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    Engineering Structures 27 (2005) 16131624

    www.elsevier.com/locate/engstruct

    Crack control of a steel and concrete composite plate girder withprefabricated slabs under hogging moments

    Hyung-Keun Ryua,,1, Sung-Pil Changa,2, Young-Jin Kimb, Byung-Suk Kimb

    aSchool of Civil, Urban & Geosystem, Seoul National University, Republic of KoreabStructural System Research Group, Korea Institute of Construction Technology, Republic of Korea

    Received 3 June 2004; received in revised form 25 May 2005; accepted 26 May 2005

    Available online 15 July 2005

    Abstract

    In this research, an experimental test on a full-scale model of a steel and concrete composite plate girder with prefabricated slabs under

    hogging moments was cautiously conducted and observed in order to study crack control. Details of prefabricated slab transverse joints were

    determined from previous research. The test specimen was an overhanging simple support beam, in total 28 m long. Through the four-point

    flexural test, the behaviour of the composite girder under hogging moments was observed. From the test results, crack development, crack

    widths and strain of the composite section before and after cracking were observed. Initial cracking load and crack spacing were viewed

    and the relations between crack spacing and transverse reinforcement spacing were studied. Moreover, the composite section behaviour of

    the precast deck with loop joints was confirmed. Test results were analyzed by design equations in each code for crack control. The flexural

    stiffness of the composite section after cracking is compared with that of the proposals in EUROCODE 4-2 and discussed.

    2005 Elsevier Ltd. All rights reserved.

    Keywords: Steel and concrete composite plate girder; Prefabricated slab; Loop joint; Hogging moment; Crack control; Crack width; Crack spacing; Flexural

    stiffness of composite section; Eurocode 4-2

    1. Introduction

    Steel and concrete composite bridges are very attractive

    solutions for short and medium span bridges. However, for

    steel and concrete composite continuous bridges, when a

    concrete slab is in tension and a lower flange of a steel

    girder is in compression under hogging moments, there are

    shortcomings in view of durability and strength. Especially,

    concrete cracking affects the durability and service life

    Corresponding address: Civil, Urban and Geo-system Engineering,Seoul National University, San 56-1 Shinlim Dong, Kwanak Gu, 71100Seoul, Republic of Korea. Tel.: +82 288 073 55; fax: +82 288 703 49.

    E-mail addresses:[email protected] (H.-K. Ryu),[email protected] (S.-P. Chang), [email protected] (Y.-J. Kim),[email protected] (B.-S. Kim).

    1 Also at: Korean Earthquake Engineering Research Center, SeoulNational University, San 56-1 Shinlim-Dong, Kwanak-Gu, Seoul 151-742,Republic of Korea.

    2 Also at: Department of Civil Engineering, Seoul National University,San 56-1 Shinlim-Dong, Kwanak-Gu, Seoul 151-742, Republic of Korea.

    0141-0296/$ - see front matter 2005 Elsevier Ltd. All rights reserved.

    doi:10.1016/j.engstruct.2005.05.015

    of bridges. Therefore, crack control is an important issue

    in steel and composite continuous bridges. There are two

    approaches for dealing with concrete cracking in composite

    bridges: one is to prevent cracking using prestressing

    methods and the other is to allow the formation of cracks but

    limit their widths to acceptable values. Prestressing methods,

    however, are inconvenient and doubtful due to prestress

    losses by the long-term behaviour of concrete. Therefore,

    it is considered that the control of crack width without

    prestressing is the more economical and interesting solution.Randl and Johnson [1] found that the first transverse

    cracks that occur in lightly reinforced concrete slabs forming

    tension flanges of composite beams were significantly wider

    than is predicted by existing methods. They showed that a

    reinforcement ratio of 0.9% is sufficient to ensure that bars

    do not yield when the first crack forms, and it was suggested

    that 0.9% is sufficient to control initial cracking in composite

    main girders only when small-diameter bars are used. In the

    study of Navarro and Lebet [2], the mechanical behaviour

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    of steelconcrete composite bridges under non-monotonic

    service loading was presented. In their study, it could

    be observed that the reinforcement ratio and longitudinal

    bar diameter do not significantly influence the crack

    widths. Since the crack spacing is equal to the transverse

    reinforcement spacing, crack widths are not influenced by

    a decrease of the transmission length induced by reducingthe longitudinal reinforcement bar diameter. Therefore,

    reducing the longitudinal reinforcement bar diameter is not

    an effective method for diminishing crack widths.

