Research ArticleBehavior and Splice Length of Deformed Bars Lapping in SpirallyConfined Grout-Filled Corrugated Duct

Yongfeng Zheng ,1 Zhangfeng Zhu ,2 Zhengxing Guo,3 and Peng Liu 4

1Key Laboratory of Building Structural Retrofitting and Underground Space Engineering (Shandong Jianzhu University),Ministry of Education, Jinan, Shandong 250101, China2College of Civil Engineering, Nanjing Tech University, Nanjing, Jiangsu 211816, China3School of Civil Engineering, Southeast University, Nanjing, Jiangsu 210096, China4School of Civil Engineering, Central South University, Changsha 410075, China

Correspondence should be addressed to Yongfeng Zheng; zhyf-fb@163.com and Peng Liu; lop868@163.com

Received 29 July 2019; Accepted 19 October 2019; Published 11 November 2019

Academic Editor: Michelina Catauro

Copyright © 2019 Yongfeng Zheng et al. .is is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

.is paper discusses the behavior of grouted noncontact lap splices under monotonic tension load. Deformed bars lapped througha grout-filled corrugated duct, and a spiral reinforcement was preembedded in the connection to improve tensile strength of thesplice. .e experimental results show that bond failure splices are always failed by the pullout of the preembedded bar other thanthe grouted bar. As the spiral pitch distance is not greater than 75mm, the tensile strength generally improves with the incrementof volumetric spiral reinforcement ratio due to the higher confinement provided by the spiral bar. Compared with the spiral bardiameter, the spiral pitch distance provides more dominant effect on the tensile strength of the connection. Based on theexperimental results and the development length specified in ACI 318-14, a revised equation with a reduction factor of 0.76 wasproposed to predict the required minimum lap length of spirally confined lap splice.

1. Introduction

Rebar lapping in grout-filled conduit is enormously used inconstruction of precast concrete structures. .e connectionsystem (Figure 1) is based on the use of consecutive columnsegments provided each with longitudinal bars protrudingfrom the upper end and corrugated steel conduits encased inthe lower end. .e steel conduits are positioned adjacent tothe embedded longitudinal bars. .e continuity of thelongitudinal reinforcement is achieved through the non-contact lapping when the lower projecting bars are insertedand grouted into the corrugated duct. In China, the con-nection of this type is not recommended to be used inprimary earthquake-resistant members [1]. Similarly, ACI318-14 [2] specifies that application of such splices in plastichinge requires demonstration through laboratory testingthat the spliced precast structural element shows anequivalent response to its cast-in-place counterpart.

Research studies to address the aforementioned concernsand the use of grouted noncontact lap splices in plastic hingeregions of structural elements have been completed in recentyears. Precast column-to-foundation specimens using groutedcorrugated steel conduits were tested under cyclic lateral loadcombined with axial compression by Belleri and Riva [3] andPopa et al. [4]..eir results indicate that the precast specimenshave similar hysteretic response and energy dissipation ca-pacity as the reference monolithic units, and the groutedcorrugated ducts are suitable to be used in seismic regions.Rave-Arango et al. [5] prepared a beam-column joint, con-necting the steel bars using grouted lap splice at the columnends, and tested under cyclic loading. .e data obtained fromthe test highlighted the seismic behaviors are comparable withcast-in-place unit and just have slight differences in cracking,damage distribution, and hysteretic behavior.

.e above test results corroborate the possibility of usingthe grouted lap splice in seismic regions from the overall

HindawiAdvances in Materials Science and EngineeringVolume 2019, Article ID 5280986, 11 pageshttps://doi.org/10.1155/2019/5280986

mailto:zhyf-fb@163.commailto:lop868@163.comhttps://orcid.org/0000-0002-8287-8532https://orcid.org/0000-0001-5591-4625https://orcid.org/0000-0001-7518-1713https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://doi.org/10.1155/2019/5280986

seismic response (capacity, hysteretic responses, energydissipation, etc.) of the precast units. However, for the timebeing, fewer references exist dealing specifically with the laplength of grouted corrugated duct connection and a cal-culation method for the required lap length which not onlycan promise sufficient strength in plastic hinge region, butalso is economical, reasonable, and urgently needed. Evenso, the following papers could give some enlightenment forthe study of this paper. Tullini and Minghini [6] performedan experimental program concerning full-scale tests onprecast reinforced concrete column-to-column connec-tions made with the grouted splices. .e direct tension testresults highlighted the effectiveness of the stress transferalong the splice region, and failure took place outside thebar splice region. .e behavior of spirally confined lapsplice was investigated by Einea et al. [7] and Hosseini andRahman [8]. .eir investigation shows that the spiralconfinement can result in significant reduction of the re-quired lap length. .e spiral diameter provides moredominant confining effect compared to the spiral pitchdistance [8]. For the conventional lap splice used in cast-in-place concrete structure, Hassan et al. [9] found that theACI318-08 Building Code provided more conservativebond strength predictions for regular bars compared tolarger diameter bars.

