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

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FRP Repair with 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

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

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FRP Repair with reinforcement Section:1 Introduction The worlds 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

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

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

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

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

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

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

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Strain [%] > Stress [MPa] FRP Repair with reinforcement Section:2 FRP Materials ISIS EC Module 4 Properties Typical FRP stress-strain behaviour FRP Fibres Matrix

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

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

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

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

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

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

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FRP Repair with reinforcement Section:3 Evaluation of Existing Structures ISIS EC Module 4 Deficiencies Deficiencies due to: Updated Design Loads Updated design code procedures ThenNow

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FRP Repair with reinforcement Section:3 Evaluation of Existing Structures ISIS EC Module 4 Deficiencies Deficiencies due to: Increase in Traffic Loads ThenNow

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FRP Repair with reinforcement Section:3 Evaluation of Existing Structures ISIS EC Module 4 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

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FRP Repair with reinforcement Section:3 Evaluation of Existing Structures ISIS EC Module 4 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

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FRP Repair with reinforcement Section:3 Evaluation of Existing Structures ISIS EC Module 4 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

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FRP Repair with reinforcement Section:4 Beam/One-Way Slab Strengthening ISIS EC Module 4 FRP rupture Failure caused by: Flexural Strengthening Assumptions Concrete crushing Plane sections remain plane Perfect 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

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FRP Repair with reinforcement Section:4 Beam/One-Way Slab Strengthening ISIS EC Module 4 Resistance Factors Material BridgeBuilding Steel S =0.90 S =0.85 Concrete C =0.75 C =0.6 FRP frp = 0.75 frp = Carbon Glass

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

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Force equilibrium in section: Beam/One-Way Slab Strengthening General Design b d Cross Section AsAs Strain Distribution frp c h b frp s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc T s + T frp = C c Eq. 4-1 C c = c 1 f c 1 bcT frp = frp A frp E frp frp T s = s A s f s

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Apply strain compatibility and use these equations to solve for neutral axis depth, c Strain Distribution frp c Beam/One-Way Slab Strengthening General Design h b frp s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Section capacity: M r = TsTs d a 2 Eq T frp h a 2

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step1: Assume failure mode Assume that section fails by concrete crushing after steel yields Strain Distribution frp cu s c Thus: frp = cu Eq. 4-6 c = cu = (h-c)/c s = cu (d-c)/c Eq. 4-7

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step 2: Determine compressive stress block factors Strain Distribution frp cu s c Eq = f c > 0.67 Eq = f c > 0.67 Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step 3: Determine neutral axis depth, c Strain Distribution frp cu s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Eq c 1 f c 1 bc frp A frp E frp frp = s A s f s +

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step 4: Check if assumed failure mode is correct Strain Distribution frp cu s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc ? frp = cu (h-c)/c frpu Eq If true, go to Step 6If false, go to Step 5

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step 5: Calculate factored moment resistance Strain Distribution frp cu s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc M r = s A s f y d a 2 Eq h a 2 frp A frp E frp frp

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step 5: Calculate factored moment resistance Strain Distribution frp cu s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Check if internal steel yields to ensure adequate deformability s = cu (d-c)/c > εy εy ? If yes, OK If no, reduce FRP amount & recalculate

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Step 6: Assume different failure mode Strain Distribution frpu c s c Stress Distribution fsfs f frpu Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Assume failure occurs by tensile failure of FRP Thus: frp = frpu c < cu

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Strain Distribution frpu c s c Stress Distribution fsfs f frpu Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Eq c 1 f c 1 bc frp A frp E frp frpu = s A s f y + Step 7: Determine depth of neutral axis

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Strain Distribution frpu c s c Stress Distribution fsfs f frpu Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Step 8: Check if assumed failure mode is correct c < cu frpu c / (h-c) < cu

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening Analysis Procedure h b frp Strain Distribution frpu c s c Stress Distribution fsfs f frpu Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Step 9: Calculate factored moment resistance M r = s A s f y d a 2 Eq h a 2 frp A frp E frp frpu

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 b d Cross Section AsAs Beam/One-Way Slab Strengthening With Compression Steel h b frp Strain Distribution frp s c Stress Distribution fsfs f frp Equiv. Stress Distribution a = 1 c 1 Φ c f c TsTs T frp CcCc Similar analysis procedure AsAs cu s fsfs CsCs Add a compressive stress resultant

