Lluis Pujades

Seismic vulnerability and risk evaluation methods for urban areas. A review with application to a pilot area

The most relevant seismic vulnerability and risk analysis methods are discussed and compared in this article using, as a pilot urban area, the city of Barcelona, Spain, where risk studies have been carried out over the last 15 years in the framework of different research projects. Most of the buildings in Barcelona, which have unreinforced masonry structure or reinforced concrete structure with waffled slab floors, show a high degree of vulnerability to earthquakes. The physical seismic risk but also the socio-economic implications of risk are considered in the article. The robustness of the innovative holistic approach, based on indicators related to the physical exposure, the social fragilities and the lack of resilience of urban area, is also proved. Using a geographic information system (GIS), the seismic risk results are described by means of scenarios of expected losses, but also as scenarios of probabilities of occurrence of predefined damage states.

GPR survey to confirm the location of ancient structures under the Valencian Cathedral (Spain)

This paper describes the ground-penetrating radar (GPR) survey performed inside the Cathedral of Valencia, Spain. It is part of historical studies performed in the Cathedral in order to add information to old maps and documents in the Cathedral Archives and also to analyze the extent and importance of potentially destructive moisture areas that were appearing on the floor. The construction of the Cathedral of Valencia occurred in three stages, all of which are well-documented in the Cathedral Archives with detailed drawings, maps, and charts. The radar data were successful in locating crypts, ossuaries, sepulchers, and graves, and the location of ancient walls that existed before the final Cathedral expansion. Three cultural layers corresponding to the three periods of construction were also identified corresponding to the Roman, Arabian and Middle Age Epochs. Measurements of relative sub-floor moisture were obtained by comparing dielectric permittivity changes and radar velocity differences between materials in humid and non-humid areas.

Experimental and analytical research on seismic vulnerability of low-cost ferrocement dwelling houses

Analytical and experimental research for determining the seismic vulnerability of ferrocement houses, which is a low-cost system using precast thin panels, is presented. The research comprises the following tasks: (a) a field survey on the ferrocement dwelling houses actually built in seismic regions in Colombia; (b) a cyclic load test on 1:1 scale models; (c) identification of the parameters of the Bouc–Wen hysteretic model for the observed panel behaviour; and (d) Monte Carlo simulations of models intended to estimate the fragility curves of the houses. Despite the models exhibiting stiffness degradation, it was concluded that the system is adequate for regions of moderate to high seismicity.

Methodology and applications for the benefit cost analysis of the seismic risk reduction in building portfolios at broadscale

This article presents a methodology for an estimate of the benefit cost ratio of the seismic risk reduction in buildings portfolio at broadscale, for a world region, allowing comparing the results obtained for the countries belonging to that region. This methodology encompasses (1) the generation of a set of random seismic events and the evaluation of the spectral accelerations at the buildings location; (2) the estimation of the buildings built area, the economic value, as well as the classification in structural typologies; (3) the development of vulnerability curves for each typology; (4) the estimation of the annual average loss of the buildings portfolio in the current conditions as well as in the case of a hypothetical structural intervention. The benefit cost ratio is estimated as the difference between the estimates of the present value of these two annual average losses, divided by the retrofitting costs. This methodology has been applied to the portfolio of public schools of 14 countries of Latin America and the Caribbean, for evaluating the feasibility of the seismic risk reduction at a national scale.

Prioritizing interventions to reduce seismic vulnerability in school facilities in Colombia

The Colombian seismic code NSR-98 establishes the requirement for the seismic vulnerability analysis and, if necessary, the strengthening of public facilities (schools). Due to the investments required by risk-reduction programs, it is necessary to establish criteria for assigning priorities for the interventions. This article proposes a methodology for obtaining a benefit-cost ratio (BCR) at the subnational level, by assessing the expected annual average loss of the built area of public schools and the retrofitting cost. The BCR is estimated as the difference between the estimates of the net present value for status quo and retrofitted states, both divided by the retrofitting costs. According to the BCR, 47.3% of the total school-built area of Colombia should be retrofitted where the retrofitting costs correspond to 25% of the total investment. Proposed BCR is useful for prioritizing regions as a function of the feasibility of reducing the seismic vulnerability of the schools.

Probabilistic seismic damage assessment of RC buildings based on nonlinear dynamic analysis

The incremental dynamic analysis is a powerful tool for evaluating the seismic vulnerability and risk of build- ings. It allows calculating the global damage of structures for different PGAs and representing this result by means of damage curves. Such curves are used by many methods to obtain seismic risk scenarios at urban level. Even if the use of this method in a probabilistic environment requires a relevant computational effort, it should be the reference method for seismic risk evaluation. In this article we propose to assess the seismic expected damage by using nonlinear dynamic analysis. We will obtain damage curves by means of the incremental dynamic analysis combined with the damage index of Park & Ang. The uncertainties related to the mechanical properties of the materials and the seismic action will be con- sidered. The probabilistic damage curves obtained can be used to calculate not only seismic risk scenarios at urban level, but also to estimate economic losses.

Probabilistic Assessment of Seismic Risk of Dwelling Buildings of Barcelona. Implication for the City Resilience

The knowledge of seismic risk of buildings can contribute to increase the resilience of cities. In the present work a new assessment of the seismic risk of dwelling buildings of Barcelona was done. This assessment was performed according to a probabilistic methodology, which is summarized in the following steps: (1) performing a probabilistic seismic hazard assessment (PSHA) to obtain exceedance rates of macroseismic intensities; (2) performing a probabilistic seismic vulnerability assessment (PSVA) of each building in order to determine probability density functions that describe the variation of a vulnerability index; and (3) performing a probabilistic seismic risk assessment (PSRA) to generate seismic risk curves in terms of frequencies of exceedance of damage states. In the present work 69,982 dwelling buildings of Barcelona were assessed. According to the results the percentage of dwelling buildings of Barcelona that have a probability equal or greater than 1% of suffer partial collapse in the next 50 years is a value between 0% and 34.29%. A value of 0% corresponds to the results of seismic risk obtained for the case where regional vulnerability modifiers were not considered during the procedure to assess the seismic vulnerability of buildings and 34.29% correspond to the case where regional vulnerability modifiers were considered. For the same two options, the losses due to the physical damage of the dwelling buildings of Barcelona assessed for an exposure time of 50 years, could vary from 807.3 to 1739.4 millions of euros, respectively. Finally, possible uses of the seismic risk results computed in the present work are mentioned.