Despite the available studies and even the existence ofdesign guidelines that include recommendations for the useof grouted lap splice [10, 11], comprehensive experimentalcharacterization of the grouted connection is still scarce, andfurther work needs to be conducted to provide the test dataon which confidence in the design and application of thisconnection could be built. In response to this, 30 sets of 90lap splices were prepared, and spiral reinforcement waspreembedded in the connected region to improve the bondbehavior of the splice. .rough monotonic tension test, theeffects of spiral configuration on tensile strength were in-vestigated as well as the calculation of the required laplength.

2. Experimental Program

2.1. Test Specimens. Experimental parameters include lap-ping bar diameter, lap length, spiral bar diameter, and spiralpitch distance. .e specimens were named with a fivecomponent ID according to their variables. Take C40-16-0.8-6-75 for example; the first part denotes the concrete type(C40), and the second component is the nominal diameter oflapping bar (db � 16 or 18mm), and the third componentdenotes the ratio (0.8, 1.0 or 1.2) of the lap length (ll,exp) tothe basic development length (laE). .e value of laE can bedefined by GB 50010-2010 [12], as follows:

laE � ζaEζaαfby

ftdb ≈ 30db, (1)

where ζaE is a correction factor reflecting the buildingaseismic grade, ζaE � 1.05; ζa is a factor reflecting the effectsof reinforcement size, epoxy coating, concrete cover, etc,ζa � 1.00; α is the reinforcement shape factor, α� 0.14; fby isthe design tensile strength of reinforcement, fby � 360MPa; ftis the design tensile strength of concrete, ft � 1.71MPa. .efourth part in the specimen ID illustrates the nominal bardiameter of spiral reinforcement (dsb � 4 or 6mm). .e lastpart indicates the pitch distance of the spiral (sv � 50, 75 or100mm). For each test type, three identical specimens wereprepared.

Configuration and dimensions of the test specimens areshown in Figure 2. Each specimen consisted of a concreteblock having a rectangular cross section of 120×150mm. Toprevent any additional restraints, an unbonded length of25mm was provided at the end of the block using a plastictube. .e spiral diameters (Ds) used in the specimens for16 mm and 18 mm bar splices were 65mm and 70mm,respectively. All the reserved conduits were formed bycorrugated metal ducts with the same diameter of 40mm.

2.2. Test Setup. Different from butt splice, the lap splice iseccentrically loaded when tested on a traditional mechanicaltesting machine due to the eccentric position of the lappingbar in the concrete block and consequently affects the ac-curacy of test values inevitably. .erefore, a tension testsetup was specially developed, as shown in Figure 3. .esupport frame is mainly composed of four screws of 45mmin diameter and three steel plates of 16mm in thickness..ree plates are welded to each other and formed into atrough structure used for placing the test specimen.Meanwhile, there are steel plates of 40mm in thickness ateach side of the frame, and an eccentric hole was drilled inthe plate to be passed through by the lapping bar. As the barloaded, the 40mm thick plate can provide enough reactionforce to ensure the lapping bar fractured. In order to reducefriction between the inner wall of the frame and the concreteblock, PTFE plates were placed on both sides and bottom ofthe steel trough. Two hydraulic centre hole jacks were usedto provide monotonic tension load. Before test, the jacks andload cell were calibrated on a universal material testingmachine. After curing for 28 days, all the specimens weretested under incremental tensile load at a rate of 2MPa/s.

Corrugatedsteel conduit

Grout inlet

In-situconcrete

Lower precastcomponent

Upper precastcomponent

Protrudingbar

Shim andGrout bed

Figure 1: Rebar lapping by corrugated steel duct.

2 Advances in Materials Science and Engineering

During the test, the tension load was recorded by thepressure value of the oil pressure gauge and the readings ofthe load cell.

2.3. Material. .e concrete was supplied by a commercialready mixing plant. .e concrete type was C40 (that is, witha specified 28-day cubic and prism compressive strengthgreater than 40.0MPa and 26.8MPa, respectively). .e testcompressive strength, which was determined at the day oftesting the lap splice specimens using 100×100× 300mmprisms cast at the same time as the specimens and curedalongside the specimens, is 27.2MPa.

High-strength nonshrinkage grout was used as fillermaterial pumped into the corrugated duct. .e grout wasprepared with a mix of 0.13 kg of dry powder in 1 liter ofwater. .e average compressive and flexural strengths at theday of testing were 80.5MPa and 11.1MPa, respectively.

Two different deformed bar diameters were used in thisexperimental program with the same specified yield strengthfbyk of 400MPa and tensile strength fbuk of 540MPa (steel bargrade: HRB400). Tension verification tests were conductedwith specimens that were cut from the same batch re-inforcements as the ones used in the pullout tests. .eaverage mechanical properties are listed in Table 1.

3. Experimental Results

3.1. Failure Mode. Two failure modes were observed,namely, bar fracture failure and bar pullout failure. Incomparison with the bond failure of bar pullout, specimenfailed by bar fracture is the desired failure mode for thebetter reliability. Taking C40-18-1.0-6-75 as an example, thecracking pattern is described as follows: first transverse crackoccurred in the middle of concrete block when the specimenwas loaded to about 60 kN; as the tension load increased toabout 100 kN, two cracks were observed at both ends of theblock; at approximately 107 kN, the bar yielded, and sub-sequently more and more splitting cracks initiated from thecorner of the block; as the load increased to about 156 kN,the lapping bar fractured or pulled out accompanied withspalling of the corner concrete, as shown in Figure 4(a). Forthe pullout failure specimens of 18mmbar, in addition to

Corrugatedsteel duct

ll + 40 120

40

150

c 2D

sc 2

c1 Ds c1Spiral reinforcement Pre-embedded bar

SpiralreinforcementCorrugated

steel duct

Grout

Grouted barPu

Pu

20 20Sv

Figure 2: Configuration of splice specimen (unit: mm).

