Simplified design of connections of concrete claddings to concrete structures

The present document refers to the panel-to-structure and panel-to panel connections used for the cladding systems of reinforced concrete frame structures of single-storey buildings, typically precast. They can be used also for multi-storey buildings with proper modifications. The fastening devices considered in the present document consist mainly of steel elements or sliding connectors. Dissipative devices with friction or plastic behaviour are also considered. Other types of common supports and bond connections are treated where needed. The use of any other existing fastening types or the connections with different characteristics than those described in the following clauses is not allowed unless comparable experimental and analytical studies do provide the necessary data and verify the design methodology for the particular type.

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Status
Published
Publication Date
02-Aug-2020
Current Stage
6060 - International Standard published
Start Date
03-Aug-2020
Completion Date
03-Aug-2020
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INTERNATIONAL ISO
STANDARD 22502
First edition
2020-08
Simplified design of connections
of concrete claddings to concrete
structures
Reference number
ISO 22502:2020(E)
ISO 2020
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ISO 22502:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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ii © ISO 2020 – All rights reserved
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ISO 22502:2020(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope .................................................................................................................................................................................................................................1

2 Normative references ......................................................................................................................................................................................1

3 Terms and definitions .....................................................................................................................................................................................1

4 Generalities ................................................................................................................................................................................................................1

4.1 Cladding panel orientations ........................................................................................................................................................ 1

4.2 Design criteria to connect frame and panels ................................................................................................................. 3

4.2.1 Isostatic approach........................................................................................................................................................... 3

4.2.2 Integrated approach ..................................................................................................................................................... 3

4.2.3 Dissipative approach .................................................................................................................................................... 3

4.3 Strategies to implement isostatic and dissipative design criteria .............................................................. 4

4.3.1 Sliding-frame (SF) ........................................................................................................................................................... 4

4.3.2 Double-hinged pendulum (DHP) ....................................................................................................................... 4

4.3.3 Rocking panel (RP) ........................................................................................................................................................ 4

4.4 Parameters ................................................................................................................................................................................................. 5

4.5 Classification ............................................................................................................................................................................................. 5

5 Isostatic systems ...................................................................................................................................................................................................5

5.1 General ........................................................................................................................................................................................................... 5

5.2 Analysis of the building ................................................................................................................................................................... 5

5.2.1 General...................................................................................................................................................................................... 5

5.2.2 Suggestions for the structural model ............................................................................................................. 5

5.2.3 Rocking systems ............................................................................................................................................................... 6

5.3 Analysis of conventional systems ........................................................................................................................................... 8

5.3.1 General aspects ................................................................................................................................................................. 8

5.3.2 General design methodology ................................................................................................................................. 8

5.3.3 Application procedure ................................................................................................................................................ 9

5.4 Design of isostatic system connections ..........................................................................................................................12

5.4.1 General...................................................................................................................................................................................12

5.4.2 Structural arrangements ........................................................................................................................................12

5.4.3 Sliding devices.................................................................................................................................................................15

5.4.4 Hinge connections .......................................................................................................................................................16

5.4.5 Supports with steel brackets ..............................................................................................................................17

6 Design of conventional connections ..............................................................................................................................................18

6.1 General ........................................................................................................................................................................................................18

6.2 Structural arrangements .............................................................................................................................................................18

6.2.1 Vertical structural arrangements ...................................................................................................................18

6.2.2 Horizontal structural arrangements ............................................................................................................19

6.3 Conventional fastening systems ............................................................................................................................................20

6.3.1 General...................................................................................................................................................................................20

6.3.2 Hammerhead strap connection ........................................................................................................................20

6.3.3 Cantilever box connection ....................................................................................................................................27

6.3.4 Steel angle connections ...........................................................................................................................................31

6.4 Conventional strengthening and fastening systems ............................................................................................34

6.4.1 Second line back up devices ................................................................................................................................34

6.4.2 Strengthening folded steel plates ...................................................................................................................36

6.4.3 Strengthening with steel cushions ................................................................................................................37

7 Integrated systems ..........................................................................................................................................................................................38

7.1 General ........................................................................................................................................................................................................38

7.2 Analysis of the buildings ..............................................................................................................................................................38

7.2.1 General...................................................................................................................................................................................38

7.2.2 Behaviour factor ............................................................................................................................................................39

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ISO 22502:2020(E)

7.2.3 Design aspects .................................................................................................................................................................39

7.2.4 Structural modelling ..................................................................................................................................................39

7.2.5 Cladding panels detailing ......................................................................................................................................44

7.3 Design of integrated systems connections ...................................................................................................................45

7.3.1 General...................................................................................................................................................................................45

7.3.2 Structural arrangements ........................................................................................................................................45

7.3.3 Base supports ..................................................................................................................................................................47

7.3.4 Connections with protruding bars ................................................................................................................47

7.3.5 Connections with wall shoes ..............................................................................................................................50

7.3.6 Connections with bolted plates ........................................................................................................................54

7.3.7 Shear keys ...........................................................................................................................................................................58

8 Dissipative systems .........................................................................................................................................................................................59

