Experimental bond behavior in masonry elements externally reinforced with FRP laminates

Transcription

1 Experimental bond behavior in masonry elements externally reinforced with FRP laminates

2 Experimental program Laboratory test on masonry components: tuff units and mortar Bond Test on tuff stones strengthened by FRP composites Parameters investigated: Type of fibers (GFRP and CFRP), Bonded lengths (1 cm, 15 cm, transversal plies) Test on masonry panels subjected to in-plane loads Parameters investigated: Type of fibers (GFRP and CFRP), Fiber density (3 g/m 2, 6 g/m 2 ), Strengthening layout (Grid( and Cross)

3 Typical masonry walls of Southern Italy Southern Italy and, more in general, countries situated in the Mediterranean area, are characterized by masonry structures inadequate to resist to seismic actions Faced masonry with irregular stones Solid tuff wall built up with regular stones Solid wall built up with tuff stones and bricks

4 Neapolitan materials Neapolitan yellow tuff has been employed since ancient times as a structural stone in South Italy Pozzolan mortar was widely used in masonry assembleges Some aspects of neapolitan yellow tuff: Mechanical properties variable depending on the quarries location Low tensile strength Highly porous structure Aspect of pozzolan mortar: low compressive strength

5 Research projects on seismic assessment of masonry structures with FRP techniques are in progress The seismic vulnerability of UMR is strongly affected by the performance of the shear walls FRP in CONSTRUCTION

6 The experimental program: Compression test on tuff units Tests were performed according to the indications of: UNI 9724 January 22, [Compressive strength] UNI 9724, October 199, [Elastic modulus] 6 Cubes 1x1x1 cm 6 prisms 4x1x1 cm Mean compressive strength: 3.3 MPa Mean Young's modulus: 185 MPa Fully and partially saturated specimens

7 The experimental program: Bond tests L CILINDRICAL HINGE FRP Lb Tuff stone size : 18.5 x 25 x 11 cm B

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9 The experimental program: Results Maximum stress level in FRP is always lower than 25% for carbon and variable between 65% and 1% for glass Transfer length in the range mm Specimens with anchorage had a higher shear stress at failure A large transfer of stress is evidenced in the first 2mm, especially for glass fibers, and then there is a low transfer for a long part of sheet Shear failure occurs before local cracking at the interface Failure mode

10 The experimental program: Results.6 ε.4.25 Fmax.5 Fmax.75 Fmax Fmax.24 ε Fmax.5 Fmax.75 Fmax Fmax C A R B O N.2 ε.3 4 x [cm] N frp = 11 kn.6.12 ε 3 x [cm] 6 9 N frp = 9.2 kn G L A S S x [cm] x [cm] 8 12

11 Top Concrete Beam Cross layout Grid layout Strain gauges Concrete Base Block Test on panels performed at Enel Hydro Laboratory LOADING HYSTORY 1) MONOTONIC COMPRESSION ACTION 2) MONOTONIC IN-PLANE SHEAR LOAD 4 RM with CFRP 3 g/m 2, in grid, diagonal arrangement; REACTION FRAME HYDRAULIC ACT UAT ORS CILINDRICAL HINGES East face 375 STEEL LOAD BEAM 4 RM with CFRP 6 g/m 2, in grid, diagonal arrangement; + BALANCER ACTUATOR 3 RM with GFRP, 3g/m 2, in grid, diagonal arrangement; STRONG FLOOR LVDTs LOAD CELL South side 157 North side + 4 RM with GFRP, 6 g/m 2 in grid, diagonal arrangement. 148 CILINDRICAL HINGES LOAD CELL

12 Test on panels subjected to in-plane loads RM panels presented a substantial initial stiffness increase. Shear tests have been proved increase in shear strength up to 6%. The highest gain was performed by grid layout. RM panels reached very high ultimate displacements. CFRP was more vulnerable to debonding.. The AVERAGE debonding strain was equal to 2948 µε for CFRP sheets, and 38 µε for GFRP sheets. RM panels with GFRP always SWOUED the composite rupture. 24 H (kn) H (kn) 16 8 Vl4 Cl4 Cl3 Vl3 Spec. 3 s (mm) Vl2 Ch2 Ch1 Vh1 Spec.3 s (mm)

13 Test on panels subjected to in-plane loads 2 H [kn] H [kn] First debonding of the compressive sheet First debonding of the compressive sheet First debonding of the tensile sheet First debonding of the tensile sheet Rupture of the tensile sheet S [mm] S [mm] Strenghtening with CFRP GFRP in cross arrangement

14 35 µε CARBON Debonding of the entire tensile sheets Starting debonding at S.G. location 25 S.G. 5 S.G. 7 S.G S.G. 4 S.G. 2 S.G. 5 S.G. 4 5 S.G. 7-5 GLASS d 1 S [mm] 2 3 CROSS PATTERN 65 µε 55 Starting debonding at S.G. location S.G. 7 FRP rupture S.G S.G S.G S [mm] 4

15 Debonding phenomenon: Conclusions WALL TEXTURE, MATERIAL PROPERTIES OF COMPONENTS, TYPES OF DECAY OF THE TUFF MASONRY WALLS PLAY AN IMPORTANT ROLE ON BOND BEHAVIUR BETWEEN TUFF MASONRY AND FRP BOND TESTS POINT OUT THAT: Dimension of stones and bond lengths influence the results in terms of both maximum load and failure mechanism Failure mode is due to the shear failure of stones TESTS ON STRENGTHENED PANELS POINT OUT THAT: Appropriate selection of type, amount and strengthening scheme of FRP can give remarkable improvement in shear capacity Adherent surface preparation and anchorage systems of composites on tuff masonry support need to be further investigate Methods of experimental and theoretical analysis need to be assessed ssed to obtain reliable and significant results