Extending the Lifespan of Structural Concrete

Transcription

1 Extending the Lifespan of Structural Concrete Jeff West, Ph.D., P.E. Dept. of Civil and Environmental Engineering

2 Two focus areas: Extending the Lifespan of Structural Concrete Strengthening of existing structures using fibre-reinforced reinforced polymer materials Improved concrete materials for new structures Research Colleagues: Prof. K.A. Soudki H.T. Choi A. El Refai T. Quayle Md. Safiuddin Prof. C.M. Hansson K. Tran

3 Strengthening of existing structures using FRP materials Strengthening of existing structures: Compensate for damage or deterioration Compensate for design or construction errors Address changes in use (increased loads) Research Goals: Study the effectiveness of FRP materials: Strength increase Deflection control Improved fatigue life Failure modes Develop and calibrate models to predict behaviour Develop practical design tools

4 FRP Materials for Strengthening Rods Plates or Strips Fabrics

5 Strengthening Methods Investigated External post-tensioning tensioning with CFRP tendons Cross Section External FRP rod Anchor Deviators Elevation External FRP rod Near surface mounted CFRP bars Externally bonded CFRP plates Epoxy FRP bar Cross Section Investigation of partially bonded systems Epoxy FRP plate Cross Section

6 Research Tools / Techniques Small and Large Scale Structural Testing Modeling using Finite Element Analysis C.L.

7 External Post-tensioning tensioning with CFRP Tendons Two external CFRP tendons installed on reinforced concrete beam Prestress = 40% f frpu Deviators at 1/3 span Beams tested under: Static loading Cyclic loading load ranges varied to establish fatigue behaviour deviator P C.L. P deviator CFRP tendon (a) Straight anchor P C.L. P (b) Harped Post-tensioning tensioning Configurations

8 External PT with CFRP Tendons Research Findings Fatigue tests of CFRP Tendon and anchorage system: Meets Post-Tensioning Institute proof-tests Establish fatigue-limit Post-tensioned tensioned beam tests: Failure occurs due to fatigue of steel bar PT increases strength PT reduces deflections PT improves fatigue behaviour: Longer life (load constant) Increased live loads (constant fatigue life) CFRP Tendon & Anchor Assembly Load-Deflection Results

9 Partially Bonded FRP Strengthening Systems Near-surface mounted (NSM) and externally-bonded (EB) strengthening systems have been investigated Provide increased load carrying capacity, but Ductility is dramatically decreased Load Prestressed FRP strengthened beam FRP strengthened beam Unstrengthened beam Flexural Improvement Load Carrying Capacity Ductility 0 Deflection Objective: Develop FRP strengthening system to balance strength and ductility Partially Bonded System

10 Fully Bonded vs. Partially Bonded Load Steel Reinforcement FRP stress before steel yielding Epoxy FRP Bonded Unbonded Bonded Fully bonded Partially bonded Strain profile at mid-span Fully bonded ε c φ ε f ε s Partially bonded ε c φ ε f ε s FRP stress after steel yielding ε c φ ε s ε f ε c φ ε f FRP Strain increases at a slower rate within unbonded length Concrete and steel strains increase faster to satisfy equilibrium Section curvature is increased increased ductility

11 Experimental Results Fully Bonded Partially Bonded Partially bonded EB Plate System Load ( (kn kn) Control beam debonding rupture Partially bonded NSM System Concrete crushing Deflection (mm) Load-Deflection Behaviour

12 Analytical Modeling Analysis based on: Force equilibrium at critical sections Cracking Yielding Transition Load point Overall strain compatibility within unbonded length

13 Partially Bonded FRP Systems Research Findings Partial bonding Enhances flexural ductility Delays debonding failure in EB plate systems Failure mode (FRP rupture or concrete crushing) depends on the unbonded length M u M y M y M cr M cr M Balanced point point Fully bonded FRP L ub =L L ubb =L ubb beam rupture Concrete Concrete crushing Fully bonded crushing Partially beam Partially Fully unbonded bonded beam bonded beam beam Unstrengthened beam beam Designer can achieve desired balance between increased strength and required ductility by varying unbonded length. φ Ductility φ = u y cr φ cr 0 φ y φ y φ u φ u φ φ Non-Prestressed Beam Beam Moment-Curvature Relationship

14 Concrete Materials Research: Extending Lifespan Using Improved Materials High performance self-consolidating concrete High strength High workability High durability Structural Efficiency Faster Construction Longer Service Life Conventional Concrete Use of waste materials Rice husk ash Concrete plant wash water Self-consolidating Concrete

15 Self-consolidating High-performance Concrete Highly flowable concrete that: Achieves consolidation under self-weight Spreads through congested reinforcement Fills every corner of the formwork Maintains stability during and after placement does not require vibration Key properties Filling ability, passing ability & segregation resistance High strength High durability: Low permeability High resistivity Resistance to freezing and thawing damage

16 Characteristics of Self-consolidating High-performance Concrete Supplementary Cementing Materials Special Material Components Special mixture design procedures and performance criteria are required Special Mixture Proportions High-range Water reducer Viscosity-modifying Admixture Low Water-Binder Ratio More Binder Less Water Higher Fine Aggregate Content Lower Coarse Aggregate Content

17 Research Techniques: Paste and Mortar Properties Paste Flow Cone Test Purpose: Assess performance of binding materials and admixtures Determine saturation dosage and water reduction of HRWR Determine water demand of supplementary cementing materials Determine influence of mortar proportions on flowing ability Predict the filling ability of concretes Mortar Flow Mold Test

18 Research Techniques: Fresh Concrete Properties Purpose: Assess: Flowing ability Slump Slump Flow Passing ability Dynamic segregation resistance Orimet Flow Inverted Slump Cone Flow

19 Research Techniques: Fresh Concrete Properties Screen Segregation Column Segregation Purpose: Assess static segregation resistance

20 Research Techniques: Hardened Concrete Properties Compressive strength Ultrasonic pulse velocity Quality or condition of concrete Coarse aggregate segregation Water absorption and permeable porosity Influence water and chloride ion permeability Resistivity Influences corrosion resistance

21 Research Areas: Self-consolidating High-performance Concrete Tools for development of SCHPC mixtures Step-by by-step procedures for mixture proportioning Relationships between flowing ability of paste/mortar and flowing characteristics of self-consolidating concrete Development of semi-empirical empirical models for prediction of fresh and hardened properties Reduced number of trial batches Simplified testing procedures for assessing filling ability, passing ability, and segregation resistance Single operator, field suitable

22 Research Areas: Self-consolidating High-performance Concrete Investigate the use of rice husk ash as a supplementary cementing material in SCHPC Effect on fresh properties Flowing ability, passing ability, segregation resistance Air-void stability in fresh concrete Effect on hardened properties Strength Porosity Resistivity Air void system

23 Questions?