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Purpose: The active tuned mass damper (ATMD) system is underactuated where the number of actuators is less than the number of system's DOF. It is well known that the regulation of an underactuated system is challenging. Few reports can be found in the literature relating to the design of ATMD systems from the view point of their underactuated dynamics. In this paper, we firstly clarify the underactuated behavior of an ATMD system whose ill-conditioned controllability matrix largely limits the flexibility of controller design. Controllers are proposed to circumvent the underactuated dynamics to ensure vibration attenuation during the earthquake and rapid state convergence in the ATMD when the earthquake vanishes. Methods: This paper proposes a redefined output function to destroy the underactuated dynamics so that a stabilizing controller can be designed to regulate the new output. A low pass filter is suggested in the control loop to give boundedness of primal and auxiliary systems simultaneously supported by BIBO stability. Results: The simulation results show that the proposed ATMD design can give much better performance in both time and frequency responses compared with the traditional TMD design under the 1940 El Centro earthquake and 1985 Mexico City earthquake. Conclusion: The proposed output redefinition design removes the underactuated dynamics in the ATMD system effectively, and the low-pass filter inclusion preserves system passivity so that convergence of the states can be obtained. These have been justified by mathematical proofs and simulation verifications. [ABSTRACT FROM AUTHOR]

This paper presents the results of a cross-sectional study on adolescents' behavioral and emotional reactions during and immediately after the 2017 Puebla earthquake that occurred in Mexico City. Convenience sampling was used to achieve a sample size of n = 362. Some of the key findings are as follows: a) some 57.0% of adolescent women and over 60.0% of men "ran out of the building" during the earthquake; only 17.4% of women and 14.2% of men took shelter. Early and late adolescent women were significantly associated with building "evacuation" immediately after the earthquake. b) Early and late adolescent men were "surprised" by the earthquake occurrence. c) The perceived vulnerability of the city (PVC) was significantly associated with men but not with women. d) Adolescents exhibited strong information-seeking behavior regarding seismic risk. The results of the study highlight a lack of adolescents' preparedness for earthquakes in terms of the protective actions taken during the ground shaking and knowledge of the functioning of the Mexican seismic alert system. An educational program aimed at better educating and preparing adolescents for a seismic emergency should be implemented in preparatory schools. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic response of two 21-story buildings was studied to assess the influence of higher modes in their structural performance. While the first building was structured with ductile moment-resisting steel frames and exhibits a global shear-dominated lateral deformation, the second one uses ductile concentrically braced steel frames and has a global bending-type response. Buildings were virtually located in a soft-soil condition of the lake-bed zone in Mexico City. Nonlinear pushover and dynamic analyses were performed through OpenSees on a detailed 3D-model with plasticity spread along the elements. For this purpose, a set of accelerograms recorded during the Mexico Earthquake of September 19, 2017, were selected, and adjusted to represent the actual seismic hazard at the site. A frequency-domain system identification technique was applied to identify the dynamic characteristics of buildings through a moving-window Fourier analysis, that allows for the estimation of the contribution of higher-modes to their overall nonlinear dynamic response. A ratio of the elastic spectral pseudo-accelerations corresponding to the first two vibration modes is proposed to quantitatively anticipate cases and conditions for which the second mode adversely affects the structural performance of upper stories. The discussion includes a comparative study from the lateral global response of the analyzed models. [ABSTRACT FROM AUTHOR]

Copyright of Revista Alea: Estudos Neolatinos is the property of Programa da Pos-Graduacao em Letras Neolatinas Fac de Letras - UFRJ and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rapid changes in geotechnical and geological ground conditions lead to significant ground motion variability. This condition mainly occurs at the so-called basin edges, where there is an abrupt transition between soft highly compressible soils and stiffer materials. This problem becomes more relevant in areas where ground subsidence drastically changes the dynamic response of high plasticity clay deposits, such as those found in Mexico City, due to fundamental site period evolution with time. This paper presents site response analyses at an abrupt transition area in the southeast Mexico City region, along the edges of the Xochimilco-Chalco lakes. Considerable damage associated with three-dimensional wave propagation effects was observed in this zone during the September 2017 Puebla-Mexico earthquake. A series of three-dimensional finite difference numerical models of the basin edge were developed to evaluate ground motion variability, considering topographic effects and soil non-linearities. Good agreement between the computed response and the observed damage during the 2017 Puebla-Mexico earthquake reconnaissance was found. In addition, several normal and subduction events with a return period of 250 years were considered to evaluate the effect that frequency content, and strong ground motion duration have on the soil response variability. From the results gathered here, it was established the relevance of accounting for three-dimensional wave propagation fields to assess site effects at basin-edge zones properly and to be able to implement proper risk mitigation measurements at these zones. [ABSTRACT FROM AUTHOR]

