Structures and Buildings Volume 165 Issue SB8 Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
Proceedings of the Institution of Civil Engineers Structures and Buildings 165 September 2012 Issue SB8 Pages 443–453 http://dx.doi.org/10.1680/stbu.10.00065 Paper 1000065 Received 09/11/2010 Accepted 01/02/2011 Published online 07/03/2012 Keywords: codes of practice & standards/concrete structures/strength and testing of materials ICE Publishing: All rights reserved
Evaluation of tension lap splices for code provisions Erdem Canbay PhD
Dogu Bozalioglu MSc
Associate Professor, Vice Chairman, Department of Civil Engineering, Middle East Technical University, Ankara, Turkey
Senior Engineer, Mega Engineering and Consulting Company, Ankara, Turkey
Six real-size beams were tested in order to examine the reliability of tension lap splices for the minimum requirements of clear cover, spacing between bars and transverse reinforcement. The beams were prepared in accordance with the minimum provisions of the American Concrete Institute building code requirements for structural concrete (ACI 318–08) and the Turkish standards on requirements for design and construction of reinforced concrete structures (TS 500). Results showed that all beams prepared in accordance with ACI 318–08 showed satisfactory behaviour. Since the specimen prepared according to TS 500 with 26 mm diameter bars failed due to bond, it can be concluded that the TS 500 clear cover is insufficient for spliced bars equal to or greater than 26 mm in diameter. In order to evaluate the ACI Committee 408 new proposal and Eurocode 2 provision for tension lap splices, a case study was also conducted. According to the results of the case study, while the ACI 318–08 requires unnecessarily longer splice lengths for bars of greater than 19 mm diameter, Eurocode 2 always gives the smallest lap splice length which leads to safety concerns.
1.
Introduction
There are several studies in the literature on the reliability assessments of the current code provisions on tension lap splices of reinforced concrete members (Azizinamini et al., 1999; Canbay, 2007; Darwin, 2005; Darwin et al., 2005; Lutz et al., 1993; Pacholka et al., 1999; Rezansoff and Sparling, 1995; Rezansoff et al., 1993; Zuo and Darwin, 2000). With the increase of test data on beams with lap splices, new attempts have been made to obtain a better estimate of splice strength. Similarly, provisions on lap splices in ACI 318 (ACI, 2008) have been continuously changing over the years. Although a huge volume of data is available with the ACI Committee 408 (ACI, 2003), there is a gap in the database. Experimental studies did not consider the minimum requirements of codes and, therefore, there is no specific test result for minimum conditions of cover, spacing and transverse reinforcement. The current paper examines this gap in the literature on lap splice requirements. The provisions in ACI 318–08 (ACI, 2008) on the development of tension reinforcement are based on confinement ratio, spacing between bars, clear concrete cover, concrete strength and yield strength of steel, see Equation 1.
potential plane of splitting through the reinforcement being developed (measured in in2 ); cb ¼ spacing or cover dimension (measured in inches) (the smaller of either the distance from the centre of the bar or wire to the nearest concrete surface should be used, or one-half the centre-to-centre spacing of the bars or wires being developed); db ¼ nominal diameter of reinforcing bars (measured in inches); f c9 ¼ specified compressive strength of concrete (measured in lb/in2 ); fy ¼ specified yield strength of reinforcement (measured in lb/in2 ); fyt ¼ specified yield strength of transverse reinforcement (measured in psi); ºd ¼ development length measured in inches; n ¼ number of bars being spliced or developed along the plane of splitting; s ¼ spacing of transverse reinforcement (measured in inches); łt ¼ reinforcement location factor; łe ¼ coating factor; łs ¼ reinforcement size factor, łs ¼ 0.8 for no. 6 (19 mm) and smaller bars, łs ¼ 1.0 for no. 7 (22 mm) and larger bars; º ¼ lightweight aggregate concrete factor. To limit the probability of a pullout failure, ACI 318–08 requires that the term (cb + Ktr )/db not be taken greater than 2.5. The Turkish standard specification for reinforced concrete structures (TS 500 (TSI, 2000)) requires only the tensile strength of concrete and yield strength of reinforcing steel for lap splice calculations, see Equation 2.
