ISO 20987:2019

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ISO/TC 71/SC 5
Date: 2018‐01‐12
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ISO/TC 71/SC 5/WG 4
Secretariat: ICONTEC
Simplified design for mechanical connections between precast
concrete structural elements in buildings
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Contents Page
Foreword . 6
Introduction . 7
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Properties . 3
5 Classification . 4
5.1 General . 4
5.2 Strength . 4
5.3 Ductility . 4
5.3.1 Ductile connections . 5
5.4 Dissipation . 5
5.5 Deformation . 5
6 Floor-to-floor connections . 6
6.1 Cast-in-situ topping . 6
6.1.1 General . 6
6.1.2 Strength . 6
6.1.3 Other properties . 6
6.2 Cast-in-situ joints . 7
6.2.1 General . 7
6.2.2 Strength . 7
6.2.3 Other properties . 7
6.3 Welded steel connectors . 7
6.3.1 General . 7
6.3.2 Strength . 8
6.3.3 Other properties . 11
6.4 Bolted steel connectors . 11
6.4.1 General . 11
6.4.2 Strength . 11
6.4.3 Other properties . 14
7 Floor-to-beam connections . 14
7.1 Cast-in-situ joints . 14
7.1.1 General . 14
7.1.2 Other properties . 15
7.2 Supports with steel angles . 15
7.2.1 General . 15
7.2.2 Strength . 17
7.2.3 Ductility . 23
7.2.4 Dissipation . 23
7.2.5 Deformation . 23
7.2.6 Cyclic decay . 23
7.2.7 Damage . 24
7.3 Supports with steel shoes . 24
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7.3.1 General . 24
7.3.2 Strength . 24
7.3.3 Ductility . 30
7.3.4 Dissipation . 30
7.3.5 Deformation . 30
7.3.6 Cyclic decay . 31
7.3.7 Damage . 31
7.4 Welded supports . 31
7.4.1 General . 31
7.4.2 Strength . 31
7.4.3 Other properties . 34
7.5 Hybrid connections . 34
7.5.1 General . 34
7.5.2 Strength . 34
7.5.3 Other properties . 37
8 Beam-to-column connections . 37
8.1 Cast-in-situ joints . 38
8.1.1 General . 38
8.1.2 Strength . 40
8.1.3 Ductility . 42
8.1.4 Dissipation . 42
8.1.5 Deformation . 42
8.1.6 Cyclic decay . 42
8.1.7 Damage . 42
8.2 Dowel connections . 42
8.2.1 General . 42
8.2.2 Strength . 43
8.2.3 Ductility . 49
8.2.4 Dissipation . 49
8.2.5 Deformation . 49
8.2.6 Cyclic decay . 49
8.2.7 Damage . 50
8.3 Mechanical coupler connections . 50
8.3.1 General . 50
8.3.2 Strength . 51
8.3.3 Ductility . 52
8.3.4 Dissipation . 52
8.3.5 Deformation . 52
8.3.6 Cyclic decay . 52
8.3.7 Damage . 52
8.4 Hybrid connections . 53
8.4.1 General . 53
8.4.2 Strength . 53
8.4.3 Ductility . 56
8.4.4 Dissipation . 56
8.4.5 Deformation . 56
8.4.6 Cyclic decay . 57
8.4.7 Damage . 57
9 Column-to-foundation connections . 57
9.1 Pocket foundations . 57
9.1.1 General . 57
9.1.2 Strength . 57
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9.1.3 Other properties . 58
9.2 Foundations for columns with protruding bars . 58
9.2.1 General . 58
9.2.2 Strength . 59
9.2.3 Ductility . 61
9.2.4 Dissipation . 61
9.2.5 Deformation . 61
9.2.6 Cyclic decay . 61
9.2.7 Damage . 61
9.3 Foundations with bolted sockets . 62
9.3.1 General . 62
9.3.2 Strength . 63
9.3.3 Ductility . 65
9.3.4 Dissipation . 66
9.3.5 Deformation . 66
9.3.6 Cyclic decay . 66
9.3.7 Damage . 66
9.4 Foundations with bolted flanges . 67
9.4.1 General . 67
9.4.2 Strength . 68
9.4.3 Other properties . 68
9.5 Foundations with mechanical couplers . 68
9.5.1 General . 68
9.5.2 Strength . 68
9.5.3 Ductility . 70
9.5.4 Dissipation . 70
9.5.5 Deformation . 70
9.5.6 Cyclic decay . 70
9.5.7 Damage . 70
10 Calculation of actions . 70
10.1 General criteria . 70
10.2 Capacity design . 70
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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 organizations, governmental and non‐governmental, in liaison with ISO, also take part in
the work. 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
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on the ISO list of patent declarations received (see www.iso.org/patents).
