Types of joints in concrete structure and their applications

2. Topics to be addressed…
• Joints
• Types of Joints
• Design of Joints

3. Joints
A Joint in a physical break or gap between members, in a concrete
structure or building is a potential weak link which may lead to
serviceability problems, lack of durability or structural failure.

4. Are Joints Necessary?
• In many situations they are necessary requirement and are sometimes
regarded as a necessary evil.
• Why?
• Concrete is subject to change in length, plane, and volume due to
changes in its temperature, moisture content, reaction with
atmospheric carbon dioxide and maintenance of loads.
• The effects may be permanent contractions to initial drying
shrinkage, carbonation, and irreversible creep.
• Other effects may result in either expansions or contractions.

5. • The movements in hardened concrete that can cause cracking can
originate from:
1. The Movements that are independent of the type of structure; these
properties include shrinkage.
2. Movements depending on the type of structure and consisting of
effects of all imposed loads such as self weight and lateral loads of
wind and earthquakes. Such movements may be deflections, elastic
strains, and strains due to creep caused by permanent loads.
3. Movements depending on the location of the structure caused by
changes in temperature and humidity.

6. Joints Terminology
• Joints will be designated by a terminology based on the
following characteristics: resistance, configuration, formation,
location, type of structure, and function.
• Resistance: Tied or reinforced, doweled, non doweled, plain.
• Configuration: Butt, lap, tongue, and groove.
• Formation: Sawed, hand-formed, tooled, grooved, insert
formed.
• Location: Transverse, longitudinal, vertical, horizontal.
• Type of Structure: Bridge, pavement, slab-on-grade building.
• Function: Construction, contraction, expansion, seismic, hinge.
• Example: Tied, tongue and groove, hand-tooled, longitudinal
pavement construction joint.

7. Jointing practice
Four primary methods are available for creating joints in concrete
surfaces forming, tooling, sawing, and placement of joint formers.
• Formed joints: These are found at construction joints in concrete
slabs and walls. Tongue and groove joints can be made with
preformed metal or plastic strips.
• Tooled joints: Contraction joints can be tooled into a concrete
surface during finishing operations. A groove intended to cause a
weakened plane and to control the location of cracking should be at
least 1/4 the thickness of the concrete.

8. Jointing practice
• Sawed joints: Use of sawed joints reduces labor during the
finishing process. Labor and power equipment are required within a
short period of time after the concrete has hardened

9. Jointing practice
• Joint formers: Joint formers can be placed in the fresh concrete
during placing and finishing operations. Joint formers can be used to
create expansion or contraction joints. Expansion joints generally
have a removable cap over expansion joint material.

10. Contraction Joints

11. Contraction Joints
• A contraction joint is formed by creating a plane of weakness. Some,
or all, of the reinforcement may be terminated on either side of the
plane. Some contraction joints, termed “partial contraction joints,”
allow a portion of the steel to pass through the joint. These joints,
however, are used primarily in water-retaining structures.
• Contraction joints consist of a region with a reduced concrete cross
section and reduced reinforcement. The concrete cross section should
be reduced by a minimum of 25 percent to ensure that the section is
weak enough for a crack to form

12. Contraction Joints
• In terms of reinforcement, there are two types of contraction joints
1. Full contraction joints (ACI 350R).
2. Partial contraction joints (ACI 350R).
• Full contraction joints:
Full Contraction joints are constructed with a complete break in
reinforcement at the joint. Reinforcement is stopped about 2 in.
from the joint and a bond breaker placed between successive
placements at construction joints.
• Partial contraction joints:
A portion of the reinforcement passes through the joint inpartial
contraction joints. Partial contraction joints are also used in liquid
containment structures.

13. Contraction Joints
• Water stoppers can be used to ensure water tightness in full and
partial contraction.
• Contraction and expansion joints within a structure should pass
through the entire structure in one plane. If the joints are not aligned,
movement at a joint may induce cracking in an un-jointed portion of
the structure until the crack intercepts another joint.

14. Spacing of Contraction Joints
• Table 1.1 shows recommendations for contraction joint spacing.
• Recommended spacing's vary from 15 to 30 ft (4.6 to 9.2 m),
from one to three times the wall height, for different structures.

15. Contraction Joint Spacing

16. Location of Contraction Joints
• The Portland Cement Association (1982) recommends that
contraction joints be placed at openings in walls, as illustrated in
following Fig.
• Sometimes this may not be possible.

