Abstract

In this work, a formulation for rod structures, able to consider coupled geometric and constitutive sources of nonlinearity in both the static and the dynamic range, is developed. It is extended for allowing the inclusion of passive energy dissipating elements as a special rod element and geometric irregularities as a full three-dimensional body connected to the framed structure by means of a two-scale model. The proposed formulation is based on the Reissner-Simo geometrically exact formulation for rods considering an initially curved reference configuration and extended to include arbitrary distribution of composite materials in the cross sections. Each material point of the cross section is assumed to be composed of several simple materials with their own thermodynamically consistent constitutive laws. The simple mixing rule is used for treating the resulting composite. Cross sections are meshed into a grid of quadrilaterals, each of them corresponding to a fiber directed along the axis of the beam. A mesh independent response is obtained by means of the regularization of the energy dissipated at constitutive level considering the characteristic length of the mesh and the fracture energy of the materials. Local and global damage indices have been developed based on the ratio between the visco-elastic and nonlinear stresses. The consistent linearization of the weak form of the momentum balance equations is performed considering the effects of rate dependent inelasticity. Due to the fact that the deformation map belongs to a nonlinear manifold, an appropriated version of Newmark's scheme and of the iterative updating procedure of the involved variables is developed. The space discretization of the linearized problem is performed using the standard Galerkin finite element approach. A Newton-Raphson type of iterative scheme is used for the step-by-step solution of the discrete problem. A specific element for energy dissipating devices is developed, based on the rod model but releasing the rotational degrees of freedom. Appropriated constitutive relations are given for a wide variety of possible dissipative mechanisms. Several numerical examples have been included for the validation of the proposed formulation. The examples include elastic and inelastic finite deformation response of framed structures with initially straight and curved beams. Comparisons with existing literature is performed for the case of plasticity and new results are presented for degrading and composite materials. Those examples show how the present formulation is able to capture different complex mechanical phenomena such as the uncoupling of the dynamic response from resonance due to inelastic incursions and suppression of the high frequency content. The study of realistic flexible pre-cast and cast in place reinforced concrete framed structures subjected to static and dynamic actions is also carried out. Detailed studies regarding to the evolution of local damage indices, energy dissipation and ductility demands are presented. The studies include the seismic response of concrete structures with energy dissipating devices. Advantages of the use of passive control are verified.

Abstract

This monograph presents the fundamental concepts related to seismic action, the structural response of buildings, the assessment of vulnerability, risk and seismic damage. Some indices proposed by different researchers are also indicated to assess the level of damage suffered by buildings under seismic actions. It also describes the ways to define the seismic action that are appropriate to the structural analysis. Techniques are developed to generate artificial accelerograms, which are necessary to perform the evaluation of the non-linear seismic response through an analysis in time. This evaluation also allows obtaining the level of damage suffered by the structures. The seismic action is focused on the city of Barcelona, ​​Spain, which is located in an area of moderate seismicity and, in addition, does not have seismic records. The seismic action is established by seismic design spectra and artificial accelerograms compatible with said spectra. At the end of this work, the responses spectra considered to define the seismic demand and the artificial accelerograms obtained are shown, which can be used for the evaluation of structures for different seismic intensities and for different locations in Barcelona. Finally, a methodology for assessing the vulnerability and the seismic risk of buildings is described. The methodology is applied in several steps and includes modeling and non-linear analysis of structures. It is focused on obtaining fragility curves, which can be generated both through an empirical evaluation and through an analytical evaluation. The first is based on the damage observed in the buildings of an area after an earthquake occurs, while the second is based on a numerical analysis, where the seismic response of the structure is predicted.

Abstract

The monograph highlights the way in which, in the long term, the application of design standards can lead to a reduction of seismic risk in urban areas. The seismic design standards make recommendations regarding the seismic loads to be used, the simplified methods of structural analysis, the criteria that must be applied to ensure a good overall behavior of the same, as well as the design details that must be incorporated. The structural analysis procedures foreseen in all the world standards are based on concepts generally used in the static and dynamic calculation of structures. However, the concepts considered when using these simplified procedures of dynamic analysis and the approximate formulas for the determination of the dynamic characteristics of buildings, are not explained. For this reason, the monograph analyzes the content of the seismic-resistant design regulations in relation to the analysis methods they propose, explaining the concepts of structural analysis that are applied in each case, with special reference to the Spanish regulations in vigor, NCSE-02. Since many design codes include rules that are not justified in the text of the regulations, this monograph also deals with aspects of the so-called conceptual design that requires decisive decisions in the initial phases of the design of structures, which condition the seismic behavior of the same. To facilitate the application of the dynamic analysis of buildings, a program developed in Matlab ® has been incorporated, which can be obtained from the web page www.cimne.com/is-56/modal, together with the data files and results, which are described in the Annex to this monograph.

