development 20 and 20 splicing

8/16/2019 Development 20 and 20 Splicing

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By Jerry M. Spiker, P.E., AIA, LEED AP

December 2008


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Reinforcement is used in concrete flexural membersto resist flexural tension or to increase the flexuralcompression capacity of the member. The AmericanConcrete Institute’s Building Code Requirements

for Structural Concrete (ACI 318-08) requires the calculatedtension or compression in reinforcement at each section tobe developed on either side of that section. The reinforce-ment may be developed by embedment length, hooks,mechanical anchorage devices, headed deformed reinforce-ment, or a combination of these methods.

This article discusses development and splicing of reinforcement steel in flexural members. It does not includereinforcement for columns, compression reinforcement in

flexural members, or deep beams. It also does not addressdevelopment or splicing of wire, welded wire fabric, orpost-tensioning cables.

The basic parameter for development and splicing of

reinforcement steel in flexural members is the tension devel-opment length, l d . According to ACI 318-08, the tensiondevelopment length is a function of the diameter of the rein-

forcement bar ( d b), the yield strength of the reinforcement(f y ), and the specified concrete compressive strength ( f c ).

Five other factors affect the tension development length: Reinforcement location ( t ): For bars that are placed sothat there is more than 12 inches of fresh concrete castbelow the development length or splice (top bars), t =1.3. For all other bars, t = 1.0.

Epoxy-coated reinforcement ( e ): For epoxy-coated barsthat are closely spaced or have limited concrete cover, e = 1.5. For other epoxy coated bars, e = 1.2. For uncoatedbars or galvanized bars, e = 1.0.

Smaller bar sizes ( s ): For bars that are No. 6 or smaller, s= 0.8. For bars that are No. 7 or larger, s = 1.0.

Lightweight concrete: For lightweight concrete, cannotexceed 0.75. For normal weight concrete, = 1.0. If theaverage splitting tensile strength, f ct , of the concrete isspecified, can be determined from the specified f ct . Thevalue of is applied in the denominator of the tensiondevelopment length equation.

Confinement: The confinement term, (c b + Ktr )/d b,accounts for close bar spacing or limited concrete coveron the reinforcement, and the lack of confining reinforce-ment, such as stirrups or ties. In many current practicalconstruction cases, the confinement term is at least 1.5.The confinement term is also applied in the denominatorof the tension development length equation.

The equation for tension development length in ACI318-08 is as follows:

By Jerry M. Spiker, P.E., AIA, LEED AP

The Professional Development Series is a unique

opportunity to earn continuing education creditby reading specially focused, sponsored articles inStructural Engineer . If you read the following arti-cle, display your understanding of the stated learningobjectives, and follow the simple instructions, you can

fulfill a portion of your continuing education require-ments at no cost to you. This article also is availableonline at www.gostructural.com/pg.asp?id=20.

First, review the learning objectives below, thenread the Professional Development Series article. Next,complete the quiz and submit your answers to theProfessional Development Series sponsor. Submittalinstructions are provided on the Reporting Form, which

follows the quiz on page PDH 7. Your quiz answers willbe graded by the Professional Development Seriessponsor. If you answer at least 80 percent of the ques-tions correctly, you will receive a certificate of comple-tion from the Professional Development Series sponsorwithin 90 days and will be awarded 1.0 professionaldevelopment hour (equivalent to 0.1 continuingeducation unit in most states). Note: It is the responsibil-ity of the licensee to determine if this method of continu-

ing education meets his or her governing board(s) ofregistration’s requirements.

This article discusses development and splicing of

reinforcement in concrete flexural members. Afterreading the article and completing the quiz, readersshould understand the requirements for developmentof longitudinal flexural reinforcement and for deter-mining tension development length and splice length

for reinforcement. The article presents the AmericanConcrete Institute’s Building Code (ACI 318-08) design

provisions for development and splicing of reinforce-ment. All referenced items are from ACI 318-08 unlessnoted otherwise. Also, all notations and definitions inthe article are in accordance with Chapter 2 of ACI318-08.

Portland Cement Association


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The equation for the developmentlength of headed deformed bars in tension

is given as follows:

l dt= 0.016 e f y

f c

d (Equation 3)b

Except where the development of f y is specifically required,the development length for headed deformed bars may bereduced by the ratio [( As required)/( As provided)] whenreinforcement in a flexural member exceeds the reinforce-ment required by analysis. Also as for hooks, the minimumdevelopment length, including the various modification

factors, is 6 inches or 8 d b. For Grade 60 reinforcement,assuming normal weight concrete ( = 1.0) and uncoated( e = 1.0) bars, the development length l dt of headeddeformed bars as a function of d b can be determined

from Table 3 for various concrete compressive strengths,provided the net bearing area of the head is not less than four times the area of the bar, and the clear cover and spac-ing requirements are met.

