Experimental and numerical evaluations of the bond behaviour between ribbed steel rebars and concrete

Funding Information: Open access funding provided by FCT|FCCN (b-on). The funding was provided by Fundação para a Ciência e Tecnologia (Grant no. UID/EMS/00667/2019). Publisher Copyright: © 2023, The Author(s).The study of interfacial behaviour between ribbed steel rebars and concrete is a subject that has been widely studied. However, the definition of the bond stress distribution throughout the embedded length of the steel rebar is still controversial due to the difficulty of experimentally obtaining such distribution for a fixed load magnitude. It is also undeniable its relevancy for the better understanding and model reinforced concrete (RC) structures. So, the definition of the local behaviour between the ribbed steel rebar and concrete is critical to correctly simulate the adherence between both materials. In this matter, the local bond-slip models recommended in codes seem to satisfy some researchers while others suggest prudence in using them. Therefore, only choosing the correct bond-slip relationship may lead to exact interpretations and conclusions of the structural behaviour of a concrete structure but with the existing different bond-slip types, researchers can be misled inadvertently. This work aims to clarify some of these aspects by numerically simulating several pull-out tests under different conditions and checking their influence (or not) on real-scale specimens. After the validation of the numerical model through a proposed new bond-slip relationship, other parameters were studied also. Although the type of the bond-slip relationship influences the detachment of the steel rebar from the concrete, the yielding of the former material was found to be the main parameter that masks the differences in the behaviour of real-scale RC structures when different types of bond-slip relationships were considered in the numerical simulations.publishersversionpublishe

Degradation of gfrp-plates bonded to concrete: An experimental approach based on mohr-coulomb failure criterion

The authors are grateful to Fundação para a Ciência e Tecnologia for partial financing of thework under Project PTDC/ECM/100538/2008. The authors would like to thank for the helpof Prof. Vladimir Cervenka and Ing. Dobromil Pryl, with ATENA.publishersversionpublishe

Numerical bond assessment of carbon-epoxy stepped-lap joints

Publisher Copyright: © 2023 The Author(s)With the main purpose of obtaining lightweight and durable structures, bonding techniques have improved significantly in several industries. Depending on the type of structure, joining different components with different materials may require different joint geometries, which may perform better or worse. Still, only the bond performance of a very limited number of joint geometries is well known. A lack of knowledge, for instance, about the debonding process of one and two-step joints persists, especially for the latter. The present work intends to mitigate this gap by studying the debonding processes of one and two-step joints made with CFRP and aluminium adherends. To that end, implicit and explicit numerical methods (finite and distinct element methods, respectively), were applied to study different joint geometries and identify which one shows the best bond performance when subjected to a monotonic load consistent with pure fracture mode II. Based on the bond stresses obtained within the interface of the joints, the debonding propagations of the one and two-step joints are analyzed thoroughly. In the case of the one-step bonded joints, the results revealed that when the ratio between the axial stiffness of the adherends is r = 1.0 the load capacity of these joint configurations is maximized. With two-step joints, the load capacity is very sensitive to the relationship between the axial stiffness on the left (ra) and right-hand side (rb). Based on 162 different numerical simulations, the results also suggest that the load capacities of the two-step joint configurations can be maximized when the axial stiffness ra and rb of the joint are equal to 1/3 and 3.0, respectively.publishersversionpublishe

Influence of temperature cycles on bond between glass fiber-reinforced polymer and concrete

Reinforced concrete (RC) beams externally strengthened with glass fiber-reinforced polymer (GFRP) strips bonded to the soffi t may see their load-carrying capacity reduced due to environmental conditions—especially due to the deterioration of bond between the adhesively bonded laminates and concrete, causing premature failure. More research has been published on the detachment of the laminate progressing from the anchorage zone than on failure induced by the formation of fl exural or shear-fl exural cracks in the midspan followed by fi ber-reinforced polymer (FRP) separation and failure designated as intermediate crack (IC) debonding. An experimental program to study degradation of the GFRP laminate beam specimens after accelerated temperature cycles, namely: 1) freezing-and-thawing type; and 2) cycles of the same amplitude (40°C [104°F]) and an upper limit approximately 70% of the glass vitreous transition temperature of the resin, Tg, is described. Effects on the bond stress and ultimate capacity are reported. Substantial differences between shear and bending-induced failure and a decrease of bond stresses and engagement of the laminates on the structural response are analyzed.proofpublishe

Experimental calibration of the bond-slip relationship of different CFRP-to-timber joints through digital image correlation measurements

