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

Bond assessment between rebars embedded into a parent material using a single-function bond-slip model

Publisher Copyright: © 2023 The Author(s)The pull-out test is usually used to evaluate the local bond behaviour between a rebar such as a ribbed steel rebar or a Fiber Reinforced Polymer (FRP) and a parent material, like concrete or timber. Although some codes recommend using a piecewise bond-slip model for ribbed or round steel rebars embedded in concrete, there is no globally accepted bond-slip model for FRP composites. Consequently, this piecewise bond-slip model is usually adapted for FRP composites embedded in a parent material (substrate). The present work therefore aims to propose a novel single-function bond-slip model that may be calibrated and used to model the pull-out test and the detachment process of an embedded rebar from a parent material. The model requires the calibration of three parameters that may vary according to the type of rebar and its parent material. Since the governing equation of the detachment between the rebar and the parent material during a pull-out test has no known analytical solution, the Finite Difference Method (FDM) was applied to find the interfacial slips throughout the embedded length. The results were compared and validated with the experimental pull-out tests of ribbed steel rebars embedded into a concrete block as well as with the numerical results obtained from the use of the Finite Element Method (FEM). To cover a broader range of materials and show the versatility of the novel bond-slip model, the results were also compared with other experimental data available in the literature. The results showed a very high precision of the new bond-slip model when applied to several pull-out tests especially when ribbed steel rebars-to-concrete and FRP-to-concrete interfaces or FRP-to-timber interfaces were used.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

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

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

Experimental and numerical modeling of basalt textile reinforced mortar behavior under uniaxial tensile stress

During the last years several projects and studies have improved the knowledge about textile reinforced mortar (TRM) technology. TRM has already been used in strengthening masonry and reinforced concrete structural elements such as walls, arches, columns and beams. This material is presented as a real alternative to the use of fiber-reinforced polymers (FRP) in situations where these composites have presented some drawbacks or their use is banned. Textile reinforced mortar show a complex mechanical behavior derived from the heterogeneity of the constituent materials. This paper aims to deepen the knowledge of this composite material in terms of tensile behavior.Following this scope, this paper presents an experimental campaign focused on thirty-one TRM specimens reinforced with four different reinforcing ratios. The results are analyzed and contrasted with two distinct models. (i) The Aveston-Cooper-Kelly theory (ACK) which is based on a tri-linear analytical approach; and (ii) a non-linear numerical simulation with a 3D finite element code.The finite element analysis (FEA) of the TRM tensile tests also showed no significant dependence on the basalt-to-mortar interface, i.e., the choice of a bond-slip curve in order to reproduce the bond stresses and slippages along the interface is irrelevant and it can be simply considered as rigid interface.Durante los últimos años diversos proyectos y estudios han mejorado el conocimiento sobre la tecnología de morteros reforzados con tejidos (TRM por sus siglas en inglés). El TRM ya se ha utilizado para reforzar elementos estructurales de mampostería y hormigón armado, como muros, arcos, columnas y vigas. Este material se presenta como una alternativa real al uso de polímeros reforzados con fibras (FRP) en situaciones en las que estos composites han presentado algunos inconvenientes o su uso está prohibido. Los morteros reforzados con tejidos presentan un comportamiento mecánico complejo derivado de la heterogeneidad de los materiales que los componen. Este artículo tiene como objetivo profundizar en el conocimiento de este material compuesto en términos de comportamiento a tracción. Siguiendo este objetivo, este artículo presenta una campaña experimental centrada en treinta y una probetas de TRM reforzadas con cuatro relaciones de refuerzo diferentes. Los resultados se analizan y contrastan con dos modelos distintos. (i) La teoría de Aveston-Cooper-Kelly (ACK), que se basa en un enfoque analítico trilineal; y (ii) una simulación numérica no lineal con un código de elementos finitos 3D. El análisis de elementos finitos (FEA) de los ensayos de tracción TRM tampoco mostró una dependencia significativa de la interfaz basalto-mortero, es decir, la elección de un enlace. -La curva de deslizamiento para reproducir las tensiones de unión y los deslizamientos a lo largo de la interfaz es irrelevante y puede considerarse simplemente como una interfaz rígida.Este trabajo de investigación fue financiado a través del proyecto de investigación DFB 7-12-TK-2009-10 y BIA2010-20789-C04-03/04; el contrato del Gobierno Vasco IT781-13; y el Programa de becas de la Fundación Centros Tecnológicos-Iñaki Goenaga