Deconstructable steel–fibre reinforced concrete deck slabs with a transverse confining system

    Deconstructable steel-fibre reinforced concrete deck slabs with a Transverse confining system M. Moradi, H. Valipour, S.J. Foster, M.A. Bradford PII: DOI: Reference:

S0264-1275(15)30635-3 doi: 10.1016/j.matdes.2015.10.059 JMADE 798

To appear in: Received date: Revised date: Accepted date:

25 April 2015 7 October 2015 14 October 2015

Please cite this article as: M. Moradi, H. Valipour, S.J. Foster, M.A. Bradford, Deconstructable steel-fibre reinforced concrete deck slabs with a Transverse confining system, (2015), doi: 10.1016/j.matdes.2015.10.059

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ACCEPTED MANUSCRIPT Title:

Deconstructable steel-fibre reinforced concrete deck slabs with a transverse confining system M. Moradi 1,, H. Valipour 2, S.J. Foster 3 and M.A. Bradford 4

Authors:

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PhD Candidate, Senior Lecturer, Professor (Head of School of Civil & 4 Environmental Engineering), Scientia Professor and Australian Laureate Fellow

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Centre for Infrastructure Engineering and Safety (CIES) School of Civil end Environmental Engineering UNSW Australia NSW 2052, Australia

Corresponding Author: Hamid Valipour

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School of Civil and Environmental Engineering UNSW Australia UNSW Sydney, NSW 2052, Australia E-mail: [email protected] Tel: 0061 2 9385 6191

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Abstract

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This paper investigates the behaviour of transversely-restrained precast steel-fibre reinforced concrete (SFRC) slabs in a demountable composite bridge deck. Fourteen precast SFRC slabs

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were tested under static point loading. The slabs were restrained using external demountable straps and cross-bracings to mobilise arch action and so enhance the load carrying capacity of the SFRC slabs, being partially or fully devoid of conventional reinforcing bars. The

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configuration and proportion of the reinforcing bars, concrete compressive strength, dosage of fibres and the type of external restraining system (cross- bracing/strap) were the main variables in the tests. It is concluded that steel fibres with 0.5% dosage can significantly increase the load carrying capacity of the externally restrained precast deck slabs devoid of steel bars and the transverse confining system (i.e. ties/straps and cross-bracings)

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increase the energy-based ductility index of the SFRC deck slabs. Furthermore, it is shown that replacing part of conventional reinforcing bars with structural steel fibres can slightly improve the energy-based ductility of externally restrained SFRC/RC precast deck slabs. Keywords Arching action; bridge deck; deconstruction; slab; steel-fibres.

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ACCEPTED MANUSCRIPT 1. Introduction Cracking of reinforced concrete (RC) sections subject to flexure is associated with a change

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in the position of neutral axis (NA) that, in turn, leads to an axial extension or growth of the

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member as the NA moves towards the extreme compressive fibre [1]. If the growth of

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cracked RC members is prevented by some external restraints, a compressive force, known as arching action, can develop in the cracked RC member. This compressive force can

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significantly increase the post-cracking stiffness and load carrying capacity of RC members so restrained [2-4].

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The development of arching action in conventionally-reinforced deck slabs has been the subject of numerous studies [5, 6], and the strength enhancement provided by arch action has

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been recognised and implemented in a few design codes [7, 8]. In addition, the concept of

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mobilising arching action to develop slab decks totally or partially devoid of conventional

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reinforcing steel has been investigated in various studies [2, 9, 10]. However, less attention has been paid to the development of compressive membrane action and its beneficial effect on the ultimate load capacity and structural behaviour of fibre reinforced concrete (FRC)

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slabs and bridge decks [11, 12].

Over the past two decades, the application FRC, particularly steel fibre reinforced concrete (SFRC), has gained popularity in the construction industry [13-15], and a significant body of experimental and analytical studies have been conducted to characterise the mechanical properties and behaviour of SFRC at the materials and structural levels [16-18]. The investigations undertaken by different research groups cover various aspects of fibre reinforced concrete members, such as the punching shear capacity of SFRC slabs [19], the development of high performance concrete with fibres [18, 20], energy absorption and the blast and impact resistance of fibre reinforced panels and slabs [21-25], the development of

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ACCEPTED MANUSCRIPT models and design provisions for predicting the punching load capacity of slabs [26, 27], the bond characteristics of SFRC [28, 29] and the development and application of reliable

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constitutive laws for modelling the behaviour of FRC [30-33].

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In general, the use of discontinuous reinforcement (fibres) in concrete increases the post-

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cracking residual tensile strength and improves the behaviour of the material with the fibres bridging crack openings. Accordingly, the improvements achieved by adding fibres are

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commonly considered to be significant within the range of service loads where the reduction in the deflections and crack width are significant [34]. It has been demonstrated that the inclusion

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of steel fibres in concrete can improve flexural-shear/shear, bending moment capacity and the punching shear capacity of beams and slabs, respectively. The enhancing effect of the steel

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fibres on the shear and punching shear capacity of beams and slabs has been investigated

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extensively [19, 35, 36]. However, less attention has been paid to the flexural strength

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enhancement provided by steel fibres in suspended concrete slabs or slabs on girders with and without conventional reinforcing bars [37]. The application of steel fibres as the secondary reinforcement in such slabs can improve their strength and ductility, and where it can be

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demonstrated that steel fibres can be used as the main reinforcement in bridge decks (provided ductility comparable to conventionally reinforced slab decks is achieved with commercially viable fibres dosages), there is significant potential for reducing the cost of both materials and labour as well as increasing the speed of construction. This study provides benchmark test data on the structural behaviour of transversely-confined precast SFRC slab decks on steel girders. Fourteen one-half scale single-span precast concrete slabs compositely connected to steel girders using post-installed friction grip bolted shear connectors (PFBSCs) are tested under a displacement-controlled point load applied at the mid-span. The dosage of steel fibres, proportion of conventional reinforcing steel bars,

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ACCEPTED MANUSCRIPT concrete compressive strength and the type, location and stiffness of the restraining system (i.e. cross-bracing and ties or straps) in the transverse direction are the main variables in the

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experimental program. The global response (the applied load and vertical displacement at

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mid-span, rotation, transverse extension and failure mode) as well as the local response (the

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strain in the steel bars, cross-bracings, straps and concrete) of the SFRC slabs were measured to determine how steel fibres contribute to the ultimate flexural capacity of concrete deck

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slabs with and without conventional steel bars.

