Deflection of GFRP RC Beams

Transcription

1 Raed Al Sunna (1,2), Kypros Pilakoutas (1), Peter Waldron (1), Maurizio Guadagnini (1), Tareq Al Hadeed (2) (1) University of Sheffield - UK (2) Royal Scientific Society - Jordan

2 OUTLINE - Background - Methodology - Experimental Programme - Experimental Results - Conclusions

3 BACKGROUND Serviceability-controlled design ACI 44.1R-3 I β e d = I cr + M cr ( βd I g Icr ) I g E f = αb + 1 Es M α b = bond coefficient =.5 a fib, 2 nd International Congress 3 Force, kn β d =.6, ( α b =.5) BG2a ACI 318 ACI 44.1 R IStructE (1999) - Steel RC equations applicable 1 linear cracked section Midspan Deflection, mm

4 BACKGROUND Key Variables - Reinforcement Ratio - Modulus of Elasticity - Bond Characteristics (Tension Stiffening) Other Variables - Concrete cover - Concrete Strength - Rebar diameter Helically wrapped Indented Indented Braided Sand coated Ribbed Ribbed

5 Experimental: - Structural tests: (Beams and Slabs, CFRP and GFRP) - Material tests (Concrete and rebars) fib, 2 nd International Congress METHODOLOGY Analytical: - Sectional analysis - Finite element analysis

6 EXPERIMENTAL PROGRAMME (GFRP RC Beams) 2Ø6mm stirrups, Ø8mm/75mm Ø6mm 25 stirrups, Ø8mm/75mm 25mm to bars 25

7 EXPERIMENTAL PROGRAMME (GFRP RC Beams) Rebar type Series designation Beam designation Rebar details Reinforcement ratio Relation to control steel beam BG1 BG1a BG1b Equal flexural capacity GFRP BG2 BG2a BG2b Equal area of rebars BG3 BG3a BG3b Equal stiffness of rebars Steel BS BSa BSb

8 EXPERIMENTAL PROGRAMME (GFRP RC Beams) Rebar type Nominal diameter, (mm) Modulus of elasticity, (MPa) Tensile strength, (MPa) GFRP FRP rebar Plastic end-piece Epoxy Steel tube Grips of tension machine

9 fib, 2 nd International Congress EXPERIMENTAL PROGRAMME (GFRP RC Beams) Strain Gauge on Rebar Strain Gauge on concrete 1/3 shear span Helical arrangement Detail of 1 strain gauges, No. (5-14), at midspan zone. Anticipated natural crack 18 mm Midspan forced crack mm 9 mm 22.5 mm Anticipated natural crack Straight arrangement

10 EXPERIMENTAL PROGRAMME (GFRP RC Beams) Dial Gauge LVDT

11 EXPERIMENTAL PROGRAMME (GFRP Beams)

12 EXPERIMENTAL RESULTS Load, kn Rebar Strain, microstrain 1 Strain Gauge 1 Strain Gauge 9 Strain Gauge 8 Strain Gauge 7 Strain Gauge 6 Strain Gauge 5 Cracked-section analysis Strain Gauge 15 Cracked-Section Analysis Concrete Strain, microstrain Load, kn Rebar Strain, microstrain Distance From Support, mm Crack Locations 8. kn 6. kn 4. kn 2.3 kn (just after adjacent crack) 14. kn (just after first crack) 13.3 kn (before cracking) Load, kn curvature derived from experimental strains Cracked-section analysis Curvature, m -1

13 EXPERIMENTAL RESULTS LVDT L6 Cracked-section analysis Flexural deflections derived from experimental curvatures Midspan Deflection, mm Load, kn Stress at crack, in MPa strain at crack 1. average strain between cracks strain, in microstrain Average Bond Stress, MPA Average Bond, MPa two cracks adjacent to crack inducer 1st crack at crack inducer Stabilized cracking phase Distance From Support, mm Average strain, microstrain

14 EXPERIMENTAL RESULTS Load = 2.8 kn Average crack width =.13 mm Standard Deviation =.6 9 BC2a 8 7 Note: Crack widths in flexure zone, at the bottom concrete fibre. Load, kn LVDT L8 Load = 31.8 kn Average crack width =.19 mm Standard Deviation =.6 BC2a 3 calculated from rebar strains 2 1 Measured at bottom concrete fibre Load = 47.2 kn Average crack width =.27 mm Standard Deviation = Crack Width, mm BC2a Load = 74.7 kn Average crack width =.4 mm Standard Deviation =.1 BC2a

15 14 12 EXPERIMENTAL RESULTS Beams BG, BS ρ f =.39 1 Load [kn] ρ s =.68 ρ f =.43 ρ f =.77 BG1a BG1b BG2a BG2b BG3a BG3b BSa BSb Midspan Deflection [mm]

16 FINITE ELEMENT ANALYSIS

17 FINITE ELEMENT ANALYSIS Load, kn Rebar Strain, microstrain 1 Strain Gauge 1 Strain Gauge 9 Strain Gauge 8 Strain Gauge 7 Strain Gauge 6 Strain Gauge 5 Cracked-section analysis FE Analysis Strain Gauge 15 Cracked-Section Analysis FE Analysis Concrete Strain, microstrain Load, kn LVDT L6 Cracked-section analysis Flexural deflections derived from experimental curvatures FE Analysis Midspan Deflection, mm Load, kn Rebar Strain, microstrain Distance From Support, mm Crack Locations 8. kn 6. kn 4. kn 2.3 kn (just after adjacent crack) 14. kn (just after first crack) 13.3 kn (before cracking) FE Analysis FE Analysis

18 CONCLUSIONS Behaviour of GFRP RC beams: Deflection of GFRP RC is mainly caused by flexural curvatures. Shear-induced deflections may not be negligible for low reinforcement ratios and deep-penetrating wide cracks. The response of the compressive concrete zone requires further consideration due to the increased localised effect of cracks. GFRP RC show good bond. fib, 2 nd International Congress CSA predicts the maximum rebar strain at a crack, underestimates the extreme-fibre concrete strain, and when shear induced deformations are sizeable may not provide an upper-bound deflection.

19 ACKNOWLEDGEMENTS The Higher Council for Science and Technology (Jordan) The Royal Scientific Society (Jordan) The University of Sheffield (UK) The Karim Rida Said Foundation (UK)