05-Summary And Interpretation Of Terminology Definitions In Clause 3.1 Of EN 15129:2018

As the core European standard in the field of anti-seismic devices, EN 15129:2018 includes Clause 3.1 ("Terms and Definitions"), which establishes a unified technical language system for this domain. This clause not only defines the core concept of "anti-seismic device" but also specifies 51 key terms covering device performance, types, system composition, and design parameters. It provides precise technical references for the design, production, testing, and application of anti-seismic devices. The following is a comprehensive overview of the key points of this clause, organized by core classification summaries and overall value interpretation.

1. Anti-seismic device: The core definition of the clause, referring to a device intended to be integrated into a structure to modify the structure's response to seismic actions by absorbing, dissipating, isolating, or redirecting seismic forces. It must meet performance requirements in both seismic and non-seismic design scenarios and possess the function of enhancing the structure's resilience. This term serves as the logical starting point for all related terminology.
2. Device: A broad-category definition encompassing all components that modify a structure's seismic response through isolating the structure, dissipating energy, or forming permanent/temporary constraints via rigid connections. It delineates the scope for subsequent classification of device types.
3. Connection to the structure: Refers to mechanical components (e.g., anchors, pins) that secure the device interface to the structure or foundation. These components must be capable of transmitting forces generated by the device and preventing relative displacement, acting as critical links for the coordinated operation of the device and the structure.

1, Displacement-related parameters

• Design displacement(d_bd): The total displacement of the device caused by translation and rotation around the vertical axis of the isolation system when the structure is subjected solely to design seismic actions. It serves as the basic displacement benchmark for device performance design.
• Design displacement of the isolation system (d_cd): The horizontal displacement of the isolation system at the center of effective stiffness in the main direction under design seismic actions, reflecting the overall displacement response of the isolation system.
• Maximum displacement (d_Ed ): For anti-seismic devices in bridges, this refers to the maximum total horizontal displacement (including all action effects and a reliability factor adjustment to d_bd; for other structures, it is d_bd amplified by a reliability factor. It represents the upper limit indicator for device displacement design.

2,  Force and stiffness-related parameters

• Design force(V_bd): The force or moment corresponding to the device's design displacement d_bd, serving as the core benchmark for the design of the device's load-bearing performance.
• Effective stiffness(K_eff,b): The ratio of the total horizontal force transmitted by the device to the component of the design displacement in the main direction (secant stiffness). It is used to simplify the characterization of the device's mechanical behavior but can only be applied to structural response calculations if the structure is analyzed linearly and all devices have consistent damping and stiffness.
• First branch stiffness(K₁): The secant stiffness of a nonlinear device (NLD) within the range of 0.1V_bd to 0.2 V_bd. Linear devices (LDs) use the same method for stiffness calculation. This parameter reflects the stiffness characteristics of the device in the initial stage.
• Second branch stiffness (K₂): The secant stiffness within the range of 0.5d_bd to d_bd based on a theoretical bilinear cycle, representing the stiffness change of the device in the large-displacement stage.

3． Energy and damping-related parameters

• Effective damping ratio(ε_eff,b): The equivalent viscous damping value of the device during cyclic response at the design displacement, calculated based on the energy dissipated in the third loading cycle. It is used to simplify the characterization of the device's energy dissipation capacity, but limitations in its application to structural analysis should also be noted.
• Ductility demand: Expressed as d_bd/d₁ (where d₁ is the displacement at the intersection of the two stiffness lines in the theoretical bilinear cycle) based on the theoretical bilinear cycle. It is a key parameter for evaluating the plastic demand of energy-dissipating devices (EDDs) based on material hysteresis.
• Energy dissipation capacity: The ability of the device to dissipate energy during load-displacement cycles, serving as the core performance indicator for energy-dissipating devices.

1, Classification by mechanical behavior

1), Linear device (LD): Exhibits a linear or near-linear load-displacement relationship within the range of d_bd. It has good cyclic stability, minimal velocity dependence, and no residual displacement after unloading (or residual displacement < 2% of the maximum displacement), e.g., some elastic support devices.

