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  • Concrete Beams Strengthened with Externally

    Bonded Glass Fiber Reinforced Plastic Plates

    Ming-Hung Hsu

    Department of Electrical Engineering, National Penghu University,

    Penghu, Taiwan 880, R.O.C.

    Abstract

    In this work, the flexural behavior of reinforced concrete beams strengthened by epoxy bonded

    glass fiber reinforced plastic plates is investigated through the finite element method. The finite

    element models based on the widely used package ABAQUS are employed in simulating the behavior

    of reinforced concrete beams strengthened by externally bonded glass fiber reinforced polymer. The

    numerical results of four-point bending test of reinforced concrete beams strengthened by externally

    bonded glass fiber reinforced plastic plates in comparing with the experimental results show satisfactory

    agreement. The results indicate that the flexure strength of reinforced concrete beams can be

    significantly increased by externally bonded glass fiber reinforced plastic plates. The dynamic behavior

    of reinforced concrete beams strengthened by epoxy bonded glass fiber reinforced plastic plates is

    investigated through the differential quadrature method. In this approach, only eleven sample points

    are required to obtain convergence.

    Key Words: Glass Fiber Reinforced Plastic Plate, Reinforced Concrete Beam, Finite Element Method,

    Differential Quadrature Method

    1. Introduction

    Existing cracking reinforced concrete beams may

    require increasing the shear capacity and cracking.

    The glass fiber reinforced plastic plate is used to bond

    the beam in order to increase flexural capacity. Sa-

    adatmanesh et al. [112] experimentally investigated

    the static strength of reinforced concrete beams and

    column strengthened by gluing glass fiber reinforced

    plastic plates. High strength fiber reinforced plastic

    straps are wrapped around the column in the potential

    plastic hinge region to increase confinement and to

    improve the behavior under seismic forces. Hamoush

    and Ahmad [13] investigated the strength of steel-pla-

    te-strengthened concrete beams. Adhikary et al. [14,15]

    investigated the shear strengthening of reinforced con-

    crete beams using steel plates bonded on beam web

    through experiments and numerical analysis. Garden

    et al. [16,17] experimentally studied the failure mo-

    des of reinforced concrete beams strengthened with

    pre-stressed carbon composite plates and the anchor-

    age length of carbon fiber composite plates used to

    strengthen reinforced concrete beams. Kankam [18]

    studied the flexural strength and deformation charac-

    teristics of concrete beams reinforced with threaded

    steel bars that were tensioned against steel plates bear-

    ing on the concrete ends by means of tighten nuts.

    Subedi and Baglin [19] analyzed the ultimate load of

    plate reinforced concrete beams. Picard et al. [20] in-

    vestigated the influence of various design parameters

    such as cube strength, size and position of main em-

    bedded tensile bars, width of the beam, plate thick-

    ness, and ratio of plate width on the magnitude of ulti-

    mate plate peeling moment. Nguyen et al. [21] inves-

    tigated an analytical model for reinforced concrete

    beams with bolted side plates accounting for longitu-

    dinal and transverse partial interaction. Shen et al.

    [22] presented an analytical-numerical procedure for

    Tamkang Journal of Science and Engineering, Vol. 9, No 3, pp. 223232 (2006) 223

    *Corresponding author. E-mail: [email protected]

  • the bending and transverse vibration analysis of mod-

    erately thick plates strengthened by a bonded thin com-

    posite plate under different kinds of boundary condi-

    tions. Ascione and Feo [23] developed a finite ele-

    ment model for predicting shear and normal stresses

    in the adhesive layer of plated reinforced concrete beams.

    Raoof et al. [24] investigated the theoretical and ex-

    perimental study on externally plated reinforced con-

    crete beams. Barnes et al. [25,26] solved the transfer

    of stress through steel to concrete adhesive bond and

    analyzed the external steel plate systems for the shear

    strengthening of reinforced concrete beams based on

    the equilibrium of forces along the critical section. Sa-

    pountzakis et al. [27,28] studied the interface forces and

    stresses in composite steel-concrete structure. Wang [29]

    investigated the analytical and experimental study on se-

    ismic performance of reinforced concrete T-beams with

    design deficiency in steel bar curtailment.

