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An Introduction to FRP-Strengthening of Concrete Structures

ISIS Educational Module 4:. An Introduction to FRP-Strengthening of Concrete Structures. Produced by ISIS Canada. Repair with. FRP. reinforcement. Module Objectives. To provide students with a general awareness of FRP materials and their potential uses

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An Introduction to FRP-Strengthening of Concrete Structures

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  1. ISIS Educational Module 4: An Introduction to FRP-Strengthening of Concrete Structures Produced by ISIS Canada

  2. Repair with FRP reinforcement Module Objectives • To provide students with a general awareness of FRP materials and their potential uses • To introduce students to the general philosophies and procedures for strengthening structures with FRPs ISIS EC Module 4

  3. Repair with FRP reinforcement Introduction Additional Info Field Applications FRP Materials Advanced Applications Evaluation of Existing Structures Specifications & Quality Control Beam & One-Way Slab Strengthening Column Strengthening Overview ISIS EC Module 4

  4. Repair with FRP reinforcement Introduction Section: 1 • The world’s population depends on an extensive infrastructure system • Roads, sewers, highways, buildings • The system has suffered in past years • Neglect, deterioration, lack of funding Global Infrastructure Crisis ISIS EC Module 4

  5. Repair with FRP reinforcement Concrete Reinforcing Steel End result Through concrete Through cracks Introduction Section: 1 • A primary factor leading to extensive degradation… Corrosion Moisture, oxygen and chlorides penetrate Corrosion products form Volume expansion occurs More cracking Corrosion propagation ISIS EC Module 4

  6. Repair with FRP reinforcement FRP Materials Introduction Section: 1 • Why repair with the same materials? • Why repeat the cycle? Lightweight High Strength Easy to install 5x steel Corrosion resistant Highly versatile Suit any project Durable structures ISIS EC Module 4

  7. Repair with FRP reinforcement Tension and/or Along long. Flexural side face of axis of beam beam Section Perpendicular Side face of Shear to long. axis beam (u-wrap) of beam Section Around Confinement Circumferential column Section FRP Materials Section: 1 FRP-Strengthening Applications Type Application Fibre Dir. Schematic ISIS EC Module 4

  8. Repair with FRP reinforcement FRP Materials Section: 2 General • Longstanding reputation in automotive and aerospace industries • Over the past 15 years have FRP materials been increasingly considered for civil infrastructure applications FRP costs have decreased New, innovative solutions needed! ISIS EC Module 4

  9. Repair with FRP reinforcement Carbon FRP sheet FRP Materials Section: 2 General • Wide range of FRP products available: • Plates • Rigid strips • Formed through pultrusion • Sheets • Flexible fabric ISIS EC Module 4

  10. Repair with FRP reinforcement Fibres Matrix FRP Materials Section: 2 Constituents • What is FRP? Provide strength and stiffness Protects and transfers load between fibres Carbon, glass, aramid Epoxy, polyester, vinyl ester Fibre Composite Matrix Creates a material with attributes superior to either component alone! ISIS EC Module 4

  11. Repair with FRP reinforcement 1800-4900 Stress [MPa] 34-130 0.4-4.8 >10 Strain [%] FRP Materials Section: 2 Properties • Typical FRP stress-strain behaviour Fibres FRP Matrix ISIS EC Module 4

  12. Repair with FRP reinforcement Epoxy Roller Resin acts as adhesive AND matrix FRP Materials Section: 2 Installation Techniques uWet lay-up Used with flexible sheets Saturate sheets with epoxy adhesive Place on concrete surface ISIS EC Module 4

  13. Repair with FRP reinforcement Resin acts as adhesive AND matrix FRP Materials Section: 2 Installation Techniques vPre-cured Used with rigid, pre-cured strips Apply adhesive to strip backing Place on concrete surface Not as flexible for variable structural shapes ISIS EC Module 4

