European Project Fire Resistance of Innovative and Slender Concrete Filled Tubular Composite Columns (FRISCC) Elliptical section members Prof Leroy Gardner Dr Finian McCann

FRISCC - Fire Resistance of Innovative and Slender Concrete Filled Tubular Composite Columns OUTLINE Elliptical section members 1. S TEEL EHS MEMBERS I NTRODUCTION S TRUCTURAL INVESTIGATIONS D ESIGN RULES 2. C ONCRETE - FILLED EHS MEMBERS I NTRODUCTION T ESTING AND SIMULATIONS D ESIGN GUIDANCE D ESIGN EXAMPLE

S TEEL EHS MEMBERS - INTRODUCTION Steel EHS members: z • Recently introduced as hot-finished products in EN 10210 a • Combine merits of CHS and RHS y • Elegant aesthetics (CHS) a • Differing rigidities about principal axes (RHS) � more suitable for applications in bending b b FRISCC

S TEEL EHS MEMBERS - APPLICATIONS Applications of steel EHS Heathrow Airport, UK Jarrold store, UK FRISCC

S TEEL EHS MEMBERS - APPLICATIONS Applications of steel EHS Society Bridge, Scotland Madrid Airport, Spain FRISCC

S TEEL EHS MEMBERS – STRUCTURAL INVESTIGATIONS Structural scenarios addressed: 1. Local buckling and cross-section classification 2. Shear resistance 3. Combined bending and shear 4. Flexural buckling of columns FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification: Elastic critical local buckling – compression and minor axis bending Initial aim was to determine an equivalent CHS diameter D e E t r max σ = cr y 2 r 3 ( 1 ) − ν max b In compression or minor z axis bending, equivalent b diameter is: D e = 2r max =2a 2 /b a a FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification: Elastic critical local buckling – major axis bending z Compression a r max Maximum y compression a Buckling initiates Tension D e = 0.8a 2 /b b r max is the maximum local b radius of curvature FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification – Testing: Material testing of Geometric Minor axis bending tests Compression tensile coupons measurements tests FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification – Finite element modelling: • 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

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification – FE validation: 1800 FE Load N (kN) Test 1200 600 0 0 6 12 18 24 End shortening δ (mm) FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification: Max. load F u normalised by yield load F y 2.0 EHS CHS FE 1.5 F u / F y 1.0 2a D e = 2r max = 2a 2 /b 0.5 2b ε = (235/f y ) 0.5 Class 1-3 Class 4 0.0 0 30 60 90 120 150 180 210 240 270 D e / t ε 2 FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification: Minor axis bending – ultimate moment to elastic moment 2.5 2a D e = 2r max = 2a 2 /b EHS CHS 2.0 2b ε = (235/f y ) 0.5 FE 1.5 M u /M el 1.0 Class 1-3 Class 4 0.5 0.0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 D e /t ε 2 FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification – summary of measurements of slenderness: Corresponding point on Loading Equivalent diameter cross-section 2a Axial D e = 2 a 2 / b 2b compression 2a Minor axis D e = 2 a 2 / b bending (z-z) 2b D e = 0.8 a 2 / b a / b > 1.36 2a Major axis 2a bending (y-y) D e = 2 b 2 / a a / b ≤ 1.36 2b 2b FRISCC

S TEEL EHS MEMBERS – CROSS - SECTION CLASSIFICATION Cross-section classification – summary of slenderness limits: Proposed slenderness limits Type of Diameter compression ratio loading Class 1 Class 2 Class 3 Axial 90 ε 2 D e / t Not applicable compression Minor axis D e / t bending (z-y) 50 ε 2 70 ε 2 140 ε 2 Major axis D e / t bending (y-y) FRISCC

S TEEL EHS MEMBERS – S HEAR RESISTANCE Shear resistance: • Three-point bending tests ( a / b = 2): • 12 major axis, 12 minor axis • Varying slenderness and length F L/2 L/2 Moment gradient Uniform shear Uniform shear FRISCC

