Cálculo de elementos estructurales

Descripció del recurs: el 21 de setembre de 2011El presente libro ha sido concebido como una introducción al cálculo de estructuras complejas y se dirige a estudiantes que ya han superado un primer curso de resistencia de materiales. Los capítulos 1 y 2 explican el cálculo de estructuras modelizables como elementos estructurales 1D (barras esbeltas). El capítulo 3 explica el cálculo de elementos estructurales bidimensionales (2D), como placas y paredes delgadas de depósitos para fluidos a presión. Los capítulos 4 y 5 estudian los elementos de cimentación que han de ser tratados como elementos estructurales 3D. Finalmente, en el capítulo 6 se introduce el cálculo dinámico aplicado al cálculo sísmico de edificios simples

Probabilistic estimation of the dynamic response of high-rise buildings via transfer functions

The significant number of seismic ground motion records to be considered when designing or assessing civil structures is a common restriction for employing advanced nonlinear dynamic methods. This is because the large computational time involved in the calculation of the nonlinear dynamic response of complex multi-degree-of-freedom systems. There are several strategies to overcome this limitation; however, the reliability estimation of the analyzed systems can be compromised. This research is focused on developing a methodology to achieve a probabilistic and reliable estimation of the seismic response of buildings by tackling the computational effort. To do so, a set of transfer functions extracted from the dynamic response of three building models have been obtained. Then, an optimal transfer function per building is identified as the one maximizing the prediction of engineering demand parameters (EDPs), when each structure is subjected to a large set of ground motions records. Results show that the response of a reduced number of records allows developing an enhanced strategy to obtain reliable results in terms of the main statistical moments of the EDPs. This increased capacity to analyze complex systems in an affordable time has important consequences in the identification of optimal designs in terms of the material-performance ratio, as well as in the estimation of expected seismic risk.We thank the companies "MUISCA Construcciones" and "Constructora Triple A", as well as the engineer Mario A. Silva and the architects Augusto Acuña and Carlos García, for having allowed the use of the monitoring results of the studied buildings. 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

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

Lab non destructive test to analyze the effect of corrosion on ground penetrating radar scans

Corrosion is a significant damage in many reinforced concrete structures, mainly in coastal areas. The oxidation of embedded iron or steel elements degrades rebar, producing a porous layer not adhered to the metallic surface. This process could completely destroy rebar. In addition, the concrete around the metallic targets is also damaged, and a dense grid of fissures appears around the oxidized elements. The evaluation of corrosion is difficult in early stages, because damage is usually hidden. Non-destructive testing measurements, based on non-destructive testing (NDT) electric and magnetic surveys, could detect damage as consequence of corrosion. The work presented in this paper is based in several laboratory tests, which are centered in defining the effect of different corrosion stage on ground penetrating radar (GPR) signals. The analysis focuses on the evaluation of the reflected wave amplitude and its behavior. The results indicated that an accurate analysis of amplitude decay and intensity could most likely reveal an approach to the state of degradation of the embedded metallic targets because GPR images exhibit characteristics that depend on the effects of the oxidized rebar and the damaged concrete. These characteristics could be detected and measured in some cases. One important feature is referred to as the reflected wave amplitude. In the case of corroded targets, this amplitude is lower than in the case of reflection on non-oxidized surfaces. Additionally, in some cases, a blurred image appears related to high corrosion. The results of the tests highlight the higher amplitude decay of the cases of specimens with corroded elements.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

Ground-penetrating radar evaluation of the ancient Mycenaean monument Tholos Acharnon tomb

The assessment of cultural heritage requires high-resolution and non-destructive methodologies. Ground-penetrating radar is widely applied in the inspection of historical buildings. However, some structures with curved surfaces make the radar data acquisition process difficult and consequently the following data interpretation. This paper describes a case study concerning a circular and buried Greek monument. This monument is a magnificent tomb buried with irregular stones. However, its structure and the internal stones arrangement are unknown. Therefore, a radar survey was carried out to achieve two main objectives: (i) identification of hidden elements and arrangement of the stones and (ii) detection of specific zones where further restoration and maintenance should be recommended. The methodology for the radar data acquisition involves the use of a laser scan in order to define accurately each radar line, covering all the internal surface of the tomb. Radar data processing was developed by converting Cartesian coordinates into polar coordinates. This procedure allows defining better the internal anomalies, improving the radar data interpretation. The main results of the survey were three: (i) the presence of a hidden target buried in the corridor access to the tomb; (ii) the description of the internal structure of the walls of the tomb, defining the stones arrangement and the position and depth to the keystone; and (iii) the existence of delimited zones where the signal is highly attenuated, probably due to a high salt content.Peer ReviewedPostprint (author's final draft

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

Probabilistic seismic assessment of a high-rise URM building

Several European urban nuclei are constituted by a significant number of ancient structures that belong to constructive typologies in which the seismic demand was not considered in their design at the time. Both, the accurate definition of the mechanical properties of their materials, and a proper seismic demand, are two of the major difficulties in the seismic damage assessment of structures due to their respective large associated uncertainties and variability, respectively. A representative high-rise unreinforced masonry (URM) building of the Eixample district in the city of Barcelona (Spain) is taken as a case-study. The building is modelled as an isolated load-bearing walls system with unidirectional iron beams-brick vaults slabs. The seismic demand variability is addressed by means of different ground motion records, which were selected following the conditional spectrum procedure, and subsequently scaled to different levels of demand (pga) according to the incremental dynamic analysis methodology. On the other hand, and due to the lack of homogeneity and level of knowledge associated with the large diversity of manufacturing and construction techniques, the compressive strength, shear modulus, shear strength and Young modulus are chosen and modelled as random variables in order to encompass the material uncertainties. Sufficient and representative samples are selected from both the population of mechanical properties of materials and the population of incrementally scaled dynamic analyses. Results are categorized in accordance to each of the selected random variables and seismic demand inputs (record and/or pga), providing, in varying degrees, their different correlations and tendencies among them.Postprint (published version

Non-linear static procedures applied to high-rise residential URM buildings

© 2016 Springer Science+Business Media Dordrecht In this work, the vulnerability of an unreinforced masonry building, evaluated on the one hand by using the incremental dynamic analysis, and on the other hand by using nine representative non-linear static incremental procedures, is compared. For comparison reasons among the different non-linear static procedures, the obtained incremental dynamic analyses results are used as reference values. The aim of this analysis is to evaluate the applicability and reliability of the diverse non-linear static procedures for unreinforced masonry buildings, and to propose modifications oriented to improve their use in this typology of structures. For this purpose, a fully representative unreinforced masonry building of the dominating building type in the Eixample district of Barcelona, is analyzed. Furthermore, the conditional spectrum approach procedure has been applied with the aim to conveniently define the seismic demand. Regarding the definition of the fragility curves, two different methodologies were used for each non-linear static procedure and incremental dynamic analyzes. Subsequently, the corresponding damage indices as well as the damage curves were calculated and compared for the different considered peak ground acceleration values. The results of this comparison seem to confirm that the damage curves obtained by performing the NSP and by applying the Risk-UE methodology overestimate the damage corresponding to low values of the PGA and underestimate the damage for higher values of the PGA.Peer ReviewedPostprint (author's final draft

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