Hydraulic jack

Manualjack

Load cellSplice specimen

D45 Screw

16mm thick steel plate

40mm thick steel

Figure 3: Test setup.

Advances in Materials Science and Engineering 3

the transverse splitting cracks, longitudinal cracks also canbe observed after the bar yielding in the side concrete surface(Figure 4(b)).

It is important to stress that all the bond failure speci-mens failed by the pullout of preembedded bar other thanthe grouted bar. .is indicates a higher bond strength ofgrouted bar and can be attributed to the following: (i) thestrength of filler grout in metal corrugated duct is greatlyhigher than the surrounding concrete and (ii) the steel ductprovides uniform confining stresses on the grout splittingdilation. .erefore, the tensile strength of lap splice iscontrolled by the bond strength of the preembedded bar, andthe grouted bar, filler grout, and corrugated duct can beassumed as a single body. Consequently, more splittingcracks are generated on the side of grouted bar due to therelatively smaller concrete cover, as shown in Figure 4(c).

Table 2 summarizes the test results of all the specimens.With the exception of specimens C40-18-0.8-6-100, allspecimens sustained maximum axial stresses, higher than125 percent of the specified strength fbyk of lapping bars and,in most cases, no less than 150 percent of fbyk. As the bardiameter increases from 16mm to 18mm, the number ofpullout failure specimens increases from 33.3% to 73.3%,and a more significant effect of the spiral reinforcement onthe tensile strength of the splice can be observed. .eminimum lap lengths to ensure bar fracture are 24db and30db, respectively, for the 16 mm and 18 mm bar splices withthe spiral bar diameter (dsb) of 6mm and pitch distance (sv)of 50 (hereafter denoted as d6@50 and similarly to the otherspiral configuration). For the specimens with the spiral ofd4@75, however, the minimum lap lengths are 36db and>36db, respectively.

3.2. Strength of Lap Splice. Figures 5 and 6 show the tensilestrength (fu) and bond strength (τb) versus lap length (ll),respectively. .e average bond strength can be calculated byequation (2). Considering that the tensile strength of the bar

fracture specimen is determined by the strength of thelapping bar, which cannot reflect the effects of the lap length,only bond failure specimens are presented. From Figure 5,nonlinear increment of the tensile strength with the increaseof lap length can be noted. As the lap length increases from0.8laE to 1.0laE, the tensile strength increases significantly andaveragely by 10.9%. However, as the length increases from1.0laE to 1.2laE, the strength increases slightly only by 2.3%.On the other hand, different from the variation of the tensilestrength, the bond strength of lapping bar decreases aver-agely by 24.3% as the lap length increases from 0.8laE to1.2laE, as shown in Figure 6. By virtue of more ribs on the barengaged to interlock with surrounding concrete, the tensilestrength increases with the lap length. But due to thenonuniform distribution of the bond stress at bar-concreteinterface, the tensile strength does not increase linearly.Meanwhile, longer bonded length creates a more apparentuneven bond stress distribution [13, 14] and a larger numberof primary cracks within the lap length [15], and hence,lower bond strength is generated.

τb �Pu,exp

πdbll( �0.25fudb

ll. (2)

In addition, Figure 5 also illustrates the effects of con-figurations of the spiral reinforcement on the tensile strengthof the splice..e specimens with the spiral of d6@75 give thehighest strength, and followed by d4@50, d4@75, and d6@100, in turn decrease. In order to see the effects of the spiralconfiguration graphically, the variation of tensile strengthwith different volumetric spiral reinforcement ratio (ρsv) isplotted in Figure 7. .e ratio can be used to appraise theamount of spiral reinforcement, which is calculated byequation (3) [2, 12]. Results show that increasing the vol-umetric ratio can generally improve the bond strength, andmore apparent influence can be observed by the specimenswith greater bar diameter and shorter lap length. For ex-ample, in the case of splice with bar diameter of 18mm and

Table 1: Properties of reinforcing steel bars (average value of three specimens).

Diameter db (mm) Actual yield strength (MPa) Actual tensile strength (MPa) Elongation rate (%) Elastic modulus (MPa)16 430 603 25.3 2.0×105

18 425 615 24.9 2.0×105

Grouted bar

(a)

Grouted bar

Longitudinal splitting crack

(b)

Grouted bar

Splitting crack

(c)

Figure 4: Typical cracking after load. (a) C40-18-1.0-6-75. (b) C40-18-0.8-4-50. (c) C40-18-1.2-6-100.

4 Advances in Materials Science and Engineering

Table 2: Summary of test results.

