Multi-regression analysis to enhance the predictability of the seismic response of buildings

Several methodologies for assessing seismic risk extract information from the statistical relationship between the intensity of ground motions and the structural response. The first group is represented by intensity measures (IMs) whilst the latter by engineering demand parameters (EDPs). The higher the correlation between them, the lesser the uncertainty in estimating seismic damage in structures. In general, IMs are composed by either a single (scalar-based IMs) or a group of features of both the ground motion and the structure (vector-valued IMs); the latter category provides higher efficiency to explain EDPs when compared to the first one. This paper explores how to find new vector-valued IMs, which are highly correlated with EDPs, by means of multi-regression analysis. To do so, probabilistic nonlinear dynamic analyses have been performed by considering a seven-story reinforced concrete building as a testbed. At a first stage, 30 scalar-based IMs have been correlated with 4 EDPs (i.e., 120 groups of IM-EDP pairs have been studied). Afterwards, the structural responses have been classified as elastic, inelastic and a combination of both. It has been analyzed how efficiency behaves when making these classifications. Then, 435 vector-valued IMs have been created to enhance the predictability of the scalar EDPs (i.e., 1740 groups of IM-EDP pairs have been analyzed). Again, the most efficient IMs have been identified. Sufficiency, which is another statistical property desired in IMs, has also been examined. Results show that the efficiency and sufficiency to predict the structural response increase when considering vector-valued IMs. This sophistication has important consequences in terms of design or assessment of civil structures.This research has been partially funded by the European Regional Development Fund (ERDF) of the European Union (EU), through project with reference EFA158/16/POCRISC (INTERREG/POCTEFA. EU) and by the Spanish Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICIN) through project with reference: PID2020-117374RB-I00/AEI/10.13039/501100011033. The support of these institutions is highly recognized and acknowledged. Yeudy F. Vargas-Alzate has been granted an Individual Fellowship (IF) in the research grant program of the Marie Sklodowska-Curie Actions (MSCA), European Union/European (H2020-MSCA-IF-2017) No 799553. This author is deeply grateful to this institution.Peer ReviewedPostprint (published version

Seismic risk assessment using stochastic nonlinear models

The basic input when seismic risk is estimated in urban environments is the expected physical damage level of buildings. The vulnerability index and capacity spectrum-based methods are the tools that have been used most to estimate the probability of occurrence of this important variable. Although both methods provide adequate estimates, they involve simplifications that are no longer necessary, given the current capacity of computers. In this study, an advanced method is developed that avoids many of these simplifications. The method starts from current state-of-the-art approaches, but it incorporates non-linear dynamic analysis and a probabilistic focus. Thus, the method considers not only the nonlinear dynamic response of the structures, modeled as multi degree of freedom systems (MDoF), but also uncertainties related to the loads, the geometry of the buildings, the mechanical properties of the materials and the seismic action. Once the method has been developed, the buildings are subjected to earthquake records that are selected and scaled according to the seismic hazard of the site and considering the probabilistic nature of the seismic actions. The practical applications of the method are illustrated with a case study: framed reinforced concrete buildings that are typical of an important district, the Eixample, in Barcelona (Spain). The building typology and the district were chosen because the seismic risk in Barcelona has been thoroughly studied, so detailed information about buildings’ features, seismic hazard and expected risk is available. Hence, the current results can be compared with those obtained using simpler, less sophisticated methods. The main aspects of the method are presented and discussed first. Then, the case study is described and the results obtained with the capacity spectrum method are compared with the results using the approach presented here. The results at hand show reasonably good agreement with previous seismic damage and risk scenarios in Barcelona, but the new method provides richer, more detailed, more reliable information. This is particularly useful for seismic risk reduction, prevention and management, to move towards more resilient, sustainable cities.This research was funded by the research grant program Marie Sklodowska-Curie Actions (MSCA), European Union/European (H2020-MSCA-IF-2017) No 799553. This research was also partially funded by the Spanish Government’s Ministry of Economy and Competitiveness (MINECO) and by the European Regional Development Funds (ERDF) of the European Union (EU) through projects with references CGL2015-65913 -P (MINECO/ERDF, EU) and EFA158/16/POCRISC (INTERREG/POCTEFA. EU). The support of these institutions is highly recognized and acknowledged.Peer ReviewedPostprint (published version

