ISO 23618:2022

INTERNATIONAL ISO
STANDARD 23618
First edition
2022-10
Bases for design of structures —
General principles on seismically
isolated structures
Bases du calcul des constructions — Principes généraux des
constructions munies d’isolateurs parasismiques
Reference number
ISO 23618:2022(E)
© ISO 2022

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ISO 23618:2022(E)
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© ISO 2022
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ISO 23618:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms related to structure . 1
3.2 Terms related to isolation system . 2
3.3 Terms related to structural design . 3
3.4 Terms related to maintenance and construction . 3
4 Symbols and abbreviations .4
5 Basic principles of structural planning . 5
5.1 General . 5
5.2 Isolation interface . 5
5.3 Superstructure and substructure . 6
5.4 Foundation . 6
5.5 Connections of isolation devices. 6
5.6 Isolation gap . 6
5.7 Non-structural components and equipment in isolation interface . 6
6 Target performance of the seismically isolated structure . 6
6.1 General . 6
6.2 Superstructure . 6
6.3 Substructure . 7
6.4 Isolation system. 7
7 Design seismic force .7
7.1 General . 7
7.2 Design response spectrum . 7
7.3 Design earthquake ground motion . 7
8 Structural analysis . 8
8.1 General . 8
8.2 Modelling of isolation system . 8
8.3 Modelling of superstructure and substructure . 8
8.4 Response spectrum analysis method for equivalent linear system . 8
8.4.1 General . 8
8.4.2 Basic requirements . 8
8.4.3 Effective stiffness . 9
8.4.4 Effective period . 9
8.4.5 Effective damping . . 9
8.4.6 Maximum displacement of isolation system . 10
8.4.7 Seismic design forces. 10
8.5 Response history analysis method. 11
8.5.1 General . 11
8.5.2 Basic requirements . 11
8.5.3 Number of earthquake ground motions . 11
8.5.4 Upper bound and lower bound of stiffness and force .12
8.5.5 Maximum displacement of isolation system .12
8.5.6 Maximum storey drift and shear force of superstructure .12
9 Construction management specified in design documents .12
9.1 Construction planning .12
9.2 Quality control of isolation device manufacturing .12
9.3 Temporary work planning .12
9.4 Construction procedures of isolation interface .12
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ISO 23618:2022(E)
10 Maintenance specified in design documents.13
10.1 Maintenance of seismic isolation system . 13
10.2 Monitoring of system performance . 13
10.3 Warning signage .13
11 Performance requirement of isolation devices .13
11.1 Performance information of isolation devices . 13
11.2 Test of isolation devices . 13
Annex A (informative) Classification and performance characteristics of isolation devices .14
Annex B (informative) Construction management of seismically isolated structures .23
Annex C (informative) Maintenance of seismically isolated structures .29
Annex D (informative) Wind-resistant design of seismically base isolated buildings .36
Annex E (informative) Mid-storey seismically isolated buildings .41
Bibliography .46
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ISO 23618:2022(E)
Foreword
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ISO 23618:2022(E)
Introduction
Seismically isolated structures have been constructed since the 1970s. Their reduction of the seismic
action has been demonstrated in many earthquakes and the usefulness of seismic isolation has been
widely recognized. It is difficult for other seismic mitigation strategies to reduce the acceleration
acting on the structure as significantly as seismic isolation. With this feature, the seismic force on the
structure as well as foundation is dramatically reduced and the vibration perception of occupants is
greatly minimized. Seismic isolation also reduces the vibrations and disruption of building contents,
such as furniture and equipment. Since the structure can be restored to the original state without
damage, it can remain operational during and immediately after the earthquake without essential
interruption in operation. Seismic isolation technique also expands architectural design freedom by
reducing seismic force and controlling deformation of superstructure. It also minimizes rate of losses,
number of injures and improves of peace of mind of occupants against earthquakes. To mitigate future
earthquake disasters, widespread of adoption of seismic isolation is advisable.
The structural design process should ensure that the capacity of structural components exceeds the
demands imposed by the design load in order to provide both safety and serviceability. In most cases,
the load effect is treated as static. In recent years, however, when a structure with seismic isolation
devices is designed for earthquake ground motion, the dynamic performance of the entire structure is
evaluated. Therefore, it is desirable to specify the principles of dynamic seismic design of seismically
isolated structures. In this document, the items to be considered in the design, and design procedures
are described. Then the standard structural calculation procedure is shown, and the methods for
construction management and maintenance unique to the seismically isolated structure are also
described.
