No abstract

Most of the soils of tropical countries, especially those in South America and Africa, are affected by erosion processes. As a result, researchers in the field of geotechnical engineering, specifically in the context of "biotechnology" or "bioengineering", have been investigating the use of microorganisms to improve the geotechnical properties and stability of soils. Using this approach, this work was developed to analyze the effects of the implementation of a calcium carbonate precipitating nutrient in native microbiota on the mitigation of erosion processes in a tropical soil profile. The methodology used in this research consisted of collecting undisturbed samples in a soil profile located in an area affected by erosion processes. In such samples, the native bacteria were identified, and it was determined that the nutrient B4 induced the precipitation of calcium carbonate. Subsequently, soil samples were characterized physically, chemically, mineralogically and mechanically in their natural state and after the addition of the nutrient. The tests were performed at least fifteen days after treatment with the nutrient. It was concluded that the use of the nutrient B4 enabled the native bacteria present in the soil to precipitate calcium carbonate, resulting in improvements in the physical, chemical, mineralogical and mechanical properties of the soil, which allowed for the mitigation of erosion processes that characterize the soil profile studied. The conclusions derived from the study apply not only to other tropical soil profiles subjected to erosion but also to improvements of the geotechnical behavior of soils in general.

This paper introduces a novel methodology for the optimum design of linear tuned mass dampers (TMDs) to improve the seismic safety of structures through a novel Whale Optimization Algorithm (WOA). The algorithm is aimed to reduce the maximum horizontal peak displacement of the structure, and the root mean square (RMS) response of displacements as well. Furthermore, four additional objective functions, derived from multiple weighted linear combinations of the two previously mentioned parameters, are also studied in order to obtain the most efficient TMD design configuration. The differential evolution method (DEM), whose effectiveness has been previously demonstrated for TMD applications, and an exhaustive search (ES) process, with precision to two decimal positions, are used to compare and validate the results computed through WOA. Then, the proposed methodology is applied to a 32-story case-study derived from an actual building, and multiple ground acceleration time histories are considered to assess its seismic performance in the linear-elastic range. The numerical results show that the proposed methodology based on WOA is effective in finding the optimal TMD design configuration under earthquake loads. Finally, practical design recommendations are provided for TMDs, and the robustness of the optimization is demonstrated.

A tuned mass damper inerter (TMDI) is a new class of passive control device based on the inclusion of an inerter mechanism into a conventional tuned mass damper (TMD). The inerter device provides inertial resisting forces to the controlled system, through relatively small masses, converting it in a mechanism with the potential to enhance the performance of passive energy dissipating systems. This work presents a study of an optimal TMDI design through an exhaustive search process. TMDI device design using the cited parameter selection methodology consists in the determination of the damper critical damping ratio, ζTMDI, and frequency ratio, υTMDI, which result in the minimum structural response of a multidegree of freedom structural system, considering predefined values for mass ratio (µ) and inertance ratio (β). The used optimization process examines all possible damping device design parameter combinations to select the set of values that results in the best device performance to reduce response parameters in a structure. Four different optimization processes are performed by independently minimizing four performance indices: J1 associated to the reduction of the structure’s maximum peak displacement, J2 calculates the minimal RMS value for the structure’s peak displacement, J3 seeks by the minimal peak interstorey drift, and JP determines the lowest value for a linear weighted combination of the abovementioned three indices. A numerical example is developed with the purpose of validating the proposed optimization procedure and to evaluate the benefits of using TMDI as controlling devices for structures under seismic excitation, by carrying out a comparative analysis to contrast the performance of the optimization alternatives developed, running up to 1968192 cases. The obtained results show that devices designed based on exhaustive search optimization produce peak displacement reductions of up to 35% and peak structure displacement RMS reductions of up to 30%.

O artigo propõe metodologias de laboratório simples para obter a envoltória de ruptura em solos não saturados. A primeira metodologia é baseada em ensaios de tração indireta de corpos de prova usados para a definição da curva característica do solo e o ensaio de cisalhamento direto saturado. Esta metodologia é avaliada numericamente a partir da distribuição do estado de tensões usando o modelo de elementos finitos em 3D. As outras metodologias consistem na combinação dos ensaios de cisalhamento direto em amostras saturadas e o ensaio de compressão simples, assim como da combinação do ensaio de compressão simples com o ensaio de tração indireta, junto com a curva característica. Estas metodologias têm como vantagem a simplicidade e economia, possibilitando a avaliação de parâmetros de resistência, para a condição não saturada, e que pode ser uma alternativa razoável quando os parâmetros de tensão não podem ser obtidos diretamente dos ensaios de cisalhamento com sucção controlada.