https://repositorio.ufu.br/handle/123456789/19022 2026-09-07T08:36:31Z 2026-09-07T08:36:31Z https://repositorio.ufu.br/handle/123456789/50000 2026-09-03T06:28:30Z 2026-02-06T00:00:00Z

Title: Análise da influência do teor e do comprimento de fibras de carbono e do consumo de cimento nas propriedades de concretos de ultra-alto desempenho Abstract: Ultra-high-performance concrete (UHPC) is characterized by high mechanical strength, low porosity, and enhanced durability. However, in the absence of fibers, it exhibits a brittle response under loading, making the incorporation of fibrous reinforcement necessary to improve ductility and energy absorption capacity. Thus, this study evaluated the interaction between carbon fibers and the UHPC matrix, as well as their influence on the mechanical properties, toughness, and electrical properties of the composite, considering a constant water-to-binder ratio of 0.23 for all mixtures. The research comprised the physical and chemical characterization of the constituent materials, followed by the definition of a central composite rotatable design for statistical experimental planning. Subsequently, the packing density of fine materials was optimized using the modified Andreassen and Andersen particle packing model. The optimized mixtures were produced and evaluated in both fresh and hardened states. The composite properties were investigated at different curing ages, according to the requirements of each test. At 28 days, compressive strength, flexural tensile strength, total porosity by absorption, and electrical resistivity were evaluated. At 56 days, compressive strength, flexural tensile strength, electrical resistivity, and modulus of elasticity were determined. The results of the experimental design enabled the development of response surfaces and the identification of statistically significant variables, highlighting cement content as the main governing factor for the mechanical properties within the studied domain. The results demonstrate that it is possible to produce ultra-high-performance concrete with low cement consumption (500 and 550 kg/m³), contributing to the advancement of knowledge on UHPC mixture design. Complementary mixtures with higher carbon fiber content indicated that increasing the fiber content significantly improves the tensile strength and toughness of the composite. The mixture containing 3.7% carbon fibers exhibited outstanding overall performance, combining high mechanical strength with enhanced energy absorption capacity, demonstrating the potential of carbon fibers to produce UHPC with improved mechanical properties.

2026-02-06T00:00:00Z https://repositorio.ufu.br/handle/123456789/49809 2026-08-26T06:18:21Z 2026-07-09T00:00:00Z

Title: Avaliação de danos em dormentes de concreto protendido por meio da técnica de análise modal Abstract: Prestressed concrete sleepers are essential components of railway superstructures, responsible for maintaining track gauge and transferring loads from the rails to the ballast. During service life, these elements may be affected by different damage mechanisms, including central cracking associated with deficient support, cracking at the rail seat, and deterioration caused by internal expansive reactions. Although visual inspection is widely used, it has limitations in detecting internal damage or cracks partially closed by prestressing. In this context, this study evaluated the application of experimental modal analysis as a complementary non-destructive diagnostic tool for prestressed concrete sleepers. Three damage mechanisms were investigated: central cracking due to center bound, cracking at the rail seat, and cracking induced by alkaliaggregate reaction. The sleepers were subjected to controlled damage induction, visual and physical crack characterization, and modal testing using impact hammer excitation. Natural frequencies, damping ratios, and mode shapes were evaluated for the first three vibration modes. The results indicated that the first flexural mode provided the most consistent response among the parameters assessed. For center bound damage, the natural frequency showed a progressive, although limited, reduction with increasing damage level. For rail seat cracking, the damping ratio was more sensitive than the natural frequency. In sleepers subjected to expansive reaction, the natural frequency was influenced by the interaction between initial stiffness gain due to continued hydration and progressive stiffness loss caused by expansive cracking, whereas damping showed a more direct response to the evolution of deterioration. The results indicate that modal analysis has potential to complement the diagnosis of prestressed concrete sleepers, provided that it is interpreted together with the physical characterization of damage, visual inspection, and identification of the active deterioration mechanisms.