  14. Repair with FRP reinforcement 2500 2000 1500 Stress [MPa] 1000 500 1 2 3 Strain [%] FRP Materials Section: 2 Properties • FRP properties • (versus steel): • Linear elastic behaviour to failure • No yielding • Higher ultimate strength • Lower strain at failure CFRP GFRP Steel ISIS EC Module 4

  15. Repair with FRP reinforcement FRP Materials Section: 2 Properties Type of fibre and matrix FRP material properties are a function of: Fibre volume content Orientation of fibres ISIS EC Module 4

  16. Repair with FRP reinforcement FRP Materials Section: 2 Pro/Con FRP advantages Will not corrode High strength-to-weight ratio Electromagnetically inert FRP disadvantages High initial material cost But not when life-cycle costs are considered ISIS EC Module 4

  17. Repair with FRP reinforcement Wet-Dry Freeze-Thaw Evaluation of Existing Structures Section: 3 Deficiencies • Deficiencies due to: Chloride Ingress uEnvironmental Effects ISIS EC Module 4

  18. Repair with FRP reinforcement Then Now Evaluation of Existing Structures Section: 3 Deficiencies • Deficiencies due to: v Updated Design Loads w Updated design code procedures ISIS EC Module 4

  19. Repair with FRP reinforcement Then Now Evaluation of Existing Structures Section: 3 Deficiencies • Deficiencies due to: xIncrease in Traffic Loads ISIS EC Module 4

  20. Repair with FRP reinforcement Evaluation of Existing Structures Section: 3 Evaluation • Evaluation is important to: Determine concrete condition Identify the cause of the deficiency Establish the current load capacity Evaluate the feasibility of FRP strengthening ISIS EC Module 4

  21. Repair with FRP reinforcement Evaluation of Existing Structures Section: 3 Evaluation • Evaluation should include: All past modifications Actual size of elements Actual material properties Location, size and cause of cracks, spalling Location, extent of corrosion Quantity, location of rebar ISIS EC Module 4

  22. Repair with FRP reinforcement Evaluation of Existing Structures Section: 3 Concrete Surface • One of the key aspects of strengthening: State of concrete substrate • Concrete must transfer load from the elements to the FRPs through shear in the adhesive • Surface modification required where surface flaws exist ISIS EC Module 4

  23. Repair with FRP reinforcement Beam/One-Way Slab Strengthening Section: 4 Flexural Strengthening Assumptions FRP rupture uFailure caused by: Concrete crushing vPlane sections remain plane wPerfect bond between steel/concrete, FRP/concrete Adequate anchorage & development length provided for FRPs FRPs are linear elastic to failure Concrete compressive stress-strain curve is parabolic, no strength in tension Initial strains in FRPs can be ignored ISIS EC Module 4

  24. Repair with FRP reinforcement fS =0.90 fS =0.85 Steel fC =0.75 fC =0.6 Concrete ffrp= 0.75 ffrp= 0. 50 Carbon FRP Glass Beam/One-Way Slab Strengthening Section: 4 Resistance Factors Bridge Building Material ISIS EC Module 4

  25. Repair with FRP reinforcement Beam/One-Way Slab Strengthening Section: 4 Failure Modes • Four potential failure modes: Concrete crushing before steel yields Steel yielding followed by concrete crushing Steel yielding followed by FRP rupture Debonding of FRP reinforcement Debonding is prevented through special end anchorages Perform analysis Check failure mode Assume failure mode *** Assume initial strains at the time of strengthening are zero *** *** Refer to EC Module 4 Notes *** ISIS EC Module 4

  26. Repair with FRP reinforcement b a1Φcf’c ec a = b1c c Cc d h As es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Ts + Tfrp = Cc Eq. 4-1 Beam/One-Way Slab Strengthening Section: 4 General Design • Force equilibrium in section: Ts = fsAsfs Tfrp = ffrpAfrpEfrpefrp Cc = fca1f’cb1bc ISIS EC Module 4

  27. Repair with FRP reinforcement Cc As a a Mr = Ts d - + Tfrp h - Eq. 4-5 2 2 Beam/One-Way Slab Strengthening Section: 4 General Design b a1Φcf’c ec a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section • Apply strain compatibility and use these equations to solve for neutral axis depth, c • Section capacity: ISIS EC Module 4

