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3 Simplified illustration of ground types according to (a) EC8 and (b) the new classification scheme of Pitilakis et al. (2013)
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This paper addresses, from engineering point of view, issues in seismic risk assessment. It is more a discussion on the current practice, emphasizing on the multiple uncertainties and weaknesses of the existing methods and approaches, which make the final loss assessment a highly ambiguous problem. The paper is a modest effort to demonstrate that,...
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Citations
... These important differences are further highlighted through an application of the proposed and literature vulnerability curves for a specific seismic scenario with T m = 475 years, with the literature generic curves generally yielding lower loss ratio estimates. In general, the dispersion shown even between the generic literature curves themselves, which represent the same structural typologies, highlight the significant aleatory and epistemic uncertainties associated with the different fragility (and vulnerability) curves, that may depend on various parameters, such as the modeling assumptions and analysis approach used for their development (Pitilakis 2015;Pitilakis, Crowley, and Kaynia 2014;Silva et al. 2019). In addition, it's worth noting that such generic curves are commonly constructed for simple residential buildings assuming either single degrees of freedom systems or simplified two-dimensional structural models to be used within a seismic risk assessment framework at regional, urban or even larger scale. ...
The aim of this paper is to investigate whether existing generic fragility curves for various residential building typologies can be safely applied for the vulnerability assessment of school buildings. We select three representative typologies of actual reinforced concrete (RC) school buildings in Thessaloniki, Greece and we conduct a detailed fragility analysis combining field inspection and structural monitoring data to advanced numerical mod-eling. Building-specific fragility and vulnerability curves are derived for the three school buildings based on 3D incremental dynamic analysis (IDA) of the calibrated numerical models. The comparisons of the developed curves with generic ones showed their significant differences.
... To decrease the human and economic losses caused due to earthquakes (Daniell, 2014), it is important to conduct seismic risk calculations. Seismic risk assessment helps in predicting the probability of the building and structural damage and economic losses (Pitilakis, 2015) according to potential seismic hazard in an area. Once the seismic risk profile for an area is calculated, it is used to bring forward design methods for new buildings, to reinforce the current buildings (Caterino et al., 2018) and to effectively overcome catastrophic situations. ...
Near-field effects like directivity pulses are known to cause severe damage to particular kinds of infrastructure but most studies have limited themselves to the level of structural response and fragility computations. In this study, state-of-the-art tools are used from the Natural Hazards Engineering Research Infrastructure to estimate normalized economic losses and injuries, by considering one particular building type and occupancy category listed in HAZUS-MH. One non-directivity scenario, and three directivity scenarios with different levels of one sided propagation are simulated using dynamic rupture modeling by shifting the hypocenter from the center of the fault towards one side by different amounts for each directivity scenario. Furthermore, multiple five station networks at fixed offsets (rupture distances) from the fault are used to establish the influence of distance away from the fault on the economic losses. Both fault parallel and fault normal components of ground motion are simulated using a spectral finite element software SPECFEM3D. The engineering demand parameter computed in terms of peak inter-storey drift is used with 2000 realizations for a three-, six- and nine-storey commercial steel moment frames to estimate the percentage of economic losses normalized in terms of repair cost and injuries normalized in terms of population. The inclusion of complex phenomena like directivity to evaluate economic losses and risk will contribute to potential reassessment of risk mitigation policies by the United Nations Office for Disaster Risk Reduction (UNDRR).
... Studies including Crowley et al. (2005), Bazurro et al. (2007), Crowley et al. (2014), Pitilakis (2015), Sousa et al. (2018), Silva (2018), Silva (2019), Silva et al. (2019) and Kalakonas et al. (2020) have tried to evidence the shortcomings and future trends in the modelling approach of seismic risk assessments. These include comments for the treatment and propagation of uncertainties, the biases in the analyses based on the assumptions and input parameters used, and recommendations of future directions for the different stages of the analyses. ...
This study addresses some critical issues in the selection of input data for probabilistic seismic risk assessment at a local scale, considering available open-source information. It focuses on the derivation of vulnerability curves, which should be consistent with the local hazard and building practices, analysing the effect of (1) the record selection methodology, (2) the regression procedure followed for the analytical vulnerability derivation and (3) the consideration or not of local structural characteristics in the modelling process. It illustrates the significant differences in the results when distinct assumptions and sources of information—global, regional, or local—are used for the analysis. Based on a case study in Medellin, Colombia for assets representing the most vulnerable building classes in the city (unreinforced masonry houses and low code reinforced concrete buildings), accounting for more than 60% of its building stock, the effects of the previously mentioned parameters are studied. It is shown that hazard-consistent record selection is extremely important in the derivation of vulnerability models to use at a local scale, for sites with contributions from different tectonic regimes. Considerable variability is found in risk metrics such as Probable Maximum Loss curves and Average Annual Loss Ratios, rendering crucial the communication to decision-makers of these assumptions and the bias they could generate. Given the hazard characteristics of the site (with common low intensity events) it was seen that the lower tails of vulnerability curves have a large impact in loss results and should be given special attention.