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Beam/One-Way Slab Strengthening Tee Beams Similar analysis procedure Neutral axis in flange: treat as rectangular section Neutral axis in web: treat as tee section bfbf hfhf h b frp A frp c MrMr M rw =+ M rf

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FRP Repair with reinforcement Section:4 Flexural Example ISIS EC Module 4 Problem statement Calculate the moment resistance (M r ) for an FRP- strengthened rectangular concrete section Section information Beam/One-Way Slab Strengthening f c = 45 MPa frpu = 1.55 % A frp = 60 mm 2 f y = 400 MPa E s = 200 GPa E frp = 155 GPa b = 105 mm h = 350 mm 3-10M bars d = 325 mm CFRP

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

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 2: Calculate concrete stress block factors Flexural Example Beam/One-Way Slab Strengthening 1 = 0.85 – f c > = 0.85 – (45) = = 0.85 – f c > = 0.85 – (45) = 0.86

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 3: Find depth of neutral axis, c Flexural Example Beam/One-Way Slab Strengthening Use Equation 4-10: c 1 f c 1 bc = frp A frp E frp frp s A s f s (0.78) (45) (0.86) (105) c 0.85 (300) (400) c 0.75 (60) (155000) c c = 90.5 mm

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 4: Check failure mode Flexural Example Beam/One-Way Slab Strengthening Therefore, FRP rupture does NOT occur and assumed failure mode is correct frp = frp = 0.01 < frpu = frp = cu (h-c)/c frpu = Eq vs.

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 4: Check failure mode Flexural Example Beam/One-Way Slab Strengthening s = cu d - c c To promote ductility, check that steel has yielded: s = > = y 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 = 0.009

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 5: Calculate moment resistance Flexural Example Beam/One-Way Slab Strengthening M r = s A s f y d a 2 Eq h a 2 frp A frp E frp frp 0.85 (300) (400) x (60) (155000) (0.01) x M r = N· mm = 50.9 kN· m 65% increase over unstrengthened beam!

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

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab 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 Section *U-wraps also improve the anchorage of flexural FRP external reinforcement n e = 1 n e = 2

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

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

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Shear resistance of a beam: V r =VcVc VsVs V frp ++ Eq. 4-18

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Shear resistance of a beam: V s = s f y A v d s Eq V c = 0.2 c f c b w d Eq. 4-19

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Shear resistance of a beam: V frp = frp A frp E frp frpe d frp (sin + cos ) s frp Eq A frp = 2 t frp w frp d frp : distance from free end of FRP to bottom of internal steel stirrups

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Eq frpe = R frpu Prevents shear cracks from widening beyond acceptable limits Ensures aggregate interlock! Effective strain in FRP, frpe : Reduction factor, R: 0.8 Carbon: 1 = 1.35, 2 = 0.30 Glass: 1 = 1.23, 2 = 0.47 Eq R 1 f c 2/3 frp E frp 2

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles FRP shear reinforcement ratio, frp : Eq frp = 2 t frp bwbw w frp s frp

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Another limit on effective strain in FRP, frpe : Eq frpe k 1 k 2 L e Parameters, k 1 and k 2 : Eq k 1 = fcfc /3 Eq k 2 = d frp - n e L e d frp

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Effective anchorage length, L e : Eq L e = t frp E frp 0.58

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Limit on spacing of strips, s frp : Eq s frp w frp + d 4

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Design Principles Limit on maximum allowable shear strengthening, V frp : Shear contribution due to steel stirrups and FRP strengthening must be less than this term Eq V r V c + 0.8λ c f c b w d

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FRP Repair with reinforcement Section:4 Shear Strengthening ISIS EC Module 4 Beam/One-Way Slab Strengthening Example Problem statement Calculate the shear capacity (V r ) for an FRP-strengthened concrete section Section information Section b = 105 mm h = 350 mm 3-10M bars d = 325 mm 4.76 mm Ø GFRP wrap Section Elevation λ = 1.0 f c = 45 MPa frpu = 2.0 % f y = 400 MPa (rebar) E frp = 22.7 GPa f y = 400 MPa (stirrup) s s = 225 mm c/c t frp = 1.3 mm w frp = 100 mm s frp = 200 mm