UIDB/EMS/00667/2020Nowadays, the use of the Digital Image Correlation (DIC) technique has spread and it is being used in several engineering areas to measure displacements. The available data obtained from the DIC measurement to evaluate the bond performance between a Carbon fibre Reinforced Polymer (CFRP) externally bonded to a timber substrate is scarce. From the existing data obtained with other materials, this contactless technique revealed to be quite useful but its accuracy with other well-established techniques, such as the use of electric strain gauges is not well understood yet. Therefore, the current work aims to study the accuracy of 2D DIC measurements with the measurements obtained from the use of strain gauges within a low-cost perspective. To that end, several CFRP-to-timber bonded joints were tested under the single-lap shear test and different bonding techniques were considered as well. Some flaws intrinsically derived from the DIC measurements that complicate the bond assessment, such as the fluctuations in the generated displacements field, are identified, and to bypass this problem a new methodology is proposed. This new methodology is based on two different closed-form solutions that, after defining the local and global bond behaviours of different CFRP-to-timber bonded joints, allowed to eliminate the fluctuations found from the DIC measurements, facilitating the estimation and the comprehension of the full debonding process of the CFRP-to-timber joints, which was achieved with a good proximity to the homologous debonding process derived from the strain gauge measurements.publishersversionpublishe

Comportamento e modelação da ligação GFRP/betão em elementos de betão armado expostos a ambientes agressivos

Dissertação para a obtenção do Grau de Doutor em Engenharia Civil, na Especialidade de Estruturas pela Universidade Nova de LisboaO presente trabalho incide sobre a degradação da ligação GFRP/betão devido à exposição a agentes ambientais. A motivação para a realização deste estudo surge com o aumento do número de reforços de estruturas através da aplicação de materiais compósitos de matriz polimérica para os quais, por terem um período ainda curto de aplicação, é ainda desconhecido o desempenho das ligações FRP/betão a longo prazo. Em particular, o real conhecimento do desempenho destas ligações quando expostas às adversidades ambientais tais como ambientes salinos, húmidos ou secos, gelo/degelo ou a temperaturas altas (próximas de Tg) é ainda deficiente. Acresce‐se maior motivação dada a localização do território português, no qual diversas regiões possuem importantes amplitudes térmicas ou ambientes salinos. A aplicação dos compósitos de FRP em vigas de betão armado proporciona um aumento substancial na sua ductilidade e resistência última. No entanto, no reforço de vigas de betão armado, as capacidades dos compósitos de FRP não são alcançadas deixando por mobilizar muito material aquando do seu descolamento das superfícies coladas de betão. A análise e compreensão dos desempenhos dos compósitos de FRP e da ligação tornam necessária a definição de critérios de ruptura que possam estimar o descolamento prematuro dos compósitos de FRP. Tais critérios têm sido implementados em programas comerciais de cálculo automático ajudando o projectista a estimar as resistências últimas dos elementos estruturais de betão armado reforçados com compósitos de FRP. Neste trabalho foram realizados ensaios de corte duplo de provetes cúbicos de betão colados com compósito de GFRP. Mantendo o mesmo comprimento de colagem de cerca de 150mm, foram estudados outros parâmetros tais como os efeitos da imposição de tensões normais de compressão (perpendiculares à superfície de colagem), das exposições a ciclos de nevoeiro salino, a ciclos de marés (seco/molhado), a ciclos de temperatura entre +7,5°C a +47,5°C e entre ‐10°C a +30°C. Os resultados permitiram constatar que, na ruptura, a ligação tem um comportamento segundo o critério de ruptura de Mohr‐Coulomb pelo que, foram determinados os ângulos de atrito interno e coesões da ligação para as diferentes condições ambientais. Realizaram‐se também 47 ensaios à flexão de vigas de betão armado sendo que 3 vigas têm dimensões mais similares à reais e as restantes vigas de secção rectangular de menores dimensões com o propósito de analisar a degradação da aderência entre o compósito de GFRP e o betão. Para os diferentes agentes ambientais, diversos parâmetros foram estudados e comparados com a situação de referência (sem qualquer envelhecimento acelerado) tais como a tensão de aderência máxima da ligação, a força máxima transmitida ao compósito de GFRP, a extensão máxima, os deslocamentos relativos entre materiais e a energia de fractura. Recorreu‐se a um programa de cálculo que permitiu modelar a ligação GFRP/betão e cujos resultados numéricos foram comparados com os experimentais. Propõem‐se ainda metodologias de cálculo para estimar o descolamento do compósito de GFRP e cujos resultados são ainda comparados com algumas normas ou códigos internacionais.Fundação da Ciência e Tecnologia - Projecto DUST‐PTDC/ECM/100538/200