Improved intensity measures considering soil inelastic properties via multi-regression analysis

At certain depths, the elastic properties of the ground are not affected by seismic waves. However, as they reach the surface, the soil density decreases and so does its elastic limit. This means that the expected ground motion acting at the foundation of a structure cannot be adequately described without considering the inelastic response of the soil near the surface. Therefore, one of the key elements in characterizing the seismic response of civil structures is the site effect. These depend mainly on the parameters of the soil beneath the structure and the features of the ground motion acting at the depth, where non-linear effects are negligible. Therefore, the main objective of this paper is to find an intensity measure that incorporates the information provided by the soil profile under the structure and the ground motion acting at the bedrock level. Due to the random nature of both elements, a probabilistic framework using Monte Carlo simulation has been developed to analyze this problem. For this purpose, random soil profiles have been generated to obtain a representative sample of likely scenarios of the study area. A large database of Colombian ground motion records has been used to model the seismic hazard. Finally, power functions capable of relating the input variables to the dynamic response of a large set of reinforced concrete structures have been derived by considering multi-regression analysis. It has been observed that, in several cases, intensity measures extracted from the displacement spectrum appear in the mathematical arrangements. These functions could be used to improve the efficiency of seismic risk prediction at the urban level.This research has been funded by the Spanish Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICIN) through the projects with references: PID2020-117374RB-I00/AEI/10.13039/501100011033 and TED 2021-132559B-I00—J-02970.Peer ReviewedPostprint (published version

Estimators for structural damage detection using principal component analysis

Structural damage detection is an important issue in conservation. In this research, principal component analysis (PCA) has been applied to the temporal variation of modal frequencies obtained from a dynamic test of a scaled steel structure subjected to different damages and different temperatures. PCA has been applied in order to reduce, as much as possible, the number of variables involved in the problem of structural damage detection. The aim of the PCA study is to determine the minimum number of principal components necessary to explain all the modal frequency variation. Three estimators have been studied: T2 (the square of the vector norm of the projection in the principal component plan), Q (the square of the norm of the residual vector), and the variance explained. In the study, the results related to the undamaged structure needed one principal component to explain the modal frequency variation. However, the high damage configurations need five principal components to explain the modal frequency. The T2 and Q estimators have been arranged in order of increasing damage for all the performed experimental tests. The results indicate that these estimators could be useful to detect damage and to distinguish among a range of intensities of structural damage.This research has been partially funded by the Spanish Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICIN) through project with reference: PID2020-117374RB-I00/AEI/10.13039/501100011033.Peer ReviewedPostprint (published version

On the equal displacement aproximation for mid-rise reinforced concrete buildings

The equal displacement approximation is a well-known procedure for estimating the non-linear behavior of structures subjected to earthquake ground motions. This procedure plays a significant role in current seismic design, since it constitutes the basic assumption for defining strength reduction factors. In this paper, calculation of the performance point based on this rule is used to estimate engineering demand parameters such as those obtained by advanced probabilistic non-linear dynamic analysis, NLDA. We present a modification to the classic approach, to improve the predictability of the equal displacement rule. Uncertainties in seismic action and structural properties are considered. Mid-rise reinforced concrete buildings will be used as a testbed. To obtain a representative sample of buildings for statistical analysis, we describe the development through implementation of a numerical tool for calculating probabilistic NLDA. This tool, which is expected to evolve into interoperable software for assessing the seismic risk of structures, is developed within the framework of the KaIROS project. The results presented in this paper could be used to estimate the seismic risk of structures in a very simplified manner.Postprint (published version

