Tensile and bond characterization of natural fibers embeeded in inorganic matrices

Innovative composite materials made of continuous fibers embedded in mortar matrices have been recently received attention for externally bonded reinforcement of masonry structures. In this regards, application of natural fibers for strengthening of the repair mortars is attractive due to their low specific weight, sustainability and recycability. This paper presents experimental characterization of tensile and pull-out behavior of natural fibers embedded in two different mortar-based matrices. A lime-based and a geopolymeric-based mortar are used as sustainable and innovative matrices. The obtained experimental results and observations are presented and discussed.

Innovative methodologies for the enhancement of the flexural strengthening performance of NSM CFRP technique for RC beams

Tese de Doutoramento em Engenharia Civil

Efeito do carregamento cíclico e da pré-fendilhação do betão no comportamento de lajes de betão armado reforçadas à flexão com laminados de CFRP inseridos

Dissertação de mestrado integrado em Engenharia Civil

Reforço à flexão de lajes de betão armado com laminados de CFRP pré-esforçados

Dissertação de mestrado integrado em Engenharia Civil (área de especialização em Estruturas e Geotecnia)

Comportamento de painéis de alvenaria reforçados com FRCM sujeitos a ações no plano: Estudo da interface

O presente trabalho dedica-se à caracterização do comportamento de modelos de alvenaria reforçada com FRCM (fiber reinforced cementitious matrix) quando sujeitos a ações que atuam no plano da parede. O sistema de reforço, composto por uma camada de argamassa cimentícia reforçada com uma malha de CFRP (carbon fiber reinforced polymer), foi aplicado a modelos de alvenaria de tijolo furado. Considerando a importância da interface entre a camada de reforço e o substrato para a eficiência do sistema de reforço, procedeu-se à caracterização do comportamento mecânico da interface por intermédio de ensaios de corte direto, com os quais foi possível definir as superfícies de cedência e de rotura da interface. Os resultados obtidos permitiram a quantificação dos parâmetros que caracterizam a interface entre o material cerâmico e uma argamassa do tipo PFRM (polypropylene fibre reinforced mortar) quando sujeita a cargas de corte combinadas com cargas normais à interface. Através de expressões analíticas e do critério de rotura de Mohr-Coloumb foi analisada a adequação de um critério baseado numa aproximação linear, aos dados obtidos experimentalmente.

Analytical approach for the flexural analysis of RC beams strengthened with prestressed CFRP

The objective of this paper is to propose a simplified analytical approach to predict the flexural behavior of simply supported reinforced-concrete (RC) beams flexurally strengthened with prestressed carbon fiber reinforced polymer (CFRP) reinforcements using either externally bonded reinforcing (EBR) or near surface mounted (NSM) techniques. This design methodology also considers the ultimate flexural capacity of NSM CFRP strengthened beams when concrete cover delamination is the governing failure mode. A moment–curvature (M–χ) relationship formed by three linear branches corresponding to the precracking, postcracking, and postyielding stages is established by considering the four critical M–χ points that characterize the flexural behavior of CFRP strengthened beams. Two additional M–χ points, namely, concrete decompression and steel decompression, are also defined to assess the initial effects of the prestress force applied by the FRP reinforcement. The mid-span deflection of the beams is predicted based on the curvature approach, assuming a linear curvature variation between the critical points along the beam length. The good predictive performance of the analytical model is appraised by simulating the force–deflection response registered in experimental programs composed of RC beams strengthened with prestressed NSM CFRP reinforcements.

Transfer zone of prestressed CFRP reinforcement applied according to NSM technique for strengthening of RC structures

This study presents an experimental program to assess the tensile strain distribution along prestressed carbon fiber reinforced polymer (CFRP) reinforcement flexurally applied on the tensile surface of RC beams according to near surface mounted (NSM) technique. Moreover, the current study aims to propose an analytical formulation, with a design framework, for the prediction of distribution of CFRP tensile strain and bond shear stress and, additionally, the prestress transfer length. After demonstration the good predictive performance of the proposed analytical approach, parametric studies were carried out to analytically evaluate the influence of the main material properties, and CFRP and groove cross section on the distribution of the CFRP tensile strain and bond shear stress, and on the prestress transfer length. The proposed analytical approach can also predict the evolution of the prestress transfer length during the curing time of the adhesive by considering the variation of its elasticity modulus during this period.