The study investigates the strength and ductility of transversely-restrained precast steel-fibre

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reinforced concrete (SFRC) slabs for demountable composite bridge decks. The behaviour under cyclic traffic loading (fatigue) is important but is beyond the scope the present

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research. A summary of research of SFRC for fatigue is given in [38].

2. Experimental Program

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2.1. Geometry and test set up

Fourteen one-half scale precast SFRC/RC slab decks were constructed with different

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reinforcing bar proportions and configuration, steel fibre dosages, concrete compressive strengths and four different types of transverse restraining systems. The prototype precast slab is part of a 12 m long simply supported steel-concrete composite bridge deck in New South Wales, Australia. The bridge deck is 7.0 m wide with no cantilevering and it is supported by four steel girders 2.2 m centre-to-centre (Fig. 1a). The bridge can accommodate two standard lanes, each lane being 3.2 m wide according to the specifications of the Australian bridge code AS5100.2 [39]. The concrete deck slab in the transverse direction was designed as being simply supported (i.e. spanning between two adjacent girders, Fig. 1a) and the slabs complied with the minimum design requirements of AS5100.5 [40].

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ACCEPTED MANUSCRIPT This study focuses on the behaviour of a one-half scale precast slab from the middle module of the full-scale bridge deck (Fig. 1a). The one-half scale precast slabs were 100 mm thick,

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600 mm wide and 1100 mm long and they had a haunch at each end, i.e. where the slabs were

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connected to the top flange of a 310UB32 supporting steel girder of Grade 300PLUS (Fig.

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1b). The outline of the geometry and test set up, the dimensions of the precast slabs, the size of the sections and the configuration of the restraining system in the transverse direction are shown in Fig. 1b. Details of the reinforcing bars including their proportion, location and the

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effective depth of the precast slabs (viz. the distance between the centroid of the tensile

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reinforcement and the extreme compressive fibre of the slab, d in Fig. 1b), are given in Table 1. The slabs were tested under a monotonically increasing displacement-controlled

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point load applied at the mid-span. The load was applied to the mid-span of slabs using a 300

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kN hydraulic actuator operated under displacement control at a rate of 0.1 mm/s (Fig. 1b).

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The composite action between the precast deck slab and steel girders is typically provided by shear connectors permanently buried in pockets filled with grout; however, this form of construction can hinder the dismantling of the structure and the possibility of the future

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recycling or reuse of the structural components. To resolve these issues, the application of bolted shear connectors for developing composite action has been investigated recently and the results of push-out tests on steel-concrete composite connections with post-installed friction-grip bolted shear connectors (PFBSCs) has demonstrated the superior composite efficiency of PFBSCs compared to conventional shear connectors [41-44]. Accordingly, in this study the composite action between the precast SFRC/RC slabs and the supporting steel girders is provided by PFBSCs to facilitate the dismantling and reusing of the structural components. At each end, the precast slabs were connected compositely to the top flange of a 310UB32 using two M16 8.8/F (friction) bolts. The M16 8.8/F shear connectors were

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ACCEPTED MANUSCRIPT tightened by a torque wrench to provide a post-tensioning force of 0.4fuf = 330 MPa, with fuf being the tensile strength of the Class 8.8 bolts used in the connectors.

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The transverse restraining systems, employed for mobilising the arch action, were cross-

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bracings only, straps only and a combination of straps and cross-bracings. The cross-bracings

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and straps were made of equal leg angle sections as L45455EA and L45453EA sections of Grade 300PLUS steel, respectively. The cross-bracing was bolted to the stiffeners,

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whereas the transverse ties or straps were bolted to the top flange of the steel girders using 16

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mm diameter high-strength 8.8 bolts and shear connectors (Fig. 1b). Two different arrangements were considered for the straps, i.e. straps under the slab and straps away from the slabs. The latter arrangement was used when straps are used in conjunction with cross-

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bracing (Fig. 1b). Furthermore, the connection of the cross-bracing and straps to the web stiffeners and top flange of the 310UB32 steel girders was achieved using M16 8.8/TF bolts

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tightened to a shank tension of 0.6fuf = 495 MPa (Fig. 1b). The 18 mm diameter bolt holes were predrilled in the top flange and the web stiffeners. Before casting the slabs, a 20 mm

PFBSCs.

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diameter PVC conduit was placed in the formwork to allow for easy installation of the

2.2. Materials

The reinforcing steel bars in the slabs were 10 mm diameter ribbed bars. The characteristic yield strength of steel bars was 500 MPa and the mean yield strength of the steel bars was

f y  575 MPa (obtained from direct tension tests on three specimens). The ultimate strength of the steel bars was f u  680 MPa and the average uniform elongation of bars at f u was

 u  8% .

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ACCEPTED MANUSCRIPT The SFRC slabs were cast with 50 and 60 MPa concrete having maximum aggregate size of 10 mm. The steel fibres were 60 mm long and 0.9 mm diameter Dramix 5D-65/60-BG (Fig.

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2a) with nominal strength of 2000 MPa at an average uniform elongation more than 6%.