8.1 General ........................................................................................................................................................................................................59

8.2 Analysis of the building ................................................................................................................................................................60

8.2.1 General...................................................................................................................................................................................60

8.2.2 Structures with friction devices.......................................................................................................................62

8.2.3 Structures with steel cushions ..........................................................................................................................63

8.3 Design of dissipative systems connections ..................................................................................................................64

8.3.1 General...................................................................................................................................................................................64

8.3.2 Structural arrangements ........................................................................................................................................65

8.3.3 Friction devices ..............................................................................................................................................................66

8.3.4 Multi-slit devices ...........................................................................................................................................................70

8.3.5 Steel cushions ..................................................................................................................................................................73

8.3.6 Folded steel plates .......................................................................................................................................................80

Annex A (informative) Design flowchart .......................................................................................................................................................83

iv © ISO 2020 – All rights reserved
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ISO 22502:2020(E)
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

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

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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

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

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expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and

prestressed concrete, Subcommittee SC 5, Simplified design standard for concrete 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.
© ISO 2020 – All rights reserved v
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ISO 22502:2020(E)
Introduction

The current design practice of reinforced concrete buildings, most commonly precast, is based on a

frame model, where the peripheral cladding panels enter only as masses without any stiffness. The

panels are then connected to the structure with fastenings dimensioned with a local calculation based

on their mass for anchorage forces orthogonal to the plane of the panels.

Furthermore, the seismic force reduction in the type of reinforced concrete structures of concern relies

on energy dissipation in plastic hinges formed in the columns. Very large drifts of the columns are

needed to activate this energy dissipation foreseen in design. However, typically, the capacity of the

connections between cladding and structure is exhausted well before such large drifts can develop.

Therefore, the design of these connections cannot rely on the seismic reduction factor typically used for

design of the bare structure.

This document contains a set of practical provisions for the design of mechanical connections of

concrete claddings to concrete structures under seismic actions as well as suggestions for structural

analysis for the specified systems.
vi © ISO 2020 – All rights reserved
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INTERNATIONAL STANDARD ISO 22502:2020(E)
Simplified design of connections of concrete claddings to
concrete structures
1 Scope

The present document refers to the panel-to-structure and panel-to panel connections used for the

cladding systems of reinforced concrete frame structures of single-storey buildings, typically precast.

They can be used also for multi-storey buildings with proper modifications.

The fastening devices considered in the present document consist mainly of steel elements or sliding

connectors. Dissipative devices with friction or plastic behaviour are also considered. Other types of

common supports and bond connections are treated where needed.

The use of any other existing fastening types or the connections with different characteristics than

those described in the following clauses is not allowed unless comparable experimental and analytical

studies do provide the necessary data and verify the design methodology for the particular type.

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 20987, Simplified design for mechanical connections between precast concrete structural elements in

buildings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
behaviour factor q
q factor by which the elastic design spectrum in linear analysis is reduced

Note 1 to entry: Directly or indirectly linked to the ductility and deformation demands on members and

connections.
4 Generalities
4.1 Cladding panel orientations

Figure 1 a) shows a vertical panel orientation referred to a system of orthogonal axes, where x is

oriented horizontally in the panel plane, y is oriented orthogonally to that plane and z is oriented

vertically parallel to the gravity loads. The origin is placed in a corner at the base side of the panel.

Four connections are foreseen at the corners of the panel, indicated respectively by A, B, C and D. Any one

of these connections is intended to give only translational restraints without any rotational restraint. E

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ISO 22502:2020(E)

and F indicate the possible joint connections with the adjacent panels. Usually, the connections A and B

are attached to the foundation beam, the connections C and D are attached to the top beam.

The couple of bottom and top connections may be replaced by single connections placed in the middle

of the bottom and top sides for a pendulum arrangement of the panel. In this case, the connections are

respectively named A and C, and the symbols B and D are omitted.

In Figure 1 b), the same reference system is associated with a horizontal panel for which the connections

A, B, C and D are usually attached to the columns, and E and F refer to the possible joint connections

with the adjacent panels, foundation or top beam where the uncertain friction effect can act due to the

superimposed panels.
a) Vertical b) Horizontal
Figure 1 — Cladding panel orientations
Table 1 — Symbols and graphic schemes for supports
Symbol Description Graphic scheme

f fixed (bilateral)
►◄,▲
f+ fixed (unilateral in + direction) ▲, ►
f- fixed (unilateral in - direction) ▼, ◄
s sliding (bilateral) ↔, ↕
d dissipative ⋀⋀⋀
/ omitted [empty]

Table 1 gives a general description of the symbols and graphic schemes regarding the effect of the

supports along the three directions x, y and z. As an example, Table 2 gives the arrangement matrix

indicating the effect of the supports for a vertical panel.
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ISO 22502:2020(E)
Table 2 — Arrangement matrix – example
Direction A B C D E F
x f / s / f f
y f / f / / /
z f / / / d d

The term “fixed” is used with reference to the restrained linear displacement while the rotational

restraints are not provided.
4.2 Design criteria to connect frame and panels
4.2.1 Isostatic approach

An isostatic arrangement of panel connections is able to allow without reactions the large displacements

expected for the frame structure under earthquake conditions. Very large displacement capacities are

required for connectors with this choice.

