Construction and Building Materials 50 (2014) 530–539

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Construction and Building Materials

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Feasibility study of grouted splice connector under tensile load

0950-0618/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.10.010

⇑ Corresponding author. Tel.: +60 128072616.E-mail address: lingjenhua@ucts.edu.my (J.H. Ling).

Ling Jen Hua a,⇑, Ahmad Baharuddin Abd. Rahman b, Izni Syahrizal Ibrahim ba School of Engineering and Technology, University College of Technology Sarawak, 96000 Sibu, Sarawak, Malaysiab Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Darul Ta’zim, Malaysia

h i g h l i g h t s

� Use of standard size steel section to confine splicing of bars.� Feasibility assessment of grout splice connection under tensile load.� Derive equations to evaluate the response of splice connection.

a r t i c l e i n f o

Article history:Received 1 March 2010Received in revised form 1 October 2013Accepted 4 October 2013Available online 26 October 2013

Keywords:Grouted spliceSleeveConnectorBondPrecast connection

a b s t r a c t

The conventional bar lapping approach to connect steel bars requires long development length andalways leads to bar congestion problems. For this reason, grouted splice connectors are used to confinethe grout surrounding the bars to improve the bond between the grout and the bars. Four series of spec-imens with a total of 35 specimens were tested under incremental tensile load. These specimens vary interms of configurations and were assessed for feasibility in the aspects of bond strength, ductilityresponse and failure modes. Equations are derived to evaluate the structural performance of the speci-mens. The typical modes of failure are bar tensile failure, grout-bar bond failure, grout-sleeve bond fail-ure, and sleeve tensile failure. These failures reveal the factors to be considered during the design of asplice connector. Under confinement, the required anchorage length of the bars can be shortened tonearly nine times the diameter of the spliced bar.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Ever since the first use of iron reinforced concrete structure byThaddeus Hyatt in 1853, many researchers started to study thebond between steel and concrete, experimentally and analytically.The scopes of study include the mechanisms of bond [1], the inter-locking effects of the geometry and patterns of the ribs on steelbars [2,3], the relative rib area to generate bond strength [4,5],the distributions of bond stress along a bar [6,7], the crack propa-gation surrounding the steel bars [7–11], etc.

The research developed further to connect steel bars in con-crete, by lapping adjacent bars [12–14]. This method requires along development length of bar for stress to entirely transfer froma bar to another in concrete. It often leads to detailing and bar con-gestion problems, especially when large diameter steel bars areused in heavily reinforced structures. To solve this problem, lateralforces and confinement were induced to increase the bondstrength and to reduce the development length [15–18].

Initially, transverse reinforcements were used to control thedevelopment of splitting cracks surrounding the anchorage region

[19,20]. This approach could only give passive confinement to alarger region of concrete, but is unable to directly confine a smallgrouted region along a bar. Nevertheless, it provides essential fun-damental for a splice connector, where the bond strength can beincreased by controlling the circumference splitting cracks aroundthe bar.

At present, the confinement can be produced in a small regionalong a bar. It is by surrounding the splice with spirals [21,22],cylindrical pipes [23–25] and fiber reinforced polymer [26]. Theseapproaches need grout as the bonding and load transferring mate-rials, for its high strength and fine particles. It is also utterly essen-tial to ensure the full capacity of bar stress is properly distributedfrom a bar to another without being compromised by bond capac-ity. In the ideal condition, the bond strength should outperform itsspliced bars.

The splice connectors available in the marketplace [27–34] areproprietary products owned by the inventors and several estab-lished companies. The designs of the shapes are rather complexand they generally need advance steel molding techniques for fab-rications. Furthermore, there is limited information on the loadresisting mechanisms, the distributions of internal stress and thedesign calculations of a splice connector published academically,except for some feasibility test reports on these established

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J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539 531

products [35,36] on the basis of several prescribed acceptance cri-teria proposed by relevant standards [37,38].

Based on the reviews from previous research, several principlesare extracted:

(a) The alignments of bar in a splice connection, in-line or adja-cent, leads to different responses. Adjacent alignment of barslead to eccentricity. Under tensile load, the load tends toself-align and causes undesired bending deformation of thespliced bars while rotating the couple [39,40]. This affectsthe performance of the spliced bar, generates excessivedeformation, and causes regional failure of the surroundingconcrete of the structural elements [39].