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In addition to the slabs, twenty four 300 mm high by 150 mm diameter cylinders and twelve

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150 mm by 150 mm by 500 mm prisms were cast and tested according to ASTM C1609/C1609M [45] to characterise the mechanical properties of the SFRC, including

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the average compressive strength of the concrete f cm , the splitting tensile strength of the concrete f ct,sp (split cylinder), the modulus of rupture f ct,fl and the modulus of elasticity E 0

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of the concrete at 28 days and on the testing day. The test specimens were cast in two batches with the same concrete mix and chemical composition. The mean compressive strength of the

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concrete f cm for the specimens was obtained from the average of three 300 mm high by

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150 mm diameter cylinders tested after 28 days, in accordance with the Australian Standard

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AS1012.9 [46]. The stress-strain curves for the plain concrete and the SFRC at the time testing, obtained from a uniaxial compression test on 300 mm by 150 mm diameter cylinders, are shown in Fig. 2b; the average compressive strengths of the concrete for different

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specimens are given in Table 1 and the splitting tensile strength f ct,sp , modulus of rupture

f ct,fl and modulus of elasticity E 0 of the SFRC at 28 days are given in Table 2. The modulus of elasticity of the SFRC was determined in accordance with AS1012.17 [47]. The modulus of rupture for the SFRC was determined from four-point bending tests on prisms in accordance with ASTM C1609/C1609M [45]. The prism testing arrangement is shown in Fig. 2c. The average load versus mid-span deflection obtained from the prism tests for the SFRC with 0.25% and 0.5% fibre dosages and the average compressive strengths of 60 MPa and 70 MPa are shown in Figs. 2d and 2e respectively. The failure of the SFRC prisms was associated with the formation and development of one major crack at the middle 7

ACCEPTED MANUSCRIPT shear span. The model developed by Amin et al. [16] was employed to determine the tensile stress versus crack opening displacement (COD) or (   w ) characteristics of the SFRC with

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respect to the load versus mid-span deflection of the prisms. The   w for the SFRC and the

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linearised form of the   w relationship obtained from the model of Amin et al. [16] are

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shown in Figs. 2f and 2g. 2.3. Instrumentation

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The load applied at mid-span was measured by a 500 kN flat load cell mounted on the loading ram and the mid-span deflection was measured using a 100 mm stroke LVDT.

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Moreover, the horizontal displacement and rotation at each end of the slab were measured using two LVDTs and inclinometers respectively (Fig. 3a). The strains in the concrete slabs

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and reinforcing steel bars were measured at their mid- and end-spans (adjacent to the haunch,

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Fig. 3b). In total, two 6 mm long steel strain gauges and two 60 mm long concrete strain

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gauges were mounted on each precast slab (Fig. 3b). In addition, four strain gauges (i.e. St-BSG1 to 4) were attached to the cross-bracing and two strain gauges (i.e. St-S-SG1 and 2) were

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attached to the ties/straps. The locations of the strain gauges are outlined in Fig. 3b.

3. Test Results and Discussion 3.1. Modes of failure The extent of damage and cracking in each slab at the ultimate stages of loading is shown in Fig. 4 and short descriptions of the failure modes are given in Table 3. With the exception of specimen SF50, cracks were observed at the sections adjacent to the supported edge of the slabs, with these cracks being indicative of bending moment and plastic hinge development in the hogging zone of the transversely-restrained slabs.

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ACCEPTED MANUSCRIPT With regard to Fig. 4 and Table 3, three distinctive failure modes can be identified. The first mode of failure was associated with the development of large cracks in the soffit of the slab

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and yielding of the reinforcing bars at mid-span, followed by partial crushing of the concrete

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on the top surface of the slabs at mid-span. This mode of failure was ductile and it was

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observed in the precast slabs with conventional reinforcing steel bars (Specimen nos. 5-8, 13 and 14).

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The second mode of failure was associated with the development of cracks in the soffit of the slab at mid-span, followed by cracking at sections adjacent to the supported edge of the slabs

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(between the bolted connectors). The second mode of failure was observed in the transversely-restrained precast slabs without any conventional reinforcing steel bars

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(Specimen nos. 1, 2, 4 and 9-12) and was less ductile than that of the first mode. The third mode of failure was only observed in specimen no. 3 (SF50 with no conventional

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reinforcing steel bars and no transverse restraining system). The third failure mode was brittle and it was triggered by the development of cracks in the slab soffit at mid-span. Accordingly,

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it was concluded that the application of external transverse restraint can alter the mode of failure and the ductility of precast slabs. At the conclusion of the tests, the bolted shear connectors were easily untightened, removed and visually inspected. In spite of extensive cracking and severe damage in the SFRC/RC slabs, no evidence of damage or excessive deformation was observed in the bolted shear connectors, and this was conducive to dismantling of the composite decks with precast slabs. One of the failure modes in the transversely-restrained deck slabs is associated with the development of horizontal cracks along the haunches and on the faces of slabs [9, 48]. In this failure mode, the development of longitudinal horizontal cracks in the haunches leads to a loss of transverse confinement and a sudden drop in the load carrying capacity of the slab [2]. 9

ACCEPTED MANUSCRIPT In the proposed deconstructable bridge deck tested in this study, no evidence of damage or cracking was observed even at the ultimate stages of the loading when slabs had undergone

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deflections as large as span/40.

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3.2. Global response

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The loads versus mid-span deflections of the SFRC/RC slabs are shown in Fig. 5; the small dip following the peak load in the load-deflection diagrams (Fig. 5a) is caused by the

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development of cracks at the supported edge of the slabs and between the bolted shear connectors (Fig. 4). The peak load capacities and the mid-span deflections corresponding to

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the peak load capacity of the slabs are given in Table 3. It is seen that the external restraint (i.e. ties/straps and bracings) has increased the peak load capacity of the precast slabs with

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conventional reinforcement significantly, as well as those with steel fibres. Furthermore, it is

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observed that the mid-span deflection corresponding to the peak load capacity for the

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transversely-confined SFRC slabs is 12 to 16 mm (Fig. 5), just slightly smaller than that of the transversely-restrained RC slabs.

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The cracking load Pcr and the mid-span deflection  cr corresponding to the cracking load of the specimens are given in Table 3. In regard to the Pcr values reported in Table 3, it is concluded that the cracking load of the precast slabs with conventional steel bars and no steel fibres (i.e. specimen nos. 6, 7 and 8) is around 20-30% less than the cracking load of the slabs with steel fibres. This can be attributed partly to shrinkage induced cracks in the nonsymmetrically reinforced sections; however, the uniform distribution of steel fibres in the SFRC section can alleviate the shrinkage induced curvature. The initiation and development of first cracking at mid-span took place at a mid-span deflection  cr of 1.6 to 2.6 mm respectively (Table 3). The development of cracks at mid-

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ACCEPTED MANUSCRIPT span is associated with a small reduction in the load (the small dip in Fig. 5). This load drop following the onset of first cracking is a characteristic of reinforced concrete members tested

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under displacement control. In the transversely-restrained SFRC slabs tested in this study, the

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load at ultimate Pu is at least 39% greater than the cracking load Pcr (Table 3). Accordingly,

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under force (load) control the cracking load would be a limit point in which a snap through occurs (a small jump in displacement at a constant load).