Specimens fu(MPa) Average (MPa)fu/fbyk

Failuremode∗

C40-16-0.8-6-100543.1

548.11.36 BP

543.5 1.36 BP557.8 1.39 BP

C40-16-0.8-6-75600.1

598.11.50 BF

598.5 1.50 BP595.8 1.49 BP

C40-16-0.8-6-50604.3

604.31.51 BF

610.6 1.53 BF598.0 1.50 BF

C40-16-0.8-4-75579.3

579.31.45 BF

582.5 1.46 BP576.1 1.44 BP

C40-16-0.8-4-50602.3

598.01.51 BF

593.6 1.48 BP598.1 1.50 BF

C40-16-1.0-6-100576.3

572.51.44 BP

560.4 1.40 BP580.7 1.45 BP

C40-16-1.0-6-75599.1

601.51.50 BF

600.6 1.50 BP604.7 1.51 BF

C40-16-1.0-6-50613.0

606.71.53 BF

608.9 1.52 BF598.1 1.50 BF

C40-16-1.0-4-75599.6

590.71.50 BF

591.2 1.48 BP581.3 1.45 BP

C40-16-1.0-4-50603.3

603.41.51 BF

598.1 1.50 BP608.7 1.52 BF

C40-16-1.2-6-100604.8

606.01.51 BF

609.1 1.52 BF604.1 1.51 BF

C40-16-1.2-6-75611.8

607.71.53 BF

603.6 1.51 BF607.7 1.52 BF

C40-16-1.2-6-50598.0

601.21.50 BF

605.0 1.51 BF600.5 1.50 BF

C40-16-1.2-4-75598.3

602.21.50 BF

607.1 1.52 BF601.1 1.50 BF

C40-16-1.2-4-50598.0

600.61.50 BF

603.6 1.51 BF600.3 1.50 BF

C40-18-0.8-6-100509.8

495.71.27 BP

495.4 1.24 BP481.8 1.20 BP

C40-18-0.8-6-75561.9

575.81.40 BP

598.0 1.50 BP567.6 1.42 BP

C40-18-0.8-6-50613.1

604.01.53 BF

601.9 1.50 BP598.1 1.50 BP

C40-18-0.8-4-75518.2

520.61.30 BP

523.1 1.31 BP520.6 1.30 BP

Table 2: Continued.

Specimens fu(MPa) Average (MPa)fu/fbyk

Failuremode∗

C40-18-0.8-4-50543.5

544.71.36 BP

535.7 1.34 BP555.0 1.39 BP

C40-18-1.0-6-100582.9

573.51.46 BP

559.2 1.40 BP578.4 1.45 BP

C40-18-1.0-6-75619.9

613.91.55 BF

607.5 1.52 BP614.2 1.54 BP

C40-18-1.0-6-50614.6

614.51.54 BF

618.7 1.55 BF610.3 1.53 BF

C40-18-1.0-4-75570.1

584.71.43 BP

580.9 1.45 BP603.1 1.51 BP

C40-18-1.0-4-50589.4

593.41.47 BP

598.0 1.50 BP592.8 1.48 BP

C40-18-1.2-6-100601.5

592.01.50 BP

594.3 1.49 BP580.2 1.45 BP

C40-18-1.2-6-75620.5

617.71.55 BF

615.7 1.54 BF616.9 1.54 BP

C40-18-1.2-6-50619.2

620.51.55 BF

625.5 1.56 BF616.8 1.54 BF

C40-18-1.2-4-75588.3

594.41.47 BP

593.1 1.48 BP601.9 1.50 BP

C40-18-1.2-4-50608.1

615.61.52 BF

618.1 1.55 BF620.7 1.55 BP

∗BF represents bar fracture failure; BP represents bar pullout failure.

480

510

540

570

600

630

Tens

ile st

reng

th, f

u (M

Pa)

0.9 1.0 1.1 1.20.8ll/laE

C40-18-x-6-75C40-18-x-6-100

C40-18-x-4-50C40-18-x-4-75

Figure 5: Tensile strength-lap length relationship.

Advances in Materials Science and Engineering 5

lap length of 0.8ld, by increasing the ratio of ρsv from 0.96%(d4@75) to 3.23% (d6@50), the tensile strength improvesdramatically from 520.6MPa to 604.0MPa.

It should be noted that all the family curves have adistinct turning point at the abscissa value of 1.74% for16 mm bar splices and 1.62% for 18 mm bar splices. .e twotroughs represent the spiral configuration of d6@100. Spiralpitch distance taken as 100mm seems too be great to be usedfor application in practice. Meanwhile, comparing d4@50with d6@75, although the ratio of ρsv increases by 45%, nosignificant improvement in tensile strength can be observed.For the 18 mm bar splices, the tensile strength is onlyimproved by an average of 3.1%, and for the 16 mm one, thetensile strength even slightly decreases. .ese results mayinfer that compared to increasing the diameter of the spiralbar, it is more effective to improve the tensile strength

through reducing the pitch distance. .e following sectionswill make further analysis on the effect of the spiralconfiguration.

ρsv �0.25πd2sb · πDs 0.25πD2s · sv(

�πd2sbDssv(

. (3)

4. Confining Mechanism of Spirally ConfinedLap Splice

.e effect of spiral reinforcement on the bond strength canbe explained by a free body diagram shown in Figure 8.Considering that all the bond failure splices failed by pulloutof the preembedded bars, the interactions between thegrouted bar, filler grout, and metal corrugated duct are

0.9 1.0 1.1 1.20.8ll/ldE

4.0

4.4

4.8

5.2

5.6

6.0

Bond

stre

ngth

, τb (

MPa

)

C40-18-x-6-75C40-18-x-6-100

C40-18-x-4-50C40-18-x-4-75

Figure 6: Bond strength-lap length relationship.

