DECivil ICIST Urban Rehabilitation in Southern Europe The Seismic Problem and the Portuguese Case Rita Bento Instituto Superior Técnico, TECHNICAL UNIVERSITY.
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DECivil
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Urban Rehabilitation in Southern EuropeThe Seismic Problem and the Portuguese Case
Rita Bento
Instituto Superior Técnico, TECHNICAL UNIVERSITY OF LISBON
December 2005
INTERNATIONAL WORKSHOP
CITY OF TOMORROW AND CULTURAL HERITAGE POMERIA OUTLOOK 2005
8-9 DECEMBER 2005
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INSTITUTO SUPERIOR TÉCNICO
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Urban Rehabilitation in Southern Europe
•New central, eastern and southern EU states face the
need to rehabilitate building stock;
•Common causes: lack of maintenance in the past;
•Different causes due to physical environment:
•Central and Northern Europe – the heating
systems;
•Southern Europe – earthquake resisting
rehabilitation
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TOPICS
• Overall view of the importance of earthquake rehabilitation building stock in southern EU states:
• Detailed discussion of Lisbon downtown and 1755 earthquake;
• Proposals of the Portuguese and European scientific communities;
• Emphasis on common actions at European level: common strategy for central, northern and southern countries to negotiate EU financial support for rehabilitation of the building stock.
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1. Introduction
• Earthquakes still remain a severe threat in Southern Europe;
• It is impossible to predict dates of occurrence of earthquakes.
Nevertheless the inadequate seismic resistance of the building
stock, lifelines and industry is well understood and can be
avoided Build and Strengthen structures
• Most critical issue: the problem of older vulnerable structures,
built before current regulations and still perform vital functions;
• Different initiatives developed at European level. In Portugal,
SPES has proposed new initiatives for the reduction of the
seismic risk:
•Workshop “Reducing Earthquake Risk in Europe” –
organized by EAEE and SPES, in October 2005
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1.Earthquakes in Europe - occurrence
• The SESAME Map of Seismic Hazard in the European Area –
uneven distribution of earthquake distribution in Europe
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• The main different types of earthquake effects at the earth’s
surface are:
•Fault rupture;
•Landslides and liquefaction;
•Tsunami;
•Fires;
•Ground motion /ground shaking.
• Ground motion is the cause of the vast majority of human and
economic losses due to earthquake.
2.Earthquakes in Europe - effects
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• Several actions have to be performed against the effect of
ground motion:
1. Evaluate the seismic resistance of existing buildings and
strengthen the weakest ones;
2. Ensure the quality of construction;
3. Evaluate de seismic resistance and strengthen where
necessary the industrial facilities and lifelines (power, gas,
water,…);
4. Protect built heritage, by strengthen monuments and
buildings of high cultural heritage.
2.Earthquakes in Europe - effects
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• Several decisions and policies can be suggested [Spence et al.,
2005]:
1. Pursuing and strengthening the policies already enforced:
• Support of research on seismology and earthquake
engineering;
• Development of Structural codes (EC8);
• Establish a centre for coordination of emergency aid;
2. Defining recommendations for Member States minimum
standards of Earthquake safety;
3. Creating a structure to coordinate tasks better performed at
European level.
3.What can be a European Risk Reduction
Programme?
DECivil
ICIST• Two different components can be referred in urban
rehabilitation of buildings:
1. Associated with conservation and improvement of living
conditions;
2. Related with improving of safety conditions.
3.1 Evaluation and strengthening of existing buildings
and monuments
• The criterion should be to strength buildings where the cost of
strengthening is less than the expected losses and buildings
that do not possess minimum safety levels.
DECivil
ICIST• To support this action the main available resource is the
European Regional Development Fund (ERDF).
• It was recently proposed [Spence et al., 2005]:
i. The regulation of ERDF be changed to allow supporting
interventions on the housing stock, with specific objectives
to provided minimum levels of safety;
ii. That upper limits for the EU financial support should be
established.
• The EU has already recognized the importance of
strengthening monuments and buildings of high cultural value.