The frame deformation demand is allowed by a relative clearance that uncouples the motion of frame

and panels. The two systems are kinematically uncoupled, except for the out-of-plane displacements

[see Figure 2 a)].
4.2.2 Integrated approach

An integrated arrangement relies on fixed connections that integrate the panels in the resistant

structural assembly with a dual wall-frame system behaviour. High forces may arise in the connections

with this choice.

Panels and frame have a coupled motion: the system is kinematically paired [see Figure 2 b)]. Panels

become part of the seismic resisting system and they act as the main restraints in the horizontal

direction thanks to their higher stiffness. As a consequence, the connections shall be over-proportioned

to carry the higher loads transferred by the frame, according to capacity design rules.

4.2.3 Dissipative approach

An arrangement of dissipative connections between the panels is added to an isostatic system of

fastenings to the structure, able to maintain displacements and forces within lower predetermined limits.

Specific devices can balance the overall building response, reducing the displacement and keeping the

load below an imposed threshold, determined by the connections themselves [see Figure 2 c)]. Like in

the isostatic configuration, the systems are kinematically uncoupled but they are also constrained by

inelastic links, like friction or yielding devices. The joints between structure and panels – or among the

panels – shall be designed to dissipate energy during the seismic action.
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ISO 22502:2020(E)
a) b) c)
Figure 2 — Design criteria to connect frame and panels
4.3 Strategies to implement isostatic and dissipative design criteria
4.3.1 Sliding-frame (SF)

Like an ideal uncoupled system, the isostatic sliding-frame is, in principle, the easiest way to disconnect

frame and panels. To achieve this result while avoiding the issues that affect current systems, proper

connections (sliders) shall be introduced. They only restrain out-of-plane motions, reproducing the

hypothesis typically assumed in the current practice, but in a safer way [see Figure 3 a)].

4.3.2 Double-hinged pendulum (DHP)

The double-hinged pendulum is the proper way to connect the cladding as simple mass without any

stiffness contribution [see Figure 3 b)]. This result can be obtained either by connecting panel edges

with hinges, or by replacing the top hinge with coupled sliders.
4.3.3 Rocking panel (RP)

Starting from DHP, the rocking panel configuration may be obtained replacing the bottom hinge with

a pair of horizontal restraints. These leave the panel free to rock around its bottom corners. Even

though this solution looks very similar to the former one, some differences in statics and in kinematic

behaviour need to be highlighted [see Figure 3 c)].
a) b) c)

Figure 3 — Isostatic and dissipative design criteria: schemes of design strategies

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ISO 22502:2020(E)
4.4 Parameters

ISO 20987 shall apply. In addition to the provisions of ISO 20987, the following applies.

Among the main parameters that characterize the seismic behaviour of the connection, the following

one is added:

slide - free linear relative displacement capacity with null or negligible reaction.

The main behaviour parameters are provided for each x, y, z direction defined in ISO 20987 specifying

possible interaction effects.
4.5 Classification

ISO 20987 shall apply. In addition to the provisions of ISO 20987, the following applies.

Connections present in existing buildings, where sufficient information about their strength and/or

ductility is not available, can be classified as unknown.

Existing connections can be classified as insufficient when a specific calculation under the expected

seismic action shows their inadequate strength.
5 Isostatic systems
5.1 General

For buildings with isostatic arrangements of cladding panel connections, the structural analysis

under seismic action shall refer to the frame system following the conventional design practice of such

structures. In expectation of large displacements, the second order effects, PΔ, should be taken into

account. In addition to the ordinary output data used for the design of member resistance at ultimate

limit state (ULS ), the sliding or rotation displacements shall be provided for the design of the pertinent

capacities of panel connection devices.
5.2 Analysis of the building
5.2.1 General

For the frame systems considered, capacity design criteria for the proportioning of the connection are

applied. It is assumed, as a rule, that the beam-to-column and column-to-foundation connections are

properly over-proportioned with respect to the bending moment ultimate capacities of the columns.

Floor connections involved in the diaphragm action can refer to some approximate methods.

In any case, the structural connections can be over-proportioned, referring to the forces obtained from

a structural analysis performed with behaviour factor q = 1,5

Figure A.1 shows a simplified design flowchart. It shows the required steps to design a cladding to

concrete structure connection. Specific suggestions regarding the isostatic systems structural model

analysis are given in 5.2.2 and 5.2.3.
5.2.2 Suggestions for the structural model

For the numerical model of the structure, the ordinary linear elements (beam type) can be used,

positioned along the axis of the members. Different eccentricities between the members should be

reproduced using link rigid elements at their joints. The connections between the elements shall be

faithfully represented with their degrees of freedom in the different planes. It should be considered

that, if the connections are modelled with no deformability (e.g. fixed built-in full support or hinged

1) ULS: state at which the material stresses are limited to the point at which the bearing elements can withstand

the design loads and maintain the safety and integrity of the structure.
© ISO 2020 – All rights reserved 5
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