Download Seismic Assessment of Existing Buildings

INTERNATIONAL WORKSHOP
CITY OF TOMORROW AND CULTURAL HERITAGE
POMERIA OUTLOOK 2005
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8-9 DECEMBER 2005
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Urban Rehabilitation in Southern Europe
The Seismic Problem and the Portuguese Case
Rita Bento
Instituto Superior Técnico, TECHNICAL UNIVERSITY OF LISBON
December 2005
INSTITUTO SUPERIOR TÉCNICO
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Urban Rehabilitation in Southern Europe
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•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
TOPICS
•
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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.
1. Introduction
• Earthquakes still remain a severe threat in Southern Europe;
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• 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
1. Earthquakes in Europe - occurrence
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• The SESAME Map of Seismic Hazard in the European Area –
uneven distribution of earthquake distribution in Europe
2. Earthquakes in Europe - effects
• The main different types of earthquake effects at the earth’s
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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.
3. What can be a European Risk Reduction
Programme?
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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. 1 Evaluation and strengthening of existing buildings
and monuments
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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.
•
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.
3. 1 Evaluation and strengthening of existing buildings
and monuments
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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. 2 Ensuring the quality of construction
•
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To the reduction of the seismic risk is fundamental to ensuring
the quality of construction to:
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•
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.
4. The Portuguese Case: 1755 Earthquake and the
‘Pombalino’ buildings
• Portugal is a seismic prone territory. 1755’s Lisbon Earthquake was
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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
Old Masonry buildings in Lisbon
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Downtown
[in Mendes-Victor et al, 1993]
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)
Pombalinos Buildings
(1755-1880)
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• 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
Gaiola Pombalina
[Mascarenhas, 1997]
‘Pombalino’ Building
Maximum number of floors: 3 + ground-floor
Gaiola 3-D
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wood
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structure
Floors –
timber slabs
St Andrew’s Crosses
Different geometries
[Mascarenhas, 1997]
Foundations – short
System of vaults
and small diameter
made of blocks of
woodpiles connected
ceramic masonry
by a timber grid
and stone arches
‘Gaiola Pombalina’: Scheme of an interior wall with St
Andrew’s crosses
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Floors
3D wood
structure
The walls are filled with
Partition
walls
masonry, so the wood
elements can not be seen.
‘Gaioleiros’ Buildings
(1800–1940)
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• As time went by, the wood
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elements
were
progressively
removed in new constructions
•The diagonal elements
gradually disappear
• Interior
walls
were
replaced
with masonry or wood-partitions
Partition
walls
•In time, masonry becomes the
only structural material.
[Mascarenhas, 1997]
‘Placa’ Buildings
(1940 - 1960)
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• At the most recent masonry
buildings, wood floors were
replaced with thin concrete
slabs.
Selft
weight
was
increased.
Thin
•As the result of construction
evolution,
old
buildings
became
concrete
masonry
slabs
less
resistant to horizontal loads
Masonry walls
[Mascarenhas, 1997]
‘Pombalino’ Building analysed
Roof/Penthouse
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Rua da Prata, 210 a 212
Main Entrance
‘Pombalino’ Building analyzed
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Main Façade
Plan of a typical
floor
in [Santos, 2000]
Numerical Model (SAP2000®)
Floors
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Floors bars
Vaults (crosses)
Masonry
Interior wall
of ‘gaiola’
Shell Elements (2D) of masonry walls
Beam elements
Numerical Model (SAP2000®) - Quarter
c)b)
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a)
a)
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c)
Building Analysis
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Evolution of Damage Levels in masonry elements from main
façade in 1st step of iterative procedure – evolution of tension
damaged masonry
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sis= 0.20
sis= 0.25
sis= 0.30
Deformed main
façade
Collapse Mechanism obtained
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COLAPSE Mechanism: Bending of
1998 Azores
Earthquake
the front façade out of its plane
Collapse Mechanism according to
original conception
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[Mascarenhas, 1997]
Fall out the plane of
exterior walls without
complete collapse – it
depends on de number
of floors
1998 Azores Earthquake
Strengthening Solutions
The overturning of the façades can only occur after the
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rupture of its connections to the exterior masonry walls.
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Solution 1 Strengthening of the
connections ‘gaiola’- façades
Steel connectors
Solution 2 Inclusion of a R.C.
beam (0.40.25m2) on the top
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Beam around the
exterior perimeter
Solution 3 Inclusion of R.C. beams
(0.40.25m2) in all the floors
Beams at the
pavements level
Actual Conservation State of ‘Pombalino’ Buildings
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 Buildings that mantain their original conception
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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
Influence of the structural modifications
• Demolition of interior walls and introduction
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different structural elements
Redistribution
of the internal
forces
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• The open larger shop windows
Increase the building vulnerability
to shear base collapse
People may
go around
Vertical continuity is interrupted
Vertical continuity is not interrupted
• Introduction of more stories at the top of the building
Mass and Finertia
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increase at the top
Changes in ‘Gaiola’ structure: removing timber elements or cutting
elements for pipe solution
Stiffness and bracing capacity of this timber structure
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Bad solution
Timber
section was
cut/reduced
Better solution
5. Portuguese Programme for the Reduction of the
Seismic Vulnerability
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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
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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.
6. Final Comments
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Old masonry buildings are an important part of the building
stock of most European cities and have to be preserve;
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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.
INTERNATIONAL WORKSHOP
CITY OF TOMORROW AND CULTURAL HERITAGE
POMERIA OUTLOOK 2005
DECivil
8-9 DECEMBER 2005
ICIST
Urban Rehabilitation in Southern Europe
The Seismic Problem and the Portuguese Case
Rita Bento
Instituto Superior Técnico, TECHNICAL UNIVERSITY OF LISBON
December 2005
More Information:
SPES – Sociedade Portuguesa de
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Engenharia Sísmica
www.spes-sismica.org
EERI – Earthquake Engineering
Research Institute
World Housing Encyclopedia
(‘Pombalino’ Buildings)
www.EERI.org
www.world-housing.net