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

The paper introduces a new global damage evaluation method which leads to a meaningful global damage index. A numerical procedure for the prediction of local and global damage in civil engineering structures using the finite element method and a continuum damage model, is presented. The method is adequate for the computation of the limit load in reinforced concrete (RC) structures and for the prediction of the failure mechanisms. Details of the applied damage model are given together with a description of the finite element implementation and the procedure for computing the global damage parameters. Examples of applications of the methodology to the nonlinear analysis of a range of RC structures, are presented.

Abstract

Capacity-spectrum-based-methods areused for assessing the vulnerability and risk of existing buildings. Capacity curves are usually obtained by means of nonlinear static analysis. Incremental Dynamic Analysis is a powerful tool based on nonlinear dynamic analysis. This method can provide results similar to the pushover analysis as the input is increasingly enlarged. It is well known that the randomness associated to the structural response can be significant, because of the uncertainties involved in the mechanical properties of the materials, among others uncertainty sources, and because the expected seismic actions are also highly stochastic. In this chapter, selected mechanical properties are considered as random variables and the seismic hazard is considered in a probabilistic way. A number of accelerograms of actual European seismic events have been selected in such a way that their response spectra fit well the response spectra provided by the seismic codes for the area where the building is constructed.A fully probabilistic approach is tackled herein by means of Monte Carlo simulation. The method is applied to a detailed study of the seismic response of a reinforced concrete building. The main purposes of this work are 1) to analyze the differences when static and dynamic techniques are used and 2) to obtain a measure of the uncertainties involved in the assessment of the vulnerability of structures. The results show that static based procedures are somehow conservative and that uncertainties increase with the severity of the seismic actions and with the damage. Low damage state fragility curves have little uncertainty while high damage grades fragility curves show great scattering.

Abstract

The difficulty of considering aspects such as the effectiveness of risk management or the ability to react in the event of a disaster in a single methodology of risk analysis requires using techniques based on indicators. Indicators, which reflect different aspects of risk components, are reference values ​​of the hazard, exposure, vulnerability or risk that consider physical economic, social and environmental aspects. The main application of a system of risk indicators is to assess all these aspects in a geographical area, which can be a country, a subnational region or a city and to allow a detailed analysis of the urban area. The basic indicators at the city level that are necessary to perform risk assessments and are presented in this chapter are the following: physical exposure indicators, economic exposure indicators, population exposure indicators, hazard and physical risk indicators, total risk index for holistic risk estimation and the risk management index.

Abstract

In the years, from a disasters perspective, risk has been dimensioned to allow a better management. However, this conceptualization turns out to be limited or constrained by the generalized use of a fragmented risk framework, which always consider first the approach and applicability of each discipline involved. To be congruent with risk definition, it is necessary to consider an integral framework, and social factors must be included. Even those indicators that could tell something about the organizational and institutional capacity to withstand natural hazards, should be invited to the table. In this article, we analyze one of the most important elements in risk formation: the social aggravation, which can be regarded as the convolution of the resilience capacity and social fragility of an urban center. We performed a social aggravation estimation over Barcelona, Spain, and Bogota, Colombia, considering a particular hazard in the form of seismic activity. The aggravation coefficient was formulated through a Mamdami fuzzy approach, supported by well-established fuzzy theory, which is characterized by a high expressive power and an intuitive humanlike manner.

Abstract

In order to ensure that a building structure do not collapse when subjected to the action of strong ground motions, modern codes include prescriptions in order to guarantee the ductile behavior of the elements and of the whole structure. Obviously, it is of special importance for the designer to know during the design process the extent of damage that the structure will suffer under the seismic action specified by the design spectrum and also the probability of occurrence of different states of behaviour. The incremental nonlinear static analysis procedure used in this paper allows formulating a new, simplified, seismic damage index and damage thresholds associated with five limit states. The seismic behavior of a set of regular reinforced concrete buildings designed according to the EC-2/EC-8 prescriptions for a high seismic hazard level is then studied using the proposed damage index and damage states. Fragility curves and damage probability matrices corresponding to the performance point are calculated for the studied buildings. The obtained results show that the collapse damage state is not reached in the buildings designed according the prescriptions of EC-2/EC-8 and also that the damage does not exceed the irreparable damage limit state.

Abstract

Risk is defined as the potential economic, social and environmental consequences of hazardous events that may occur in a specified area unit and period. The evaluation of physical vulnerability and risk of buildings is the main purpose of this chapter. Nevertheless, it is shown the necessity of considering not only the expected physical damage but also the social fragility and the lack of resilience of the exposed community, that is, a holistic evaluation of risk aiming at guiding decision making.  Both the vulnerability index and capacity spectrum methods for the evaluation of the physical risk are discussed herein. Both provide good results for the considered case study the urban area of Barcelona, Spain. Both methods show how a city, located in a low to moderate hazard region, which has paid no attention to the seismic performance of their buildings, has buildings with a high seismic vulnerability and a considerable seismic risk.

Abstract

Performance-Based Design is accepted commonly as the most advanced design and evaluation approach. However, its successful application depends on the ability to accurately estimate the parameters of structural response. The determination of these parameters requires applying analysis procedures where the non-linear behavior features of structures are included. This chapter presents and discusses these features of non-linear behavior and how they are incorporated in the process of static or dynamic structural analyses. Non-linear analysis allows obtaining from the seismic response significant structural response parameters such as ductility, overstrength, response reduction factor and damage thresholds. In order to illustrate the application of the non-linear analysis procedures, a set of concrete-reinforced moment-resisting framed buildings with various numbers of levels, was designed according to ACI-318 for high and very high level of seismic hazard. Their seismic safety is studied using both the static and dynamic non-linear analyses.