    Ramm and Elz [3] mentioned that local weakening of

    the tensile capacity of a concrete slab can lead to an early

    occurrence of cracks and can cause decreased need of

    minimum reinforcement. In the case of composite beams,

    such local weakening can be caused by shear connectors

    or transverse reinforcement. This can lead not only to an

    earlier development of cracks, but also can influence the

    crack spacing. Thus, the development of cracking in slabs

    as part of composite beams is decisively influenced by the

    transverse reinforcement.

    A precast concrete deck could be very attractive because

    the system can ensure the quality of concrete decks, improve

    working environments for the workers, and reduce man

    hours outdoors and traffic disruption. A shorter construction

    time could be an important factor in choosing precast deck

    bridges. A precast deck bridge has two types of connection:

    shear connection between steel girder and precast deck,

    and transverse joint between precast panels. Shim and

    Chang [4]suggested a design basis for longitudinal prestress

    of continuous composite bridges with full-depth precast

    decks having female-to-female joints through experimental

    and analytical studies.Recently, Ryu et al. [5]carried out experimental works on

    the mechanical behaviour of precast concrete elements with

    loop joints. From the observation of crack distribution, crack

    widths, ductility and ultimate strength considering variable

    diameters of reinforcements and joint widths of cast-in-place

    parts, they suggested details of precast elements with loop

    joints.

    However, in order to apply precast decks to continuous

    composite bridges, the tensile behaviour of precast decks

    or transverse joints between slabs in hogging moment

    regions should be confirmed in view of serviceability and

    durability. Particularly, stiffness of the composite sectionduring cracking should be evaluated precisely, because it is

    very important to estimate crack widths, deflection and stress

    ranges applied to structural members under service loads. In

    this paper, an experimental test on a full-scale model of a

    steel and concrete composite plate girder with prefabricated

    slabs under hogging moments was cautiously conducted

    and observed in order to study crack control. Details of

    prefabricated slab transverse joints were determined from

    previous research [5]. The test specimen was an overhanging

    simple support beam, in total 28 m long. Through the four-

    point flexural test, the behaviour of the composite girder

    under hogging moments was observed. The test results

    showed crack development, crack widths and strain of the

    composite section before and after cracking. Initial cracking

    load and crack spacing were observed and the relations

    between crack spacing and transverse reinforcement spacing

    were studied. Moreover, the composite section behaviour

    of the precast deck with loop joints was confirmed. Test

    results were analyzed by design equations in each code forcrack control. The flexural stiffness of the composite section

    after cracking is compared with that of the proposals in

    EUROCODE 4-2 and discussed.

    2. Static test

    2.1. Test specimen

    The testing was carried out with the four-point flexural

    bending test. The span of the overhanging cantilever part

    is 11 m on either side. The length of mid-span simply

    supported is 6 m.Fig. 1illustrates the composite plate girdersection and elevation. This specimen is an effective one-

    girder full-scale model of a bridge designed by current

    Korean highway standard specifications. The bridge is

    a first rate three span continuous composite plate girder

    and four lane highway bridge (Fig. 2) having a width of

    12.145 m.

    In the test specimen, the precast deck panel was 260 mm

    thick and had three shear pockets for stud shear connectors

    (Fig. 1(b)). Details of transverse loop joints in precast

    decks were determined from previous research [5]. The

    longitudinal reinforcement ratio was 2.0%, which is a

    limitation for bridge slabs under hogging moments in

    Korean Highway Standard Specification [6]. 22 mm studshear connectors were welded at 680 mm spacing for a full

    shear connection.

    Vertical stiffeners were welded in supports, loading

    points and among those to prevent shear buckling failure

    and crippling of the web before flexural failure (Fig. 1(c)).

    Also, to prevent lateral torsional buckling of the overhanging

    beam, lateral bracings were installed at each end of the

    overhanging beam to allow vertical deflection but lateral

    displacement and rotation.

    2.2. Fabrication procedure

    First, the prefabricated slabs were placed on a steel

    plate girder. Then, shear pockets were filled with mortar

    for achieving composite action. Transverse reinforcements

    were arranged in loop joints and then filled with

    expansive concrete to connect precast decks longitudinally.

    A composite plate girder was completed as shown inFig. 3.

    2.3. Loading and measurements

    The test specimen was an overhanging simply supported

    beam using roller supports (Fig. 4). A concentrated load was

    applied at each edge of the beam (Fig. 1(c)). A closed-loop

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    (a) Composite girder section.

