3/25/2016
1
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
1
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
2
3/25/2016
2
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.
3/25/2016
3
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.
5
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
6
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.
3/25/2016
4
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.
8
ℓd =3
40
��
λ ��′ Ψ�Ψ�
Ψ�
�� + �����
��
3/25/2016
5
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
9
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 ��
���
10
When λ, Ψt and Ψs values are taken equal to 1
3/25/2016
6
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
11
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
12
ℓdh =
�� ��
65 λ ��′
3/25/2016
7
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
13
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.
14
For more details refer to
section 5.4 of Design of
Concrete Structures 14th
Ed. by Nilson, Darwin and
Dolan.
3/25/2016
8
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
15
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
16
3/25/2016
9
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.
17
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
18
3/25/2016
10
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.
19
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).
20
3/25/2016
11
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
21
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).
22
3/25/2016
12
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.
23
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.
24
3/25/2016
13
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.
25
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.
26
3/25/2016
14
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
27
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
3/25/2016
15
Department of Civil Engineering, University of Engineering and Technology Peshawar, Pakistan
Prof. Dr. Qaisar Ali CE 320 Reinforced Concrete Design-I
Curtailment of reinforcement
29
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