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The load versus average end support rotation of the slabs is shown in Fig. 6. With the exception of specimen SF50 (without reinforcing bars and without transverse restraint), a

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non-linear relationship between load and average rotation at the supporting points was observed. It is therefore concluded that the external restraining system in the transverse

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direction (i.e. cross-bracings and ties/straps) can provide some level of rotational fixity for

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single-span precast slabs that, in turn, leads to the development of a hogging bending moment

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and cracks in the sections parallel to the supporting girders, as can be seen in Fig. 4. The load versus total elongation of the slabs is shown in Fig. 7. It can be seen that the

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maximum elongation of the slabs is inversely proportional to the stiffness of the restraining system. The total elongation of the slabs in the transverse direction was obtained from the algebraic sum of the horizontal movements measured by LVDT-1 and LVDT-2 mounted on the edges of the slabs. The locations of LVDT-1 and LVDT-2 are shown in Fig. 3a. 3.3. Local response The load versus the maximum tensile strain in the reinforcing steel bars (the results from strain gauge St-SG(1) at mid-span) are shown in Fig. 8; it is seen that yielding of reinforcing steel bars has taken place well before the peak load of the slabs is reached. Accordingly, it is concluded that the failure mode of transversely-restrained precast RC slabs in the proposed

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ACCEPTED MANUSCRIPT demountable composite system is not brittle and some level of ductility is available in the transversely-restrained RC slabs.

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The load versus maximum concrete compressive strain (the results from strain gauge C-

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SG(1) mounted on top of the slab at mid-span) are shown in Fig. 9. It is observed that the

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maximum strain in the extreme compressive fibre of the RC slab section at mid-span has reached values greater than the ultimate strain of concrete adopted in design codes (i.e.

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 cu  0.003 ).

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The load versus average strain εbu in the cross-bracings and ties/straps (the average results from strain gauges St-B-SG 1 to 4) and St-S-SG1 and 2) are shown in Fig. 10. It can be seen

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that at all stages of loading, the tensile strain in the cross-bracing and straps remains well

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below the yield strain of the 300PLUS grade steel (i.e. ε y  0.0016 ). Furthermore, it is seen that strain in the ties/straps and cross-bracing continuously increases/decreases as the applied

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load increases/decreases and, as a result, it is concluded that the friction grip bolts (including the bolted shear connectors) effectively prevent the relative slip between the different

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structural components (i.e. the precast slab, straps, cross-bracing and steel girders). 3.4. Ductility of specimens Over the past two decades, different indices have been introduced by researchers to evaluate the structural ductility of concrete beams and slabs reinforced with steel and polymeric reinforcing bars and/or fibres [49]. In this study, an energy-based ductility index is used to assess and compare the ductility of different SFRC/RC slabs. The energy-based ductility index  E is defined as,

E 

W 0.75 u Wy

,

(1)

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ACCEPTED MANUSCRIPT where W y is area under the load-deflection response from the first loading to the deflection corresponding to the onset of yielding in steel bars and W 0.75 u is the area under the load-

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deflection curve from first loading to the deflection at which the load has reduced to 75% of

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the peak load. Similar energy-based measures have been used by other researchers to evaluate

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the structural ductility of concrete members strengthened with FRP sheets [50]. For the SFRC slabs without conventional reinforcing bar, W y is the area under the load-deflection response

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from first loading to the deflection corresponding to the cracking load. Using Eq. (1), the  E index for the tested precast slabs was calculated and the results are given in Table 3. It is seen

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that providing transverse confinement for the deck slabs (by using external ties/straps or bracing) can increase the energy-based ductility index of SFRC slabs with no conventional

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reinforcing bars; whereas transverse confinement reduces the ductility index  E of deck slabs with conventional reinforcing bars.

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The ductility index  E of the SFRC slabs with respect to the stiffness of the restraining system relative to the axial stiffness of slab (K Restraining system / KSlab) is shown in Fig. 11a. It is

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seen that for the SF50 series of tests (containing a 0.5% volume of fibre), the ductility index  E increases as the stiffness of the restraining system increases. This increase in the energy-

based ductility of transversely-restrained SFRC slabs with 0.5% fibre dosage is in marked contrast to the reduction of ductility in externally restrained slabs with FRP or conventional steel bars [51]. It is observed that the ductility indices  E of the transversely-restrained SFRC slabs with 0.25% and 0.50% 5D fibres were within the same range ( 20   E ) indicating that a 0.25% fibre dosage can provide sufficient ductility under static loads. The energy-based ductility index  E given in Table 3 and Fig. 11a exhibit a large scatter that is attributed to the significant contribution of several factors such as the reinforcing ratio, the 13

ACCEPTED MANUSCRIPT transverse confining system stiffness and the steel fibre dosage in the ductility of the SFRC/RC slabs.

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3.5. Peak load capacity and strength enhancement provided by arching action The peak load capacities of the RC and SFRC slabs obtained from the experiments are given

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in Table 3 and the experimental peak load capacity of the slabs with respect to the fibre dosage and the stiffness of restraining system (in the transverse direction) to the axial

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stiffness of slab (K Restraining system / KSlab) are shown in Fig. 11b. It is seen that the pattern of strength enhancement provided by the development of arching action in the transversely-

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restrained precast slabs is similar for the SF25, SF50 and SF25+M2 series of tests. Furthermore, it is observed that the peak load capacities of the restrained SFRC slabs with

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0.25% and 0.50% 5D fibres are nearly identical.

The peak load capacities of the transversely-restrained slabs normalised with respect to the

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ultimate capacity of the SF50 slab (with no restraint) are shown in Fig. 12. The figure shows the significant enhancement in the peak load capacity due to development of arching action.

