literature review
When assessing seismic vulnerability of buildings it is fundamental to establish the objectives pursued, and in function of those chose the most adequate strategy and tools for the assessment. First of all it is very important to understand the difference of detailed approaches used on single buildings and others most efficient in large scale analysis for groups of buildings. In the first case, the use of detailed methodology implies a very reliable evaluation with necessarily a very good level of information on the analysed structure [4]. The seismic vulnerability of the constructions can be evaluated in ways more or less complex in function of the scale and specificity of the study case. The definition and nature of the criteria (qualitative and quantitative) naturally condition the formulation of the methodologies and evaluation level, that can go from the expedite evaluation of the constructions based on visual observation until the most complex, modelling single buildings [5].
In last decade, many authors have proposed different methodologies with varied approaches and application scales. On the first attempts to classify all these methodologies was undertaken by Corsanego and Petrini [6], proposing a division of different methods in accordance with the result that they intent to produce in four groups:direct, indirect, conventional and hybrid techniques. The former ones estimate directly the structural damage by the application of typological or mechanical methods. Typological methods consider the building structure as belonging to classes depending on materials, construction techniques and other factors that influence the building response. The vulnerability is defined as the probability of a certain structure through an appropriate mechanical model, more or less complex of the buildings. A very recognised and effective approach consists of the identification of feasible collapse mechanisms and by the calculation of their associated failure load factors using limit state theory (displacement capacity and demand). This theory applied to masonry structures was first formulated by Heyman [7], who describes the masonry structure as ruled by rigid bodies with mono-lateral constraints, excluding the possibility of sliding along joints. Previous research on the vulnerability assessment of masonry building carried out by Sinha [8], Spence et al. [9], Giuffré et al. [10] and by Calvi [11], confirmed the validity of this theory applied in this research field. In 1995, at the Seismic Engineering Congress in Siena, D'Ayala and Spence [12] presented a new methodology developed specially for extensive analyses, based on expedite investigation while including a mechanical interpretation of the seismic behaviour of masonry buildings. It was applied for the first time in a historical centre of Lisbon as part of the TOSQA project [13,14], and later developed following the 1997 Italian earthquake [15,16]. The indirect techniques determinate a vulnerability index, establishing subsequently relationships between the post-earthquake damage and seismic intensity, or another characteristic that describes the seismic action (Peak Ground Acceleration, PGA), defining curves or vulnerability functions. This evaluation form is particularly effective when intended to evaluate the vulnerability in a wide area scale. Among various techniques the methodology developed in 1994 by the GNDT-SSN, Gruppo Nazionale per la Difesa dai Terremoti [17] in Italy is still applied extensively. It consists of carrying out a vulnerability classification of buildings, by the observation of physical constructive and structural characteristics, based on simple structural calculations, and on the identification of the factors most influent in the structural seismic response and behaviour. Each building is classified by a vulnerability index that is related with a damage grade through vulnerability functions. These vulnerability functions allow to formulate, for each degree of seismic intensity (or PGA) and vulnerability index, the damage suffered by buildings [3]. The conventional techniques are essentially heuristic and they introduce a vulnerability index independently of the prediction of damage. Finally, the hybrid technique combine features of the methods described previously. The Macroseismic method, developed in 2004 by Lagomarsino and Giovinazzi [18], is an example of a technique that combines the characteristics of the typological and indirect methods, resorting to the vulnerability classes defined in the EMS-98 scale [19].
In Italy there are numerous cases of vulnerability assessment and risk evaluation activities. Their methodologies have been used and updated from the lessons of recent earthquakes, from the Pollino earthquake in 1998 (23.000 buildings assessed), Molise 2002 earthquake (23.00 buildings assessed) and recently the Aquila Earthquake (20.000 buildings assessed). From the post-earthquake usability assessment (damage and safety evaluation) they have improved and calibrated their methodologies for their masonry building stock. Other European experiences are the RISK-UE project [20] terminated in the late 2004 and culminated in the risk evaluation of 7 European cities and the Project LESSLOSS - Risk Mitigation for Earthquakes and Landslides [21].
The methodology of this project proposal consists in characterising the seismic vulnerability of the building stock of historical city centres for façades and aggregates, using improved statistical and mechanical model [22]. Other recent European and Mediterranean Countries funded by FP7 and CAPRA - Central American Probabilistic Risk Assessment reveal the present importance of risk mitigation research.