Abstract

Once an earthquake has occurred, the inspection of the buildings should be carried out as quickly as possible, in order to reduce the risk and discomfort of the people. This means that it is not possible to perform a detailed evaluation, making a complete geometric survey of the building, taking samples for a detailed analysis of the seismic pathology and performing a numerical analysis using computers. On the contrary, damage assessments and the habitability of buildings should be carried out based on visual inspection and expert judgment. This monograph aims to develop a general methodology for the inspection and classification of buildings affected by an earthquake. It starts by collecting and analyzing the information existing in different countries on the main methodologies of damage assessment and habitability, in order to compare different approaches and identify the necessary bases to propose a methodology for the evaluation of buildings affected by earthquakes. Then, it establishes the procedure to be used to assess the damage and the safety of the buildings after an earthquake. Finally, it proposes a form, of quick and easy application, for the inspection and classification of buildings affected by an earthquake, according to their state of damage and their level of security.

Abstract

The system of indicators described in this monograph has been the main objective of the operation ATN / JF-7907-RG of the IDB, coordinated by the Instituto de  Environmental Studies, IDEA, of the Universidad Nacional de Colombia, sede Manizales, within the regional program on "Information and Risk Indicators and Risk Management" for the Americas, promoted by the IDB, ECLAC and the IDEA between March 2003 and May 2005. The purpose of the indicator system described herein is to assess vulnerability and risk, using relative indicators, to facilitate the decision makers of each country, region or city to have access to relevant information that allows them to identify and propose effective risk management actions, considering economic, social, institutional and technical aspects. This system of indicators makes possible the description of risk and risk management at the national, subnational and urban levels, facilitating the identification of the essential aspects that characterize it from an economic and social perspective, as well as comparing these aspects or the risks themselves among different countries or territorial units. The proposed indicators have been designed for measuring and monitoring purposes over time and for the identification of conditions of insecurity and their causes, using criteria related to the degrees of threat to which the territorial units are exposed and their socio-economic circumstances that influence their vulnerability. The system of indicators described here is framed within a holistic evaluation approach, which, due to its flexibility and possible compatibility with other specific evaluation approaches, will be increasingly used and accepted as one of the best options for the representation of risk and of its management, due to its complex and imprecise nature. Its strength lies in the possibility of disaggregating the results and identifying the factors towards which risk management actions should be oriented, in order to assess their effectiveness. Its main objective is to stimulate decision-making and not the precise evaluation of the risk that is commonly supported in the concept of physical truth.

Abstract

The Risk Management Index, IGR, is an essential technical contribution of operation ATN / JF-7907-RG of the IDB, coordinated by the Institute of Environmental Studies, IDEA, of the Universidad Nacional de Colombia, sede Manizales, within the regional program on "Information and Indicators of Risk and Risk Management" for the Americas, promoted by the IDB, ECLAC and the IDEA between March 2003 and May 2005. It is a composite indicator based on a multi-attribute technique. It represents a series of risk factors that must be minimized through policies and actions to reduce vulnerability and through the maximization of resilience, that is, of the capacity to face and absorb the impacts of dangerous phenomena. Each composite index is made up of various factors that are represented by existing indicators or variables. For purposes of formulating the IGR, it was necessary to propose qualitative indicators, valued with subjective scales, due to the nature of the aspects that are evaluated and due to the lack of pre-existing parameters. The weighting of the indicators that constitute it was made based on the criterion of experts of each country, using numerical techniques consistent from the theoretical and statistical point of view. The IGR is the first systemic approach - based on fuzzy sets - that is used at the international, national and urban levels to assess the performance of risk management, in order to establish targets that improve the management effectiveness. Decision makers, at different territorial levels, now have a useful tool for monitoring the risk management and have the possibility to observe the relative position over time of the studied area and compare the obtained results with other countries, regions or cities. The strength of the IGR lies in the possibility of disaggregating the results and identifying the progress and deficiencies of risk management, with the aim of guiding the actions in order to improve its effectiveness. Its main objective is to stimulate decision-making.