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 1: Calculate concrete and steel contributions Beam/One-Way Slab Strengthening Shear Strengthening Example Concrete:Steel: V s = s f y A v d s = 0.85 (400) (36) (325) 225 V s = N = kN V c = 0.2 c f c b w d V c = 0.2 (0.6) 45 (105) (325) V c = N = kN

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 2: Determine A frp, frp, L e for effective strain calculation Beam/One-Way Slab Strengthening Shear Strengthening Example A frp : A frp = 2 t frp w frp = 2 (1.3) (100) A frp = 260 mm 2 frp : frp = 2 t frp bwbw w frp s frp = 2 (1.3) frp =

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 2: Determine A frp, frp, L e for effective strain calculation Beam/One-Way Slab Strengthening Shear Strengthening Example Le:Le: L e = t frp E frp 0.58 = x L e = 64.8 mm

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Step 3: Determine k 1, k 2 and effective strain, frpe [Limit 2] Beam/One-Way Slab Strengthening Shear Strengthening Example k1:k1: k 1 = fcfc /3 = /3 = 1.38 k2:k2: k 2 = d frp - n e L e d frp = 325 – 1 (64.8) 325 = 0.80 Because of u-wrap

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example frpe : frpe = 0.8 (1.38) (0.80) (64.8) 9525 frpe = frpe k 1 k 2 L e 9525 Eq Note: This strain is one of three limits placed on the FRP Step 3: Determine k 1, k 2 and effective strain, frpe [Limit 2]

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example R: Step 4: Determine R and effective strain, frpe [Limit 1] R = R 1 f c 2/3 frp E frp 2 R = 0.8 (1.23) 45 2/ (22700) 0.47

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example frpe : Step 4: Determine R and effective strain, frpe [Limit 1] Note: This strain is one of three limits placed on the FRP Eq frpe = R frpu frpe = (0.02) frpe =

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example Step 5: Determine governing effective strain, frpe For design purposes, use the smallest limiting value of: frpe = Eq frpe = Eq frpe = Eq. 4-23

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example Step 6: Calculate contribution of FRP to shear capacity V frp : V frp = frp A frp E frp frpe d frp (sin + cos ) s frp Eq V frp = 0.5 (260) (22700) (0.004) (325) (sin90 + cos90) 200 V frp = N = 19.2 kN

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example Step 7: Compute total shear resistance of beam Vr:Vr: V r =VcVc VsVs V frp ++ Eq V r = V r = 64.4 kN

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example Step 8: Check maximum shear strengthening limits Eq V r V c + 0.8λ c f c b w d (1) (0.6) (45) (105) (325) OK

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Solution Beam/One-Way Slab Strengthening Shear Strengthening Example Step 9: Check maximum band spacing d Eq s frp w frp Not true, therefore use 180 mm spacing

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FRP Repair with reinforcement Section:4 ISIS EC Module 4 Addl Considerations FRP anchorage and development length Beam/One-Way Slab Strengthening Additional factors to consider: Deflections Crack widths Vibrations Creep Fatigue Ductility Creep-rupture stress limits sometimes govern FRP- strengthened design External strengthening with FRPs may reduce flexural deformability Deflection Load No FRP 1-layer FRP 3-layers FRP

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Overview Column Strengthening FRP sheets can be wrapped around concrete columns to increase strength How it works: Concrete shortens… …and dilates… …FRP confines the concrete… f l frp …and places it in triaxial stress… Internal reinforcing steel Concrete FRP wrap

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Overview Column Strengthening The result: Increased load capacity Increased deformation capability

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Overview Column Strengthening Design equations are largely empirical (from tests) ISIS equations are applicable for the following cases: Undamaged concrete column Short column subjected to concentric axial load Fibres oriented circumferentially

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Slenderness Limits Strengthening equations only valid for non- slender columns. Thus, from CSA A23.3: A g = gross cross-sectional area of column f c = concrete strength P f = factored axial load l u = unsupported length D g = column diameter lulu DgDg Eq P f / f c A g 0.5

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Slenderness Limits Strengthening equations only valid for non- slender columns. Thus, from CSA A23.3: lulu DgDg Eq P f / f c A g 0.5 The axial load capacity is increased by the confining effect of the wrap Ensure that column remains short Column may become slender!