Effect of environmental ageing on the numerical response of FRP-strengthened masonry walls

Recent durability studies have shown the susceptibility of bond in fiber-reinforced polymer (FRP) strengthened masonry components to hygrothermal exposures. However, it is not clear how this local material degradation affects the global behavior of FRP-strengthened masonry structures. This study addresses this issue by numerically investigating the nonlinear behavior of FRP-masonry walls after aging in two different environmental conditions. A numerical modeling strategy is adopted and validated with existing experimental tests on FRP-strengthened masonry panels. The model, once validated, is used for modeling of four hypothetical FRP-strengthened masonry walls with different boundary conditions, strengthening schemes, and reinforcement ratios. The nonlinear behavior of the walls is then simulated before and after aging in two different environmental conditions. The degradation data are taken from previous accelerated aging tests. The changes in the failure mode and nonlinear response of the walls after aging are presented and discussed.

Moisture-induced degradation of interfacial bond in FRP-strengthened masonry

Externally bonded strengthening of masonry structures using Fiber Reinforced Polymers (FRPs) has been accepted as a promising technique. Although the effectiveness of FRPs in improving the performance of masonry components has been extensively investigated, their long-term performance and durability remain poorly addressed. This paper, tackling one of the aspects related to durability of these systems, presents an experimental investigation on the effect of long-term (one year) water immersion on the performance of GFRP-strengthened bricks. The tests include materials' mechanical tests, as well as pull-off and single-lap shear bond tests, to investigate the changes in material properties and bond behavior with immersion time, respectively. The effect of mechanical surface treatment on the durability of the strengthened system as well as the reversibility of the degradation upon partial drying are also investigated. The experimental results are presented and critically discussed.

Bond performance in NSM-strengthened masonry brick

The use of Near Surface Mounted (NSM) Fiber Reinforced Polymers (FRPs) for strengthening masonry structures can be a suitable substitute for Externally Bonded Reinforcement (EBR) technique. NSM technique has many advantages such as larger bonded area, better anchorage capacity, higher resistance, higher percentage exploitation of the FRP and reduced installation time. However, information regarding the effectiveness of this strengthening technique for masonry structures is scarce and characterization of the critical mechanisms such as bond behavior is necessary. This paper presents experimental investigation of the bond performance in NSM-strengthened brick specimens. CFRP laminates are used for NSM strengthening of masonry bricks with different bonded lengths. The bond between FRP and masonry substrate is investigated by performing conventional pull-out tests and the experimental results are presented and discussed.

Seismic evaluation of environmentally degraded FRP-strengthened masonry walls

Fiber Reinforced Polymers (FRPs) have been extensively used for externally bonded reinforcement of masonry structures during the last years. Available information shows that FRPs can significantly improve the seismic performance of masonry elements without altering their structural mass. However, the durability and long-term performance of the strengthened elements are not clearly known yet. Recent experimental results show that environmental conditions can lead to degradation of the bond between FRP and masonry and FRP delaminations. But the effect of these local degradation mechanisms on the global structural response is not studied yet. This paper is therefore aimed at numerically investigating the effect of environmental degradation on the global performance of strengthened masonry walls. The nonlinear behavior of masonry walls strengthened with FRP composites is initially simulated with the aim of a FE package. The adopted numerical modeling strategy is verified by comparison of numerical and experimental results. The model, once validated, is used for investigating the effect of materials and bond degradation on the global behavior and failure modes of strengthened walls. The effect of strengthening scheme on the long-term performance of strengthened walls is also investigated. The degradation data are taken from experimental tests previously performed by the authors. The numerical results show that the effect of local material degradation on the global response of strengthened walls depends on the strengthening schemes, and severity of the environmental conditions. Moreover, environmental induced degradations and FRP delaminations can lead to change of expected failure modes in the strengthened elements. These observations, that are usually neglected at the design stage, can be critical in the long-term performance of strengthened structures.

Fused deposition modeling with polypropylene

This paper addresses the potential of polypropylene (PP) as a candidate for fused deposition modeling (FDM)-based 3D printing technique. The entire filament production chain is evaluated, starting with the PP pellets, filament production by extrusion and test samples printing. This strategy enables a true comparison between parts printed with parts manufactured by compression molding, using the same grade of raw material. Printed samples were mechanically characterized and the influence of filament orientation, layer thickness, infill degree and material was assessed. Regarding the latter, two grades of PP were evaluated: a glass-fiber reinforced and a neat, non-reinforced, one. The results showed the potential of the FDM to compete with conventional techniques, especially for the production of small series of parts/components; also, it was showed that this technique allows the production of parts with adequate mechanical performance and, therefore, does not need to be restricted to the production of mockups and prototypes.

Mechanical, fatigue and wear properties of sintered Carbon Nanotube-based functionally graded materials

Tese de Doutoramento Engenharia Mecânica

Bases de trabalho para a avaliação do ciclo de vida de vigas em betão armado reforçadas com laminados de CFRP de acordo com as técnicas EBR e NSM

Dissertação de mestrado integrado em Engenharia Civil

Desenvolvimento de materiais auxéticos para aplicações estruturais

Dissertação de mestrado integrado em Engenharia Civil