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Analytical modeling of interface behavior in reinforced concrete jacketed members

This seminar discusses the importance of retrofitting existing buildings and presents analytical modeling techniques for evaluating the behavior of reinforced concrete jacketed members. It explores various retrofitting schemes and intervention techniques, including RC jacketing and FRP jacketing. The seminar also covers the accurate assessment of retrofitted structures and the effects of retrofitting on global response.

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Analytical modeling of interface behavior in reinforced concrete jacketed members

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  1. Analytical modeling of interface behavior in reinforced concrete jacketed members Georgia E. Thermou, Civil Engineer, MSc, DIC, PhD Candidate DUTh Supervised by Professors: SJ Pantazopoulou, AS Elnashai, A. Karabinis Mid-America Earthquake Center Seminar Series Wednesday May 12th 2004 Imperial College of Science, Technology and Medicine Demokritus University of Thrace

  2. Performance of Structures in Earthquakes Demokritus University of Thrace 2/22

  3. Why retrofitting is important? • Socio-economic issues - Direct effect on market place and community • 95% of existing buildings stock have been designed with out-of-date codes • Seismic risk mitigation programs Demokritus University of Thrace 3/22

  4. Current codes Old generation of codes Direct design Capacity design Μc,u Μ’c,u Μb Μb,max Μc,b Μ’c,b Μc,u + Μc,b + Μb = 0 Μ’c,u + Μ’c,b + Μb,max = 0 Μ’c,u =Mc,u∙Μb,max/Mb Μ’c,b =Mc,b∙Μb,max/Mb Design Approaches Demokritus University of Thrace 4/22

  5. Earthquake Performance Level Fully Operational Operational Life Safety Near Collapse Collapse Elastic Range Inelastic Range Unacceptable Performance (for New Construction) Frequent (43 years) Ductility Strength Stiffness Basic Objective Occasional (72 years) Essential/Hazardous Objective Earthquake Design Level Safety Critical Objective Rare (475 years) Lateral Load Very Rare (970 years) Collapse Prevention Serviceability Life Safety Deflection Framework for Seismic Rehabilitation (1) • Rehabilitation Objectives [SEAOC, 1995] Demokritus University of Thrace 5/22

  6. Selection of the retrofit scheme Technical & Socio-economic issues • Structural compatibility • Materials/Technology • Foundation system • Structural irregularities • Cost vs importance • Workmanship • Quality control • Duration of work • Functionality • Level of intervention Framework for Seismic Rehabilitation (2) Demokritus University of Thrace 6/22

  7. Ductility enhancement Design Parameters rehabilitated structure rehabilitated structure rehabilitated structure Base shear Stiffness Strength Ductility Base shear ΔV existing structure existing structure existing structure Stiffness & Strengthenhancement Δu Stiffness, Strength & Ductilityenhancement Roof displacement Roof displacement Base shear ΔV Δu Roof displacement Framework for Seismic Rehabilitation (3) • Retrofit Strategy Demokritus University of Thrace 7/22

  8. Intervention Techniques Local Global • RC jacketing • Addition of RC walls • External buttresses • Steel bracing • Base isolation • Injection of cracks • Shotcrete (Gunite) • Steel Plate Adhesion • Steel Jacketing • FRP Jacketing Selective • Stiffness-only • Strength-only • Ductility-only Demokritus University of Thrace Rehabilitation Schemes for RC Structures 8/22

  9. Demokritus University of Thrace Reinforced Concrete Jacketing (1) 9/22

  10. Local intervention Side Jacketing Demokritus University of Thrace Reinforced Concrete Jacketing (2) 10/22

  11. Columns Beams Shear strengthening* * Triantafillou TC,1998, ACI Struct. J., 95(2), 107-115 Demokritus University of Thrace Fibre Reinforced Polymers (FRPs) Jacketing 11/22

  12. Base shear ΔV Δu FRPs Jacketing RC Jacketing Roof displacement Demokritus University of Thrace Effect of Retrofit on Global Response Accurate assessment of the retrofitted structure Accurate modeling at local level 12/22

