Search

Interfaces in metal matrix composites (MMCs) are crucial in determining the mechanical properties and functionality of MMCs. This article reviews recent scientific advances and issues related to MMC interfaces from four different perspectives: interfacial structural design, interfacial defect control, thermodynamics and kinetics of interfacial reactions, and interfacial microstructure properties‐based numerical simulation. The influence of interfacial microstructural features on interfacial strength–toughness trade‐offs and their functionality is given special attention. The interfacial problem is still one of the main challenges to be solved in the composite system, which is mainly reflected in the following aspects: interfacial microstructure–deformation mechanisms in complex systems, precise control of interfacial defects and interfacial reaction products, and the efficient and cost‐effective application of numerical simulation techniques. The integrated computation and intelligent design (artificial intelligence) of composites through multiscale computational simulation with the guidance of "interface design‐property prediction" will be the key area of MMC interface research in the future. [ABSTRACT FROM AUTHOR]

Numerical analysis of a U-type solid oxide fuel cell stack was performed using computational fluid dynamics to investigate the effects of stack capacities and fuel/air utilization rates on the internal flow uniformity. The results indicated that increasing the fuel/air utilization rate improved the gas flow uniformity within the stack for the same stack capacity. The uniformity in the anode fluid domain was better than that in the cathode fluid domain. Furthermore, the flow uniformity within the stack was associated with the percentage of pressure drop in the core region of the stack. The larger the percentage of pressure drop in the core region, the more uniform the flow inside the stack. Additionally, under a fuel utilization rate of 75%, the computational results exhibited excessively high fuel utilization rates in the top cell of a 3 kWe stack, indicating a potential risk of fuel depletion during actual stack operation. [ABSTRACT FROM AUTHOR]

The importance of recycling engineering components and thus obtaining low‐cost production solutions has become prominent in today's world. In this study, the mechanical and dynamic behaviors of three‐dimensional‐printed recycled polyethylene terephthalate glycol (RePET‐G) beams were investigated numerically and experimentally for the first time in the literature. Initially, the governing equations of the beams were determined according to the Bernoulli–Euler beam theory, and these equations were numerically solved using the differential quadrature method and ANSYS program. Subsequently, to validate the accuracy of the numerical models, the obtained natural frequencies were compared with experimental results. It was observed that the numerical results showed good agreement with the experimental results. Finally, the effects of beam length, infill rate, and building direction on the natural frequencies of RePET‐G beams were investigated. The outcomes showed that as the beam length changed, natural frequencies were significantly affected. Increasing the infill rate, especially for beams with vertical building direction, from 20% to 100% led to a slight decrease in the natural frequency values of the structure. Moreover, it was found that for beams with an infill rate of 100%, the natural frequency values obtained in the horizontal building direction were higher than those obtained in the vertical building direction. Highlights: Printable recycled filaments have great potential for vibration applications.Sample length affects the first natural frequency value of RePETG parts.Differential quadrature and ANSYS methods can be utilized for the vibration.For the 3D‐printed samples, rising infill rate causes a natural frequency drop. [ABSTRACT FROM AUTHOR]

Steel–concrete composite connections play a crucial role in facilitating the transfer of forces between steel and concrete structural elements. The safety of structures during fire incidents has garnered significant global attention. This study focuses on examining the behavior of steel–concrete composite beam–column connections with flush end-plate under both ambient temperature and fire conditions through numerical analysis. Parametric analysis was conducted after adjusting the numerical models. The parameters considered include beam and column profiles (represented as profile sets), negative longitudinal reinforcement ratio, degree of steel–concrete interaction, slab type, moment orientation, concrete strength, and steel strength. At ambient temperature, the primary failure mechanisms include local buckling of the column flange, bolt yielding, plate distortion, reinforcement yielding, excessive slab damage, and local buckling of the beam web near the connection. In fire scenarios, the flush end-plate beam-to-column connection failed due to local buckling and reinforcement yielding. Additionally, during the fire, the failure of bolts connecting the end-plate to the column was observed. Importantly, all variables in the parametric analysis influenced the behavior of the composite connection, both at ambient temperature and during fire scenarios. Furthermore, this study provides practical equations for calculating moment resistance and initial stiffness at ambient temperature, as well as reduced stiffness during a fire and accumulated rotational capacity variation, specifically for steel–concrete composite beam–column connections with a flush end-plate. [ABSTRACT FROM AUTHOR]

To improve the construction performance and seismic resilience of precast reinforced-concrete frame structures, an innovative self-centering precast steel–concrete hybrid frame has been proposed and subjected to cyclic loading tests. In this paper, a comprehensive numerical analysis was conducted to further investigate the frame's hysteretic behavior. Initially, a numerical model was developed using the finite element software OpenSees. Numerical analyses of two frame specimens were conducted, demonstrating good agreement between the numerical and experimental hysteretic characteristics, thus validating the model's accuracy. Subsequently, based on the numerical simulations, a quantitative comparison of hysteretic performance between a novel frame and a traditional reinforced-concrete frame of the same scale was performed. While the proposed frame exhibited slightly lower initial stiffness and energy dissipation capacity than the traditional frame, it outperformed in terms of load-carrying capacity and self-centering ability. Finally, parametric analyses were carried out to assess the influence of various design parameters on the hysteretic performance, including friction force in the web frictions devices, initial post-tensioned force of the prefabricated steel–concrete hybrid beams, the steel arm length, and the column longitudinal reinforcement ratio. The results showed that increases in these four parameters improved the load-carrying capacity and initial stiffness of the proposed frame. Additionally, an increase in the friction force, steel arm length, or column longitudinal reinforcement ratio enhanced the frame's energy dissipation capacity, while an increase in the initial post-tensioned force or a decrease in the friction force enhanced the frame's self-centering capacity. [ABSTRACT FROM AUTHOR]