    ABAQUS standard finite element analysis code is

    used to model the reinforced concrete beams bonding

    glass fiber reinforced plastic plates to the tension sur-

    face. ABAQUS offers the facility of nonlinear model-

    ing for the reinforced concrete beam. The differential

    quadrature method (DQM) is used to form the vibration

    problems of reinforced concrete beams strengthened by

    epoxy bonded glass fiber reinforced plastic plates in

    matrix form. To the authors knowledge, very few pub-

    lished papers in the literature have presented the dy-

    namic analysis of reinforced concrete beams strength-

    ened by epoxy bonded glass fiber reinforced plastic pla-

    tes using the DQM.

    2. Flexural Strength of Reinforced Concrete

    Beams Strengthened by Epoxy Bonded Glass

    Fiber Reinforced Plastic Plates

    Figure 1 shows the geometry of a reinforced concrete

    beam strengthened by epoxy bonded a glass fiber rein-

    forced plastic plate for four-point bending test. L is the

    length of the reinforced concrete beam. An epoxy layer is

    applied to the straps while wrapping for inter laminar

    bond. The finite element models based on the widely used

    package ABAQUS are employed in simulating the be-

    havior of reinforced concrete beams strengthened by ex-

    ternally bonded glass fiber reinforced plastic plates. We

    use the method for measuring the shear strength to get

    the simple compressive strength and the simple tensile

    strength by Mohr-Columb criterion. Meshes with trian-

    gle type elements are created with an automatic mesh ge-

    nerator. In this two dimensional non-linear finite element

    model, the boundary nodes are considered simple sup-

    ported. The modeling approach performed in this study

    is based on finite element method to describe the total

    strain. ABAQUS provides an elastic plastic damage the-

    ory; including tension cracking, compression crushing,

    and post crack response. In this study of FEM model, the

    elastic plastic damage theory is adopted to solve the stress

    distribution.

    224 Ming-Hung Hsu

    Figure 1. Schematic view of the reinforced concrete beam strengthened by epoxy bonded a glass fiber reinforced plastic platealong the tension face.

  • Figure 2 shows the central deflection of the reinfor-

    ced concrete beam. The beam size used is 0.20 m (b)

    0.30 m (h) 3.00 m (L). b is the width of the reinforced

    concrete beam. h is the thickness of the reinforced con-

    crete beam. The beams are reinforced with two D6 bars

    in the compression zone, whereas two D9 bars are pro-

    vided in the tension. The diameter of D6 bar is 6.35 mm.

    The diameter of D9 bar is 9.53 mm. Youngs modulus of

    the concrete is 21000 MPa. The experimental ultimate

    load is 91.9 kN [30]. The analytical ultimate load is 98.9

    kN. The agreement between numerical and experimentcurves is satisfactory.

    Figure 3 shows the central deflection of the reinfor-

    ced concrete beam strengthened by epoxy bonded a 2 mm

    thick glass fiber reinforced plastic plate along the tension

    face. Youngs modulus of the glass fiber reinforced plas-

    tic plate is 37230 MPa. The experimental ultimate load is

    172.4 kN [30]. The analytical ultimate load is 165.5 kN.

    The results solved using FEM and experimental results

    are put together for comparison. Results indicate that the

    central deflection calculated using the FEM agreed very

    well with the measured deflection. Figure 4 shows the

    central deflection of the reinforced concrete beam stren-

    gthened by epoxy bonded a 4 mm thick glass fiber rein-

    forced plastic plate along the tension face. The experi-

    mental ultimate load is 182.5 kN [30]. The analytical ul-

    timate load is 220.0 kN. The numerical results and the re-

    sults measured experimentally correspond closely. Fig-

    ure 5 shows the central deflection of the reinforced con-

    crete beam strengthened by epoxy bonded a 6 mm thick

    glass fiber reinforced plastic plate along the tension face.

