The Strength of Anchored Bars

90 Pages·2007·2.08 MB·English

TECHNICAL REPORT STANDARD TITLE PAGE
1. Report No. 2. Government Accession No. 3. Recipient's Calalog No.
4. Tille and Subtitle 5. Reporl Dole
January 1975
"The Strength of Anchor Bars: A Reevaluation of
6. Per/orming Organi zalion Code
Test Data on Development Length and Splices"
7. AUlhor's) 8. PerformIng Organi zalion Reporl No.
C. O. Orangun, J. O. Jirsa, and J. E. Breen Research Report l54-3F
9. Performing Organizalion Nome and Address 10. Wor~ Unil No.
Center for Highway Research
11. Conlrocl or Gronl No.
The University of Texas at Austin
Research Study 3-5-72-154
Austin, Texas 78712
13. Type of Reporl and Period Covered
r----------------------------------------------------------~
12. Sponsoring Agency Name and Address
Final
Texas Highway Department
Planning & Research Division
P.O. Box 5051 14. Sponsori ng Agenc y Code
Austin, Texas 78763
15. Supplemenlary Noles
Work done in cooperation with the Federal Highway Administration, Department
of Transportation.
Research Study Title: ''Factors Affecting Splice Development Length"
16. Ab.'roc'
An equation has been developed for calculating lengths of lap splices of
deformed bars from a nonlinear regression analysis of test results of beams with
lap splices. It reflects the effect of length, cover, spacing, bar diameter,
concrete strength, transverse reinforcement, and moment gradient on the strength of
lap splices. The equation is also applicable in determining basic development
lengths. Based on the equation developed, design recommendations are proposed for
development lengths and lap splices and compared with AASHTO Interim Specifications
for Bridges, 1974. The comparison shows that for the most unfavorable splice
conditions (a clear cover of 1-1/2 in. on sides or bottom, splices with no trans
verse reinforcement, all bars spliced in a region of maximum moment, and bar
spacing less than 6 in. on centers) AASHTO provisions overestimate lap lengths
by 11 percent for #6, 16 percent for #8, and 25 percent for #11 bars. If cover is
increased to 3 in. or transverse reinforcement is added, the splice length of large
bars may be reduced by as much as 60 percent over that required by present AASHTO
provisions. Furthermore, the equations governing development length are essen
tially the same as those for splice length.
17. Key Word. 18. Di.tribution Statement
lap splices, deformed bars, test,
beams
19. S.curity Clallil. (of this report) 20. S.c:urity Clollil. (of thi s page) 21. No. of Page. 22. Price
Unclassified Unclassified 90
Form DOT F 1700.7 IS-69)
THE STRENGTH OF ANCHORED BARS: A REEVALUATION OF TEST DATA
ON DEVELOPMENT LENGTH AND SPLICES
by
C. O. Orangun
J. O. Jirsa
J. E. Breen
Research Report No. l54-3F
Research Project 3-5-72-154
Factors Affecting Splice Development Length
Conduc ted for
The Texas Highway Department
In Cooperation with the
U. S. Department of Transportation
Federal Highway Administration
by
CENTER FOR HIGHWAY RESEARCH
THE UNIVERSITY OF TEXAS AT AUSTIN
January 1975
.... '
..
, "
The contents of this report reflect the views of the
authors, who are responsible for the facts and the
accuracy of the data presented herein. The contents
do not necessarily reflect the official views or
policies of the Federal Highway Administration. This
report does not constitute a standard, specification, -
or regula tian.
11
PRE F ACE
This report presents an extensive study of data on lap splices
and development lengths with the aim of developing design provisions for
inclusion in AASHTO Specifications.
This is the final report on work conducted under Project 3-5-72-154,
"Factors Affecting Splice Development Length." Reports 154-1 and 154-2
describe experimental work conducted under this program. The program was
sponsored by the Texas Highway Department and Federal Highway Administra
tion, and administered by the Center for Highway Research at The University
of Texas at Austin. Close liaison with Texas Highway Department has been
maintained through Mr. Wesley Pair and with the Federal Highway Administra
tion through Mr. Jerry Bowman.
This study, made while the principal author was on sabbatical leave
from the University of Lagos, Nigeria, was under the general direction of
Professor J. E. Breen and the immediate supervision of Professor James O.
Jirsa. Special thanks are due to Professor Breen for giving the principal
author an opportunity to participate in the program and also for his con
tinued interest and advice. There were extensive discussions during this
study with Professor Phil M. Ferguson, whose suggestions are gratefully
acknowledged.
iii
-
A B S T RAe T
An equation has been developed for calculating lengths of lap
splices of deformed bars from a nonlinear regression analysis of test
results of beams with lap splices. It reflects the effect of length,
cover, spacing, bar diameter, concrete strength, transverse reinforce
ment, and moment gradient on the strength of lap splices. The equation
is also applicable in determining basic development lengths. Based on
the equation developed, design recommendations are proposed for develop
ment lengths and lap splices and compared with AASHTO Interim Specifica
tions for Bridges, 1974. The comparison shows that for the most
unfavorable splice conditions (a clear cover of 1-1/2 in. on sides or
bottom, splices with no transverse reinforcement, all bars spliced in
a region of maximum moment, and bar spacing less than 6 in. on centers)
AASHTO provisions overestimate lap lengths by 11 percent for #6, 16 per-
cent for #8, and 25 percent for #11 bars. If cover is increased to 3 in.
or transverse reinforcement is added, the splice length of large bars may
be reduced by as much as 60 percent over that required by present AASHTO
provisions. Furthermore, the equations governing development length are
essentially the same as those for splice length.