In US customary units In SI units 1:
‘d 3 fy łt łe łs º ¼ pffiffiffiffiffi d b 40 f c9 ð cb þ K tr Þ=d b 2:
where Ktr ¼ transverse reinforcement index, K tr ¼ (Atr f yt )= (1500 s n); Atr ¼ total cross-sectional area of all transverse reinforcement that is within the spacing s and that crosses the
f yd ‘d ¼ 0:12 > 20 db f ctd
where fyd is the design yield strength of steel, fyd ¼ fyk /1.15 (in 443
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
MPa), and fctd is the design value of concrete tensile strength, pffiffiffiffiffiffiffi f ctd ¼ 0:35 f ck =1:5 (in MPa).
clear cover limitations of code provisions. The length of the specimens was 5.0 or 5.5 m. The dimensions of six specimens and their a/d ratios are shown in Table 3. a is the distance between the point load and support, which was 1.4 m for all tests, and d is the effective depth of the specimen. In the table, all specimens are identified with their corresponding code and bar diameter.
This is a simple approach but it needs to be investigated further from a safety perspective. Thus, six beam specimens were prepared and tested in order to evaluate the TS 500 and ACI 318–08 expressions for the above-mentioned unfavourable conditions.
2.
Experimental study
Six beam specimens were prepared according to the minimum requirements of TS 500 and ACI 318 for clear cover, bar spacing, lap splice length and amount of transverse reinforcement. 2.1 Materials Concrete was supplied by a ready-mix company. Curing was applied properly for the first 4 weeks. Concrete strength was determined from standard cylinder tests. Table 1 shows the compressive strength ( f c9 ) and split tensile strength ( f cts ) of concrete on the day of testing. Three bars were used as tension reinforcement at the bottom of the cross-section and two 12 mm bars were used as assembly (hanger) bars at the top. The diameters of the tension steel in each set of three beams (ACI as opposed to TS 500) were 16 mm, 22 mm and 26 mm, respectively. The diameter of the stirrups for all specimens was 8 mm. Table 2 shows the yield strength ( fsy ), ultimate strength ( fsu ), and ultimate percentage elongation of the reinforcing bars. 2.2 Specimen geometry and reinforcement details The depth of all specimens was 400 mm. The width of the specimens was determined according to minimum spacing and
Specimen TS26 ACI22 ACI26 TS16, ACI16, TS22
fc : MPa
fcts : MPa
Test day
36.6 37.0 37.7 37.7
2.30 2.38 2.46 3.11
65 85 154 171
The beams were tested as inverted, simply supported beams. The length of the constant-moment region (the distance between the two supports) was 1.9 or 2.4 m. Lap splice lengths, spacing between bars, and bottom and side clear cover depths were determined according to minimum requirements of the TS 500 and ACI 318–08 standard specifications. All these data were calculated for a concrete compressive strength of 30 MPa and yield strength of 420 MPa for both transverse and longitudinal reinforcing bars. All specimens contain three bottom-cast spliced bars. Along the length of the specimen, 8 mm closed stirrups were used. Associated data are given in Table 4 and in Figure 1. TS 500 requires minimum clear cover of 20 mm. The spacing between bars should be a minimum of 25 mm or bar diameter or 4/3 of the maximum aggregate size of the concrete mix. The inside diameter of bend for stirrups and ties should not be less than six times the bar diameter. The aforementioned limitations determine the cross-section of the TS specimens. According to ACI 318–08, the minimum clear spacing between parallel bars in a layer shall be equal to the bar diameter and not less than 1 in (25.4 mm). Coarse aggregate size must not be larger than three-
Specimen ACI26 ACI22 ACI16 TS26 TS22 TS16
Dimensions, h 3 b 3 ‘
a=d
400 3 306 3 5500 400 3 285 3 5500 400 3 255 3 5000 400 3 324 3 5500 400 3 284 3 5000 400 3 234 3 5000
4.11 4.08 4.05 3.97 3.90 3.85
Table 3. Dimensions of the beams
Table 1. Concrete properties
Diameter: mm 8 12 16 22 26
fsy : MPa
fsu : MPa
Elongation: %
482 440 429 456 487
712 683 671 725 747
20.0 18.0 17.5 16.7 15.3
Table 2. Steel properties
444
Specimen
cso
cbb
2csi
cc
ACI26 ACI22 ACI16 TS26 TS22 TS16
38 38 38 26 22 20
38 38 38 26 22 20
26 25 25 39 33 25
49 51 54 45 43 44
Table 4. Sectional properties of specimens
d
‘s
341 1380 343 1060 346 500 353 890 359 750 364 550
‘s db 53 48 31 34 34 34
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
location, the calculated development length needs to be increased according to both codes. However, the main reason for the multipliers in the codes is to encourage the designer to use staggered lap splices. Therefore, these multipliers for the lap splice calculations were not considered during the present experimental study. The splice lengths ‘s given in Table 4 do not include the multiplier required by the codes. According to ACI 318–08 and TS 500, these multipliers are 1.3 and 1.5, respectively.
