EUROPEAN CENTER OF PREVENTION AND FORECASTING OF EARTHQUAKES – ECPFE

1. EUROPEAN CENTER OF PREVENTION AND FORECASTING OF EARTHQUAKES – ECPFE EARTHQUAKE PLANNING AND PROTECTION ORGANIZATION – EPPO Athens Workshop April 12/2013 IMPLEMENTATION OF THE EC8-P3:2005ASSESSMENT AND INTERVENTIONS ON BUILDINGS IN EARTHQUAKE PRONE AREAS T.TASSIOSA.KOUTSIASome comparisonsbetween retrofitting provisions of EC8-P3 and other Codesfor RC elements

2. Table of Contents

3. 1. Scope (a) EC8-P3 will need, as all Codes do, to be improved and modified on a regular basis, to intergrade: • the ongoing work, • the feedback from Code-users and • continuing developments in “repair technology”; as well as to eliminate: • possible mistakes and • internal inconsistencies.

4. 1. Scope (b) This study attempts to make some comparisons between retrofitting provisions of EC8-P3 and KANEPE (GCSI) for RC elements; regarding: • Strengthening against shear, • Confinement action versus local ductility and • Clamping of lap-splices.

5. i. EC8-P3 2. Strengthening against shear 2.1 FRP jacketing NOTE:γfd=1,5 is the partial factor for FRP debonding a. Design formulae For fully wrapped (i.e. closed) or properly anchored (in the compression zone) jackets:

6. i. EC8-P3 2. Strengthening against shear 2.1 FRP jacketing b. Notation • θ: strut inclination angle, • β: angle between the (strong) fibre direction in the FRP sheet and the axis of the member, • wf: width of the FRP sheet measured orthogonally to the (strong) direction of the fibres (for sheets: wf=min(0,9d,hw)sin(θ+β)/sinθ), • sf:spacing of FRP sheet measured orthogonally to the (strong) fibre direction (=wf), • Le: effective bond length, • z =0,9d;internal lever arm, • ffdd: design debondingstrength, • ffu,W(R): ultimate strength of the FRP sheet wrapped around the corner with a radius R and • fdd,e,W: design FRP effective debondingstrength

7. ii. KANEPE 2. Strengthening against shear 2.1 FRP jacketing Design formulae NOTE:γRd=1,5 For beams: For columns: U-shaped (i.e., open) jackets Fully wrapped (i.e., closed) or properly anchored (in the compression zone) jackets

8. 2.1.1 Numerical example (a) 2. Strengthening against shear 2.1 FRP jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 FRP: ffu=2900 MPa, Ef=260000 MPa, tl=0,12 mm Additional shear load: ΔV=70 kN NOTE: the partial factor of the FRP is taken equal to 1,1 EC8-P3 for θ=π/4 in favor of safety and β=π/2, 4 layers of FRP with Σtf=0,48 mm account for: • ffdd =467,88 MPa • <ηRffu-ffdd>=903,03 MPa>0 • ffu,w=1370,91 MPa • τmax=2,73 MPa • ffdde,w=392,70 MPa • VRd,f=74,64 kN KANEPE • σj0=1757,58 MPa • z0=176 mm • tj,req=0,23 mm 2 layers of FRP with Σtj=0,24 mm are required

9. 2.1.1 Numerical example (b) 2. Strengthening against shear 2.1 FRP jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 FRP: ffu=2900 MPa, Ef=260000 MPa, tl=0,12 mm (VRd,f=74,64 kN)

10. 2.1.2 Conclusion 2. Strengthening against shear 2.1 FRP jacketing • The two documents lead in average to the same values of required FRP thickness. • However, we confess that we were unable to understand why, following EC8-P3 A.4.4.2 (5), such a simple strengthening, in such a small column, fails by debonding in spite of the equilibrium offered near the curved corner (forces Fc). Fully wrapped (i.e., closed) or properly anchored (in the compression zone) jackets

11. i. EC8-P3 2. Strengthening against shear 2.2 Steel jacketing a. Design formulae b. Notation • θ:as previously stated, • β:as previously stated, • b: width of the steel straps and • s: spacing of the steel straps Evidently b/s=1 in case of continuous steel plates.

