Terms and definitions of EN15129
3.Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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NOTE In this European Standard, compressive forces, stresses and strains are positive.
3.1.1
activation velocity
velocity at which a Temporary Connection Device (TCD) or a Shock Transmission Unit (STU) reacts with its design force
3.1.2
connection to the structure
mechanical component or system of mechanical components to fix the device interface to the structure or to the foundation
Note 1 to entry: The mechanical components should be able to transfer the forces developed in the device and to avoid any relative movement.
Note 2 to entry: Example of mechanical components:
Anchor bolts and/or pins to fix the base plate of an isolator to the concrete foundation or to the concrete or steel elements of the structure.
Anchor bolts to fix the clevis plate of the hinge of a hydraulic device to the concrete foundation or to the concrete or steel elements of the structure.
3.1.3
core element
component of a Linear Device (LD) or of a Non Linear Device (NLD) on which the mechanism characterizing the device's behaviour is based
Note 1 to entry: Core elements of a LD or of a NLD are the device's components that provide it with the flexibility and, eventually, with the energy dissipation and/or re-centring capacity or any other mechanical characteristic compatible with the requirements of a LD or of a NLD. Examples of core elements are steel plates or bars, shape memory alloy wires or bars, rubber elements.
3.1.4
design displacement
dbd
total displacement (due to both translation and rotation about the vertical axis of the isolation system) that a device will undergo when the structural system is subjected to the design seismic action alone
3.1.5
design displacement
dcd
horizontal displacement of an isolation system in a principal direction at the effective stiffness centre, occurring under the design seismic action alone
3.1.6
maximum displacement
dEd
for an anti-seismic device in a bridge dEd equals dmax, the maximum total horizontal displacement of a device in a principal direction at the location of the device including all actions effects and the application of the reliability factor to dbd
Note 1 to entry: For devices in other structures dEd equals γx dbd, the design displacement increased by the reliability factor.
3.1.7
design force
Vbd
force (or moment) corresponding to dbd
3.1.8
element which contributes to modify the seismic response of a structure by isolating it, by dissipating energy or by creating permanent or temporary restraints via rigid connections
Note 1 to entry: The devices considered are described in the various clauses of this European Standard.
3.1.9
ductility demand
displacement ductility demand referred to the theoretical bilinear cycle, and is evaluated as dbd/d1
Note 1 to entry: See 3.1.4 and 3.1.42.
Note 2 to entry: The ductility demand is a useful parameter to evaluate the plastic demand of an EDD based on material hysteresis (see 3.1.17).
3.1.10
effective damping ratio
ξeff,b
value of the effective viscous damping, corresponding to the energy dissipated by the device during cyclic response at the total design displacement:
ξeff,b = H(dbd) /(2π Vbd dbd) (1)
where
|
H(dbd) |
is the energy dissipated by a device during the 3rd load cycle at design displacement dbd |
Note 1 to entry: ξeff,b is introduced for a simple characterization of the behaviour of any device. It cannot be used in the analytical calculations of the response of the structural system, unless they can be carried out by linear
analysis and all the devices have the same damping and stiffness in the given direction. Where different devices are used, reference is made to the overall effective damping of the isolation system.
3.1.11
effective period
Teff
period of a single degree of freedom system moving in the direction considered, having the mass of the superstructure and the stiffness equal to the effective stiffness of the isolation system
3.1.12
effective radius
Reff
radius of simple pendulum with same natural frequency as the curved surface slider under consideration
3.1.13
effective stiffness
Keff,b
ratio between the value of the total horizontal force transferred through the device and the component of the total design displacement of a device in a principal direction in the same direction, divided by the absolute value of the total design displacement (secant stiffness)
Keff,b = Vbd /dbd (2)
Note 1 to entry: Keff,b is introduced for a simple characterization of the behaviour of a device. It cannot be used in the analytical calculations of the response of the structural system, unless they can be carried out by linear analysis and all the devices have the same damping and stiffness in the given direction. Where different devices are used, reference is made to the overall effective stiffness of the isolation system.
3.1.14
effective stiffness
Keff
sum of the effective stiffness of the devices located at the isolation interface of an isolation system in a principal direction
3.1.15
effective stiffness centre
stiffness centre of an isolation system, accounting for the effective stiffness of the devices
3.1.16
energy dissipation capacity
ability of a device to dissipate energy during the load-displacement cycles
3.1.17
energy dissipating device EDD
device which has a large energy dissipation capacity, i.e. which dissipates a large amount of the energy
Note 1 to entry: After unloading it normally shows a large residual displacement. A device is classified as EDD if
the effective damping ratio ξ is greater than 15 %.
