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
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
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