(b) The performance of grouted splice is heavily influenced bythe quality of the grout in the sleeve. The strength of thegrout and the completeness or segregation of grout in thesleeve would affect the capacity of the splice [25,41].

(c) The bar slippage resistance can be generated by the bondbetween the grout and the bar, or by the frictional grippingbetween the coupler and the bar, or by using a threaded sys-tem to connect steel bars and the couple [23,34,36,39].Under tensile load, undesired sudden slippage of bar usuallyoccurs when the frictional gripping approach is used [35].

(d) The performance of the bond in a sleeve can be increased byreducing in the diameter of the sleeve and increasing theanchorage length of the splice bars [25].

Based on these fundamentals, grouted splice was studied andthe bars were spliced in-line. This study uses standard-sizedsteel sections (pipes, square hollow sections and aluminumsleeves) to bridge the discontinuity and to confine the groutedregion around of steel bars, as initiated by Einea et al. in 1995[23]. The objective was to determine whether these sectionsare suitable as the connectors. For this reason, incremental ten-sile load tests were carried out on a total of 35 specimens withdifferent configurations. The results were analyzed and the feasi-bility of the specimens was determined based on several evalu-ation criteria.

2. Experimental program

A test program was carried out on four series of 35 grouted splice connectorswith various sizes and configurations to understand the effects of the interactingvariable; material properties, sleeve configurations, confinement mechanism, etc.

2.1. Specimens

Fig. 1 illustrates the details of the grouted splice connectors. These connectionswere used to splice 16 mm diameter high strength bars of 460 N/mm2 specifiedyield strength. The configurations of the connectors are briefly described as follows:

� AS-Series – bars were spliced, in-line or adjacent, with the surrounding groutconfined by a corrugated aluminum sleeve with 43 mm diameter and 1 mmthick.� BS-Series – 65 mm diameter and 4.5 mm thick mild steel pipes with the speci-

fied yield strength of 250 N/mm2 were used to splice in-line bars. 10 mm Diam-eter high strength steel bars were welded to sleeves BS-01 to BS-06 from bothends to interlock with the grout. The amounts and the provided lengths of the10 mm diameter bars varied among these specimens. For specimens BS-08 toBS-11, 30 mm holes were provided at 50 mm and 100 mm from the ends ofthe pipes. The holes provide space to be occupied by the grout to engage a largeshear area for interlocking with the pipes to prevent slippage of the grout. Spec-imens BS-12 and BS-13 used rings of welded ribs of 2 mm height. These weldedribs were located at 25 mm and 50 mm from the ends of pipes to interlock withgrout. Also, taper nuts of 37� inclined angle were welded on the bars to givemore bearing area for interlocking with grout.� CS-Series – specimens CS-01 to CS-09 comprised sets of two semi-cylindrical

mild steel pipes. Two steel plates, 5 mm thick and with 22 mm opening, werewelded to the pipes to lock the movement of nuts on the spliced bars. Thethreaded length of the bars was 70 mm so that the nuts can be flexibly adjustedalong it to fit in the compartment between the two steel plates.

� DS-Series – specimens DS-01 to DS-11 were modified from mild steel squarehollow section (SHS). Plates of 3 mm thick were inserted through the four cor-ners at 20 mm, 50 mm and 100 mm from the ends of SHS. These plates interlockwith grout to resist slippage of grout. For specimens DS-08 to DS-11, severalbolts were used to laterally compress on the spliced bar. This generates an addi-tional resistance to prevent slippage of the spliced bars.

2.2. Test plan and setup

The specimens were made by inserting bars from both ends of the sleeve beforehigh strength Sika Grout-215 (proportion of 25 kg grout: 4 l water) was poured in,to fill the void in the sleeve. The specimens were ready for testing after the grouthad achieved the intended strength of 40 N/mm2. The incremental tensile loadwas applied at a rate of 0.5 kN/s by a hydraulic actuator with a capacity of250 kN (Fig. 2). The relationships of the applied loads versus the longitudinal dis-placement of the bars were plotted and recorded for analysis.

3. Test results

The displacements of the bars corresponding to the applied loadwere measured throughout the test and the largest axial forcemeasured was considered as the ultimate capacity of the speci-mens, as shown in Table 1.