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INTERNATIONAL STANDARD ISO 23618:2022(E)
Bases for design of structures — General principles on
seismically isolated structures
1 Scope
This document specifies the principles regarding the design of seismically isolated structures under
earthquake effects.
This document also describes the principles of construction management and maintenance, since
proper construction management and maintenance are important for realizing high quality seismic
isolation structures.
This document is not applicable to bridges and LNG tanks, although some of the principles can be
referred to for the seismic isolation of those structures.
This document is not applicable to seismic isolation structures that reduce the vertical response to
earthquake ground motions, since this document mainly specifies seismic isolation structures that
attenuate the horizontal response to horizontal earthquake ground motions.
This document is not a legally binding and enforceable code. It can be viewed as a source document that
is utilized in the development of codes of practice by the competent authority responsible for issuing
structural design regulations.
NOTE This document has been prepared mainly for the seismically isolated structures which have the
seismic isolation interface applied between a superstructure and a substructure to reduce the effect of the
earthquake ground motion onto the superstructure. In most cases, the substructure refers to the foundation of
the structure. However, the substructure in this document consists of a structural system below the isolation
interface that has been designed with sufficient rigidity and strength. Examples include locating the isolation
interface in a mid-storey of the building or above the bridge piers (see Annex E).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3010:2017, Bases for design of structures — Seismic actions on structures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms related to structure
3.1.1
superstructure
portion of the structure above the seismic isolation interface
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ISO 23618:2022(E)
3.1.2
seismic isolation interface
space where seismic isolation devices are installed between superstructure and substructure
3.1.3
substructure
portion of the structure beneath the seismic isolation interface
3.1.4
foundation
lowest part of the substructure such as spread footing, pile foundation, mat foundation, and moat walls
3.2 Terms related to isolation system
3.2.1
seismic isolation system
collection of seismic isolation devices arranged over the seismic isolation interface
3.2.2
isolator
device installed between a substructure and a superstructure that supports the weight of the
superstructure, provides lateral mainly and some vertical flexibility, and can have a capacity to
dissipate energy and re-centring capability
Note 1 to entry: See Annex A.
3.2.3
hysteretic damper
device having the capacity to dissipate energy by the relationship between resistance force and
deformation
Note 1 to entry: See Annex A.
3.2.4
fluid damper
device having the capacity to dissipate energy by the relationship between resistance force of fluid and
velocity
Note 1 to entry: See Annex A.
3.2.5
isolation gap
horizontal or vertical space (clearance) between the structure and the moat wall, or the space between
adjacent structures in which the structure is free to move sideways without contacting the surrounding
structure
3.2.6
scratch plate
metal plate and probe recording the relative movement between a substructure and a superstructure
by marking scratches
3.2.7
equipment in isolation interface
equipment connecting the superstructure and the substructure, such as piping and wiring
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ISO 23618:2022(E)
3.3 Terms related to structural design
3.3.1
design response spectrum
spectrum used for the design of seismically isolated structure as a function of the fundamental period
of the structure
3.3.2
design earthquake ground motion
earthquake ground motion used for the design of seismically isolated structure in response history
analysis
3.3.3
effective stiffness
secant stiffness obtained by dividing the peak force of isolation system or an isolation device by the
corresponding displacement
3.3.4
effective damping
equivalent viscous damping corresponding to the energy dissipation of the isolation system or an
isolation device
3.3.5
equivalent linear system
system to evaluate the maximum response of a seismically isolated structure based on the response
spectrum using effective stiffness and effective damping of the isolation system
3.3.6
response spectrum analysis
calculation method to evaluate the maximum response of a seismically isolated structure under
earthquake ground motions based on the response spectrum
3.3.7
response history analysis
calculation method to evaluate the time history response of a seismically isolated structure under
earthquake ground motions
3.4 Terms related to maintenance and construction
3.4.1
warning signage
signboard to give notice the danger of the movement of the seismically isolated structure during an
earthquake
3.4.2
type test
test to validate material properties and performance of isolation products
Note 1 to entry: See ISO 22762-1 for elastomeric bearings.
3.4.3
routine test
test for quality control of isolation products
Note 1 to entry: See ISO 22762-1 for elastomeric bearings.
