ab

tal E

h i g h l i g h t s

A deconstructable steelconcrete composite b Experimental data on arch behaviour of preca

rse tiesin a de

se straps were the main test variables. It is concluded that friction grip bolted

posite bridge decks, this axial extension of the RC deck slab can beprevented by adjacent spans and cross-bracing/transverse dia-phragms, generating a compressive thrust in the restrained RCdeck slab [1]. This phenomenon, known as compressive membrane(or arching) action, can signicantly increase the post-crackingstiffness as well as the exural and punching shear capacities oflaterally restrained RC deck slabs [210].

the internal steelof concretction to dome resea

[4,5,13]. In existing steel-free deck slabs that rely on the dement of arching action, the internal steel bars are tyreplaced by external transverse straps with or without cro[14]. The straps rest (or are welded) on the top ange of the steelgirders and close to the soft of the deck slab and the concrete slabis separated from the top ange of the steel girders by a haunchthat encases the cross-bars and a small portion of the transversestraps. Alternatively, the lateral restraint/connement requiredfor the development of arching action in the concrete slab can beprovided by threaded bars (i.e. steel or CFRP/GFRP) and/or

Corresponding author. Tel.: +61 2 9385 6191.E-mail address: H.Valipour@unsw.edu.au (H. Valipour).

Construction and Building Materials 87 (2015) 6777

Contents lists availab

B

evsection in the tensile zone is associated with a change in the neu-tral axis (NA) position that, in turn, causes an axial extension of themember as the neutral axis moves away from the centroidal axisand towards the farthest compressive bre. In steelconcrete com-

resolve the issues associated with corrosion ofreinforcing bars and to extend the service lifeslabs, the concept of mobilising this arching asteel-free deck slabs has been proposed by shttp://dx.doi.org/10.1016/j.conbuildmat.2015.04.0060950-0618/ 2015 Elsevier Ltd. All rights reserved.e deckeveloprchersvelop-picallyss-barsDeconstructionRehabilitation

shear connectors can prevent relative slip between the steel girders and concrete deck slabs, so that theequilibrating tension force in the cross-bracing/transverse straps, required to develop compressive arch-ing in the slabs, can be developed. The arching effect in the slabs is very benecial, and cannot be ignoredin rational structural design processes.

2015 Elsevier Ltd. All rights reserved.

1. Introduction

In reinforced concrete (RC) exural members, cracking of the

The enhancing effect of arching action on the ultimate loadcapacity of restrained RC deck slabs has been recognised andimplemented in some design standards [11,12]. Moreover, toBolted shear connectorComposite deck cross-bracing and transver Efciency of cross-bracing and transve Application of bolted shear connectors

a r t i c l e i n f o

Article history:Received 4 December 2014Received in revised form 3 April 2015Accepted 9 April 2015

Keywords:Arching actionridge deck is proposed.st RC deck slabs are provided.for inducing arch action is studied.constructable deck is studied.

a b s t r a c t

This paper describes the results of the testing of precast concrete slabs in a deconstructable compositesteelconcrete system for the construction of bridge decks. Benign arching action is utilised to carrythe point (wheel) loads to the supports and to develop the required slab capacity; the failure modeand loaddeection response of the precast concrete slabs being investigated in the study. Twelvehalf-scale precast reinforced concrete slab strips were tested, with the slabs being attached to steel gird-ers using friction grip bolts to provide shear connection between the deck and the supporting steel gir-ders. The systems were tested under a monotonically increasing point load, which simulates vehiclewheel loading. The conguration and proportion of the reinforcing steel bars and the types of transverseArching behaviour of precast concrete slcomposite bridge deck

H. Valipour , A. Rajabi, S.J. Foster, M.A. BradfordCentre for Infrastructure Engineering and Safety (CIES), School of Civil and Environmen

Construction and

journal homepage: www.elss in a deconstructable

ngineering, UNSW Australia, UNSW Sydney, NSW 2052, Australia

le at ScienceDirect

uilding Materials

ier .com/locate /conbui ldmat

d Bu68 H. Valipour et al. / Construction anintermediate diaphragms [4,15]. Amongst different alternatives,transverse straps permanently connected to the concrete slaband top ange of the steel girder appears to be the most efcientconning system, whilst threaded steel bars can be replaced easily[4].

In current engineering practice, the composite interactionbetween the concrete slab and steel girders is typically achievedby welded headed shear studs buried permanently in the castin situ concrete or in pockets lled with grout for precast slabs.However, this form of construction is not conducive to deconstruc-tion and it also hinders the speedy and cost-effective replacementof defective slabs and/or the transverse conning system.

The ability of bolted shear connectors in developing efcientcomposite action between the steel girders and precast concreteslabs has been demonstrated through several studies [1623]. Inparticular, recently conducted three-point bending tests on

Fig. 1. Geometry, cross-section, conguration of restraining/conning system in transvPFBSCs.

