Gustavo Henrique Siqueira

This study presents an updated probabilistic seismic hazard analysis model for Northeastern Brazil, a stable continental region, taking into account more comprehensive epistemic uncertainties compared to previous studies, which is critical for robust decision making related to earthquake risk management. The model incorporates updated models and datasets, and provides gridded values of seismic hazard for various intensity measures, return periods, and site conditions across the study region. In addition, more detailed results are provided for selected locations to support engineering applications. Sensitivity analysis is also carried out to identify possible relevant parameters that deserve further investigations. The results reveal that peak ground acceleration across the target region remains below 0.05 and 0.22 g for return periods of 475 and 2475 years, respectively, and an average shear wave velocity of 760 m/s, supporting the current classification of the region as Zone 1 of the seismic design code (PGA 0.05 g for the 475‐year return period). Variations in hazard levels across the study area, relative to previous models and design ground motions, have potential implications for risk assessments and suggest the need to revisit seismic design zones and spectrum shape. Sensitivity analysis indicates that the minimum magnitude considered in hazard calculations and the incorporation of regional characteristics into ground motion models have the potential to significantly affect hazard estimates, highlighting the need for further investigations in the future.

In low to medium-seismicity countries, seismic design is often not mandatory. Furthermore, zoning is frequently adopted to justify simplified calculations based on force methods without capacity criteria. However, risk analysis should merge vulnerability, threat, and exposure. So even regions with low seismicity can face potentially high consequences due to earthquakes. This is the case of Brazil, where seismic provisions were lacking until 2006 when the first standard was approved, being updated in 2023. Therefore, this study selected a typical RC frame configuration and focuses on assessing the differences in seismic performance between the provisions outlined in EN1992-1-1/EN1998-1 and ABNT NBR15421. The research highlights how different requirements affect low and medium-seismicity regions. Hence, the methodology and conclusions can serve as a guide for decision-making in other countries regarding impact and effectiveness. There are considered different scenarios of design, seismicity, and ductility class. The nonlinear static Pushover analysis was conducted and also validated with nonlinear dynamic Time-history analysis. The assessment of the results is based on the design assumptions, capacity curves, collapse mechanism, IDA curves, PSDM, damage limit states and cost-benefits. Non-seismic design structures had a premature brittle collapse. The global ductility condition was the main key to changing into a ductile mechanism, and seismic detailing was the variable that addresses the ductility level.

Bridges are the most vulnerable components in a transportation system. Therefore, extraordinary events such as seismic activities should also be considered in bridge design. In Brazil, since the last few decades, representative earthquakes with magnitudes above 5 have been registered by the seismological center of the University of São Paulo (USP). The newest edition of the Brazilian regulation for seismic-resistant structure design, NBR 15421:2023, does not apply to special structures, such as bridges. It is not clear whether the existing infrastructure can resist seismic demands. This work aims to evaluate the vulnerability of a reinforced concrete bridge with typical geometry located in the northeast of Brazil, a region known for relatively high seismic activity in Brazilian territory. The structural system is composed of a “T” section deck supported by non-integral U-type or gravity abutments and by frames with two circular columns through elastomeric bearings. The seismic records were collected from the Pacific Earthquake Engineering Research Center, which is compatible with the target spectrum of the city of Natal/RN. The study of vulnerability is conducted through the assembly of fragility curves, which provide the conditional probability of the demand (obtained by nonlinear dynamic analysis) exceeding the structural capacity for different structural damage limit states. Traditional approaches to evaluating fragility curves are time-consuming, mainly because of the relatively high computational cost of running several finite element-based models. Here, we present a computationally efficient scheme based on Machine Learning techniques to evaluate the application of artificial intelligence tools, such as Support Vector Machine, Decision Tree and Random Forest, for seismic vulnerability for structures situated in the northeastern region of Brazil. The fragility curves obtained by traditional approach and Machine Learning techniques were very similar.

Considering the importance of deepening the knowledge of the structural behavior of free‐form shell structures with a triangular plan, this work presents the results of research on the analysis of seismic vulnerability, verified through linear time‐history analysis (NLTHA), generating fragility curves through PSDM models. The analyzes carried out are based on uncertainties regarding both the mechanical properties of the materials and the geometric characteristics of the structures, as well as the action of seismic events. Real accelerograms, compatible with the elastic response spectra for Lisbon and Ouren, Portugal given by the EC8 standard, are used to consider seismic events. In the analyses, fundamental factors are considered, such as the accumulation of damage and the degradation in the resistance of materials. The structure presents highly ductile behavior in the face of seismic loads, attributed to its rigidity, geometry, lightness, and modal behavior, with participation in the horizontal components of the mass in the first five vibration modes greater than 80% and with minimal influence of the vertical component, characteristics inherent to this type of structure. However, it should be noted that the area close to the support, in the same direction as the ground acceleration, is the most vulnerable. This occurs due to the plastic yielding of the concrete during the earthquake, which promotes the appearance of cracks and compression damage. This is verified for the structure when subjected to earthquakes with PGA in the horizontal direction between 0.01 and 0.8 g. The probability of considerable damage increases with seismic events having PGA greater than 0.6 g, which, in turn, can compromise the stability of the structure. It is, therefore, of great importance to study the seismic behavior of shell structures, especially free‐form shells, considering the variability and uncertainties related to the structural stress arising from the seismic demand.