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Confinement Based on equilibrium, the lateral confinement pressure exerted by the FRP, f lfrp : f lfrp = Eq N b frp f frpu t frp DgDg N b = number of FRP layers frp = material resistance factor for FRP f frpu = ultimate FRP strength t frp = FRP thickness

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Confinement The benefit of a confining pressure is to increase the confined compressive concrete strength, f cc f cc = f c + k 1 f l frp Eq. 5-3 f c = ultimate strength of unconfined concrete k 1 = empirical coefficient from tests

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Confinement ISIS design guidelines suggest a modification to f cc : f cc = f c + k 1 f l frp = f c (1 + pc w ) Eq. 5-4 pc = performance coefficient depending on: FRP type fcfc member size (currently taken as 1.0) = w = 2 f l frp c f c Eq. 5-5

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Confinement Limits Minimum confinement pressure Maximum confinement pressure Why? To ensure adequate ductility of column Limit f l frp 4 MPa To prevent excessive deformations of column Limit Why? = 0.85 (Strength reduction factor to account for unexpected eccentricities) f l frp fcfc 2 pc 1 keke - c

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Circular Columns Column Strengthening Axial Load Resistance Factored axial load resistance for an FRP-confined reinforced concrete column, P rmax : P rmax = k e [ 1 c f cc (A g -A s ) + s f y A s ] Eq. 5-9 Same equation as for conventionally RC column, except includes confined concrete strength, f cc

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Rectangular Columns Column Strengthening External FRP wrapping may be used with rectangular columns There is far less experimental data available for rectangular columns Strengthening is not nearly as effective Confinement all around Confinement only in some areas

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Addl Considerations Column Strengthening External FRP wrapping may be used with circular and rectangular RC columns to strengthen also for shear Particularly useful in seismic upgrade situations where increased lateral loads are a concern Shear

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Addl Considerations Column Strengthening The confining effects of FRP wraps are not activated until significant radial expansion of concrete occurs Therefore, ensure service loads kept low enough to prevent failure by creep and fatigue Strengthening Limits

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FRP Repair with reinforcement Section:5 Example ISIS EC Module 4 Problem statement Determine the FRP wrap details for an RC column as described below Information RC column factored axial resistance (pre-strengthening) = 3110 kN Column Strengthening New axial live load requirement P L = 1550 kN New axial dead load requirement P D = 1200 kN New factored axial load, P f = 4200 kN l u = 3000 mm D g = 500 mm A g = mm 2 A st = 2500 mm 2 f y = 400 MPa f c = 30 MPa f frpu = 1200 MPa t frp = 0.3 mm f frp = 0.75

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 1: Check if column remains short after strengthening Column Strengthening Example Eq. 5-1 lulu DgDg 6.25 P f / f c A g 0.5 OK /(30 x )

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 2: Compute required confined concrete strength, f cc Column Strengthening Example P rmax = k e [ 1 c f cc (A g -A s ) + s f y A s ] Eq. 5-9 Take equation 5-9 and rearrange for f cc : f cc = PfPf keke s f y A s 1 c (A g - A s )

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 2: Compute required confined concrete strength, f cc Column Strengthening Example f cc = (400) (2500) 0.81 (0.6) ( ) 1 = 0.85 – f c = 0.85 – (30) = : f cc : f cc = 43.4 MPa

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 3: Compute volumetric strength ratio, w Column Strengthening Example w : f cc = f c + k 1 f l frp = f c (1 + pc w ) Eq. 5-4 Take equation 5-4 and rearrange for w : w = f cc fcfc - 1 pc = w = 0.447

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 4: Compute required confinement pressure, f lfrp Column Strengthening Example f l frp : Take equation 5-5 and rearrange for f lfrp : w = frp frp f frpu c f c = 2 f l frp c f c Eq. 5-5 f l frp = 2 w c f c = (0.6) (30) f l frp = 4.02 MPa

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 4: Compute required confinement pressure, f l frp Column Strengthening Example Check f l frp again confinement limits: f l frp = 4.02 > 4.0 Minimum: f l frp = 4.02 < Maximum: fcfc 2 pc 1 keke - c f l frp = 4.02 < 30 2 (1) = 8.65 OK, limits met

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 5: Compute required number of FRP layers Column Strengthening Example Take Equation 5-2 and rearrange for N b : f l frp = Eq N b frp f frpu t frp DgDg Nb:Nb: NbNb = f l frp D g 2 frp f frpu t frp = 4.02 (500) 2 (0.75) (1200) (0.3) N b = 3.72 Use 4 layers