Table 1Designation of specimens, details of exural reinforcement and bar conguration and tran

Designation of specimens# Reinforcement-1 Reinforcement-2 q = Ast/bd

M6B 6N10 1.5M4B 4N10 1.0B4B 4N10 4N10 0.7B6B 6N10 6N10 1.0M6 6N10 1.5M4 4N10 1.0B4 4N10 0.7M6S 6N10 1.5M6BS 6N10 1.5M4BS 4N10 1.0B4BS 4N10 4N10 0.7B6BS 6N10 6N10 1.0

# Mx and Bx designations are used for slabs with main exural reinforcement at middlilding Materials 87 (2015) 6777composite beams and push-out tests on composite connectionswith post-installed friction-grip bolted shear connectors (PFBSCs)have shown that the composite efciency and fatigue strength ofPFBSCs are signicantly higher than those for beams having studshear connectors [19,20,24]. Furthermore, the steelconcrete com-posite decks with PFBSCs can be deconstructed easily, so that thepossibility for future reuse and the recycling of the structural com-ponents are maximised [16,17]. Thus, composite bridge decks withPFBSCs can allow for speedy and cost-effective rehabilitation,replacement and repair of deteriorated deck slabs with minimaltrafc disruption.

In this paper, the ability of PFBSCs in preventing the relative slipbetween the precast concrete slabs and steel girders in a trans-versely-conned steelconcrete composite bridge deck is exploredexperimentally. The anchoring provided by PFBSCs allows for thedevelopment of compressive membrane (or arching) action that

erse direction and test set up for precast RC slabs connected to steel girders using

sverse conning/restraining system.

(%) c1 (mm) c2 (mm) Transverse restraining system 45 45 5EA45 Bracing45 Bracing25 25 Bracing25 25 Bracing45 45 25 45 Strap45 Bracing + strap45 Bracing + strap25 25 Bracing + strap25 25 Bracing + strap

e and bottom layer, respectively and x denotes the number of reinforcing steel bars.

d (b

d Bucan signicantly enhance the load carrying capacity and stiffness of

Fig. 2. Locations of (a) LVDTs and inclinometers anH. Valipour et al. / Construction anRC exural members in this application. A total of twelve half-scalesingle-span precast RC slab strips connected compositely to steelgirders using PFBSCs are tested under a monotonically increasingdisplacement-controlled point load applied at mid-span. Thearrangement of the exural steel reinforcement (the number andlocation of the bars) as well as the type and stiffness of the trans-verse connement/restraint (i.e. cross-bracing and straps) providedfor the precast slabs are the main variables in the experimentalprogram. In addition to the vertical displacement and applied load,the rotation and horizontal translation (i.e. transverse extension ofthe slab) as well as strain in the steel bars, cross-bracing, straps andthe concrete were measured during the tests. The experimentaldata is used to evaluate the structural performance (viz. the exu-ral behaviour and load carrying capacity) and the ductility of trans-versely restrained precast bridge deck slabs with PFBSCs.

2. Experimental program

2.1. General

To study the arching behaviour of transversely-restrained steelconcrete com-posite bridge decks with PFBSCs, a 15 m long simply supported steelconcrete com-posite bridge deck was designed according to the Australian bridge standardAS5100.6-2004 [25]. The bridge deck comprised of 200 mm thick RC slabs con-nected compositely to 1200WB249 welded steel beams spaced 2.0 metres apart.The loads considered for the strength limit state design of the concrete deck slabsinclude gravity loads (i.e. the self-weight of the structure plus 50 mm of surfacingasphalt), the stationary distributed trafc load denoted S1600 and a wheel pointload of 80 kN, as specied in the Australian bridge standard AS5100.2 for loading[26]. In the experimental program, the response of a 1200 mm wide middle slabstrip was investigated. Twelve half-scale model precast slabs were constructed withdifferent quantities and congurations of the reinforcement (i.e. middle, bottomand top layers) and four different types of transverse connement/restraint (i.e.no straps or cross-bracing, cross-bracing only, straps only and a combination ofstraps and bracing) were provided for the slab. The cross-bracing and horizontalstraps were made of 45 45 5EA equal-leg angles of Grade 300PLUS. At eachend, the cross-bracing and horizontal straps were bolted to the stiffeners and thetop ange of the steel girders respectively using high-strength 8.8 grade bolts of

) steel and concrete strain gauges on precast slab.

ilding Materials 87 (2015) 6777 6916 mm diameter (Fig. 1). The precast slabs were tested under a monotonicallyincreasing displacement-controlled point load applied at mid-span, to replacewheel loading on the bridge.

2.2. Geometry and test setup

The precast slabs that were tested complied with minimum design require-ments of the Australian standard AS5100.5-2004 [27] for concrete bridges. Fig. 1shows the test setup for the half-scale single (non-continuous) precast reinforcedconcrete slab strip connected compositely to the steel girders using PFBSCs. Theload was applied on the precast RC slabs through a 300 kN hydraulic actuatoroperated under displacement control at a rate of 0.1 mm/s (Fig. 1). The overalldimensions of the tested slabs, size of the sections, conguration of the restrain-ing/conning system in the transverse direction and the testing setup are shownin Fig. 1. Details of the reinforcing bar sizes and congurations (i.e. bottom and mid-dle) and the concrete cover to the steel bars (c1 and c2 in Fig. 1) are given in Table 1.The M or B designation in Table 1 was used for slabs with main exural reinforcingbars at middle or bottom layer, respectively. With regard to the reinforcing ratios(q), the specimens can be classied as being over-reinforced (series M6 withq = 1.5%), those with high reinforcement (series M4 and B6 with q = 1.0%) and thosewhich are moderately-reinforced (series B6 with q = 0.7%).