When subjected to external forces, the mechanical behavior of granular materials may range from static to dynamic. Unconfined granular beds, for example, are easily fluidized by vibratory loading. Under confinement, this type of material may also exhibit observable effects due to vibrations regarding their volumetric and strength behaviors. In this paper, the shear strength and dilatancy of dry confined granular materials subjected to vibrations are investigated using discrete element simulations of a triaxial cell. The material is first subjected to isotropic compression. Then, with controlled lateral stresses and imposed vertical motion, shear and compressive stresses are applied to a cubic sample. Additional harmonic displacements of the walls induce vertical and horizontal vibrations in the system during the shear tests. Finally, the impact of the amplitude, frequency, and direction of the vibrations on the angles of internal friction and dilatancy of the material is analyzed and compared to observations from the literature.

Este estudo visa aprofundar a compreensão sobre o comportamento dinâmico em sistemas mistos de madeira e concreto, focando-se na análise de painéis de Cross Laminated Timber (CLT) e concreto armado. Para isso, é necessário o conhecimento das propriedades desses materiais, como densidades dos materiais, módulos de elasticidade e resistência, e característica geométrica, como a inércia da seção transversal. Tais parâmetros influenciam no comportamento dinâmico dos elementos estruturais e permitem avaliar sua suscetibilidade aos movimentos de vibrações, o que pode gerar sensação de insegurança aos usuários. A partir de resultados experimentais e numéricos de frequência natural, estabelece-se relações do comportamento dinâmico dessas placas que atendam aos critérios normativos. Cinco placas com diferentes configurações de conectores entre o CLT e o concreto foram avaliadas usando acelerômetros ao longo do eixo longitudinal das peças. As placas com conectores HBV^® e Chapas Expandidas tiveram desempenhos superiores àquelas conectadas com parafusos inclinados. Os valores obtidos da primeira frequência natural de vibração mais crítica ficaram acima de 17 Hz. Tais resultados atendem aos critérios da norma NBR 7190-1:2022, que preconiza o valor mínimo de 8 Hz para análise simplificada.

Earthquakes represent a concern for several countries, since they have the potential to cause a great number of casualties and damages in structures. Brazil is a mid-plate country located in the South America tectonic plate, which is considered a stable region when compared to places near the boundaries of tectonic plates. For the sake of comparison, a seismic event of magnitude 5 occurs in Brazil once in five years on average, while in the Andean region an earthquake of this magnitude happens on average twice a week [¹ 1 M. Assumpção, M. Pirchiner, J. C. Dourado, and L. V. Barros, "Terremotos no Brasil: preparando-se para eventos raros," Soc. Bras. Geofísica, Bol. SBGf, no. 96, pp. 25-29, 2016. ]. Even though Brazil is located inside a tectonic plate, it presents a considerable history of small to moderate earthquakes, also including two events with moment magnitude (M) higher than 6. Nievas et al. [² 2 C. I. Nievas, J. J. Bommer, H. Crowley, J. Van Elk, M. Ntinalexis, and M. Sangirardi, "A database of damaging small-to-medium magnitude earthquakes," J. Seismol., vol. 24, pp. 263-292, 2020, http://dx.doi.org/10.1007/s10950-019-09897-0. http://dx.doi.org/10.1007/s10950-019-098... ] presents a database of events in several parts of the world with M ranging from 4.0 to 5.5 in which damage or casualties have been reported on them. In Brazil, studies report damages occurred in the João Camara earthquake sequence, in Rio Grande do Norte state and Itacarambi earthquake, in the state of Minas Gerais [³ 3 M. Takeya, J. M. Ferreira, R. G. Pearce, M. Assumpção, J. M. Costa, and C. M. Sophia, "The 1986-1988 intraplate earthquake sequence near João Câmara, northeast Brazil—evolution of seismicity," Tectonophysics, vol. 167, no. 2-4, pp. 117-131, Oct 1989, http://dx.doi.org/10.1016/0040-1951(89)90062-0. http://dx.doi.org/10.1016/0040-1951(89)9... ], [⁴ 4 C. Chimpliganond, M. Assumpção, M. Von Huelsen, and G. S. França, "The intracratonic Caraíbas-Itacarambi earthquake of December 09, 2007 (4.9 mb), Minas Gerais State, Brazil," Tectonophysics, vol. 480, no. 1-4, pp. 48-56, Jan 2010, http://dx.doi.org/10.1016/J.TECTO.2009.09.016. http://dx.doi.org/10.1016/J.TECTO.2009.0... ]. Such damages are explained in places with small to moderate hazards due to the definition of risk, which considers not only hazard, but also exposure, vulnerability and consequences. One should note, therefore, that a low hazard does not imply low seismic risk in a region [⁵ 5 L. Reiter, Earthquake Hazard Analysis: Issues and Insights. New York: Columbia University Press, 1991. vol. 22, no. 3. ], especially if buildings are not properly designed to withstand seismic loads.

This article presents a new proposal to estimate structural capacity models for bridge portfolios. A common approach is the use of ductility-based capacity models. Herein, a ductility replacement for curvature or drift as engineering demand parameters is conducted, as variability within the bridge’s classes is considered in the results and multidirectional pushover analyses are performed to assess a bi-directional load scenario. Application of the methodology is exemplified for an inventory of Northeastern Brazilian bridges. Parametric analyses are performed by varying the reinforcement ratios to estimate the capacity limit states within the range of values used. These results from probabilistic models define the capacity limit state that can be used to perform vulnerability assessment of bridges to different hazard sources, such as earthquakes.