High Performance Fiber Reinforced Concrete Composites for Bridge Columns

1. High Performance Fiber Reinforced Concrete Composites for Bridge Columns C.P. Ostertag and S.L. Billington University of California, Berkeley and Stanford University Quake Summit Meeting October 9, 2010 Civil and Environmental Engineering Departments University of California, Berkeley Stanford University

2. Outline • Motivation & Objective of Research • Overview of Composite Materials Being Studied • Experimental Program • Compression and Confinement Experiments • Tension-Stiffening Experiments • Future Work • Conclusions

3. Motivation for ResearchDuctile fiber-reinforced composites are being studied in bridge pier designs Self-Compacted HyFRC ECC Models are needed to predict structural-scale performance

4. Motivation for ResearchDamage reduction & enhanced performance with lower transverse reinf. Self-compacted HyFRC column rv=0.37% Conv. reinforced concrete column rv=0.70% Self-compacted HyFRC column at 11.3% drift PEER (Ostertag & Panagiotou)

5. Motivation for Research Higher strength and ductility observed in reinforced HPFRCs Kesner & Billington, 2004

6. Objective To conduct fundamental, small-scale experiments on unreinforced and reinforced HPFRC materials to develop analytical models and design guidelines for application to bridge pier designs. Additional Questions: • By how much can transverse reinforcement be reduced? • How much additional strain capacity does HPFRC have when reinforced?

7. Materials Being StudiedHigh Performance Fiber-Reinforced Composites Deflection hardening Deflection softening Tension Hardening High Performance if it achieves hardening with less than 2% fiber volume

8. 10 mm Materials Being StudiedHigh Performance Fiber-Reinforced Composites Less than 2% by volume of (PVA) fibers

9. Materials Being StudiedHigh Performance Fiber-Reinforced Composites HyFRC (1.5% fiber volume) Can be self-compacting

10. Experimental ProgramCompression testing of confined HyFRC and ECC ? PI: Claudia Ostertag

11. Compression ExperimentsThree levels of confinement Five mix designs: Plain concrete and HyFRC, Plain SCC and SC-HyFRC, and ECC 1” 2” 3” v = 0.95% v = 0.48% v = 0.32% • #3 bars longitudinally • 10-Gage wire (0.13mm) spirals

12. Compression ExperimentsSpecimens and measurements • Unconfined 6”x 12” cylinders • Confined 6”x12” cylinders • Strain via 2 LVDTS within 8 inch section • Equipment limited to displacements < 0.4” • Confined 6”x12” cylinders w/ strain gages • Strain gages installed on spiral reinforcement • Strain averaged over entire height using 2 LVDTs • Equipment enabled strain calculations at large displacements (~ 1”)

13. Compression ExperimentsHyFRC compared with conventional concrete 7 HyFRC has stable, extended softening behavior on its own 6 5 4 Stress (ksi) 3 2 Control (conventional) concrete 1 HyFRC 0 0 0.002 0.004 0.006 0.008 0.01 0.012 Strain

14. SC-HyFRC SC-HyFRC Compression ExperimentsHigh confinement ratio not needed with SC-HyFRC SCC SCC 1” 2” 3” SCC (1.91%) rv = 0.95% rv = 0.49% rv = 0.32%

15. Compression ExperimentsConfined HyFRC Results (2” spacing) Extensive spalling Plain HyFRC Delay in damage initiation and damage progression SC-HyFRC

16. Compression ExperimentsNo damage localization in SC-HyFRC rv =0.95% rv =0.95% rv=1.91% rv =0.95% SC-HyFRC Plain SCC

17. Experimental ProgramTension stiffening in ECC & HyFRC Tension stiffening Bar in ECC Bar in Concrete Bare bar Fischer & Li, 2002 Blunt & Ostertag, 2009 No recording beyond 0.5% strain No uniaxial tension data

18. Tension-stiffening experimentsQuestions • What is the tension stiffening effect with HyFRC? • How does the HyFRC and ECC perform at large strains when reinforced? • Can basic material properties and geometry be used to predict the tension stiffening and reinforced response? • How does rebar size and volume of surrounding material impact tension stiffening?

19. Tension Stiffening ExperimentsTwo specimen designs evaluated 34” Dogbones Prisms

20. Tension Stiffening ExperimentsSpecimen Variables 2 geometries: prism & dogbone 3 mix designs: ECC, HyFRC, SC-HyFRC 2 reinforcing ratios: 1.25% and 1.9% Plain specimens: (no reinforcing bar) Material characterization tests (cylinders, beams, plates)

21. Tension Stiffening ExperimentsSpecimen design and set-up validation Dogbone specimen designed Inserts and grips machined 6” Stress concentration factor of 1.16

22. Dogbones - Typical Failures ECC3-4-1 HyFRC-4-1 SC-HyFRC-4-1 SC-HyFRC-4-2 ECC3-4-2 HyFRC-4-2

23. Tension Stiffening ExperimentsECC Dogbones – Preliminary Data Rebar fyAs + ECC stress block

24. Tension Stiffening ExperimentsHyFRC and SC-HyFRC Dogbones Average strength of plain HyFRCdogbones ~3-4 kips

25. Future WorkExperiments and Model Development • Develop modeling approaches with experimental data (additional tension/compression experiments needed) • Validate modeling on new reinforced beam and column tests, and recent and upcoming bridge pier experiments • Longer-term: Bond/pull-out testing for bond-slip characterization

26. Material Characterization for ModelingCan simple material testing be used to predict performance in reinforced components? Beam Plate 12” ECC ECC

27. Material Characterization for ModelingCan simple material testing be used to predict performance in reinforced components? Plate Plate Inverse analysis of flexural response to estimate uniaxial tensile data ECC ECC

28. Conclusions • Lower transverse steel ratios are possible with SC-HyFRC • No damage localization in compression with SC-HyFRC • Large-scale tensile dogbones loaded in curve of dogbone provide robust results • In tension, reinforced HPFRC materials can reach higher strains before forming a dominant failure crack than when they are unreinforced

29. Acknowledgements Pacific Earthquake Engineering Research Center Graduate Researchers Gabe Jen, Will Trono & Daniel Moreno Headed Reinforcement Corporation