At each end, two M16 8.8/F post-installed bolts were used to connect the pre-cast RC slabs to the top ange of a 310UB32 steel girder of Grade 300PLUS (Fig. 1).These post-installed friction grip bolted shear connectors were tightened to a shanktension of 0.4fuf = 330 MPa, where fuf = 830 MPa is the tensile strength of class 8.8bolts. The cross-bracing and straps for the transverse connement of the slabs wereconnected to the web-stiffeners and top ange of the 310UB32 steel girders respec-tively by the M16 bolts (Fig. 1). The post-tensioning stress induced in all of the fric-tion grip bolts was checked using a calibrated torque wrench. The pre-drilled boltholes in the top ange and web stiffeners of the steel girder were 18 mm in diame-ter and the holes in the precast slab were 20 mm in diameter to allow for easyinstallation of the PFBSCs, and to facilitate potential deconstruction.

2.3. Materials

The steel reinforcing bars were 10 mm diameter ribbed bars with a nominalyield strength of 500 MPa. Two sets of tensile tests (three specimens in each set)on the bars were conducted; the mean yield strength being fy = 575 MPa. The aver-age ultimate strain of the bars was eu 0:08 and the ultimate strength wasf u 680MPa.

d BuCrack began on the top surface of slab & ran between PFBSCs

Bolt holeSpecimen M6B

Crushing of concrete

Specimen B6BS

Crack began on the top surface of slab & ran between PFBSCs

Crushing of concrete

70 H. Valipour et al. / Construction anThe average compressive strength of the concrete used for the precast slabs atthe time of testing of each specimen was fcm = 38 MPa, having been determinedfrom the average of three 300 mm by 150 mm diameter cylinders strengths inaccordance with AS1012.9.

2.4. Instrumentation

In addition to the applied load and vertical displacement at the mid-span of theprecast RC slab, the horizontal transverse deection and rotation at each end of theslab were measured using LVDTs and inclinometers respectively (Fig. 2a). Thestrains in the concrete and longitudinal reinforcing bars were measured at varioussections along the transverse length of the precast slab. In total, ve strain gauges(three steel strain gauges on the reinforcement and two concrete strain gauges)were mounted along each precast slab strip. The locations of the concrete and steelstrain gauges along the precast slab are shown in Fig. 2b. In addition, two straingauges, viz. St-B-SG(1) and St-B-SG(2), were mounted on the cross-bracing and astrain gauge (St-S-SG) was attached to the strap.

3. Test results

3.1. Modes of failure

Three different modes of failure were observed in the precastslabs tested. The rst mode of failure was only observed in speci-mens M4 and B4 (with no transverse connement or restraint),

(a)

(b)

Bolt hole

Specimen M6S

Bolt holeCrushing of concrete

Fig. 3. Brittle modes of failure associated with (a) development of cracks on topsurface of slabs between bolted connectors followed by crushing of concrete incompressive zone at mid-span and (b) crushing of compressive concrete at mid-span.and this mode of failure was associated with yielding of reinforcingsteel bars at mid-span. The secondmode of failure was triggered bycracks that developed on the top surface of the slabs between thebolted connectors and was then followed by crushing of the con-crete in the compressive zone at the mid-span of the slabs(Fig. 3a). For the third mode of failure, only compressive crushingof the concrete on top surface of the slab at mid-span occurred(Fig. 3b). It is noteworthy that except for the rst mode of failure,the other modes of failure were fairly brittle owing to crushing ofthe compressive concrete at mid-span.

The modes of failure for all specimens tested are reported inTable 2, and it can be seen that the transverse connement/re-straint provided by straps and cross-bracings has altered the modeof failure. It is seen further that only specimens M4 and B4 (with notransverse connement/restraint) had a ductile mode, with thefailure of other specimens partly associated with crushing of theconcrete at the slab mid-span. In particular, the somewhat brittlefailure of specimen M6 with no transverse connement/restraintcan be attributed to over-reinforcement (approximately 1.5%)and possibly the higher than normal yield strength of the steelbars.

At the conclusion of each test, the bolted shear connectors wereuntightened and inspected visually; despite extensive cracking,crushing and severe damage in the precast slabs, no evidence ofdamage or deformation was observed in the bolted shear connec-tors and they could be taken out of the sleeve easily and so wereconducive to the deconstruction, repair or rehabilitation of thebridge decks.

3.2. Global response

Plots of the applied load versus vertical displacement at themid-span of the precast slabs are shown in Fig. 4; the small dip fol-lowing the rst peak load in these loaddeection diagrams wascaused by the development of cracks on the top surface of the pre-cast slab. These cracks ran between the PFBSCs as shown in Fig. 3a.The second peak in the loaddeection response of the slabs wasassociated with compressive crushing of the concrete at mid-span(Fig. 3).

The load versus rotation response of the left and right ends ofthe precast slabs is shown in Fig. 5, exhibiting a non-linearrelationship between the load and average rotation of the slabends. The rotation data for some of the specimens are not reportedin Fig. 5, because they were spoiled by the noise in the data acqui-sition system.

The end rotations for different specimens at a load of 54.2 kN,which is the peak load capacity of specimen M4 with no bracingor straps, are shown in Fig. 6. It is seen that the straps and, particu-larly, the cross-bracing in the transversely conned bridge deckprovide the slabs with partial rotational xity. The rotational stiff-ness of the end supports for the single-span precast slabs is muchgreater than the idealised pinned boundary conditions of simply-supported members. Accordingly, accurate analysis of transverselyconned/restrained precast slabs necessitates modelling of therotational stiffness as well as translational stiffness provided bythe transverse conning system (e.g. cross-bracing and/or straps).

