Scipedia: Alex Barbat's chapters of books

Incremental dynamic analysis and pushover analysis of buildings. A probabilistic comparison

Alex Barbat — Thu, 10 May 2018 18:31:26 +0200

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.

Indicators for hazard, exposure and urban risk

Alex Barbat — Thu, 10 May 2018 17:22:18 +0200

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.

Social Aggravation Estimation to Seismic Hazard Using Classical Fuzzy Methods

Alex Barbat — Thu, 10 May 2018 11:38:42 +0200

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.

Seismic Response of RC Framed Buildings Designed According to Eurocodes

Alex Barbat — Thu, 10 May 2018 10:55:09 +0200

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.

VULNERABILITY ASSESSMENT OF DWELLING BUILDINGS

Alex Barbat — Thu, 10 May 2018 10:42:28 +0200

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.

NON LINEAR STRUCTURAL ANALYSIS. APPLICATION FOR EVALUATING SEISMIC SAFETY

Alex Barbat — Wed, 09 May 2018 12:55:14 +0200

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.

Holistic Evaluation of Seismic Risk in Barcelona

Alex Barbat — Wed, 09 May 2018 12:33:04 +0200

Within the framework described in Chapter 1, this chapter shows the evaluation of the seismic risk of the city of Barcelona, Spain, by applying a probabilistic analysis. On this basis a holistic evaluation of risk is performed taking into account social fragilityand lack of resilience aspects. Finally, the evaluation of the disaster risk management performance is conducted.

Theoretical and Conceptual Framework for the Assessment of Vulnerability to Natural Hazards and Climate Change in Europe

Alex Barbat — Wed, 09 May 2018 12:12:17 +0200

This chapter outlines a framework for multidimensional, holistic vulnerability assessment that is understood as part of risk evaluation and risk management in the context of Disaster Risk Management and Climate Change Adaptation. As a heuristic, the framework is a thinking tool to guide systematic assessments of vulnerability and to provide a basis for comparative indicators and criteria development to assess key factors and various dimensions of vulnerability, particularly in regions in Europe. However, it can also be applied in other world regions. The framework has been developed within the context of the research project MOVE (Methods for the Improvement of Vulnerability Assessment in Europe; www.move-fp7.eu) sponsored by the European Commission within the framework of the FP 7 program.

Numerical analysis of of repair and reinforcement of structures with FRP

Alex Barbat — Mon, 07 May 2018 15:08:09 +0200

In this chapter, we present a procedure to evaluate the local damage and global damage in structures subjected to static and dynamic actions, with special emphasis on the seismic problem. In addition to the formulation for the evaluation of damage, we introduce the concept of reinforcement and structural repair by using laminated epoxy matrix composites with carbon fiber reinforcement. For this purpose, the theory of mixtures is used to define a composite material from its basic components. Damage is also evaluated in these reinforced and/or repaired structures and the influence of these improvements on the overall damage assessment of the structure is discussed.

Revealing the Impact of Small Disasters to the Economic and Social Development

Alex Barbat — Mon, 07 May 2018 10:34:03 +0200

This chapter presents the results of the evaluation of the proneness of Colombia to small scale and chronic disasters, and the type of impact they have for the local and country development. This analysis detected the spatial variability and dispersion of vulnerability and risk in the country because of events that rarely enter the international or even national disaster databases. But these events pose an accumulative development problem for local areas and, given their overall probable impacts, for the country as a whole. First, the database of small disasters used is described to identify the strengths and weaknesses of the available data and how that information was prepared for this research. A conceptual framework regarding the impact of small disasters is then presented, to characterize the risk associated to this type of disasters together with a quantification of their effects and their economic costs in order to illustrate their relevance due to the accumulated impact and recurrence. Finally, the conclusions of the study are given, which identify new risk concepts: The concept of ‘intensive risk’ to refer to the concentrated risk manifesting infrequently in specific locations, and the concept of ‘extensive risk’ to refer to the diffuse risk manifesting frequently over wide territories.

Holistic Urban Seismic Risk Evaluation of Megacities: Application and Robustness

Alex Barbat — Mon, 07 May 2018 10:06:39 +0200

From a holistic perspective, disaster risk requires a multidisciplinary evaluation that takes into account not only the expected physical damage, the number and type of casualties or economic losses, but also the conditions related to social fragility and lack of resilience conditions, which favor the second order effects when a hazard event strikes an urban center. In this chapter, the urban risk is evaluated using composite indicators or indices. Expected building damage and losses in the infrastructure, obtained from loss scenarios are basic information for the evaluation of the physical risk index in each unit of analysis. The holistic evaluation of disaster risk is achieved affecting the physical risk with an impact factor, obtained from contextual conditions, such as the socioeconomic fragility and the lack of resilience, that aggravate the physical risk. Available data about these conditions at urban level are necessary to apply the method. The model is explained and the benefits of this approach are illustrated, inviting to the risk management of urban centers.

