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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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.

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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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ICIST

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)