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 6: Compute factored axial strength of FRP-wrapped column Column Strengthening Example Use Equations 5-2, 5-5, 5-4 and 5-9: f l frp : f l frp = 2 N b frp f frpu t frp DgDg = 4.32 MPa w : w = = 2 f l frp c f c 0.48

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FRP Repair with reinforcement Section:5 ISIS EC Module 4 Solution Step 6: Compute factored axial strength of FRP-wrapped column Column Strengthening Example Use Equations 5-2, 5-5, 5-4 and 5-9: f cc : P rmax : f cc = f c (1 + pc w ) = 44.4 MPa P rmax = k e [ 1 c f cc (A g -A s ) + s f y A s ] P rmax = 4230 kN > P f = 4200 kN Note: Additional checks should be performed for creep and fatigue

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FRP Repair with reinforcement Section:6 ISIS EC Module 4 Specifications & Quality Control Strengthening of structures with FRP is a relatively simple technique However, it is essential to performance to install the FRP system properly Specifications Quality Control / Quality Assurance

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FRP Repair with reinforcement Section:6 ISIS EC Module 4 Specifications & Quality Control Specifications Approval of FRP materialsHandling and storage of FRP materialsStaff and contractor qualificationsConcrete surface preparationInstallation of FRP systemsAdequate conditions for FRP cureProtection and finishing for FRP system

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FRP Repair with reinforcement Section:6 ISIS EC Module 4 Specifications & Quality Control Quality Control and Quality Assurance Material qualification and acceptanceQualification of contractor personnelInspection of concrete substrateFRP material inspectionTesting to ensure as-built condition

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FRP Repair with reinforcement Section:7 ISIS EC Module 4 Additional Applications Prestressed FRP Sheets One way to improve FRP effectiveness is to apply prestress to the sheet prior to bonding This allows the FRP to contribute to both service and ultimate load-bearing situations It can also help close existing cracks, and delay the formation of new cracks Prestressing FRP sheets is a promising technique, but is still in initial stages of development

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FRP Repair with reinforcement Section:7 ISIS EC Module 4 Additional Applications NSM Techniques Newer class of FRP strengthening techniques: near surface mounting reinforcement (NSMR) Unstrengthened concrete T-beam Longitudinal grooves cut into soffit FRP strips placed in grooves Grooves filled with epoxy grout Research indicates NSMR is effective and efficient for strengthening

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FRP Repair with reinforcement Section:8 ISIS EC Module 4 Field Applications Maryland Bridge Winnipeg, Manitoba Constructed in 1969 Twin five-span continuous precast prestressed girders CFRP sheets to upgrade shear capacity

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FRP Repair with reinforcement Section:8 ISIS EC Module 4 Field Applications John Hart Bridge Prince George, BC 64 girder ends were shear strengthened with CFRP Increase in shear capacity of 15-20% Upgrade completed in 6 weeks Locations for FRP shear reinforcement

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FRP Repair with reinforcement Section:8 ISIS EC Module 4 Field Applications Country Hills Boulevard Bridge Calgary, AB Deck strengthened in negative bending with CFRP strips New wearing surface placed on top of FRP strips

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FRP Repair with reinforcement Section:8 ISIS EC Module 4 Field Applications St. Émélie Bridge Sainte-Émélie-de-l'Énergie, Quebec Single-span, simply supported tee-section bridge Strengthened for flexure and shear Site preparation: 3 weeks, FRP installation: 5 days

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FRP Repair with reinforcement Section:9 Design Guidance ISIS EC Module 4 Canadian codes exist for the design of FRP- reinforced concrete members CAN/CSA-S806-02: Design and Construction of Building Components with Fibre Reinforced Polymers CAN/CSA-S6-00: The Canadian Highway Bridge Design Code (CHBDC)

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Additional Information ISIS EC Module 4 ISIS Design Manual No. 3: Reinforcing Concrete Structures with Fiber Reinforced Polymers ISIS EC Module 1: An Introduction to FRP Composites for Construction ISIS Design Manual No. 4: Strengthening Reinforced Concrete Structures with Externally-Bonded Fiber Reinforced Polymer ISIS EC Module 4: An Introduction to FRP-Strengthening of Reinforced Concrete Structures ISIS EC Module 3: An introduction to FRP-Reinforced Concrete Structures FRP Repair with reinforcement Section:9 Available from

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