Based on the results, due to limited specimens available, it isdifficult to distinguish the effects of different configurations ofBS-Series. All the specimens failed in the same mode – bar tensilefailure. For this reason, the enhancements like (a) the tapered nutat the end of the bars, (b) the interlocking bars welded throughoutthe length of BS-01, (c) the extra shear area provided by the groutoccupying the holes on sleeve BS-08 to BS-11, and (d) the inter-locking ribs welded to the inner surface of sleeve BS-12 and BS-13, might not be necessary.

Fundamentally, as long as (a) the sleeve is strong enough towithstand the tensile stress induced by the load, (b) the bond be-tween the bar and the grout is sufficient to prevent slippage ofbar, and (c) the bond between the grout and the sleeve is sufficientto resist the grout from slipping out of the sleeve, the splice con-nection would adequate. Fabrication wise, it is more practical to in-duce a minimum efforts of modification to the pipe section. Thus,the interlocking bars welded to the inner surface of the sleeveshould be of a minimum length, but just adequate to prevent thegrout from slipping out of the sleeve. No tapered nut is requiredfor this series of specimens.

As observed from DS-Series, tapered nut indeed improves thebond between the bar and the grout, especially when the develop-ment length is inadequate. The specimens with the tapered nuts atthe ends of the bars (DS-01 and DS-03) always outperform thespecimens without the tapered nuts (DS-02 and DS-04).

The ribs at the corner of the SHS of DS-Series seems to providebond-slip resistance for the grout only. As observed from DS-01,DS-03, DS-05, DS-06 and DS-07, the capacities of the connectionwere about the same regardless the amount and the positions ofthe ribs provided. Similarly, when the ribs generate sufficientbond-slip resistance to the grout, an addition of shear areas pro-vided by the grout that occupied the holes of the sleeve wouldnot be necessary.

The test results show that BS-Series is more efficient in provid-ing confinement to the splicing of bars in the sleeve as comparedwith DS-Series. The bar embedded lengths of BS-03, DS-02 andDS-04 were same, and tapered nut was not provided at the endsof the bars. BS-03 apparently outperformed DS-02 and DS-04 witha higher ultimate capacity without symptoms of bond failure. Thesquare section (DS-Series) appeared to be less superior to the cir-cular section (BS-Series), especially when it is used to generateconfinement to the splicing of bars. The circular section is moreefficient in generating tangential tensile resistance to confine thegrout surrounding the spliced bar.

Fig. 1. Details of specimens (dimensions in mm).

532 J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539

3.1. Failure modes

Fig. 3 shows the typical failure modes of the specimens; bartensile failure, grout-bar bond failure, sleeve tensile failure andgrout-sleeve bond failure, each of which offered different rangesof ultimate capacity. Specimens with bar tensile failure failed at

high tensile capacities, ranging from 118 kN to 143 kN. The corre-sponding displacements ranged from 22.4 mm to 43.7 mm. Thephenomenon of bar tensile failure signifies an excellent bondstrength developed in the sleeve that outperformed the tensilestrength of the splice bars. The peripheral tensile strength of thesleeves provided resistance to control radial splitting of the grout,

Hydraulic actuator

Pressured grips

Grouted splice specimen

Pulling force

Reaction force

Fig. 2. Setup of tensile load test.

Table 1Test results of specimens under incremental tensile load.

Specimens Grout strength, fcu (N/mm2) Ultimate load, Pu (kN) Displacement at failure, d (mm) Failure mode