  28. Repair with FRP reinforcement As ec = ecu = 0.0035 efrp = ecu (h-c)/c Eq. 4-6 es = ecu (d-c)/c Eq. 4-7 Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b ecu c d h es efrp bfrp Strain Distribution Cross Section Step1: Assume failure mode Assume that section fails by concrete crushing after steel yields Thus: ISIS EC Module 4

  29. Repair with FRP reinforcement Cc As a1 = 0.85-0.0015f’c > 0.67 Eq. 4-8 b1 = 0.97-0.0025f’c > 0.67 Eq. 4-9 Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ecu a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 2: Determine compressive stress block factors ISIS EC Module 4

  30. Repair with FRP reinforcement Cc As fsAsfs + ffrpAfrpEfrpefrp = fca1f’cb1bc Eq. 4-10 Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ecu a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 3: Determine neutral axis depth, c ISIS EC Module 4

  31. Repair with FRP reinforcement Cc As efrpu Eq. 4-11 efrp = ecu (h-c)/c Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ecu a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 4: Check if assumed failure mode is correct > ? If true, go to Step 6 If false, go to Step 5 ISIS EC Module 4

  32. Repair with FRP reinforcement Cc As a a Mr = fsAsfy d - + ffrpAfrpEfrpefrp h - Eq. 4-12 2 2 Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ecu a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 5: Calculate factored moment resistance ISIS EC Module 4

  33. Repair with FRP reinforcement Cc As es = ecu (d-c)/c > εy ? Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ecu a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 5: Calculate factored moment resistance Check if internal steel yields to ensure adequate deformability If yes, OK If no, reduce FRP amount & recalculate ISIS EC Module 4

  34. Repair with FRP reinforcement Cc As efrp = efrpu ec < ecu Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ec a = b1c c d h es fs Ts Tfrp ffrpu efrpu bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 6: Assume different failure mode Assume failure occurs by tensile failure of FRP Thus: ISIS EC Module 4

  35. Repair with FRP reinforcement Cc As fsAsfy + ffrpAfrpEfrpefrpu = fca1f’cb1bc Eq. 4-15 Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ec a = b1c c d h es fs Ts Tfrp ffrpu efrpu bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 7: Determine depth of neutral axis ISIS EC Module 4

  36. Repair with FRP reinforcement Cc As ec < ecu efrpu c / (h-c) < ecu Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ec a = b1c c d h es fs Ts Tfrp ffrpu efrpu bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 8: Check if assumed failure mode is correct ISIS EC Module 4

  37. Repair with FRP reinforcement Cc As a a Mr = fsAsfy d - + ffrpAfrpEfrpefrpu h - Eq. 4-17 2 2 Beam/One-Way Slab Strengthening Section: 4 Analysis Procedure b a1Φcf’c ec a = b1c c d h es fs Ts Tfrp ffrpu efrpu bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section Step 9: Calculate factored moment resistance ISIS EC Module 4

  38. Repair with FRP reinforcement A’s Cc As Beam/One-Way Slab Strengthening Section: 4 With Compression Steel b a1Φcf’c ecu Cs e’s f’s a = b1c c d h es fs Ts Tfrp ffrp efrp bfrp Equiv. Stress Distribution Strain Distribution Stress Distribution Cross Section • Similar analysis procedure Add a compressive stress resultant ISIS EC Module 4

  39. Repair with FRP reinforcement bf hf c h Afrp Mr Mrf Mrw bfrp Beam/One-Way Slab Strengthening Section: 4 Tee Beams = + • Similar analysis procedure Neutral axis in flange: treat as rectangular section Neutral axis in web: treat as tee section ISIS EC Module 4

  40. Repair with FRP reinforcement Afrp = 60 mm2 d = 325 mm h = 350 mm f’c = 45 MPa efrpu = 1.55 % 3-10M bars fy = 400 MPa Efrp = 155 GPa CFRP Es = 200 GPa b = 105 mm Beam/One-Way Slab Strengthening Section: 4 Flexural Example Problem statement Calculate the moment resistance (Mr) for an FRP-strengthened rectangular concrete section Section information ISIS EC Module 4

