Experimental and numerical analysis of reinforced concrete beams strengthened in shear with steel bars using the near-surface mounted (NSM) technique Leonardo Medeiros Costa, Tiago Ancelmo de Carvalho Pires, José Jéferson do Rêgo Silva, Geilson Márcio de Alburquerque Vasconcelos Revista Materia, 2024 RESUMO Há uma necessidade crescente de intervenção nas estruturas de concreto armado existentes para recuperar ou aumentar a sua capacidade resistente. O uso de materiais compósitos, como a fibra de carbono, tem sido eficiente, mas o custo ainda é um entrave. A aplicação de barras de aço como elemento de reforço apresenta-se como material alternativo e tecnicamente viável, porém existem poucos trabalhos na literatura. Desse modo, este trabalho realizou uma série experimental com três vigas de concreto armado sem armadura transversal, e reforçadas ao cisalhamento com barras de aço utilizando a técnica near-surface mounted (NSM). Foram monitorados no experimento a carga, o deslocamento e o padrão de fissuração. Os resultados demonstraram a eficiência do reforço com aumento de 69% da carga última e 63% da carga para surgimento das primeiras fissuras comparados a viga de referência. O reforço também aumentou a ductibilidade das vigas antes da ruptura brusca por cisalhamento. Modelos numéricos via método dos elementos finitos (MEF) foram realizados no software ABAQUS utilizando diferentes tipos de elementos e malhas. Os resultados numéricos foram validados com os resultados experimentais e foi observado que o uso de elementos quadráticos comparados a elementos lineares consegue representar melhor o padrão de fissuração e a capacidade de carga das vigas. A relação média dos resultados numérico/experimental para carga máxima das vigas reforçadas foi de 0,94.
Influence of silicon-dioxide nanoparticles in cementitious mortars: verification using x-ray diffraction, thermal analysis, physical, and mechanical tests F K G Andrade, T A C Pires, J J R Silva Materials Research Express, 2023 In recent years, nanotechnology has been applied to building materials, such as cementitious composites (e.g., mortar and concrete), to improve their properties. The aim of this study was to analyze the thermal, physical, and mechanical properties of mortars with and without silicon-dioxide (SiO2) nanoparticles. Experiments such as thermogravimetry and differential thermal analysis (TG-DTA), x-ray diffraction (XRD), fresh density, incorporated-air content, bulk density, capillary absorption, capillarity coefficient, flexural tensile strength, and compressive strength on prismatic specimens were performed on mortars and analyzed for different levels of nanosilica (nS). These levels were 1% and 3%, in addition to the reference mortar (0% nS). The TG-DTA curves showed an elevated content of chemically combined water and a lower content of calcium hydroxide (Ca(OH)2) in the 3% nS compositions, while the XRD curves presented a lower content of calcite and portlandite in the same mortar. These results indicate the fixation capacity of lime for the formation of calcium silicate hydrate (C-S-H), which is the primary cause of resistance in cementitious mortars. In addition, it was found that the use of nanosilica contributed to a fresh density increase of approximately 15%, which caused a minimum air-incorporated content decrease of 37% and a minimum bulk density increase of 10%. Higher densities resulted in a minimum water absorption reduction of 36%, owing to fewer pores in the mortars. Therefore, the capillarity coefficient decreased by a minimum of 41%. These nanoparticles also improved the minimum flexural tensile and compressive strengths by 88% and 158%, respectively, when using a 3% nS composition. These results can enable the use of lightweight aggregates in cementitious composites, improving their physical and mechanical characteristics and allowing greater reuse of these materials, including construction waste.
Numerical analysis on circular concrete-filled tubular columns subjected to fire Tiago A. de C. Pires, João Paulo C. Rodrigues, Jose J.R. Silva Journal of Structural Fire Engineering, 2019 Purpose Nowadays, circular concrete-filled tubular (CFT) columns are largely used in construction because of structural and architectural advantages such as high load bearing capacity and aesthetic appearance. The behavior of CFT columns at ambient and high temperatures is good; however, there are problems related to their behavior in fire when inserted in a real building structure, as for example, the influence of the restraining to thermal elongation that have to be addressed in order to improve their design. This study aims to present the results of a numerical study on the behavior of CFT columns with restrained thermal elongation in case of fire. Design/methodology/approach The parameters tested in the numerical simulations included column slenderness, load level, surrounding structure stiffness and steel reinforcement ratio. A sequentially coupled thermal stress analysis was carried out. The numerical model was validated with results from a large series of fire resistance tests carried out at Coimbra University, in Portugal. From these, simple equations to evaluate CFT column critical times were derived. Findings The results were also compared with the ones obtained from the current EN 1994-1-2:2005 simplified calculation and tabulated data methods. For the analyzed cases, it was verified that, while the simplified calculation method led to safe results on the evaluation of the fire resistance of CFT columns with restrained thermal elongation, the tabulated data method led, in certain cases, to unsafe results. This research showed also lower critical times than those from literature on similar type of columns. Originality/value The influence of the stiffness of the surrounding structure on the behavior of CFT columns subjected to fire was not yet clear in the major part of the studies already carried out. So, this paper has the originality to consider this parameter in the numerical simulations of this type of columns.
Buckling of concrete filled steel hollow columns in case of fire Proceedings of Sdss Rio 2010 International Colloquium Stability and Ductility of Steel Structures, 2010