12. ii. KANEPE/TH.P.T. 2. Strengthening against shear 2.2 Steel jacketing Design formulae NOTE:γRd=1,5 For beams: For columns: U-shaped (i.e., open) jackets Fully wrapped (i.e., closed) or properly anchored (in the compression zone) jackets

13. 2.2.1 Numerical example (a) 2. Strengthening against shear 2.2 Steel jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 Steel plate: f 'sy=275 MPa Additional shear load: ΔV=70 kN NOTE: the partial factor of the steel plate is taken equal to 1,15 EC8-P3 for θ=π/4in favor of safety and β=π/2, tj,req=1,17 mm KANEPE • σj0=159,42 Mpa • z0=176 mm tj,req=2,50 mm

14. 2.2.1 Numerical example (b) 2. Strengthening against shear 2.2 Steel jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 Steel plate: f 'sy=275 MPa

15. 2.2.2 Conclusion 2. Strengthening against shear 2.2 Steel jacketing EC8-P3 leads to much lower values of required steel-plate thickness because: • it considers zo~h and • it does not leave stress-margins (~ 30%) for possible local overstress along the diagonal crack.

16. i. EC8-P3 3. Confinement action versus local ductility 3.1 FRP jacketing a. Design formulae b. Notation • bw: larger section width, • εcu=0,0035, • εju=ffu/Ef; adopted FRP jacket ultimate strain, lower than the ultimate strain εfu=0,015 for CFRPand • f’1: confinement pressure f1 applied by the FRP sheet after its corners have been rounded to allow wrapping around them Effectively confined area in an FRP-wrapped section

17. ii. KANEPE 3. Confinement action versus local ductility 3.1 FRP jacketing Design formulae NOTE: If the number of required FRP layers k is higher than 3, the effectiveness of the additional FRP layers is reduced;

18. 3.1.1 Numerical example (a) 3. Confinement action versus local ductility 3.1 FRP jacketing Column: b=250 mm, μφ,av=1,00 Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 FRP: ffu=2900 MPa, Ef=260000 MPa Additional axial load: N=800 kN In order to achieve μφ,tar=9,00: NOTE: the partial factor of the FRP is taken equal to 1,1 EC8-P3 • Ix=9,000 • εju=0,0112 • f’1=6,40 MPa • ks=0,400 • f1=16,00 MPa tf,req=0,69 mm KANEPE • fjd=2636,36 MPa • v=0,674 • εsy=0,0020 • ano=0,333 • an=0,733 tj,req=0,81 mm • for k=7>3, ψ=0,615 • f’jd=ψfjd=1620,81 MPa t’j,req=1,32 mm

19. 3.1.1 Numerical example (b) 3. Confinement action versus local ductility 3.1 FRP jacketing Column: b=250 mm, μφ,av=1,00 Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 FRP: ffu=2900 MPa, Ef=260000 MPa Additional axial load: N=800 kN

20. 3.1.2 Conclusion 3. Confinement action versus local ductility 3.1 FRP jacketing • A question may be raised here about the first approach of EC8-P3 (A.34) on confinement action versus local ductility; the cross sectional effectiveness factor a is not included in the design formulae – as opposed to the second EC8-P3 approach A.4.4.3 (6) - which was examined by Prof. Dritsos in the previous presentation - and KANEPE provisions. • It is also noted that EC8-P3, as opposed to KANEPE provisions, does not consider the reduced effectiveness of additional FRP layers after a certain number (say 5). • As a result, it is rather a numerical coincidence that the values of required FRP thickness for this first approach (A.34) are quite similar in the case of EC8-P3 and KANEPE provisions for targeted local ductility values around 10,00 – as opposed for the case of lower (<9) and higher (>11) μ1/r-values when EC8-P3 values become disproportionally low and high respectively.

21. i. EC8-P3 3. Confinement action versus local ductility 3.2 Steel jacketing

22. ii. EC8-P1 3. Confinement action versus local ductility 3.2 Steel jacketing a. Design formulae b. Notation • bc: gross cross-sectional width and • bo: width of confined core Evidently bc/bo=1in case of continuous steel plates. NOTE: According to Table 5.1 and assuming au/a1=1,0, qo,DCM=3,0 and qo,DCH=4,5. Furthermore, assuming Tc=2T1 in accordance with Equation 5.5 μφ=1+2(qo-1)Tc/T1, μφ,DCM=9 and μφ,DCH=15.