Influence of uniform temperature variations on hybrid bonded joints with a circular or tubular cross-sectional area

Funding Information: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Hugo C. Biscaia reports financial support was provided by Foundation for Science and Technology. Marta S. Carvalho reports financial support was provided by Foundation for Science and Technology. Ana P. Martins reports financial support was provided by Foundation for Science and Technology. Publisher Copyright: © 2023 The AuthorsThe use of lightweight structures is a current concern in several engineering domains. To obtain such types of structures, the bonding technique using Carbon Fibre-Reinforced Polymers (CFRP) has been most recently considered a primary option. If CFRP is known to have a high strength-to-weight ratio or high corrosion resistance, the bonding technique does not need to add other fixation components and it also prevents stress concentrations. However, when combined with, e.g. a metallic surface, the high difference between the thermal expansion coefficient of the CFRP composite and the metallic material may raise some issues when the adhesively bonded structure is subjected to thermal loading. Therefore, the present work presents an analytical model that facilitates the comprehension of the impact of temperature on a hybrid bonded joint with a circular or tubular cross-sectional area. The full debonding process of a double but bonded joint with a regular curvature is discussed thoroughly. Due to the susceptibility of current adhesives to lose their mechanical properties for relatively high temperatures, the vitreous transition temperature of the adhesives and their influence on the local adhesive model is considered in a deeper analysis. The Finite Element Method (FEM) was used to validate all the derived analytical equations, which were achieved due to the close predictions obtained from both ways, i.e. from the numerical simulations and the proposed closed-form solutions.publishersversionpublishe

ENSAIOS NÃO DESTRUTIVOS USADOS NA INSPEÇÃO E DIAGNÓSTICO DE EDIFÍCIOS HISTÓRICOS DE ALVENARIA DE PEDRA

Ao longo da sua vida útil os edifícios históricos estão sujeitos a alterações de uso, a agentes ambientais e a diferentes ações como assentamentos do solo, incêndios, inundações ou sismos, para os quais podem não estar preparados. Além disso, a falta de manutenção contínua ajuda a colocar grande parte desse património em risco devido a problemas estruturais que reduzem sua própria segurança e a dos seus utilizadores. A preservação e mitigação de riscos do património cultural construído requer o uso de ferramentas confiáveis, a fim de avaliar o seu estado de conservação e identificar e prevenir potenciais vulnerabilidades. Os testes destrutivos tradicionais não são possíveis de realizar na maioria dos edifícios históricos, por isso é necessário selecionar testes não destrutivos (NDT) que permitam a caracterização física e mecânica dos materiais e do comportamento da estrutura. Neste artigo apresenta-se uma visão geral de diferentes equipamentos e testes NDT que permitem o levantamento geométrico e o mapeamento dos danos do edifício, a análise petrográfica da pedra de alvenaria, a caracterização das propriedades físicas e mecânicas dos materiais e o comportamento estrutural do edifício

Stainless Steel Bonded to Concrete: An Experimental Assessment using the DIC Technique

Abstract The durability performance of stainless steel makes it an interesting alternative for the structural strengthening of reinforced concrete. Like external steel plates or fibre reinforced polymers, stainless steel can be applied using externally bonded reinforcement (EBR) or the near surface mounted (NSM) bonding techniques. In the present work, a set of single-lap shear tests were carried out using the EBR and NSM bonding techniques. The evaluation of the performance of the bonding interfaces was done with the help of the digital image correlation (DIC) technique. The tests showed that the measurements gathered with DIC should be used with caution, since there is noise in the distribution of the slips and only the slips greater than one-tenth of a millimetre were fairly well predicted. For this reason, the slips had to be smoothed out to make it easier to determine the strains in the stainless steel and the bond stress transfer between materials, which helps to determine the bond–slip relationship of the interface. Moreover, the DIC technique allowed to identify all the states developed within the interface through the load–slip responses which were also closely predicted with other monitoring devices. Considering the NSM and the EBR samples with the same bonded lengths, it can be stated that the NSM system has the best performance due to their higher strength, being observed the rupture of the stainless steel in the samples with bond lengths of 200 and 300 mm. Associated with this higher strength, the NSM specimens had an effective bond length of 168 mm which is 71.5% of that obtained for the EBR specimens (235 mm). A trapezoidal and a power functions are the proposed shapes to describe the interfacial bond–slip relationships of the NSM and EBR systems, respectively, where the maximum bond stress in the former system is 1.8 times the maximum bond stress of the latter one