FATIGUE BEHAVIOR AND HIGH TEMPERATURE EFFECTS Valter Carvelli - - PowerPoint PPT Presentation
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
Politecnico di Milano
SOME APPLICATIONS OF GFRP (Glass Fiber Reinforced Polymer) REBARS IN CONCRETE STRUCTURAL ELEMENTS
Some advantages:
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” ………..……
High temperature effects on beams Materials features
Cycle period Load jack A jack B 500000 1000000 1500000 cycles number 2 4 6 8 10 displacement [mm] slab S1 - max load 140kN Jack A: max Jack A: min Jack B: max Jack B: min Fatigue behaviour of slabs
Open discussion
Numerical and analytical modelling
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
Unidirectional pultruded bars (E-glass fibre / vynilester) External surface: sanding of quartz and wrapping of aramidic yarn
Experimental static tensile properties Ø16mm: E ≈ 39 GPa sult ≈ 885 MPa
(Fibre volume fraction ≈ 60%) test of rebars: Ø 16÷40mm
GFRP REBARS
TENSILE STRENGTH VS. TEMPERATURE
GFRP REBARS
Nigro et al., CICE 2008 Conference (CFRP bars)
GFRP REBARS
Wang et al., Composite Structures, 2007 (GFRP + CFRP bars)
TENSILE STRENGTH VS. TEMPERATURE
Experimental measurements of concrete C55/67
STRENGTH VS. TEMPERATURE
CONCRETE
23 200 500 23 200 500
Temperature [oC]
1 2 3 4 5
Tensile strength [MPa]
4.0 2.8 1.1 (indirect tensile test, EN 12390-6) (cylinder strength)
Design quality: C55/67 characteristic cubic strength = 67 MPa Experimental cubic strength (average of 16 samples) ≈ 66 MPa FATIGUE LIFE IN COMPRESSION European Codes: Palmgren-Miner rule
m i i i
1
number of intervals with constant amplitude actual number of constant amplitude cycles ultimate number of constant amplitude cycles
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
CONCRETE
GFRP REBARS - CONCRETE ADHESION
6 8 10 12 14 16 18 20 22 24 26 nominal diameter Ø [mm] 5 10 15 20 tmax [MPa] GFRP rebar Steel rebar
PULL-OUT Test BEAM- Test
5 10 15 20 tmax [MPa] Pull-out Beam-test GFRP Ø12mm
Steel rebar Fava G., Carvelli V., Pisani M.A., to appear
Personal knowledges Lack or very few investigations on
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
Carvelli V, Pisani M A, Poggi C. Composites Part B, 2010
LOAD CONDITIONS FOR TRAFFIC ON BRIDGES European Codes define five fatigue load models.
Among those the most heavy condition is for a twinned wheel:
To accelerate the failure of the slabs in the experimental fatigue tests: minimum load in cycles 140 kN (+48%) contact area 20x30cm (-400%) European Code 1 and 2 as guidelines for slab design
Length L = 500 cm Width W = 248 cm Thickness t = 20 cm Span length S = 150 cm
BRIDGE SLABS GEOMETRY
5 . 7 t W 37 . 1 S D D
small influence of free edges minimize the arch effect
S W t L
Transverse Longitudinal
Longitudinal Reinforcement Transverse Reinforcement
GFRP REINFORCEMENT OF THE SLABS
Ø12/20cm Ø16/10cm Ø16/10cm Ø16/20cm
The bottom reinforcement was designed to reduce the slab deformability: maximum displacement < Span/250 = 6mm bottom top
Manufacturing
CONSTRAINS SIMULATION
Cylindrical support (Ø 50mm) Layer of rubber (5mm thick)
Service condition
Bilateral constrain (as connectors)
5 displacement transducers LVDT (max 50 mm)
DISPLACEMENT MEASUREMENT DEVICES
LOADING SETUP
Hydraulic Jack A Hydraulic Jack B Contact area for European code is 40x60cm. Contact area
20cm 30cm
Hydraulic Jack A
Spherical Hinge Laminated neoprene plate
LOADING SETUP
Hydraulic Jack B
FEATURES OF THE LOADING CYCLE
Maximum load for European code is 95 kN
Reproducing a moving wheel
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
SLAB 1 : max load = 140kN
Max displacement ≈2.5mm < 6mm = Span/250
No failure after 1.500.000 cycles
European codes predict concrete failure after 1.138.000 cycles
SLAB 2 : max load = 290kN
1 2 3 4 5
Test stopped: excessive deformation after 140.000 cycles
Max displacement ≈12mm
SLAB 3 : max load = 440kN Failure after 400 cycles
No bilateral constrain (as damaged connectors)
SUMMARY OF THE FATIGUE TESTS
Fatigue life prediction > 3 x 108 95 kN
QUASI-STATIC THREE-POINTS BENDING TEST
Reduction with respect to S4 Stiffness Strength S1 45,9% 1,2% S2 76,4% 3,4%
(140 kN) (290 kN)
LOADING-UNLOADING up to 200kN and 400kN RAMP TO FAILURE
QUASI-STATIC FAILURE MECHANISMS S4 S2 S1
UNFATIGUED Post-fatigue 140.000 cycles max load 290 kN Post-fatigue 1.500.000 cycles max load 140 kN
Carvelli V, Pisani M A, Poggi C. Composites Part B, 2013
BEAM GEOMETRY
Bridge slab for cyclic loading
Longitudinal Reinforcement
GFRP REINFORCEMENTS
(no shear reinforcement)