16 mm Bar 133.2 55.1 Bar tensile failureAS-01 58.10 11.9 2.7 Sleeve tensile failureAS-02 58.10 135.6 35.5 Bar tensile failureBS-01 62.97 125.6 36.0 Bar tensile failureBS-02 62.97 119.2 22.4 Bar tensile failureBS-03 62.97 141.2 32.0 Bar tensile failureBS-04 62.97 118.0 23.5 Bar tensile failureBS-05 62.97 143.6 42.2 Bar tensile failureBS-06 62.97 124.9 36.9 Bar tensile failureBS-07 62.97 124.4 35.8 Bar tensile failureBS-08 62.97 121.2 36.3 Bar tensile failureBS-09 62.97 124.4 37.8 Bar tensile failureBS-10 62.97 136.3 31.2 Bar tensile failureBS-11 62.97 120.0 37.3 Bar tensile failureBS-12 62.97 125.1 38.1 Bar tensile failureBS-13 62.97 135.4 29.5 Bar tensile failureCS-01 43.32 87.0 8.72 Bar-grout bond failureCS-02 43.32 98.4 26.3 Bar-grout bond failureCS-03 43.32 80.0 4.54 Bar-grout bond failureCS-04 43.32 85.3 17.1 Bar-grout bond failureCS-05 43.32 84.3 6.8 Bar-grout bond failureCS-06 43.32 40.9 1.0 Grout-sleeve bond failureCS-07 43.32 72.5 7.0 Bar-grout bond failureCS-08 43.32 70.5 6.7 Bar-grout bond failureCS-09 43.32 101.8 5.6 Bar-grout bond failureDS-01 49.28 129.1 41.6 Bar tensile failureDS-02 49.28 112.0 16.6 Bar-grout bond failureDS-03 49.28 123.4 41.9 Bar tensile failureDS-04 49.28 110.6 4.8 Bar-grout bond failureDS-05 49.28 130.1 43.7 Bar tensile failureDS-06 49.28 123.7 29.4 Bar-grout bond failureDS-07 49.28 127.5 33.3 Bar-grout bond failureDS-08 49.28 122.3 31.6 Bar-grout bond failureDS-09 49.28 120.7 37.1 Bar-grout bond failureDS-10 49.28 118.2 36.2 Bar tensile failureDS-11 49.28 122.4 38.8 Bar tensile failure

J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539 533

and subsequently, improve the efficiency of the mechanical inter-lock between grout keys and bar ribs [23]. It also enhanced the fric-tion resistance between the grout and the sleeve [42]. Moreover,the 10 mm bars welded on specimens BS-01 to BS-07 generate

an addition confinement stress that derived from the resultantsacting perpendicularly to the inclined surface of the ribs [25].

The bar-grout bond failed at a moderate high strength, rangingfrom 70.6 kN to 135.6 kN. The mode of failure can be ductile or

(b) Bar-grout bond failure

(c) Grout-sleeve bond failure

(d) Sleeve tensile failure

(a) Bar tensile failure

Bar necking and tensile fracture

Damage of grout keys as the bond failed

Tensile fracture of grout as it slipped out of sleeve

Tensile fracture of sleeve and grout

Fig. 3. Typical modes of failure.

534 J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539

brittle. Specimens DS-02, DS-04, DS-06, DS-07 DS-08 and DS-09,gave ductile responses because the bond failed shortly after sur-passing the yield strength of the spliced bars. On the other hand,CS-Series failed in a brittle mode, as the bond failed before thespliced bars yielded.

CS-Series failed earlier than DS-Series due to inappropriate barsurface condition. The threaded surface of the bars changed thegeometry of grout keys that occupied the spacing between thethreads to be sharp and narrow. This led to a larger bearing/sheararea of grout keys, and hence, led to a smaller regional shear-slipresistance to withstand the high stress concentrated at the endsof the sleeve near to the source of the pulling force [43]. This in-creased the tendency of the load to trigger a progressive failureof the grout keys starting from either end of the sleeve. Eventually,the bar-grout bond failed completely as the spliced bar slipped outof the sleeve. This phenomenon is proven when CS-09, where thesurface of the bars were not threaded, offered a higher bondstrength of 17% than CS-01.

The comparison of bond strength among specimens DS-01 toDS-04 revealed the effects of the taper-headed bars. The

interaction between taper-headed bars and SHS ribs could improvethe bond between the grout and the bars. The tapered nut providedbearing area for interlocking with the grout. It also converted thelongitudinal pulling force into stress acting perpendicularly to itsinclined surface. The stress triggered the counteraction of thesleeve, specifically from the welded ribs on the SHS at 100 mmfrom the ends of the sleeve. This generated a regional compressivefield in the sleeve along the spliced bars to control the peripheralsplitting cracks around the spliced bars, and hence, decreased thedeterioration rate of the bond between the bar and the grout.