    (b) Precast panel.

    (c) Elevation.

    Fig. 1. Test specimen.

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    Fig. 2. Model bridge section.

    Fig. 3. Completed composite plate girder.

    electro-hydraulictesting system was used as shown inFig. 3.

    Static tests to investigate elastic and inelastic behaviour of

    the specimen were carried out.

    Displacements of the composite plate girder were mea-

    sured at both ends and each mid-part of the overhang-

    ing girder with an LVDT (Linear Variable Differential

    Transformer). An LVDT was also installed to measure the

    relative displacements (slips) between the steel girder and

    the concrete slab as presented in (Fig. 5(a)). Several strain

    gauges were installed on the composite sections to observe

    Fig. 4. Support condition.

    composite section behaviour. After cracking, crack widths

    were measured with Omega gauges.

    2.4. Material properties

    The material properties of the steel sections and of

    concrete and mortar are listed in Tables 1 and 2,respectively.

    As mentioned in previous research [4], the compressive

    strength of the filling material should be higher than that

    of the precast concrete to obtain the same elastic modulus

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    (a) Deflection and slip.

    (b) Sectional strain.

    Fig. 5. Instrumentation.

    and to ensure the quality of the mortar in actual construction

    sites. It is very important to control the quality of the fillingmaterial as specified in a design guideline of a precast deck

    bridge. In this experiment, the compressive strength of the

    mortar was higher than the required strength.

    Table 1

    Material properties of steel

    Yield strength Tensile strength (in spec.)

    (MPa) (MPa)

    Flange & web 320 500650

    Stiffeners, diaphragm 240 410520

    Reinforcements 400 520

    Table 2

    Compressive strength of concrete and mortar (MPa)

    Strength (MPa) Note

    Precast concretea 36 28 days

    Transverse jointb 57 Loading time

    Shear connectionb 43 Loading time

    a Average value of all the precast concrete panels.b Average value of material test specimens.

    In the Table 2, the strength of the prefabricated slab

    specimen was 28 days strength. However, the real strength

    of precast elements was expected to be higher than 28 days

    strength, because the loading time was over 28 days.For shear connection, shear pockets were filled with non-

    shrink mortar and transverse slab joints were filled with

    expansive concrete expecting chemical prestressing to be

    locally introduced at joints.

    3. Test results and analysis

    3.1. Elastic behaviour

    In the test specimen, it was intended that shear

    connections were installed to achieve full shear connections.

    The ultimate strength of a stud shear connector was

    determined from Eq.(1)developed by Kim et al. [7].

    Pd= (0.36Ash + 18.71) (1)

    = 1 0.0086(bh 20)

    Pd: ultimate strength of shear connection,

    Ash: stud area of shear connection(mm2),

    bh: thickness of bedding layer.

    To achieve full shear connection, the degree of shear

    connection, , which is defined as the strength of the shear

    connection in a shear span, as a proportion of the strength

    required for full shear connections, should be higher than

    unity.

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    Fig. 6. Loadslip curve.

    Fig. 7. 3-D finite element model.

    =Psh

    Pcp 1. (2)

    Psh can be calculated using Eq. (1) over the shear spans,

    and Pcp is the horizontal force of the concrete slabs or steel

    girders at the full sectional plastic moment.

    In the test specimen, the degree of shear connection wasestimated to be higher than unity according to Eq. (2), and

    then in the test, maximum slips were measured at 0.06 mm

    until 80% of maximum load (Fig. 6). It is considered that the

    experimental slips monitored during the tests were scattered

    due to the very low values measured. From this result, it

    is considered that the shear connection would not reach

    the ultimate load state [7], thus the test specimen could

    be assumed as the full composite section until the ultimate

    state.

    To be compared with the test results, elastic analyses

    were carried out with a 3-D finite element model (Fig. 7)

    by the commercial finite element code, ABAQUS v6.3. Theconcrete slab and the steel girder were modeled with 8-node

    shell elements. The slab and the plate girder were connected

    by beam elements to describe the shear connection. The

    number of finite element in which the test specimen was

    divided was 3024 in total. From the analysis, the flexural

    stiffness of the composite section could be evaluated, and

    variation of the flexural stiffness with increasing load in the

    test could be compared with results of the finite element

    analysis.

