European Project Fire Resistance of Innovative and Slender Concrete - - PowerPoint PPT Presentation

European Project

Fire 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 t E

max cr 2

1 3 ν − = σ

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 measurements Compression 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

600 1200 1800 6 12 18 24

End shortening δ (mm) Load N (kN)

FE

Test

FRISCC Cross-section classification:

STEEL EHS MEMBERS – CROSS-SECTION CLASSIFICATION

De/tε2 Fu/Fy

0.0 0.5 1.0 1.5 2.0 30 60 90 120 150 180 210 240 270

2a 2b

EHS CHS FE

Class 1-3 Class 4

De = 2rmax = 2a2/b ε = (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/tε2 Mu/Mel

0.0 0.5 1.0 1.5 2.0 2.5 20 40 60 80 100 120 140 160 180 200 220 240 260

EHS CHS FE

2a 2b

Class 4 Class 1-3

De = 2rmax = 2a2/b ε = (235/fy)0.5

FRISCC Cross-section classification – summary of measurements of slenderness:

STEEL EHS MEMBERS – CROSS-SECTION CLASSIFICATION

Loading Equivalent diameter Corresponding point on cross-section

2a 2b

Axial compression De = 2a2/b

2a 2b

Minor axis bending (z-z) De = 2a2/b

2b 2a

Major 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 De/t Not applicable 90ε2 Minor axis bending (z-y) De/t 50ε2 70ε2 140ε2 Major axis bending (y-y) De/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, γM0 = 1.0)

,

3 /

M y v Rd pl

f A V γ =

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 Av = (4a-2t)t

FRISCC

STEEL EHS MEMBERS – SHEAR RESISTANCE

Moment–shear 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/Mpl,Rd or Mu/Mel,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 C L Hydraulic jack

FRISCC Column buckling – finite element validation:

STEEL EHS MEMBERS – COLUMN BUCKLING

250 500 750 15 30 45 60 Lateral deflection at mid-height ω (mm) Load 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 λ

Buckling about z-z Buckling about y-y

Nu/Ny or Nu/Neff

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
• f 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 150×75×6.3 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 MEMBERS – NUMERICAL MODELLING

concrete core steel tube Buckling axis end-plate

FRISCC Validation of numerical model – ultimate loads:

CONCRETE-FILLED EHS MEMBERS – NUMERICAL MODELLING

200 400 600 800 1000 1200 1400 200 400 600 800 1000 1200

Nu,exp (kN) Nu,FEA (kN)

Present study +10% Unity

• 10%

Nu,exp / Nu,FEA: average = 1.12, STDEV = 0.07

FRISCC Validation of numerical model – load–deflection behaviour:

CONCRETE-FILLED EHS MEMBERS – NUMERICAL MODELLING

100 200 300 400 500 600 700 800 5 10 15 20 25 Load (kN) Axial displacement (mm)

E20:L2-MA-50-R - test E20:L2-MA-50-R - FEA E21:L1-MA-50-R - test E21:L1-MA-50-R - FEA E22:L3-MI-25-R - test E22:L3-MI-25-R - FEA

FRISCC Validation of numerical model – failure mode:

CONCRETE-FILLED EHS MEMBERS – NUMERICAL MODELLING

FRISCC Numerical parametric study:

• 360 specimens modelled, varying
• cross-section
• slenderness
• reinforcement ratio
• cover to reinforcement
• load eccentricity (also modelled concentric loading)
• buckling axis
• Results used as basis to formulate design rules

CONCRETE-FILLED EHS MEMBERS – NUMERICAL MODELLING

FRISCC Design guidance strategy:

• Apply rules for concrete-filled CHS and RHS to CFEHS columns
• Buckling curve relates to EC3 curve for members in axial compression
• Member imperfection used to determine first-order moments for members

in combined compression and uniaxial bending (i.e. eccentrically-loaded)

CONCRETE-FILLED EHS MEMBERS – DESIGN GUIDANCE

FRISCC Assessment of use of CHS and RHS rules for CFEHS columns:

CONCRETE-FILLED EHS MEMBERS – DESIGN GUIDANCE Ratios of FE parametric study results to EC4 predictions (using design strengths i.e. with partial factors)

Conclusion: CHS and RHS rules are suitable for design of CFEHS columns

0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30

Nult,FE / Nult,EC4

Design strengths

SAFE UNSAFE

FRISCC Design example: determine capacity of concentrically-loaded CFEHS

Column is 400 × 200 × 12.5 EHS, L = 4 m, B.C. = P-P 2a = 400 mm, 2b = 200 mm, t = 12.5 mm fcd = 30 MPa, fyd = 355 MPa, Ea = 210 GPa, Ecm = 36 GPa Cross-sectional properties of concrete element: Ac = = 515 cm2 Ic,z= = 9865 cm4 Cross-sectional properties of steel element: As= 113 cm2

, Is,z = 5843 cm4 (from Tata section tables)

CONCRETE-FILLED EHS MEMBERS – DESIGN EXAMPLE

400 mm 200 mm 12.5 mm

( ) ( ) ( )( )

5 . 12 2 200 5 . 12 2 400 4 2 2 2 2 4 × − × − = − − π π t b t a

( ) ( ) ( )( )

3 3

5 . 12 2 200 5 . 12 2 400 64 2 2 2 2 64 × − × − = − − π π t b t a

FRISCC Design example: determine capacity of concentrically-loaded CFEHS

Plastic resistance to compression: Npl,Rd = Aa fyd + Ac fyc = (113)(355)+(515)(30) = 5557 kN Effective minor axis flexural rigidity: (EI)eff,z = EaIa,z + 0.6 EcmIc,z= (210000)(5843)+(36000)(9865) = 13790 kN m2 Elastic critical load for buckling about minor axis: Ncr,z = π2(EI)eff,z / L2 = π2(13790) / 42 = 8506 kN

CONCRETE-FILLED EHS MEMBERS – DESIGN EXAMPLE

400 mm 200 mm 12.5 mm

FRISCC Design example: determine capacity of concentrically-loaded CFEHS

Nondimensional slenderness: Reinforcement ratio ρ = 0, therefore use buckling curve a: Imperfection factor α = 0.21

CONCRETE-FILLED EHS MEMBERS – DESIGN EXAMPLE

82 . 8508 5676

cr,z Rd pl,

= = = N N λ

( )

( )

( )

( )

898 . 82 . 21 . 82 . 21 . 1 5 . 1 5 .

2 2

• =

+ − + = + − + = Φ λ λ λ α

( )

786 . 850 . 898 . 898 . / 1 / 1

2 2 2 2

= − + =       − Φ + Φ = λ χ kN 4461 6526 767 .

Rd pl, Rd b,

= × = = N N χ

FRISCC

Thank you!

CONCRETE-FILLED EHS MEMBERS – DESIGN EXAMPLE