Tens

ile st

reng

th, f

u (M

Pa)

540

560

580

600

620

2.4 2.80.8 1.2 3.21.6 3.62.0Volume-stirrup ratio, ρsv (%)

All the specimens failedby bar fracture.

d4@75 d6@75

d6@100

d4@50 d6@50

C40-16-0.8-x-xC40-16-1.0-x-x

(a)

Tens

ile st

reng

th, f

u (M

Pa)

Volume-stirrup ratio, ρsv (%)1.0 1.5 2.0 2.5 3.0 3.5

All the specimens failedby bar fracture.

d4@75 d6@75

d6@100

d4@50 d6@50

480

520

560

600

640

C40-18-0.8-x-xC40-18-1.0-x-xC40-18-1.2-x-x

(b)

Figure 7: Tensile strength-volume stirrup ratio relationship: (a) d16; (b) d18.

6 Advances in Materials Science and Engineering

ignored, and the three components are deemed as a singlebody in the figure.

Under direct tension load, the bar rib bearing actionsagainst the concrete occur, as seen in Figure 8(a). .esebearing actions can be divided into tangential stress (τ1) andnormal stress (σ1), similarly to the interaction between thecorrugated duct and the concrete..e normal stresses whichcause radial cracks in concrete have been confined effectivelyby the spiral reinforcement, and consequently creates tensilestress in the spiral, as seen in Figure 8(b). .e followingequations can be driven from the equilibrium of axial andhoop forces:

Pu � 0.25fuπd2b � πτ1dbll, (4)

ftkcsv + 0.5πσsd2sb � σ1db + σ2dc( sv, (5)

τ1db � τ2dc, (6)

τ1 � σ1 tan α1;τ2 � σ2 tan α2,

(7)

where dc is diameter of corrugated duct; sv is spiral pitchdistance; c is the smaller thickness of the concrete cover (c1or c2 in Figure 2); dsb is diameter of the spiral bar. With theincrease of tension load, the ribs of steel bar and metalconduit can crush the surrounding concrete by wedgingaction. When the concrete is crushed into a compactedpowder, it becomes lodged in front of the ribs [16]. .is ineffect produces ribs with face angles of about 45°, i.e.,α1 � α2 � 45°. Consequently, the bond stress can be derived as

τ1 �Pu

πdbll�

fudb

4ll�

ftkcsv + 0.5πσsd2sb

dbsv 1/ tan α1( + 1/ tan α2( (

�ftkcsv + 0.5πσsd

2sb

2dbsv.

(8)

Substituting the test bond strength (τb) in equation (8),the tensile stress of the spiral reinforcement when the splicefailed by bond can be calculated, as listed in Table 3. It is seen

that all the calculated stresses of σs are less than the specifiedyield strength of 300MPa.

As the lap length increases, dramatic decrease in thespiral bar stress can be observed. Taking the splices of C40-18-x-4-75 series as an example, as the lap length increasesfrom 0.8laE to 1.2laE, the σs decreases by 61.6%, from226.0MPa to 86.8MPa. Meanwhile, for the 18 mm barsplices, comparing d6@100 splices with d4@50 splices, it canbe found that by reducing the volumetric stirrup ratio from1.62% to 1.44%, the spiral bar stress and the tensile strengthof lapping bar increase averagely 35.1% and 5.4%, re-spectively. .is indicates a more effective confinementprovided by the spiral of d4@50. In general, it can beconcluded that (i) as the lap length increases, the effect ofspiral reinforcement declines and (ii) under the premise ofsimilar volumetric stirrup ratios, smaller spiral bar and pitchdistance can improve the material utilization of the spiraland achieve a higher tensile strength.

5. Design Method and Recommendation

According to ACI 318-14 [2], with an appropriate simpli-fication, the development length ld needed to develop stressfs in a deformed bar may be expressed as

ld �fs

1.1��

fc′

c + Ktr( /db( ⎛⎜⎜⎜⎝ ⎞⎟⎟⎟⎠db. (9)

In equation (9), terms are defined and values areestablished as follows: Ktr is the transverse reinforcementindex: Ktr � 40Atr/nsv; Atr is the total cross-sectional area ofall transverse reinforcement within spacing sv that crossesthe potential plane of splitting through the reinforcementbeing developed; n is the number of bars being developedalong the plane of splitting; and fc′ is the specified com-pressive strength of concrete. For full development of thebar, fs is set equal to the specified yield strength fbyk, and theterm (c+Ktr)/db should not be taken greater than 2.5.

Nevertheless, for the precast concrete structures, themain bars usually spliced in the potential plastic hinge forconstruction convenience. To ensure sufficient strength and

τ1

τ1

τ2

τ2

Pu

Pu

α1

α2

σ1

σ2

(a)

σ1

σs

σs

Ds

cc

d cd b

σ2

ftk

150

(b)

Figure 8: Free body diagram. (a) Axial forces equilibrium. (b) Hoop forces equilibrium.

