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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Lecture 05
Development Length, Lap Splices and curtailment of
reinforcement
By: Prof Dr. Qaisar Ali
Civil Engineering Department
UET Peshawar
[email protected]
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Topics Addressed
Development Length
Development Length of Compression Reinforcement
ACI provisions for Development of Tension Reinforcement
ACI provisions for Development of Standard Hook in Tension
Dimensions & Bends for Standard Hooks
Various Scenarios where ldh must be satisfied
Splices of Deformed Bars
Curtailment of reinforcement
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Development Length
3
P
ℓ
If the force P applied on the concrete block is gradually
increased then
depending on the embedment length provided the following two
conditions are
possible:
1. The bar will be pulled out of the concrete block.
2. Or the steel will be yielded without pulling the bar out of
concrete block
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Development Length
4
P
ℓ
Development length (ℓd) is the minimum length of the bar to be
embedded in
the concrete block so that the bar is yielded but not pulled out
of the concrete
block due to bond failure.
If the provided embedment length (ℓ) is less than the
development length (ℓd),
the bar will be pulled out of the concrete block which is termed
as bond failure.
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
There are two types of Bond Failure
1. Direct pullout of reinforcement: Direct pullout of
reinforcement
occurs in members subjected to direct tension.
2. Splitting of concrete: In members subjected to tensile
flexural
stresses, the reinforcement causes splitting of concrete as
shown.
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Development Length
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Development Length of Compression
Reinforcement
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In the case of bars in compression, a part of the total force
is
transferred by bond along the embedded length, and a part is
transferred by end bearing of the bars on the concrete.
As the surrounding concrete is relatively free of cracks and
because of the beneficial effect of end bearing, shorter
basic
development lengths are permissible for compression bars than
for
tension bars.
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Development Length of Compression
Reinforcement
7
In the next portion of the lecture we will discuss the
development
length of tension reinforcement only because it is the
governing
criteria in most of the cases in reinforced concrete
structures.
For more details refer to section 5.8 of Design of Concrete
Structures 14th Ed. by Nilson, Darwin and Dolan.
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
ACI Provision for Development of
Tension Reinforcement
Basic Equation (ACI 25.4.2.3)
For deformed bars or deformed wire, ld shall be:
For practical construction the (c + Ktr)/db is taken 1.5.
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ℓd =3
40
��
λ ��′ Ψ�Ψ� Ψ��� + ���
��
��
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
ACI Provision for Development of
Tension Reinforcement
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
ACI Provision for Development of
Tension Reinforcement
Basic Equation (ACI 25.4.2.3)
For for No. 7 and larger bars, (Ψe = 1), the equation is reduced
to
ℓd = ��
20 ��
���
For No. 6 and smaller bars, (Ψe = 0.8), the equation is reduced
to
ℓd = ��
25 ��
���
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When λ, Ψt and Ψs values are taken equal to 1
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
ACI Provision for Development of
Tension Reinforcement
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ld for grades 40 and 60
ℓd = ��
�� ��
��� (No. 7 bars and larger)
ℓd = ��
�� ��
��� (No. 6 bars and smaller)
Bar No Grade 40 Grade 60
#3 12 16
#4 15 22
#5 18 27
#6 22 33
#7 32 48
#8 37 55
#9 41 62
For more details refer to
section 5.3 of Design of
Concrete Structures 14th
Ed. by Nilson, Darwin and
Dolan.
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
ACI Provision for Development of
Standard hook in Tension
If a hook is provided at the end of the embedded bar, the
requirement
on the straight length portion of embedded bar is reduced.
The
development length with hook (ldh) is given as follows
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ℓdh = �� ��
65 λ ��′
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
ACI Provision for Development of
Standard hook in Tension
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ldh (inches) for grades 40 and 60( fc′ = 3000 psi λ = 1)
ldh = fy db / (65 λ √fc′)
Bar No. Grade 40 Grade 60
#3 4.2 6.3
#4 5.6 8.4
#5 7 10.5
#6 8.4 12.6
#7 9.8 14.7
#8 11.2 16.8
#9 12.6 18.9
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Dimensions and bends for standard
hooks Standard bends in reinforcing bars are described in terms
of the inside
diameter of bend since this is easier to measure than the radius
of bend.
