Evaluation of the Response of Posttensioned Steel Frames with Energy Dissipators Using Equivalent Single-Degree-of-Freedom Systems

The hysteretic energy (EH) dissipated in posttensioned steel frames (PTSF) with hysteretic dampers is calculated by using equivalent single-degree-of-freedom systems (ESDOFS), where the nonlinearity of both the steel bars (beam and columns) and the connections of the structural frame is separately considered. Five multi-degree-of-freedom (MDOFS) PTSF and their corresponding ESDOFS are studied under the action of 30 seismic motions recorded in soft ground, scaled in terms of the spectral pseudoacceleration evaluated at the fundamental period of the structures. Several simple mathematical expressions are proposed. The first expression is useful to calculate modifying factors (FMEH) to relate EH of the ESDOFS with that of the MDOFS; the second is to determine the interstory drift (γ) as a function of the seismic intensity. The third equation is to calculate the factor of the relative participation of the energy that the connections dissipate with respect to the total energy EH and the fourth equation, which is function of the γ, is to obtain the distribution factors of EH through the height of the structure. The methodology proposed can be used for the design or the structural revision of PTSF with dampers

Morphological variation of the labellum of Vanilla planifolia Andrews (Orchidaceae) in Oaxaca, Mexico

Infraspecific variation has transcendental ecological consequences for species adaptation to new niches. Estimating levels of variation is key for understanding the life history of a species, as well as for designing strategies for use and conservation. For this reason, the objective of this study was to characterize infra-specific morphological variation of the labellum of V. planifolia, of 122 flowers from 28 specimens from the state of Oaxaca and two specimens from Veracruz, Mexico. The labellum of each flower was dissected and analyzed by morphometry. Sixty variables were obtained and grouped into basal, middle and apical regions. An analysis of variance was performed considering the collections and the origin of each individual as sources of variation. Principal components and cluster analyses were also conducted. Differences in the 60 variables analyzed were highly significant among the collections. Among environments, 18 variables showed significant differences, which were situated in the lateral and middle lobes of the labellum. Thus, these structures were considered susceptible to environmental changes. The remaining 42 variables situated in the basal and middle regions of the labellum, which were fused to the edges of the floral column were not significantly different among environments. With the first three principal components, the model explained 73% of the total variation studied. Morphological variation of the flower labellum was represented by four morphotypes distributed in three environments. Highlights The evaluation of vanilla flowers wild does not allow to have the same number of treatments or repetitions, for the inaccessibility of the species. Morphometric analysis of the labellum revealed infra-specific variation in the germplasm of Vanilla planifolia. The features of the basal and middle regions of the labellum are the most informative in distinguishing the variation between vanilla specimens.Infraspecific variation has transcendental ecological consequences for species adaptation to new niches. Estimating levels of variation is key for understanding the life history of a species, as well as for designing strategies for use and conservation. For this reason, the objective of this study was to characterize infra-specific morphological variation of the labellum of V. planifolia, of 122 flowers from 28 specimens from the state of Oaxaca and two specimens from Veracruz, Mexico. The labellum of each flower was dissected and analyzed by morphometry. Sixty variables were obtained and grouped into basal, middle and apical regions. An analysis of variance was performed considering the collections and the origin of each individual as sources of variation. Principal components and cluster analyses were also conducted. Differences in the 60 variables analyzed were highly significant among the collections. Among environments, 18 variables showed significant differences, which were situated in the lateral and middle lobes of the labellum. Thus, these structures were considered susceptible to environmental changes. The remaining 42 variables situated in the basal and middle regions of the labellum, which were fused to the edges of the floral column were not significantly different among environments. With the first three principal components, the model explained 73% of the total variation studied. Morphological variation of the flower labellum was represented by four morphotypes distributed in three environments. Highlights The evaluation of vanilla flowers wild does not allow to have the same number of treatments or repetitions, for the inaccessibility of the species. Morphometric analysis of the labellum revealed infra-specific variation in the germplasm of Vanilla planifolia. The features of the basal and middle regions of the labellum are the most informative in distinguishing the variation between vanilla specimens

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

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

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

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

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

Challenges in the COVID-19 vaccination era: Prioritization of vaccines among essential workers in Mexico

The coronavirus disease-2019 (COVID-19) pandemic gave rise to a massive global health concern that has placed an unprecedented strain on healthcare systems, education and economy. The recent vaccine roll-out gave humanity a glimpse of hope. However, more than 50% of the vaccine supply has been acquired by high-income countries, forcing low- and middle-income countries to prioritize who should be vaccinated. In Mexico, the first phase of the vaccination program prioritized healthcare personnel working in front-line COVID-19 public institutions. The second phase was planned for the remaining healthcare workers attending at both COVID and non-COVID areas. The government, however, aiming to reopen schools, decided to vaccinate teachers instead. This raised several concerns, since Mexico tops the ranking of deaths among healthcare workers due to COVID-19 worldwide. Furthermore, the possible framing of vaccines as a political tool has caused commotion among the Mexican people and media, especially since 2021 is the Midterm Election year in Mexico, and the Teachers’ Union has historically played an essential role in this matter. Therefore, it is relevant to share the vaccination experience in resource-constrained settings to provide help and advice to reach an optimal strategy and deflate this pandemic