... The most significant dynamic forces occurring in a structure are related to peak ground acceleration (PGA) [15]. In this paper, the PGA has been extracted from the data of recent earthquakes in Iran [16], which is given as: ...
... In this paper, PGA is selected as the seismic parameter for earthquakes. The fragility curves of the distribution line and low-voltage substation are represented in Fig. 3 [15]. ...
... Nowadays, various seismic fragility assessment methods are available in the literature. Many of them are based on empirical procedures, while others rely on more sophisticated numerical models (Lang 2002;Calvi et al. 2006;Rossetto et al. 2014;Pitilakis 2015). The common goal of these procedures is to assess buildings and their structural performance under earthquake loading. ...
Assessing seismic performance and identifying effective mitigation plans to improve resilience of non-engineered housing construction in developing countries pose a major challenge. Although reliable methods to evaluate current seismic risk levels and retrofitting interventions to engineered structures are available, they are not directly applicable to informal buildings because construction materials and connections between the walls and floors are very weak, resulting in premature failures of the structures. This leads to significant bias and uncertainty in the seismic building performance assessment and risk mitigation, which are difficult to identify. The present chapter proposes a seismic mitigation framework, consisting of four-steps, to increase the seismic resilience of non-engineered masonry buildings in developing countries through retrofitting solutions. The first and second steps identify non-engineered building typologies using global and local datasets. Thirdly, to assess structural performance, existing methods to derive fragility curves are presented to identify applicable methods to different situations in terms of data availability, highlighting the trade-off between rigour of investigations and accuracy of evaluations. The final step offers a mitigation approach based on low-cost engineering strategies for improving seismic resilience. The proposed framework is demonstrated on informal houses in Malawi, located within the East African Rift zone.
... In this study, we apply the macroseismic method developed by Lagomarsino and Giovinazzi (2006) and the resulting risk metrics are compared with the results from another recent study of Pavel and Vacareanu (2016) which employed a different methodology for risk assessment, namely the well-known HAZUS (FEMA 2012) approach. The aspect of the differences between the different methodologies for seismic performance assessment was discussed by Pitilakis (2015) with respect to the city of Thessaloniki. ...
In this paper, seismic risk scenarios for Bucharest, the capital city of Romania, are proposed and assessed. Bucharest has one of the highest seismic risk levels in Europe, and this is due to a combination of relatively high seismic hazard and a building stock built mainly before the devastating Vrancea 1977 earthquake. In this study, the seismic risk of Bucharest is assessed using the most recent information regarding the characteristics of the residential building stock. The ground motion amplitudes are evaluated starting from random fields obtained by coupling a ground motion model derived for the Vrancea intermediate-depth seismic source with a spatial correlation model. The seismic risk evaluation method applied in this study is based on the well-known macroseismic method. For several structural typologies, the vulnerability parameters are evaluated based on a damage survey performed on 18,000 buildings in Bucharest after the March 1977 earthquake. Subsequently, the risk metrics are compared with those from other studies in the literature that apply a different risk assessment methodology in order to gain a better view of the uncertainties associated with a seismic risk study at city level. Finally, the impact of several Vrancea intermediate-depth earthquake scenarios is evaluated and the results show that the earthquake which has the closest epicenter to Bucharest appears to be the most damaging.
... The study focuses on the investigation of two main sources of uncertainties inherently involved in the above described procedure: (a) uncertainties related with the building capacity, which reflect the variability of the properties of the structure, the fact that the modelling procedures are not perfect and the differences between any real RC building belonging in a certain typology and the idealized model 6 and (b) uncertainties related with the fragility curves, which are associated with the parameters describing the fragility curves, the methodology applied, as well as the selected damage states and the performance indicators of the element at risk 6 . Quantification of epistemic uncertainties for these two groups of parameters is performed using the logic tree approach, which is based on the concept of applying alternative methods or models, each of which is assigned a weighting factor that is interpreted as the relative likelihood of that method being correct 7 . ...
Seismic risk assessment and loss estimation are of major importance for decision-making with respect to the reduction of earthquake-induced losses in large urban areas. However, the methodological chain of seismic risk assessment, from seismic hazard assessment to evaluation of potential losses, encompasses both aleatory and epistemic uncertainties associated with different sources. The present study aims to give an insight into epistemic uncertainties in seismic risk assessment at urban scale when applying the Capacity Spectrum Method (CSM), using the city of Thessaloniki, Greece as a case study. Quantification of uncertainties related to structural capacity and fragility curves parameters was performed using a logic tree approach. A sensitivity analysis of the computed seismic risk results was also performed in order to determine which input parameters have the greatest impact on the output. For the considered set of input parameters, it was found that the epistemic uncertainties related to damage states thresholds of the fragility curves are the most significant ones, while those associated with the capacity curve parameters may also be substantial. On the contrary, the sensitivity of computed seismic risk on CSM parameters a1, a2 and γ appears to be negligible. The results highlight the critical points to which special attention should be paid when implementing the Capacity Spectrum Method for seismic risk assessment.