S TEEL EHS MEMBERS – S HEAR RESISTANCE A f / 3 v y V Design plastic shear resistance: = pl , Rd γ M 0 (A v = shear area, f y = yield strength, γ M0 = 1.0) For shear along y-y: For shear along z-z: z y a b z y b a a a b b A v = (4 b -2 t ) t A v = (4 a -2 t ) t FRISCC

S TEEL EHS MEMBERS – S HEAR RESISTANCE Moment–shear interaction design guidance based on test results: 1.5 Shear along y-y Shear along z-z M u / M pl,Rd or M u / M el,Rd 1.0 0.5 Proposed shear-moment interaction 0.0 0.00 0.25 0.50 0.75 1.00 1.25 V u / V pl,Rd FRISCC

S TEEL EHS MEMBERS – C OLUMN BUCKLING Column buckling: • Column tests performed ( a / b = 2): • 12 major axis, 12 minor axis, varying slenderness and length Load cell Knife edge C L Strain gauge LVDT Hydraulic jack FRISCC

S TEEL EHS MEMBERS – C OLUMN BUCKLING Column buckling – finite element validation: 750 FE Load N (kN) 500 Test 250 0 0 15 30 45 60 Lateral deflection at mid-height ω (mm) FRISCC

S TEEL EHS MEMBERS – C OLUMN BUCKLING 1.5 Buckling about y-y N u /N y or N u /N eff 1.0 Buckling about z-z y z 0.5 EC3 – curve ‘a’ 0.0 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 Member slenderness λ Buckling curve ‘a’ can be used for EHS, as for other hot-finished hollow sections

S TEEL EHS MEMBERS – C OLUMN 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

S TEEL EHS MEMBERS – S UMMARY Steel EHS members - conclusions: • 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

C ONCRETE - FILLED EHS MEMBERS - INTRODUCTION 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) FRISCC

C ONCRETE - FILLED EHS MEMBERS - INTRODUCTION 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 FRISCC

C ONCRETE - FILLED EHS MEMBERS - EXPERIMENTS 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) FRISCC

C ONCRETE - FILLED EHS MEMBERS - EXPERIMENTS Cross-sectional geometry of experimental specimens: Position of eccentric load e y T10 reinforcing bar b 18 mm a 40 mm 15 mm 10 mm e z Specimen buckling about major Specimen buckling about minor axis axis FRISCC

C ONCRETE - FILLED EHS MEMBERS - EXPERIMENTS Testing of columns: FRISCC

C ONCRETE - FILLED EHS MEMBERS – NUMERICAL MODELLING 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 end-plate steel tube concrete core Buckling axis FRISCC

C ONCRETE - FILLED EHS MEMBERS – NUMERICAL MODELLING Validation of numerical model – ultimate loads: 1400 1200 1000 N u,exp (kN) 800 600 400 Present study +10% 200 Unity -10% 0 0 200 400 600 800 1000 1200 N u,FEA (kN) N u,exp / N u,FEA : average = 1.12, STDEV = 0.07 FRISCC

C ONCRETE - FILLED EHS MEMBERS – NUMERICAL MODELLING Validation of numerical model – load–deflection behaviour: 800 E20:L2-MA-50-R - test E20:L2-MA-50-R - FEA 700 E21:L1-MA-50-R - test E21:L1-MA-50-R - FEA 600 E22:L3-MI-25-R - test E22:L3-MI-25-R - FEA 500 Load (kN) 400 300 200 100 0 0 5 10 15 20 25 Axial displacement (mm) FRISCC

C ONCRETE - FILLED EHS MEMBERS – NUMERICAL MODELLING Validation of numerical model – failure mode: FRISCC

C ONCRETE - FILLED EHS MEMBERS – NUMERICAL MODELLING 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 FRISCC

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