New tension-compression damage model for complex analysis of concrete structures

A new damage model, based on continuum damage mechanics and simulating the opening, closing, and reopening of cracks in concrete using only one surface of discontinuity, is proposed in this article. The model complies with the thermodynamics principles of nonreversible, isothermal, and adiabatic processes. Two scalar internal variables have been defined: a tensile damage variable d+d+ and a compressive damage variable d-d-; the threshold of damage is controlled by only one surface of discontinuity and a new parameter controlling the damage variable that should be activated. This new parameter represents the ratio of tensile stress to compressive stress in the damaged material. The continuity of response under complex loads, which is one of the aims of this work, is ensured. An adequate response under different types of loads leads to the conclusion that the proposed model provides a powerful tool to numerically analyze reinforced concrete structures. Validation and illustrative examples are included in the article.Peer ReviewedPostprint (author's final draft

Hybrid loss exceedance curve (HLEC) for disaster risk assessment

Taken into account that the natural hazard risk is a contingent liability and, therefore, a sovereign risk for national governments, it is important to assess properly the potential losses to design a suitable risk reduction, retention and transfer strategy. In this article, a disaster risk assessment methodology is proposed based on two approaches: on the one hand, the empiric estimation of losses, using information available from local disaster databases, allowing estimating losses due to small-scale events and, on the other hand, probabilistic evaluations to estimate losses for greater or even catastrophic events, for which information usually is not available due to the lack of historical data. A ‘‘hybrid’’ loss exceedance curve is thus determined, which combines the results of these two approaches and represents the disaster risk in a proper and complete way. This curve merges two components: the corresponding to small and moderate losses, calculated using an inductive and retrospective analysis, and the corresponding to extreme losses, calculated using a deductive and prospective analysis. Applications of this risk assessment technique are given in this article for eleven countries

Probabilistic dynamic analysis of steel buildings with long duration earthquakes

El análisis probabilista del comportamiento sísmico de una estructura requiere cuantificar las incertidumbres de las variables y parámetros involucrados, incluyendo la acción sísmica y las propiedades mecánicas de sus elementos. En este artículo se analiza el comportamiento sísmico de edificios de acero bajos, medianos y altos, sometidos a las acciones sísmicas de larga duración probables de la Ciudad de México. El análisis se efectúa bajo una perspectiva probabilista. Las acciones sísmicas se han seleccionado de forma que sean compatibles con los espectros de diseño, para suelos blandos y sismos de larga duración de esta área. Los análisis dinámicos, se llevan a cabo usando simulaciones Monte Carlo. La resistencia y la ductilidad de vigas y columnas se consideran como variables aleatorias; las acciones sísmicas también se consideran de forma probabilista. El daño esperado es evaluado con el índice de Park y Ang. Los resultados muestran que las incertidumbres esperadas en la respuesta son significativas, siendo la aleatoriedad de la acción sísmica la principal causa. De la comparación entre los valores medianos del enfoque probabilista con los del caso determinista se observa una buena consistencia de los resultados correspondientes a edificios de baja y mediana altura, siendo menor en el comportamiento no lineal de los edificios altos. Los edificios bajos y medianos analizados tienen un comportamiento adecuado antes las acciones sísmicas de la zona de estudio, pero los edificios altos tienen un mayor riesgo sísmico y podrían tener daños leves o moderados. Se concluye que el enfoque probabilista proporciona información más rica sobre la respuesta estructural.The probabilistic analysis of the seismic performance of a structure requires quantifying the uncertainties of the involved variables and parameters, including the seismic action and mechanical properties of its elements. In this article, the seismic performance of high-rise, mid-rise and low-rise of steel buildings, subjected to long duration seismic actions like those of Mexico City, is analyzed. The analysis is conducted by using a probabilistic approach. The seismic actions are selected to be compatible with the design spectra of the Mexican seismic code for soft soils and long duration earthquakes, characteristic for this region. The dynamic analyses are performed by using Monte Carlo simulations. The strength and ductility of the beams and columns are considered random variables; the seismic actions are also modelled in a probabilistic way. The damage index of Park and Ang is used. The results show that the uncertainties expected in the response are significant, being the randomness of the seismic action the main cause. From the comparison between the mean values of the probabilistic approach and those corresponding to the deterministic case, a good consistency of the result obtained for low-rise and mid-rise buildings is observed. Nevertheless, the consistency is lower in the case of high-rise buildings. The analyzed low-rise and mid-rise buildings show a good seismic performance to seismic actions, but the high-rise buildings show slight or moderate damage. It is concluded that the probabilistic approach provides a more complete information on the structural response.Peer ReviewedPostprint (published version