Sleeve AS-01 fractured at the discontinuity of bars. The corru-gated aluminum sleeve generated excellent bond with the grout,while the grout bonded with the spliced bars. The stress generatedby the tensile load transferred from the spliced bars to the groutand to the sleeve. Due to low tensile resistance properties andinadequate effective cross-sectional area of the aluminum sleeve(about 1 mm thick), it fractured together with the grout as its ten-sile capacity was exceeded.

The grout-sleeve bond failure demonstrated by CS-06 revealsthat the interlocking mechanism between sleeve and grout is

J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539 535

utterly important. Without it, the splice would have to depend onthe chemical adhesion and the surface friction between the groutand the sleeve to prevent the grout from slipping out of the sleeve[1], both of which were apparently less efficient than mechanicalinterlocking mechanism.

The load–displacement curves in Fig. 4 show the behaviour ofthe specimens. These curves represent the information such as(a) the ultimate tensile capacity, which is rendered from the high-est peaks of the curves, (b) the stiffness, which is represented bythe tangent slopes of the curves, (c) the yield points, which is iden-tified upon the first drastic decrease in the slope after the elasticresponse, and (d) the ductility characteristic, which is determinedfrom the degree of the post-yielding. The specimens with the load–displacement responses similar a 16 mm high strength steel bar

0

20

40

60

80

100

120

140

160

Displacement (mm)

Load

(kN

)

Y16-1BS-11BS-12BS-13

0

20

40

60

80

100

120

140

160

Displacement (mm)

Load

(kN

)

Y16-1BS-05BS-06BS-07

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35Displacement (mm)

Load

(kN

) Y16-1AS-01AS-02

Fig. 4. Load–displacement graph of test sp

(control specimen) were considered adequate. This is based onthe fundamental that splice connection should not compromisethe ability (structural performance) of the spliced bars.

3.2. Analysis for feasibility

Table 2 shows the feasibility evaluations of the specimens,which are derived from the measured variables presented in Ta-ble 1. The yielding strength, Py, and displacement, dy, of the speci-mens are obtained from the load–displacement curves presentedin Fig. 4, when the stiffness of the specimens degraded suddenly.The bar stress at the ultimate and yielding states, fbu and fby respec-tively, is calculated by dividing the applied force with the nominalcross sectional area of the bar, as given in the following equations:

0

20

40

60

80

100

120

140

Displacement (mm)

Load

(kN

)

Y16-1CS-01CS-02CS-03

0

20

40

60

80

100

120

140

160

Displacement (mm)

Load

(kN

)Y16-1BS-01BS-02BS-03BS-04

0

20

40

60

80

100

120

140

160

Displacement (mm)

Load

(kN

)

Y16-1BS-08BS-09BS-10

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

ecimens up to 35 mm displacement.

0

20

40

60

80

100

120

140

Displacement (mm)

Load

(kN

) Y16-1CS-04CS-05CS-06

0

20

40

60

80

100

120

140

Displacement (mm)

Load

(kN

) Y16-1CS-07CS-08CS-09

0

20

40

60

80

100

120

140

Displacement (mm)

Load

(kN

)

Y16-1DS-09DS-10DS-11

0

20

40

60

80

100

120

140

Displacement (mm)

Load

(kN

) Y16-1DS-01DS-02DS-03DS-04

0

20

40

60

80

100

120

140

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

Displacement (mm)

Load

(kN

)

Y16-1DS-05DS-06DS-07DS-08

Fig. 4 (continued)

536 J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539

fbu ¼Pu � 103

p db2� �2 ¼ 4Pu � 10

3

pd2bð1Þ

fby ¼Psy � 103

p db2� �2 ¼ 4Psy � 10

3

pd2bð2Þ

Steel bars are connected in-line in the grouted splice connector.Due to the discontinuity, the materials that bridge the bars wouldhave to endure the tensile load. This involved the grout and thesleeve.

The tensile resistance of the grout is estimated by multiplyingits effective cross sectional area, Agr, with its tensile capacity, which

is conservatively approximated as 1/10 of its compressive strength[44], as expressed in Eq. (3). The effective cross sectional areas ofthe connectors vary depending on the size and the shape of thesleeve as shown in Table 3.

