Seismic Risk Analysis & Management as a decision-making tool for the Retrofit Intervention at Territorial scale
Principal Researcher: Stefano Pampanin
Staff involved: Sonia Giovinazzi,
Students involved:
Remembering the “bigger picture”: Seismic Risk Analysis & Management as a decision-making tool for the Retrofit Intervention at Territorial scale.
The selection of the most appropriate retrofit solution to be implemented is typically accomplished by targeting, on a case-by-case basis, an acceptable weighted balance between the benefits due to the improved seismic performance and the direct (and sometimes indirect) costs associated to the intervention. The aforementioned recent developments of viable and low-cost retrofit solutions according to a multi-level retrofit approach, suggest the possibility to implement ‘standardised’ solutions at an urban or territorial scale.
However, when expanding the scale of the intervention (and analysis) to a territorial level (city, region, country), more complex criteria and intervention strategies should be considered and evaluated to define the most effective action plan to minimise the overall risk. In particular, the actual limits of available resources, including budget, material, human and technical resources, logistics and supporting infrastructures, can represent the critical constraints for a large scale intervention. Damage scenarios and seismic risk analysis, devoted to the evaluation of the expected losses for a specific earthquake event or the possible losses in a time period, and the representations of their results in a GIS environment are receiving an increasing attention as helpful tools to support decision making, e.g. planning and prioritizing of retrofit or seismic intervention programs at large scale as well as implementing alternative non structural mitigation strategies and risk transferring through insurance/reinsurance industry.
The efficiency of alternative structural mitigation strategies has been under investigation within the framework of a seismic risk analysis approach ([45-46]). In Fig. 20 the benefits of different retrofit solutions on the performance of a specific class of existing frames can be appreciated in terms of fragility curves, describing the probability of exceed or equal pre-defined levels of damage.
Fig.20 Efficiency of alternative retrofit solutions (strength-only, ductility-only, selective weakening) in terms of fragility curves.(adopted after [45])
The effectiveness of targeting a partial or total retrofit intervention (thus aiming at different targeted performance) as part of a territorial scale retrofit strategy (via the adoption of standardized multi-level retrofit strategies) has been investigated and confirmed ([45]). A virtual implementation of alternative retrofit strategy and mitigation analyses, consisting on a traditional cost-benefit analysis as well as on a more refined multi-criteria decision approach, has been carried out on a case study region identified with Western Liguria, Italy. A multi-level performance-based retrofit strategy has been implemented with reference to alternative retrofit techniques, i.e. FRP or diagonal haunch (Fig. 21). In particular, two levels of upgrading plus a “do nothing” option were considered in this contribution: No Action–As Built condition (AB), Partial Retrofit (PR), Total Retrofit (TR).
Fig. 21Fragility curves representing the effects of general multi-level performance-based retrofit strategies (using FRP or haunch solution) on a frame system based on two levels of structural upgrading.
Based on the results of these damage scenario analyses pre and post-retrofit intervention (Fig. 22), it was confirmed that a quick implementation in critical sub-areas or regions of “partial” retrofit strategies could be an efficient approach to drastically reduce to a manageable level the consequences of the seismic event, more so when, due to resources constraints, a massive global intervention is not feasible.
Fig. 22. Effects of a controlled (partial) retrofit intervention at a territorial scale (Case Study: Western Liguria, Italy). Homeless people: a) as built conditions, b) after a partial retrofit intervention [46]
Refinement of macro-modelling vulnerability assessment and damage scenarios
Refinement of most up-to-date vulnerability assessment and damage scenario procedures (implemented in a GIS platform and based on either deterministic or probabilistic methodologies) related pre- and post-retrofit intervention.
Collaboration with the University of Genova researchers (part of a major EU-funded European Project on seismic risk analysis) has been agreed to further develop their proposed vulnerability methodology (used within the EU project) to a) accommodate recent findings on the mechanical model side (i.e. project on seismic response of existing building) b) account for appropriate retrofit strategies proposed in the FRST, c) suit NZ construction practice and ERP building details.
The work on earthquake damage scenario at a territorial scale prior to and after the proposed retrofit intervention in collaboration with the University of Genova has moved ahead very well with a paper presented at the European Conference on Earthquake Engineering, (1st ECEES 2006). See publications page, or click on this link to download the paper.
Selected References:
Giovinazzi, S. & Pampanin, S. (2007) " Multi-criteria Decision Approach for Performance-Based Seismic Retrofit of Existing Reinforced Concrete Buildings." Proc. of the Pacific Conference on Earthquake Engineering (PCEE), Singapore 2007. pdf
Giovinazzi, S. & Pampanin, S. (2007) "Mitigation Analyses for the Selection of Effective Seismic Retrofit Strategies at a Territorial Scale." Proc of New Zealand Society for Earthquake Engineering Annual Conference 2007, Palmerston North, 2007. [pdf coming soon]
Giovinazzi, S. Lagomarsino, S. & Pampanin, S. (2006) Vulnerability Methods and Damage Scenario for Seismic Risk Analysis as Support to Retrofit Strategies : an European Perspective." Proc of New Zealand Society for Earthquake Engineering Annual Conference 2006, Napier, 2006. pdf