ISO 23618:2022

Bases for design of structures — General principles on seismically isolated structures

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).

Bases du calcul des constructions — Principes généraux des constructions munies d’isolateurs parasismiques

General Information

• Status: Published
• Publication Date: 09-Oct-2022
• ICS: 91.080.01 - Structures of buildings in general
• ICS: 91.120.25 - Seismic and vibration protection
• Technical Committee: ISO/TC 98/SC 2 - Reliability of structures
• Drafting Committee: ISO/TC 98/SC 2/WG 13 - Design principles of seismically isolated structures
• Current Stage: 6060 - International Standard published
• Start Date: 10-Oct-2022
• Due Date: 20-Nov-2021
• Completion Date: 10-Oct-2022

Overview - ISO 23618:2022 (Seismically isolated structures)

ISO 23618:2022 provides general principles for the design, construction management and maintenance of seismically isolated structures subjected to earthquake effects. The standard focuses on systems that attenuate the horizontal response via an isolation interface placed between the superstructure and substructure (commonly the foundation, but can be a mid‑storey). It is a non‑binding source document intended to inform codes of practice and design regulations. Note: the standard is not applicable to bridges, LNG tanks or systems that primarily reduce vertical seismic response, though some principles may be referenced for those cases.

Key topics and technical requirements

ISO 23618 organizes essential design content and practical requirements, including:

• Structural planning principles
  • Isolation interface location, substructure and superstructure roles, foundation considerations, isolation gaps, connections and non‑structural items at the interface.
• Target performance
  • Performance objectives for superstructure, substructure and the isolation system to achieve safety and serviceability under seismic action.
• Design seismic force
  • Use of design response spectra and specification of design earthquake ground motion for isolated structures.
• Structural analysis and modelling
  • Modelling of isolation devices and building systems.
  • Two main analysis approaches: equivalent linear response spectrum methods (including effective stiffness, effective period, effective damping, and maximum isolation displacement) and nonlinear response history analysis (ground motion selection, bounds on stiffness/force, story drift and shear checks).
• Construction management
  • Requirements for construction planning, manufacturing quality control of isolation devices, temporary works and documented procedures for the isolation interface.
• Maintenance and monitoring
  • Inspection, maintenance schedules, performance monitoring and warning signage to ensure long‑term functionality.
• Device performance and testing
  • Information and testing requirements for isolation devices; annexes classify device types and performance characteristics.

Applications and intended users

ISO 23618 is useful for:

• Structural and seismic engineers designing base‑isolated buildings or mid‑storey isolation systems
• Architects and project teams integrating seismic isolation into building layouts
• Manufacturers and suppliers of seismic isolation devices for procurement and testing criteria
• Construction managers and quality control teams responsible for installation
• Facility owners, asset managers and regulators preparing maintenance plans and local codes

Practical benefits include improved occupant safety, reduced structural and non‑structural damage, greater post‑quake operability and expanded architectural freedom.

Related standards

• ISO 3010:2017 (Seismic actions on structures) is referenced by ISO 23618 for seismic action bases and related procedures.

Standards Content (Sample)