3.1 Evaluation and strengthening of existing buildings
and monuments
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• To the reduction of the seismic risk is fundamental to ensuring
the quality of construction to:
• New buildings and another infrastructures;
• To the design and execution of the rehabilitation of existing
structures.
• The proposed is: EU would incentive the process by
demanding guarantees from the Member-States:
• The responsible by the construction process should
present external revision documents, assuming the
responsibility for the quality of the final product and, if
possible, insurance covering seismic risk.
3.2 Ensuring the quality of construction
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• Portugal is a seismic prone territory. 1755’s Lisbon Earthquake was
very strong (M=8.7):
•Destroyed large areas in Lisbon and Algarve. In Lisbon it was followed by a tsunami and a fire, out of control for several days
• Lisbon was rebuilt following an urban plan. The fear of another
earthquake led of the enforcement of new construction rules
Pombalino
Buildings
4. The Portuguese Case: 1755 Earthquake and the
‘Pombalino’ buildings
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Old Masonry buildings in Lisbon
LEGENDA:A - EDIFÍCIOS DE ALVENARIA (<1755)B - EDIFÍCIOS POMBALINOS E SEMELHANTES (1755 a 1880)C - EDIFÍCIOS ALTOS DE ALVENARIA COM PAVIMENTOS DE MADEIRA OU DE BETÃO E PAREDES RESISTENTES DE ALVENARIA (1880 a 1940)D – EDIFÍCIOS DE ALVENARIA, COM PAVIMENTOS EM BETÃO OU COM ESTRUTURA PORTICADA DE BETÃO (1940 a 1960) E – EDIFÍCIOS RECENTES DE BETÃO ARMADO (>1960)
[in Mendes-Victor et al, 1993]
Downtown
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ICIST• After 1755 Lisbon Earthquake,
masonry buildings were built
with a 3D wood structure
named gaiola pombalina. The
gaiola structure is like a cage
made of vertical and horizontal
elements braced with diagonals
Pombalinos Buildings
(1755-1880)
Gaiola Pombalina
[Mascarenhas, 1997]
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‘Pombalino’ Building
Gaiola 3-D
wood
structure
St Andrew’s Crosses
Different geometries
Maximum number of floors: 3 + ground-floor
Foundations – short
and small diameter
woodpiles connected
by a timber grid
System of vaults
made of blocks of
ceramic masonry
and stone arches
Floors –
timber slabs
[Mascarenhas, 1997]
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‘Gaiola Pombalina’: Scheme of an interior wall with St Andrew’s crosses
The walls are filled with
masonry, so the wood
elements can not be
seen.
Partition walls
3D wood structureFloors
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‘Gaioleiros’ Buildings
(1800–1940)
[Mascarenhas, 1997]
• As time went by, the wood
elements were progressively
removed in new constructions
•The diagonal elements
gradually disappear
• Interior walls were replaced
with masonry or wood-partitions
•In time, masonry becomes the
only structural material.
Partition
walls
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‘Placa’ Buildings
(1940 - 1960)
Thin
concrete
slabs
[Mascarenhas, 1997]
Masonry walls
• At the most recent masonry
buildings, wood floors were
replaced with thin concrete
slabs. Selft weight was
increased.
•As the result of construction
evolution, old masonry
buildings became less
resistant to horizontal loads
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‘Pombalino’ Building analysed
Rua da Prata, 210 a 212
Roof/Penthouse
Main Entrance
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‘Pombalino’ Building analyzed
in [Santos, 2000]
Main Façade
Plan of a typical
floor
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Numerical Model (SAP2000®)
Vaults (crosses)
Floors bars
Floors
Shell Elements (2D) of masonry walls Beam elements
Masonry Interior wall
of ‘gaiola’
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Numerical Model (SAP2000®) - Quarter
c)b)
c)
a)a)
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Building Analysis
sis= 0.20 sis= 0.25 sis= 0.30
Evolution of Damage Levels in masonry elements from main façade in 1st step of iterative procedure – evolution of tension damaged masonry
Deformed main
façade
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COLAPSE Mechanism: Bending of
the front façade out of its plane
1998 Azores
Earthquake
Collapse Mechanism obtained
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1998 Azores Earthquake
Collapse Mechanism according to
original conception
Fall out the plane of exterior walls without complete collapse – it depends on de number of floors
[Mascarenhas, 1997]
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Strengthening Solutions
Solution 1 Strengthening of the
connections ‘gaiola’- façades
The overturning of the façades can only occur after the
rupture of its connections to the exterior masonry walls.
