the shaking force. The theoretical basis of this method is that the resonant frequency of the frequency response of the force corresponds to the natural frequency when the building and inertial shaker are regarded as a single structure, and that the anti-resonant frequency corresponds to the natural frequency when the building is regarded as the sole structure. After formulating the above relationship, the validity and applicability of this method was verified through numerical simulations and experiments using experimental models.

　Assistant Professor Daiki Tajiri of the Department of Mechanical Engineering provided the following explanation regarding the background of this study:

“Reducing the number of sensors installed in a building can avoid the costs associated with installing and incorporating sensors and prevent the prolonged maintenance. Therefore, reducing the number of sensors is expected to accelerate the introduction and operation of abnormality-diagnosis methods.

While I was exploring ways to reduce the number of sensors, I happened to be working on another research project that required identifying the frequency characteristics of a vibrator. During that experiment, I ended up focusing solely on the frequency response of force for the first time. Although this may be evident to researchers who are familiar with vibration engineering, I would like to remark that the base on which the vibrator is attached should be composed of an extremely heavy and hard metal or a similar material. However, in my ignorance, I thoughtlessly used metal plates and blocks readily available in my laboratory as the base for the vibrator and then measured the frequency response of force. I discovered that not only the vibrator’s resonant frequency, which was the original desired parameter, but also the resonant and anti-resonant frequencies appeared, and that they differed depending on the size and rigidity of the base. Thus, I decided to use them to my advantage to diagnose abnormalities in structures using only the frequency response of force.”

　This study involved experimental verification using experimental models in conjunction with simple materials and structures; additionally, the applicability of the developed method is evaluated. Future studies shall entail examining the practicality and scalability of the method when utilizing experimental models that use materials and structures similar to actual buildings, and when targeting actual buildings.

Additionally, structures such as high-rise buildings are equipped with devices that suppress vibrations, which are known as active dynamic vibration absorbers. These devices operate only when a building shakes due to earthquakes or wind. We are exploring the possibility of intentionally using these devices as vibrators for abnormality diagnosis. If they can be used in such a way, they may contribute to fulfilling SDGs Goal 12, 'responsible consumption and production.