cso
d h
cc
2csi
TS 500 requires at least six stirrups with a minimum spacing of h/4 along the splice region. Therefore, specimens prepared according to Turkish standards have 100 mm spacing of transverse reinforcement in the lap splice region and 150 mm spacing outside the splice region. The spacing of transverse reinforcement along the whole length for all ACI specimens was calculated as 150 mm.
db
cbb
quarters of the minimum clear spacing between individual reinforcing bars. Minimum cover should be greater than 1.5 in (38 mm) for cast-in-place concrete beams.
2.3 Test set-up Specimens were tested as inverted, simply supported beams. The load was applied by means of two hydraulic rams attached to the loading frame. The distance between the supports was 1.9 m and 2.4 m for short and long specimens, respectively. A load cell was located at the bottom of the ram. A hinge at the top and a roller at the bottom were provided to the ram–load cell couple in order to obtain a rotationally free system. Figure 2 shows details of the test set-up. In this test set-up tension occurs on the top of beam, which facilitates the observation and the marking of cracks.
All longitudinal bars were spliced at the centre of the beam. The required splice length was calculated based on the development length expressions. Because all bars were spliced at the same
Vertical tip and mid-span displacements were measured by linear variable differential transformers (LVDTs). Support displacement was also measured in order to examine the vertical displacement
b
Figure 1. Section details
Loading frame Hinge
Hydraulic ram
Load cell
150
1400
1400
Simple support
150
400
Roller
Roller support
1550
1900 or 2400
1550
Shear span
Constant-moment region
Shear span
Figure 2. Details of test set-up (not to scale; all dimensions in mm)
445
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
of the supports. Figure 3 shows the location of the displacement transducers. The two hydraulic rams were attached to the same hand pump, which enables the same amount of load application to the tips of the beam. Load was applied very slowly and manually until the specimen yielded. At certain load levels, loading was paused temporarily so that cracks could be marked on the beam. The test was progressed in proportion to yield displacement after yielding of the beam occurred. Strain measurements were taken from both longitudinal and transverse bars along the lap splice. There were a total of six strain gauges on the two longitudinal bars. These were located at the free end, middle and end of the lap splices. Strain gauges were also located on three stirrups in the splice region. Straingauge-applied stirrups were the nearest stirrup to the middle of the lap splice, the nearest stirrup to the end of the lap splice and the intermediate stirrup of the former two. Each stirrup had two strain gauges. One of them was attached near the edge at the bottom leg; the other was applied at the middle of the bottom leg. Figure 4 shows the locations of these strain gauges.
3.