3.1.18
essential characteristic
characteristic of the construction product which relates to the basic requirements for construction works
3.1.19
Factory Production Control FPC
documented, permanent and internal control of production in a manufacturing plant, in accordance with the relevant harmonized technical specifications
3.1.20
first branch stiffness
K1
initial stiffness of a NLD defined as the secant stiffness between the points corresponding to the forces 0,1 Vbd and 0,2 Vbd:
K1 = (0,2 Vbd – 0,1 Vbd) /[d(0,2 Vbd) - d(0,1 Vbd)] (3)
where
|
d(0,2 Vbd) |
is the displacement corresponding to 0,2 Vbd; |
|
d(0,1 Vbd) |
is the displacement corresponding to 0,1 Vbd. |
Note 1 to entry: K1 is referred to as initial or elastic stiffness when dealing with softening devices.
3.1.21
anti-seismic device whose output is an axial force that depends on the imposed velocity only; its principle of functioning consisting of exploiting the reaction force of a viscous fluid forced to flow through an orifice and/or valve system
3.1.22
anti-seismic device whose output is an axial force that depends on both imposed velocity and displacement; its principle of functioning consisting of exploiting the reaction force of a viscous fluid forced to flow through an orifice and/or valve system and at the same time is subjected to progressive compression
3.3.23
device that, below a certain pre-established force threshold (break-away force), prevents any relative movement between connected parts, whilst it permits movement after the aforesaid threshold has been exceeded
3.1.24
Hardening Device HD
NLD whose effective stiffness Keff,b and second branch stiffness K2 are greater than the first branch stiffness K1
3.1.25
Hydraulic Fuse Restraint HFR
SR whose behaviour is hydraulic in nature and depends upon the opening of relief valves
3.1.26
stiffness K1 of a LD
stiffness of a LD is defined as the secant stiffness between the points corresponding to the forces 0,1 Vbd and 0,2 Vbd:
K1 = (0,2 Vbd – 0,1 Vbd) /[d(0,2 Vbd) - d(0,1 Vbd)] (4)
where
|
d(0,2 Vbd) |
is the displacement corresponding to 0,2 Vbd; |
|
d(0,1 Vbd) |
is the displacement corresponding to 0,1 Vbd. |
Note 1 to entry: The evaluation of K1 as secant stiffness is justified by the difficulty of tracing the tangent to a curve at the origin in an experimentally obtained diagram.
3.1.27
collection of devices used for providing seismic isolation
3.1.28
isolation interface
in the case of seismic isolation, the surface which separates the substructure and the superstructure and where the isolation system is located
3.1.29
device possessing the characteristics needed for seismic isolation, namely, ability to support gravity load of superstructure, and ability to accommodate horizontal displacements
Note 1 to entry: Isolators may also provide energy dissipation, and contribute to the isolation system's re- centring capability.
Note 2 to entry: In EN 1998-2, isolator may also designate the devices belonging to an isolation system, whether they support gravity loads or not.
3.1.30
linear device LD
anti-seismic device which is characterized by a linear or almost linear load-displacement relationship up to the displacement dbd, with a stable behaviour under a large number of cycles and substantial independence from velocity
Note 1 to entry: After unloading, it does not show a residual displacement. Even when some energy dissipation occurs in the device, it is important that residual displacements are negligible, and in any case less than 2 % of the maximum displacement.
Note 2 to entry: For visco-elastic devices, residual displacements can be partially or totally recovered after some hours. In this case, the final residual displacement should be referred to.
Figure 1 - Initial and effective stiffness of a linear device
3.1.31
Mechanical Fuse Restraint MFR
SR whose behaviour is determined by the break-away of sacrificial components
3.1.32
Nonlinear Device NLD
anti-seismic device which is characterized by a nonlinear load-displacement relationship, with a stable behaviour under the required number of cycles and substantial independence from velocity
Note 1 to entry: A device is classified as nonlinear if either ξeff,b is greater than 15 % or the ratio | Keff,b - K1|/K1 is greater than 20 %, where ξeff,b and Keff,b are evaluated from the 3rd cycle with maximum displacement equal to dbd.
3.1.33
Nonlinear Elastic Devices NLED
NLD in which the elastically stored energy is much greater than the dissipated energy during the loading phase
Note 1 to entry: A device is classified as NLED if ξeff,b is less than 15 % while the ratio | Keff,b -K1|/K1 is greater than 20 %.
Figure 2 - Effective stiffness of a nonlinear device
3.1.34
normal force
NEd
normal force acting on an isolator in seismic design situation
Note 1 to entry: The maximum compression force is denoted NEd,max and the minimum compression force, or (if tensile normal forces occur) the maximum tension force is denoted NEd,min.