The two LVDTs attached to the sides of slabs (Fig. 2a) were usedto determine the horizontal displacement in the transverse direc-tion and the algebraic sum of these displacements is the total elon-gation of the slabs. The load versus elongation response of theprecast slabs is shown in Fig. 7.

3.3. Local response

ilding Materials 87 (2015) 6777The load versus strain response in the reinforcing bars at themid-span of the slab (the results from strain gauge St-SG(1)) are

Table2

Peak

load

capacity

P u,loadP y

correspo

ndingto

onsetof

steelyielding

,mod

eof

failu

re,d

uctilityindexl,m

id-spandee

ctiond y

aton

setof

steelyielding

andmid-spandee

ctiond u

correspo

ndingto

failu

reload.

Designationof

specim

ens

P u(kN)peak

load

P u(Exp.)/P

u

(Plastic)

d u(m

m)

Yield

e c=0.00

1#Ductilityindexlor

Jfactor

Mod

eof

failure

4545

5E

A

Exp.

Plastic#

#

analysis

1st

2nd

P y (kN)

d y (mm)

P 0.001

(kN)

d 0.001

(mm)

d u (2nd)/d y

Energy-

based

J factor

1st

2nd

M6B

89.3

87.5

64.0

1.37

18.8

24.6

70.4

11.7

35.6

4.05

2.10

3.64

11.64

Develop

men

tof

cracks

betw

eenbo

ltholes

follow

edby

concrete

crushingat

mid-span

M4B

69.8

70.1

45.2

1.55

14.9

20.9

62.1

12.2

38.7

5.09

1.72

2.99

5.28

B4B

107.9

103.6

63.6

1.63

16.9

19.5

79.9

8.3

46.7

4.21

2.35

6.29

9.27

B6B

141.1

135.9

91.5

1.48

22.5

24.9

114.1

12.0

52.8

4.89

2.08

4.92

12.30

M6

68.0

64

.01.06

24.2

54

.514

.223

.85.35

1.70

2.98

12.92

Crushingof

concrete

M4

54.2

45

.31.20

26.6

37

.99.2

16.1

2.61

2.89

10.9

34.31

Yieldingof

steelbars

B4

72.8

63

.71.14

25.7

40

.28.3

33.2

2.43

3.10

11.9

23.19

M6S

88.7

64

.01.39

23.2

66

.811

.752

.88.31

1.98

4.04

4.69

Crushingof

concrete

M6B

S10

2.7

86.8

64.0

1.36

25.6

27.2

83.0

14.4

47.2

6.43

1.89

3.21

8.66

Develop

men

tof

cracks

betw

eenbo

ltholes

follow

edby

concrete

crushingat

mid-span

M4B

S84

.175

.745

.21.67

23.9

27.1

70.9

15.1

45.5

6.72

1.79

3.28

6.57

B4B

S11

4.0

63

.61.79

24.2

87

.611

.148

.66.19

2.18

6.11

9.17

Crushingof

concrete

B6B

S13

6.6

91

.51.49

24.8

10

1.9

11.9

65.8

7.43

2.08

4.71

6.93

Crushingof

concrete

#Com

pressive

strain

ofconcreteat

mid-spanon

thetopsurfaceof

theslab.

##Plastican

alysiswas

condu

cted

assumingthat

theprecastslab

strips

aresimplysupp

orted,

ultim

atestrengthf u=68

0MPa

inthean

alysis.

H. Valipour et al. / Construction and Bu0

20

40

60

80

100

120

140

0 10 20 30 40

Loa

d (k

N)

B6BB4BM6B M4B

Concrete crushing

Cracks develop between bolted connectors

ilding Materials 87 (2015) 6777 71shown in Fig. 8. It is seen that in all cases, reinforcing bars yieldedwell before the load capacity of the slabs was attained. The loadversus compressive strain for the concrete on the top surface andat the mid-span of the slabs (the results from strain gauge C-SG(1)) are shown in Fig. 9, from which it can be seen that the com-pressive strain in the concrete has reached values greater than0.003 (adopted typically by different standards as being the maxi-mum compressive strain in concrete). Accordingly, it is concludedthat the failure of the specimens is not fully brittle, and some levelof ductility is available in the transversely conned or restrainedprecast bridge deck slabs.

Curves of the load versus tensile strain ebu in the straps andbracing (being from strain gauges St-B-SG(1) and St-S-SG) areshown in Fig. 10. It is seen that at all stages of the loading, the ten-sile strains and stresses in the cross-bracing and straps remain well

(a)

(b)

(c)

Deflection (mm)

0

20

40

60

80

100

120

140

0 10 20 30 40L

oad

(kN

)

Deflection (mm)

M6SB4M6 M4

0

20

40

60

80

100

120

140

0 10 20 30 40

Loa

d (k

N)

Deflection (mm)

B6BSB4BSM6BSM4BS

Concrete crushing

Plastic hinge (yielding of steel bars)

Concrete crushing

Cracks develop between bolted connectors

Fig. 4. Load versus vertical displacement at mid-span of slabs (a) transverselyconned/restrained by cross bracing (b) without bracing and straps or with onlystraps (c) transversely conned/restrained by cross bracings plus straps.

d Bu(a)

0

20

40

60

80

100

120

140

-5 -4 -3 -2 -1 0 1 2 3 4 5

Loa

d (k

N)

Rotation at end of slab (degree)

B6B-Left B6B-RightB4B-Left B4B-RightM6B-Left M6B-RightM4B-Left M4B-Right

72 H. Valipour et al. / Construction anbelow the yield strain and stress of the Grade 300PLUS steel. Thefriction grip bolts employed in the transverse conning/restrainingsystem have effectively prevented slip in the transverse directionand only a small slip was observed for the bolts connecting thestraps to the top ange of the steel girder in specimen M6S (seeFig. 10a).