Test results
In all specimens, the first cracks initiated at the end of the lap splices owing to bar discontinuity. Similarly, the largest crack width at the end of each test was observed at these locations. Between the two supports in the constant-moment region, only flexural cracks were seen. These cracks spread towards the loading points. With the increasing load, the cracks between the point loads and the supports (shear span) inclined due to shear force. All specimens, except TS26, failed by reaching their flexural yield capacities. Only TS26 failed prior to its flexural capacity by bond failure. The crack pattern at the end of each test is given in Figures 5–10. In the crack pattern, the middle strip shows the top face, whereas top and bottom regions show the crack patterns of the side faces. The tip and mid-deflection curves are also provided in the same figures. Analytically obtained curves are
LVDT
Dial gauge
Figure 3. Transducer locations
446
Load cell
350 Ω strain gauges on longitudinal bars 120 Ω strain gauges on stirrups
Figure 4. Strain gauge locations
given on the same chart as well. In order to obtain the analytical non-linear load–deflection curves, first the moment–curvature relationship was calculated and then the curvature diagram for each beam was determined for each load level from the moment diagram and moment–curvature relationship of beams. Finally mid and end deflections were computed by applying the second moment area theorem to curvature diagrams of the beams. The analytically calculated and experimentally measured yield loads of all beams are tabulated in Table 5. The last column of the table shows the ratio of the experimental load to analytical load. The difference between the experimental measurement and analytical prediction remains within 8%. The TS26 beam failed prior to its flexural capacity. Failure was brittle and sudden. The failure type comprised both side and face splitting. The rest of the beams showed ductile behaviour with excessive deformations. Typically, in all beams, some longitudinal cracks on both upper and side faces of the specimen at the splice region were observed, even if no splitting failure occurred. ACI26 specimen was loaded twice because the rotation capacity of the rollers employed in the test set-up was not adequate. Owing to safety concerns, the rotational capacities of the rollers were increased and the specimen was loaded again. In the ACI22 specimen, the strain gauge measurements could not be recorded due to the failure of the data acquisition system. This specimen was loaded twice in order to obtain the post-yielding behaviour. During the test, strains were measured both on longitudinal and transverse reinforcement. Table 6 shows the strain values of the longitudinal bars at the yielding of beams. The yield points of the beams were determined from the experimental curves. An abrupt change in the slope of the load–deflection curves of the beams was taken as the yield point. Strain gauge locations are illustrated in Figure 4. As can be seen from the table, near the free end, strains on the longitudinal bars are close to zero and then increase along the bar, as would be expected. Examination of the strains on the transverse reinforcement showed that strain distribution on the stirrups is not uniform over the lap splice. Stirrups at the ends of the lap splice showed higher
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
180 Analytical Left Right
160 140
TS26 – tip deflection
Load: kN
120 100 80
40
60
20
40
0 1
0
20
2
3
4
5
0 180 160
LVDT 100
120
Load: kN
TS26 – mid deflection
Analytical
140
40 30 20 10 0
100 80 60 40
1
0
2
3
20 0 5
0
15
10
20
25
30
35
40
Deflection: mm (a)
1550
755
890
755
1550
Lap splice (b)
Figure 5. TS26: (a) load–deflection curves; (b) crack pattern
strains, which decreased towards the middle of the splice. At the yielding of the beams, the stirrup strains at the end of the splices were approximately 350 ìå. The strain values of the stirrups decrease to approximately 200 ìå at the centre of the lap splice.
4.
Case study
A case study was conducted to compare the lap splice lengths calculated according to TS 500 (TSI, 2000), ACI 318–08 (ACI, 2008) and Eurocode 2 (BSI, 2004). A new design expression proposed by ACI Committee 408 (ACI, 2003) has also been included in this case study. The most complicated provision is the Eurocode 2 provision among the codes considered. The fact that no explicit information is specified in Eurocode 2 for the
calculation of the transverse pressure may be given as an example. In order to look at the failure of the TS26 specimen from another perspective, the splice lengths of all beams were recalculated using the TS 500, the ACI 318, the Eurocode 2 and the ACI 408 approaches and these are given in Table 7. It should again be noted that the required multiplication factors 1.5 in the TS 500 and Eurocode 2, and 1.3 in the ACI 318–08 were not incorporated into the calculations. In order to use a factor of 1.0 in the ACI 408 proposal, ø was taken as 1.0. According to Table 7, the ACI 318–08 provision requires 15% more splice length when compared to the TS 500 provision for the TS26 specimen. This difference increases to 56% for the ACI 408 proposal while it 447