Neuro-fuzzy assessment of building damage and safety after an earthquake

Alex Barbat — Sun, 06 May 2018 19:16:41 +0200

This chapter describes the algorithmic basis of a computational intelligence technique, based on a neuro-fuzzy system, developed with the objective of assisting nonexpert professionals of building construction to evaluate the damage and safety of buildings after strong earthquakes, facilitating decision-making during the emergency response phase on their habitability and reparability. A hybrid neuro-fuzzy system is proposed, based on a special three-layer feedforward artificial neural network and fuzzy rule bases. The inputs to the system are fuzzy sets, taking into account that the damage levels of the structural components are linguistic variables, defined by means of qualifications such as slight, moderate or severe, which are appropriate to handle subjective and incomplete information. The chapter is a contribution to the understanding of how soft computing applications, such as artificial neural networks and fuzzy sets, can be used to complex and urgent processes of engineering decision-making, like the building occupancy after a seismic disaster.

Seismic Evaluation of Low Rise RC Framed Building Designed According to Venezuelan Codes

Alex Barbat — Sat, 05 May 2018 20:41:15 +0200

This chapter uses a mechanical method that involves non-linear analysis with deterministic and probabilistic approaches, as well as procedures of analysis based on limits states defined by displacements, in order to evaluate the behavior of a low rise RC building with plan irregularity designed according to Venezuelan codes and subjected to seismic actions. By using adequate structural models and computational tools, the seismic behavior of the building is obtained in a suitable way. Among these tools, the quadrants method was chosen, which provides the rapid assessment of the seismic capacity of a structure through its non-linear response. The results of the research show that the current design of this kind of structures is not safe when they are designed for the maximum seismic actions prescribed by codes. Therefore, it is necessary to review the design procedures in order to fulfill the goals of the performance-based design.

Monte Carlo analysis of structural systems using neural networks

Alex Barbat — Sat, 05 May 2018 19:42:50 +0200

Monte Carlo simulation is increasingly being used in the analysis of large and complex structural systems for the assessment of the uncertainty spread and the reliability. A major handicap for the popularization of this technology is the large number of deterministic evaluations needed to such purposes, inasmuch as linear or nonlinear finite element solvers are required for each output sample
calculation. In order to simplify this task neural networks are evaluated in this paper as a partial surrogate of the deterministic solver. The neural networks are trained with the input/output pairs resulting from a few number of finite element simulations, and are henceforth used in a Monte Carlo context. It is shown that when employed in this way, neural networks constitute a promising tool for a drastic reduction of the computational cost needed by a Monte Carlo simulation in this field of application. Three types of networks have been selected for the study, two of which correspond to supervised and the other one to hybrid learning procedures. The paper compares the network designs in their more relevant aspects, which are the training speed and accuracy, the extrapolation ability and the accuracy of the estimated probabilities.

Soil-structure-fluid seismic interaction

Alex Barbat — Fri, 04 May 2018 18:56:11 +0200

The behavior of structures subjected to earthquakes demonstrates that the phenomena of soil-structure and fluid-structure interaction have a great influence on the structural response, especially in the case of structures such as dams, tanks, elevated water tanks, marine platforms, intake towers, etc. The numerical study of these phenomena requires solving problems in which the coupling between two solids or between a solid and a fluid occurs only at the surfaces of contact between them. This chapter describes several numerical procedures used to solve the problem of seismic interaction. For this, it is necessary to have a record of seismic motion on the interface that separates the area of the soil considered in the analysis, which defines a theoretical surface sometimes called base rock. Below this, the soil can be assumed infinitely stiff or with a certain flexibility. To obtain an accelerogram at the level of the base rock, a deconvolution of the seismic motion available on the ground surface must be made. Then, this calculated accelerogram is applied on the soil-structure-fluid system.

Seismic risk of structures

Alex Barbat — Fri, 04 May 2018 16:38:51 +0200

From the perspective of disasters, risk has been defined in order to carry out its management, as well as to control the possible economic, social and environmental consequences that may occur in a specific area and time. This means that to estimate the risk it is necessary to take into account, from a multidisciplinary point of view, not only the expected physical damage, the victims or equivalent economic losses, but also social, organizational and institutional factors related to the development of the communities. At the urban level, for example, vulnerability, as an internal risk factor, must be related not only to the exposure of the material context or its physical susceptibility to being affected, but also to the social fragilities and the lack of resilience of the communities. In this chapter, conceptual, theoretical and practical problems related to seismic risk are presented. The definitions of hazard and seismic vulnerability, necessary to analyze the risk, are introduced. All the developments that are carried out are examined from the point of view of the possibilities of preventing seismic risk.