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The total volumetric ratios of reinforcement ( Total) including the conventional steel bars and 

5D steel fibres were calculated and are given in Table 1. The ductility index  E and the peak load capacity of the precast slabs with only conventional reinforcing bars and with a combination of conventional reinforcement and steel fibres are shown in Fig. 13. It is seen that replacing part of conventional reinforcing steel bars with 5D steel fibres (i.e. using 0.25% fibres+M2 instead of an M3 steel bar configuration that lead to a similar  Total  0.5% for the precast slabs with the same transverse restraining system has a negligible influence on the peak load carrying capacity. In addition, it is observed that replacing part of the steel bars with steel fibres (depending on the proportion of the steel bars replaced with fibres) does not

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ACCEPTED MANUSCRIPT significantly affect the ductility index  E of the transversely restrained precast slab decks. In fact, replacing conventional reinforcing bars with 5D fibres led to a small increase in the

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ductility index  E of the specimens tested in this study (see Fig. 13a). This is demonstrative

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of the potential application of 5D structural steel fibres as a replacement for conventional

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steel bars.

4. Summary and Conclusions

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A set of fourteen one-half scale transversely-restrained precast RC/SFRC deck slabs were

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tested under a monotonically increasing point load applied at the mid-span. The precast slabs were connected compositely to steel girders using post-installed friction grip bolts for shear

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connection (PFBSC). The application of three types of transverse restraining systems (i.e.

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ties/straps under the slab strip, cross-bracing and combination of ties and cross-bracing away from the slab strip), in conjunction with high strength friction grip bolted connections for the

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mobilising of arching action, were studied experimentally. Also studied was the use of SFRC and the influence of the steel fibre dosage (0.25% and 0.50%) on the strength and ductility.

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The results of this experimental study have provided benchmark data for evaluating the structural performance, mode of failure, load-deflection response and ductility of transversely-restrained SFRC slabs with and without conventional reinforcing bars. Moreover, the following conclusions can be drawn from experimental data:  PFBSCs are effective in preventing relative slip between the precast slab and steel girders in the transverse direction. This full composite action is essential for mobilising the arching action in the proposed deconstructable composite deck slabs with transverse restraining systems.

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ACCEPTED MANUSCRIPT  The slabs underwent extensive damage and large deflections following each test; however, no sign of damage or excessive deformation was observed in the bolted shear

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connectors and the severely damaged slabs were easily dismantled after testing. This can

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facilitate repairing and dismantling of the proposed composite deck system.

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 During the tests, no horizontal cracks were sighted on the faces of the slabs along the haunches. Accordingly, it is hypothesised that the clamping force provided by PFBSCs

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and steel fibres can hinder development of longitudinal cracks in the haunched edge and improve load capacity of transversely confined concrete slabs.

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 Comparing the cracking load of the transversely-restrained precast slabs with and without steel fibres showed that replacing conventional reinforcing bars (an unsymmetric

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configuration in the section) with steel fibres can increase the cracking load of the precast slabs (a 20-30% increase was observed in this study). The shrinkage-induced curvature in

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unsymmetrically reinforced slabs can lower the cracking load. However, the more uniformly distributed nature of fibres compared to unsymmetric reinforcing bars can

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alleviate shrinkage induced warping in the concrete sections.  The failure of transversely-restrained SFRC slabs was associated with development of cracks in the soffit at mid-span and the onset of cracks at top of the slab at end span (adjacent to the haunches and between PFBSCs). This failure mode is consistent with development of plastic hinges at the mid-span and at the clamped ends.  The energy-based ductility of SFRC slabs with 0.5% 5D steel fibres increased with increasing stiffness of the restraining system. This observation is in marked contrast to that of transversely restrained RC slabs in which the ductility decreases as the stiffness of the transverse restraining system increases.

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ACCEPTED MANUSCRIPT  Assuming that the cracking load in SFRC slabs is equivalent to the yield load in RC slabs, the energy-based ductility of SFRC slabs tested was greater than the energy-based

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ductility of RC slabs with conventional steel bars. In addition, comparing the SF25-M2

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and SF00-M3 series (with bracing or bracing and straps) shows that the partial

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replacement of conventional steel bars with steel fibres can slightly increase the energybased ductility but the ultimate strength of the slabs remains unchanged.

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 The development of arching action in the transversely-restrained SFRC slabs significantly enhances the peak load capacity. For example, in the SF50 series (0.50% 5D fibres) with

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straps, the development of arching action has led to 105% enhancement in the capacity.  The capacities of the restrained SFRC slabs with 0.25% and 0.50% 5D fibres were

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identical and increasing fibre dosage from 0.25% to 0.50% did not improved the ductility

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of the SFRC slabs or enhanced their capacity under static loading condition. Finally, this study has investigated the strength and ductility of transversely-restrained precast steel-fibre reinforced concrete slabs; while SFRC has been shown to perform well under

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cyclic loading (fatigue), further research for the proposed system under cyclic-loading is needed for adoption.

5. Acknowledgements This project was funded by ARC Discovery Grant DP150104107 and the steel fibres were provided by BOSFA Australia. Both sources are acknowledged with thanks.

