GFRP REINFORCED GFRC FOR THIN PERMANENT FORMWORK APPLICATIONS

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1 GFRP REINFORCED GFRC FOR THIN PERMANENT FORMWORK APPLICATIONS Dr. Gi Beom KIM, Prof. P. WALDRON, Prof. K. Pilakoutas July, 2007 Presented by Gi Beom KIM

2 Outline New systems incorporating GFRP reinforced GFRC Interaction between FRP and GFRC Bond (GFRC and FRP) GFRC tensile characteristics Deflections Shear capacity Maximise span / length of unreinforced thin GFRC element Design guidelines for FRP / GFRC thin structural elements

3 Introduction Thin concrete permanent formwork and other structural elements Minimum cover for durability; For aggressive environments, minimum 100mm thickness GFRC is lightweight, high strength and has excellent resistance to corrosion FRP reinforcement can be used to structurally reinforce GFRC to enable the development of much larger spans

4 Main design issues Bond Tension stiffening Deflections Shear capacity GFRP reinforced GFRC of thin panels

5 Bond behaviour in GFRC Dongbu Corporation Standard pull-out tests Splitting pull-out tests GFRC cubic block specimens (200 x 200 x 200 mm) LVDTs 1 Bond Stress (MPa) Loaded end 2. Free end 3. Net extension 4. Crack LVDTs 3 LVDTs 1 Rubber Rubber LVDTs Crack Width (mm) Slip (mm) Mounting Rig Pull-out Force = F LVDTs 2 LVDTs 4 Mounting Rig Pull-out Force = F Bond Stress (MPa) Loaded end 2. Free end 3. Net extension GFRC prismatic elements (30 or 40 x 200 x 100 mm ) Slip (mm)

6 Bond behaviour in GFRC Dongbu Corporation MATERIALS - W/C = 0.35, S/C = f c = 54 and 66 MPa - f ct = 6 and 7MPa (by Brazilian Test ) -f t_steel = 500 MPa, f t_gfrp = 900 MPa - E GFRP = 41 GPa, E steel = 205 GPa Summary of test results Specimen type Strength (MPa) Bond strength, t (MPa) Normalised bond strength, t (MPa) GFRC GFRC Plain concrete GFRP reinforced GFRC similar to steel RC Pull-out resistance of FRP is greater in GFRC (by 16%)

7 Optimised Section Dongbu Corporation Thin GFRC section (t = 10 mm) was chosen after an optimisation exercise* was undertaken to identify the sections that minimise weight for a particular span * Kim, G. B., Development of thin FRP GFRC permanent formwork systems PhD Thesis,, Department of Civil and Structural Engineering, Sheffield, UK, 2006.

8 Test specimens Structural Testing (I) L15G3 (II) L30G3 (III) L30G2

9 GFRC tensile characteristics Dongbu Corporation To evaluate the GFRC tensile characteristics GFRC panel (L15G3) Reinforced with 3% (by weight) of chopped glass fibre Length of panel = 1500 mm Four point loads test

10 Optimised Section Load (kn) Softening model with trilinear gives the best results!! Experiment (L15G3) a) Elastic - plastic b) Elastic - hardening c1) Elastic - softening (Linear) c2) Elastic - softening (Trilinear) Midspan deflection (mm) ε tu = 0.05

11 Deflections of FRP GFRC Dongbu Corporation Two GFRC panels (L30G2, L30G3) Reinforced with 2 and 3% (by weight) of chopped glass fibre Single 8mm square rebar Length of panel = 3000 mm Four point loads test

12 Deflections of FRP GFRC Both panels achieved remarkable deformations up to about 110mm before shear failure Excessive deformation is normally the governing design criterion for thin permanent formwork, especially for long spans Acceptance deflection limits for this type are limited to L / 250

13 Deflections of FRP GFRC Test Results: Flexural capacity I M = cr cr, e d g M β 1 a 3 I M + M cr a 3 I cr I g Load (kn) 8 6 β d E f = α b + 1 Es L30G3 - Exp. L30G3 - ACI440 L30G2 - Exp. L30G2 - ACI Central Deflection (mm) Bond dependent coefficient ACI440 equations are appropriate for thin GFRC reinforced with FRP