17. Location of Contraction Joint

18. Expansion Joints
and Seismic Joints
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19. Expansion Joints
Expansion joints are used to allow for expansion and contraction
of concrete during the curing period and during service.
These Joints are used;
• To permit dimensional changes in concrete due to load.
• To separate, or isolate, areas or members that could be affected by
any such dimensional changes.
• To allow relative movements or displacements due to expansion,
contraction.
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20. Expansion Joints
• Differential foundation movement, or applied loads.
• Expansion joints are frequently used to isolate walls from floors or
roofs, columns from floors or cladding, pavement slabs and decks
from bridge abutments or piers, and in other locations where
restraint or transmission of secondary forces is not desired.
• Many designers consider it good practice to place expansion joints
where walls change direction as in L- T- Y-, and U-shaped
structures.
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21. • Expansion joints should not be provided unless they are very
necessary, since they can be an embarrassment to the structural and
architectural designer, as they are often incompletely detailed and
frequently badly constructed.
• They act as stress relief planes.
• The shape, size, and type of joint will function correctly for all
conditions of movement.
• Factors that should be considered in the design and detailing of
expansion joints are: shrinkage, creep, thermal movements,
foundation settlements, and elastic deformations of adjacent
structural units.
Expansion Joints
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22. Location of Expansion Joint
1.Many designers consider it good practice to place expansion joints
where walls change direction as in L- T- Y-, and U-shaped
structures, and where different cross sections develop.
Figure 3 :Joints related to shapes of Building
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23. Location of Expansion Joint
2. Expansion joints may be necessary at the junction of tall and short
buildings (Fig.4) to avoid distress due to differential settlements
3. When expansion joints are required in nonrectangular structures,
they should always be located at places where the plan or elevation
dimensions change radically.
Figure 4 :Joints related to shapes of Building
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24. Location of Expansion Joint
4. The simplest expansion joint is one on a column line with double
columns.
Figure 5 :Joints related to shapes of Building 24

25. Location of Expansion Joint
5. Expansion joints without a double column may be used by introducing
them in the third or quarter point in the slab as in figure 6.
Figure 6 :Joints related to shapes of Building
6. Joints should extend through foundation walls, but column footings
need not be cut at a joint unless the columns are short and rigid. No
reinforcement should pass through these joints.
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26. ACI Committee 350, 2006 Standards
• ACI 350R stipulates that “in general, expansion joint spacing
preferably should not be greater than 120 ft ”; however, engineering
practice over the decades and effluent leakage failures have revealed
that this spacing limit is too excessive. A modification of the ACI 350
standard given in Table 1 recommends joint spacing and widths, with
a maximum spacing of 100 ft otherwise, wide liquid-leaking cracks
could develop. It should be emphasized that the actual width of the
joint should be at least twice the expected movement.
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27. Table 1 : Recommended Joint Width and spacing
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28. Joints in Concrete Construction ACI 224.3R-95
Table 1.1 Expansion Joint Spacing
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29. Images of expansion joints
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30. 30

31. Seismic Joints
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32. Seismic Joints
• Seismic joints are wide expansion joints provide to separate portions of
buildings dissimilar in mass and in stiffness. The seismic joint coverage
must allow movement, and be architecturally acceptable.
• The width of a seismic joint should be equal to the sum of the total
deflections at the level involved from the base of the two buildings, but
not less than the arbitrary rule of 1 in. for the first 20 ft of height above
the ground, plus 1/2 in. for each 10 ft additional height.
• The determination of these deflections will be the summation of the
story drift in addition to the building's flexural deflection to the level
involved. Shear wall buildings, being much stiffer, need a seismic joint
only ,say, half as wide, since the earthquake oscillations of shear wall
buildings will be much smaller than those of framed buildings. 32

33. Seismic Joints
(a) Roof parapet separation. (b) Plan at exterior vertical closure.
Seismic separation joint details
33

34. Seismic Joints
• Nonsymmetrical configuration with reentrant corners (e.g., L-or H-
shaped buildings) are particularly susceptible to destructive torsional
effects. Primary damage often occurs at the reentrant corners.
• Allowing separate building masses to vibrate independently by using
seismic separator joints that allow free movement to occur generally
improves structural performance. 34

35. 35

36. 36

37. JOINTS IN
CONCRETE
STRUCTURE

38. Construction
Joint

39. Construction Joints
Construction joints are installed to break up the structure into
smaller units in accordance with the production capacity of the
construction site. They are stopping places in the process of
placing concrete.
Construction joint may be designed to permit movement and to
transfer load but true construction joints are not designed to
provide for any movements

40. Types of
Construction Joint
Construction joints can be of multiple types
Keyed (Tongue and Groove)
Butt Joint (Doweled/Tied)
Straight Horizontal Joint