Pgr ¼ Agr � fgr ¼ Agr �1

10fcu ð3Þ

The tensile load resisted by the sleeve is expressed in the fol-lowing equation:

Psl ¼ Pu � Pgr ð4Þ

It is assumed that the tensile stress is equally shared by theeffective cross sectional area of the sleeve, although some of whichwere made from different materials. For example, BS-01 was made

Table 2Feasibility evaluation of test specimens.

Specimen ld Asl (mm2) Agr (mm2) Psl (kN) Py (kN) fy(N/mm2)

dy (mm) fbu(N/mm2)

fsu(N/mm2)

ub(N/mm2)

esy(mm)

Reff Rst D Remark–b

AS-01 150 67 1184 5 11.5 57 1.9 59 75 1.6 0.8 0.3 0.14 1.4 NAAS-02 300 67 983 129.9 109.1 543 4.3 674 –a 9.0 31.2 –a 1.64 8.3 ABS-01 150 1297 2803 107.9 106.1 528 3.1 625 83 16.7 32.9 0.33 1.52 11.6 ABS-02 150 983 3117 99.6 122.1 607 3.5 593 101 15.8 18.9 0.40 1.45 6.4 ABS-03 150 983 3117 121.6 98.0 487 2.5 702 124 18.7 29.5 0.50 1.71 12.8 ABS-04 150 983 3117 98.4 98.1 488 3 587 100 15.7 20.5 0.40 1.43 7.8 ABS-05 150 983 3117 124.0 112.2 558 3.5 714 126 19.0 38.7 0.50 1.74 12.1 ABS-06 150 983 3117 105.3 106.2 528 3 621 107 16.6 33.9 0.43 1.51 12.3 ABS-07 150 983 3117 104.8 108.1 538 2.8 619 107 16.5 33 0.43 1.51 12.8 ABS-08 150 983 3117 101.6 102.2 508 2.6 603 103 16.1 33.7 0.41 1.47 14.0 ABS-09 150 983 3117 104.8 106 527 3.6 619 107 16.5 34.2 0.43 1.51 10.5 ABS-10 150 983 3117 116.7 118.1 587 3.3 678 119 18.1 27.9 0.48 1.65 9.5 ABS-11 150 983 3117 100.4 102.1 508 2.7 597 102 15.9 34.6 0.41 1.46 13.8 ABS-12 150 983 3117 105.5 108.1 538 3.2 622 107 16.6 34.9 0.43 1.52 11.9 ABS-13 150 983 3117 115.8 118.1 587 3.4 673 118 18.0 26.1 0.47 1.64 8.7 ACS-01 100 1070 1473 80.6 80.1 398 4.6 433 75 17.3 4.12 0.30 1.06 1.9 NACS-02 50 1070 1473 92.0 60.0 298 4.2 489 86 –c 22.1 0.34 1.19 6.3 NACS-03 150 1070 1473 73.6 76.1 378 3.1 398 69 10.6 1.44 0.28 0.97 1.5 NACS-04 100 1052 1473 78.9 74.1 369 3.3 424 75 17.0 13.8 0.30 1.03 5.2 NACS-05 100 1283 1473 77.9 74.1 369 2.7 419 61 16.8 4.1 0.24 1.02 2.5 NACS-06 100 1070 1473 34.5 40.9 203 1 203 32 8.1 0 0.13 0.50 1.0 NACS-07 100 1070 1473 66.1 72.5 361 3.1 361 62 14.4 3.9 0.25 0.88 2.3 NACS-08 100 1070 1473 64.1 70.5 351 6.7 351 60 14.0 0.0 0.24 0.86 1.0 NACS-09 100 1070 1473 95.4 100.1 498 4.4 506 89 20.3 1.2 0.36 1.23 1.3 NADS-01 150 981 2299 117.8 112.0 557 4.4 642 120 17.1 37.2 0.48 1.57 9.5 ADS-02 150 981 2299 100.7 112.0 557 3.2 557 103 14.9 13.4 0.41 1.36 5.2 ADS-03 150 981 2299 112.1 106.1 528 3.3 614 114 16.4 38.6 0.46 1.50 12.7 ADS-04 150 981 2299 99.3 110.6 550 4.8 550 101 14.7 0.0 0.40 1.34 1.0 NADS-05 150 981 2299 118.8 112.0 557 4.2 647 121 17.3 39.5 0.48 1.58 10.4 ADS-06 150 981 2299 112.4 108.1 538 3.9 615 115 16.4 25.5 0.46 1.5 7.5 ADS-07 150 981 2299 116.2 112.1 558 5.8 634 118 16.9 27.5 0.47 1.55 5.7 ADS-08 150 981 2299 111.0 106.0 527 3.8 608 113 16.2 27.8 0.45 1.48 8.3 ADS-09 150 981 2299 109.4 104.1 518 4.5 600 112 16.0 32.6 0.45 1.46 8.2 ADS-10 150 981 2299 106.9 100.1 498 3.7 588 109 15.7 32.5 0.44 1.43 9.8 ADS-11 150 981 2299 111.1 104.1 518 4.4 609 113 16.2 34.4 0.45 1.49 8.8 A