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Farhangvesali, N., Valipour, H., Samali, B. & Foster, S., Development of arching action in longitudinally-restrained reinforced concrete beams. Construction and Building Materials 2013; 47 (October): 7-19. Bakht, B. & Lam, C., Behavior of transverse confining systems for steel-free deck slabs. ASCE, Journal of Bridge Engineering 2000; 139-147. Hon, A., Taplin, G. & Al-Mahaidi, R. S., Strength of reinforced concrete bridge decks under compressive membrane action. ACI, Structural Journal 2005; 102 (3): 393-403. Klowak, C. S. & Mufti, A. A., Behaviour of bridge deck cantilever overhangs subjected to a static and fatigue concentrated load. Construction and Building Materials 2009; 23 (4): 1653-1664. Rankin, G. I. B. & Long, A. E., Arching action strength enhancement in laterallyrestrained slab strips. Proceedings of the Institution of Civil Engineers, Structs & Bldgs 1997; 122 (4): 461-467. Taylor, S. E., Rankin, B., Cleland, D. J. & Kirkpatrick, J., Serviceability of Bridge Deck Slabs with Arching Action. ACI Structural Journal 2007; 104 (1): 39-48. ACI Innovation Task Group 3, "Report on Bridge Decks Free of Steel Reinforcement". Report No. ACI ITG-3-04, American Concrete Institute, Farmington Hills, Mich., 2004. CAN/CSA-S6-06, Canadian Highway Bridge Design Code (CHBDC). Ontario, Canada, Canadian Standard Association. Klowak, C., Memon, A. & Mufti, A., Static and fatigue investigation of second generation steel-free bridge decks. Cement and Concrete Composites 2006; 28 (10): 890-897. Mufti, A. A., Bakht, B. & Newhook, J. P., Precast concrete decks for slab-on-girder systems: A new approach. ACI Structural Journal 2004; 101 (3): 395-402. Bednář, J., Wald, F., Vodička, J. & Kohoutková, A., Experiments on membrane action of composite floors with steel fibre reinforced concrete slab exposed to fire. Fire Safety Journal 2013; 59 111-121. Belletti, B., Vitulli, F. & Walraven, J. C., Compressive membrane action in confined RC and SFRC circular slabs, Computational Modelling of Concrete Structures Proceedings of EURO-C 2014, 2014, 807-818. Foster, S. J., The application of steel-fibres as concrete reinforcement in Australia: From material to structure. Materials and Structures/Materiaux et Constructions 2009; 42 (9): 1209-1220. Alberti, M. G., Enfedaque, A., Gálvez, J. C., Cánovas, M. F. & Osorio, I. R., Polyolefin fiber-reinforced concrete enhanced with steel-hooked fibers in low proportions. Materials & Design 2014; 60 57-65. Amin, A., Foster, S. J. & Watts, M., Modelling the tension stiffening effect in SFRRC. Magazine of Concrete Research 2015. Amin, A., Foster, S. J. & Muttoni, A., Derivation of the σ-w relationship for SFRC from prism bending tests. Structural Concrete 2014. Trapko, T., Behaviour of fibre reinforced cementitious matrix strengthened concrete columns under eccentric compression loading. Materials & Design 2014; 54 947-954. Yap, S. P., Bu, C. H., Alengaram, U. J., Mo, K. H. & Jumaat, M. Z., Flexural toughness characteristics of steel–polypropylene hybrid fibre-reinforced oil palm shell concrete. Materials & Design 2014; 57 652-659. Maya, L. F., Fernández Ruiz, M., Muttoni, A. & Foster, S. J., Punching shear strength of steel fibre reinforced concrete slabs. Engineering Structures 2012; 40 (0): 83-94.

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Kaïkea, A., Achoura, D., Duplan, F. & Rizzuti, L., Effect of mineral admixtures and steel fiber volume contents on the behavior of high performance fiber reinforced concrete. Materials & Design 2014; 63 493-499. Mohammadi, Y., Carkon-Azad, R., Singh, S. P. & Kaushik, S. K., Impact resistance of steel fibrous concrete containing fibres of mixed aspect ratio. Construction and Building Materials 2009; 23 (1): 183-189. Hao, Y. & Hao, H., Dynamic compressive behaviour of spiral steel fibre reinforced concrete in split Hopkinson pressure bar tests. Construction and Building Materials 2013; 48 (0): 521-532. Haido, J. H., Bakar, B. H. A., Abdul-Razzak, A. A., Jayaprakash, J. & Choong, K. K., Simulation of dynamic response for steel fibrous concrete members using new material modeling. Construction and Building Materials 2011; 25 (3): 1407-1418. Pantelides, C. P., Garfield, T. T., Richins, W. D., Larson, T. K. & Blakeley, J. E., Reinforced concrete and fiber reinforced concrete panels subjected to blast detonations and post-blast static tests. Engineering Structures 2014; 76 24-33. Su, H., Xu, J. & Ren, W., Mechanical properties of ceramic fiber-reinforced concrete under quasi-static and dynamic compression. Materials & Design 2014; 57 426-434. Moraes Neto, B. N., Barros, J. a. O. & Melo, G. S. S. A., A model for the prediction of the punching resistance of steel fibre reinforced concrete slabs centrically loaded. Construction and Building Materials 2013; 46 211-223. Moraes Neto, B. N., Barros, J. a. O. & Melo, G. S. S. A., Model to simulate the contribution of fiber reinforcement for the punching resistance of RC slabs. Journal of Materials in Civil Engineering 2014; 26 (7). Schumacher, P., Den Uijl, J., Walraven, J. & Bigaj-Van Vliet, A., Bond of reinforcing bars in steel fiber reinforced concrete, 5th International PhD Symposium in Civil Engineering - Proceedings of the 5th International PhD Symposium in Civil Engineering, 2004, 1205-1212. García-Taengua, E., Martí-Vargas, J. R. & Serna, P., Splitting of concrete cover in steel fiber reinforced concrete: Semi-empirical modeling and minimum confinement requirements. Construction and Building Materials 2014; 66 743-751. Blanco, A., Cavalaro, S., De La Fuente, A., Grünewald, S., Blom, C. B. M. & Walraven, J. C., Application of FRC constitutive models to modelling of slabs. Materials and Structures 2014. Luccioni, B., Ruano, G., Isla, F., Zerbino, R. & Giaccio, G., A simple approach to model SFRC. Construction and Building Materials 2012; 37 111-124. Xu, Z., Hao, H. & Li, H. N., Dynamic tensile behaviour of fibre reinforced concrete with spiral fibres. Materials & Design 2012; 42 72-88. Sanjayan, J. G., Nazari, A. & Pouraliakbar, H., FEA modelling of fracture toughness of steel fibre-reinforced geopolymer composites. Materials & Design 2015; 76 215222. Abas, F. M., Gilbert, R. I., Foster, S. J. & Bradford, M. A., Strength and serviceability of continuous composite slabs with deep trapezoidal steel decking and steel fibre reinforced concrete. Engineering Structures 2013; 49 (0): 866-875. Meda, A., Minelli, F., Plizzari, G. A. & Riva, P., Shear behaviour of steel fibre reinforced concrete beams. Materials and Structures/Materiaux et Constructions 2005; 38 (277): 343-351. Kwak, Y. K., Eberhard, M. O., Kim, W. S. & Kim, J., Shear strength of steel fiberreinforced concrete beams without stirrups. ACI Structural Journal 2002; 99 (4): 530538.

