Abstract

The seismic risk evaluation usually works with a fragmented concept of risk, which depends on the scientific discipline in charge of the assessment. To achieve an effective performance of the risk management, it is necessary to define risk as the potential economic, social and environmental consequences due to a hazardous phenomenon in a period of time. This article presents a methodology which evaluates the seismic risk from a holistic perspective, which means, it takes into account the expected physical damage and also the conditions related to social fragility and lack of resilience, which favour the second order effects when a hazard event strikes an urban centre. This seeks to obtain results which are useful in the decision making process for risk reduction. The proposed method for urban seismic risk evaluation uses the fuzzy sets theory in order to handle qualitative concepts and variables involved in the assessment, the physical risk level and aggravation level, related to the social fragility and the lack of resilience, are evaluated and finally a total risk level is determinate.

Abstract

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.

Abstract

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.

Abstract

The most important aspects of the design, seismic damage evaluation and safety assessment of structures with low ductility like waffle slabs buildings or flat beams framed buildings are examined in this work. These reinforced concrete structural typologies are the most used in Spain for new buildings but many seismic codes do not recommend them in seismic areas. Their expected seismic performance and safety are evaluated herein by means of incremental non linear structural analysis (pushover analysis) and incremental dynamic analysis which provides capacity curves allowing evaluating their seismic behaviour. The seismic hazard is described by means of the reduced 5% damped elastic response spectrum of the Spanish seismic design code. The most important results of the study are the fragility curves calculated for the mentioned building types, which allow obtaining the probability of different damage states of the structures as well as damage probability matrices. The results, which show high vulnerability of the studied low ductility building classes, are compared with those corresponding to ductile framed structures.

Abstract

A problem of feedback stabilization is addressed for a class of uncertain nonlinear mechanical systems with n degrees of freedom and nc < n control inputs. Each system of the class has the structure of two coupled subsystems with nc and nr degrees of freedom, respectively, a prototype being an uncertain base isolated building structure with n degrees of freedom actively controlled via actuators applying forces to specific degrees of freedom of the base movement, nc < n in number. A nonlinear adaptive feedback strategy is described, which, under appropriate assumptions on the system uncertainties, guarantees a form of practical stability of the zero state. Numerical simulations are also presented to illustrate the application of the control strategy to a base isolated building.

Abstract

Qualitative reasoning is an alternative problem-solving technique useful for the conceptual design of structures. Qualitative reasoning represents the relationships between parameters in a model, and a search computation assigns values represented by intervals and relevant points in the behavior. The traditional difference between analysis and design or input and output parameters in a procedural computation is not existent in qualitative reasoning, since all the parameters in a model are equally represented. Qualitative reasoning derives values for parameters even with incomplete and imprecise knowledge about the model. This work presents a qualitative structural analysis framework, suitable for the evaluation of conceptual designs as well as for tutoring systems. The framework has been implemented in a computer program called Agrippa using the computer language Prolog. Based on a representation of fundamental principles of equilibrium, compatibility, and force-deformation and an incomplete knowledge of geometry and topology, Agrippa derives the signs and relative magnitude of forces and displacements for three-dimensional models of structures.

Abstract

Nowadays, the use of energy dissipating devices to improve the seismic response of RC structures constitutes a mature branch of the innovative procedures in earthquake engineering. However, even though the benefits derived from this technique are well known and widely accepted, the numerical methods for the simulation of the nonlinear seismic response of RC structures with passive control devices is a field in which new developments are continuously preformed both in computational mechanics and earthquake engineering. In this work, a state of the art of the advanced models  for the numerical simulation of the nonlinear dynamic response of RC structures with passive energy dissipating devices subjected to seismic loading is made. The most commonly used passive energy dissipating devices are described, together with their dissipative mechanisms as well as with the numerical procedures used in modeling RC structures provided with such devices. The most important approaches for the formulation of beam models for RC structures are reviewed, with emphasis on the theory and numerics of formulations that consider both geometric and constitutive sources on nonlinearity. In the same manner, a more complete treatment is given to the constitutive nonlinearity in the context of fiber-like approaches including the corresponding cross sectional analysis. Special attention is paid to the use of damage indices able of estimating the remaining load carrying capacity of structures after a seismic action. Finally, nonlinear constitutive and geometric formulations for RC beam elements are examined, together with energy dissipating devices formulated as simpler beams with adequate constitutive laws. Numerical examples allow to illustrate the capacities of the presented formulations.

Abstract

A state of the art on simulation methods in stochastic structural analysis is presented. The purpose of the paper is to review some of the di erent methods available for analysing the effects of randomness of models and data in structural analysis. While most of these techniques can be grouped under the general name of Monte Carlo methods, the several published algorithms are more suitable to some objectives of analysis than to others in each case. These objectives have been classiffed into the following cathegories: (1), The Statistical Description of the structural scattering, a primary analysis in which the uncertain parameters are treated as random variables; (2) The consideration of the spatial variability of the random parameters, that must then be modelled as Random Fields (Stochastic Finite Elements); (3) The advanced Monte Carlo methods for calculating the usually very low failure probabilities (Reliability Analysis) and, (4), a deterministic technique that depart from the random nature of the above methods, but which can be linked with them in some cases, known as the Response Surface Method. All of these techniques are critically examined and discussed. The concluding remarks point out some research needs in the field from the authors' point of view.

Abstract

This paper presents a survey of the numerical simulation of base isolation systems for the vibration control of buildings and their equipment, primarilly against earthquakes. Base isolation has received much attention in the recent twenty years and many buildings have been protected using this technology. The article focusses mainly on the different numerical methods used in the analysis of base isolated buildings. The conventional form of solving the equations of motion governing the seismic response of building structures with nonlinear base isolation consists of using monolithic step by step integration methods. As an effcient alternative, static condensation and block iterative schemes can be applied. The particularities of the equations of motion of buildings equiped with various base isolation systems are described. The linear theory of base isolated buildings is then presented. After this, numerical solution techniques for the analysis of the seismic response of buildings with isolation systems are developed in detail in the paper. Finally, numerical results for elastic and inelastic structures are described. A complete set of references coverning a wide range of studies is included.

Abstract

En este artículo se desarrolla un controlador digital predictivo con aplicación en la reducción de la respuesta sísmica de estructuras. Su eficacia se comprueba controlando la respuesta de un modelo de reactor nuclear.