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
140 120
TS22 – tip deflection
Load: kN
100
Analytical Left Right
80
20 15
60
10
40
5
0
20
1
0
2
3
0 140 TS22 – mid deflection 120 Analytical
Load: kN
100
LVDT 100 80 30 20 10 0
60 40 20
0
1·0
2·0
0 5
0
1550
10
15 Deflection: mm (a)
575
750
20
575
25
1550
Lap splice (b)
Figure 6. TS22: (a) load–deflection curves; (b) crack pattern
decreases 15% for the Eurocode 2 provision. If the required multipliers are used, both the TS 500 and the ACI 318–08 provisions give an ‘s =d b ratio of 51, which is quite close to the ACI 408 proposal. The reason of the bond failure of the TS26 beam can be explained both by insufficient concrete cover and by short splice length. The Turkish standard TS 500 requires relatively smaller cover when compared to the ACI 318–08 which causes a premature initiation of splitting cracks at the surface of the lap splice. It should, however, be noted that the bond problem may be overcome by using longer splice lengths. As a result of the comparisons in Table 7, it can be concluded that the multipliers in all codes are mandatory not only for detailing purposes but also for safety reasons, especially when small cover dimensions are concerned. 448
In order to investigate the differences of all the aforementioned design provisions, a case study considering the minimum requirements of the ACI 318–08 was conducted. The diameter of the longitudinal bar is shown along the x-axis and the normalised splice length is shown as the y-axis. The clear cover, the spacing between bars and the amount of transverse reinforcement were calculated according to the ACI 318–08 requirements. It is assumed that all the bars were spliced at the same location and, therefore, the required multipliers were also introduced into the calculations. Figures 11 and 12 were prepared for 30 MPa and 50 MPa concrete compressive strengths, respectively. As can be observed from the figures, when the required multiplier is used
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
70 TS16 – tip deflection
60
Analytical Left Right
Load: kN
50 40
15
10
30
5
20 0 10
0
4
2
0 70 TS16 – mid deflection
60
Analytical
Load: kN
50
LVDT 100
40 20 15 10 5 0
30 20 10
0
0·5
1·0
0 5
0
1550
10
15 Deflection: mm (a)
675
550
20
675
25
1550
Lap splice (b)
Figure 7. TS16: (a) load–deflection curves; (b) crack pattern
for the ACI 318–08 approach, the ACI 318–08 and ACI 408 provisions yield almost the same results up to 19 mm (no. 6) diameter bars. Approximately for 19 mm diameter bars, the TS 500 provision requires the same amount of splice length as well. As the bar diameter decreases, TS 500 remains oversafe with longer splice length requirements, whereas it falls below the ACI 318–08 and ACI 408 curves for bars greater than 19 mm. Therefore, it can be said that beams with splice lengths calculated according to the TS 500 provision may have bond failure instead of a flexural failure for bars greater than 19 mm in diameter. Therefore, it is recommended for TS 500 that concrete cover dimensions given in the current TS 500 should be increased by 50% for bars equal to or greater than 20 mm.
According to Figures 11 and 12, the ACI 318–08 provision requires approximately 20% more splice length when compared to the ACI 408 proposal for bars greater than 19 mm in diameter. It should be noted that the ACI 318–08 curve includes a 1.3 multiplier. The test results, however, showed that the ACI 318–08 approach without the multiplier showed the desired flexural behaviour. Therefore, it can be concluded from both the experimental study and the case study that the ACI 408 proposal requires shorter splice lengths, which is more economical yet safe for bars greater than 19 mm in diameter. In both figures, Eurocode 2 curves constitute the lower bound even when a 1.5 multiplier is used. As bar diameter increases, the difference between Eurocode 2 provision and ACI 408 proposal becomes greater. Assuming that the ACI 408 proposal yields the most 449
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
Load: kN
180 160
ACI26 – tip deflection
140
Analytical
120
Left
40
Right
30
100 80
20
60
10
40
0
20
0
1
2
3
4
0 180 160
ACI26 – mid deflection
140
30
Analytical
100
20
LVDT 100
80
10
Load: kN
120
60 0
40
1
0
2
20 0 0
5
1550
15
10
20 25 Deflection: mm (a)
510
1380
30
510
35
40
1550
Lap splice (b)
Figure 8. ACI26: (a) load–deflection curves; (b) crack pattern
reliable results, it can be deduced that Eurocode 2 provision for lap splice length calculation may produce relatively unsafe results when bar diameter increases.
5.