Probabilistic seismic assessment of a high-rise URM building

According to the Sendai Framework for Disaster Risk Reduction (2015–2030), disasters have demonstrated that the recovery, rehabilitation and reconstruction phase, which needs to be prepared ahead of a disaster, is a critical opportunity to “Build Back Better”, integrating disaster risk reduction into development measures. In this respect, a significant number of structures, that constitute several European urban nuclei, belong to old constructive typologies, which were designed and built without any consideration for the seismic hazard. One of the most used typologies exhibiting this shortcoming is unreinforced masonry (URM). Therefore, an important step towards increasing resilience of European cities is to deeply understand the seismic behavior of this frequent typology. In order to do so properly, detailed probabilistic nonlinear building models should be developed. However, including the uncertainties associated with this typology is challenging due to the heterogeneity of the different manufacturing techniques, executed under primitive industrial standards, and to the construction techniques, which are dependent on regional uses and criteria in a pre-code scenario. The object of this research is twofold. First, a detailed quantification of the uncertainties related to the mechanical properties of this construction material is conducted. Then, the influence of this variability on the seismic performance of a representative building model of the Eixample district in Barcelona, Spain, is analysed. This building typology represents 72% of the building stock in this district with an average age of 90 years, which means that the construction practice, at that time, was only regulated by early council guidelines that are considered pre-code rules. Specifically, the probabilistic approach is illustrated with a case study performed on an existing seven-story (high-rise) URM. A detailed numerical model of this structure has been developed and randomized taking into account the variability of the material properties. Accordingly, 1000 models were generated and analysed by considering as input different sets of material random variables. The compressive strength, Young modulus, shear modulus and shear strength are chosen and modelled to encompass the material uncertainties. The seismic response of each variant (i.e. selected set of mechanical properties) is obtained through a simplified non-linear static procedure aiming to compare and categorize the influence of the probabilistic input on the seismic performance of the building. Results are presented in terms of correlations between damage parameters and material properties. The analysis carried out shows that the variability in the material properties generates significant uncertainties in the seismic response of URM buildings, leading to over or underestimate expected damage when compared with results based on approaches that do not consider the probabilistic nature of the problem.Peer ReviewedPostprint (published version

Un enfoque probabilista de la fragilidad y daño sísmico esperado en edificios porticados de hormigón armado

Las curvas de fragilidad y de daño son herramientas básicas para el análisis del riesgo sísmico. Estas curvas son imprescindibles para estimar los niveles de daño esperado para diferentes escenarios, incluyendo aquellos terremotos con una determinada tasa anual de excedencia o, en su caso, los sismos de diseño. A pesar de las incertidumbres en las acciones sísmicas esperadas y en las propiedades geométricas y resistentes de los edificios, la mayoría de los enfoques propuestos en las últimas décadas son deterministas y los resultados se suelen interpretar como valores medios de muchos escenarios probables. En este artículo, se revisa primeramente un enfoque determinista basado en curvas y espectros de capacidad y se usa un modelo paramétrico para las curvas de capacidad y una forma novedosa de considerar el daño teniendo en cuenta la deformación y la disipación de energía. Posteriormente, se formula el problema desde una óptica probabilista. Un edificio porticado regular, de hormigón armado, con 4 niveles y 4 vanos se usa como caso de estudio ilustrativo, pero el método puede aplicarse a otros tipos y otras geometrías estructurales. El trabajo permite poner de relieve la mayor robustez, versatilidad, riqueza y relevancia de los resultados de un enfoque probabilista que, por otra parte, tiene una alta relación beneficio/coste debido a los espectaculares progresos que se siguen consiguiendo en las herramientas de computación, incluyendo equipos y programas.   ARK: http://id.caicyt.gov.ar/ark:/s25457012/qae89bhybFragility and damage curves are basic tools for seismic risk analysis. These curves are essential to estimate the expected damage levels for different risk scenarios, just defined by earthquakes with a certain annual exceedance rate, or by design earthquakes. Despite the uncertainties in the expected seismic actions, and in the geometric and resistant properties of the buildings, most of the approaches proposed in recent decades are deterministic, and the results are often interpreted as mean values of many likely scenarios. This article firstly reviews a deterministic approach based on capacity curves and capacity spectra, which uses a parametric model for capacity curves and a novel way of considering damage, which includes the contributions to damage of the deformation and the one due to the energy dissipation. Afterwards, the problem is formulated with a probabilistic approach. A symmetric reinforced concrete building with 4 stories and 4 spans is used as case study, but the method can be applied to other building typologies and to other structural geometries. This work highlights the greater robustness, versatility, richness and relevance of the probabilistic approach, which, besides, has an increasing benefit/cost ratio, due to the huge progress that computers and software have attained, and are keeping on achieving.   ARK: http://id.caicyt.gov.ar/ark:/s25457012/qae89bhy