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Michels, J., Waldmann, D., Maas, S. & Zürbes, A., Steel fibers as only reinforcement for flat slab construction - Experimental investigation and design. Construction and Building Materials 2012; 26 (1): 145-155. Parvez, A. & Foster, S. J., Fatigue behavior of steel fiber reinforced concrete beams. ASCE, Journal of Structural Engineering 2015; 141 (4): 04014117. AS5100.2 (2004) Bridge design - Part2: Design load. Standards Australia, Sydney, Australia. AS5100.5 (2004) Bridge design, Part 5: Concrete. Standards Australia, Sydney, Australia. Bradford, M. A. & Pi, Y. L. (2012) Numerical modelling of composite steel-concrete beams for life-cycle deconstructability. 1st International Conference on PerformanceBased and Life-Cycle Structural Engineering. Hong Kong. Liu, X., Bradford M. A. & Lee, S. S. M. (2014) Behavior of high-strength friction-grip bolted shear connectors in sustainable composite beams. Journal of Structural Engineering, ASCE 10.1061 /(ASCE)ST.1943-541X.0001090. Kwon, G., Engelhardt, M. D. & Klinger, R. E., Experimental behavior of bridge beams retrofitted with post-installed shear connectors. ASCE, Journal of Bridge Engineering 2011; 16 (4): 536-545. Lee, S. S. M. & Bradford, M. A. (2013) Sustainable composite beams with deconstructable shear connectors. 5th International Conference on Structural Engineering, Mechanics and Computation, Cape Town, South Africa. 5th International Conference on Structural Engineering, Mechanics and Computation. Cape Town, South Africa. ASTM C1609/C1609M, Standard test method for flexural performance of fiberreinforced concrete (using beam with third-point loading). ASTM International, West Conshohocken, PA, US. AS1012.9 (1999) Methods of testing concrete - Determination of the compressive strength of concrete specimens. Standards Australia, Sydney, Australia. AS1012.17 (1997) Methods of testing concrete: Determination of the static chord modulus of elasticity and Poisson’s ratio. Standards Australia, Sydney, Australia. Edalatmanesh, R. & Newhook, J. P., Behavior of externally restrained noncomposite concrete bridge deck panels. ACI Structural Journal 2012; 109 (2): 161-170. Wang, H. & Belarbi, A., Ductility characteristics of fiber-reinforced-concrete beams reinforced with FRP rebars. Construction and Building Materials 2011; 25 (5): 23912401. Spadea, G., Swamy, R. N. & Bencardino, F., Strength and ductility of RC beams repaired with bonded CFRP laminates. Journal of Bridge Engineering 2001; 6 (5): 349-355. Taylor, S. E. & Mullin, B., Arching action in FRP reinforced concrete slabs. Construction and Building Materials 2006; 20 (1-2): 71-80.

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7. List of Figures

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(a)

(b) Fig. 1 Outline of the geometry, cross-section and configuration of the (a) real composite bridge deck (b) restraining system in the transverse direction and test set up for the one-half scale precast RC slabs compositely connected to 310UB32 steel girders using PFBSCs.

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ACCEPTED MANUSCRIPT Plain concrete (SF00) SFRC (0.25%) SFRC (0.50%)

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Compressive stress (MPa)

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0 0

4000

8000

12000

16000

Compressive Micro-Strain (10-6)

(c)

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(f)

(g)

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Fig. 2 (a) Geometry of the Dramix 5D-65/60-BG steel fibre (b) uniaxial stress-strain diagram of plain and SFRC with 0.25% & 0.5% fibres (c) dimensions and set up of the prism test and average load versus mid-span deflection obtained from prism tests on SFRC with average compressive strength of (d) 60 MPa and (e) 70 MPa and tensile stress versus crack opening displacement for (f) 60 MPa and (g) 70 MPa concrete, derived from the prism test results using Amin et al. model . 22

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(a)

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Fig. 3 Locations of (a) LVDTs and inclinometers and (b) steel and concrete strain gauges on the precast slab.

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SF25-B

SF00- S Major cracks

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Major cracks

SF25-BS

SF50- S

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Major cracks

Major cracks SF50

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Major cracks

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SF25- S Major cracks

SF50-B

Major cracks SF50-BS Major cracks

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Minor cracks

SF25-B -M2 Concrete crushing

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SF25- S-M2

Partial concrete crushing

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Major cracks

Minor cracks

SF25-BS-M2 Concrete crushing

SF00-B -M3

Major cracks

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Major cracks

Minor cracks

Major cracks

Fig. 4 The pattern and extend of cracking/damage and modes of failure in different specimens.

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Fig. 5 Load versus vertical displacement at mid-span of the slabs no. (a) 1-5, (b) 6 -10 and (c) 6 and 11-14.

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Fig. 6 Load versus average rotation at the end of precast slabs no. (a) 1-5, (b) 6 -10 and (c) 11-14.

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Fig. 7 Load versus total elongation of the precast slab measured by horizontal LVDTs at the end of precast slabs no. (a) 1-5, (b) 6 -10 and (c) 11-14.

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Fig. 8 Load versus tensile strain at mid-span in reinforcing steel bars (St-SG1) for

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precast slabs no. 5-8 and 13 and 14.

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Fig. 9 Load versus concrete compressive strain at mid-span on the top surface of the precast slabs no. (a) 1-5, (b) 6 -10 and (c) 11-14.

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(b)with only bracings

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(a) with only straps

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(c) with straps + bracings

(d) with straps +bracings

Fig. 10 Load versus tensile strain in the cross bracings/straps for the slabs transverselyrestrained with (a) only straps, (b) only cross bracings and load versus tensile strain in the (c) straps and (d) cross bracings of the slabs with straps + cross bracings.