Nonlinear structural dynamics

Alex Barbat — Fri, 04 May 2018 15:51:13 +0200

When solving dynamic problems, it is necessary to define in some way the damping of the structure. Generally, a damping term that depends on the velocities is incorporated directly into the dynamic equilibrium equation. To do this, we define a structural damping matrix, such as Rayleigh's, which is quite difficult to estimate. Once the damping has been defined, the problem is solved as a linear elastic one, what enters in contradiction with the fact that a dissipative phenomenon is being treated. In this chapter, an alternative with greater conceptual basis is described, which considers the structural damping based on a viscoelastic constitutive models in which the stress depends in some way on the strain velocity. In this way, the term of structural damping arises directly in the dynamic equilibrium equation, where the properties of the materials can be determined through simple laboratory tests.

Fundamenteal aspects of the seismic design codes

Alex Barbat — Fri, 04 May 2018 15:19:32 +0200

The earthquake resistant design codes in force in the different countries are applied to the field of building structures. However, some of the standards give a certain appearance of "generality" that can give the impression that these are mandatory for any type of structure. In fact, the rules are general only in the definition of the seismic hazard of the area to which they apply, that is, in relation to the maximum ground acceleration. However, in each country, there are other specific codes for the design of non-building structures. This chapter describes the dynamic calculations foreseen in the building seismic design standards; the use of simplified, shear building models; the usual procedure of dynamic calculation of structures based on modal analysis; and, finally, the use of linear and non-linear response seismic spectra, which provides only the maximum response of the structure.

Computational simulation of the seismic response of buildings with energy dissipating devices

Alex Barbat — Thu, 03 May 2018 16:15:51 +0200

In this work, the nonlinear dynamic response of RC buildings with energy dissipating devices is studied using advanced computational techniques. A fully geometric and constitutive nonlinear model is used for describing the dynamic behavior of structures. The equations of motion are expressed in terms of cross sectional forces and strains and its weak form is solved using the displacement based finite element method. A suitable version of Newmark’s scheme is used in updating the kinematics variables in a classical Newton type iterative scheme. Material points of the cross section are assumed to be composed of several simple materials with their own constitutive laws. The mixing theory is used to treat the resulting composite. A specific finite element based on the beam theory is proposed for the dissipators including constitutive relations. Finally, several numerical tests are carried out to validate the proposed model.

PROBABILISTIC ASSESSMENT OF THE SEISMIC PERFORMANCE OF STEEL BUILDINGS DESIGNED ACCORDING TO THE LRFD SPECIFICATION

Alex Barbat — Thu, 03 May 2018 12:28:13 +0200

Seismic regulations and building codes experienced major advances in the last decades. Nevertheless, current trends in earthquake engineering are the assessment of the computational procedures provided by such design rules, by using probabilistic techniques, in order to test the anticipated levels of reliability and performance of the structures. While some consideration is given in codes to the uncertainties associated to the seismic action, no probabilistic requirements are posed on the responses, which determine the final design. Consequently, the risk associated to the design formulas remains unknown. The objective of this chapter is to study whether steel buildings designed and constructed according to the Load and Resistance Factor Design (LRFD) specification for Structural Steel Buildings, reasonably meet the probabilistic requirements on structural member safety applying non-linear dynamic analyses and Monte-Carlo techniques. Starting from a specific low-rise braced frame steel building existing in Manizales, Colombia, we also analyze mid-rise and high-rise braced frame buildings. Similar low- mid- and high-rise Moment-resisting frame buildings are also studied. For each building we performed more than ten thousand dynamic simulations, covering a wide range of combinations of demand and strength. In this way, we determine the exceedance probability of the construction capacity and we verify the safety and reliability of the structural members of the buildings. In the analysis of demand, we consider the probabilistic variation of the vertical gravity loads as well as of the seismic horizontal ones. The analyses of the strength of the studied buildings take into account the uncertainties and probability distributions of several parameters as: the yielding strain, the elasticity modulus, the cross-sectional area and their inertia moments. The analysis shows that in the cases here analyzed, but especially in moment-resisting frame buildings, the uncertainties in the input parameters may lead to significant failure probabilities. We conclude that braced frame steel buildings fulfil the seismic safety requirements while moment-resisting frame buildings would require a safety factor of about 2.7 for the column anchorages to the foundations.