Fire Resistance of Innovative and Slender Concrete Filled ... Resistance of Innovative and Slender Concrete Filled Tubular Composite Columns ... Flexural buckling of ... • Buckling

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  • European ProjectFire Resistance of Innovative and Slender Concrete Filled

    Tubular Composite Columns (FRISCC)

    Prof Leroy Gardner

    Dr Finian McCann

    Elliptical section members

  • OUTLINE

    FRISCC - Fire Resistance of Innovative and Slender Concrete Filled Tubular Composite Columns

    1. STEEL EHS MEMBERS

    INTRODUCTION

    STRUCTURAL INVESTIGATIONS

    DESIGN RULES

    2. CONCRETE-FILLED EHS MEMBERS

    INTRODUCTION

    TESTING AND SIMULATIONS

    DESIGN GUIDANCE

    DESIGN EXAMPLE

    Elliptical section members

  • FRISCC

    Steel EHS members:

    Recently introduced as hot-finished products in

    EN 10210

    Combine merits of CHS and RHS

    Elegant aesthetics (CHS)

    Differing rigidities about principal axes

    (RHS) more suitable for applications in

    bending

    STEEL EHS MEMBERS - INTRODUCTION

    a

    a

    b b

    z

    y

  • FRISCC

    Applications of steel EHS

    STEEL EHS MEMBERS - APPLICATIONS

    Heathrow Airport, UK Jarrold store, UK

  • FRISCC

    Applications of steel EHS

    STEEL EHS MEMBERS - APPLICATIONS

    Madrid Airport, Spain Society Bridge, Scotland

  • FRISCC

    Structural scenarios addressed:

    1. Local buckling and cross-section classification

    2. Shear resistance

    3. Combined bending and shear

    4. Flexural buckling of columns

    STEEL EHS MEMBERS STRUCTURAL INVESTIGATIONS

  • FRISCC

    Cross-section classification:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    b

    b

    a a

    z

    y

    In compression or minor

    axis bending, equivalent

    diameter is:

    De

    = 2rmax

    =2a2/b

    Elastic critical local buckling compression and minor axis bending

    Initial aim was to determine an equivalent CHS diameter De

    rmax)(r

    tE

    max

    cr2

    13

    =

  • FRISCC

    Cross-section classification:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    rmax

    is the maximum local

    radius of curvature

    a

    a

    b b

    rmax

    Maximum

    compression

    Compression

    Tension

    z

    y

    Buckling

    initiates

    De= 0.8a2/b

    Elastic critical local buckling major axis bending

  • FRISCC

    Cross-section classification Testing:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    Material testing of

    tensile coupons

    Geometric

    measurementsCompression

    tests

    Minor axis bending tests

  • FRISCC

    Cross-section classification Finite element modelling:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    FE models developed in ABAQUS

    Models validated against test results

    Full loading history and failure modes well predicted

    Parametric studies conducted, varying:

    Cross-section slenderness

    Aspect ratios (for all tests, a/b = 2)

  • FRISCC

    Cross-section classification FE validation:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    0

    600

    1200

    1800

    0 6 12 18 24

    End shortening (mm)

    Lo

    ad

    N(k

    N)

    FE

    Test

  • FRISCC

    Cross-section classification:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    De/t2

    Fu/F

    y

    0.0

    0.5

    1.0

    1.5

    2.0

    0 30 60 90 120 150 180 210 240 270

    2a

    2b

    EHS

    CHS

    FE

    Class 1-3 Class 4

    De = 2rmax = 2a2/b

    = (235/fy)0.5

    Max. load Fu

    normalised by yield load Fy

  • FRISCC

    Cross-section classification:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    Minor axis bending ultimate moment to elastic moment

    De/t2

    Mu/M

    el

    0.0

    0.5

    1.0

    1.5

    2.0

    2.5

    0 20 40 60 80 100 120 140 160 180 200 220 240 260

    EHS

    CHS

    FE

    2a

    2b

    Class 4Class 1-3

    De = 2rmax = 2a2/b

    = (235/fy)0.5

  • FRISCC

    Cross-section classification summary of measurements of slenderness:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    Loading Equivalent diameterCorresponding point on

    cross-section

    2a

    2b

    Axial

    compressionDe = 2a

    2/b

    2a

    2b

    Minor axis

    bending (z-z)De = 2a

    2/b

    2b

    2aMajor axis

    bending (y-y)

    De = 0.8a2/b a/b > 1.36

    2b

    2a

    De = 2b2/a a/b 1.36

  • FRISCC

    Cross-section classification summary of slenderness limits:

    STEEL EHS MEMBERS CROSS-SECTION CLASSIFICATION

    Type of

    compression

    loading

    Diameter

    ratio

    Proposed slenderness limits

    Class 1 Class 2 Class 3

    Axial

    compression D

    e/t Not applicable 902

    Minor axis

    bending (z-y)D

    e/t

    502 702 1402

    Major axis

    bending (y-y)D

    e/t

  • FRISCC

    Shear resistance:

    STEEL EHS MEMBERS SHEAR RESISTANCE

    Three-point bending tests (a/b = 2):

    12 major axis, 12 minor axis

    Varying slenderness and length

    L/2 L/2

    F

    Moment gradient

    Uniform shear

    Uniform shear

  • FRISCC

    STEEL EHS MEMBERS SHEAR RESISTANCE

    Design plastic shear resistance:

    (Av = shear area, fy = yield strength, M0 = 1.0)

    0

    ,

    3/

    M

    yv

    Rdpl

    fAV

    =

    b b

    a

    a

    z

    y

    For shear along z-z:

    a a

    b

    b

    z

    y

    For shear along y-y:

    Av = (4b-2t)t A

    v = (4a-2t)t

  • FRISCC

    STEEL EHS MEMBERS SHEAR RESISTANCE

    Momentshear interaction design guidance based on test results:

    0.0

    0.5

    1.0

    1.5

    0.00 0.25 0.50 0.75 1.00 1.25

    Vu/Vpl,Rd

    Mu/M

    pl,Rd

    or M

    u/M

    el,Rd

    Shear along y-y

    Shear along z-z

    Proposed shear-moment

    interaction

  • FRISCC

    Column buckling:

    STEEL EHS MEMBERS COLUMN BUCKLING

    Column tests performed (a/b = 2):

    12 major axis, 12 minor axis, varying slenderness and length

    Knife edge

    Load cell

    LVDT

    Strain gauge

    CL

    Hydraulic jack

  • FRISCC

    Column buckling finite element validation:

    STEEL EHS MEMBERS COLUMN BUCKLING

    0

    250

    500

    750

    0 15 30 45 60

    Lateral deflection at mid-height (mm)

    Lo

    ad

    N (

    kN

    )

    Test

    FE

  • 0.0

    0.5

    1.0

    1.5

    0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8

    Member slenderness

    Buckling about z-z

    Buckling about y-yN

    u/N

    yo

    r N

    u/N

    eff

    z

    y

    EC3 curve a

    STEEL EHS MEMBERS COLUMN BUCKLING

    Buckling curve a can be used for EHS, as for other hot-finished

    hollow sections

  • STEEL EHS MEMBERS COLUMN BUCKLING

    Design guidance:

    Presented proposals are

    reflected in the Blue book

    Also in equivalent US

    design guidance

    Expected to be

    incorporated in future

    revisions of EC3

  • FRISCC

    Steel EHS members - conclusions:

    STEEL EHS MEMBERS SUMMARY

    New addition to hot-rolled range

    Significant testing and FE modelling programmes

    Design rules for primary structural configurations

    Incorporation into structural design codes ongoing

  • FRISCC

    Concrete-filled EHS columns:

    Design guidance currently exists for other concrete-filled tubular

    columns (CHS, SHS, RHS)

    No current guidance for emerging CFEHS structural solution

    Among aims of FRISCC project: develop guidance on the design

    of CFEHS columns

    At room temperature (Imperial College)

    In fire conditions (UP Valencia)

    CONCRETE-FILLED EHS MEMBERS - INTRODUCTION

  • FRISCC

    Current guidance:

    Cross-section classification - Eurocode 4: composite section classified

    according to least favourable class of steel elements in compression (using

    Eurocode 3 limits)

    Resistance of compression members: not available for CFEHS

    adopt rules for CHS / RHS?

    Strategy for development of design guidance:

    Experimental programme

    Validation of numerical model against experiments

    Numerical parametric study

    Develop design rules for CFEHS columns and beam-columns based on results

    CONCRETE-FILLED EHS MEMBERS - INTRODUCTION

  • FRISCC

    Experimental investigation:

    27 concrete-filled 150756.3 EHS

    specimens tested in compression

    Grade S355 steel, grade C30 concrete

    Loading was either concentric or with various

    major / minor axis eccentricities

    Specimens with different global slenderness

    (lengths) examined

    Some specimens with steel reinforcement

    (4No. T10 bars)

    CONCRETE-FILLED EHS MEMBERS - EXPERIMENTS

  • FRISCC

    Cross-sectional geometry of experimental specimens:

    CONCRETE-FILLED EHS MEMBERS - EXPERIMENTS

    a

    b

    ez

    ey

    Position of eccentric load

    10 mm

    18 mm

    Specimen buckling about major

    axis

    Specimen buckling about minor

    axis

    40 mm

    15 mm

    T10 reinforcing bar

  • FRISCC

    Testing of columns:

    CONCRETE-FILLED EHS MEMBERS - EXPERIMENTS

  • FRISCC

    Numerical modelling:

    Finite element model of CFEHS column developed in ABAQUS

    Steel material model based on tensile testing of coupons

    Concrete damage plasticity model used

    CONCRETE-FILLED EHS ME

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