When beam reinforcement with headed bars terminatesat a column, the reinforcement should extend through thecolumn to the far face of the confined core (while still main-taining the required cover and avoiding interference with thevertical column reinforcement), even though the anchoragelength exceeds l dt , to anchor compressive forces that maydevelop and to improve the performance of the joint.

ACI 318-08 requires flexural reinforcement steel to be

developed at critical sections, which are defined as points

of maximum stress, and at points within the span whereadjacent bars are terminated. It is usually not economical toprovide the same amount of reinforcement that is requiredat the point of maximum stress for the entire length of a

flexural member. ACI 318-08 permits reinforcement to beomitted beyond the point where calculation indicates thatreinforcement is not required, provided that the continuingreinforcement bars have adequate anchorage, l d , beyond

the theoretical cut-off point of the terminated bars.Moment diagrams used to determine the points of

maximum positive or negative momentare typically approximate; the point ofmaximum moment may shift approxi-mately a distance d due to changes inloading, settlement of supports, lateralloads, or other causes. To provide forthese shifts, ACI 318-08 requires flexuralreinforcement to extend a distance of d or 12 d b , whichever is greater, beyondthe point where the reinforcement istheoretically no longer required.

When flexural reinforcement is termi-nated in a tension zone, additionalconditions must be satisfied to preventdiagonal tension cracks from openingearly (see ACI 318-08 section 12.10.5).

For simple span members, at least one-third the positive moment reinforcement

Table 2: Development length l dh (inches) of standard hooks foruncoated Grade 60 bars *

fc (Normalweight Concrete), psi

Bar Size No. 3,000 4,000 5,000 6,000 8,000 10,000 3 8.2 7.1 6.4 5.8 5.0 4.5 4 11.0 9.5 8.5 7.7 6.7 6.0 5 13.7 11.9 10.6 9.7 8.4 7.5 6 16.4 14.2 12.7 11.6 10.1 9.0 7 19.2 16.6 14.8 13.6 11.7 10.5 8 21.9 19.0 17.0 15.5 13.4 12.0 9 24.7 21.4 19.1 17.5 15.1 13.5 10 27.8 24.1 21.6 19.7 17.0 15.2 11 30.9 26.8 23.9 21.8 18.9 16.9 14 37.1 32.1 28.7 26.2 22.7 20.3 18 49.5 42.8 38.3 35.0 30.3 27.1

* Development length l dh (including modification factors)must not be less than the larger of 8d b or 6 inches.

Headed deformed bars utilized on the Trump International Hoteland Tower, Chicago.


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must extend into the support at least 6 inches. For continu-ous members, one-fourth of the positive rein-

forcement must extend into the support. If thebeam is part of a primary seismic load-resistingsystem, this reinforcement must be anchoredto develop f y in tension at the face of supportto ensure ductility in the event of a seriousoverstress. It is not acceptable to use morereinforcement at lower stresses.

At locations with small moment but a largeshear, such as at simple supports or at pointsof inflection, the development length, l d ,

computed for f y must not exceed the valueM n /V u + l a , where M n is the nominal strengthof the beam without the -factor. At a simplesupport, l a is the embedment length beyondthe center of support. At an inflection point,l a is limited to d or 12 d b , whichever is greater.The value of M n /V u can be increased by 30percent if the end of the reinforcement isconfined by a compressive reaction, such asprovided by a column below the beam, butnot when a beam frames into a girder. If thecomputed l d exceeds the given value, smallerbars must be used to decrease the computedl d , or at a simple support, the reinforcementmust terminate beyond the centerline of the

support with a standard hook or a mechan-ical anchor equivalent to a standard hook.

In addition to the requirements for devel-opment of the reinforcement, the code requiresreinforcement to be detailed to improve the integrityof the overall structure. At beams along the perimeter ofthe building, at least one-fourth of the positive momentreinforcement must be continuous over the length of thespan and pass through the vertical column reinforcement.