  13. Addition of RC Jacket ξtot prioritizing of failure modes M Composite section ΔΜ Aim: flexural failure Ideal behavior Δφ φtot φ φc´ φc Premature failure Demokritus University of Thrace Monolithic Approach 13/22

  14. Composite section Monolithic approach Analytical modeling Demokritus University of Thrace Analytical Model: slip at the interfaces 14/22

  15. Stresses at crack Stresses at mid-crack N.A. ft,o hc fms,o fcrs,o τ h1 fcrs,n fms,n c/2 Shear Flow: τ = (nn∙fb,n∙π∙db,n)/btot Crack Spacing: c=(2∙ft,o∙hc∙btot)/(no∙fb,o∙π∙db,o+ τ∙btot) Estimation of Crack Spacing Demokritus University of Thrace 15/22

  16. Aggregate interlock Clamping vci vci σlat fy fy Dowel action Fd Fd Fd Fd Fd Fd Total shear force V =τ∙A+n∙Fd Α=l∙bnew (shear area) n: number of dowels Shear Transfer Mechanisms (1) τ =μ∙σlat + vci Demokritus University of Thrace 16/22

  17. Frictional resistance* Dowel resistance** Fd,scrit τu Fd1 τ1 Fd2 τ2 s1 s2 su s1 s2 su τu = 0.44 ∙(fc2∙σc)1/3 Fdu = 1.3∙db2∙(fsy∙fc)1/2 Shear Transfer Mechanisms (2) Shear stress supply: * Tassios &Vintzileou,1987, J. of Struct. Eng., ASCE, 113(4), 411-428 ** Vintzileou & Tassios, 1987, ACI Struct. Journal, 84(1): 18-30 Demokritus University of Thrace 17/22

  18. A B jacket v1 ΣF’i core L v2 B c ΣF’3 ΣF’1 ΣF’2 ΣF2 ΣF3 ΣF1 jacket ΣFi A c/2 vi=ΣFi/(bnew∙c/2) Demokritus University of Thrace Presentation of the Algorithm (1) Shear stress demand: 18/22

  19. Define curvature φ Modify longitudinal strain gradient in order to obtain section equilibrium Estimate slip at top and bottom interfaces, s1 & s2(analytical approach) The algorithm aims at establishing equilibrium: Calculate the shear stresses, τ΄1 & τ΄2 making use of the shear stress resistance model • of the entire cross-section • between shear stress demandand shear stress supply Perform dual section analysis in order to obtain vertical shear stresses, τ1 & τ2 Compare τ1 & τ2 with the corresponding τ΄1 & τ΄2. Is equilibrium established? ΝΟ YES Check section equilibrium. Is section equilibrium satisfied? ΝΟ YES Calculate the axial, shear and moment resultant Demokritus University of Thrace Presentation of the Algorithm (2) 19/22

  20. SRi=KiSMi Κi≈70% Demokritus University of Thrace Analytical Results Experimental work ofRodriguez & Park* S1 & S2: old type columns (New Zealand Code late 50’s), ρc=2.05%, Φ6/265 SS1: repaired/strengthened column SS2: strengthened column *Rodriguez & Park, 1994, ACI Struct. Journal, 91(2): 150 -159 20/22

  21. Demokritus University of Thrace Conclusions Analytical modeling of the interface behavior in RC jacketed members* • Design diagrams for RC jacketed members • Accurate modeling at local level Retrofitting *Thermou GE, Pantazopoulou SJ & Elnashai AS. Structures Congress 2004, Nashville, Tennessee 2004. Paper No 349. 21/22

  22. Demokritus University of Thrace Acknowledgements This research project was funded by the European Research Project SPEAR (Seismic Performance Assessment and Rehabilitation), Contract Number G6RD-CT-2001-00525) through Imperial College of Science, Technology and Medicine, London. 22/22

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