3.4. Ductility of specimens

Different denitions have been used by researchers to evaluatethe structural ductility of reinforced concrete members. For thepurpose of this study, three different measures, viz. the displace-ment-based ductility lD, the energy-based ductility lE and J factorare employed to evaluate the structural ductility of the system. Thedisplacement-based ductility (deformability) is [28]:

lD DuDy

; 1

(b)

(c)

0

20

40

60

80

100

120

140

-5 -4 -3 -2 -1 0 1 2 3 4 5

Loa

d (k

N)

Rotation at end of slab (degree)

M6S-Left M6S-RightM6-Left M6-RightM4-Left M4-Right

0

20

40

60

80

100

120

140

-5 -3 -1 1 3 5

Loa

d (k

N)

Rotation at end of slab (degree)

B6BS-Left B6BS-RightB4BS-Left B4BS-RightM6BS-Left M6BS-RightM4BS-Left M4BS-Right

Fig. 5. Load versus average rotation at end of precast slab (a) transversely conned/restrained by cross bracing (b) without bracing and straps or with only straps (c)transversely conned/restrained by combination of cross bracing and straps.where Dy and Du are the displacements corresponding to the onsetof steel yielding and to the peak load capacity respectively.

The energy-based ductility in this study is dened as [29]:

lE W0:75uWy

; 2

whereWy is the area under the loaddeection response curve fromrst loading to the deection corresponding to onset of steel baryielding andW0.75u is the area under the loaddeection curve fromrst loading to the deection at which the load has reduced to 75%of the peak load. Similar energy-based measures have been used byother researchers to evaluate the structural ductility of concretemembers reinforced with low-ductility steel bars or strengthenedwith FRP sheets [28,30].

The J factor was introduced by Mufti et al. [31] and adopted byCanadian Highway Bridge Design Code [12]. It is dened as:

J Cc Cs wuw0:001

Mu

M0:001; 3

where Cc and Csare curvature and strength factors, respectively, andare dened as the ratio of curvature w, or bending moment M, val-

0

0.5

1

1.5

2

2.5

3

3.5

0

Rot

atio

n (D

egre

e)

Transverse confinement

Only strap

Only brac-ing

Strap +

brac-ing

Non

Fig. 6. Average rotation at end of precast slabs at load of 54.2 kN (peak loadcapacity of specimen M4 with no strap and/or bracing).

ilding Materials 87 (2015) 6777ues at ultimate load to the corresponding values at concrete com-pressive strain of 0.001. The strain of 0.001 is assumed to be thebeginning of inelastic deformation in concrete or the strain in con-crete under service load condition [32].

A slightly modied J factor is used in this study,

J DuD0:001

Pu

P0:001

; 4

where Du/D0.001 is the mid-span displacement at ultimate relativeto the value at concrete compressive strain of 0.001 and Pu/P0.001is the load at ultimate relative to the value at a concrete compres-sive strain of 0.001. The J factor adopted in study is similar torobustness index proposed by Van Erp [32].

The displacement-based and energy-based ductility indices andthe J factor of the transversely restrained precast slabs are given inTable 2 and the variation of the ductility index lE and J factor withrespect to the reinforcing ratio q and the ratio of conning systemstiffness KConning system (in the transverse direction) divided by theaxial stiffness of slab KSlab are shown in Fig. 11a and b. It is observedthat all the measures used in this study consistently represent therelative ductility of transversely restrained slabs. Specimen M4without transverse restraint (lE = 10.9 andlD = 2.89) and specimenB4 without transverse restraint (lE = 11.9 and lD = 3.10) have the

d Bu(a)

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6

Loa

d (k

N)

Elongation of slab (mm)

B6BB4BM6B M4B

H. Valipour et al. / Construction anhighest ductility indices, whereas the lowest ductility index(lE = 2.98 and lD = 1.70) belongs to the series M6, which are overreinforced. Transversely-conned precast slab decks with mediumto low reinforcing proportions (i.e. B4B, B6B, B4BS and B6BS) havemedium ductility indices (lE = 4.71 to 6.29). Moreover, it is seenthat the transversely restrained series B slabs with a low reinforcingratio (q = 0.7%) has ductility index lE, exceeding 6.0. The J factor forall transversely restrained slabs was above the minimum require-ment of 4.0 specied in CHBDC code [12] for rectangular sectionswith FRP reinforcements.

In this study, the stiffness of conning system KConning systemand the slab KSlab are obtained from

KConfining system Xni1

EsAili

cos2 h;

n total number of bracings=straps 5

(b)

(c)

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6

Loa

d (k

N)

Elongation of slab (mm)

M6SB4M6 M4

0

20

40

60

80

100

120

140

0 1 2 3 4 5 6

Loa

d (k

N)

Elongation of slab (mm)

B6BSB4BSM6BSM4BS

Fig. 7. Load versus elongation of precast slab measured by horizontal LVDTs at endof precast slab (a) transversely conned/restrained by cross bracing (b) withoutbracing and straps or with only straps (c) transversely conned/restrained bycombination of cross bracing and straps.ilding Materials 87 (2015) 6777 73KSlab EcAclc

; 6

where Es 200 GPa is the elastic modulus of steel, Ai 394 mm2is the cross-sectional area of a single cross-bracing/strap, li is thelength of cross-bracing/strap and h is the angle between thecross-bracing/strap and the horizontal plane. For cross-bracingsli 1045 mm and h 12 and for straps li 1020 mm andh 0. Ec is the concrete modulus of elasticity and it is taken asEc 29 GPa, Ac 600 100 6 104 mm2 is the cross-sectionalarea of concrete slab and lc 1100 mm is the span length of slab.It is noteworthy that the effect of reinforcing bars on the axial stiff-ness of slab has been ignored in Eq. (6).