    During the static test in the elastic range of loading,

    the flexural stiffness of the composite girder showed linear

    elastic behaviour. Deflection of the end of the girder from

    Fig. 8. Loaddisplacement curve in the elastic range.

    the analysis was compared with the test results (Fig. 8). It is

    worth noting that, in the elastic range, the stiffness of the slab

    in hogging moment regions can be included in the flexural

    stiffness of the composite section. In the serviceability limitstate, an uncracked section could be assumed for the flexural

    stiffness of composite sections.

    3.2. Cracking

    Crack distribution on the deck of the uniform negative

    moment regions was observed as presented inFig. 9. In the

    test specimen, in total 14 precast panels were used; panels

    7 and 8 are prefabricated slabs in a middle position of the

    composite girder under uniform hogging bending as shown

    in Fig. 9. The initial cracks were detected by the naked

    eye at the edge of transverse joints (Fig. 10). It is consid-ered that the cracks occurred because the age of concrete

    material in precast panels and joints of cast-in-place parts

    were different. Due to the different casting ages, construc-

    tion joint surfaces were made and the surfaces have weak

    points of cracking. Thus, before casting in the transverse

    joints, the surfaces should be cleaned, and it is necessary to

    consider effective methods for increasing bonding between

    precast panels and joints; for example, surfaces can be made

    rough using a water jet to increase bonding. The cracking

    load of the test specimen was observed as 340 kN, which is

    lower than the design value of 405 kN. The value was ob-

    tained from the following equation given in EUROCODE4-2 [8].

    Ns = Ns,cr= Act fctm1

    1 + hc2z0

    (1 + s n0) (3)

    wheres = As/ActAct is the area of the tensile zone immediately prior to

    cracking of the cross section (for simplicity the area of the

    concrete section within the effective width should be used),

    As is the area of reinforcement steel within the effective

    width,

    fctmis the mean tensile strength of concrete,

    hc is the depth of the concrete slab,

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    Fig. 9. Crack distribution under uniform hogging moments (units: kN).

    z0 is the vertical distance between the centroids of the

    uncracked unreinforced concrete flange and the uncracked

    unreinforced composite section.

    As in Eq. (3), the shrinkage effect was not considered.

    Therefore, it is considered that the cracking load can be eval-

    uated by reducing the tensile strength of concrete consider-

    ing the shrinkage effects, particularly in cast-in-place (CIP)

    parts (transverse joints). In the case of continuous compositebridges with CIP slabs, it is considered that initial shrinkage

    effects can be more important for estimating the cracking

    load, crack width and flexural stiffness.

    It is noted that the spacing of the initial transverse crack

    was significantly wide because the crack occurred mainly in

    the transverse joints and edges of shear pockets. After the

    initial cracking, cracks developed on deck surfaces which

    are shown inFig. 9.

    As in previous research [2,3], it could be observed

    that the crack spacing was very similar to the transverse

    reinforcement spacing. Local weakening of the tensile

    capacity of the concrete slab which was caused by shear

    connectors or transverse reinforcements can lead to the

    occurrence of cracks and can influence the crack spacing.

    Thus, it can be said that the development of cracking in

    slabs as part of composite girders is decisively influenced

    by transverse reinforcements.

    In the crack development of the slabs, the crack spacing

    was observed, and then minimum, maximum and average

    crack spacings were recorded as shown in Table 3. FromTable 3,it is seen that the average crack spacing was similar

    to the average spacing of the transverse reinforcements.

    3.3. Flexural stiffness during cracking

    Fig. 11shows loaddisplacement curve of each ends of

    the overhanging beam of the present test. Before cracking,

    the stiffness of the composite section was similar to that of

    the uncracked composite section. However, after cracking,

    the cracks were propagated and distributed, and the stiffness

    of the composite section became similar to that of the

    cracked composite section in Fig. 11with increasing load.

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    Table 3

    Cracking load (kN) and crack spacing (mm)

    Cracking load Cracking load Ratio Minimum crack Maximum crack Average crack Average tr-re-bar

    (cal.) (test) (test/cal.) spacing spacing spacing spacinga

    405 340 0.84 77 280 165 173

    a tr-re-bar means transverse reinforcement.

    Fig. 10. Initial cracking at the joints.

    Fig. 11. Loaddisplacement curve.

    The loaddeflection curve named uncracked was evaluated

    from the 3-D elastic finite element analysis (Fig. 7).

