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The interfacial behaviour between ribbed steel rebars and concrete has been extensively studied because the contribution of the adherence between these two materials is of the utmost importance for the behaviour of Reinforced Concrete (RC) structures. The majority of the available studies on this topic indicate that the local adherence between these two materials can be defined through a bond-slip relationship, which is obtained with short embedded lengths. Although this seems to be widely accepted, some incoherencies, mainly regarding the local and the global detachment process in that “conventional theory”, are identified in the present work. To facilitate the understanding of the detachment process between a ribbed steel rebar and concrete, an analytical solution is developed. An experimental program with 33 pull-out tests covering three different ribbed steel rebars with different diameters and embedded lengths was carried out. Based on the experimental load–displacement at the pulled end responses, a new local bond-slip relationship with friction is proposed. In the end, the new bond-slip relationship, as well as other known relationships, is implemented into a Finite Element (FE) commercial code and the results are compared to the experimental data. Based on these preliminary results and up to the yielding point of the steel rebars, the new proposed local bond-slip model is the only one able to clearly distinguish and simulate either the local and the global performances of the tested specimens. © 2020 Institution of Structural Engineers

The paper is focused on the calibration of non-linear 3D finite element (FE) analyses to simulate punching failure of R/C flat slabs. The calibration procedure is developed with reference to the code ABAQUS, which is one of the most used computer codes in nonlinear modelling of R/C structures. Generally, the calibration of a nonlinear FE model is grounded on one test only, so its reliability could be limited. Here a hybrid method for the calibration of FE models of R/C flat slabs failing in punching is proposed and discussed. The method consists in calibrating input data by comparison of finite element model (FEM) results with both experimental data and predictions provided by analytical models. The procedure allows for a consistent calibration to be performed, valid for a wide range of longitudinal reinforcement ratios, from 0.5% to 2.00%, and concrete grades, from C20/25 to C50/60. A case study is investigated using the proposed method. Results show that calibrated values of the fracture energy lie between those provided by Model Code 1990 and Model Code 2010. From the new calibration procedure, a relationship between fracture energy and concrete compressive strength is also derived and blind analyses are performed to check its reliability against experimental results.

The cyclic failure observed in structural components such as pipelines subjected to extreme loading conditions highlights some limitations concerning the application of existing fatigue damage models. The evaluation and prediction of this type of failure in these steel components under large-scale plastic yielding associated with high levels of stress triaxiality are not sufficiently known nor explored. This fatigue domain is conventionally called ultra-low-cycle fatigue (ULCF) and damage features are representative of both low-cycle fatigue (LCF) and monotonic ductile fracture. Thus, in order to understand the ULCF damage mechanisms both monotonic and LCF tests are required to get representative bounding damage information to model the material damage behaviour under such extreme loading conditions. This paper aims at exploring the Theory of Critical Distances (TCD) in the LCF and ULCF fatigue regimes, including the application of the point, line and area methods. The application of the TCD theories has not been explored so far in the ULCF fatigue regimes, despite its promising results in the LCF and high-cycle fatigue. An experimental program was carried out on several specimens’ geometries made of X52 piping steel. In detail, smooth plane specimens and notched plane specimens were cyclic loaded under tension/compression loading in order to obtain fatigue lives within the range of 101-104 cycles. In addition, cyclic bending tests on notched plane specimens were also incorporated in this study. Finite element simulations of all small-scale tests were conducted allowing to derive elastoplastic stress/strain fields along the potential crack paths. The numerical data were subjected to a post-processing in order to find characteristic lengths that can be treated as a fatigue property according to the TCD. A unified strain-life relation is proposed for the X52 piping steel together with a characteristic material length, consisting of a practical relation for pipeline strain-based design under extreme cyclic loading conditions.

This work studies the low-velocity impact response of 3D-printed layered structures made of thermoplastic materials (PLA and PETg), which form sacrificial claddings for impact protection. The analyzed structures are composed of crushable cellular cores placed in between terminal stiffening plates. The cores tessellate either honeycomb hexagonal unit cells, or hexagonal cells with re-entrant corners, with the latter exhibiting auxetic response. The given results highlight that the examined PETg protectors exhibit higher energy dissipation ratios and lower restitution coefficients, as compared to PLA structures that have the same geometry. It is concluded that PETg qualifies as an useful material for the fabrication of effective impact protection gear through ordinary, low-cost 3D printers.

The aim of this study is to evaluate the elemental composition of six food supplements of plant origin, commonly sold in the Portuguese market, by energy dispersive X-ray fluorescence. The presence of arsenic in all the Maca, Ashwagandha, Camu-Camu and Hemp protein samples (except the generic form) is a reason of concern due to the long-term effects of As mainly in its inorganic form. Thus, great caution must be taken on some food supplements, particularly the cases of Moringa from Egypt and Yellow/Xpresso Maca, whose inorganic As concentrations are in line with the upper bound concentration for the 95th dietary exposure according to the European Food Safety Authority which is 0.64 μg/kg bw/day. In what regards Hemp protein, if the supplier’s daily intake recommendation (30 g) is followed, values as high as 1.75 μg/kg bw/day of inorganic As will be consumed, which are dangerously above the upper bound. In this case this specific supplement lot should be removed from the market. Also the consumption of Hemp protein leads to a daily intake of Mn above the Daily Reference Intake (DRI) and Adequate Intakes (AIs) for adults. The contamination of Goji berries by Pb is a reason for concern—organic berries contained 11.3 μg/g while berries derived from conventional agriculture 11.6 μg/g, leading to daily intake doses of 315.3 μg and 324.8 μg, respectively, if the recommended daily intake of 28 g is followed. Our findings point out to an inadequacy of the recommended intakes by the supplier vis a vis the concentrations observed, greatly increasing the risk for public health.