    The experimental ultimate load is 255.7 kN [30]. The an-

    alytical ultimate load is 248.4 kN. The agreement between

    numerical and experiment curves is satisfactory.

    Figure 6 displays the central deflection of the rein-

    forced concrete beam strengthened by epoxy bonded a 6

    mm thick glass fiber reinforced plastic plate along the

    Concrete Beams Strengthened with Externally Bonded Glass Fiber Reinforced Plastic Plates 225

    Figure 2. Central deflection of the reinforced concrete beam.

    Figure 3. Central deflection of the reinforced concrete beamstrengthened by epoxy bonded a 2 mm thick glassfiber reinforced plastic plate along the tension face.

    Figure 4. Central deflection of the reinforced concrete beamstrengthened by epoxy bonded a 4 mm thick glassfiber reinforced plastic plate along the tension face.

  • tension face. The beam size used is 0.205 m (b) 0.565

    m (h) 4.875 m (L). The beams are reinforced with two

    D13 bars in the compression zone, whereas three D25

    bars are provided in the tension. The diameter of D13 bar

    is 12.7 mm. The diameter of D25 bar is 25.4 mm. The ex-

    perimental ultimate load is 325.0 kN [30]. The analytical

    ultimate load is 352.0 kN. The agreement between nu-

    merical and experiment results is satisfactory. Figure 7

    reveals the central deflection of the reinforced concrete

    beam strengthened by epoxy-bonding a 6 mm thick glass

    fiber reinforced plastic plate along the tension face. The

    beams are reinforced with two D13 bars in the compres-

    sion zone, whereas two D25 bars are provided in the ten-

    sion. The experimental ultimate load is 255.0 kN [30].

    The analytical ultimate load is 263.0 kN. The numerical

    results of four-point bending test of reinforced concrete

    beams strengthened by externally bonded glass fiber re-

    inforced plastic plates in comparing with the experimen-

    tal results show satisfactory agreement.

    3. Dynamic Analysis of Reinforced Concrete

    Beams Strengthened by Epoxy Bonded Glass

    Fiber Reinforced Plastic Plates

    This work demonstrates the dynamic behavior of re-

    inforced concrete beams strengthened by epoxy bonded

    glass fiber reinforced plastic plates using the DQM. The

    influences of glass fiber reinforced plastic plate thickness

    on the dynamic behavior of reinforced concrete beams

    strengthened by epoxy bonded glass fiber reinforced plas-

    tic plates are investigated. The DQM is used to form the

    reinforced concrete beams strengthened by epoxy bond-

    ed glass fiber reinforced plastic plates problems in matrix

    form. The calculated accuracy and integrity of this prob-

    lem is demonstrated by a series of case studies using the

    226 Ming-Hung Hsu

    Figure 5. Central deflection of the reinforced concrete beamstrengthened by epoxy bonded a 6 mm thick glassfiber reinforced plastic plate along the tension face.

    Figure 6. Central deflection of the reinforced concrete beamstrengthened by epoxy bonded a 6 mm thick glassfiber reinforced plastic plate along the tension face.

    Figure 7. Central deflection of the reinforced concrete beamstrengthened by epoxy bonded a 6 mm thick glassfiber reinforced plastic plate along the tension face.

  • DQM. There are many computational methods available

    for vibration analysis. Bellman et al. [31,32] introduced

    the DQM. DQM reduces the partial differential equations

    into a set of algebraic equations and has been used exten-

    sively to solve a variety of problems in different fields of

    science and engineering [3348].

    The efficiency and accuracy of the DQM are not de-

    pendent on the number and accuracy of the selected com-

    parison functions. The essence of the DQM is that the de-

    rivative of a function at a sample point is approximated

    by a weighted linear sum of the functional values at all

    the sample points in the domain. DQM approximates the

    mth order partial derivate of f(z) with respect to z as:

    for i, j = 1, 2, ,N

    (1)

    where f(zi) is the functional value at the sample point zi,

    and Dijm( )

    are the DQ coefficients of the mth order differ-

    entiation attached to these functional values.