2). Nonlinear device (NLD): Exhibits a nonlinear load-displacement relationship, with satisfactory cyclic stability and minimal velocity dependence. It is classified as such if it meets either of the following conditions: "effective damping ratio > 15%" or " (K_eff,b-K₁)/K₁ > 20%". It is further subdivided into:

• a).Energy-dissipating device (EDD): Possesses strong energy dissipation capacity (effective damping ratio > 15%) and typically has significant residual displacement after unloading, e.g., fluid viscous dampers.
• b).Nonlinear elastic device (NLED): Stores much more elastic energy than the energy dissipated during the loading stage (effective damping ratio < 15%, but stiffness difference ratio > 20%), e.g., some nonlinear spring devices.

3). Hardening device (HD): A type of nonlinear device where both the effective stiffness K_eff,b and the second branch stiffness K₂ are greater than the first branch stiffness K₁. Its stiffness increases with displacement.

4). Softening device (SD): A type of nonlinear device where both the effective stiffness K_eff,b and the second branch stiffness K₂ are less than the first branch stiffness K₁. Its stiffness decreases with displacement.

2, Classification by function and principle

1).Isolator: Possesses core characteristics required for seismic isolation, capable of bearing the gravitational load of the superstructure and adapting to horizontal displacement. Some isolators also have energy dissipation and self-centering capabilities, serving as core components of the isolation system, e.g., rubber isolators, curved surface sliding isolators.

2).Fluid viscous damper (FVD): Its output axial force depends solely on the applied velocity. It achieves energy dissipation through the reaction force generated by viscous fluid flowing through orifices/valves, making it a typical velocity-dependent energy-dissipating device.

3).Fluid spring damper (FSD): Its output axial force depends on both the applied velocity and displacement. It combines fluid viscous energy dissipation with the progressive compression effect of a spring, featuring both energy dissipation and stiffness adjustment functions.

4).Fusible restraint device (FR): Restricts the relative movement of connected components when the load is below a preset force threshold (breakthrough force) and allows movement when the threshold is exceeded. It is further classified by principle as:

a).Hydraulic fusible restraint device (HFR): A restraint device that achieves the fusible function through the opening of a relief valve based on hydraulic principles.

b).Mechanical fusible restraint device (MFR): A restraint device that achieves the fusible function through the fracture of a sacrificial component.

5). Connection-type devices:

• a).Permanent connection device (PCD): Provides stable restraint in one or two horizontal directions, capable of adapting to rotation and vertical displacement without transmitting bending moments or vertical loads. It is divided into movable connection devices (with restraint in one direction) and fixed connection devices (with restraint in two directions).
• b).Rigid connection device (RCD): Connects two structural elements without transmitting bending moments or vertical loads, encompassing permanent connection devices, fusible restraint devices, and temporary connection devices.
• c).Temporary connection device (TCD): Its output force depends on the applied velocity. It provides the required reaction force when dynamically activated and minimal reaction force during slow movement, used in temporary seismic restraint scenarios.
• d).Shock transmission unit (STU): Its output force depends on the applied velocity. It provides a high-stiffness dynamic connection through the reaction force generated by viscous fluid flowing through orifices, with negligible reaction force under low-velocity loads. It is used in specific shock load transmission scenarios.

6). Self-centering devices:

a).Static self-centering device (StRD): A type of energy-dissipating device whose load-displacement curve in the third cycle passes through or is close to the origin of coordinates (distance ≤ 0.1d_bd), possessing basic self-centering capability.

b).Supplemental self-centering device (SRCD): Its load-displacement curve in the third cycle passes through or is close to the origin of coordinates, and it provides a force of at least 0.1V_bd during small-displacement unloading (0.1d_bd). It is used to counteract the effects of non-conservative forces and provide overall self-centering capability for the structural system.