... Aleatory uncertainty is related to the intrinsic randomness of a phenomenon and reflects its stochastic nature, and thus cannot be reduced with the collection of additional data. Epistemic uncertainty on the other hand, related to the lack of proper knowledge about the system under consideration and to the necessity to use simplified models to simulate the complex nature or the response of the elements at risk, can theoretically be reduced by improving the inventory, the methods and generally the state of knowledge [4,[12][13][14]. ...
... The different steps of the process of risk assessment, from the estimation of hazard for rocksite conditions and the incorporation of site effects through appropriate soil amplification factors, to the estimation of the performance point and the resulting damage probabilities, are illustrated schematically in Figure 4 [12]. There are several uncertainties inherently involved in each step of the procedure described in Figure 4. ...
... There are several uncertainties inherently involved in each step of the procedure described in Figure 4. For example, uncertainties in the capacity curve reflect the variability of the properties of the structure, the fact that the modelling procedures are not perfect and the differences between any real RC building belonging in a certain typology and the idealized model [12], while uncertainties in the fragility curves are related to the parameters describing the fragility curves, the methodology applied, as well as the selected damage states and the performance indicators of the element at risk [12]. Because of all these uncertainties, the scatter of the resulting damages among different models can be very high [44]. ...
Seismic risk assessment and loss estimation are of major importance for decision-making with respect to the reduction of earthquake-induced losses in large urban areas. However, the methodological chain of seismic risk assessment, from seismic hazard assessment to evaluation of potential losses, encompasses numerous uncertainties, both aleatory and epistemic, associated with different sources. The present study is a comprehensive application of the Capacity Spectrum Method to the seismic risk assessment of the city of Thessaloniki, aiming to give an insight into epistemic uncertainties involved in the above methodology, owing to hazard modelling, structural capacity, fragility and damping, as well as shaking duration. To quantify and discuss the uncertainties, a logic tree approach is used. A sensitivity analysis of the computed seismic risk results is performed to determine the input parameters having the greatest impact. The analyses were carried out for the building stock of the city of Thessaloniki, Greece, for which detailed building inventory and very good knowledge of the soil conditions are available. Only physical losses due to the structural damage of the building stock were considered. Considerable scatter in the risk estimates was observed due to epistemic uncertainties. The sensitivity analyses demonstrated that the most influencing parameters when applying the Capacity Spectrum Method are the selection of the fragility curves for the buildings and the seismic hazard model adopted in the analysis. The decision-making process with respect to seismic risk assessment should therefore carefully account for uncertainties and pay attention to the most influencing parameters regardless of the methodology used.
The lack of empirical data regarding earthquake damage or losses has propelled the development of dozens of analytical methodologies for the derivation of fragility and vulnerability functions. Each method will naturally have its strengths and weaknesses, which will consequently affect the associated risk estimates. With the purpose of sharing knowledge on vulnerability modeling, identifying shortcomings in the existing methods, and recommending improvements to the current practice, a group of vulnerability experts met in Pavia (Italy) on April 2017. Critical topics related with the selection of ground motion records, modeling of complex real structures through simplified approaches, propagation of aleatory and epistemic uncertainties, and validation of vulnerability results were discussed, and suggestions were proposed to improve the reliability and accuracy in vulnerability modeling.
A coherent approach is presented to evaluate the seismic vulnerability of buildings founded on precarious
landslide slopes. In the first part a set of new predictive analytical expressions for assessing the co-seismic displacements of slopes is presented and compared with existing empirical models generally referred to as Newmark-type models. Advanced statistics of a comprehensive set of numerical results allowed the derivation of analytical predictive expressions of the co-seismic slope displacements with the best-correlated scalar and vector intensity measures (IMs) describing seismic hazard and site effects. In the second part of the paper an analytical method for assessing the vulnerability of RC buildings subjected to seismically induced slope displacements is presented. The methodology is based on the derivation of generic
probabilistic fragility functions for typical reinforced concrete (RC) buildings considering the slope inclination, the height and the soil material of the precarious slope. The vulnerability is finally assessed through a vulnerability index dm depending on the estimated probabilistic co-seismic slope displacements. The new predictive analytical expressions can be used in engineering practice while the general methodology for the vulnerability assessment can be extended to any type of building.