    The DQ coefficients are difficult to obtain, because

    they may be ill conditioned. To overcome the numerical

    ill-conditioning in determining the DQ coefficients Dijm( )

    ,

    Quan and Chang [42,43] established a set of algebraic

    expressions to calculate the DQ coefficients, namely:

    (2)

    where

    ,

    for i = 1, 2, , N

    Substituting equation (2) into equation (1) yields:

    for i, j = 1, 2, ,N and i j

    (3)

    and

    for i = 1, 2, , N (4)

    The second-order and higher-order derivatives of the DQ

    coefficients can also be obtained by matrix multiplica-

    tion [33,34], thus:

    for i, j = 1, 2, , N (5)

    for i, j = 1, 2, , N (6)

    for i, j = 1, 2, , N (7)

    for i, j = 1, 2, , N (8)

    The selection of sample points always plays an im-

    portant role in the solution accuracy of the DQM. The

    unequally spaced sample points of each beam using the

    Chebyshev-Gauss-Lobatto distribution in the present com-

    putation are chosen as the following equation:

    for i, j = 1, 2, , N (9)

    By assuming the reinforced concrete beam strength-

    ened by epoxy bonded a glass fiber reinforced plastic

    plate is long, the strain energy of the reinforced concrete

    beam strengthened by epoxy bonded a glass fiber rein-

    forced plastic plate can be simplified as:

    (10)

    where E1 is Youngs modulus of the reinforced concrete

    beam and E2 is Youngs modulus of the glass fiber rein-

    forced plastic plate. u1 is the transverse displacement of

    the reinforced concrete beam and u2 is the transverse de-

    flection of the glass fiber reinforced plastic plate. I1 is

    the 2nd moment area of concrete beam section and I2 is

    Concrete Beams Strengthened with Externally Bonded Glass Fiber Reinforced Plastic Plates 227

    1 1

    2 2m

    m

    ijm

    N N

    f z f z

    f z f zD

    z

    f z f z

    1 1

    N

    i

    i i i

    M zf z f z

    z z M z

    1

    N

    j

    j

    M z z z

    1

    1,

    N

    i i j

    j j i

    M z z z

    1(1)

    1

    i

    ij

    j i j

    M zD

    z z M z

    1 1

    1,

    N

    ii ij

    j j i

    D D

    (2) (1) (1)

    1

    N

    ij ik kj

    k

    D D D

    (3) (1) (2)

    1

    N

    ij ik kj

    k

    D D D

    (4) (1) (3)

    1

    N

    ij ik kj

    k

    D D D

    ( ) (1) ( 1)

    1

    Nm m

    ij ik kj

    k

    D D D

    i

    i 11z 1 cos

    2 N 1

    2 22 2

    L Le 1 21 1 2 22 20 0

    u u1 1U E I dz E I dz

    2 2z z

    L 2

    1 20

    1k u u dz

    2

  • the 2nd moment area of glass fiber reinforced plastic plate

    section. k is the stiffness of the epoxy adhesive. The ki-

    netic energy of the reinforced concrete beam strength-

    ened by epoxy bonded a glass fiber reinforced plastic

    plate is

    (11)

    where 1 is the density of the material of the concrete

    beam and !2 is the density of the material of the glass fi-

    ber reinforced plastic plate. The cross-section area of the

    concrete beam is A1 and the cross-section area of the

    glass fiber reinforced plastic plate is A2. Substituting equ-

    ations (10) and (11) into Hamiltons equation,

    (12)

    the differential equations governing the dynamics of re-

    inforced concrete beam strengthened by epoxy bonded

    a glass fiber reinforced plastic plate are:

    (13)

    (14)

    The corresponding boundary conditions of the reinfor-

    ced concrete beam strengthened by epoxy bonded a glass

    fiber reinforced plastic plate are:

    (15)

    (16)