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 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
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
iii
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
iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
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Attention is drawn to the possibility that some of the elements of this document may be the subject of
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 98, Subcommittee SC 2, Reliability of
structures.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
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.
vi
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
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
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
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
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.
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 referred to as the ultimate limit state.
The seismically isolated structure shall protect occupants against extraordinary and possibly
unforeseen events like natural hazards, accidents, or human errors by providing sufficient robustness.
The seismically isolated structure shall be safe and operational under wind loads (see Annex D).
6.2 Superstructure
In the SLS, the superstructure shall remain undamaged.
In the ULS, the superstructure shall withstand with limited and reparable damage such that the
building can remain operational.
6.3 Substructure
In the SLS, the substructure shall remain undamaged.
In the ULS, the substructure shall withstand with limited and reparable damage.
6.4 Isolation system
a) The isolation system shall support the loads during deformation in a stable manner.
b) The sustained compressive stress of the isolator shall be less than the design capacity.
c) The maximum lateral deformation of the isolator under design seismic forces shall be less than the
design capacity.
d) The tension force and deformation of the isolator under design seismic forces induced by the
vertical component of the earthquake ground motion and/or the superstructure’s overturning
moment shall be less than the design capacity.
e) The isolation system shall resist wind loads and other design loads. The fatigue characteristics of
the seismic isolation devices should be considered when evaluating response due to earthquake or
wind load (see Annex D).
f) The effect of aging, creep, temperature, moisture, and other environmental conditions to the
characteristics of isolation devices shall be considered appropriately.
g) The isolator shall have adequate fire protection if necessary.
7 Design seismic force
7.1 General
The seismically isolated structures shall be designed using appropriate design earthquake ground
motions or design response spectra established considering the seismicity and site conditions as
described in ISO 3010:2017.
7.2 Design response spectrum
A design response spectrum shall be defined as the input to perform a response spectrum analysis for
equivalent linear system. This spectrum may either be a code specified response spectrum for the site
or a site-specific design response spectrum developed for the proper damping ratio.
7.3 Design earthquake ground motion
A set of earthquake ground motions is required as the input to perform a response history analysis
with two horizontal and one vertical components. These motions may either be recorded or simulated
earthquake ground motions that are selected and scaled to generally match the design response
spectrum for the site. For both types of ground motions, the stochastic nature of earthquake ground
motions should be considered.
The earthquake ground motions shall be determined for each limit state, considering the seismicity,
local soil conditions, return period of past earthquakes, distance to active faults, source characteristics
of possible earthquakes, uncertainty in the prediction, design service life of the structure, and
occupancy category of the structure.
8 Structural analysis
8.1 General
The following analysis methods are considered appropriate for the structural analysis of seismically
isolated structures depending on the determined conditions:
a) Response spectrum analysis method for equivalent linear system;
b) Response history analysis method.
8.2 Modelling of isolation system
The isolation system shall be modelled based on the characteristics of isolation devices.
The model of each isolation device should be verified by natural scale testing results.
Upper and lower bounds of restoring force characteristics of isolation devices shall be evaluated
considering the influence of production variability, environmental condition, heating by cyclic dynamic
deformation, and time deterioration.
8.3 Modelling of superstructure and substructure
For a structure with irregular configuration, a three-dimensional structural model should be used to
evaluate the torsional response.
8.4 Response spectrum analysis method for equivalent linear system
8.4.1 General
Response spectrum analysis method for equivalent linear system is a practical calculation method
evaluating the maximum response of a seismically isolated structure based on the design response
spectrum using linearized effective stiffness and effective damping of the isolation system.
8.4.2 Basic requirements
a) Response spectrum analysis for equivalent linear system shall be used for the design of a seismically
isolated structure that consists of an isolation interface at the base of the structure.
b) The horizontal elastic stiffness of the superstructure shall be sufficiently larger than the effective
stiffness of the isolation system so that the superstructure behaves as an almost rigid body and the
structure can be modelled as a single degree of freedom system.
c) The height of the superstructure shall be limited so that the higher mode effect of vibration can be
ignored.
d) The superstructure shall have regular forms in both plan and elevation to minimize torsional
movement.
e) The nonlinear restoring force characteristic of the seismic isolation system shall be replaced with
an equivalent linear restoring force having effective stiffness and effective damping.
f) The design response spectrum shall be defined as the acceleration response spectrum of input
earthquake ground motion as a function of the fundamental natural period and a damping ratio.
g) The maximum response of the isolation system shall be evaluated by the iterative manner until
convergence from the reduced response spectrum for the effective stiffness and the effective
damping ratio.
h) Response spectrum analysis for equivalent linear system shall be performed separately for upper
bound and lower bound of the restoring force characteristics of the isolation system to determine
the maximum shear force and the maximum displacement of the isolation system.
i) The superstructure shall be designed using the maximum shear force. This shear force shall be
distributed as the lateral static force over the height of the superstructure.
j) The seismic devices shall be designed against the maximum displacement considering the
appropriate safety factor.
k) At the maximum response, no tension is allowed in isolators.
8.4.3 Effective stiffness
The effective stiffness, K , of the isolation system shall be calculated as the secant stiffness obtained
e
by dividing the peak force by the design maximum displacement, D , in the force-deflection behaviour
M
of the isolation system.
8.4.4 Effective period