3.1.35
normal force
NSd
force acting on an isolator in the persistent or transient design situations
Note 1 to entry: NSd,ULS is the maximum compression action effect in the persistent or transient design situations at Ultimate Limit States according to EN 1990. The appropriate combination of actions to be used is given in the relevant clause of this standard.
Note 2 to entry: NSd,SLS is the compression action effect in the persistent or transient design situations at Service Limit States according to EN 1990. The appropriate combination of actions to be used is given in the relevant clause of this standard.
3.1.36
Permanent Connection Device PCD
device which provides steady restraint in one or two horizontal directions, accommodates rotations and vertical displacements, i.e. does not transmit bending moments and vertical loads
Note 1 to entry: The device which restrains the movements in one horizontal direction only is referred to as Moveable Connection Device, while the device which restrains the movements in two horizontal directions is defined as Fixed Connection Device.
Note 2 to entry: In certain circumstances, the above devices may be required to operate in a plane inclined to the horizontal axis. In such case, the terms "vertical" and "horizontal" take on the appropriate significance.
3.1.37
device which links two structural elements without transmitting bending moments and vertical loads; this category of devices includes Permanent Connection Devices (see 5.2), Fuse Restraints (see 5.3) and Temporary Connection Devices (see 5.4)
3.1.38
product range
group of products produced by one manufacturer for which the Type Test results obtained from specimen/s tested (for one or more characteristics) are valid for all other products within this range
3.1.39
product-type
set of representative performance levels or classes of a construction product, in relation to its essential characteristics, produced using a given combination of raw materials or other elements in a specific production process
3.1.40
Restoring Stiffness RS
Restoring Stiffness of the Curved Surface Slider (see 8.3)
3.1.41
second branch stiffness K2
parameter referred to the theoretical bilinear cycle and defined as (see Figure 2):
3.1.42
design approach in which appropriate mechanisms (isolation systems) are provided at a certain level of the structure to decouple the mass of the structure located above this level from the structure below this level, therefore modifying the seismic response of the structure and its contents
3.1.43
service life of a device
period over which a device is expected to perform within its specified parameters
Note 1 to entry: The value is taken as that given in Technical Specifications of the Project, based on declarations made by manufacturers.
Note 2 to entry: Additional information concerning the service life is given in informative Annex B.
3.1.44
Shock-Transmission Unit STU
device whose output is an axial force that depends on the imposed velocity; its principle of functioning consisting of exploiting the reaction force of a viscous fluid forced to flow through an orifice in order to provide a very stiff dynamic connection whilst for low velocity applied loads the reaction is negligible
3.1.45
Softening Device SD
NLD whose secant stiffness Keff,b and second branch stiffness K2 are smaller than the first branch stiffness K1
3.1.46
Statically Re-centring Device StRD
Energy Dissipating Device whose force-displacement cyclic curve at the 3rd cycle passes through or very near the origin of the force-displacement axes, at a distance not greater than 0,1 dbd
3.1.47
part of the structure which is located under the isolation interface and is anchored to the foundations
3.1.48
part of the structure which is isolated and is located above the isolation interface
3.1.49
Supplemental Re-centring Device SRCD
device whose force-displacement cyclic curve at the 3rd cycle passes through or very near the origin of the force-displacement axes and, for small displacement at unloading (0,1 dbd), provides a force which is at least 0,1 Vbd
Note 1 to entry: The supplemental force > 0,1 Vbd is meant to counteract the effect of parasitic non- conservative forces (e.g. friction in other devices, yielding in structural elements) or other energy dissipating non re-centring devices, in order to provide the entire structural system with an overall re-centring capability. The supplemental force is calibrated according to the re-centring requirements of the structural system.
3.1.50
Temporary Connecting Device TCD
anti-seismic device whose output is a force that depends on the imposed velocity; its principle of functioning consisting of a system providing for the required reaction force when dynamically activated whilst for slowly applied movements it provides a minor reaction
3.1.51
theoretical bilinear cycle of a NLD
cycle defined to identify the main mechanical characteristics of a nonlinear device through the first and second branch stiffness values and by the following parameters:
d1 = abscissa of the intersection point of the straight line starting at the origin with stiffness K1 and the straight line passing through (dbd, Vbd) with stiffness K2 in the experimental 3rd load cycle of a quasi- static test;
V1 = ordinate of the intersection point of the straight line starting at the origin with stiffness K1 and the straight line passing through (dbd, Vbd) with stiffness K2 in the experimental 3rd load cycle of a quasi- static test;
Vbd = force corresponding to dbd, obtained from the 3rd load cycle during a quasi-static test