Continuous rebars (no overlap) Overlap with bent rebars Overlap 56 cm Overlap 40 cm Overlap 24 cm
FIVE CONFIGURATIONS OF REINFORCEMENT
HEATING FEATURES
Heating device (max 800 oC)
Bottom heating zone
QUASI-STATIC 3-POINTS BENDING after heating
LVDTs Spherical hinge
EXPERIMENTAL PROGRAM
LOADING HISTORY
5 10 15 20 25 LVDT displacement [mm] 50 100 150 200 Load [kN] LVDT 1 LVDT 2
0.2 0.4 0.6 0.8 1 LVDT displacement [mm] 10 20 30 40 50 Load [kN] LVDT 1 LVDT 2
Number of specimens Sample Temperature Type 23oC 230oC 550oC 1 2 2 2 2 2 1 3 2 2 1 4 2 5 1 1
Continuous rebars Overlap with bent rebars Overlap 56 cm Overlap 40 cm Overlap 24 cm
Heating time Imposed bottom Temperature [hours] 23oC (RT) 1+1.5 230oC 1+1.5 550oC
HEATING PHASE: TEMPERATURE RECORDING
30 60 90 120 150 Time [min] 50 100 150 200 250 300 Temperature [oC] TC1 TC2 TC3 30 60 90 120 150 180 Time [min] 100 200 300 400 500 600 Temperature [oC] TC1 TC2 TC3
Heating time Imposed bottom Temperature [hours] 23oC (RT) 1+1.5 230oC 1+1.5 550oC
Resin Tg ≈ 180 °C ≈400°C ≈130°C Rebars temperature
T T T T T continuous rebars bent rebars 56cm overlap 40cm overlap 24cm overlap
LOADING RESPONSE
56cm
RT continuous rebars
LOADING RESPONSE
T T T T T continuous rebars bent rebars 56cm overlap 40cm overlap 24cm overlap
56cm
continuous rebars
Overlap 56 cm
Room Temperature tests: FAILURE MECHANISM
Continuous rebars (no overlap) Overlap with bent rebars Overlap 40 cm Overlap 24 cm
550oC tests: FAILURE MECHANISM
Continuous rebars Overlap with bent rebars
Overlap 56 cm
Pagani R, Bocciarelli M, Carvelli V, Pisani M A. Engineering Structures, 2014
Analytical model: constitutive behaviour of materials GFRP REBARS
Hypotheses linear elastic behaviour of GFRP and elasto-“plastic” of concrete perfect bond between concrete and GFRP rebars planarity of the cross-section after bending throughout temperature exposure
Elastic modulus vs. temperature
12 4.3
0.28 20 0.28 6 10
g g
E T E C T
Nigro et al. Composites Part B, 2014
3 4
20 tanh 7.91 10 320.35 0.525 0°C T 400°C 20 0.25 4.17 10 400 T 400°C
g g g
E C T if E T E C T if
Yu et al. Composite Structures, 2013
Thermal strain
6
6.58 10 20
th g T
T C
coefficient of thermal expansion
CONCRETE
EN 1992-1-2:2005, Euro Code 2 Stabler J. The University of Queensland, 2000
Elastic modulus vs. temperature Thermal strain
4 6 11 3 3
1.8 10 9 10 2.3 10 20 700 14 10 700 1200
th c
T T if C T C T if C T C
2
1 0.2 0.01 0.2 0.01 0.01 0.2 20 20 800 800
c c
T T E C if C T C E T if T C
Tensile strength vs. temperature
20 20 100 100 1.0 20 100 600 500
ct ct ct
f C if C T C f T T f C if C T C
EN 1992-1-2:2005, Euro Code 2
Analytical model: constitutive behaviour of materials
CONCRETE
Sargin M. University of Waterloo, 1971 Carreira D C, Chu K H. ACI Journal 1986
Tensile stress-strain relationship Compressive stress-strain relationship
EN 1992-1-2:2005, Euro Code 2
2 2 2 2 2
2 1 1
el el c c el el c c el el c c cu c el c el c
D f T if T D s
2
0.002
el c
10 1
el c ct el ct el el el c ct c ct el c el ct
f T T if T T T
s
el ct ct c
T f T E T 1.5
Analytical model: constitutive behaviour of materials
ANALYTICAL MODEL
( ) el el el c g cj cj cj cj cj gi gi gi gi j i A
M y dA y w b y A s s s
weights of the Gaussian integration
moment M corresponding to the curvature
GFRP reinforcement area section width at integration point
tot
non-linear equation solved by an iterative Newton–Raphson scheme
Position of the neutral axis
tot G tot
X y
total axial strain in the centre of gravity
* * tot tot j j j j beam
M dx w M
Section displacement
bending moment distribution due to a single unit virtual force
NUMERICAL FE MODELLING of beam with continuous rebars
Plane stress model (2D) Three-dimensional model (3D)
reinforcement modelled as strips having equivalent area of the GFRP bars
d.o.f. n° CPS4T elements 7239 2268 d.o.f. concrete n° C3D8T elements rebars n° C3D4T elements 170796 31992 23178
NUMERICAL FE MODELLING of beam with continuous rebars
HEATING PHASE SIMULATION (adopted in the analytical model)
Concrete moisture content
2D model 3D model Prediction of the temperature distribution
Experimental imposed temperature
ANALYTICAL and NUMERICAL RESULTS
Beam with continuous rebars - ROOM TEMPERATURE
ANALYTICAL MODEL RESULTS
Beam with continuous rebars - MAX TEMPERATURE 550°C
12 4.3
0.28 20 0.28 6 10
g g
E T E C T
3 4
20 tanh 7.91 10 320.35 0.525 0°C T 400°C 20 0.25 4.17 10 400 T 400°C
g g g
E C T if E T E C T if Nigro et al. Composites Part B, 2014 Yu et al. Composite Structures, 2013
ANALYTICAL and NUMERICAL RESULTS
Beam with continuous rebars - MAX TEMPERATURE 550°C