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Seismic Devices: Types and Benefits

Seismic devices enhance the seismic response of new or existing structures. Types, applications, and advantages.

The primary purpose of structural design is undoubtedly the seismic safety of constructions, especially if they arise in high-risk areas.

Seismic devices play a crucial role in mitigating seismic risk, as they offer additional protection to structures during an earthquake by absorbing, dissipating, or diverting seismic energy to reduce the amplitude of the stresses transmitted to the structure.

Let’s explore together how many and what types of seismic protection devices exist!

What are seismic devices and what benefits do they offer?

Seismic devices are components or systems designed to reduce the effects of an earthquake on buildings, bridges, and other structures. These devices exploit engineering principles to absorb, dissipate, or divert seismic energy, thus reducing the stresses transmitted to the structure and enhancing its resistance to seismic events (structural ductility).
There are 3 main types of seismic protection devices (seismic isolators, seismic dissipators, temporary restraint devices), each with specific characteristics and operating mechanisms.

Seismic devices offer a range of significant benefits that contribute to improving the safety and resilience of structures during an earthquake. Let’s take a closer look at these advantages:

  • Enhanced structural safety: The most obvious advantage of seismic devices is the improvement of structural safety. These devices are designed to absorb and dissipate seismic energy, thus reducing the amplitude of the stresses transmitted to the structure. This reduces the risk of structural damage and building collapse, ensuring occupant safety;
  • Damage reduction: By using seismic devices, it is possible to significantly reduce damage to structures during an earthquake. This means that buildings can better withstand seismic forces without suffering irreparable structural damage. This translates into lower repair costs and post-seismic downtime;
  • Operational continuity: Structures equipped with seismic devices are more likely to maintain their functionality during and after an earthquake. This is particularly important for critical infrastructure such as hospitals, transportation hubs, and industrial facilities, which must remain operational even in emergency situations;
  • Extension of structure lifespan: The use of seismic devices helps to extend the lifespan of structures by reducing wear and tear caused by earthquakes. This means that structures can maintain their performance over time, reducing the need for costly repairs and renovations.

What are the main seismic protection devices?

Seismic protection devices are technological systems aimed at enhancing the seismic response of a newly constructed building or improving it or adapting it in the case of an existing structure.
The different seismic isolation techniques share the fundamental principle of introducing a discontinuity along the vertical development of the structure. Introducing a discontinuity in the structure allows it to be separated into different “sections,” thus reducing the transmission of seismic actions along its vertical development.

Seismic protection techniques are divided into:

  • Passive control techniques: Devices based on this technique are installed at the base of the structure – between the foundations and the superstructure – allowing the superstructure of the building to be decoupled from the ground motion and reducing the transmission of seismic energy;
  • Active control techniques: In this case, active control is provided by electronically controlled devices that activate in the event of an earthquake exceeding a certain threshold. By activating, they apply “dynamic” seismic forces to the structure opposite to those of the earthquake, thus counteracting and minimizing oscillations;
  • Hybrid control techniques: Combines active control with passive control according to design needs.

What’s the difference between passive and active seismic devices?

In the previous section, we introduced the three main groups into which seismic protection techniques are divided. Let’s now delve into the details of how passive seismic devices differ from active ones and some concrete examples of both categories.
Active seismic devices are smart technologies that react to earthquakes by activating only when shaking exceeds a certain threshold. These devices develop a modulated force based on accelerations, counteracting and minimizing oscillations. The main characteristic that sets them apart from passive control devices is their reduced installation and maintenance costs, primarily because they do not require invasive interventions to be installed on the building. Some of them, for example, are installed on the building’s roof and perform automatic and periodic self-checks.

Passive seismic devices, on the other hand, decouple the superstructure of the building from ground motion, reducing the transmission of seismic energy. Within passive seismic devices, two main categories are identified:

  1. Seismic isolators: Applied at the base of the structure, they are characterized by high vertical stiffness and limited horizontal stiffness. A structure isolated seismically is more flexible, and consequently, the natural period of the structure shifts to higher values. The main types of seismic isolators are:
    • Elastomeric isolators;
    • Sliding isolators, including sliding pendulum ones.
earthquake-proof device

earthquake-proof device

  1. Seismic dissipators: They are tasked with dissipating absorbed seismic energy. Within this category, various types are found (viscous, hysteretic, and tuned mass);
  2. Temporary restraint devices (fuse-type or dynamic-type): These devices are used to force movements in one or more directions according to differentiated methods depending on the type and magnitude of the action. They come into operation and stop acting when earthquakes occur and stop.

Passive seismic devices and the modeling of seismically isolated structures

During the design of new structures with passive seismic devices, it is essential to consider several critical factors to ensure the effectiveness and safety of the entire system. Below are some fundamental considerations to take into account:

  • Type and characteristics of seismic devices: The choice of type depends on the specific characteristics of the structure, including its shape, mass, height, and geographical location;
  • Integration with other structural elements: Seismic devices must be harmoniously integrated with other structural elements of the building, such as beams, columns, and foundations. It is important to consider the effects of the presence of seismic devices on the overall response of the structure to seismic events and ensure that there are no interferences with other structural components;
  • Structural analysis and verification: It is crucial to conduct careful structural analysis to assess the impact of the seismic dissipation system on the entire structure. In-depth checks are required to ensure that the presence of seismic devices does not compromise the structural integrity or load-bearing capacity of the building.

Structural design requires a thorough understanding of seismic dynamics, energy dissipation technologies, and industry regulations. It is essential to adopt an integrated approach that takes into account all the factors mentioned above to ensure the maximum effectiveness and safety of the seismic dissipation system.
Structural and seismic design is undoubtedly highly delicate and requires significant responsibility and knowledge, especially when carried out in high-seismic-risk areas. Seismic design requires, first and foremost, the safeguarding of human life, and for some strategic constructions such as hospitals or buildings destined for civil protection, it is necessary not only to ensure the evacuation of people but also to remain operational immediately after the earthquake.

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