Advances in Materials Science and Engineering 7

displacement ductility in the connection region and realize afull-yield strength of the bar, 50 percent increase above thespecified yield strength was selected according to ACI 550.1R[10]. Furthermore, because the bars are usually lapped at thesame section of high tensile stress, the length of ld should bemultiplied by 1.3 according to ACI 318-14. As a result, thelap length ll can be written as

ll,cal � φ1.95fbyk

1.1��

fc′

c + Ktr( /db( ⎛⎜⎜⎜⎝ ⎞⎟⎟⎟⎠db, (10)

where φ is a reduction factor. It should be noted that theupper limit of 2.5 for the term (c+Ktr)/db seems too con-servative according to the test results in this paper. Forexample, the tensile strength of specimen d6@50 is dis-tinctively improved compared with that of correspondingspecimen configured with d4@50 by virtue of the higherconfinement, although the calculated values of (c+Ktr)/dbare greater than 2.5. Consequently, equation (10) may beused with a recommendation to increase the limit to 4.0instead of 2.5 [7, 17, 18].

.e value of φ can be obtained by the statistical method..e sequence for adopting the required lap length (ll) and itsfrequency (nfl) is outlined in Figure 9. Substituting the laplength in equation (10), the factor φ and its fitted probabilitydistribution are derived and shown graphically in Figure 10.Assuming that φ is normally distributed, the mean value andstandard deviation are 0.645 and 0.073, respectively. As aresult, a 95% confidence value of 0.76 is adopted, andequation (10) can be expressed as

ll,cal �1.35fbyk

��

fc′

c + Ktr( /db( ⎛⎜⎜⎜⎝ ⎞⎟⎟⎟⎠db, (11)

where (c+Ktr)/db should not exceed 4.0. .e calculated laplengths ll,cal are listed in Table 4. .e criterion for de-termining the experimental minimum lap length ll,exp of thespecimens with the same spiral configuration in Table 4 isthat the tensile strengths of the three specimens are all notless than 150% of fbyk. It can be seen that with the exceptionof specimens C40-16-x-6-75, all the calculated/experimentalratios ll,cal/ll,exp are greater than 1.0, which shows an reliableprediction. For the specimens C40-16-0.8-6-75, only onespecimen does not meet the above length adopting criteriawith a slightly lower tensile strength, as shown in Table 2..at means the required lap length may be a little higher than384mm (0.8laE), but less than the value of 480mm (1.0laE) inthe table. Consequently, the predicted ll,cal should be moreclose to or higher than the actual minimum lap length.

Moreover, considering that the spirals are inexpensive[7], the upper limit of 4.0 for the term (c+Ktr)/db can be usedto determine the minimum amount of spiral reinforcementfor a simplification. And then, evaluation of equation (11)results in

ll,cal �0.34fbyk

��

fc′⎛⎜⎜⎜⎝ ⎞⎟⎟⎟⎠db. (12)

It should be noted that the above equation for estimatingthe required lap length of deformed bar in spirally confinedconnection is based on the bar with 16mm and 18mmdiameter and additional testing is recommended to confirmthe performance of spirally confined lap splice for otherdiameters. It is also important to experimentally evaluate theperformance of the proposed lap splice under cyclic loadingand in a full-scale setting (e.g., connecting wall panels) whennecessary before implementation to ensure adequate per-formance based on application requirements.

Table 3: Calculated tensile stress of spiral reinforcement.

Specimens ll,exp (mm) Ds (mm) c (mm) ρsv (%) Failure mode∗ fu (MPa) τb (MPa) σs (MPa)C40-16-0.8-6-100 384 65 28 1.74 BP (3) 548.1 5.71 90.6C40-16-0.8-6-75 384 65 28 2.32 BP (2) 598.1 6.23 90.1C40-16-0.8-4-75 384 65 28 1.03 BP (2) 579.3 6.03 184.0C40-16-0.8-4-50 384 65 28 1.55 BP (1) 598.0 6.23 135.0C40-16-1.0-6-100 480 65 28 1.74 BP (3) 572.5 4.77 37.5C40-16-1.0-6-75 480 65 28 2.32 BP (1) 601.5 5.01 38.4C40-16-1.0-4-75 480 65 28 1.03 BP (2) 590.7 4.92 77.8C40-16-1.0-4-50 480 65 28 1.55 BP (1) 603.4 5.03 58.6C40-18-0.8-6-100 432 70 25 1.62 BP (3) 495.7 5.16 117.4C40-18-0.8-6-75 432 70 25 2.15 BP (3) 575.8 6.00 127.9C40-18-0.8-6-50 432 70 25 3.23 BP (2) 612.3 6.38 97.4C40-18-0.8-4-75 432 70 25 0.96 BP (3) 520.6 5.42 226.0C40-18-0.8-4-50 432 70 25 1.44 BP (3) 544.7 5.67 168.6C40-18-1.0-6-100 540 70 25 1.62 BP (3) 573.5 4.78 92.9C40-18-1.0-6-75 540 70 25 2.15 BP (2) 613.4 5.11 85.6C40-18-1.0-4-75 540 70 25 0.96 BP (3) 584.7 4.87 166.8C40-18-1.0-4-50 540 70 25 1.44 BP (3) 593.4 4.95 116.4C40-18-1.2-6-100 648 70 25 1.62 BP (3) 594.0 4.13 51.3C40-18-1.2-6-75 648 70 25 2.15 BP (1) 617.7 4.29 46.3C40-18-1.2-4-75 648 70 25 0.96 BP (3) 594.4 4.13 86.8C40-18-1.2-4-50 648 70 25 1.44 BP (1) 615.6 4.28 68.4∗BP (n) represents bar pullout failure and the figure in the parenthesis is the number of the bond failure specimens.

