GFRP REINFORCED CONCRETE STRUCTURAL ELEMENTS: FATIGUE BEHAVIOR AND HIGH TEMPERATURE EFFECTS Valter Carvelli Politecnico di Milano
SOME APPLICATIONS OF GFRP (Glass Fiber Reinforced Polymer) REBARS IN CONCRETE STRUCTURAL ELEMENTS Some advantages: No rebars corrosion; Electrical insulation.
AVAILABLE STANDARDS AND GUIDES FOR DESIGN OF FRP REINFORCED CONCRETE STRUCTURES CHBDC - Canadian Highway Bridge Design Code – CSA “Fibre Reinforced Structures ” ACI 440.1R - American Concrete Institute “ Guide for the design and construction of concrete reinforced with FRP bars ” JSCE - Japan Society of Civil Engineer’s “Recommendations for design and construction of concrete structures using continuous fiber reinforcing materials ” IStructE - British Institution of Structural Engineers “ Interim guidance on the design of reinforced concrete structures using fibre composite reinforcement” CNR-DT 203 - Italian National Research Council “Guide for design and construction of concrete structures reinforced with fiber- reinforced polymer bars” ………..……
OUTLINE Materials features jack A jack B Load Fatigue behaviour of slabs Cycle period 10 slab S1 - max load 140kN Jack A: max 8 displacement [mm] Jack A: min Jack B: max 6 Jack B: min 4 2 0 0 500000 1000000 1500000 cycles number High temperature effects on beams Numerical and analytical modelling no overlap 200 55cm overlap bent rebars 35cm overlap 150 Load max [kN] 24cm overlap 100 50 0 Open discussion 23 200 500 Temperature bottom [ o C]
MATERIALS FEATURES Carvelli V, Fava G, Pisani M A. ASCE Journal of Composites for Construction, 2009 Fava G, Carvelli V, Pisani M A. Composites Part B, 2012
MATERIALS FEATURES GFRP REBARS Unidirectional pultruded bars (E-glass fibre / vynilester) External surface: sanding of quartz and wrapping of aramidic yarn (Fibre volume fraction ≈ 60%) test of rebars: Ø 16÷40mm Experimental static tensile properties Ø16mm: E ≈ 39 GPa s ult ≈ 885 MPa
MATERIALS FEATURES GFRP REBARS TENSILE STRENGTH VS. TEMPERATURE
MATERIALS FEATURES GFRP REBARS TENSILE STRENGTH VS. TEMPERATURE Nigro et al., CICE 2008 Conference Wang et al., Composite Structures, 2007 (CFRP bars) (GFRP + CFRP bars)
MATERIALS FEATURES CONCRETE STRENGTH VS. TEMPERATURE Experimental measurements of concrete C55/67 5 Tensile strength [MPa] 4 4.0 3 2.8 2 1 1.1 0 (cylinder strength) 23 23 200 200 500 500 Temperature [ o C] (indirect tensile test, EN 12390-6)
MATERIALS FEATURES CONCRETE FATIGUE LIFE IN COMPRESSION European Codes: Palmgren-Miner rule m n actual number of constant number of intervals with i 1 amplitude cycles constant amplitude N ultimate number of i 1 i constant amplitude cycles Design quality: C55/67 characteristic cubic strength = 67 MPa Experimental cubic strength (average of 16 samples) ≈ 66 MPa The ultimate number of constant amplitude cycles, for max cyclic load of 140 kN applied on a 200x300mm contact area, should be N = 1.138.000