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For more details refer to
section 5.4 of Design of
Concrete Structures 14th
Ed. by Nilson, Darwin and
Dolan.
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Various scenarios where ldh must be
satisfied
Beam Column Joint
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Development of beam reinforcement in column shall be >
ldh
Development of beam reinforcement in column shall be >
ldh
ColumnBeam
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Various scenarios where ldh must be satisfied
Development of column reinforcement in foundation
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Introduction
Splice means “to join”.
In general, reinforcing bars are stocked by supplier in lengths
upto
60′. For this reason, and because it is often more convenient
to
work with shorter bar lengths, it is frequently necessary to
splice
bars.
Splices in the reinforcement at points of maximum stress should
be
avoided.
Splices should be staggered.
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Types
Bar splicing can be done in three ways:
Lap Splice
Mechanical Splice
Welded Splice
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Lap Splice
Splices for #11 bars and smaller are usually made simply lapping
the
bars by a sufficient distance to transfer stress by bond from
one bar
to the other.
The lapped bars are usually placed in contact and lightly wired
so
that they stay in position as the concrete is placed.
According to ACI 25.5.1.3, bars spliced by noncontact lap
splices in
flexural members shall not be spaced transversely farther apart
than
one-fifth the required lap splice length, nor 6 inches.
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Lap Splice
According to ACI 25.5.2.1, minimum length of lap for tension
lap
splices shall be as required for Class A or B splice, but not
less
than 12 inches, where:
Class A splice
................................................... 1.0ld
Class B splice
................................................... 1.3ld
Where ld is as per in ACI 25.4 (discussed earlier).
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Lap Splice
Lap splices in general must be class B splices according to
ACI
25.5.2.1, except that class A splice is allowed when the area of
the
reinforcement provided is at least twice that required by
analysis
over the entire length of the splice and when ½ or less of the
total
reinforcement is spliced within the required lap length.
The effect of these requirements is to encourage designers
to
locate splices away from regions of maximum stress to a
location
where the actual steel area is at least twice that required
by
analysis and to stagger splices
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Lap Splice
According to ACI 25.5.5.2, tension lap splices shall not be used
for
bars larger than #11 (Because of lack of adequate
experimental
data on lap splices of No. 14 and No. 18 bars).
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Mechanical Splice
In this method of splicing, the bars in direct
contact are mechanically connected through
sleeves or other similar devices.
According to ACI 25.5.7.1, a full mechanical
splice shall develop in tension or compression,
as required, at least 125 percent of specified
yield strength fy of the bar.
This ensures that the overloaded spliced bar
would fail by ductile yielding in the region away
from the splice, rather than at the splice where
brittle failure is likely.
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Welded Splice
Splicing may be accomplished by welding in which bars in
direct
contact are welded so that the stresses are transferred by
weld
rather than bond.
According to ACI 25.5.7.1, A full welded splice shall develop
at
least 125 percent of the specified yield strength fy of the
bar.
This is for the same reason as discussed for mechanical
splices.
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Welded Splice
Splicing may be accomplished by welding in which bars in
direct
contact are welded so that the stresses are transferred by
weld
rather than bond.
According to ACI 25.5.7.1, A full welded splice shall develop
at
least 125 percent of the specified yield strength fy of the
bar.
This is for the same reason as discussed for mechanical
splices.
For more details refer to section 5.13 of Design of Concrete
Structures 14th Ed. by Nilson, Darwin
and Dolan.
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Splices of Deformed Bars
Lap splice location
The splicing should be avoided in the critical locations, such
as at
the maximum bending moment locations and at the shear
critical
locations.
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
a
a
b
b
Curtailment of reinforcement
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Curtailment of reinforcement
28
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3/25/2016
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Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Curtailment of reinforcement
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For more details refer to section 5.10 of Design of Concrete
Structures 14th Ed. by Nilson, Darwin and Dolan.
Department of Civil Engineering, University of Engineering and
Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Design of Concrete Structures 14th Ed. by Nilson, Darwin and
Dolan.
Building Code Requirements for Structural Concrete (ACI
318-14)
30
References