41. Types of
Construction Joint

42. Types of
Construction Joint

43. Types of
Construction Joint

44. Functions
The main concern in joint placement is to provide
adequate shear transfer and flexural continuity through
the joint as if it were monolithic across the joint with no
significance impairment of strength. A construction
joint normally be required to transmit one or more of
following stresses
Axial Tension/Compression
Flexure
Shear
Torsion

45. Joint Location
Construction joint should be located where they will least affect
the structural integrity of element under consideration and be
compatible with building appearance.
For continuous members it should be located where bending
moments are low and shear force
is modest

46. Joint Location
Beam and Slab: (ACI-Ref. 2, Section 6.4.4)
Perpendicular to the main reinforcement.
Point of minimum shear or point of contra flexure, usually located at middle third of span.
Where beam intersects a girder; construction joint in girder should be offset a distance equal to twice the width
of incident beam.

47. Joint Location
Horizontal construction joint in beam and girder are usually not recommended.
For beam and girder of considerable depth, it is recommended to place concrete in beam section up to the slab
soffit, then placing slab in a separate operation.

48. Joint Location

49. Joint Location
Columns and Retaining Walls:
Undersides of floor slab and beams.
Top of floor slab.
Corners of walls, besides columns, or where they become an architectural feature of structure.
Avoid vertical construction joint at or near corner.
For water tightness a continuous water stop of plastic or rubber is essential.

50. Joint Location

51. Joint Construction
To achieve a well bonded watertight interface,
few conditions should be met before placement of
fresh concrete:
If only few hours elapsed between successive placement the hardened concrete is
specified to be clean and free of laitance. The new concrete will be adequately
bonded to hardened concrete, provided that the new concrete is vibrated
thoroughly.
Older joints need additional surface preparation. Cleaning by air water jet or wire
brooming can be done, when the concrete is soft enough that laitance can be
removed but hard enough to prevent aggregate from loosening.

52. Joint Construction
Dry concrete should be moistened thoroughly, it should be saturated for a day or more.(ACI committee 318,
2008)
Where concrete is to be placed on hardened concrete a layer of mortar on hardened surface is needed to
provide a cushion against which the new concrete can be placed. The fresh mortar prevents stone-pockets and
assists in securing a tight joint. The mortar should have a slump of less than 6” and should be made of same
materials as the concrete but without coarse aggregate.

53. Construction Joint
in Slab

54. Construction Joint
for Raft Foundation

55. Construction Joint in
Retaining Wall

56. Beam-column
Joint

57. Beam-Column
Joint
Beam-Column joint In RCC buildings the portion of column that
are common to the beam at their intersection are called beam
column joints.
Beam-Column joints are the weakest link in RC moment resisting
frame.(so need proper designing)

58. Classification
based on location
Depending upon the location of joint in the structure,
the joints are classified in three groups as follows:
• Corner Joint
• Exterior Joint
• Interior Joint

59. Classification
based on location

60. Classification based
on loading
The ACI Committee 352 on the design of reinforced concrete beam column joints
divides joints into two groups depending on the deformations the joints are subjected to:
Type I: Structures that are not subjected to large inelastic deformations and do not need
to be designed according to ACI Code Chapter 21 are referred to as non seismic
structures.
Type II: Structures that must be able to accommodate large inelastic deformations and
as a result must satisfy ACI Code Chapter 21 are referred to as seismic structures.

61. Types of Analysis
A number of models have been developed for force transfer in beam-column
joints. The two most popular models are the
Truss model: Assumes perfect bond of rebar in joint and assumes all forces are
transmitted to the joint by longitudinal reinforcement.
Diagonal strut model: Assumes no bond of rebar in joint; force is applied as a
compression force in the concrete on the opposite side of the joint.
Truss Model Diagonal strut model

62. Failure Mechanism

63. Design Approach
The ACI Committee 352 design procedure for beam-
column joints consists of three main stages:
1. Provide confinement to the joint region by means of
beams framing into the sides of the joint or by a
combination of the confinement from the column bars
and from the ties in the joint region.
2. The beam steel must be inside the column steel.
3. Limit the shear in the joint.
4. Limit the bar size in the beams to a size that can be
developed in the joint.
5. For best joint behavior, the longitudinal column
reinforcement should be uniformly distributed around
the perimeter of the column core

64. Column Longitudinal
Reinforcement
For Type 1 connections, longitudinal column bars may be
offset within the joint.
For Type 2 connections, longitudinal column bars
extending through the joint should be distributed around
the perimeter of the column core.
 Uniform distribution of the column longitudinal
reinforcement improves confinement of the column
core.
 Extra ties are recommended where column longitudinal
bars are offset within the joint to resist tension arising
from
the tendency for straightening of the offset bends.

