Composite Structures made of Ultra-High Performance Concrete and Carbonfiber-Reinforced Polymers

Transcription

1 9 th fib International PhD Symposium in Civil Engineering, Karlsruhe, Germany, July 22 th 25 th 2012 Composite Structures made of Ultra-High Performance Concrete and Carbonfiber-Reinforced Polymers Dipl.-Ing Univ.-Prof. Dr.-Ing. Institute for Structural Design Graz, University of Technology

2 Content of the Presentation 1. Motivation 2. Key Steps 3. Introduction into Materials 4. Methods 5. Results 6. Conclusion and Outlook

3 Motivation

4 Motivation Development of thin-walled composite structures made of UHPC and CFRP Characterized by low self-weight, high durability and simplicity Robust alternative to prefabricated steel, timber or normal concrete elements Substitution of short steel fiber reinforcement in UHPC UHPC CFRP 2.5 cm Figure: UHPC-Plate with centric CFRP-strip

5 Motivation 1.1 cm 1.8 cm Figure: Carbon Grid Sigratex 600, Company SGL Germany

6 Motivation PRESTRESSED CFRP-STRIPS WITH SANDED SURFACE Figure: CFRP-Strip SGL Sigrafil 20 x 3 mm

7 Motivation Figure: Concept of a folded plate structure made of UHPC with CFRP-reinforcement

8 Key Steps

9 Key Steps Research into the bond behavior of UHPC and (prestressed) CFRP-strips UHPC CFRP-STRIP Figure: Test concept for evaluation of pre-stressing Figure: Pull-out test for investigation of bond behavior

10 Key Steps Research into the bending behavior of UHPC with CFRP-reinforcement and into influence of pre-stressing. Figure: 4-point bending test

11 Key Steps Evaluation of technical and economical feasibility by building a prototype Figure: Structure made of prefabricated folded plate elements

12 Introduction into Materials

13 Introduction into Materials Table: Mechanical properties of normal concrete C25/30 and UHPC with 2.5 vol.-% steel fibers Characteristic Concrete UHPC values C25/ Specific weight [kn/m³] Elastic modulus [N/mm²] Compressive strength [N/mm²] Breaking strain [ ] Tensile strength [N/mm²] Thermal expansion coefficient [10-6 /K] 10 11

14 Introduction into Materials 200 UHPC C C Stress c [N/mm²] C 100/115 C 100/115 C 80/95 C 80/95 UHPC C 150 UHPC C 150 Good balance between compressive strength and factory costs 50 C 60/70 C 60/70 C 40/50 C 40/50 C 25/30 C 20/25 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 Strain [ ]

15 Introduction into Materials Table: Mechanical properties of different materials Characteristic Steel GFRP CFRP values S 235 JR rebar lamella Specific weight [kn/m³] Elastic modulus [N/mm²] Tensile strength [N/mm²] Breaking strain [ ] Thermal expansion coefficient [10-6 /K] Therm. conductivity [W/mK] nr * * not reported by manufactures. Used material for CFRP-strips!

16 Stress [N/mm²] Introduction into Materials UHPC without fibers Tension Compression 0 Strain [ ]

17 Stress [N/mm²] Introduction into Materials UHPC with fibers Tension Compression 0 Strain [ ]

18 Stress [N/mm²] Introduction into Materials UHPC without CFRPreinforcement fibers Tension Compression 0 Strain [ ]

19 Stress [N/mm²] Introduction into Materials UHPC without pre-stressed fibers CFRP-strips and Carbo-grids Tension Compression 0 Strain [ ]

20 Results

21 Results Pull-out tests according to RILEM recommendations bond behavior of thin CFRP-strips and UHPC in principle influences of surface roughening Figure: Experiment setup Figure: Formwork

22 Results Figure: Investigated surfaces

23 Results Pull-out test experimental setup: Crosshead travel Slip

24 bond stress [N/mm²] Results Bond stress - slip relationship measured at the load-free end: 10 Test series 1: Smooth surface 8 6 test series 1a test series 1b test series 1c ,00 0,05 0,10 0,15 0,20 slip [mm]

25 bond stress [N/mm²] Results Bond stress - slip relationship measured at the load-free end: 10 Test series 2: Fine sanded surface test series 2a test series 2b 2 test series 2c 0 0,00 0,05 0,10 0,15 0,20 slip [mm]

26 bond stress [N/mm²] Results Bond stress - slip relationship measured at the load-free end: 10 Test series 3: Rough sanded surface 8 test series 3a test series 3b 6 test series 3c ,00 0,05 0,10 0,15 0,20 slip [mm]

27 bond stress [N/mm²] Results 10 8 test series 3a test series 3b 6 test series 3c ,00 0,05 0,10 0,15 0,20 slip [mm] Table: Mean values and coefficients of variation (COV) of maximum bond stress and corresponding slip Characteristic test test test values series 1 series 2 series Number of tests Maximum bond stress COV Corresponding slip (mm) COV

28 Bond stress [[N/mm²] Results Bond stress - crosshead travel relationship: 10 Area 1: Static Friction Area 2: Slip & Stic Area 3: Dynamic Friction 8 6 Probereihe 2a Probereihe 2b Probereihe 2c Crosshead travel [mm]

29 Results 3-point-/ 4-point-bending to explore: failure mechanism load capacity stiffness influence of reinforcement ratio influence of pre-stressing crack formation Figure: 4-point bending test

30 Results 20 cm Test series 1 ρ CFK = 1.68 % ρ Fiber = 1.00 % 2.5 cm Test series 2 ρ CFK = 0.00 % ρ Fiber = 1.00 % 2.5 cm Figure: Experiment setup 4-point bending test

31 bending moment [knm] Results Bending moment - deformation relationship: Test series 2: steel fibers only 3,50 3,00 2,50 2,00 1,50 test series 2a test series 2b test series 2c 1,00 0,50 0, deformation [mm]

32 bending moment [knm] Results Bending moment - deformation relationship: Test series 1: steel fibers only + 3 centric CFRP-strips 3,50 3,00 test series 1a 2,50 test series 1b 2,00 1,50 1,00 0,50 0, deformation [mm]

33 bending moment [knm] bending moment [knm] Results 3,50 3,50 3,00 test series 2a 3,00 2,50 test series 2b test series 2c 2,50 test series 1a test series 1b 2,00 2,00 1,50 1,50 1,00 1,00 0,50 0,50 0, , deformation [mm] deformation [mm] Table: Mechanical properties of the investigated plate elements Characteristic test test values series 2 series Number of tests 3 2 Max. bending moment 40 kncm 287 kncm % Crack moment 31 kncm 35 kncm + 12 % Bending stiffness EJ I kncm² kncm² + 35 % Bending stiffness EJ II kncm² Average crack distance cm

34 Results continuous crack leads to material failure Figure: Material failure test series 2 (fiber reinforcement only)

35 Results Concrete failure Figure: Material failure test series 1 (fiber reinforcement + centric CFRP strips)

36 Results Average crack distance = 3.0 cm Figure: Material failure test series 1 (fiber reinforcement + centric CFRP strips)

37 Conclusion and Outlook

38 Conclusion and Outlook The tests for evaluation of feasibility showed that bending load capacity can be increased enormously by CFRP-reinforcement without enlarging the material thickness. However, bending stiffness in the cracked condition is rather low, which makes it difficult to utilize the high strength of the material. This problem could be solved by preloading the centric CFRP-lamellae in the prestressing bed. By that, tensile stresses can be suppressed and crack formation can be prevented. However, this way of improving the bending stiffness is only possible with flat plate elements.