(a)

(b)

(c)Fig. 8. Load versus tensile strain at mid-span in reinforcing bars (St-SG1) for precastslabs (a) transversely conned/restrained by cross bracing (b) without bracing andstraps or with only straps (c) transversely conned/restrained by combination ofcross bracing and straps.

d Bu0

20

40

60

80

100

120

140

Loa

d (k

N)

B6B B4B M6BM4B

strain at ultimate in design

74 H. Valipour et al. / Construction anThe stiffness of a single cross-bracing and a strap obtained fromEq. (5) is 72.5 and 77.3 kN/mm, respectively, and stiffness of theprecast slab obtained from Eq. (6) is 1580 kN/mm.

3.5. Strength enhancement provided by arching action

The maximum loads carried by the specimens are given inTable 2. The theoretical peak load capacities of the specimenscan be calculated using an elementary plastic analysis assumingpinned ends; the theoretical over the experimental load capacitiesof the specimens are given in Table 2. The results show that ignor-ing the arching effect and the rotational restraint lead to overlyconservative design. For specimens M4BS and B4BS, for example,the failure load is underestimated by 67% and 79%, respectively.

(a)

(b)

(c)

-5000 -4000 -3000 -2000 -1000 0

0

20

40

60

80

100

120

140

-5000 -4000 -3000 -2000 -1000 0

Loa

d (k

N)

M6SM6M4

0

20

40

60

80

100

120

140

-5000 -4000 -3000 -2000 -1000 0

Loa

d (k

N)

Strain (

B6BSB4BS M6BSM4BS

strain at ultimate in design

strain at ultimate in design

mm/mm)

Strain (mm/mm)

Strain (mm/mm)

Fig. 9. Load versus concrete compressive strain at mid-span on top surface ofprecast slabs (a) transversely conned/restrained by cross bracing (b) withoutbracing and straps or with only straps (c) transversely conned/restrained bycombination of cross bracing and straps.(a)

(b)

0

30

60

90

120

150

0 100 200 300 400 500

Loa

d (k

N)

B6B-bracingB4B-bracingM6B-bracingM4B-bracingM6S-strap

0

30

60

90

120

150

0 100 200 300 400 500L

oad

(kN

)

Strain (

B6BS-bracingB4BS -bracingM6BS-bracingM4BS-bracing

Slip

mm/mm)

Strain (mm/mm)

ilding Materials 87 (2015) 6777The load capacities of the precast concrete deck slabs withrespect to the reinforcement ratio q and the relative stiffness(KConning system/KSlab) for the transverse conning system (i.e.cross-bracing and/or straps) are shown in Fig. 11c. It should benoted that the load capacity of the tested precast slabs dependson the reinforcement ratio and conguration as well as the stiff-ness of the transverse conning system, which is characteristic ofstrength enhancement provided by compressive membrane action[2].

With regard to Fig. 11a and b, it can be concluded that mobilis-ing the arching action and the subsequent strength enhancementin the transversely conned precast slab decks (TCPSD) come at acost of lower ductility. It is observable that for slabs with less than1% tensile reinforcement, the measures of ductility (i.e. lE and J)consistently decrease with an increase in the stiffness of conningsystem in the transverse direction. However, it should be notedthat the variation of ductility indices for the TCPSD depends notonly on the transverse stiffness provided for the precast slabs butalso on the conguration of the conning system (i.e. only bracing,only strap, strap + bracing) as well as reinforcing ratio in the slab.For example, in series M with q = 1.5%, it is seen that the J factorincreases from 4.69 to 11.64 (Fig. 11b), when the KConning system/KSlab ratio increases from 0.1 (with only strap) to 0.185 (with onlybracing). This increase in the J factor (despite increase in the trans-verse stiffness of conning system) can be attributed to the largerrotational stiffness provided for the slabs by the crass bracingscompared to the system with only straps.

The normalised experimental peak load capacities of the trans-versely conned slabs with respect to identical slabs without anytransverse restraint (i.e. ratio of the peak load capacity of the slabwith transverse connement over the peak load capacity of theidentical slab without transverse connement) for slabs with

Fig. 10. Load versus tensile strain in cross bracing/straps for the slabs transverselyconned/restrained by (a) only cross bracing or straps and (b) cross bracing plusstraps.

d BuH. Valipour et al. / Construction andifferent transverse conning system (i.e. cross-bracing, strap,cross-bracing + strap) are shown in Fig. 12. It can be seen thatthe strength enhancement due to arching action varies inverselywith the reinforcing bar ratio, i.e. those precast slabs with a lowerreinforcing ratio (series B4) have a higher strength enhancement.