VISCOUS DAMAGE MODEL FOR TIMOSHENKO BEAM STRUCTURES

A local damage constitutive model based on Kachanov’s theory is used within a finite element frame and applied to the case of 2D and 3D Timoshenko beam elements. The model takes into account viscous effects, thus allowing damping to be considered in a rigorous way. A damage index based on potential energy criteria, useful in evaluating the behaviour of structures or of parts of structures, is proposed. The procedure is applied to estimate the damage produced by seismic actions in reinforced concrete building structures, whose response is computed by using a non-linear Newmark-type incremental time integration scheme. Three numerical examples are included; one of them compares results obtained by using the proposed model with results of a laboratory test. &nbsp

Una nueva estrategia para el estudio de la vulnerabilidad de edificios expuestos a explosiones a cielo abierto

ResumenEn este artículo se describe una nueva metodología para evaluar el efecto de las explosiones a cielo abierto sobre estructuras equivalentes a las fachadas de los edificios. El daño sufrido por la estructura se define mediante superficies de vulnerabilidad que son función de la magnitud de la explosión, la distancia de esta a la estructura y del índice de daño por detonación desarrollado en este artículo. El índice propuesto considera la degradación de la capacidad de carga de la estructura, la fracturación y la perdida de material debido a la explosión. Para ello, la estructura se modela mediante elementos discretos (DEM) los cuales permiten representar adecuadamente estados de multifractura. La capacidad de carga de la estructura se cuantifica mediante un ensayo virtual sobre la estructura dañada. Las fuerzas provocadas sobre la estructura por la explosión se modelan utilizando una metodología semiempírica, lo que permite obviar el análisis con base en la dinámica de fluidos reduciendo el tiempo de cálculo.AbstractIn this paper, a new methodology is described to evaluate the effect of open air explosions on equivalent structures to the facades of buildings. The structural damage is defined by vulnerability surfaces that are a function of the explosion magnitude, the distance to the structure and the detonation damage index developed in this article. The proposed index considers the structural load capacity degradation, the fracturing and the loss material due to the explosion. The structure is modeled by means of discrete elements (DEM) which allows describing the multifracturing state. The load capacity of the structure is quantified by a virtual compression test on the damaged structure. The forces on the structure caused by the explosion are modeled by a semi-empirical methodology, which avoids the fluid-dynamic analysis and reduces the computation time

Seismic response and torsional effects of RC structure with irregular plant and variations in diaphragms, designed with Venezuelan codes

The objective of this study is to determine the seismic response and torsional effects of an existing Reinforced Concrete building with irregular plant and five levels projected according to an older version of Venezuelan seismic design code. Two structures were analysed: the original building and a redesigned version. Nonlinear static analysis and nonlinear 3D dynamic analysis were applied, based on registers of three synthetic accelerograms compatible with the elastic design spectrum for the used code. In 3D analysis, four structures were simulated, with and without rigid diaphragms so as to compare the seismic behaviour of the buildings. Through this nonlinear analysis parameters were determined that define the behaviour of the structure, torsional moments and rotations in columns reached for simulated buildings. Also, to obtain damage fragility curves for five states damage were generated. Results show that the original structure has an inadequate resistant behaviour and a high probability of exceeding the moderate damage state, while the redesigned structure presents good performance under seismic events according to the existing code. It was also observed that maximum torsional effects occur in the entrant corners of the  irregular plant, which are reduced in mid-rise buildings by using a rigid diaphragm

Ground-Shaking Scenarios and Urban Risk Evaluation of Barcelona using the Risk-UE Capacity Spectrum Based Method

The Capacity Spectrum Based Method (CSBM) developed in the framework of the European project Risk-UE has been applied to evaluate the seismic risk for the city of Barcelona, Spain. Accordingly, four damage states are defined for the buildings, the action is expressed in terms of spectral values and the seismic quality of the buildings, that is, their vulnerability, is evaluated by means of capacity spectra. The probabilities of the damage states are obtained considering a lognormal probability distribution. The most relevant seismic risk evaluation results obtained for Barcelona, Spain, are given in the article as scenarios of expected losses

Seismic hazard and risk scenarios for Barcelona, Spain, using the Risk-UE vulnerability index method

The vulnerability index method, in its version developed in the framework of the European project Risk-UE, has been adapted and applied in this article, to evaluate the seismic risk for the city of Barcelona (Spain) through a GIS based tool. According to this method, which defines five damage states, the action is expressed in terms of the macroseismic intensity and the seismic quality of the buildings by means of a vulnerability index. The probabilities of damage states are obtained considering a binomial or beta-equivalent probability distribution. The most relevant seismic risk evaluation results obtained, for current buildings and monuments of Barcelona, are given in the article as scenarios of expected losses