CONCRETE-FILLED FRP TUBES

Transcription

1 Canada Research Chairs CONCRETE-FILLED FRP TUBES FOR PILE APPLICATIONS: AN OVERVIEW Amir Fam, P.Eng. Associate Professor and Canada Research Chair in Innovative and Retrofitted Structures Queen s s University

2 Description of CFFT Fiber Composite tube Conventional concrete pile Concrete core To replace f x, E x f y, E y Layers of fibers oriented at various directions Strength & stiffness in axial & hoop directions

3 Why FRP Tube? Permanent / structural Form-work Multi - directional non-corrosive reinforcement More efficient concrete confinement & protection Ribbed outer surface to improve skin friction or uplift resistance Ice smooth Rough

4 APPLICATIONS

5 Most Common Applications High M, Low N High N, Low M I I I I I Marine Piles Bridge Piers

6 Bridges: Route 40 Bridge, Virginia mm diameter strands #5 gage wire spiral ties 3 in. 508 mm 508 mm 1 in. pitch 3 in. pitch 6 in. pitch 13.1 m 5 turns 16 turns 16 turns 5 turns 3 in. pitch 1 in. pitch 5.4 mm GFRP tube (E-glass / polyester composite) [ ± 34 / 85 / ± 34 ] Concrete f u = 221 MPa (axial), 353 MPa (hoop) E = 15.2 GPa (axial), 17.7 GPa (hoop) Layer 3 Layer 2-34 Layer mm 13.1 m in.

7 Marine Piles (Total ~ piles in US) Washington Texas

8 EXPERIMENTAL BACKGROUND UNREINFORCED CFFTs

9 Bending Tests (M) Compression 350 zone 300 Prestressed pile (Analytical) 6 in. 250 Moment (kip.ft) Tension (cracked) 100 zone 50 0 Test 1 Test 2 Analytical Composite pile Curvature x 10 (1/in.)

10 Axial Load Tests (N) 2.5 Axial Compression Tests Confined Normalized strength stress / f c ksi 3.7 ksi Normalized strain

11 Combined Bending & Axial Load Tests (M & N) 8000 Load 7000 Axial Load (kn) Theoretical Experimental 1000 Tension failure Compression failure Moment (kn.m)

12 Spun-Cast CFFTs.. Lighter for large diameter t = c Sealed Form

13 EXPERIMENTAL BACKGROUND REINFORCED & PRESTRESSED CFFTs

14 Why? Relatively Low Flexural Stiffness GFRP GFRP E = 40 GPa E <<< 40 GPa Objective & Methodology: 1. Use Prestressing or internal reinforcement 2. Tube still contributes longitudinally, but largely for confinement

15 Prestressed CFFTs.. Parameters Degree of prestressing D = 325 mm x y Jacking stress 80%, 40 % f pu Prestress. reinf. ratio: 4, 8 strands Pre-tensioned vs. unbonded post-ten. t = 4.5 mm Laminate structure of tube (Axial / hoop) (y : x) = (1:2), (2:1) (2:1) tube 8 φ 13 steel (2:1) tube 8 φ 13 steel (1:2) tube 4 φ 13 steel (1:2) tube 4 φ 13 steel Spiral 8 φ 13 steel f jack = 0.8 f pu f ce = MPa f jack = 0.4 f pu f ce = 5.36 MPa f jack = 0.8 f pu fce = 5.36 MPa f jack = 0.8 f pu fce = 5.36 MPa Post-tensioned f jack = 0.8 f pu f ce = MPa

16 Fabrication.. Pre-Tensioned Wooden bulkhead Steel abutment GFRP tubes Concrete pump Steel strands Hosepipe

17 Fabrication.Post.Post-Tensioned Inserting strand through ducts Inserting anchorages Hydraulic jack

18 Results 0.2 GFRP tube vs. steel spiral 8 φ 13 steel strands f jack = 0.8 f pu f ce = 10.7 MPa Normalized Moment 0.1 M D o f c M = 3 Normalized Moment 0.15 Steel spiral 0.1 GFRP tube Deflection (mm) Yielding of bottom strands Rupture of tube in tension PCFFT- 4 CFFT ( Literature) Normalized Curvature [ψ.d o ] ( x10-3 )

19 Failure Modes Crushing after yielding of tension strands (No tube) Failure of tube in comp. side after yielding of strands Hydraulic jack Tension failure of tube after yielding of strands

20 GFRP Tube GFRP Tube Spiral Spiral None None 10M 10M steel steel 1.6% 1.6% 15M 15M steel steel 3.2% 3.2% 5/8 5/8 GFRP GFRP 3.2% 3.2% 3/8 3/8 GFRP GFRP 1.1% 1.1% 15M 15M steel steel 3.2% 3.2% 15M 15M steel steel 3.2% 3.2% 3/8 3/8 CFRP CFRP 1.1% 1.1% Cardboard tube Cardboard tube GFRP tube GFRP tube GFRP GFRP Bars Bars Steel Steel Spiral Spiral Reinforced Reinforced CFFTs CFFTs

21 Flexure Effect of Tube Tension Compression Steel 3.2% Load (kn) With Tube: 40 1) Progressive Warning Signs of Failure 20 0 Steel 3.2% 2) Higher Strength Deflection (mm) Confinement Steel 3.2% 3) 0Still Confining After Axial Tension and Compression Failures

22 Flexure.. Effect of Rebar Type 140 Steel rebar 3.2% Load (kn) GFRP rebar 3.2% 40 GFRP Rebar vs. Steel Rebar: 20 1) Comparable Moment Capacity (GFRP 5% Higher) 2) No Ductility 0 Compared to Steel FRP rebar not justified in this case.also no corrosion risk! Deflection (mm)

23 Shear Steel Spiral FRP Tube Shear Stress (MPa) Deflection (mm)

24 EXPERIMENTAL BACKGROUND PILE DRIVING, JOINTS & SPLICES

25 Joint to RC Beam.Route 40 bridge, VA 39.4 in. 30 in. 18 in in. 6 in. 6 No.7 No.4@ 6 in. 2 No.4 2 No.4 2 No.4 2 No.8 4 No in in.