3.4.4
base plate
steel plate which connects an isolator to the superstructure and the substructure with bolts
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ISO 23618:2022(E)
3.4.5
construction clearance
isolation gap considering the construction error which is generally wider than the design clearance
3.4.6
creep
permanent deformation induced by long-term compressive load on isolators, especially rubber bearings
3.4.7
design clearance
isolation gap decided by the SE in the design stage, where horizontal clearance is decided based on the
maximum response displacement at an isolation interface and vertical clearance is decided considering
creep deformation and short-term compressive deformation of isolators
3.4.8
inspection at completion
inspection conducted when the building construction is completed
3.4.9
inspection under construction
inspection conducted immediately after the isolation interface is constructed
4 Symbols and abbreviations
C effective damping coefficient of the isolation system
e
D design maximum displacement
M
F lateral force at i-th level of structure
i
h effective damping of the hysteretic dampers
d
h effective damping of the fluid dampers
v
K effective stiffness of the isolation system
e
M
mass of the superstructure
Q seismic design base shear of superstructure
s
S design acceleration response spectrum
a
T effective period of the structure or isolation system
e
V effective velocity at the design maximum displacement, D
e M
ΔW
total energy dissipated in the hysteretic dampers during a full cycle of response at the design
maximum displacement, D
M
W
total potential energy in the isolation system at the design maximum displacement, D
M
β
modification factor of the effective damping of the hysteretic dampers
d
β modification factor of the effective damping of the fluid dampers
v
β modification factor of the seismic design base shear of superstructure
s
k seismic force distribution factor over the height of the superstructure
Fi,
CM construction manager in charge of the construction of isolation interface
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ISO 23618:2022(E)
CS construction supervisor responsible for the total quality of the whole building
GM general manager at a construction site
MFR manufacturer of the SI devices, base plates, flexible pipe joints etc.
IE inspection engineer
SE structural engineer
SI seismic isolation or seismically isolated structural system
5 Basic principles of structural planning
5.1 General
The seismically isolated structure shall be designed to have an isolation interface between a
superstructure and a substructure.
The reduction of seismic response of superstructure is obtained by increasing the fundamental natural
period of the structure and increasing the effective damping using isolators or dampers installed in the
isolation interface.
The seismically isolated structure shall be designed considering earthquake ground motions with the
effects of multi-directional input.
Seismic isolators are designed to support the weight of structure in a stable manner under the design
seismic forces.
Dampers are designed to have damping effect by absorbing vibration energy to reduce the response of
the structure.
The foundation of the seismically isolated structure shall be constructed so as not to cause settlement.
The ground condition of the site and its effect to the response of seismically isolated structure shall be
investigated.
5.2 Isolation interface
The centre of resistance of the isolation interface shall be as close as possible to the vertical projection
of the centre of masses of the superstructure on the isolation interface to minimize torsional movement.
Isolators shall have appropriate compressive strength to resist vertical loads from the superstructure.
The vertical loads shall also include vertical loads generated due to earthquakes.
Isolators shall be designed to increase the fundamental period of the structure to reduce the inertia
force induced by the earthquake vibration.
Dampers shall be designed to have damping effect by absorbing vibration energy to reduce the response
of the structure.
The isolation system shall have appropriate restoring force to re-centre the structure.
The isolation system shall have appropriate horizontal deformation capacity under seismic forces.
The isolation interface shall have enough space to allow inspection, maintenance and replacement of
the devices.
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ISO 23618:2022(E)
5.3 Superstructure and substructure
Isolation system shall be designed such that most of the lateral deformation of isolated structure is
concentrated at the isolation interface.
The substructure shall have sufficient stiffness and strength against the lateral and vertical force,
bending moment, shear force transmitted by the superstructure.
5.4 Foundation
The foundation of the seismically isolated structure shall have sufficient rigidity and strength to
support the structure in a stable manner and not to cause settlement.
5.5 Connections of isolation devices
Connections between the isolation devices and structures shall have sufficient stiffness and strength
against shear, tension, compression forces, and bending moments generated by the deformation of the
isolation devices.
5.6 Isolation gap
The isolation gap shall be sufficiently wide to accommodate the displacement of isolation system in
both horizontal and vertical directions, so that the structure does not collide with the moat wall during
an earthquake under the ultimate limit state (ULS).
Gap covers should be kept in place to prevent passers-by from falling into the moat.
5.7 Non-structural components and equipment in isolation interface
Non-structural components and equipment crossing the isolation interface, such as piping and wiring,
shall be designed to accommodate the displacement of the isolation system under the ULS.
6 Target performance of the seismically isolated structure
6.1 General
The seismically isolated structure shall remain operational without any damage to structures by
earthquakes which may be expected to occur at the site during the service life of the structure. This
limit state is referred to as the serviceability limit state (SLS).
The seismically isolated structure shall withstand with limited and reparable damage to structures
by severe earthquakes that could occur at the site, such that the building can remain operational even
right after the earthquakes. This limit state is
...