MATERIALS FEATURES GFRP REBARS - CONCRETE ADHESION 20 20 GFRP Ø12mm GFRP rebar PULL-OUT Steel rebar Pull-out 15 15 Test Beam-test t max [MPa] t max [MPa] 10 10 5 5 0 0 BEAM- Test 6 8 10 12 14 16 18 20 22 24 26 nominal diameter Ø [mm] Steel rebar Fava G., Carvelli V., Pisani M.A., to appear
MATERIALS FEATURES Personal knowledges Lack or very few investigations on • Fatigue behaviour of the FRP REBARS • Fatigue behaviour of the FRP REBARS-CONCRETE ADHESION Fatigue life domain of fibre – glass sucker rods (FIBEROD Info Catalog. TX, USA) Load level in our experiment of slabs for a max load of 140 kN
FATIGUE BEHAVIOUR OF SLABS Carvelli V, Pisani M A, Poggi C. Composites Part B, 2010
FATIGUE BEHAVIOUR OF SLABS LOAD CONDITIONS FOR TRAFFIC ON BRIDGES European Code 1 and 2 as guidelines for slab design European Codes define five fatigue load models. Among those the most heavy condition is for a twinned wheel : maximum load of 95 kN, contact area of 40x60cm . To accelerate the failure of the slabs in the experimental fatigue tests: minimum load in cycles 140 kN (+48%) contact area 20x30cm (-400%)
FATIGUE BEHAVIOUR OF SLABS BRIDGE SLABS GEOMETRY t D S W L D 1 . 37 small influence of free edges Length L = 500 cm S Width W = 248 cm W Thickness t = 20 cm 7 . 5 minimize the arch effect Span length S = 150 cm t
FATIGUE BEHAVIOUR OF SLABS GFRP REINFORCEMENT OF THE SLABS Transverse The bottom reinforcement was designed to reduce the slab deformability: maximum displacement Longitudinal < Span/250 = 6mm Longitudinal Reinforcement Transverse Reinforcement Ø12/20cm Ø16/20cm top bottom Ø16/10cm Ø16/10cm Manufacturing
FATIGUE BEHAVIOUR OF SLABS: experimental setup CONSTRAINS SIMULATION Service condition Bilateral constrain (as connectors) Layer of rubber (5mm thick) Cylindrical support (Ø 50mm)
FATIGUE BEHAVIOUR OF SLABS: experimental setup DISPLACEMENT MEASUREMENT DEVICES 5 displacement transducers LVDT (max 50 mm)
FATIGUE BEHAVIOUR OF SLABS: experimental setup LOADING SETUP Hydraulic Hydraulic Jack A Jack B Contact area 30cm 20cm Contact area for European code is 40x60cm .
FATIGUE BEHAVIOUR OF SLABS: experimental setup LOADING SETUP Hydraulic Hydraulic Jack B Jack A Spherical Hinge Laminated neoprene plate
FATIGUE BEHAVIOUR OF SLABS: experimental setup FEATURES OF THE LOADING CYCLE Reproducing a moving wheel Maximum load for European code is 95 kN Slab Test Max load in cycles Frequency [kN] [Hz] S1 cyclic + static 140 1 S2 cyclic + static 290 0.7 S3 cyclic 440 0.2 S4 static
FATIGUE BEHAVIOUR OF SLABS SLAB 1 : max load = 140kN No failure after 1.500.000 cycles European codes predict concrete failure after Max displacement ≈2.5mm 1.138.000 cycles < 6mm = Span/250
FATIGUE BEHAVIOUR OF SLABS SLAB 2 : max load = 290kN 1 2 3 4 5 Test stopped: excessive deformation after 140.000 cycles Max displacement ≈12mm
FATIGUE BEHAVIOUR OF SLABS No bilateral constrain SLAB 3 : max load = 440kN (as damaged connectors) Failure after 400 cycles