3.6. Experimental versus analytical strength enhancement

As demonstrated in Table 2, simple plastic analyses ignore theeffect of arching action and consistently underestimate the loadcapacity of the restrained precast slabs. Accordingly, severalattempts have been made to develop analytical methods that cancapture the enhancing effect of arching action [3335]. The exist-ing analytical models are, however, cumbersome and require sev-eral iterations to predict the failure load of restrained RC memberswith reasonable accuracy [33]. Accordingly, there is still a need to

(a)

(b)

(c) Fig. 11. Variation of (a) ductility index lE and (b) J factor and (c) peak load capacityof slabs, with respect to reinforcing steel proportion and relative stiffness oftransverse conning system.

Fig. 12. Normalised peak load capacity (ratio of the peak load capacity of the slabwith transverse connement over the peak load capacity of the identical slabwithout transverse connement) for slabs with different transverse conningderive simple empirical formulas that can capture the enhancingeffect of arching action with sufcient accuracy.

Valipour et al. [36] used an enhanced bre element model toconduct a parametric study on a generic model (see Fig. 13a) anddetermine the inuence of different parameters including span/depth ratio, concrete compressive strength, reinforcing ratio, stiff-ness of transverse conning system KConning system and rotationalstiffness Kh of end supports (see Fig. 13a) on the enhancing effectof arching action in RC beams. Fig. 13b shows the strengthenhancement factor versus relative stiffness of transverse conn-ing system (KConning system/Kaxial) obtained from the parametricstudy conducted by Valipour et al. [36]. It is noteworthy that thestrength enhancement factor in Fig. 13b is dened as the ratio ofpeak load capacity of the transversely conned/restrained RCmember over peak load capacity of the identical RC member with-out transverse conning system (KConning system = 0). Furthermore,the xed and pinned conditions in Fig. 13b refer to the end supportconditions adopted for analyses of the generic model in Fig. 13a.

The plots shown in Fig. 13b are used to estimate an upper andlower bound value for strength enhancement factor in the testedslabs and the results are compared with the experimental results

system.1

1.2

1.4

1.6

0 0.1 0.2 0.3

Nor

mal

ised

pea

k lo

ad c

apac

ity

KConfining system /KSlab

M6 series (p=1.5%)M4 series (p=1.0%)B4 series (p=0.7%)

Onlybracing

Strap + bracing

No transverse confining system

ilding Materials 87 (2015) 6777 75in Fig. 14. It is seen that the bound of strength enhancement pre-dicted by the results of the parametric study correlates reasonablywell with the test data.

4. Concluding remarks

A set of twelve half-scale precast reinforced concrete slabs wereconnected to steel girders using post-installed friction grip boltedshear connectors (PFBSCs). The slabs were tested under a mono-tonically increasing point load applied at the mid-span to simulatewheel loading on a deconstructable composite deck. In the experi-mental program, the application of three types of transverse con-ning system (i.e. straps, cross-bracing and a combination ofstraps and cross-bracing) in conjunction with friction grip boltedconnections for mobilising arching action and enhancing the peakload capacity of the precast concrete slabs was studied. Althoughthe experimental work was focused mainly on steelconcrete com-posite decks with PFBSCs, the results of the tests can be alsoextended to the rehabilitation and structural strength assessmentof conventional steelconcrete composite decks, where the appli-cation of cross-bracing (or considering the effect of existingcross-bracing or cross-beams) can signicantly enhance the load

a)

d Bu(

76 H. Valipour et al. / Construction ancarrying capacity of concrete slab decks and, consequently, preventunnecessary repair and/or replacement of these decks.

The experimental program in this study provided benchmarkdata for evaluating the structural performance (i.e. the mode offailure, loaddeection response and ductility) and for validatingnumerical models of the transversely-restrained precast RC slabsof composite decks with PFBSCs. In specic regard to the archingbehaviour of precast slabs, the following conclusions are drawn:

PFBSCs can effectively prevent relative slip between precastslabs and steel girders in the transverse direction. This is of par-ticular importance for the development of arching action indeconstructable composite bridge decks with transversely con-ned precast slab decks (TCPSD) where the restraining system

(b)Fig. 13. (a) Outline of the generic model and denition of parameters (b) strength enhanpeak load capacity of the RC member without transverse conning system KConning systemusing generic bre-element models (span/depth = 11) [36].

1

1.5

2

2.5

0.1 0.2 0.3

Nor

mal

ised

pea

k lo

ad

KConfining system /KSlab

Analytic-Fixed (p=0.8%)Analytic-Fixed (p=1.2%)Exp. (p=1.5%)Exp. (p=1.0%)Exp. (p=0.7%)Analytic-Pinned (p=0.8%)Analytic-Pinned (p=1.2%)

Fig. 14. Comparison between experimental and analytical strength enhancementpredicted by the results of parametric study [36].

cement factor (i.e. peak load capacity of the transversely conned RC member overilding Materials 87 (2015) 6777(cross-bracing and straps) is connected mechanically (usingfriction bolts) to the steel girders instead of slab itself, in orderto facilitate dismantling of the structure.

Despite extensive damage (cracking and crushing) and fairlylarge displacements and rotations that the precast slabs experi-enced at their ultimate loading state, no apparent damage ordeformation was observed in the bolted shear connectors andthe PFBSCs could be removed from the sleeves easily. Thisdemonstrates the ability of proposed system to accommodatefuture repair, rehabilitation and/or dismantling.