    As shown in Fig. 11, the stiffness of the composite section

    after cracking became similar to that of the cracked section

    gradually, but the stiffness did not directly become equal

    to that of the cracked section as soon as a crack occurred.Thus, the tension stiffening effect between cracks should be

    considered to evaluate the more exact flexural stiffness of

    the composite section under hogging moments. At 1200 kN,

    the deflection of the test specimen was larger than the

    calculated deflection of the cracked section. It is considered

    that local buckling or yielding due to residual stress reduces

    the stiffness of the composite section as well as cracking.

    In the crack formation of composite beams, there are

    three stages before yielding of the composite section. First,

    a stage before cracking an uncracked section, second,

    after cracking and development of cracks, and last, a

    crack stabilizing stage which continues before yielding. To

    Fig. 12. The stiffness of a composite plate girder.

    divide the first and second stages, the initial cracking load

    should be considered, which can be evaluated from Eq. (3).

    Also, the moment at the beginning of the stabilized crack

    formation should be evaluated to define the level of crack

    stabilizing. The bending moment, Mcr,ts, at the beginning of

    the stabilized crack formation can be calculated using thefollowing equation,

    Mcr,ts = [Ns,crNs,ts]I2

    Asz2(4)

    where Ns,ts is the additional normal force of the concrete

    section due to tension stiffening. I2 is the second moment

    of area of the composite section neglecting concrete. z2is the distance between the centroidal axis of the cracked

    composite section with the second moment of area I2 and

    the center of area of the reinforcement.

    The normal force of the concrete slab is determined in

    the stages of cracking mentioned above. During cracking

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    and before stabilizing, the axial force is maintained to

    be constant even with increasing external moments. But

    after stabilizing moments, the axial force increased with

    increasing external moments linearly.

    After initial cracking, the internal normal force of the

    concrete section can be defined by the following equation.

    Ns = Ns0 +Ns,ts. (5)

    The additional normal force Ns,ts of the concrete section

    due to tension stiffening for bridges without prestressing by

    tendons is given by

    Ns,ts = 0.4fctmAs

    sst(6)

    st = A I2/AaIa , where A is the area of the composite

    section neglecting concrete in tension, and Aa and Ia are

    the corresponding properties of the structural steel section.

    Therefore, the effective stiffness of the composite section

    after cracking can be defined in all load levels, continuously.

    The effective stiffness EaI2,ts depends on the bending

    moment M acting on the composite section. The bending

    moment M, calculated with the uncracked stiffness, may be

    used. The stiffness EaI2,tsmay be calculated from

    EaI2,ts =EaIa

    1 Ns aM

    (7)

    where EaIa is the stiffness of the structural steel section,

    Mis the bending moment for the relevant load combination

    and Ns is the tension force in the slab. a is the distance

    between the neutral axes of the structural steel section and

    the uncracked concrete section.

    From the above equations, the flexural stiffness of thecomposite section for the test specimen could be estimated

    as shown in Fig. 12. Initial cracking and stabilizing moments

    were evaluated and the effective stiffness was calculated

    with external moments. After the initial cracking moment,

    the stiffness which gradually decreased due to cracking can

    be observed as in this figure.

    From the curve in Fig. 12, the momentcurvature

    relationship of the composite plate girder can be calculated.

    Then this result could be compared with the test results

    for the momentcurvature of the test specimen. From the

    experimental results, momentcurvature relationships of the

    composite sections were evaluated as shown inFig. 13.In the figures, sections AE refer to those shown in

    Fig. 5(b). Among the curves, the curve for section A

    in Fig. 13(a) is overestimated by the EC4-2 curve at a

    high moment level compared with the other curves. It is

    considered that because the section A is the nearest to

    the supports, the stiffness was reduced by yielding and

    local buckling as well as cracking with increasing external

    moments. Except for section A, the curves of the composite

    sections in the test specimen were very consistent with the

    EC4-2 curve. It is also confirmed that the precast decks with

    loop joints are continuous because the curve for section E

    inFig. 13(e) also showed good consistency of the effective

    stiffness in the EC4-2. In section E, there are transverse

    joints of the slabs.

    Under uniform hogging moments, the momentcurvature

    curve of all composite sections was very consistent with

    the moment curvature curve defined in Eurocode 4-2. From

    these results, it is concluded that the momentcurvature

    curve relation or effective flexural stiffness of the compositegirder section considering tension stiffening effects in

    Eurocode 4-2 can be also applied to composite plate girders

    with loop joint prefabricated slabs.