At noncontinuous supports, the reinforcement must bedeveloped using development length, a standard hook,or a headed deformed bar. As with bars that are extendedinto the support to provide ductility for seismic members,the reinforcement must develop the full f y in tension. It isnot acceptable to use more reinforcement at lower stresses.In addition, the continuous positive reinforcement mustbe enclosed by transverse reinforcement (closed stirrups),except the transverse reinforcement does not need toextend through the column. In non-perimeter beams, either

the transverse reinforcement or the continuous positivemoment reinforcement described above must be provided.

Table 3: Development length l dt (inches) of headeddeformed bars for uncoated Grade 60 bars *

fc (Normalweight Concrete), psi

6,000Bar Size No. 3,000 4,000 5,000 or larger 3 6.6 5.7 5.1 4.6 4 8.8 7.6 6.8 6.2 5 11.0 9.5 8.5 7.7 6 13.1 11.4 10.2 9.3 7 15.3 13.3 11.9 10.8 8 17.5 15.2 13.6 12.4 9 19.8 17.1 15.3 14.0 10 22.3 19.3 17.2 15.7 11 24.7 21.4 19.1 17.5

* Development length l dt (including modification factors) must notbe less than the larger of 8d b or 6 inches.

Figure 1: Positive moment reinforcement — Note:a portion of total positive reinforcement (As+)must be continuous (or spliced with a Class Bsplice or a mechanical or welded splice satisfying12.14.3) along the full length of perimeter beamsand of beams without closed stirrups (7.13.2.2).

Bars B Bars AP.I.

See Fig. 2 fordevelopment of negativemoment reinforcement

Note (b)

Point of infl ection P.I.

d, 12d (12.10.3)b

Criticalsectionfor bars A(12.10.2)

Flexural strengthof bars A & B

+Mu

Criticalsectionfor bars B(12.10.2)

d bars A (12.1)

Note: See ACI 318-08 Section 12.10.5 fortermination of reinforcementin a tension zone.

Flexural strengthof bars B

Embedment of Bars B (12.10.4)


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1. Which of the following is not included in the calculation fordetermining tension development length?a) Specified compressive strength of concrete, f c

b) Strength reduction factor,

c) Specified yield strength of reinforcement, f y d) Reinforcement location factor, t

2. What value for the lightweight concrete factor is to be used indetermining the tension development length when lightweightconcrete is used?a) = 1.0b) = 0.85 for sand-lightweight concrete or = 0.75 for all-lightweight

concretec) shall not exceed 0.75 unless f ct is specifiedd) = 1.3

3. What is the minimum size of the head required to anchor a headeddeformed bar?a) A diameter of 2 inchesb) Twice the diameter of the reinforcement bar c) The net bearing area of the head must be at least four times the

area of the bar.d) No more than one-half the clear spacing between the headed bars

4. Which of the following is not included in the calculation fordetermining the development length of standard hooks in tension?a) Specified compressive strength of concrete, f c

b) Reinforcement location factor, t

c) Lightweight concrete factor, d) Specified yield strength of reinforcement, f y

5. Which of the following is a critical section for development ofreinforcement in a flexural member?a) At the maximum positive moment near midspanb) At the maximum negative moment at the face of the support

c) At points within the span where adjacent reinforcement bars areterminated

d) All of the above

6. In perimeter beams, how much of the positive momentreinforcement is required to extend into the supporting column toprovide for structural integrity?a) All of the positive moment reinforcement barsb) At least one-fourth of the positive moment reinforcement, but not

less than two barsc) Positive moment reinforcement need not extend beyond the point

where it is no longer theoretically required.d) Two bars if b 24 inches, 4 bars if b 24 inches

7. The largest bar that may use a tension lap splice is:a) #18 bar c) #11 bar b) #14 bar d) #10 bar

8. Class B lap splices are required where:a) The area of reinforcement steel at a lap splice is less than twice the

areas of steel determined by analysisb) More than one-half of the total reinforcement is to be lap spliced

within the lap lengthc) Structural integrity reinforcement is to be lap splicedd) All of the above

9. Mechanical or welded splices for a #8 bar must develop:a) 125 percent of the tension yield strength, f y

b) 48 kips in tensionc) The actual tensile strength of the reinforcementd) The stress in the reinforcement determined by analysis

10. The minimum development length for hooks and for headeddeformed bars is:a) 12 inches c) 4 d bb) 6 inches or 8 d b, whichever is greater d) No minimum required

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Structural Engineers Article Title: Development and Splicing of Flexural Reinforcement Based on ACI 318-08 Publication Date: December 2008Sponsor: Portland Cement Association Valid for credit until: December 2010

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