The effective period of the isolation system at the design maximum displacement, D , shall be
M
calculated from Formula (1):
M
T = 2π (1)
e
K
e
where
T is the effective period of the isolation system,
e
M
is the mass of the superstructure,
K is the effective stiffness of the isolation system.
e
8.4.5 Effective damping
8.4.5.1 Effective damping of hysteretic dampers
The effective damping ratio of the isolation system should be calculated from Formula (2):
1 ΔW
h = β (2)
dd
4π W
where
h is the effective damping ratio of the hysteretic dampers,
d
β is the modification factor of the effective damping of the hysteretic dampers that takes into
d
account the non-stationarity of the seismic response, usually less than 1.0,
ΔW
is the total energy dissipated in the hysteretic dampers during a full cycle of response at the
design maximum displacement D ,
M
W
is the total potential energy in the isolation system at the design maximum displacement, D
M
, as calculated from Formula (3):
WK= D (3)
eM
8.4.5.2 Effective damping of fluid dampers
The effective damping ratio of the isolation system with fluid dampers should be calculated from
Formula (4):
TC
ee
h = β (4)
vv
4π M
where
h is the effective damping ratio of fluid dampers,
v
β is the modification factor of the effective damping of fluid dampers that takes into account the
v
non-stationarity of the seismic response, usually less than 1.0,
C is the effective damping coefficient of the fluid dampers obtained by dividing the damping force
e
of the fluid dampers F by the equivalent velocity VD=2π /T at the design maximum
D eM e
displacement D as calculated from Formula (5):
M
CF= /V (5)
eD e
8.4.6 Maximum displacement of isolation system
8.4.6.1 Response spectrum
The seismic input is defined as a design acceleration response spectrum, ST(),h , as a function of the
a
fundamental natural period, T , and a damping ratio, h , of the structure.
8.4.6.2 Maximum displacement including torsion
The maximum displacement, D , of the isolation interface at the centre of mass shall be calculated
M
from Formula (6) by the iterative manner.
MS Th,
()
ae D
D = (6)
M
K
e
whereh is the effective damping ratio considering the combined effect of hysteretic damping and
D
viscous damping.
The maximum displacement at the individual element of isolation interface should include additional
displacement caused by the torsional movement of isolation interface by an appropriate manner.
8.4.7 Seismic design forces
8.4.7.1 Seismic design base shear of the superstructure
The superstructure shall be designed based on the seismic design base shear, Q , calculated from
s
Formula (7):
QK=β D (7)
ss eM
where
Q is the seismic design base shear of superstructure,
s
β is the modification factor of the seismic design base shear of superstructure.
s
8.4.7.2 Seismic design forces of the foundation
The foundation shall be designed to against the lateral and vertical force, bending moment, shear force
transmitted by the superstructure.
8.4.7.3 Vertical distribution of lateral forces
The lateral forces applied at each level of the superstructure shall be calculated from Formula (8):
Fk= Q (8)
iF ,is
where
F is the lateral force at i-th level of the superstructure,
i
k is the force distribution factor to distribute the seismic design base shear, Q , to the i-th level
Fi, s
of the superstructure, which characterizes the distribution of seismic forces in elevation.
where ∑=k 1
Fi,
8.4.7.4 Drift limit of the superstructure
The maximum storey drift of the superstructure corresponding to the design lateral force shall be less
than the design limit.
8.5 Response history analysis method
8.5.1 General
The response history analysis is a calculation method evaluating the time history response of a
seismically isolated structure under earthquake ground motions.
8.5.2 Basic requirements
a) The nonlinear restoring force characteristics of the seismic isolation interface shall be explicitly
modelled based on the constitutive law of each isolation device.
b) Vertical response of the isolation devices should be evaluated to confirm the tension force and
deformation to be below the design capacity.
c) Appropriate consideration shall be given to the fatigue characteristics of isolation devices due to
earthquakes and winds that may occur during the service life of the structure.
8.5.3 Number of earthquake ground motions
Because of the large uncertainties in the characteristics of seismic motions, a sufficient number of
earthquake ground motions with different time-frequency characteristics shall be used to evaluate the
response of seismically isolated structures as described in ISO 3010:2017.
8.5.4 Upper bound and lower bound of stiffness and force
Response history analysis shall be performed separately for upper bound and lower bound of the
stiffness and the force of the hysteresis model of the isolation system considering the influence of
production variability, environmental condition, and time deterioration to determine the maximum
shear force and the maximum displacement.
8.5.5 Maximum displacement of isolation system
The maximum displacement of the isolation system shall be calculated from the vector sum of the two
horizontal and vertical orthogonal displacements at each time step.
8.5.6 Maximum storey drift and shear force of superstructure
The maximum storey drift and shear force of the superstructure obtained by response history analysis
shall be less than the design limit.
9 Construction management specified in design documents
9.1 Construction planning
Construction plan shall be prepared including manufacturing of the isolation devices, installation
procedures of the isolation devices, piping and electrical wiring and expansion joints, temporary works,
detailed construction procedures considering the possibility of earthquakes and strong winds in the
construction period, and inspection details (see Annex B).
9.2 Quality control of isolation device manufacturing
The delivered isolation devices and non-structural components crossing isolation interface shall be
confirmed to meet the requirements specified in the design documents (see Annex B).
9.3 Temporary work planning
Temporary works such as scaffolding, cranes, construction lifts, bridges over the isolation gap, shall be
planned to avoid the interference or collision with the superstructure.
Temporary horizontal restraints shall be applied to avoid excessive relative deformation at the isolation
interface due to earthquakes and strong winds in the construction period (see Annex B).
9.4 Construction procedures of isolation interface
In the construction period, the isolation devices should be covered to keep away from any damages
caused by, for example, impact, heat, chemicals, oil, and rainwater (see Annex B).
If the isolation interface is dedicated to some building usage such as office room, machine room and
parking lot, permanent fire protection for isolators shall be utilized (see Annex B).
Inspection of the isolation interface such as the precision of the position and slope for the isolation
devices, the clearance between the flexible pipe joints and the superstructure and the isolation gap
shall be conducted during and after the construction period (see Annex B).
10 Maintenance specified in design documents
10.1 Maintenance of seismic isolation system
The isolation system maintenance plan shall be submitted to the building owner so that the isolation
system can be kept in good condition and periodically checked and maintained (see
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