  41. Repair with FRP reinforcement Beam/One-Way Slab Strengthening Section: 4 Flexural Example Solution Step 1: Assumed failure mode Assume failure of beam due to crushing of concrete in compression after yielding of internal steel reinforcement ISIS EC Module 4

  42. Repair with FRP reinforcement Beam/One-Way Slab Strengthening Section: 4 Flexural Example Solution Step 2: Calculate concrete stress block factors a1 = 0.85 – 0.0015 f’c > 0.67 a1 = 0.85 – 0.0015 (45) = 0.78 a b1 = 0.85 – 0.0025 f’c > 0.67 b1 = 0.85 – 0.0025 (45) = 0.86 a ISIS EC Module 4

  43. Repair with FRP reinforcement fsAsfs + ffrpAfrpEfrpefrp fca1f’cb1bc = 350 - c 0.75 (60) (155000) 0.0035 c Beam/One-Way Slab Strengthening Section: 4 Flexural Example Solution Step 3: Find depth of neutral axis, c Use Equation 4-10: 0.85 (300) (400) 0.6 (0.78) (45) (0.86) (105) c c = 90.5 mm ISIS EC Module 4

  44. Repair with FRP reinforcement vs. efrpu = 0.0155 Eq. 4-11 350 - 90.5 efrp = 0.0035 90.5 efrp = 0.01 < efrpu = 0.0155 efrp = ecu (h-c)/c Beam/One-Way Slab Strengthening Section: 4 Flexural Example Solution Step 4: Check failure mode Therefore, FRP rupture does NOT occur and assumed failure mode is correct ISIS EC Module 4

  45. Repair with FRP reinforcement d - c es = ecu c Beam/One-Way Slab Strengthening Section: 4 Flexural Example Solution Step 4: Check failure mode To promote ductility, check that steel has yielded: 325 - 90.5 = 0.009 es = 0.0035 > 0.002 = ey 90.5 If the steel had NOT yielded, the beam failure could be expected to be less ductile, and we would need to carefully check the deformability of the member ISIS EC Module 4

  46. Repair with FRP reinforcement a Mr = fsAsfy d - + ffrpAfrpEfrpefrp Eq. 4-12 2 0.86 x 90.5 325 - 0.85 (300) (400) 2 0.86 x 90.5 0.75 (60) (155000) (0.01) 350 - a 2 h - 2 Beam/One-Way Slab Strengthening Section: 4 Flexural Example Solution Step 5: Calculate moment resistance Mr = 50.9  106 N· mm = 50.9 kN· m 65% increase over unstrengthened beam! ISIS EC Module 4

  47. Repair with FRP reinforcement Beam/One-Way Slab Strengthening Section: 4 Shear Strengthening Assumptions • FRP sheets can be applied to provide shear resistance • Many different possible configurations May be aligned at any angle to the longitudinal axis May be applied in continuous sheets or in finite widths ISIS EC Module 4

  48. Repair with FRP reinforcement ne = 2 Section ne = 1 Section Beam/One-Way Slab Strengthening Section: 4 Shear Strengthening Assumptions • FRP sheets can be applied to provide shear resistance • Many different possible configurations May be applied on sides only or as U-wraps *U-wraps also improve the anchorage of flexural FRP external reinforcement ISIS EC Module 4

  49. Repair with FRP reinforcement wfrp b sfrp Section Beam/One-Way Slab Strengthening Section: 4 Shear Strengthening Assumptions To avoid stress concentrations, allow for a minimum radius of 15 mm ISIS EC Module 4

  50. Repair with FRP reinforcement Beam/One-Way Slab Strengthening Section: 4 Shear Strengthening Design Principles External strengthening with FRPs: Flexural failure Generally fairly ductile Shear failure Sudden and brittle Undesirable failure mode Control shear deformation to avoid sudden failure ISIS EC Module 4

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