I MATERIALI COMPOSITI PER L INGEGNERIA CIVILE FRP Introduzione alle tecniche di rinforzo 1
FRP Introduzione alle tecniche di rinforzo 2
Reasons for strengthening Lack of maintenance or protection New codes Changes to the structure Users Increase of traffic loads on bridges Change of use of buildings Explosion Fire De-icing salts Steel corrosion Earth quakes Environment & accidents Chemical aggressive environment Strengthening Lack of detailing Design & execution Low quality of materials Wrong or bad execution Mistakes in calculation or plans FRP Introduzione alle tecniche di rinforzo 3
FRP per il rinforzo esterno prefab wet lay-up FRP EBR = externally bonded FRP reinforcement FRP Introduzione alle tecniche di rinforzo 4
Legami costitutivi 6 σ (GPa) 4 CFRP AFRP GFRP 2 Mild steel 0.02 0.04 ε FRP Introduzione alle tecniche di rinforzo 5
Legami costitutivi 3500 CFRP (Replark) CFRP (CarboDur) Spanning [N/mm 2 ] Stress [N/mm²] 3000 2500 2000 1500 1000 500 0 CFRP (C640) CFRP (C240) HFRP (hybride) GFRP (SyncoTape) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Rek [mm/m] Strain [mm/m] GFRP (Roviglas) S500 FRP Introduzione alle tecniche di rinforzo 6
Shape of FRP PREFAB (PRE-CURED) FRP EBR basic technique Strips or laminates WET LAY-UP (IN-SITU CURING) Sheets or fabrics Thickness Bonding agent Fibre volume About 1.0 to 1.5 mm Thixotropic adhesive for bonding About 70 % About 0.1 to 0.5 mm Low viscosity resin for bonding and impregnation About 30 % (after impregnation) Application Applicability Number of layers Surface unevenness Ease-ofapplication Quality control Simple bonding of the factory made elements with adhesive If not pre-shaped only for flat surfaces Normally 1 layer, multiple layers possible Stiffness of strip and use of thixotropic adhesive allow for certain surface unevenness Simple in use, higher quality guarantee (prefab system) Bonding and impregnation of the sheets or fabrics with resin (shaped and cured in-situ) Regardless of the shape, sharp corners should be rounded Often multiple layers Often a putty is needed to prevent debonding due to unevenness Very flexible in use, needs rigorous quality control Wrong application and bad workmanship = loss of composite action between FRP EBR and substrate/structure, lack of long term integrity of the system, etc. FRP Introduzione alle tecniche di rinforzo 7
Basic technique (FRP EBR systems) Prefab FRP EBR FRP Introduzione alle tecniche di rinforzo 8
Basic technique (FRP EBR systems) Wet lay-up FRP EBR FRP Introduzione alle tecniche di rinforzo 9
Externally bonded reinforcement Extra reinforcement to: - to restore or increase bearing capacity FRP Introduzione alle tecniche di rinforzo 10
Automatic wrapping FRP Introduzione alle tecniche di rinforzo 11
many applications worldwide FRP Introduzione alle tecniche di rinforzo 12
many applications worldwide FRP Introduzione alle tecniche di rinforzo 13
many applications worldwide FRP Introduzione alle tecniche di rinforzo 14
many applications worldwide FRP Introduzione alle tecniche di rinforzo 15
many applications worldwide FRP Introduzione alle tecniche di rinforzo 16
many applications worldwide FRP Introduzione alle tecniche di rinforzo 17
many applications worldwide FRP Introduzione alle tecniche di rinforzo 18
many applications worldwide FRP Introduzione alle tecniche di rinforzo 19
FRP EBR: YES Steel plates need corrosion protection; still corrosion in interface possible ~ FRP excellent corrosion resistance Steel is heavy: short lengths (6 m), connection detailing, manipulation difficult, heavy scaffolding ~ FRP is light and flexible, available in quasi-continues lengths FRP (mostly CFRP and AFRP) have excellent fatigue behaviour Pre-tensioned FRP EBR can be applied: crack width and deflection reduced Aesthetic reasons FRP Introduzione alle tecniche di rinforzo 20
FRP EBR: NO High material cost reduced of labour and disrupt of (economical) activity Low transverse strength: vandalism, complex to anchor Design: stiffness may be determining, debonding failure modes high strength of FRP difficult to use In general excellent durability specific aspects still to take into account (eg. UV-radiation) FRP Introduzione alle tecniche di rinforzo 21
Feasibility and efficiency Experimental validation 20 A4 A3 A2 15 F [kn] 10 5 0 0 20 40 60 80 100 δ [mm] A1 crisi per delaminazione incremento di rigidezza e di resistenza FRP Introduzione alle tecniche di rinforzo 22
Feasibility and efficiency Experimental validation FRP Introduzione alle tecniche di rinforzo 23
fib Bulletin 14 FRP strengthening materials and techniques Basis of design and strengthening concept Flexural strengthening Strengthening in shear and torsion Confinement Detailing rules Practical execution and quality control Special design considerations and environmental effects FRP Introduzione alle tecniche di rinforzo 24
Near surface mounted FRP CFRP strip concrete bonding agent FRP Introduzione alle tecniche di rinforzo 25
Conclusion FRP EBR: a new dimension on strengthening and rehabilitation FRP Introduzione alle tecniche di rinforzo 26