Steel connectors
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Solution 2 Inclusion of a R.C.
beam (0.40.25m2) on the top
Beam around the
exterior perimeter
Solution 3 Inclusion of R.C. beams
(0.40.25m2) in all the floors
Beams at the
pavements level
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Actual Conservation State of ‘Pombalino’ Buildings
Buildings that mantain their original conception
Main problems result from deficient/no maintenance: roof broken
ceramic tiles that allow water inflitration causing masonry and
timber degradation, etc.
Buildings that suffered structural changes
In most of the cases are critical as they reduce the seismic
resistance and therefore are not advisable
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Influence of the structural modifications
Vertical continuity is not interrupted
People may
go around
• The open larger shop windows
Vertical continuity is interrupted
Increase the building vulnerability
to shear base collapse
• Demolition of interior walls and introduction
different structural elements
Redistribution
of the internal
forces
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• Introduction of more stories at the top of the building
Mass and Finertia
increase at the top
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Changes in ‘Gaiola’ structure: removing timber elements or cutting elements for pipe solution
Timber
section was
cut/reduced
Bad solution Better solution
Stiffness and bracing capacity of this timber structure
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• The Portuguese Association for Earthquake Engineering
(SPES) has been working actively for the reduction of the
Seismic Risk in Portugal. In 2001, it was presented a
programme with 7 tasks:
1. Surveying and seismic evaluation of the building stock;
2. Definition of more efficient strategies of intervention;
3. Improvement of seismic strengthening solutions;
4. Formation of a legal framework for rehabilitation actions;
5. Civil and technical education and spread of information;
6. Creation of master-plans for seismic rehabilitation;
7. Interventions.
5. Portuguese Programme for the Reduction of the
Seismic Vulnerability
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• Albeit the importance of the programme, it is not yet effectively
supported by any member of the government, group of
municipalities or politicians or by any private sector entity;
• For all these groups it is important:
• to decide in view of very short-terms horizons;
• To have some immediate return of their investment.
• The last initiative of SPES was the definition of the European
Risk Reduction Programme;
• This cooperation seems to be the right way to the seismic risk
reduction at all levels: local, national and European.
5. Portuguese Programme for the Reduction of the
Seismic Vulnerability
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• Old masonry buildings are an important part of the building
stock of most European cities and have to be preserve;
• The rehabilitation and strengthen should be promoted and
coordinated at a European level;
• Because of the large number of structures evolved it is
necessary to define priorities: start in regions of high seismic
intensity and be directed at vital and weaker buildings;
• The European Regional Development Fund (ERDF) could
support this action, although urban rehabilitation programmes
supported by ERDF aimed essentially the regeneration of
socially degraded areas.
6. Final Comments
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• It is herein suggested to negotiate a global programme in the
EU to support the following components of the interventions on
the rehabilitation of building stock:
• The heating conditions in the central and northern
European countries;
• The earthquake rehabilitation of the weakest and
strategic buildings from southern European countries.
6. Final Comments
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Urban Rehabilitation in Southern EuropeThe Seismic Problem and the Portuguese Case
Rita Bento
Instituto Superior Técnico, TECHNICAL UNIVERSITY OF LISBON
December 2005
INTERNATIONAL WORKSHOP
CITY OF TOMORROW AND CULTURAL HERITAGE POMERIA OUTLOOK 2005
8-9 DECEMBER 2005
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More Information:
SPES – Sociedade Portuguesa de
Engenharia Sísmica
EERI – Earthquake Engineering
Research Institute
www.spes-sismica.org
www.EERI.org
World Housing Encyclopedia www.world-housing.net(‘Pombalino’ Buildings)
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