    3.4. Crack widths

    Fig. 15shows the relation between external moments and

    reinforcement strain. LP1 and LP2 were attached in lon-

    gitudinal top reinforcement in joint parts (Fig. 14). Also,

    RE1RE3 were installed in top reinforcement as shown in

    Fig. 14. InFig. 15,it can be seen that strain of the reinforce-

    ment in loop joints measured by LP1 and LP2 is less than

    that of the reinforcement in decks (RE1RE3) because, in

    the joints, reinforcements are overlapped to connect longitu-

    dinally. In all reinforcements, the strain did not yield.

    Momentcrack width curves are presented inFig. 16. It

    is considered that the curve could show the limitation of

    service load for crack control in composite girders with loop

    joint prefabricated slabs.

    According to the Korean Highway Standard Specifica-

    tion [6]for the design of plate girder bridges such as Fig. 2,

    the design moment for the test specimen is 6050 kN m,

    which includes dynamic effects by truck loads. In this mo-

    ment, the measured maximum crack width was shown as

    0.14 mm in CR3 (Fig. 16). This value does not violate thelimitation of crack width for serviceability of the general

    condition.

    Also, to estimate the maximum crack width of the slab,

    test results were compared with values of design equations

    for crack control in each code.

    Steel strain and crack width curves could be obtained

    from the measurements as in Fig. 14. There are variable

    design equations for crack width in each code. In this

    research, experimental results were compared with design

    values in equations such as the GergelyLutz equation, the

    equation in CEB-FIP 78 [9]and in Eurocode 2(90) [10]. The

    GergelyLutz equation is recommended in ACI-318-99 [11]and in AASHTO-LRFD specifications (1998) [12].

    wmax = 1.08cfs3

    dcA 105 (8)

    where c is the ratio of the distances to the neutral axis

    from the extreme tension fiber and from the centroid

    of the reinforcement. fs is the stress calculated in the

    reinforcement at service loads. dc is the thickness of the

    concrete cover measured from the extreme tension fiber to

    the center of the bar or wire located closest to it. A is the

    effective tension area of concrete surrounding the flexural

    tension reinforcement and having the same centroid as that

    reinforcement, divided by the number of bars or wires.

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    (a) Section A. (b) Section B.

    (c) Section C. (d) Section D.

    (e) Section E.

    Fig. 13. Momentcurvature curve.

    As shown in Fig. 17, the crack width curve of the

    test results is similar to that of CEB-FIP 78 and EC 2.

    However, the crack width of the test result is somewhat

    larger than that of GergelyLutz equation. It is considered

    that crack widths of the composite girder with prefabricated

    slabs were more enlarged in weak surfaces of construction

    joints. Moreover, crack spacing is decisively influenced by

    transverse reinforcement spacing. Therefore, it is necessary

    to consider the existence of construction joints and the

    influence of transverse reinforcement spacing on the crack

    spacing in the calculation of crack widths. Also, it is

    considered that a safety factor or an enlargement factor for

    estimation of maximum crack width of a plate girder bridge

    with prefabricated slabs with loop joints is needed.

    4. Conclusions

    From the experimental study, it is concluded that:

    1. Initial crack spacing of the slab in the composite girder

    with prefabricated slabs can be wider than those of

    general RC beam structures.

    2. Initial cracking can occur earlier than calculation because

    there are construction joint surfaces between a precast

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    Fig. 14. Position of omega gauges and strain gauges.

    Fig. 15. Momentsteel strain curve.

    Fig. 16. Momentcrack width curve.

    panel and a transverse joint that is a cast-in-place part

    in slabs; thus the construction joint surfaces should be

    cautiously maintained and cleaned before casting.

    3. It is considered that crack spacing is mainly dependent on

    the transverse reinforcement spacing.

    4. The momentcurvature relationship or the flexural

    stiffness defined in Eurocode 4-2 can be applied well to

    Fig. 17. Steel stress versus crack width.

    the composite plate girder with loop joint prefabricated

    slabs.5. It is considered that crack widths of the composite

    girder with prefabricated slabs were more enlarged in

    weak surfaces of construction joints. Moreover, the

    crack spacing is decisively influenced by transverse

    reinforcement spacing. Therefore, it is necessary to

    consider the existence of construction joints and the

    influence of transverse reinforcement spacing on the

    crack spacing in the calculation of crack width.

    Acknowledgement

    This study is a part of projects Bridge 200. The authors

    would like to thank the Korea Institute of Construction

    Technology.

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