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

drqaisarali@uetpeshawar.edu.pk

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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

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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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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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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 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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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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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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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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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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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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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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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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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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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

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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)

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References