Two distinctive modes of failure were identied for trans-versely-conned precast slab decks with PFBSCs; the rst modeof failure was triggered by the development of cracks on the topsurface of the slabs between the PFBSCs and then followed bycrushing of the concrete at mid-span, whereas the second modeof failure was only associated with crushing of the concrete atmid-span.

The development of arching action in the single-span TCPSDsenhanced the peak load capacity, by up to 51%, but the higherload capacity of TCPSDs came at a cost of lower ductility, par-ticularly for slabs with a reinforcing ratio in excess of 1%. Forslabs reinforcing with less than 1% tensile reinforcement, whichis typical of slabs in practice, a good compromise between duc-tility and strength enhancement can be achieved by adjustingthe stiffness of the transverse conning system.

References

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[2] Farhangvesali N, Valipour H, Samali B, Foster S. Development of arching actionin longitudinally-restrained reinforced concrete beams. Constr Build Mater2013;47:719.

= 0) versus relative stiffness of conning system, obtained from a parametric study

[3] Ruddle ME, Rankin GIB, Long AE. Arching actionexural and shear strengthenhancements in rectangular and Tee beams. Proc Inst Civ Eng Struct Build2002;156:6374.

[4] Bakht B, Lam C. Behavior of transverse conning systems for steel-free deckslabs. ASCE J Bridge Eng 2000:13947.

[5] Mufti AA, Bakht B, Newhook JP. Precast concrete decks for slab-on-girdersystems: a new approach. ACI Struct J 2004;101(3):395402.

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[7] Klowak CS, Mufti AA. Behaviour of bridge deck cantilever overhangs subjectedto a static and fatigue concentrated load. Constr Build Mater 2009;23(4):165364.

[8] Mufti AA, Newhook JP. Punching shear strength of restrained concrete bridgedeck slabs. ACI Struct J 1998;95(4):37581.

[9] Taylor SE, Rankin B, Cleland DJ, Kirkpatrick J. Serviceability of bridge deck slabswith arching action. ACI Struct J 2007;104(1):3948.

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[18] Rowe M, Bradford MA. Partial shear interaction in deconstructable compositesteel-concrete composite beams with bolted shear connectors. Miskolc,Hungary: International Conference on Design, Fabrication and Economy of

[20] Kwon G, Engelhardt MD, Klinger RE. Behavior of post-installed shearconnectors under static and fatigue loading. Constr Steel Res 2010;66(4):53241.

[21] Marshall WT, Nelson HM, Banerjee HK. An experimental study of the use ofhigh-strength friction-grip bolts as shear connectors in composite beams.Struct Eng 1971;49(4):1718.

[22] Dallam LN, Harpster JL. Composite beam tests with high-strength bolt shearconnectors. Report No. 683, University of Missouri-Columbia, MO, USA; 1968.

[23] Dallam LN, Push out tests with high strength bolt shear connectors. Report No.687, University of Missouri-Columbia, MO, USA; 1968.

[24] Lee SSM, Bradford MA. Sustainable composite beams with deconstructableshear connectors. 5th International Conference on Structural Engineering,Mechanics and Computation, Cape Town, South Africa. 5th InternationalConference on Structural Engineering, Mechanics and Computation. CapeTown, South Africa; 2013.

[25] AS5100.6. Bridge design steel and composite construction. AustralianStandard; 2004.

[26] AS5100.2. Bridge design Part 2: design load. Australian standard; 2004.[27] AS5100.5. Bridge Design, Part 5: concrete. Australian Standard; 2004.[28] Spadea G, Swamy RN, Bencardino F. Strength and ductility of RC beams

repaired with bonded CFRP laminates. J Bridge Eng 2001;6(5):34955.[29] Grace NF, Soliman AK, Abdel-Sayed G, Saleh KR. Behavior and ductility of

simple and continuous FRP reinforced beams. J Compos Constr1998;2(4):18694.

[30] Sakka ZI, Gilbert I. Effect of reinforcement ductility on strength and failuremodes of one-way reinforced concrete slabs. Report No. UNICIV R-450, TheUniversity of New South Wales, NSW, Australia; 2008.

[31] Mufti AA, Newhook JP, Tadros G. Deformability versus ductility in concretebeams with FRP reinforcement. Montreal, Quebec: Proceeding of the secondinternational conference on advanced composite materials in bridges andstructures; 1996. p. 18999.

[32] Erp GM. Robustness of bre composite structures loaded in exure. HongKong, China: Proceeding of international conference on FRP composites in civilengineering (CICE); 2001. p. 14216.

[33] Yu J, Tan KH. Analytical model for the capacity of compressive arch action ofreinforced concrete sub-assemblages. Mag. Concr. Res. 2014;66(3):10926.

[34] Taylor SE, Rankin GIB, Cleland DJ. Arching action in high-strength concreteslabs. Proc Inst Civ Eng Struct Build 2001;146(4):35362.

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retrotted with post-installed shear connectors. ASCE J Bridge Eng 2011;16(4):53645.[35] Rankin GIB, Long AE. Arching action strength enhancement in laterally-restrained slab strips. Proc Inst Civ Eng Struct Build 1997;122(4):4617.

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Arching behaviour of precast concrete slabs in a deconstructable composite bridge deck1 Introduction2 Experimental program2.1 General2.2 Geometry and test setup2.3 Materials2.4 Instrumentation

3 Test results3.1 Modes of failure3.2 Global response3.3 Local response3.4 Ductility of specimens3.5 Strength enhancement provided by arching action3.6 Experimental versus analytical strength enhancement

4 Concluding remarksReferences