2026-07-09T00:00:00Z https://repositorio.ufu.br/handle/123456789/49801 2026-08-25T06:20:10Z 2026-02-26T00:00:00Z

Title: Análise térmica de habitações emergenciais em contêineres situados em cidades portuárias pertencentes a diferentes zonas bioclimáticas Abstract: The growing need for sustainable housing solutions that can be implemented quickly in emergency situations caused by natural disasters, conflicts, and humanitarian crises has been growing exponentially. In line with this demand, the choice of containers for housing purposes is well suited to these situations due to the accumulation of disused modules in ports and the potential for reusing these structures as modular elements in civil construction. Although containers are a good construction solution for this purpose, they present challenges in relation to overheating inside. The literature presents studies on insulating elements associated with the envelope in order to reduce heat gains, but studies that correlate the use of containers as housing with bioclimatic thermal adaptation strategies are scarce. In this sense, this research aimed to analyse the thermal performance of emergency housing in shipping containers in different port cities located in different bioclimatic zones. The analyses were performed using computer simulations integrating BIM-BES with Revit and Design Builder software. Natural ventilation and shading strategies were tested, as well as three types of roofing: thermoacoustic with EPS, reflective, and green roof. For the envelope, the application of thermal insulation previously tested in the study by Da Costa et al. (2024) was considered. The simulation scenarios were developed based on a combination of bioclimatic strategies and applied in the port cities of Santos (AF), Los Angeles (CSA), and Shanghai (CFA). The results indicated that for Santos, the combination of shading, ventilation and green roof strategies (MVSV) showed a reduction of up to 14.47ºC and an increase of up to 9 hours within the operating temperature range in summer, at critical times. For Los Angeles, the same solution (MVSV) proved to be efficient in this same scenario, with a reduction of 11.33ºC and an increase of up to 8 hours within the limit range. For Shanghai, the combined use of shading and green roof strategies stands out, reducing temperatures by up to 11.85ºC and remaining 7 hours longer within the operating temperature limits. It was observed that the use of bioclimatic strategies can mitigate the problems of internal overheating in this type of housing, providing better conditions of use and reducing the need for mechanical cooling/heating systems.

2026-02-26T00:00:00Z https://repositorio.ufu.br/handle/123456789/49708 2026-08-21T06:20:14Z 2026-07-29T00:00:00Z

Title: Desenvolvimento de um modelo constitutivo para solos arenosos reforçados com fibras utilizando redes neurais artificiais Abstract: The reinforcement of sandy soils with randomly distributed fibers significantly improves their mechanical properties, posing challenges to constitutive modeling due to complex nonlinear interactions between the matrix and the reinforcement. This work develops a constitutive model based on Artificial Neural Networks (ANN) to predict the stress-strain behavior of a uniform sand reinforced with polymeric fibers. The methodology employs a two-phase hybrid approach, combining experimental triaxial test data with synthetic data generated through an adapted Modified Cam-Clay model. The experimental database, obtained at the Federal University of Bahia, encompasses fiber contents of 0%, 0.5%, and 1.0%, fiber lengths of 12.5, 25, and 51 mm, and confining stresses of 50, 100, 200, and 300 kPa; from it, the 24 conventional drained triaxial compression tests were used, totaling 1,207 points. The synthetic data generation produced about 19.5 thousand points across 42 scenarios, expanding the experimental domain to include intermediate confinement levels. The adopted architecture is a multilayer perceptron (MLP) neural network that directly maps the test conditions and the axial strain level onto the state variables of interest, namely the deviatoric stress, the mean effective stress, and the volumetric strain. Training combines pre-training with the physically consistent synthetic data and finetuning, through transfer learning, with the experimental data. Validation, carried out by exhaustive leave-one-out cross-validation, yielded an aggregate coefficient of determination of 0.977 for the deviatoric stress, 0.991 for the mean effective stress, and 0.914 for the volumetric strain. The model reproduces the progressive mobilization of the fibers, the peak strength, and the transition to dilatant behavior, offering a computationally efficient alternative to traditional analytical models that are difficult to calibrate.

2026-07-29T00:00:00Z