Abstract

In this monograph, we study the definition of possible damage in bridges by using simplified structural models. The state-of-the-art of the seismic vulnerability of bridges is first discussed and the theoretical background of the methods to evaluate their vulnerability is commented. The existing methodologies to evaluate the vulnerability of bridges are then described in detail; The methods are classified as: (1) methods based on the vulnerability index; (2) methods based on structural analyses; (3) methods based on expert opinion and statistical evaluations; and (4) methods based on statistical evaluations of the observed damages. A simplified methodology to estimate the seismic vulnerability of reinforced concrete bridges with simple pier bent and elastic girders is then proposed. The methodology is applied to an existing bridge, built 30 years ago. The elastic and the non-linear procedures of evaluation are first discussed. The non-linear procedure includes an analytical methodology to estimate the local damage in the piers, using a continuous damage model, and the global damage of the bridge. Thereinafter, a numerical process allows considering artificial seismic actions compatible with the velocity spectrum of deterministic records. Finally, an application of the proposed analytical procedure to estimate the seismic vulnerability of the real bridge is given. The obtained damage results show that the studied bridge would suffer only a minor damage when  a seismic action similar to that of the expected seismic scenario is considered. The proposed methodology is compared with previous experimental results and with analytical results obtained by using commercial codes. It is shown that the proposed simplified methodology is less computational time consuming and that it provides reliable values of the maximum damage suffered by the bridge piers.

Abstract

In this monograph, a complete review of the state of the art of the seismic vulnerability of motorway bridges is carried out. The work begins with a review of the damage caused by the last major earthquakes in the world. Next, the theoretical framework of the methods of evaluation of the seismic vulnerability of structures is described. Then, different methodologies for the evaluation of the seismic vulnerability of bridges are examined in detail. Advances in assessing their seismic vulnerability should be sought using expert judgment, the study of damage data associated with past earthquakes and the numerical simulation of bridge response. For this reason, in the monograph the seismic vulnerability evaluation methods are classified into the following groups: (1) methods based on vulnerability indexes; (2) methods that use structural analysis; (3) methods based on statistical evaluations and expert opinion; and (4) methods that use the observed damage statistics. Finally, some of the main methods for obtaining the indices that characterize the importance of motorway bridges are described, as well as indices for the evaluation of the liquefaction effect.

Abstract

In this monograph, a numerical model based on the finite element method is developed to analyze buildings with base seismic isolation, discretizing the structure-isolator system. In this way, the response of such systems is estimated with greater precision and, thus, the tasks of designing and verifying them is facilitated. The development of the model requires the resolution of the following problems: • Development of an appropriate constitutive model for elastomers that considers large elastic deformations, incompressibility, visco-elasticity and elasto-plasticity in large strains. • Incorporation of the constitutive model developed in a general model of dynamic analysis of structures using the finite element method that combines bar elements with plane elements; appropriate constitutive models for the numerical simulation of the structural materials; mixing theory; discretization by layers. • Application of damage indices that facilitate the evaluation of the global state of the structure after a seismic ground motion. • Numerical study of the behavior of structures with elastomeric isolation system subjected to earthquakes and their comparison with the corresponding fixed base structures.

Abstract

The standards make recommendations regarding the seismic loads, the simplified methods of structural analysis, the criteria that must be applied to ensure its good global seismic behavior, as well as the earthquake resistant design details that must be applied. The structural analysis procedures included in all the seismic design standards are based on concepts generally used in the static and dynamic analysis of structures. However, when considering the possibility of using simplified procedures of dynamic calculation and of formulas that allow approximating the values of the dynamic characteristics of buildings, the mentioned concepts are not explained in a clear way. For this reason, the present monograph analyzes the content of the earthquake-resistant design codes in relation to the calculation methods they propose, explaining the concepts of structural analysis that are applied in each case, with special reference to Spanish regulations in force, NCSE-02. In addition, this monograph deals with aspects of conceptual design, which provides qualitative descriptions of design solutions based on the designer's experience. In this phase, the structural typology, the plan form of the structure, the distribution of the masses in height and the rigidities are chosen, the organization of the resistant system is specified, etc. It should be mentioned that in many regulations the conceptual design is specified in rules that are not justified in the text. All this implies taking decisive decisions in the initial phases of the design of structures, which condition the seismic behavior of the structures to such an extent that all the subsequent calculations, as well as the design details that are applied, may not have the expected effect.