When assessing seismic vulnerability of buildings it is fundamental to establish the objectives pursued, and in function of those chose the most adequate strategy and tools for the assessment. First of all it is very important to understand the difference of detailed approaches used on single buildings and others most efficient in large scale analysis for groups of buildings. In the first case, the use of detailed methodology implies a very reliable evaluation with necessarily a very good level of information on the analysed structure [4]. The seismic vulnerability of the constructions can be evaluated in ways more or less complex in function of the scale and specificity of the study case. The definition and nature of the criteria (qualitative and quantitative) naturally condition the formulation of the methodologies and evaluation level, that can go from the expedite evaluation of the constructions based on visual observation until the most complex, modelling single buildings [5].
In last decade, many authors have proposed different methodologies with varied approaches and application scales. On the first attempts to classify all these methodologies was undertaken by Corsanego and Petrini [6], proposing a division of different methods in accordance with the result that they intent to produce in four groups:direct, indirect, conventional and hybrid techniques. The former ones estimate directly the structural damage by the application of typological or mechanical methods. Typological methods consider the building structure as belonging to classes depending on materials, construction techniques and other factors that influence the building response. The vulnerability is defined as the probability of a certain structure through an appropriate mechanical model, more or less complex of the buildings. A very recognised and effective approach consists of the identification of feasible collapse mechanisms and by the calculation of their associated failure load factors using limit state theory (displacement capacity and demand). This theory applied to masonry structures was first formulated by Heyman [7], who describes the masonry structure as ruled by rigid bodies with mono-lateral constraints, excluding the possibility of sliding along joints. Previous research on the vulnerability assessment of masonry building carried out by Sinha [8], Spence et al. [9], Giuffré et al. [10] and by Calvi [11], confirmed the validity of this theory applied in this research field. In 1995, at the Seismic Engineering Congress in Siena, D'Ayala and Spence [12] presented a new methodology developed specially for extensive analyses, based on expedite investigation while including a mechanical interpretation of the seismic behaviour of masonry buildings. It was applied for the first time in a historical centre of Lisbon as part of the TOSQA project [13,14], and later developed following the 1997 Italian earthquake [15,16]. The indirect techniques determinate a vulnerability index, establishing subsequently relationships between the post-earthquake damage and seismic intensity, or another characteristic that describes the seismic action (Peak Ground Acceleration, PGA), defining curves or vulnerability functions. This evaluation form is particularly effective when intended to evaluate the vulnerability in a wide area scale. Among various techniques the methodology developed in 1994 by the GNDT-SSN, Gruppo Nazionale per la Difesa dai Terremoti [17] in Italy is still applied extensively. It consists of carrying out a vulnerability classification of buildings, by the observation of physical constructive and structural characteristics, based on simple structural calculations, and on the identification of the factors most influent in the structural seismic response and behaviour. Each building is classified by a vulnerability index that is related with a damage grade through vulnerability functions. These vulnerability functions allow to formulate, for each degree of seismic intensity (or PGA) and vulnerability index, the damage suffered by buildings [3]. The conventional techniques are essentially heuristic and they introduce a vulnerability index independently of the prediction of damage. Finally, the hybrid technique combine features of the methods described previously. The Macroseismic method, developed in 2004 by Lagomarsino and Giovinazzi [18], is an example of a technique that combines the characteristics of the typological and indirect methods, resorting to the vulnerability classes defined in the EMS-98 scale [19].
In Italy there are numerous cases of vulnerability assessment and risk evaluation activities. Their methodologies have been used and updated from the lessons of recent earthquakes, from the Pollino earthquake in 1998 (23.000 buildings assessed), Molise 2002 earthquake (23.00 buildings assessed) and recently the Aquila Earthquake (20.000 buildings assessed). From the post-earthquake usability assessment (damage and safety evaluation) they have improved and calibrated their methodologies for their masonry building stock. Other European experiences are the RISK-UE project [20] terminated in the late 2004 and culminated in the risk evaluation of 7 European cities and the Project LESSLOSS - Risk Mitigation for Earthquakes and Landslides [21].
The methodology of this project proposal consists in characterising the seismic vulnerability of the building stock of historical city centres for façades and aggregates, using improved statistical and mechanical model [22]. Other recent European and Mediterranean Countries funded by FP7 and CAPRA - Central American Probabilistic Risk Assessment reveal the present importance of risk mitigation research.