    (17)

    (18)

    (19)

    (20)

    (21)

    (22)

    Consider the displacements to be of the form

    (23)

    (24)

    Equations (13) and (14) can be simplified to

    (25)

    (26)

    The corresponding boundary conditions of the reinfor-

    ced concrete beam strengthened by epoxy bonded a glass

    fiber reinforced plastic plate are:

    (27)

    (28)

    (29)

    (30)

    (31)

    (32)

    (33)

    (34)

    By employing the DQM, the equations of motion of the

    reinforced concrete beam strengthened by epoxy bond-

    ed a glass fiber reinforced plastic plate can be discre-

    228 Ming-Hung Hsu

    2 2L Le 1 2

    1 1 2 20 0

    u u1 1T A dz A dz

    2 t 2 t! !

    2

    1

    t e e

    tT U dt 0" "

    ( )2 22

    1 11 1 1 1 1 22 2 2

    u uA E I k u u 0

    t z z!

    ( )2 22

    2 22 2 2 2 2 12 2 2

    u uA E I k u u 0

    t z z!

    ,1u 0 t 0

    21

    1 1 2

    0,0

    u tE I

    z

    ,1u L t 0

    21

    1 1 2

    ,0

    u L tE I

    z

    ,2u 0 t 0

    22

    2 2 2

    0,0

    u tE I

    z

    ,2u L t 0

    22

    2 2 2

    ,0

    u L tE I

    z

    1 1, expu z t U z i t#

    2 2, expu z t U z i t#

    1U 0 0

    1U L 0

    2U 0 0

    ,2U L t 0

    21

    1 1 2

    00

    d UE I

    dz

    21

    1 1 20

    d U LE I

    dz

    22

    2 2 2

    00

    d UE I

    dz

    22

    2 2 20

    d U LE I

    dz

    ( )22

    2 11 1 1 1 1 1 22 2

    d UdAU E I k U U

    dz dz# !

    ( )22

    2 22 2 2 2 2 2 12 2

    d UdA U E I k U U

    dz dz# !

  • teized in a matrix form as the following equation:

    (35)

    where

    (36)

    The elements in the mass matrix are:

    Mii = !1A1 for i = 3, 4, , N 2 (37)

    Mii = !2A2 for i = N + 3, N + 4, , 2N 2 (38)

    Mii = 0 for i = 1, 2,N 1,N,N + 1,N + 2, 2N 1, 2N

    (39)

    Mij = 0 for i j, i = 1, 2, , 2N and j = 1, 2, , 2N

    (40)

    The elements in the stiffness matrix are:

    for i j, i = 3, 4, , N 2 and j = 1, 2, , N (41)

    for i = 3, 4, , N 2 (42)

    Cij = 0

    for i j N, i = 3, 4, , N 2 and j = N + 1, N + 2,

    2N (43)

    Ci,i+N = -k

    for i = 3, 4, , N 2 (44)

    Cij = 0

    For i j +N, i =N + 3,N + 4, , 2N 2 and j = 1, 2,

    , N (45)

    Ci,iN = -k

    for i = N + 3, N + 4, 2N 2 (46)

    for i j, i = N + 3, N + 4, , 2N 2

    and j = N + 1, N + 2, , 2N (47)

    for i = N + 3, N + 4, , 2N 2 (48)

    The boundary conditions of the simple supported rein-

    forced concrete beam strengthened by epoxy bonded a

    glass fiber reinforced plastic plate can be rearranged into

    the matrix form as

    for j = 1, 2, ..., N (49)

    for j = 1, 2, ..., N (50)

    for j = 1, 2, ..., N (51)

    for j = 1, 2, ..., N (52)

    Concrete Beams Strengthened with Externally Bonded Glass Fiber Reinforced Plastic Plates 229