Copyright of Disasters is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The goal of this paper is to examine the seismic resilience of existing eccentrically braced frames (EBFs) in Mexico City under intraslab earthquake ground motions. For this purpose, detailed analytical models representative of EBF buildings designed under the 2004 edition of the Mexico City Code seismic criteria were developed as part of this investigation. These analytical models take into account the nonlinear behavior of the shear links including a failure criterion. Results of this investigation revealed that the archetype EBFs exhibit a nonuniform distribution of maximum interstorey drift, IDRmax, and link plastic rotation, γp, along height, which tend to concentrate at the bottom stories. Furthermore, it was found that γp demands computed from nonlinear dynamic time-history analyses are smaller than that estimated from the current code criterium in Mexico City. Relevant statistical results also include the relationship among IDRmax, permanent interstorey drift demand, RIDRmax, and γp. Suitable equations to predict γp and IDRmax demands are proposed based on the empirical trends of the pairs RIDRmax-γp, IDRmax-γp, and IDRmax-RIDRmax. An estimation of the state of damage of the shear links along-height was performed based on the plastic rotation-based damage states introduced in the literature, which allowed suggesting repair measures to build component-based recovery functions. It is shown that eccentric braced frames are a very resilient structural system to be used in a region of high seismicity such as Mexico City, particularly under strong intraslab earthquakes. [ABSTRACT FROM AUTHOR]

Following the 1923 Kanto earthquake in Japan, Japanese researchers noticed the strong effects of surface geology on seismic motion (ESG) and began to investigate these effects to quantify the site amplification factors (SAFs) associated with soft surface sediments. On the other side of the Pacific Ocean, ESG received limited attention until the 1985 Michoacan, Mexico earthquake revealed significant long-period amplification inside Mexico City that manifested as the source of devastating damage to high-rise buildings. Since then, seismologists and earthquake engineers have performed a lot of studies on various ESG issues worldwide. We have not yet reached common conclusions on how to quantitatively predict SAFs over a broad frequency band of engineering interest, 0.1 to 20 Hz, for moderate to strong input from different types of earthquakes in different tectonic settings. However, we found here several basic guidelines useful for successfully modeling ground motions as a common approach to ESG studies. First, in this letter, we briefly review our history of understanding ESG, which is closely related to the key settings required for reliable quantifications of SAFs, and then introduce various emerging techniques for broadband quantitative evaluations of SAFs based on the vast amount of observed ground motions primarily from dense Japanese strong-motion networks. Based on the findings of our investigation and the physical relationships behind the parameters, the authors would like to recommend that researchers on ESG and related topics would refer to the five basic guidelines proposed in the conclusions for the successful implementation of techniques to delineate SAFs in a specific region of interest, such as the use of Fourier spectra instead of response spectra. We have started applying the proposed techniques to regions outside Japan. The implementation of the statistical validation exercises will follow. [ABSTRACT FROM AUTHOR]

Weak first-story buildings are susceptible to experience severe structural damage, and even collapse, during strong earthquakes as was evidenced during the September 19, 2017 (M w = 7.1) intraslab earthquake that hit Mexico City. Such type of buildings are prone to exhibit a negative slope in their capacity curve due to weak first-story mechanism that might lead to dynamic instability during earthquake excitation. Therefore, this paper presents the main results of an investigation focused on evaluating the collapse strength ratios, R c (i.e., the normalized lateral strength ratio in the onset of dynamic instability) of single-degree-of-freedom (SDOF) systems whose force-displacement nonlinear envelope (backbone) behavior is representative of that observed in existing multistory weak first-story buildings. Particularly, their envelope exhibit several levels of negative slope after a post-yield displacement ductility capacity. Median and dispersion of R c ratios were obtained for degrading SDOF systems subjected to a set of 136 earthquake ground motions recorded in soft soil sites of Mexico City from instraslab earthquakes. Results of this investigation showed that R c ratios depend on the normalized period of vibration with respect to the predominant period of the ground motion, T/T g , the displacement ductility capacity, μ c , and the negative slope after peak strength, α c. Additionally, the spectral trend of R c ratios at soft soil sites is different to that reported for firm soil sites. A continuous functional form is introduced to obtain estimates of median R c ratios for the preliminary seismic assessment of weak first-story buildings in this seismic environment. • Dynamic instability in buildings can be evaluated through collapse strength ratios Rc. • Rc ratios follows a different spectral trend for soft soil sites than for firm sites. • Displacement ductility capacity of structures is beneficial to increase Rc. • Robust equation to estimate median Rc is proposed based on statistical results. [ABSTRACT FROM AUTHOR]

The Mexican Seismic Alerting System (SASMEX) successfully alerted for the June 23, 2020, La Crucecita earthquake (Mw 7.4) in southern Mexico. The time between the alert broadcast and the initiation of strong shaking ranged from 30 s in the city of Oaxaca to 134 s in Mexico City. SASMEX messages are presented from the time the earthquake was detected to the generation of maps of peak ground acceleration in Mexico City. A first pre-alert message was issued based on the tS-tP algorithm by a station located 3 km away from the epicenter. Confirmation of the magnitude (Mw > 6) came from an adjacent station located 43 km from the epicenter, 16 s after the origin time. The decision to broadcast the alert took longer than in previous large earthquakes, due to the relatively large interstation spacing in this region. An algorithm called tP + 3, that estimates magnitude based on the first three seconds after the onset of the P wave, would have issued the alert 4 s earlier. However, the triggering procedures in place require that the same algorithm is used to issue the alert. SASMEX warned all cities where it operates with ample time. Peak ground acceleration in key sites in Mexico City was estimated 3.5 min after the origin time of the earthquake and one minute after strong shaking began, allowing authorities to launch civil protection procedures and building inspections. Also, the earthquake of June 23, 2020 provided important lessons to further improve the performance of SASMEX. [ABSTRACT FROM AUTHOR]