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see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-
stressed 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.
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Introduction
This document contains a set of practical provisions for the design of the mechanical connections in
precast elements under seismic actions. Design of the connections is carried out in terms of strength
verifications. Indications are also provided for defining the actions to be used in design.
If national standards provide alternate formulae for the same typology, those can be used instead of the
ones given in this document.
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Simplified design for mechanical connections between precast
concrete structural elements in buildings
1 Scope
This document refers to connections in precast frame systems, either for single‐storey or multi‐storey
buildings. The connections for all orders of joints are considered. Large wall panel and three‐
dimensional cell systems are not considered.
According to the position in the overall construction and of the consequent different structural
functions, the seven following orders of joints are considered:
a) mutual joints between floor or roof elements (floor‐to‐floor) that, in the seismic behaviour of the
structural system, concern the diaphragm action of the floor;
b) joints between floor or roof elements and supporting beams (floor‐to‐beam) that give the peripheral
constraints to the floor diaphragm in its seismic behaviour;
c) joints between beam and column (beam‐to‐column) that ensure in any direction the required degree
of restraint in the frame system;
d) joints between column segments (column‐to‐column) used for multi‐storey buildings usually for
dual wall braced systems;
e) joints between column and foundation (column‐to‐foundation), able to ensure in any plane a fixed
full support of the column;
f) fastenings of cladding panels to the structure (panel‐to‐structure) that ensure the stability of the
panels under the high forces or the large drifts expected under seismic action;
g) joints between adjacent cladding panels (panel‐to‐panel) possibly used to increase the stiffness of
the peripheral wall system and provide an additional source of energy dissipation.
Simple bearings working by gravity load friction are not considered. Sliding and elastic deformable
supporting devices neither, being all these types of connections not suitable for the transmission of
seismic actions.
The document provides formulae for the strength design of a large number of joint typologies.
2 Normative references
There are no normative references in this document.
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:
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— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
union
generic linking constraint between two or more members
3.2
connection
local region that includes the union (3.1) between two or more members
3.3
connector
linking device (usually metallic) interposed between the parts to be connected
3.4
node
local region of convergence between different members
3.5
joint
equipped interface between adjacent members
3.6
system
set of linking practices classified on the basis of the execution technology
3.7
typical joint
dry joint (3.5) with mechanical connectors (3.3) generally composed of angles, plates, channel bars,
anchors, fasteners, bolts, dowel bars, etc., including joints completed in‐situ with mortar for filling or
fixing
3.8
emulative joint
wet joint (3.5) with rebar splices and cast‐in‐situ concrete restoring the monolithic continuity typical of
cast‐in‐situ structures and leading usually to “moment‐resisting” unions (3.1)
3.9
strength
maximum value of the force which can be transferred between the parts
3.10
ductility
ultimate plastic deformation compared to the yielding limit
Note 1 to entry: The ductility values or ranges provided refer to the connections (3.2) themselves and, in general,
have no direct relation with the global ductility of the structure. Those values are given for the sake of classifying
the connection and are not supposed to intervene in the design, which is carried out in terms of strength (3.10).
Note 2 to entry: Instead of the plastic deformation of steel element beyond the yield limit, other physical
equivalent non‐conservative phenomena can be referred to (such as friction).
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3.11
dissipation
specific energy dissipated through the load cycles related to the corresponding perfect elastic‐plastic
cycle
Note 1 to entry: The values or ranges provided refer to the connections (3.2) themselves and, in general, have no
direct relation with the global energy dissipation of the structure. Those values are given for the sake of classifying
the connection and are not supposed to intervene in the design, which is carried out in terms of strength (3.10).
3.12
cyclic decay
decay
strength (3.10) loss through the load cycles compared to the force level
3.13
damage
residual deformation at unloading compared to the maximum displacement and/or evidence of rupture
4 Properties
A connection is composed of three parts: two lateral parts A and C, corresponding to the local regions of
the adjacent members close to the connector; and a central part B constituted by the connector itself
with its metallic components (see Figure 1).
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Figure 1 — Scheme of connection
The main parameters which characterize the seismic behaviour of the connection, as measured through
monotonic and cyclic tests, refer to the six properties of:
— strength;
— ductility;
— dissipation;
— deformation;
— decay;
— damage.
A ductile dissipative behaviour of the connection can be provided by the steel connector B:
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— when parts A and C have a non‐ductile non‐dissipative behaviour characterized by a brittle failure,
with small displacements, due to the tensile cracking of concrete; and
— if it is correctly designed for a failure involving flexural or tension‐compression modes and not
shear modes or by other dissipative phenomena like friction.