a The stress in the sleeve longitudinal to the direction of the force is not measurable due to the adjacent arrangement of the bars. This arrangement does not require thesleeve to resist the pulling force.

b The rating for the feasibility of the specimens: ‘‘A’’ indicates that the specimen meets the evaluation criteria (fbu/fs P 1.25, and du/dy P 4.0), while ‘‘NA’’ represents thatthere is at least one of the evaluation criteria is not met.

c The maximum bond stress was hard to determine because of early failure of the bond and the tensile resistance of the specimen relied upon the interlocking between thenuts on the bars and the welded plates on the sleeve.

Table 3Cross sectional area of grout in sleeves.

Specimens Cross sectional area of grout in sleeves, Agr

DS-SeriesD2si � p

db2

� �2BS-01

p Dsi2� �2

� p db2� �2� �

� 4p dwb2� �2

All other specimens p Dsi2� �2

� p db2� �2

J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539 537

up of high strength steel bars and mild steel pipes. Therefore, thestress developed in sleeves, fsu, is estimated by dividing the loadwith the effective cross sectional area, Asl, as derived in Table 4.

fsu ¼Psl � 103

Aslð5Þ

Substitute, Asl, from Table 4 into Eq. (5), acquires equations inTable 5, which is generalized into the following equation:

fsu ¼ K � ðPu � PgrÞ ð6Þ

where K ¼ 4�103pðD2so�D2siÞþC

, C ¼ 4pd2wb, for specimen BS-01; 16bwphwp, forCS-Series; 0, for others specimens.

For DS-Series, Eq. (6) is multiplied with p/4 in order to cancelout the factor of 4/p in the equation in order to obtained the equa-tion as presented in Table 5.

The average bond stress, ub, is calculated from the existing for-mula as a function of the total surface area of embedded in thegrout (Eq. (7)).

ub ¼Pu � 103

pdblbð7Þ

The post yielding elongation of the bar, epy, is expressed in Eq.(8), with the assumptions that the bond-slip of the bar and theelongation of the pipe are negligible.

epy ¼ du � dsy ð8Þ

The efficiency ratio of the sleeve indicates the level of capacityutilization. It is calculated by dividing the stress developed in thesleeve at the ultimate state, fsl, with the specified yield strengthof the material used for the sleeve, as expressed in the followingequation:

Reff ¼fslfsly

ð9Þ

ACI-318 [37] and AC-133 [38] recommend the acceptance crite-ria for a mechanical splice. The capacity a splice should be at least125% of the specified yield strength of the bar. BS-8110 [45],

Table 4Effective cross sectional area of grouted splices.

Specimen Cross sectional area of sleeve, Asl

AS-01, AS-03p Dso

2

� �2� p Dsi

2

� �2

BS-01Aps þ 4Awb ¼ p

Dso2

� �2� p Dsi

2

� �2" #þ 4 p dwb

2

� �2" #

BS-02 to BS-13p Dso

2

� �2� p Dsi

2

� �2

CS-SeriesAps þ 4Awp ¼ p

Dso2

� �2� p Dsi

2

� �2" #þ 4bwphwp

DS-Series D2so � D2si

Table 5Stress developed in sleeves, fsu, for different specimens.

