Probabilistic seismic response transformation factors between SDOF and MDOF systems using artificial neural networks

An approach to obtain with acceptable accuracy probabilistic response transformation factors by training an artificial neural network (ANN) model is presented. The transformation factors are defined as the ratio of the seismic response of multi-degree-of-freedom structures and their equivalent single-degree-of-freedom systems, associated with a given annual exceedance rate. The approach is used for predicting the seismic response of steel framed buildings. Equations useful to obtain probabilistic response transformation factors for maximum ductility and inter-story drift, as functions of their mean annual rate of exceedance, and of the fundamental vibration period of the structure, are proposed. It is shown that artificial neural networks are a useful tool for reliability-based seismic design procedures of framed buildings and for the improvement toward the next generation of earthquake design methodologies based on structural reliability

Ductility and Strength Reduction Factors for Degrading Structures Considering Cumulative Damage

The effect of cumulative damage on the strength requirements of degrading structures is assessed through the evaluation of the target ductility and corresponding strength reduction factors of simple degrading structures. While the reduction on ductility is established through the use of Park and Ang index, the suggestions given by Bojórquez and Rivera are used to model the degradation of the structural properties of the simple systems. Target ductilities and their corresponding reduced strength reduction factors are established for five sets of ground motions; most of them are recorded in California. The results given in this paper provide insight into all relevant parameters that should be considered during seismic design of earthquake-resistant structures. Finally, some recommendations to evaluate the effect of cumulative damage on seismic design are suggested

Prediction of Inelastic Response Spectra Using Artificial Neural Networks

Several studies have been oriented to develop methodologies for estimating inelastic response of structures; however, the estimation of inelastic seismic response spectra requires complex analyses, in such a way that traditional methods can hardly get an acceptable error. In this paper, an Artificial Neural Network (ANN) model is presented as an alternative to estimate inelastic response spectra for earthquake ground motion records. The moment magnitude (MW), fault mechanism (FM), Joyner-Boore distance (dJB), shear-wave velocity (Vs30), fundamental period of the structure (T1), and the maximum ductility (μu) were selected as inputs of the ANN model. Fifty earthquake ground motions taken from the NGA database and recorded at sites with different types of soils are used during the training phase of the Feedforward Multilayer Perceptron model. The Backpropagation algorithm was selected to train the network. The ANN results present an acceptable concordance with the real seismic response spectra preserving the spectral shape between the actual and the estimated spectra

Enhanced Seismic Structural Reliability on Reinforced Concrete Buildings by Using Buckling Restrained Braces

The control of vibrations and damage in traditional reinforced concrete (RC) buildings under earthquakes is a difficult task. It requires the use of innovative devices to enhance the seismic behavior of concrete buildings. In this paper, we design RC buildings with buckling restrained braces (BRBs) to achieve this objective. For this aim, three traditional RC framed structures with 3, 6, and 9 story levels are designed by using the well-known technique nondominated sorting genetic algorithm (NSGA-II) in order to reduce the cost and maximize the seismic performance. Then, equivalent RC buildings are designed but including buckling restrained braces. Both structural systems are subjected to several narrow-band ground motions recorded at soft soil sites of Mexico City scaled at different levels of intensities in terms of the spectral acceleration at first mode of vibration of the structure Sa(T1). Then, incremental dynamic analysis, seismic fragility, and structural reliability in terms of the maximum interstory drift are computed for all the buildings. For the three selected structures and the equivalent models with BRBs, it is concluded that the annual rate of exceedance is considerably reduced when BRBs are incorporated. For this reason, the structural reliability of the RC buildings with BRBs has a better behavior in comparison with the traditional reinforced concrete buildings. The use of BRBs is a good option to improve strength and seismic behavior and hence the structural reliability of RC buildings subjected to strong earthquake ground motions

An Efficient Approach to Obtain Optimal Load Factors for Structural Design

An efficient optimization approach is described to calibrate load factors used for designing of structures. The load factors are calibrated so that the structural reliability index is as close as possible to a target reliability value. The optimization procedure is applied to find optimal load factors for designing of structures in accordance with the new version of the Mexico City Building Code (RCDF). For this aim, the combination of factors corresponding to dead load plus live load is considered. The optimal combination is based on a parametric numerical analysis of several reinforced concrete elements, which are designed using different load factor values. The Monte Carlo simulation technique is used. The formulation is applied to different failure modes: flexure, shear, torsion, and compression plus bending of short and slender reinforced concrete elements. Finally, the structural reliability corresponding to the optimal load combination proposed here is compared with that corresponding to the load combination recommended by the current Mexico City Building Code

Videovigilancia y segregación espacial en tiempos del neoliberalismo autoritario. El caso de Los Cabos, Baja California Sur (México)

