Earthquake early warning-enabled smart base isolation system

https://doi.org/10.1016/j.autcon.2020.103203Get rights and content

Highlights

  • An innovative base-isolation system which mitigates seismic-risks to buildings.

  • Connectivity to Earthquake Early Warning system

  • Mechanical system lock or unlock base isolation system

  • Backup sensors to trigger base isolation.

  • Laboratory-scaled shake table tests verification

Abstract

Recent deployments of Earthquake Early Warning (EEW) system in Japan and some other earthquake-prone regions provide the vital warning signals prior to the arrival of destructive ground motions. The EEW system uses the different traveling speed of seismic P- and S-waves to achieve the goal of earthquake warning. This technology is primarily used to produce warning signals to alert the public to avoid potential risks, such as to evacuate from buildings. It is also used to mitigate other risks such as reducing train speed of Shinkansen trains. The present study suggests a new seismic-risk mitigation technique by connecting a base isolation system with the EEW. Base isolation is a mature technology which decouples structure from its base and lengthens its natural period of vibration. However, existing base isolation devices must possess certain lateral resistance to withstand service lateral forces such as wind, and such stiffness hinders the effectiveness of vibration isolation. In addition, supplementary damping devices are sometimes added to control excessive displacements in isolation level. This paper proposes a smart system which changes the property of a base isolation system upon EEW signal. In normal times when earthquake risk is not present, the base isolation system is locked by shear keys. When an earthquake is signalled by the EEW system, a mechanical system releases the base isolation system. When the earthquake ceases, the system resets and base isolation is locked again. On-board vibration sensors are added to activate the system in case of EEW fails to detect incoming waves. A crucial benefit of the system is that supplementary damper is no longer required to control excessive isolator displacements, and elastic stiffness of base isolation is no longer required to re-enter the base isolation system. The result is that it maximizes the vibration isolation effectiveness. A conceptual framework of proposed system is described and demonstrated by laboratory-scaled experiments. A 6-storey test frame is excited on a shake table subjected to historical earthquakes. Results indicates that the proposed system is effective in reducing earthquake responses on the building. It is an IoT-enabled earthquake-risk mitigation system.

Introduction

Earthquakes are constant threats to human civilization. In the last few decades, with the deployment of seismometers in many parts of the world, we are now able to detect tremors around the globe, including those in remote areas and seafloors. Government agencies such as the United State Geological Survey (USGS) and Japan Meteorological Agency (JMA) publish real-time or near real-time earthquake information. However, prediction of earthquakes is still difficult, and large earthquakes in areas near populous urban areas continue to cause enormous damages and casualties. Recent earthquakes such as the 2008 Sichuan Earthquake, the 2011 Tohoku Earthquake and 2015 Nepal Earthquake caused a large number of lives and widespread destructions. Continual efforts have been made to mitigate seismic risks. Recently, the Earthquake Early Warning (EEW) System has been developed and deployed. The principle of EEW is based on the characteristics that the seismic P-Wave travels 1.73 to 1.85 times faster than the more destructive S-wave [1]. When P-wave is detected, the approximate location of the epicentre is estimated, and a warning signal is broadcasted to the affected areas prior to the arrival of the S-wave. The principle of EEW is presented in Fig. 1. Japan is the first nation in the world to offer nation-wide EEW to the public in 2007. Estimated seismic intensity [2] are broadcasted. Earthquake warning is broadcast through television, radio, mobile networks, the Internet and specific EEW-enabled devices. Similar warning systems are now available in Taiwan, parts of China and many other earthquake-prone regions of the world. In Japan, EEW provides earthquake warnings in the order of seconds, providing reaction time to mitigate larger earthquake disasters such as shutting down certain industrial operations, reducing train speed and evacuating personnel [3]. For areas close to the epicentre, there will be insufficient time to send out warning signal due to operational delays and this area is called the blind zone. The current blind zone of EEW is about 50–70 km2 [4].

The possibilities offered by EEW system may not be limited to the issue of warning signals. In highly urbanized areas, the time required to evacuate an entire building such as a high-rise structure is much longer than the time provided by the EEW. In contrast, the activation of certain mechanisms appears to be feasible to mitigate seismic risks in some industrial processes and to enhance the protection of critical systems. This paper presents an investigation into an EEW-enabled smart base isolation system. The proposed system consisted of a base isolation that can be disabled or enabled by locking or releasing movable components. Compared to traditional passive base isolation systems, the proposed system has the following key features:

  • (1)

    When the base isolation system is disabled by a locking mechanism, the main structure possesses high lateral-force resistance and prevents excessive wind-induced displacements;

  • (2)

    The base isolation system is designed with minimal friction and no supplemental stiffness or damping. It maximizes performance when the structure is subjected to horizontal ground motions; and

  • (3)

    After ground motion ceases, actuators re-centre the main structure to its initial position and re-engages the shear keys to lock the base isolation, and

  • (4)

    The system is fully-automated and repeatable.