14 Shear capacity Dongbu Corporation Two GFRC panels (L30G2, L30G3) Reinforced with 2 and 3% (by weight) of chopped glass fibre Single 8mm square rebar Length of panel = 3000 mm Four point loads test Both panels failed due to the shear

15 Test Results: Shear capacity Shear capacity Load (kn) Central Deflection (mm) V cd RILEM TC162-TDF V = V + V + V RILEM recommendation shown to offer the least conservative estimate of shear resistance c cd 1/ 3 [ 0.12k( 100ρ f ) ] b d = σ 1 ck cp w V fd fd = 0.7k f k τ l fd V b w wd sw wd = ywd d A s 0.9df (1 + cot α) sinα

16 t Design thin FRP GFRC Dongbu Corporation Type W 1 = 10mm Type W 2 = 20mm Type W 3 = 20mm Type W L d =200 (typical of buildings) L d =500 (typical of bridges) For the cracked section, the crack widths and deflections are calculated by using the ACI 440 equations 8 mm square GFRP rebar w Shear capacity is calculated by using the RILEM TC162.

17 Analysis of thin FRP GFRC Type W 1 ( t w =10mm, t t = 10mm) Ww I (mm 4 ) (kg/m) y b (mm) y t (mm) Type W Type W Type W GFRP square rebar (mm) f t (MPa) f t M sag M hog L d=200 L d=500 (MPa) (kn-m) (kn-m) (mm) (mm) Crack Deflection Flexure Shear width (<L/250) (<0.5) M ult L d=200 P ult, L d=200 (kn-m) (mm) (kn) (mm) L d=200 (mm) L d=200 (mm) For slabs up to 200mm thick (Building) 2.23m 3.85m For slabs up to 500mm thick (Bridge) 1.33m Beyond 2.6m, it could have problems with deflection and or cracking, as shown Table.

18 Type W 2 ( t w =20mm, t t = 10mm) Ww (kg/m) I (mm 4 ) y b (mm) y t (mm) f t (MPa) M sag (kn-m) M hog (kn-m) L d=200 (mm) L d=500 (mm) For slabs up to 200mm thick (Building) Type W m Type W Type W For slabs up to 500mm thick (Bridge) GFRP square rebar (mm) f t (MPa) Flexure M ult L d=500 (kn-m) (mm) Shear P ult, L d=500 (kn) (mm) Deflection (<L/250) L d=500 (mm) Crack width (<0.5) L d=500 (mm) 1.43m m Beyond 1.8m, it will have problems with deflection and possible cracking, as shown Table.

19 Type W 3 ( t w =20mm, t t = 20mm) Ww I (mm 4 ) (kg/m) y b (mm) y t (mm) Type W Type W Type W GFRP square rebar (mm) f t (MPa) f t M sag M hog L d=200 L d=500 (MPa) (kn-m) (kn-m) (mm) (mm) Crack Deflection Flexure Shear width (<L/250) (<0.5) M ult L d=500 P ult, L d=500 (kn-m) (mm) (kn) (mm) L d=500 (mm) L d=500 (mm) For slabs up to 200mm thick (Building) 2.49m For slabs up to 500mm thick (Bridge) 1.48m 2.93m Beyond 1.9m, it will have problems with deflection and possible cracking, as shown Table.

20 For slabs up to 200mm thick (Building) Hogging Moment!! W1 4.8m EBR 10.0m For slabs up to 500mm thick (Bridge) W2 3.1m EBR 7.0m W3 3.8m EBR 7.8m

21 Conclusions For design purposes for FRP RC GFRC - Modified ACI 440 equation can be used for deflections and crack widths - Modified RILEM TC162 equations can be used for shear For building slabs up to 200mm thick, W shape - Without reinforcement SS up to 2.23m; Reinforced up to 3.85m, - With intermediate support and EBR, a total span of 10m is possible. A 3.29m by 0.5m panel weights less that 55kg and can be put in place by two men For bridge slabs up to 500mm thick, - Without reinforcement SS up to 1.43m; Reinforced up to 2.66m, - With intermediate support and EBR, a total span of 7.8m is possible.

22 Thank you for your attention!!