Specimen Stress in sleeves, fsu

AS-01 4ðPu�Pgr Þ�103pðD2so�D

2siÞ

BS-01 4ðPu�Pgr Þ�103pðD2so�D

2siþ4d

2wbÞ

BS-02 to BS-13 4ðPu�Pgr Þ�103pðD2so�D

2siÞ

CS-Series 4ðPu�Pgr Þ�103pðD2so�D

2siÞþ16bwp hwp

DS-Series ðPu�Pgr Þ�103D2so�D

2si

538 J.H. Ling et al. / Construction and Building Materials 50 (2014) 530–539

however, in Clause 2.4.2.2 recommended that the design strengthof a material and the limit state for analysis should be derived fromthe characteristic strength divided by the partial safety factor, cm,of 1.4. Therefore, the ultimate strength of the specimens shouldbe at least 1.4 times the specified yield strength of the spliced barsfor the design analysis. For these reasons, the calculated relativestrength ratio of the specimens, Rst, which is expressed in Eq.(10), should be at least 1.25 and 1.4 accordingly.

Rst ¼fufy

ð10Þ

It is generally accepted that the ductility requirement of a struc-ture in low-moderate seismic regions should be at least 4.0 [46].Hence, the ductility ratio of the specimens, D, (Eq. (11)) shouldbe greater than 4.0.

D ¼ dudsy

ð11Þ

4. Discussion

In this study, the feasibility of the test specimens is determinedbased on two major criteria, where the tensile strength ratio, Rst,should be at least 1.25 and the ductility ratio, D, should be greaterthan 4.0. Twenty-three out of thirty-four specimens meet therequirements, where most of which were BS-Series and DS-Series.

The results show that not all of the specimens which sufferedbar-grout bond failure were not feasible. Specimens like AS-01,DS-06, DS-07, DS-08 and DS-09 could still give Rst and D largerthan 1.25 and 4.0, respectively. It only happened when the bondfailed after yielding of the spliced bar.

Table 2 shows that the efficiency ratios of the sleeves, Reff, ran-ged from 0.13 to 0.50. Less than 50% of the capacity of the sleevewas utilized, which was rather inefficient. The sleeve provides ten-sile resistance in two directions; longitudinally and perpendicularto the alignment of the bars [23,25]. The tensile resistance in thelongitudinal direction is more critical as it needs to sustain all

the stress induced by the applied tensile load, while the perpendic-ular direction is solely used to resist the lateral expansion of thegrout due to propagation of splitting cracks. Thus, as long as suffi-cient resistance in the longitudinal direction is provided, the thick-ness of the sleeve can be reduced. An excessive provision of thethickness of the sleeve would offer no further enhancement tothe capacity of a splice connection.

5. Conclusion

In this study, thirty-five splice connectors were made fromstandard size steel sections. These specimens were tested underincremental tensile load to assess for feasibility according to ACI-318 and BS-8110. Twenty-three out of them were feasible.

It is concluded that:

(i) From the failure modes, the bar-grout bond, grout-sleevebond, sleeve’s tensile capacity and the spliced bar’s tensilecapacity are recognized as the factors that govern the failureof splice connector. Hence, these factors must be consideredduring the design of splice connectors.

(ii) Different configurations of sleeve leads to different forms ofstress distribution and different degree of confinement. Thissubsequently causes different efficiency of bond betweenbar and grout.

(iii) By taking the advantages of confinement effects generatedfrom sleeve and tapered nuts, the required developmentcan be as short as nine times the bar diameter or less, whichis approximately 26% of the anchorage length recommendedby BS8110 (35 times diameter of bar).

(iv) The equations derived in Section 3.2 provide the basis for thedesign and evaluation of a typical grouted splice connectorwith the bars spliced in-line.

(v) The experiments and analysis presented are based on thestatic incremental load without considering the potentialslippage of the splice bars. Moreover, the degree of confine-ment might vary depending upon the tensile force applied[25]. Hence, unless the behaviour of these splice connectionsis proven adequate under cyclic and fatigue loads, the spliceshould not be used in structures subjected to cyclic or fati-gue loads.

Acknowledgments

The authors gratefully thank the Construction Industry Re-search Institute of Malaysia (CREAM) and Construction IndustryDevelopment Board (CIDB) for financial support under researchGrant Vot 73713.

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Feasibility study of grouted splice connector under tensile load1 Introduction2 Experimental program2.1 Specimens2.2 Test plan and setup

3 Test results3.1 Failure modes3.2 Analysis for feasibility

4 Discussion5 ConclusionAcknowledgmentsReferences