65. Development of Reinforcement
(Critical Sections)
The critical section for development of reinforcement,
should be taken at the face of the column for Type 1
connections.
For Type 2 connections critical section is taken at the
outside edge of the column core for Type 2
connections.

66. Development of
Reinforcement
Type 1 connections, the development length ldh of a bar
terminating in a standard hook within a joint should be computed
as follows

67. Development of
Reinforcement
For Type 2 connections, bars terminating within
the confined core of the joint should be anchored using a 90-
degree standard hook. The development length, measured from the
critical section as
where a is the stress multiplier for longitudinal reinforcement

68. ACI 318M-02 suggests the length of tail as 12 db.
Development of Reinforcement

69. For Type 1 connections, no recommendations are
made.
For Type 2 connections, all straight beam and column bars
passing through the joint should be selected such that
db = nominal diameter of bar
hc = full depth of column
The purpose of the recommended value for h/db is to
limit slippage of the beam and column bars through the
joint.
Development of Reinforcement
(Member Size)

70. Joint shear
The horizontal shear in the joint should be checked independently in each direction. The
design shear force Vu should be computed on a horizontal plane at the midheight of the
joint. The following equation should be satisfied
where ϕ = 0.85 and Vn, the nominal shear strength of the joint
If this is not satisfied, either the size of the column will need to be increased or the
amount of shear being transferred to the joint will need to be decreased.

71. Vn, the nominal shear strength of the joint given by
bj is the effective joint width
hc is the depth of the column in the direction of joint
γ is the constant that depends on the connection classification
Joint shear

72. Joint shear

73. Joint shear
The effective joint width bj should not exceed the smallest of

74. Joint Transverse
Reinforcement
Transmission of the column axial load through the
joint region, and transmission of the shear demand
from columns and beams into the joint, require
adequate lateral confinement of the concrete in the
joint core by transverse reinforcement, transverse
members, or both.
Shear reinforcements for the horizontal shear are
supported by stirrups and hoops whereas the
vertical shear is taken care by intermediate column
bars.

75. Detailing of Shear
Reinforcement
Detailing features relevant to beam-column joints are concerned
with aspects such as spacing of longitudinal and transverse
reinforcement and development length for embedded bars

76. Detailing of Shear
Reinforcement
For Type-1 joints, ACI Committee 352 recommends that at least two layers of transverse
reinforcement (ties) be provided between the top and the bottom levels of the longitudinal
reinforcement. The vertical center-to-center spacing of the transverse reinforcement should not
exceed 12 in. in frames resisting gravity loads and should not exceed 6 in. in frames resisting
nonseismic lateral loads.
In nonseismic regions, the transverse reinforcement can be closed ties, formed either by U-
shaped ties and cap ties or by U-shaped ties that are lap spliced within the joint.
The hoop reinforcement can be omitted within the depth of the shallowest beam entering an
interior joint, provided that at least three-fourths of the column width is covered by the beams on
each side of the column.

77. Detailing of Shear
Reinforcement
The preferred shape of a single leg cross-tie would have a 135-degree bend at both ends.
Installation with such a configuration is difficult.
ACI 318M-02 allows standard 90-degree hook at one end of the cross tie with an extension not
less than 6 times the diameter of the stirrup. But a 90- degree hook does not provide effective
anchorage since it is not embedded in the confined column core. Hence, ACI code recommends
alternate placement of a 90-degree hook on opposite faces of the column.
In case of exterior and corner connections, where the loss of cover could affect the anchorage of
crossties at the 90-degree bend, it is recommended that only the 135-degree bend be used at the
exterior face of the joint.

78. Detailing of Shear
Reinforcement

79. Detailing of Shear
Reinforcement

80. Detailing of Shear
Reinforcement
The vertical spacing of ties in columns should not exceed D/4 or
6db at a distance of hc/6 above and below the beam-column
junction. Maximum spacing shall not be more than D/2
D is the smallest dimension of the column.
db is the dia of longitudinal bars.
hc is the clear height of the column.
Horizontal spacing of stirrups in beams should not exceed d/4.
Maximum Spacing shall be less tha db/2
where d is the effective depth of the beam.

81. Detailing of Shear Reinforcement

82. Detailing of Shear Reinforcement

83. Column Detailing. (ACI 315-99)

84. Column Detailing. (ACI 318-02)

85. Placement of Ties
in Joints

86. Beam Column
Joint

87. Beam Column
Joint

88. Beam Column
Joint