In this case, for a ductile connection, in addition to a ductile connector, the criteria of capacity design
shall be applied, under‐proportioning the connector with respect to the lateral parts.
Also, the geometric compatibility of deformations shall be checked (e.g. against the loss of bearing).
Non‐ductile connections shall be:
— suitably over‐proportioned by capacity design with respect to the resistance of the critical
dissipative regions of the structure; or
— proportioned on the basis of the action obtained from a structural analysis that does not account
for any energy dissipation capacity.
The ductility of the connections can contribute to the global ductility of the structure or not depending
on their position in the structural assembly and on their relative stiffness.
5 Classification
5.1 General
For any single type of connection, the strength is quantified by the relevant formulae. The other
behaviour properties listed in this clause are quantified by specific numerical values. When this precise
numerical quantification is not possible, because of lack of experimental data or excessive variability of
performances, the type of connection is classified in qualitative terms corresponding to ranges of
values.
5.2 Strength
For strength, the following information shall be given:
— behaviour models corresponding to the working mechanisms of the connection;
— failure modes of the resistant mechanisms;
— calculation formulae for the evaluation of the ultimate strength for any failure mode;
— other data concerning the specific properties of the connection.
Reference is made to the strength obtained from cyclic loading tests.
5.3 Ductility
For ductility, the following classification is deduced from the force‐displacement diagrams obtained in
experiments:
— brittle connections, for which failure is reached without relevant plastic deformation;
— over-resisting connections, for which failure has not been reached at the functional deformation
limit;
— ductile connections, for which a relevant plastic deformation has been measured.
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In this classification, intentional friction mechanism is equal to plastic deformation. Brittle connections
can be used in seismic zones provided they are:
— over‐proportioned by capacity design with respect to the critical regions of the overall structure; or
— proportioned with the action deducted from a structural analysis that does not account for any
energy dissipation capacity.
5.3.1 Ductile connections
Furthermore, ductile connections are divided into:
— high ductility connections, with a displacement ductility ratio of at least 4,5;
— medium ductility connections, with a displacement ductility ratio of at least 3,0;
— low ductility connections, with a displacement ductility ratio of at least 1,5.
With ductility ratio lower than 1,5, the connection is classified as brittle.
These definitions refer to the connection itself and, in general, have no direct relation with the global
ductility of the structure. For any single order of connections, specific indications are given on this
aspect, referring both to ductility and dissipation.
5.4 Dissipation
For dissipation, the following classification is deduced from the force‐displacement diagrams of cyclic
tests and related enveloped area histograms:
— low dissipation, with specific values of dissipated energy between 0,10 and 0,30;
— medium dissipation, with specific values of dissipated energy between 0,30 and 0,50;
— high dissipation, with specific values of dissipated energy over 0,50.
With dissipated energy lower than 0,1, the connection is classified as not dissipative.
The theoretical value 1,00 would correspond to the maximum energy dissipated through a perfect
elastic‐plastic cycle, e.g. by a massive section of ductile steel under alternate flexure, medium
dissipation corresponds to well confined reinforced concrete sections under alternate flexure and high
dissipation can be achieved with the use of special dissipative devices.
5.5 Deformation
For deformation, indications can be given about the order of magnitude of the relative displacements of
the connection at certain relevant limits, such as the first yielding of steel devices, the ultimate failure
limit or the maximum allowable deformation referred to its functionality.
Indications about cyclic decay and damage are given if relevant and when specific experimental
information is available.
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6 Floor-to-floor connections
6.1 Cast-in-situ topping
6.1.1 General
Figure 2 shows the details of a floor made of precast elements interconnected by a concrete topping
cast over their upper surface. The concrete topping, with its reinforcing steel mesh, provides a
monolithic continuity to the floor that also involves the precast elements if properly connected to it. The
diaphragm action for the in‐plane transmission of the horizontal forces to the bracing vertical elements
of the structure can be allotted entirely to the topping. Unless greater dimensions are defined from
design, for its structural functions, the concrete topping shall have a minimum thickness, t , related
min
also to the maximum aggregate size of the concrete, d, such as t = 2,4 d ≥ 60 mm.
g min g
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Figure 2— Floor made by precast elements
6.1.2 Strength
Interface shear strength of the connection between the precast element and the topping under seismic
action can be evaluated neglecting the friction contribution due to gravity loads. Transverse vertical
shear at the joint between adjacent floor elements is diverted into the topping. For the good behaviour
of the connection, proper steel links crossing the interface shall ensure, with adequate anchorages, an
effective shear tie between the two parts (see Figure 3).