FATIGUE BEHAVIOUR OF SLABS SUMMARY OF THE FATIGUE TESTS 95 kN Fatigue life prediction > 3 x 10 8
POST-FATIGUE RESIDUAL PROPERTIES OF SLABS QUASI-STATIC THREE-POINTS BENDING TEST RAMP TO FAILURE LOADING-UNLOADING up to 200kN and 400kN Reduction with respect to S4 Stiffness Strength S1 45,9% 1,2% (140 kN) S2 76,4% 3,4% (290 kN)
POST-FATIGUE RESIDUAL PROPERTIES OF SLABS QUASI-STATIC FAILURE MECHANISMS S1 S2 S4 Post-fatigue Post-fatigue UNFATIGUED 1.500.000 cycles 140.000 cycles max load 140 kN max load 290 kN
HIGH TEMPERATURE EFFECTS ON BEAMS Carvelli V, Pisani M A, Poggi C. Composites Part B, 2013
HIGH TEMPERATURE EFFECTS ON BEAMS BEAM GEOMETRY Bridge slab for cyclic loading
HIGH TEMPERATURE EFFECTS ON BEAMS GFRP REINFORCEMENTS (no shear reinforcement) Longitudinal Reinforcement FIVE CONFIGURATIONS OF REINFORCEMENT Continuous rebars (no overlap) Overlap with bent rebars Overlap 56 cm Overlap 40 cm Overlap 24 cm
HIGH TEMPERATURE EFFECTS ON BEAMS HEATING FEATURES Heating device (max 800 o C) Bottom heating zone
HIGH TEMPERATURE EFFECTS ON BEAMS QUASI-STATIC 3-POINTS BENDING after heating Spherical hinge LVDTs
HIGH TEMPERATURE EFFECTS ON BEAMS EXPERIMENTAL PROGRAM Number of specimens Sample Temperature Heating Imposed bottom Type 23 o C 230 o C 550 o C time Temperature 2 2 1 Continuous rebars [hours] 2 2 2 1 Overlap with bent rebars 23 o C (RT) 3 2 2 1 Overlap 56 cm 1+1.5 230 o C 2 4 Overlap 40 cm 1+1.5 550 o C 5 1 1 Overlap 24 cm 200 150 LOADING HISTORY 50 Load [kN] LVDT 1 40 Loading up to 10 kN and unload LVDT 2 100 Load [kN] 30 Loading up to 20 kN and unload 50 20 LVDT 1 Loading up to 40 kN and unload 10 LVDT 2 0 Loading up to failure 0 0 5 10 15 20 25 0 0.2 0.4 0.6 0.8 1 LVDT displacement [mm] LVDT displacement [mm]
HIGH TEMPERATURE EFFECTS ON BEAMS HEATING PHASE: TEMPERATURE RECORDING Imposed bottom Heating time Temperature [hours] 23 o C (RT) 1+1.5 230 o C 1+1.5 550 o C 300 600 250 500 Rebars Temperature [ o C] Temperature [ o C] ≈400 °C 200 400 temperature 150 300 ≈130 °C TC1 100 200 TC1 TC2 TC2 50 100 TC3 TC3 0 0 Resin T g ≈ 180 °C 0 30 60 90 120 150 0 30 60 90 120 150 180 Time [min] Time [min]
HIGH TEMPERATURE EFFECTS ON BEAMS LOADING RESPONSE continuous rebars 56cm overlap RT continuous rebars T bent rebars T 56cm overlap T 40cm overlap T 24cm overlap T
HIGH TEMPERATURE EFFECTS ON BEAMS LOADING RESPONSE continuous rebars 56cm overlap continuous rebars T bent rebars T 56cm overlap T 40cm overlap T 24cm overlap T
HIGH TEMPERATURE EFFECTS ON BEAMS Room Temperature tests: FAILURE MECHANISM Continuous rebars (no overlap) Overlap with bent rebars Overlap 56 cm Overlap 40 cm Overlap 24 cm
HIGH TEMPERATURE EFFECTS ON BEAMS 550 o C tests: FAILURE MECHANISM Continuous rebars Overlap with bent rebars Overlap 56 cm
HIGH TEMPERATURE EFFECTS ON BEAMS Numerical and analytical modelling Pagani R, Bocciarelli M, Carvelli V, Pisani M A. Engineering Structures, 2014
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