23. iii. KANEPE 3. Confinement action versus local ductility 3.2 Steel jacketing Design formulae

24. 3.2.1 Numerical example (a) 3. Confinement action versus local ductility 3.2 Steel jacketing Column: b=250 mm, μφ,av=1,00 Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 Steel plate: f 'sy=275 MPa Additional design axial load: Nd=800 kN In order to achieve μφ,tar=9,00: NOTE: the partial factor of the steel plate is taken equal to 1,15, while the reduced partial factors of concrete and reinforcing steel are taken equal to 1,3 and 1,05 respectively EC8-P1KANEPE vd=0,876 εsyd=0,0019 an=0,333 as=1,000 a=0,333 ωwd,min=1,246 tj,req=3,38 mm tj,req=4,76 mm

25. 3.2.1 Numerical example (b) 3. Confinement action versus local ductility 3.2 Steel jacketing Column: b=250 mm, μφ,av=1,00 Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 Steel plate: f 'sy=275 MPa Additional design axial load: Nd=800 kN

26. 3.2.2 Conclusion 3. Confinement action versus local ductility 3.2 Steel jacketing • EC8-P3 does not offer any quantitative guidance regarding the use of external steel confinement in the form of steel jacketing as a strengthening method for increasing the local ductility of a member. • Following EC8-P1 on this subject, however, with the appropriate modifications regarding the partial factors of existing materials, the values of required steel-plate thickness are relatively high for higher targeted local ductility values compared to the values resulting from KANEPE provisions.

27. i. EC8-P3 (a) 4. Clamping of lap-splices 4.1 FRP jacketing a. Design formulae NOTE:CFKL3= 1,00 is the confidence factor for full knowledge b. Notation • bw: as previously stated, • p: perimeter line in the column cross-section along the inside of longitudinal steel, • n: number of spliced bars along p, • fyL=fy/CFKL3;yield strength of longitudinal steel reinforcement; • σ1: clamping stress over the lap- splice length Lsand • σ’1: active pressurefrom the grouting between the FRP and the column at a strain of 0,001

28. i. EC8-P3 (b) 4. Clamping of lap-splices 4.1 FRP jacketing “For members of rectangular section with longitudinal bars lapped over a length Lsstarting from the end section of the member, an alternative to the previous for the calculation of the effect of FRP wrapping over a length exceeding by no less than 25% the length of the lapping, is:”

29. ii. KANEPE 4. Clamping of lap-splices 4.1 FRP jacketing Design formulae

30. 4.1.1 Numerical example (a) 4. Clamping of lap-splices 4.1 FRP jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 FRP: ffu=2900 MPa, Ef=260000 MPa Assuming ls/db=25: NOTE: the partial factor of the FRP is taken equal to 1,1 EC8-P3 (a) • σ1=1,52 MPa • ks=0,4 • σ’1=0,61 MPa tf,req=0,29 mm EC8-P3 (b) • a=al,f=0,760 • ρf=0,0022 • ff,e=2081,21 Mpa tf,req=0,27 mm KANEPE • su=2,0 mm • sd=0,4 mm • wd=0,33 mm tj,req=0,36 mm

31. 4.1.1 Numerical example (b) 4. Clamping of lap-splices 4.1 FRP jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 FRP: ffu=2900 MPa, Ef=260000 MPa

32. 4.1.2 Conclusion 4. Clamping of lap-splices 4.1 FRP jacketing • Several opinions exist about the meaning of the symbol εf,u being used in the alternative second approach A.4.4.4 (3) of EC8-P3 regarding the clamping of lap-splices along with FRP jacketing. • Our application is literally in accordance with the provisions of the text of the Code putting εf,u equal to the actual ultimate elongation of the FRP that however should not be taken higher than 0,015. • On the other hand, if εf,u were the real strain of the FRP under the given conditions, the resulting values of required FRP thickness would then be approximately 100% higher than the previous ones.

33. i. EC8-P3 4. Clamping of lap-splices 4.2 Steel jacketing

34. ii. KANEPE 4. Clamping of lap-splices 4.2 Steel jacketing Design formulae

35. 4.2.1 Numerical example (a) 4. Clamping of lap-splices 4.2 Steel jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 Steel plate: f 'sy=275 Mpa Assuming ls/db=25: NOTE: the partial factor of the steel plate is taken equal to 1,15 KANEPE • su=2,0 mm • sd=0,4 mm • (AB)=99 mm provided that: wy=0,13 mm<wd=0,33 mm tj,req=2,32 mm

36. 4.2.1 Numerical example (b) 4. Clamping of lap-splices 4.2 Steel jacketing Column: b=250 mm Concrete: fc=19 MPa, c=20 mm Reinforcement: S400, 4Φ20, Φ6/250 Steel plate: f 'sy=275 Mpa

37. 4.2.2 Conclusion 4. Clamping of lap-splices 4.2 Steel jacketing It is hoped that in the near future EC8-P3 will also offer quantitative guidance regarding the use of external steel confinement in the form of steel jacketing as a strengthening method of inadequate splices.

38. Thank you!