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Figure 3— Precast elements with and without interface connections with topping
6.1.3 Other properties
No specific parameters of seismic behaviour (ductility, dissipation, deformation, decay, damage) have
been experimentally measured for this type of indirect connection provided by the cast‐in‐situ topping
that can be calculated like an ordinary reinforced concrete element.
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6.2 Cast-in-situ joints
6.2.1 General
Figure 4 shows the floor‐to‐floor connection made with the concrete filling of a continuous joint
between adjacent elements. It is typical of some precast products like hollow‐core slabs. The joint has a
proper shape to ensure good interlocking with the transmission of the vertical transverse shear forces,
when filled in. For the transmission of the horizontal longitudinal shear forces, the interface shear
strength can be improved providing the adjoining edges with vertical indentations. With reference to
the diaphragmatic action, this type of connections ensures that the floor has the same performance as a
monolithic cast‐in‐situ floor, provided that a continuous peripheral tie is placed against the opening of
the joints. For good filling, the maximum size of the aggregate of the cast‐in‐situ concrete shall be
limited with reference to the joint width.
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Figure 4 — Floor-to-floor connection made by concrete filling
Other types of floor‐to‐floor cast‐in‐situ connections, possibly provided with spliced tying steel links,
are not considered in this document.
6.2.2 Strength
The type of connection of concern is usually intended as a continuous longitudinal hinge. Its strength is
ensured following the specifications for the erection of the elements given by the manufacturer.
6.2.3 Other properties
No ductility and dissipation capacities are expected from the concerned type of connections that are
located away from the critical regions of the structure.
6.3 Welded steel connectors
6.3.1 General
In Figure 5 two types of floor‐to‐floor welded connections are represented. The solution a) is
constituted by two steel angles inserted at the edges of the adjacent elements and fixed to them with
anchor loops. On the joint lap, a bar is placed welded in site to the angles, compensating the erection
tolerances. Two steel plates inserted at the edges of the adjacent elements and fixed to them with
anchor loops constitute the solution b). Over the joint, a middle smaller plate is placed, welded in site to
the lateral ones. In both solutions, the steel components may be placed within a recess in order to save
the upper plane surface of the finishing. In the first solution, the angles may be replaced with plates
placed inclined so to leave in the joint the room for the positioning of the middle bar. These kinds of
connections are used to join ribbed floor elements without topping. They are also used to join special
roof elements when placed in contact one to the other.
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a)  Steel angles b)  Steel plates
Key
1 steel angles 3 steel bar
2 anchor loops 4 steel plates
Figure 5 — Floor-to-floor welded connections
These connections are distributed in some local position along the length of the floor elements. They
provide the transverse deflection consistency with the uniform distribution of the load between the
elements. Under seismic conditions, they mainly provide the transmission of the diaphragm action with
horizontal longitudinal shear forces.
6.3.2 Strength
The following indications about the mechanical behaviour of this type of connections leave out of
consideration the transverse vertical shear forces that are related to the distribution of the loads
between the elements and refer to a non‐seismic action. Proper combinations of effects should be added
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to evaluate the compatibility with the seismic action.
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6.3.2.1 Behaviour models
With reference to the transmission of the diaphragm action under seismic conditions, the behaviour
model is given in Figure 6 both for the solutions a) and b) described in 6.3.1. The longitudinal shear
force, R, shall be mainly transmitted, with no relevant transverse normal forces.
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a)  Action of the connection b)  Action with normal forces c)  Free body diagram
Key
Fc normal compression force
Ft normal tension force
Figure 6 — Behaviour models for welded steel connectors
6.3.2.2 Failure modes
The principal failure modes are as follows:
a) rupture of the welding between the angles and the interposed bar or plate;
b) failure of the interposed plate for solution b); Deleted:
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c) failure of the anchor loops for tensile yielding (see NOTE);

d) failure of the anchor loops for pull‐out(see NOTE);
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e) spalling of concrete edges due to tensile stresses.
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NOTE It is assumed that the anchor loops are fixed to the angles with an adequate welding.
6.3.2.3 Calculation formulae
In expectation of a brittle behaviour of the connection, the action R is evaluated through the analysis of
the overall structural system with an adequately reduced behaviour factor or through a reliable model
of capacity design with respect to the resistance of the critical sections of the structure, using the due
overstrength factor, γ.
R
NOTE Values γR = 1,20 for medium ductility structures and γR = 1,35 for high ductility structures.
a) welding. For the verification of the welding the usual rules shall be applied.
b) plate. Formulae (1) and (2) apply.
RR (1)
vR
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with
f
yd
Rt0,67a (2)
vR p
where
t is the plate thickness;
p
a is the plate width;
fyd is the design tensile yielding
...