B belev mdcms_2007

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B belev mdcms_2007

  1. 1. Analysis and Design of Structures withDisplacement-Dependent DampingSystems Borislav Belev, Atanas Nikolov and Zdravko Bonev Faculty of Civil Engineering, UACEG Sofia, Bulgaria
  2. 2. Introduction and essential definitions STRUCTURAL PROTECTIVE SYSTEMS SEISMIC PASSIVE ENERGY SEMI-ACTIVE (BASE) DISSIPATION AND ACTIVE ISOLATION SYSTEMS CONTROLSource: Soong, T.T. and G.F. Dargush. Passive Energy Dissipation Systems in Structural Engineering. J. Wiley & Sons, 1997. 2
  3. 3. Basic Components of a Damping System 1 = Primary frame; 2 = Damper device; 3 = Supporting memberDamping system = damping devices + supporting members (braces, walls, etc.) 3
  4. 4. Classification of FEMA 450 (Chapter 15: Structures with damping systems) The chapter defines the damping system as: The collection of structural elements that includes: (1) all individual damping devices, (2) all structural elements or bracing required to transfer forces from damping devices to the base of the structure, and (3) all structural elements required to transfer forces from damping devices to the seismic-force-resisting system (SFRS).…………………………… The damping system (DS) may be external or internal to the structure and may have no shared elements, some shared elements, or all elements in common with the seismic-force-resisting system. 4
  5. 5. Possible configurations 5
  6. 6. Possible configurations (cont.) 6
  7. 7. Types of damper devices (FEMA 273)Displacement-dependent devices(metallic dampers, friction dampers)Velocity-dependent devices(fluid viscous dampers,solid visco-elastic dampers, etc.)Other types (shape-memory alloys, self-centering devices,etc.) 7
  8. 8. Expected benefits of application of DS Added damping (viscous dampers) Added stiffness and damping (visco-elastic, metallic, friction) As a result, enhanced control of the interstorey drifts------------------------------------------ In new structures: Enhanced performance (reduced damage) Less stringent detailing for ductility (economy) In existing structures: Alternative to shear walls (speed-up retrofit) Correction of irregularities Supression of torsional response 8
  9. 9. Performance in terms of energy dissipation Global energy balance: Ei = Ek + Es + Eξ + Eh The structures differ in the way they “manage” and ”distribute” the total input seismic energy Ei Conventional structures: energy dissipation through cyclic plastic deformation ductile response means damage and losses code-based design does not explicitly evaluate Eh/Ei dissipation capacity is exhausted after a major quake Structures with damping systems: energy dissipation performed by “specialized parts” primary structure/frame has mainly gravity load supporting function and re-centering function 9
  10. 10. Advantages of displacement-dependent damper devices Relatively cheap Easy maintenance Durability Well-defined and predictable response, so that the supporting members can be safely designed according to the capacity design rules 10
  11. 11. Drawbacks of displacement-dependent damper devices Nonlinear response which complicates the analysis/design Relatively stiff and thus not very efficient in weak quakes Relatively small number of working cycles and potential low-cycle fatigue problems (metallic dampers only) Possible variation of the coefficient of friction with time and degradation of contact surfaces (friction dampers only) React to static displacements due to temperature effects and long-term deformations (shrinkage, creep) 11
  12. 12. Parameters influencing the response of a simple friction-damped frame Illustration of the damper action 12
  13. 13. Definition of the equivalent bilinear-hysteresis SDOF-modelF K t = K f + K bd Yield strength Fs = U s K t = (M f ha ) (K t K bd ) Kp = Kf Normalized damper strength η M = M f M u SR = K bd K f KpFs 1 1 Kt Kbd Kf 1 1 O Us U 13
  14. 14. Criteria for efficiency of supplemental damping (1) Fu & Cherry (1999) Rd + R 2 → min 2 f 14
  15. 15. Criteria for efficiency of supplemental damping (2) Belev (2000) 15
  16. 16. Numerical evaluation of DS efficiency for asimple friction-damped frame (PGA=0.35g) Seismic performance index, SPI = f(Rd, Rf, Re) 3 2.5 2 El Centro SPI 1.5 Taft EW Cekmece 1 0.5 0 0 0.2 0.4 0.6 0.8 1 Normalized damper strength 16
  17. 17. Comparison of performance of several displacement-dependent devicesList of the damper devices under consideration: TADAS (steel triangular plate damper, analog of ADAS) FDD (friction damper device, already discussed) UFP (steel U-shaped Flexure Plate)Frames used as “Primary structure”: Steel six-storey frame, originally designed as CBF RC single-storey portal frame (L=7.6 m, H=5.3 m)Software tools: SAP2000 Nonlinear (for the steel frame) DRAIN-2DX (for the RC frame) EXTRACT (for the RC cross-section analysis) 17
  18. 18. TADAS steel damper 18
  19. 19. Arrangement of UFP or FDD devices within the primary RC portal frame 19
  20. 20. Layout of original steel frameOriginally designed as CBF for design GA=0.27g and q=2.0 20