8 Advances in Materials Science and Engineering

All the three specimensmeet: fu ≥ 1.5fbykY

ll,exp = 0.8laE

fu ≥ 1.5fbyk,nfl1 = 1 or 2

N

ll,exp = 1.0laE

ll = 0.8laE,nfl1 = nfl2

All the three specimensmeet: fu ≥ 1.5fbyk

ll = 0.8laE,nfl = 3

ll = 1.0laE,nfl2 = 3 – nfl1

No specimen meets:fu ≥ 1.5fbyk

N

ll,exp = 1.2laE

All the three specimensmeet: fu ≥ 1.5fbyk

Y

ll,exp = 1.0laE

All the three specimensmeet: fu ≥ 1.5fbyk Y

ll = 1.0laE,nfl1 = 3

fu ≥ 1.5ffbyk,nfl1 = 1 or 2

ll = 1.0laE,nfl1 = nfl1

Y

fu ≥ 1.5fbyk, nfl2 = 1 or 2

N

ll = 1.0laE, nfl2 = nfl2

ll ,exp = 1.2laE

All the three specimensmeet: fu ≥ 1.5fbyk

ll = 1.2laE,nfl2 = 3 – nfl2Y

NN

ll = 1.2laE, nfl3 = 1

fu ≥ 1.5fbyk, nfl2 = 1 or 2

N

ll = 1.4laE, nfl3 = 1

Ending

Ending

nfl1 + nfl2 ≥ 3Y

nfl1 + nfl2 = 3ll = 1.0laE,nfl2 = nfl2

nfl1 + nfl2 > 3 ll = 1.0laE,

nfl2 = 3 – nfl1Ending

Ending

nfl1 + nfl2 ≥ 3 Y

nfl1 + nfl = 3ll = 1.2laE,nfl2 = nfl2

nfl1 + nfl2 > 3ll = 1.2laE,

nfl2 = 3 – nfl1Ending

Ending

Figure 9: Experimental lap length adopting sequence.

Freq

uenc

y (n

fl)

0

2

4

6

8

10

12

14

0.90.4 0.5 0.70.6 0.8Reduction factor (φ)

Normal

Figure 10: Fitted normal distribution of the reduction factor.

Table 4: Comparison of lap lengths.

Specimens Asb (mm2) Ktr (mm) (c+Ktr)/db ll,exp (mm) ll,cal (mm) ll,cal/ll,expC40-16-x-6-50 56.5 22.62 4.00 384 414 1.08C40-16-x-6-75 56.5 15.08 3.60 480 460 0.96C40-16-x-4-50 25.1 10.05 2.98 480 557 1.16C40-16-x-4-75 25.1 6.70 2.56 576 648 1.13C40-18-x-6-50 56.5 22.62 3.90 432 478 1.11C40-18-x-6-75 56.5 15.08 3.06 540 608 1.13C40-18-x-4-50 25.1 10.05 2.51 648 744 1.15C40-18-x-4-75 25.1 6.70 2.13 756 874 1.16

Advances in Materials Science and Engineering 9

6. Conclusion

.e following conclusions can be drawn based on the testand analytical studies:

(1) For the spirally confined grout-filled lap splice, thebond failure usually featured by the pullout of thepreembedded bar and the grouted bar, filler grout,and metal corrugated conduit can be regarded as asingle body in the mechanical analysis.

(2) Increasing the volumetric ratio of spiral from 0.96%to 3.23% leads to an increment of 16% higher tensilestrength, as demonstrated by the lapped splice with18mmbars and 24db bar embedded length. Mean-while, the spiral reinforcement is generally difficultto yield, and reducing the spiral pitch distance ismore effective to confine the filler grout comparedwith increasing the spiral bar diameter.

(3) Based on the equation of tensile development lengthin ACI 318-14, a modified equation of required laplength corresponding to the bar stress of 1.5 fbyk isproposed. .e calculated values show a reliableprediction compared to the experimental results.

Nomenclature

Atr: Total cross-sectional area of all transversereinforcement within spacing sv that crosses thepotential plane of splitting through thereinforcement being developed (mm2)

C: Clear cover of reinforcement (mm)db: Nominal diameter of lap bar (mm)dc: Diameter of corrugated duct (mm)dsb: Nominal diameter of spiral bar (mm)Ds: Spiral diameter (mm)fby: Design tensile strength of reinforcement (MPa)fbyk: Specified tensile strength of reinforcement (MPa)fc′: Specified compressive strength of concrete (MPa)ft: Design tensile strength of concrete (MPa)ftk: Specified tensile strength of concrete (MPa)fu: Tensile strength of splicelaE: Basic development length in tensionll,cal: Calculated lap length in tension of deformed barll,exp: Experimental lap length in tension of deformed barnfl: Frequency of required minimum lap lengthnff : Frequency of tensile strength fu which not less than

1.5 fbyksv: Spiral pitch distanceKtr: Transverse reinforcement indexPu,exp: Experimental pullout load (kN)α: Reinforcement shape factorρsv: Volumetric spiral reinforcement ratioζaE: Correction factor reflecting the building aseismic

gradeζa: Factor reflecting the effects of reinforcement size,

epoxy coating, concrete cover, etcτb: Bond strength of lap barτ1: Tangential stress at bar-concrete interfaceσ1: Normal stress at bar-concrete interface

τ2: Tangential stress at conduit-concrete interfaceσ2: Normal stress at conduit-concrete interfaceφ: Reduction factor of calculated lap length.