    2[ ]{ ( )} [ ]{ ( )}ij j ij jC W z M W z#

    1 1 1

    2 1 2

    1

    1 2 1

    2 2 2

    2 2

    N N

    N

    N

    N N

    W z U z

    W z U z

    W z U z

    W z U z

    W z U z

    W z U z

    2 32

    1 1 1 1

    2 2 32

    ii

    ij ij

    ij

    z zz z

    D Dd E I z dE I zC

    dzdz L L

    4

    1 1 4

    ij

    i

    DE I z

    L

    2 2 3

    1 1 1 1

    2 2 32

    ii

    ii iiii

    z zz z

    d E I z dE I zD DC

    dzdz L L

    4

    1 1 4

    iii

    DE I z k

    L

    22

    ,2 2 2 2

    2 22

    i Ni N

    i N j N

    ij

    z zz z

    Dd E I z dE I zC

    dzdz L

    3 4

    , ,

    2 23 4

    i N j N i N j N

    i N

    D DE I z

    L L

    22

    ,2 2 2 2

    2 22

    i Ni N

    i N i N

    ii

    z zz z

    Dd E I z dE I zC

    dzdz L

    3 4

    , ,

    2 23 4

    i N i N i N i N

    i N

    D DE I z k

    L L

    (2) (2)(2)(2) (2)11, 1 1,1311 12

    2 2 2 2 2

    1 0 0 0 00

    { ( )}0

    jN NU zD DDD D

    L L L L L

    (2) (2)(2)(2) (2)21, 1 1,1311 12

    2 2 2 2 2

    1 0 0 0 00

    { ( )}0

    jN NU zD DDD D

    L L L L L

    (2) (2)(2) (2) (2)1, 1 ,1 2 3

    2 2 2 2 2

    0 0 0 0 10

    { ( )}0

    jN N N NN N NU zD DD D D

    L L L L L

    (2) (2)(2) (2) (2)2, 1 ,1 2 3

    2 2 2 2 2

    0 0 0 0 10

    { ( )}0

    jN N N NN N NU zD DD D D

    L L L L L

  • Figure 8 illustrates the frequencies of the reinforced

    concrete beams strengthened by epoxy bonded glass fi-

    ber reinforced plastic plates with different thicknesses.The beam size used is 0.20 m (b) 0.30 m (h) 3.00 m

    (L). The beams are reinforced with two D6 bars in the

    compression zone, whereas two D9 bars are provided in

    the tension. The numerical results show that higher fre-

    quencies are found for the beam with a higher thickness

    glass fiber reinforced plastic plate. The frequency of the

    reinforced concrete beam strengthened by epoxy-bond-

    ing a 2 mm thick glass fiber reinforced plastic plate along

    the tension face is greater than the frequency of the rein-

    forced concrete beam strengthened by no epoxy-bonding

    glass fiber reinforced plastic plate for mode 1. The fre-

    quencies of the reinforced concrete beam strengthened

    by epoxy-bonding a 2 mm thick glass fiber reinforced

    plastic plate along the tension face is smaller than the fre-

    quency of the reinforced concrete beam strengthened by

    no epoxy bonded glass fiber reinforced plastic plate for

    mode 2 to mode 6.

    4. Conclusion

    The results conduct that the flexure strength of rein-

    forced concrete beams can be significantly increased by

    externally bonded glass fiber reinforced plastic plates.

    The calculated results agreed closely with the measured

    results in the literature. This paper demonstrates the dy-

    namic behavior of reinforced concrete beams strengthened

    by epoxy bonded glass fiber reinforced plastic plates us-

    ing the DQM. The results indicate that bonding compos-

    ite plates to concrete beams increase the stiffness, yield

    moment, and flexural strength of the beams. The simplic-

    ity of this formulation makes it a desirable candidate for

    modeling reinforced concrete beams strengthened by ep-

    oxy bonded glass fiber reinforced plastic plates.

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    Figure 8. The frequencies of the reinforced concrete beamsstrengthened by epoxy bonded glass fiber reinfor-ced plastic plates with different thicknesses.

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    Manuscript Received: Dec. 21, 2004

    Accepted: Nov. 4, 2005

    232 Ming-Hung Hsu