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(a)

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Fig. 11 Variation of (a) energy-based ductility index  E and (b) peak load capacity of the 

precast steel fibre reinforced concrete slabs, with respect to fibre dosage/reinforcing proportion and relative stiffness of transverse confining system.

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Fig. 12 Normalised experimental peak load capacity of the transversely-restrained

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SFRC slabs with respect SF50 slabs (with no transverse restraint).

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Fig. 13 Comparison between the (a) energy-based ductility index  E and (b) peak load 

capacity of precast SFRC/RC slabs with the same volumetric reinforcing steel bar/fibre proportion.

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8. List of Tables

----

3 SF50

----

4 SF25- S

----

 

Vol.=Ast /bh (%)

=Ast /bd (%)

 Total =  F + Vol.



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 F Fibre dosage (%)

---- 0.50 ---- ---- 0.50

Strap

---- 0.50 ---- ---- 0.50

--------------

---- 0.25 ---- ---- 0.25

Strap

5 SF25- S-M2 2N10 (middle)

56 0.25 0.48 0.26 0.51

Strap

6 SF00

56 0.00 0.72 0.40 0.40

--------------

7 SF00-B -M3 3N10 (middle)

56 0.00 0.72 0.40 0.40

Bracing

8 SF00-BS-M3 3N10 (middle)

56 0.00 0.72 0.40 0.40 Bracing + strap

9 SF25-B

----

---- 0.25 ---- ---- 0.25

10 SF25-BS

----

11 SF50-B

----

12 SF50-BS

----

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Strap

60

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-M3 3N10 (middle)

70

Bracing

---- 0.25 ---- ---- 0.25 Bracing + strap ---- 0.50 ---- ---- 0.50

Bracing

---- 0.50 ---- ---- 0.50 Bracing + strap

13 SF25-B -M2 2N10 (middle)

56 0.25 0.48 0.26 0.51

14 SF25-BS-M2 2N10 (middle)

56 0.25 0.48 0.26 0.51 Bracing + strap

Bracing

under the slab

2 SF50- S

---- 0.00 ---- ---- 0.00

Away from the slab (Fig. 1)

----

Restraining system in the transverse direction ## (see Fig. 1)

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1 SF00- S

Effective depth d (mm)

Numbers & f cm Location of (MPa) reinforcing bars

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Designation of # specimens

Specimen No.

Table 1 Designation of specimens.

# SFxx: 0.xx% steel fibre dosage, -B: bracing, -S: straps and -BS: bracing + strap. ## The cross-bracings and straps were made of Equal Leg Angle, L45X45X5EA and L45X45X3EAGrade 300PLUS, respectively. ### The total volumetric ratio of reinforcement including steel bars and fibres.

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Table 2 Mechanical properties of SFRC (average of three specimens).

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Compressive Fibre splitting tensile Modulus of Modulus of Tensile strength rupture elasticity E0 strength strength dosage (%) f ct,fl (MPa) f ct,sp (MPa) f cm (MPa) fct (MPa)# (MPa) 7.2 5.90 32.7 0.25 3.9 60 7.3 6.00 33.1 0.50 7.7 6.20 36.5 0.25 4.2 70 7.9 6.20 35.7 0.50 # The mean tensile strength of concrete is taken as f ct  0.5 f cm [16].

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Experiment Ductility index  E

Designation Ultimate Yield Cracking of specimens Pu u Py  y Pcr  cr 



kN mm kN mm kN mm

Mode of failure

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Specimen No.

Table 3 Test results and observations.

SF00- S

43.71 13.71 ---- ---- 31.5 1.9

2

SF50- S

62.70 12.78 ---- ---- 31.4 2.2

20.1 Development of cracks at mid-span (slab soffit) & 28.2 end span (between the PFBSCs)

3

SF50

30.63 3.17

14.2 Development of cracks only at mid-span

4

SF25- S

65.90 13.43 ---- ---- 33.3 2.0

5

SF25- S-M2 81.63 24.80 63.7 10.1 25.2 2.6

6

SF00

7

SF00-B -M3 73.58 33.24 63.1 19.3 19.4 2.1

8

SF00-BS-M3 81.88 38.84 55.1 14.2 19.0 2.0

Development of cracks at mid-span (lab soffit) & 8.3 end span, yielding of steel bars at mid-span 3.9 followed by partial crushing of concrete at midspan 6.8

9

SF25-B

49.34 14.74 ---- ---- 25.1 2.6

19.7

10 SF25-BS

52.19 13.89 ---- ---- 28.0 1.7

11 SF50-B

54.98 16.11 ---- ---- 25.5 2.7

46.7 Development of cracks at mid-span (slab soffit) 31.9 and end span (between the PFBSCs)

12 SF50-BS

56.92 10.91 ---- ---- 24.8 2.3

51.2

---- ---- 28.0 2.0

29.6 Development of cracks at mid- & end-span 6.5

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-M3 47.0 25.72 34.6 8.9 17.5 1.6

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13 SF25-B -M2 71.16 36.07 63.9 19.1 28.7 3.1

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14 SF25-BS-M2 81.65 37.67 63.3 13.3 22.8 2.3

5.2 Development of cracks at mid- & end-span, yielding of steel bars at mid-span followed by 9.4 partial crushing of concrete at mid-span

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Conventional shear studs

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Reinforcing steel bars

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Steel girder

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Conventional RC deck slabs

High strength bolts

- Reduce labour cost - Improve serviceability - Facilitate future rehabilitation

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- Promote deconstruction/recycling - Facilitate future rehabilitation

Precast SFRC slab

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Transverse ties/straps

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- Provide transverse confinement - Mobilise arching action - Increase loading capacity - Facilitate future rehabilitation

Deconstructable SFRC deck slabs with transverse confinement

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Graphical abstract

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ACCEPTED MANUSCRIPT Highlights A deconstructable composite bridge deck with SFRC slabs is developed



Experimental results for transversely confined RC/SFRC deck slabs are produced



Transverse confinement increases the energy-based ductility index of SFRC slabs



Transverse confinement significantly increases the loading capacity of SFRC slabs



Steel bars in deck slabs with transverse confinement can be replaced by steel fibres

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