In a context of acute spatial segregation derived from beaches’ privatization processes and the coastal landscape in the Los Cabos Tourist Corridor (Baja California Sur, Mexico), the state government has responded to the threat of organized crime to the functioning of international hotel chains with video surveillance schemes and the criminalization of acts considered to be against tourist interests in the area. This paper uses the concepts of authoritarian neoliberalism associated with a type of space production to analyze the phenomenon of video surveillance in a context of conflicts and social tensions under the auspices of the tourism growth model in Los Cabos region. A qualitative methodology was used, relying on field work by observing the study area, analysis of relevant bibliography, and press reports. En un contexto de aguda segregación espacial derivada de procesos de privatización de las playas y el paisaje costero en el Corredor Turístico de Los Cabos (Baja California Sur, México), la amenaza del crimen organizado al funcionamiento de las cadenas hoteleras internacionales ha sido respondida por el gobierno estatal con esquemas de videovigilancia y la criminalización de actos que se considere atenten contra los intereses turísticos en la zona. En este trabajo se emplean los conceptos de neoliberalismo autoritario, asociados a un tipo de producción del espacio, para analizar el fenómeno de videovigilancia en un contexto de conflictos y tensiones sociales auspiciadas por el propio modelo de crecimiento turístico en la región cabeña. Se utilizó una metodología cualitativa, recurriendo al trabajo de campo mediante observación por el área de estudio, análisis de bibliografía pertinente y reportes de prensa.&nbsp

El derecho a la ciudad y rescate del espacio público en zonas urbanas turistizadas. Una reflexión para Los Cabos, Baja California Sur (México)

A partir de dos propuestas para la revitalización del espacio público de la ciudad de Cabo San Lucas, destino turístico en el noroeste mexicano, en este artículo se realiza una reflexión sobre las posibilidades emancipadoras de esos proyectos a la luz de las aportaciones a la conceptualización del derecho a la ciudad de Lefebvre, Harvey, y Marcuse. Los casos señalados exhiben la contradicción entre la tendencia a la neoliberalización y privatización del espacio, por una parte, y la demanda exigente de democratización de los espacios urbanos en tanto un aspecto clave del derecho a la ciudad, por otra. En ese marco, los planes municipales de desarrollo urbano, rectores de la planeación urbana local, tendrían que constituirse en instrumentos fundamentales para resistir estas tendencias y abonar a la participación activa de la ciudadanía en el fortalecimiento del espacio público

Reduction of Maximum and Residual Drifts on Posttensioned Steel Frames with Semirigid Connections

The aim of this paper is to study the seismic performance of self-centering moment-resisting steel frames with posttensioned connections taking into account nonlinear material behavior, for better understanding of the advantages of this type of structural system. Further, the seismic performance of traditional structures with rigid connections is compared with the corresponding equivalent posttensioned structures with semirigid connections. Nonlinear time history analyses are developed for both types of structural systems to obtain the maximum and the residual interstory drifts. Thirty long-duration narrow-banded earthquake ground motions recorded on soft soil sites of Mexico City are used for the analyses. It is concluded that the structural response of steel buildings with posttensioned connections subjected to intense earthquake ground motions is reduced compared with the seismic response of traditional buildings with welded connections. Moreover, residual interstory drift demands are considerably reduced for the system with posttensioned connections, which is important to avoid the demolition of the buildings after an earthquake

A vector-valued ground motion intensity measure incorporating normalized spectral area

A vector-valued intensity measure is presented, which incorporates a relative measure represented by the normalized spectral area. The proposed intensity measure is intended to have high correlation with specific relative engineering demand parameters, which collectively can provide information regarding the damage state and collapse potential of the structure. Extensive dynamic analyses are carried out on a single-degree-of-freedom system with a modified Clough–Johnston hysteresis model, using a dataset of 40 ground motions, in order to investigate the proposed intensity measure characteristics. Response is expressed using the displacement ductility, and the normalized hysteretic energy, both of which are relative engineering demand parameters. Through regression analysis the correlation between the proposed intensity measure and the engineering demand parameters is evaluated. Its domain of applicability is investigated through parametric analysis, by varying the period and the strain-hardening stiffness. Desirable characteristics such as efficiency, sufficiency, and statistical independence are examined. The proposed intensity measure is contrasted to another one, with respect to its correlation to the engineering demand parameters. An approximate procedure for estimating the optimum normalized spectral area is also presented. It is demonstrated that the proposed intensity measure can be used in intensity-based assessments, and, with proper selection of ground motions, in scenario-based assessments

Cálculo de la incertidumbre en la medida de dosis absorbida basado en el TRS 398

La determinación de la dosis absorbida en agua a la profundidad de referencia, para un haz de calidad Q, según el TRS 398