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. Overview
 Introduction
 The Charter of Athens
 The Model Building
 Seismic Assessment
 The Concept of Retrofit Elements
 Discussion of Retrofit Strategies and Systems
 Conclusions

3. Introduction
 Retrofit measure; retrofit strategy
 Retrofit strategy; retrofit systems
 Interest groups
 Technical strategies, management
strategies
 Retrofit elements

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. 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

7. Set-back floors

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

19. 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

20. 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

21. 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

22. 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)

23. 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

24. Acknowledgements
CA‘REDIVIVUS project
MEIF-CT-2005-009765
supervisor: Dr. Rui Pinho

25. Thank you!
Questions?