Data Availability

.e data used to support the findings of this study areavailable from the corresponding author upon request.

Conflicts of Interest

.e authors declare that they have no conflicts of interest.

Acknowledgments

.is work was supported by the National Key Research andDevelopment Program of China (grant nos.2016YFC0701703 and 2016YFC0701705-1); a Project ofShandong Province Higher Educational Science and Tech-nology Program (grant no. J17KA207), and the NationalNatural Science Foundation of China (grant nos. 51778632and 51408614).

References

[1] JGJ1-2014, Technical Specification for Precast ConcreteStructures, Chinese Industry Standard, China Architecture &Building Press, Beijing, China, 2014, in Chinese.

[2] ACI318-14, Building Code Requirements for Structural Con-crete and Commentary, American Concrete Institute, Farm-ington Hills, MI, USA, 2014.

[3] A. Belleri and P. Riva, “Seismic performance and retrofit ofprecast concrete grouted sleeve connections,” PCI Journal,vol. 57, no. 1, pp. 97–109, 2012.

[4] V. Popa, A. Papurcu, D. Cotofana, and R. Pascu, “Experi-mental testing on emulative connections for precast columnsusing grouted corrugated steel sleeves,” Bulletin of EarthquakeEngineering, vol. 13, no. 8, pp. 2429–2447, 2015.

[5] J. F. Rave-Arango, C. A. Blandón, J. I. Restrepo, andF. Carmona, “Seismic performance of precast concrete col-umn-to-column lap-splice connections,” Engineering Struc-tures, vol. 172, pp. 687–699, 2018.

[6] N. Tullini and F. Minghini, “Grouted sleeve connections usedin precast reinforced concrete construction—experimentalinvestigation of a column-to-column joint,” EngineeringStructures, vol. 127, pp. 784–803, 2016.

[7] A. Einea, S. Yehia, and M. K. Tadros, “Lap splices in confinedconcrete,” ACI Structural Journal, vol. 96, no. 6, pp. 947–955,1999.

[8] S. J. A. Hosseini and A. B. A. Rahman, “Effects of spiralconfinement to the bond behavior of deformed reinforcementbars subjected to axial tension,” Engineering Structures,vol. 112, pp. 1–13, 2016.

[9] T. K. Hassan, G.W. Lucier, and S. H. Rizkalla, “Splice strengthof large diameter, high strength steel reinforcing bars,”Construction and Building Materials, vol. 26, pp. 216–225,2012.

[10] ACI550.1R-09, Emulating Cast-In-Place Detailing for SeismicDesign of Precast Concrete Structures, American ConcreteInstitute, Farmington Hills, MI, USA, 2009.

[11] Precast and Prestressed Concrete Institute, PCI DesignHandbook: Precast and Prestressed Concrete, Precast Pre-stressed Concrete Institute, Chicago, IL, USA, 2010.

10 Advances in Materials Science and Engineering

[12] GB 50010-2010, Code for Design of Concrete Structures,Chinese National Standards, China Architecture & BuildingPress, Beijing, China, 2016, in Chinese.

[13] Y. Zheng, Z. Guo, J. Liu, X. Chen, and Q. Xiao, “Performanceand confining mechanism of grouted deformed pipe spliceunder tensile load,” Advances in Structural Engineering,vol. 19, no. 1, pp. 86–103, 2016.

[14] Y. Zheng, Z. Guo, D. Guan, and X. Zhang, “Parametric studyon a novel grouted rolling pipe splice for precast concreteconstruction,” Construction and Building Materials, vol. 166,pp. 452–463, 2018.

[15] R. I. Gilbert and A. E. Kilpatrick, “.e strength and ductility oflapped splices of reinforcing bars in tension,” AustralianJournal of Structural Engineering, vol. 16, no. 1, pp. 35–46,2015.

[16] R. Tepfers, “Cracking of concrete cover along anchored de-formed reinforcing bars,” Magazine of Concrete Research,vol. 31, no. 106, pp. 3–12, 1979.

[17] D. Darwin, M. L. .olen, E. K. Idun, and J. Zuo, “Splicestrength of high relative rib area reinforcing bars,” ACIStructural Journal, vol. 93, no. 1, pp. 95–107, 1996.

[18] D. Darwin, L. R. A. Lutz, and J. Zuo, “Recommended pro-visions and commentary on development and lap splicelengths for deformed reinforcing bars in tension,” ACIStructural Journal, vol. 102, no. 6, pp. 892–900, 2005.

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