Summary and conclusion
A total of six beams were prepared according to TS 500 and ACI 318–08. Clear cover, spacing between bars, amount of transverse reinforcement and splice length were calculated according to the minimum requirements given in the codes. Based on the limited number of tests conducted, the following conclusions can be drawn: If the minimum cover, spacing and transverse reinforcement requirements are met, specimens produced according to ACI 450
318–08 behave satisfactorily with a flexural failure at the ultimate stage. Although the multiplier 1.3 given in the ACI 318–08 for bars spliced at the same location was not considered in the splice length calculations, the results were reasonable. Using this multiplier as 1.0 is in accordance with the ACI Committee 408 proposal. While TS22 and TS16 specimens show acceptable behaviour, TS26 failed in a brittle manner prior to yielding of the beam. The Turkish standard for building code requires much less cover concrete as compared to ACI 318–08. This small cover does not cause any problem for small diameter bars. For large diameter
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
160 ACI22 – tip deflection
Load: kN
140 120
Analytical
100
Left
30
Right
20
80 60
10
40 0
20
0
2
4
0 160 140 ACI22 – mid deflection
Load: kN
120 100
30
80
20
60
10
40
Analytical LVDT 100
0 0
20
2
4
0 5
0
1550
10
15 Deflection: mm (a)
670
1060
20
25
670
30
1550
Lap splice (b)
Figure 9. ACI22: (a) load–deflection curves; (b) crack pattern
bars, however, the beam cannot show the expected performance. It should be noted that the multiplier for the lap splice length was not applied in the calculations of TS 500 specimens. Since the main idea behind the multiplier is to encourage the designer to use staggered splices, the TS26 specimen should have shown flexural failure without the multiplier, and therefore a revision for the cover dimensions of beams should be considered in TS 500. It is recommended to increase concrete cover dimensions given in TS 500 by 50% for bars equal to or greater than 20 mm in diameter. Another solution for the bond failure of spliced bars with large diameter would be to keep using the multiplier given in the provision for additional safety. The case study showed that the ACI 318–08 approach gives higher results when compared to both the ACI 408 and TS 500
approaches for bars of diameter greater than 19 mm, which indicates with the observed behaviour of experimental results that the multiplier in ACI 318–08 causes unnecessarily long splice lengths. Eurocode 2 provision always gives the smallest lap splice length among the considered codes, which leads to safety concerns. Moreover, the complexity of the provision may be cited as another disadvantage.
Acknowledgements The project was financially supported by the Office of the Coordinator of the Scientific Research Projects of the Middle East Technical University (BAP-2005–03–03–09), and this support is gratefully acknowledged. 451
Structures and Buildings Volume 165 Issue SB8
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
70 60 Analytical
Load: kN
50 40
Left
20
Right
15
30
10
20
5
0
10
ACI16 – tip deflection
0 1 2 3 4
0 70 60
20
Load: kN
50 40
Analytical
15
LVDT 100
10
30
5
20
0
10
1
0
2
ACI16 – mid deflection
0 5
0
1550
10
700
15 Deflection: mm (a)
500
20
700
25
1550
Lap splice (b)
Figure 10. ACI16: (a) load–deflection curves; (b) crack pattern
Specimen
ACI26 ACI22 ACI16 TS26 TS22 TS16
Analytical Experimental yield load: kN yield load: kN 169 119 60 169 124 64
159 120 57 138 120 62
Table 5. Analytical and experimental yield loads
452
Yield load: kN
Exp’l/ Analytical 0.94 1.01 0.95 0.82 0.97 0.97
ACI26 ACI22 ACI16 TS26 TS22 TS16
159 120 57 138 120 62
Bar Strain Middle Bar Strain Edge free centre cont. free centre cont. end end end end 14 — 2 45 2 74
787 — 493 1032 1347 1287
2800 — 1890 1736 NA 4761
151 — 33 108 10 62
