As a top construction material worldwide, concrete has core weakness relating to low tensile resistance without reinforcement. It is the reason that a variety of innovative materials are being used on concrete to overcome its weaknesses and make it more reliable and sustainable. Further, the embodied carbon of concrete is high because of cement being used as the integral binder. Latest research trends indicate significant potential for carbon fiber as an innovative material for improving concrete mechanical strength. Although significant literature is available on the use of carbon fiber in concrete, a limited number of studies have focused on the utilization of carbon fiber for concrete mechanical strength improvement and the reduction of embodied carbon. Following the gap in research, this study aimed to investigate and optimize the use of carbon fiber for its mechanical characteristics and embodied carbon improvements. The use of carbon fiber in self-compacting concrete lowers sagging. The greatest quantity of carbon fiber is that it reduces the blockage ratio, forcing the concrete to solidify as clumps develop. With time, carbon fiber improves the durability of concrete. Self-compacting concrete with no carbon fiber has a poor tensile strength. Experiments were conducted by adding carbon fiber at 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% by weight. Fresh concrete tests including slump test and L-box test, hardened concrete tests involving compressive strength and splitting tensile strength, and durability tests involving water absorption and acid attack test were conducted. Embodied carbon ratios were calculated for all of the mix ratios and decreasing impact, in the form of eco-strength efficiency, is observed with changes in the addition of carbon fiber in concrete. From the testing results, it is evident that 0.6% carbon fiber is the ideal proportion for increasing compressive strength and split tensile strength by 20.93% and 59%, respectively, over the control mix. Response Surface Methodology (RSM) is then applied to develop a model based on results of extensive experimentation. Optimization of the model is performed and final modelled equations are provided in terms of calculating the impact of addition of carbon fiber in concrete. Positive implications are devised for the development of concrete in the future involving carbon fiber.
Given that a significant fraction of buildings and architectural heritage in Europe’s historical centers are masonry structures, the selection of proper diagnosis, technological surveys, non-destructive testing, and interpretations of crack and decay patterns is paramount for a risk assessment of possible damage. Identifying the possible crack patterns, discontinuities, and associated brittle failure mechanisms within unreinforced masonry under seismic and gravity actions allows for reliable retrofitting interventions. Traditional and modern materials and strengthening techniques create a wide range of compatible, removable, and sustainable conservation strategies. Steel/timber tie-rods are mainly used to support the horizontal thrust of arches, vaults, and roofs and are particularly suitable for better connecting structural elements, e.g., masonry walls and floors. Composite reinforcing systems using carbon, glass fibers, and thin mortar layers can improve tensile resistance, ultimate strength, and displacement capacity to avoid brittle shear failures. This study overviews masonry structural diagnostics and compares traditional and advanced strengthening techniques of masonry walls, arches, vaults, and columns. Several research results in automatic surface crack detection for unreinforced masonry (URM) walls are presented considering crack detection based on machine learning and deep learning algorithms. In addition, the kinematic and static principles of Limit Analysis within the rigid no-tension model framework are presented. The manuscript sets a practical perspective, providing an inclusive list of papers describing the essential latest research in this field; thus, this paper is useful for researchers and practitioners in masonry structures.
Current standards related to welded joint defects (EN ISO 5817) only consider individual cases (i.e., single defect in a welded joint). The question remains about the behaviour of a welded joint in the simultaneous presence of several different types of defects, so-called multiple defects, which is the topic of this research. The main focus is on defects most commonly encountered in practice, such as linear misalignments, undercuts, incomplete root penetration, and excess weld metal. The welding procedure used in this case was metal active gas welding, a common technique when it comes to welding low-alloy low-carbon steels, including those used for pressure equipment. Different combinations of these defects were deliberately made in welded plates and tested in a standard way on a tensile machine, along with numerical simulations using the finite element method (FEM), based on real geometries. The goal was to predict the behaviour in terms of stress concentrations caused by geometry and affected by multiple defects and material heterogeneity. Numerical and experimental results were in good agreement, but only after some modifications of numerical models. The obtained stress values in the models ranged from noticeably lower than the yield stress of the used materials to slightly higher than it, suggesting that some defect combinations resulted in plastic strain, whereas other models remained in the elastic area. The stress–strain diagram obtained for the first group (misalignment, undercut, and excess root penetration) shows significantly less plasticity. Its yield stress is very close to its ultimate tensile strength, which in turn is noticeably lower compared with the other three groups. This suggests that welded joints with misalignment and incomplete root penetration are indeed the weakest of the four groups either due to the combination of the present defects or perhaps because of an additional unseen internal defect. From the other three diagrams, it can be concluded that the test specimens show very similar behaviour with nearly identical ultimate tensile strengths and considerable plasticity. The diagrams shows the most prominent yielding, with an easily distinguishable difference between the elastic and plastic regions. The diagrams are the most similar, having the same strain of around 9% and with a less obvious yield stress limit.
The realistic determination of damage estimation and building performance depends on target displacements in performance-based earthquake engineering. In this study, target displacements were obtained by performing pushover analysis for a sample reinforced-concrete building model, taking into account 60 different peak ground accelerations for each of the five different stories. Three different target displacements were obtained for damage estimation, such as damage limitation (DL), significant damage (SD), and near collapse (NC), obtained for each peak ground acceleration for five different numbers of stories, respectively. It aims to develop an artificial neural network (ANN)-based sustainable model to predict target displacements under different seismic risks for mid-rise regular reinforced-concrete buildings, which make up a large part of the existing building stock, using all the data obtained. For this purpose, a hybrid structure was established with the particle swarm optimization algorithm (PSO), and the network structure’s hyper parameters were optimized. Three different hybrid models were created in order to predict the target displacements most successfully. It was found that the ANN established with particles with the best position revealed by the hybrid models produced successful results in the calculation of the performance score. The created hybrid models produced 99% successful results in DL estimation, 99% in SD estimation, and 99% in NC estimation in determining target displacements in mid-rise regular reinforced-concrete buildings. The hybrid model also revealed which parameters should be used in ANN for estimating target displacements under different seismic risks.
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