Comparative evaluation of Panbio and SD Biosensor antigen rapid diagnostic tests for COVID-19 diagnosis

The aim of our study was to evaluate the diagnostic performance of two antigen rapid diagnostic tests (Ag‐RDTs) to diagnose severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection. We evaluated Panbio and SD‐Biosensor Ag‐RDTs. We employed 186 polymerase chain reaction (PCR) negative samples to evaluate the specificity and 170 PCR positive samples to assess the sensitivity. We evaluated their sensitivity according to Cycle threshold (Ct) values and days post onset of symptoms (d.p.o.). Tests were compared using the McNemar's test. Agreement was evaluated using the kappa score. Specificity was 100% for Panbio and 97.3% for SD‐Biosensor. Sensitivity for samples with Ct ≤ 20 was 100% for both assays and for samples with Ct = 20–25 was 93.0% (Panbio) and 95.3% (SD‐Biosensor) (p = 1.000). Sensitivity decreased for samples wit Ct = 25–30 (Panbio: 41.3%, SD‐Biosensor: 52.2%, p = 0.125) and samples with Ct ≥ 30 (Panbio: 5.0%, SD‐Biosensor: 17.5%, p = 0.063). Sensitivity within seven d.p.o. was 87.7% for Panbio and 90.4% for SD‐Biosensor and notably decreased after seven d.p.o. Agreement with PCR was excellent for high viral load samples (Ct ≤ 25): Panbio, 98.9%, kappa = 0.974; SD‐Biosensor, 97.4%, kappa = 0.940. Agreement between Ag‐RDTs was excellent (94.9%, kappa = 0.882). Panbio and SD‐Biosensor Ag‐RDTs showed excellent agreement and diagnostic performance results for samples with high viral loads (Ct ≤ 25) or samples within seven d.p.o

Improving Accessibility in Online Education: Comparative Analysis of Attitudes of Blind and Deaf Students Toward an Adapted Learning Platform

15 p.People with different capacities, such as the deaf and blind, have problems accessing educational content due to lack of accessible technology. Accessibility and usability are closely related concepts that share the goals for a satisfactory user experience. Existing literature establishes a direct relation between accessibility and usability, and reports that there are problems with both in learning platforms, and more generally with most websites. The objective of this paper is to evaluate the accessibility and usability of a learning platform by interrogating its participants. Three groups of students with different capacities (blind, deaf and deaf-blind) used an accessible learning platform prototype to assess the accessibility and usability of the platform and its contents. This article presents a comparative study of the perception and attitude of blind and deaf students towards the use of a learning platform adapted to their personal needs. Results showed that their attitude to the adaptation was very positive but there were differences in the perception of the ease of use of the application and with the level of difficulty to access the learning content. This work contributes to the body of knowledge by showing the effects that adaptations have on learning contents for blind and deaf students in terms of accessibility and ease of use through the analysis of the perceptions of participants. Future work may consider increasing the sample of students, as well as developing and testing new technologies and approaches that address other forms of functional diversit