1443 — 1467 544 1414 1213
Table 6. Strains in longitudinal reinforcement (measured in microstrain, ìå)
— — 1187 1377 2732 4985
Structures and Buildings Volume 165 Issue SB8
Specimen
ACI26 ACI22 ACI16 TS26 TS22 TS16
TS 500, ‘ s =d b
Evaluation of tension lap splices for code provisions Canbay and Bozalioglu
ACI 318, ‘ s =d b
34 34 34 34 34 34
53 48 31 39 37 26
ACI 408, ‘ s =d b
Eurocode 2, ‘ s =d b
59 55 45 46 45 41
31 29 26 29 27 24
Table 7. Theoretical splice lengths of the specimens
8
13
18
db: mm 23
28
33
38
80 70
ls /db
60 50 40 30 20 0·3
f y ⫽ 420 MPa ⫽ 60·9 kg/in f ⬘c ⫽ 30 MPa ⫽ 4350 lb/in 2 0·5
0·7
0·9 db: in
2
1·1
ACI 318-08 ACI 408 TS 500 Eurocode 2 1·3
1·5
Figure 11. Comparison of the code provisions for 30 MPa concrete strength
80
8
13
18
ls /db
50
28
33
f y ⫽ 420 MPa ⫽ 60·9 kg/in f ⬘c ⫽ 50 MPa ⫽ 7250 lb/in 2
70 60
db: mm 23
ACI 318-08 ACI 408 TS 500 Eurocode 2
38 2
Azizinamini A, Darwin D, Eligehausen R, Pavel R and Ghosh SK
(1999) Proposed modifications to ACI 318–95 tension development and lap splice for high-strength concrete. ACI Structural Journal 96(6): 922–926. BSI (British Standards Institution) (2004) BS EN 1992–1–1: 2004 Design of concrete structures. General rules and rules for buildings. BSI, London, UK. Canbay E (2007) Comparison of code provisions on lap splices. Structural Engineering and Mechanics 27(1): 63–75. Darwin D (2005) Tension development length and lap splice design for reinforced concrete members. Progress in Structural Engineering and Materials 7(4): 210–225. Darwin D, Lutz LA and Zuo J (2005) Recommended provisions and commentary on development and lap splice lengths for deformed reinforcing bars in tension. ACI Structural Journal 102(6): 892–900. Lutz LA, Mirza SA and Gosain NK (1993) Changes to and applications of development and lap splice length provisions for bars in tension (ACI 318–89). ACI Structural Journal 90(4): 393–406. Pacholka K, Rezansoff T and Sparling BF (1999) Stirrup distribution across the beam width in tension lap splices. Canadian Journal of Civil Engineering 26(1): 83–95. Rezansoff T and Sparling BF (1995) Correlation of the bond provisions of CSA A23.3–94 with tests on tension lap splices in beams. Canadian Journal of Civil Engineering 22(4): 755–769. Rezansoff T, Akanni A and Sparling B (1993) Tensile lap splices under static loading: a review of the proposed ACI 318 code provisions. ACI Structural Journal 90(4): 374–384. TSI (Turkish Standards Institute) (2000) TS 500–2000: Requirements for design and construction of reinforced concrete structures. TSI, Ankara, Turkey. Zuo J and Darwin D (2000) Splice strength of conventional and high relative rib area bars in normal and high-strength concrete. ACI Structural Journal 97(4): 630–641.
40 30 20 0·3
0·5
0·7
0·9 db: in
1·1
1·3
1·5
Figure 12. Comparison of the code provisions for 50 MPa concrete strength
REFERENCES
ACI (American Concrete Institute) (2003) ACI 408R-03: Bond
and development of straight reinforcing bars in tension. American Concrete Institute, Farmington Hills, MI, USA. ACI (2008) ACI 318–08: Building code requirements for structural concrete, and 318R-08: Commentary. American Concrete Institute, Farmington Hills, MI, USA.
WH AT DO YO U T HI NK?
To discuss this paper, please email up to 500 words to the editor at
[email protected]. Your contribution will be forwarded to the author(s) for a reply and, if considered appropriate by the editorial panel, will be published as a discussion in a future issue of the journal. Proceedings journals rely entirely on contributions sent in by civil engineering professionals, academics and students. Papers should be 2000–5000 words long (briefing papers should be 1000–2000 words long), with adequate illustrations and references. You can submit your paper online via www.icevirtuallibrary.com/content/journals, where you will also find detailed author guidelines. 453