  21. 21. Performance comparison of TADAS and FDD installed in the steel frame Record PGA scaled Roof displacement (cm) Base Shear (kN) Energy Ratio (%) Energy T-ADAS Energy FDD 2 m/s to BRACED T-ADAS FDD BRACED T-ADAS FDD T-ADAS FDD Ei Ed Ei EdEl Centro NS 3.417 0.27g 8.21 8.12 5.35 1351 644 281 45 70 155.1 69.98 146.7 102.3Taft EW 1.505 0.27g 6.12 8.78 7.27 1153 583 301 38 68 144.6 54.8 156 105.8Cekmece NS 2.296 0.27g 11.20 8.00 7.47 1974 610 310 37 69 123.6 45.58 159.8 110.8Vrancea NS 1.949 0.20g 4.71 24.3 29.2 900 1173 530 69 53 540.7 375.5 314.4 167.2 Roof Displacement Base Shear Energy Ratio 35 2000 100 Hysteretic / Input Energy, % 1750 90 30 Roof Displacement, cm 80 25 1500 Base Shear, kN 70 1250 60 20 TADAS BRACED 1000 BRACED 50 15 40 750 10 30 TADAS 500 TADAS 20 FDD 5 250 10 0 FDD 0 FDD 0 El Centro Cekmece Vrancea El Centro Cekmece El Centro Cekmece Vrancea Vrancea Taft EW Taft EW Taft EW NS NS NS NS NS NS NS NS NS Note: All acceleration histories scaled to PGA=0.27g except Vrancea NC, which was left with its original PGA=0.20g 21
  22. 22. Performance comparison of UFP and FDD installed in the RC frame El Centro NS, PGA = 1.5x0.35g=0.52g 40 30 Displacement (mm) 20 10 0 0 2 4 6 8 10 12 14 16 18 20 -10 -20 -30 -40 Time (s) FDD (1.5) UFP (1.5) Bare frame (1.5) 22
  23. 23. Estimated plastic rotations in the primary RC frame members Мax. plastic rotation in the columns Мax. plastic rotation in the girder Ground (mRad) (mRad) PGAacceleration (g) Bare RC Frame Frame Bare RC Frame Frame history frame with UFPs with FDDs frame with UFPs with FDDsEl Centro NS 0,35 6,3 2,7 1,7 4,9 1,9 0,7El Centro NS 0,52 18,5 7,9 7,8 10,2 4,9 5,3 23
  24. 24. Pushover analysis:Deformed shape and plastic hinges at roof displacement = 30cm 24
  25. 25. Basic steps of improved analysis procedure 1. Conventional modal analysis – estimate T1 and {Φ1} 2. Nonlinear static pushover analysis – trace the “roof displacement vs. base shear” relationship 3. Calculate the properties of the Equivalent SDOF-system 4. Nonlinear time-history analysis of the ESDOF-system – find the max. base shear, max. displacement and Ed / Ei 5. Determine the performance point of the real MDOF- structure (in terms of base shear and roof displacement) 6. Check the location of the performance point on the pushover curve from Step 2 7. Estimate deformations and forces in the members and dampers corresponding to the performance point 25
  26. 26. Comparison of results for El Centro NS with PGA=0.27g RESPONSE PARAMETERANALYSIS PROCEDURE Lateral roof Energy ratio Ed/Ei Base shear (kN) displacement (cm) (%) Direct partially NL dynamic TH Analysis 8.12 644 45 of the MDOF-system NL Static Pushover + NLdynamic TH Analysis of the 8.78 613.5 50 equivalent SDOF-system Difference (%) 8 5 10 26
  27. 27. Shake table testing of friction-damped frame in NCREE, Taiwan (2001) 27
  28. 28. Numerical predictions of the seismic performance 50 Experiment 40 Numerical Displacement, (mm) 30 20 10 0 0 5 10 15 20 25 30 -10 -20 -30 Time, (s)Note 1: Seismic input – El Centro NS with PGA=0.2gNote 2: Modal damping ratios for the first and second modes of vibration assumed 1.5% and 0.5%, respectively, to reflect the findings of previous system identification analyses 28
  29. 29. Conclusions from the shake-table testingThe full-scale testing at the NCREE proved the excellentcapacity of the proposed damping system to significantlyreduce earthquake-induced building vibrationsThe seismic performance of such friction-damped framescould be predicted reasonably well by conventionalsoftware for non-linear time history analysis such asDRAIN-2DX and SAP2000Dampers supported by tension-only braces seem sensitiveto imperfections - deviations from the design brace slopeinfluenced the brace stiffness, periods of vibration andseismic response. 29
  30. 30. An example of successful application Seismic protection of industrial facility Design PGA=0.24g, I=1.00, Soil type=B (stiff soil) Seismic weight W=7800 kN Design objective: To reduce the base shear to levels below 1120 kN, for which the existing supporting RCsub-structure was originally designed Conventional design as CBF system with chevron braces is inappropriate due to higher base shear level (2.5x0.24x7800/1.5=3120 kN) Design solution: use friction dampers with slip capacity of 50- 60 kN per device (total slip capacity per direction ≤ 600 kN) 30
  31. 31. Typical FDD arrangement in X-direction 31
  32. 32. Energy dissipation by the damping system 32
  33. 33. Under construction… 33
  34. 34. Concluding remarksThe passive energy dissipation systems are now a matureand reliable technology for seismic protectionThe metallic and friction dampers offer certain advantagesthat can be put to work if a proper system of supportingmembers is employedThe analysis and design of such displacement-dependentdamping systems require increased efforts and time butcould be really rewardingThe option of supplemental damping should be consideredat the very early stages of conceptual design and planning 34
  35. 35. Thank you for your attention!

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