26 Splicing a Long Pile Steel plate I-shape key 8 No. 20, 2.7 m T- groove Threaded end steel rebar screwed into plate

27 Pile Driving Driving 1 st segment Splicing 2 nd segment Firm silty clay soil Conventional pile driving hammer (rated energy = 3665 kg.m) 50 mm thick wooden cushion Piles were driven to depth = 14.3 m

28 Pile Extraction 600 mm diameter holes drilled around pile

29 Effect of Driving on Flexure, Spliced Pile 275 load (kn) Reduction > 4 % Control undriven Control undriven Driven Deflection (mm)

30 Splice Effectiveness - Failure Mode M r = 200 kn.m (unspliced) crushing M r = 215 kn.m Fracture of bars slip

31 EXPERIMENTAL BACKGROUND DURABILITY

32 Experimental Program Hydraulic ram Load cell CFFT specimens Steel plates Threaded rods 50% Sustained load Freeze-thaw cycles Temp. ( C) Concrete core Air Time (hrs)

33 Results Confined strength (MPa) Normal weight ( = 22 MPa) FS-nw F-nw f ' c RS-nw R-nw Light weight ( = 41 MPa) FS-lw F-lw ' f c RS-lw R-lw 0 Freeze-Thaw + Sustained load Control Freeze-Thaw + Sustained load Control

34 ANALYSIS & DESIGN

35 Classical Lamination Theory - ULF FRP / constitutive relationships x y 1 Classical lamination theory Progressive & ULF approach θ 1 Predicted θ 2 Input: 0 [ E 12 G θ ] E1 2 Output: [ E E,...] x Stress (MPa) y Experimental Failure of [-88] 5 layers n υ K=1 C Strain ( x 10-3 ) Failure of [+8] 4 layers +8 o 40% E y T 60% -88 o T E x

36 Flexural Analysis - Equilibrium - Strain compatibility Layer - by - layer / cracked section analysis For ε = M & ψ =?? M =? c ε = ψ C f shell concrete C c T T c f M = ψ = strain d 2 y ψ = y = d x 2 Moment - area method stresses ψ dx dx = y ψ 1

37 Axial Load Analysis & Confinement ε cc Use radial displacement compatibility to estimate the confining pressure: σ R Radial σ R =? u R u R u R = u R ( ) tube ( ) core ε cc u R σ R u R Only the core is loaded: σ R R = R E t Core and tube are loaded: σ = s s υc ε 1 υc + E ( υc υ s ) ε R 1 υc + E t E c c cc cc

38 Failure Criteria σ x (tension) σ y (Comp.) σ x (tension) at failure σ x = ( σ x ) u at failure σ x < ( σ x ) u axial compressive strength ( σ ) y u σ y stress path σ x bi-axial stress failure envelope (Tsai-Wu) ( σ x ) u hoop tensile strength

39 Beam Column Analysis 300 mm Axial Load (kn) Small e Fibre Ratio (Axial : Hoop) 1:9 1:1 9:1 t = 2 mm D/t = Large e Bending Moment (kn.m)

40 Sample Design Charts Unreinforced CFFT Moment-curvature design charts of the composite piles in bending Moment (kn.m) Axial load (kn) FOS = FOS = FOS = Axial load - strain design charts of the composite piles Axial load (kn) Axial load moment interaction charts for composite piles 16.5 in in in in. in in in in in in in FOS = in FOS = 2 FOS = 3 Curvature (1/m) Balanced condition Axial strain (mm/mm) Bending moment (kn.m)

41 Sample Design Charts Reinforced CFFT Rebar Reinf.. Ratio - Varied from 0 to 4.8% Moment (kn m) Varied from 3 Hoop:1 Axial 4.8% to 1 Hoop:3 Axial H:3A 3.2% 70 1H:1A 1.6% % 3H:1A % Curvature (m 40-1 ) Moment (kn m) Tube Laminate Structure Varied from 3 Hoop:1 Axial to 1 Hoop:3 Axial 0 Moment (kn m) Concrete Strength - Varied from 25 to 75 MPa MPa 25 MPa Curvature (m -1 ) Curvature (m -1 )

42 Closing Remarks. Fundamental research on CFFTs is well established.. Mechanics & behavior are now very well understood For some products design charts readily available.. No single simple equation like conventional RC (at least not yet). What is needed is more field applications.engineering community needs awareness, encouragement & realization of system & advantages

43 Acknowledgements All my Graduate Students ISIS Canada Lancaster Composite VDOT Queen s s University Virginia Tech

44 Thank You, (613) Check out ACI Committee ask for J