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

Overview

Introduction

The Charter of Athens

The Model Building

Seismic Assessment

The Concept of Retrofit Elements

Discussion of Retrofit Strategies and Systems

Conclusions

Introduction

Retrofit measure; retrofit strategy

Retrofit strategy; retrofit systems

Interest groups

Technical strategies, management

strategies

Retrofit elements

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

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

Set-back floors

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

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

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

Seismic retrofit provisionsStructural 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

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

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

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

pushover X

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 50 100 150 200 250

Displacement N6206 (mm)

Ba

se

sh

ea

r (k

N)

Base Shear X

Base Shear X retrofit2

Base Shear X retrofit 3

pushover Y

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

-15 35 85 135 185 235 285 335

Displacement N6206

Base s

hear

(N)

Base Shear Y

Base Shear Y retrofit2

Base Shear Y retrofit3

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

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)

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

Acknowledgements

CA‘REDIVIVUS project

MEIF-CT-2005-009765

supervisor: Dr. Rui Pinho

Thank you!

Questions?