1. Isolation system: A collection of devices used to achieve seismic isolation, serving as the integral unit for structural isolation design.
2. Isolation interface: In seismic isolation design, the interface that separates the substructure from the superstructure and accommodates the isolation system. It acts as the installation and functional carrier of the isolation system.
3. Substructure: The part of the structure below the isolation interface that is anchored to the foundation. It bears and transmits the load of the superstructure to the foundation.
4. Superstructure: The part of the structure above the isolation interface that is isolated from seismic actions. It experiences reduced seismic effects through the isolation system.
5. Core element: The key component of a linear or nonlinear device that determines its mechanical behavior, providing core characteristics such as flexibility, energy dissipation, and self-centering capability, e.g., steel plates, shape memory alloy wires, rubber components.
6. Factory production control (FPC): A permanent internal production control implemented by manufacturing facilities in accordance with relevant harmonized technical specifications, with documented records. It ensures consistency and compliance in the production process of anti-seismic devices.
7. Product range: A group of products manufactured by the same manufacturer, for which the type test results of one or more characteristics are valid for all products within the range. It simplifies the product certification process.
8. Product-type: A collection of products manufactured using specific raw material combinations and production processes, representing a specific performance level or grade, based on the key characteristics of construction products. It serves as the basis for product standardization and classification management.
9. Service life of a device: The period during which the device is expected to operate normally within specified parameters. It is based on the manufacturer's declaration and specified in the project's technical specifications, providing a basis for device maintenance and replacement planning.

The terminology definitions in Clause 3.1 of EN 15129:2018 are not an isolated list of concepts but form a logically rigorous technical language system covering the entire life cycle of anti-seismic devices. Its value is mainly reflected in the following three aspects:

Research, design, production, and regulatory institutions related to anti-seismic devices are distributed across different countries in Europe. By precisely defining the connotation and extension of terms, this clause provides a unified benchmark for cross-regional and cross-entity technical communication. For example, the quantitative criteria (damping ratio, stiffness difference ratio) for distinguishing between "linear devices" and "nonlinear devices" avoid confusion in device classification caused by subjective judgment; the clear calculation methods for parameters such as "effective stiffness" and "design displacement" ensure the comparability of device performance evaluation results across different institutions, removing language barriers for technical collaboration and trade circulation in the pan-European market.

The terminology definitions in the clause run through the entire process of device design, production, and application, providing clear technical guidance. In the design phase, "design displacement d_bd" and "design force V_bd" provide benchmarks for setting device performance parameters, while "ductility demand" and "effective damping ratio" guide the plastic design and energy dissipation capacity verification of energy-dissipating devices. In the production phase, definitions such as "factory production control (FPC)" and "product range" standardize production process management and product certification logic. In the application phase, the definition of "isolation system" and "isolation interface" clarifies the positioning of devices in the structure and requirements for system integration, while the definition of "service life" provides a time-based reference for later maintenance. Additionally, the clause repeatedly references standards such as EN 1990 (Basic of Structural Design) and EN 1998 (Seismic Design of Buildings), further ensuring the compliance alignment between anti-seismic device design and overall structural design.

The terminology definitions in the clause balance "precision" and "inclusiveness," reserving space for technological innovation in anti-seismic devices. For example, the definition of "anti-seismic device" focuses on "function (modifying seismic response)" rather than specifying specific structures or principles, allowing emerging technologies such as shape memory alloy devices and smart dampers to be naturally incorporated into the standard framework. The classification criteria for "nonlinear devices" adopt quantitative indicators (damping ratio, stiffness difference ratio) instead of listing specific types, avoiding obsolescence of the terminology system due to technological iteration. This "function-oriented + quantitative definition" approach not only ensures the standardization of current technology applications but also provides a flexible adaptation framework for future technological development.

The terminology definition system in Clause 3.1 of EN 15129:2018 serves as the cornerstone of technical standardization in the field of European anti-seismic devices. Through clear classification, precise quantification, and rigorous logic, it transforms the full-chain technical elements of anti-seismic devices-from concept to application-into operable and verifiable linguistic symbols. It not only provides a unified technical communication tool for engineers, manufacturers, and regulatory institutions but also fundamentally ensures the performance reliability of anti-seismic devices and the safety of structural applications. For practitioners engaged in seismic engineering, a deep understanding of the connotation of the terms in this clause is a key prerequisite for mastering the core content of EN 15129:2018 and promoting the standardized application and innovative development of anti-seismic device technology.