30 years V

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30 years V

  1. 1. RETROFIT SYSTEMS AND RETROFIT STRATEGIES INVESTIGATED ON THE MODEL OF TYPICAL MID-RISE INTERWAR BUILDINGS IN BUCHAREST, ROMANIA Maria BOSTENARU DAN ROSE School / IUSS di Pavia
  2. 2. Overview  Introduction  The Charter of Athens  The Model Building  Seismic Assessment  The Concept of Retrofit Elements  Discussion of Retrofit Strategies and Systems  Conclusions
  3. 3. Introduction  Retrofit measure; retrofit strategy  Retrofit strategy; retrofit systems  Interest groups  Technical strategies, management strategies  Retrofit elements
  4. 4. The Charter of Athens  1933  Organisation of cities in functional zones  Bucharest Master Plan 1934 > design of buildings in the interwar time  Ground occupancy > planimetric irregularity  Raised permitted height to define streets by their fronts > set-back floors  Encouraged mixed use in central zone
  5. 5. The Model Building  What is a cybernetic model?  Design in „interwar style“ (student project)  Irregular parcel  Basement, GF and 5 upper floors, 2 recessed  Mixed use with Kindergarten and luxury flats  Reinforced concrete frame structure  3D beam-column elements, non-linear confined concrete model, elastic elements for slab models
  6. 6. Set-back floors
  7. 7. Seismic Assessment  P100-92  Pure residential: good behaviour  No secondary beams in the model  higher generality – Greece;  more stable in software)  Higher importance class (Kindergarten): needs retrofit
  8. 8. The Concept of Retrofit Elements  Spatial elements which  Are characteristic bearers in architectural survey  Are characteristic bearers in engineering simulations  Are characteristic bearers in costs estimation  Present typical earthquake damages  Are decisive for better behaviour in case of retrofitting  Define the realms perceived by the inhabitants
  9. 9. Seismic features Element Seismic Deficiency Earthquake Resilient Features Earthquake Damage Patterns Infill panels consoles Increasing stiffness rifts Columns No moment resisting frames Low reinforcement - Plastic hinges at soft storey Concrete spalling Beams No moment resisting frames Well reinforced Plastic hinge in long beams Oblique rifts in short beams Roof and Floors too elastic Alternative solutions with embeded bricks More rifts at stair flights
  10. 10. Seismic retrofit provisions Structural Deficiency Seismic strengthening provision 1. Damaged RC columns Local repairing after (fracture)+crush+spall+(yield)+crack 2. Deeply damaged RC beams See above 3. Superficially damaged RC beams Repairing with plating with glass wraps embedded in epoxy resins 4. Rifts in masonry infill walls Injecting masonry walls 5. Reduced column section Column jacketing Side walls 6. Reduced beam section Beam jacketing in different ways 7. Insuficient stiffness Adding structural walls
  11. 11. Discussion of Retrofit Strategies and Systems  Systems investigated  FRP wrapping of existing elements  Replacement with new elements of higher strength provided with FRP wrapping  Jacketing with higher strength concrete with FRP wrapping
  12. 12. Discussion of Retrofit Strategies and Systems  Pushover analysis + P100-92  Main deficiency is at yield, not at ultimate  Retrofit strategy: strength increase, rather than ductility increase  Rebuilding elements with higher strength concrete (30MPa instead 15 MPa)  Alternative: jacketing, but increase section
  13. 13. Discussion of Retrofit Strategies and Systems  Technical strategy: strength increase  Retrofit system: vertical elements  Management strategy:  First: soft storey eliminated  Second: Elements in alternate directions at corners strengthened – large flats affected  Third: Smaller vertical elements strengthened in the interior – relocation within apartments
  14. 14. pushover X 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 50 100 150 200 250 Displacement N6206 (mm) Baseshear(kN) Base Shear X Base Shear X retrofit2 Base Shear X retrofit 3
  15. 15. pushover Y 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 -15 35 85 135 185 235 285 335 Displacement N6206 Baseshear(N) Base Shear Y Base Shear Y retrofit2 Base Shear Y retrofit3
  16. 16. Discussion of Retrofit Strategies and Systems  A phase-wise management retrofit strategy is not an option since the first phase brings a worsening of the seismic behaviour
  17. 17. Conclusions  ‚retrofit elements‘ useful for determining best retrofit elements and strategies  Retrofit strategy for a building, which for its importance category does not resist in yeidl is system strengthening  Two retrofit systems:  Element replacement (with higher strength concrete) – chosen, for architectural reasons  Element retrofit (jacketing with higher strength concrete)
  18. 18. Conclusions  Phased retrofit proved unsuitable: the retrofit elements have to be rebuilt all simultaneously in order to reach an efficient seismic retrofit system  For a complete view on actors‘ preferences a decision tree is necessary – subject of another study
  19. 19. Acknowledgements CA‘REDIVIVUS project MEIF-CT-2005-009765 supervisor: Dr. Rui Pinho
  20. 20. Thank you! Questions?

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