KEY WORDS: lap splices, deformed bars, test, beams.
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IMP L E MEN TAT ION
The design proposals made in this study are based on equations
derived empirically using test results from a number of well-documented
studies. The basic equation proposed for splice or development length
is a function of steel stress, concrete strength, bar diameter, side or
bottom cover and transverse reinforcement, is expressed as follows:
For Grade 60 reinforcement
10200 db
It is reconnnended that the value of C/d to be used in this equa'tion be
b
not more than 2.5 and the resulting ts or td be not less than 12 in. The
factor K represents the effect of transverse reinforcement. A capacity
tr
reduction factor In of 0.8 is reconnnended. Modification factors for other
grade steel~ for wide spacing~ and for top cast bars are presented.
The use of the proposed design can produce splices as much as
60 percent shorter than those designed under current AASHTO provisions.
Such changes can materially reduce the congestion in spliced regions of
reinforced concrete members and simplify construction procedures. In
addition, the proposed design approach consolidates development and splice
length provisions under a single specification which is convenient to use
and interpret. Therefore, the implementation of the proposed design
should result in substantial economies in design time and material costs.
v
-
CON TEN T S
Chap ter Page
1. INTRODUCTION . . . . . . . 1
1.1 AASHTO Specifications for Tension Splices 1
1,2 Background of Current Specifications 4
2. A FAILURE HYPOTHESIS FOR ANCHORED BARS. 7
2.1 Stress Transfer between Reinforcing Bars
in Concrete . . . . • . • . . . . 7
3. BARS WITHOUT TRANSVERSE REINFORCEMENT 17
3.1 Influence of Cover and Spacing 17
3.2 Formulation of Equation--Splice Tests 17
3.3 Other Splice Tests--No Transverse Reinforcement 25
3.4 Limitation on Influence of Cover 26
3.5 Effect of Staggering Splices 26
3.6 Splices in Retaining Walls 26
3.7 Splices under Impact Loads 27
3.8 Application to Development Lengths 27
3.9 Effect of Wide Spacing 30
4. BARS WITH TRANSVERSE REINFORCEMENT 33
4.1 Influence of Transverse Reinforcement 33
4.2 Other Tests--Effect of Transverse Reinforcement 36
4.3 Effect of Top Casting 41
4.4 Ligh tweigh t Aggrega te Concrete 41
5. PROPOSED DESIGN RECOMMENDATIONS 43
5.1 Modification of Empirical Equation for Design 43
5.2 Design Recommendations for Development Length and
Splice Length of Deformed Bars in Tension .. 44
5.3 Comments and Comparison of Proposed Recommendations
with ACI 318-71 and 1974 AASHTO Interim
Spec ifica tions 46
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Chapter Page
6. SUMMARY AND CONCLUSIONS Sl
BIBLIOGRAPHY . S3
APPENDIX ... SS
vii
LIS T o F TABLES -
Table Page
1 Comparison of Calculated Bond Stress with Test
Values--Lap Splices without Transverse Reinforcement,
Constant Moment K = 1.0 .............. . 57
2 Comparison of Calculated Bond Stress with Test
Values--Lap ~plices without Transverse Reinforcement,
K < 1.0 ................. . 59
3 Comparison of Calcula ted Average Bond Stress wi th
Test Values--Lap Splices wi thou t Transverse Reinforcement 60
4 Comparison of Calcula ted Average Bond Stress with
Test Values--Lap Splices wi thout Transverse Reinforcement,
. . . . .
Tep fers (6) 61
5 Comparison of Calculated Average Bond Stress with Test
Values--Development Length Tests, Ferguson and
Thompson (12, 13) ......... . 64
6 Comparison of Calculated Average Bond Stress with Test
Values--Development Length Tests, Chamberlin (14) ... 65
7 Comparison of Calculated Average Bond Stress with Test
Values: Splices with Transverse Reinforcemen t,
Ferguson, et al. (1, 2, 4) ... 66
8 Comparison of Calculated Average Bond Stress with Test
Values: Splices in Wide Beams with Transverse
Reinforcement, Thompson et al. (10) .... 67
9 Comparison of Calculated Average Bond Stress with Test
Values: Development Length Tests with Transverse
Reinforcement, Ferguson and Thompson (12) 67
10 Comparison of Calculated Average Bond Stress wi th Test
Values: Development Length Tests with Heavy Transverse
Reinforcement, Mathey and Watstein (16) 68
11 Comparison of Calculated Average Bond Stress with Test
Values--Splices with Transverse Reinforcement, Tepfers(6) 69
12 Comparison of Calculated Average Bond Stress wi th Tes t
Values: Effect of Transverse Reinforcement,
Robinson, Zsutty, et al. (9) ..••••.• 70
13 Comparison of Calculated Average Bond Stress wi th Tes t
Values: Effect of Transverse Reinforcement,
Robinson, Zsutty, et al. (9) ....... . 71
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Table Page
14 Comparison of Calculated Average Bond Stresses with Test
Values: Effect of Transverse Reinforcement, Robinson,
Zsutty, et al. (9) •................. 72
15 Comparison of Calculated Average Bond Stress with Test
Values: Effect of Transverse Reinforcement, Robinson,
Zsutty, et a1. (9) .••............... 73
16 Comparison of Calculated Average Bond Stress with Test
Values: Effect of Transverse Reinforcement, Robinson,
Zsutty, et a1. (9) .•........... 74
17 Comparison of Calculated Average Bond Stress with Test
Values: Effect of Transverse Reinforcement, C.U.R. (11) 76
18 Effect of Top Casting on Strength 78
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