In a previous study, the authors investigated into a one-dimensional base-isolation system using EEW [5]. The previous design used electromagnetic switches to facilitate rapid deployment of base isolation. This paper presents a design which is a successor to the previous design that it is a two-dimensional base isolation system and it uses linear actuators instead of electromagnetic switches. This paper first presents the current state-of-the practice of base isolation, particularly focuses in the use of cross-linear bearings (CLBs) in Japan. It is followed by a numerical study into the effect of using supplementary damping devices in conjunction with CLB systems. The paper then describes the conceptual design of the proposed EEW-enabled smart base isolation system. A laboratory-scale experimental verification using a shake table is presented.

Section snippets

General descriptions

In the last few decades, there has been a massive growth for development of earthquake-resistant structures and their associated technologies. Supplemental energy dissipating devices such as viscous fluid dampers, friction dampers, metallic yielding dampers; buckling-restrained-braces, etc. have been commercially available and widely applied worldwide. On the other hand, base-isolation is regarded as one of the most mature technologies. Isolation devices are typically positioned at the base of

General descriptions

The proposed EEW-enabled base isolation system is a combination of a passive isolation system, EEW connectivity, sensors, shear keys and actuators. Fig. 7 shows a schematic diagram of the proposed system. A structure is supported on low-friction cross-linear bearings which permits the main structure to decouple from horizontal ground shaking. However, the base isolation system is locked against movement by horizontal shear keys. The shear keys unlock the base isolation under three conditions:

Experimental setup and instrumentations

A lightweight 6-level test model made of acrylic plastic and aluminium strips is used in the experimental investigation. Columns are made of 4 mm thick clear acrylic plastic strips. Floor plates are made of 3 mm thick timber boards and they are connected to columns via aluminium brackets and steel bolts. Steel masses are positioned centrally on each floor and the total mass of the model frame is 7.5 kg (excluding base plate and base isolation rails). The first three natural frequencies when the

Conclusion

The deployment of Earthquake Early Warning (EEW) system in Japan and other earthquake-prone regions in the world open new opportunities of seismic-risk mitigation for structures. EEW systems are capable of detecting fast traveling earthquake P-waves and send warning signals to the public prior to the arrival of more destructive S-waves. This paper proposes a smart base-isolation system which is connected to the EEW system. The system consists of a microcontroller which is programmed to

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (22)

  • Yoshioka, H., Ramallo, J., and Spencer Jr, B., “Smart” base isolation strategies employing magnetorheological dampers....
  • Cited by (11)

    • Structural health monitoring of civil engineering structures by using the internet of things: A review

      2022, Journal of Building Engineering
      Citation Excerpt :

      IoT-based SHM can be used to capture crucial parameters that directly or indirectly affect the health status of civil engineering structures in other applications. Lin et al. [143] connected a base isolation system with the IoT to allow an earthquake warning system to modify the properties and the effectiveness of a base isolation system which can be locked by employing shear keys in absence of an earthquake event (i.e., in the standby mode) and retractable shear keys in the activated mode. The working of the aforementioned technology is based on the differences in the traveling speeds of P and S waves, and it provides an early earthquake warning.

    • Isolation performance of a small modular reactor using 1D periodic foundation

      2021, Engineering Structures
      Citation Excerpt :

      In the past few decades, passive seismic control systems have been proposed and implemented to protect structures from the damage of earthquakes [5–7]. As a common passive vibration isolation system, the base isolation system is formed by installing isolation devices between the superstructure and the foundation, which has been proved to be an effective technique in practical engineering [8–11]. The traditional base isolation systems mitigate the dynamic response by reducing the structural stiffness and increasing the natural vibration period of the structure to avoid the phenomenon of resonance [12–15].

    • Evaluating Retrofitting Strategies of Low-to-Mid-Rise Reinforced Concrete Structure Based on Its Seismic Fragility

      2023, International Journal on Advanced Science, Engineering and Information Technology
    View all citing articles on Scopus
    View full text