The construction of major hydropower projects globally is challenged by slope deformation in reservoir areas. The deformation and failure mechanisms of large rock slopes are complex and poorly understood, making prevention and management extremely challenging. In order to explore the influence mechanism of the water level variation on the deformation of steep toppling bedding rock slopes, this paper takes the right bank slope near the dam area of the Longtou Hydropower Station as an example, and field investigations, deformation monitoring, physical simulation tests and numerical analyses are carried out. It is found that the slope deformation response is obvious under the influence of the reservoir water level variation, which is mainly reflected in the change in the slope groundwater level, rock mechanical parameters and seepage field in the slope body. The toe of the slope produces plastic deformation and maximum displacement. With the increase in the reservoir water level, the plastic zone expands and the displacement increases, which leads to the intensification of the slope deformation. This paper puts forward that the deformation and failure modes of the steep and toppling bedding rock slope caused by water level variation are due to shear dislocation, bending deformation and toppling fracture. This study reveals the influence mechanism of the water level variation on the deformation of steep and toppling bedding rock slopes, which can provide theoretical support for the construction of major hydropower projects. [ABSTRACT FROM AUTHOR]

Manufacturing of bent composite tubes with variable cross-section is a challenge. The traditional process in composite materials uses retractable mandrels that in case of inflated or bent tubes cannot be applied. The tubular composite elements are often used in high performance bicycles, in the manufacturing of frames, handlebars, saddle pipe supports, etc. This paper presents research on the design of a Mountain Bike (MTB) riser handlebar made of Fiber Reinforced Polymer (FRP). The handlebar is numerically analyzed to estimate the most suitable stacking sequence of Carbon Fiber Reinforced Polymer (CFRP) layers. Depending on the safety standard of bicycle handlebars, a case of longitudinal bending tests was numerically evaluated. Comparing the weight of the CFRP handlebar with the steel handlebar of the same shape, the mass reduction is 5.2 times. The obtained results indicate a two-fold reduction in the weight of the handlebar if it is compared to a handlebar made of aluminum alloys. The research also presents the manufacturing process of the composite mold, and CFRP tubular element. Prepreg CFRP materials are used to manufacture the handlebar, the employed technology being the vacuum bag forming and autoclave curing process. [ABSTRACT FROM AUTHOR]

The seismic behavior of earth retaining structures continues to remain a critical consideration in engineering design and lessons learned from the full-scale performance of retaining walls during earthquakes are invaluable. The observed performance of several retaining walls in the area affected by the 2014 Cephalonia, Greece, earthquakes is presented. Subsequently, the case of measured kinematic response (i.e. residual seismic movements) of a 6.0 m high concrete gravity-type "retaining wall-backfill" system, which displaced during the earthquake, but remained functional is presented. The recording of a strong motion station—located at a distance of less than 200 m from the wall—was used to describe the horizontal earthquake ground excitation. The inertial response of the "wall-backfill" system was analyzed through a finite element numerical model based on in-situ shear wave velocity measurements and values of mechanical soil properties back-calculated from the measured kinematic response of the system to the particular earthquake. The selection of soil material values of stiffness and strength was based on the results of post-earthquake Vs-depth measurements at the wall site. The measured kinematic response of the "wall-backfill" system was compared to predictions of several published empirical relations. The empirical relations were all found to overpredict the observed displacements and in some cases, significantly. The derived numerical model of the "wall-backfill" system was subsequently used to investigate (a) the magnitude and distribution of seismic earth pressures on the wall as well as the backfill settlements, and (b) the beneficial phase difference developed between the peak values of wall inertia and active earthquake thrust increment during the particular earthquake event. The results of this case history agree well with previously published results concerning the inertial response (seismic earth pressures and phasing issues) for walls retaining cohesionless and cohesive backfills. [ABSTRACT FROM AUTHOR]

Abstract Traditional support structures cannot meet the complex conditions of different excavation depths and areas in underground transportation hubs. On the basis of fully considering the spatial position relationship of foundation pit groups, this article proposes a multilevel retaining system that meets the requirements of multilevel foundation pit excavation. The evolution law of the support structure during the excavation process of the inner pit was explored using on-site monitoring and numerical simulation methods. The results indicate that the excavation of the inner pit reduces the passive earth pressure, and the deformation of the outer support structure can be effectively suppressed by setting a retaining structure or a bottom slab in the bench zone. The excavation of the inner pit causes significant vertical deformation of the support structure adjacent to the foundation pit, while the impact on the structure far away from the foundation pit is relatively small. According to the contact force chain and soil pressure between the two rows of support structure, the soil in this area is divided into a “relaxation zone” and a “compression zone.” The evolution mechanism of earth pressure in the case of mutual-effect failure between two rows of piles is revealed. This paper addresses the deformation properties of multilevel support structures as well as the mechanism of earth pressure evolution between structures.

Low yield point (LYP) structural steels had been developed and used for the seismic energy dissipating, however, the fracture of various LYP steel energy dissipation components may lead to progressive collapse of structures. To address this issue, the fracture behavior of LYP steels under various stress states were comprehensively investigated using experiments, theoretical analysis, and numerical simulations in this work. There are three meaningful contribution points. First, an improved weighted average (WA) method and dichotomy-based optimization are proposed to calibrate true stress–strain relation after necking onset. The maximum deviation for the prediction of full-range tensile load-displacement behavior based on the proposed WA method is less than 3%, which is better than the existing WA methods. Second, a modified ductile fracture model is developed to identify the fracture of LYP steels under various stress states. Comparison results among existing fracture models, the proposed fracture model and tests indicate that the fracture plastic strain can be more reasonably predicted by the proposed ductile fracture model than the existing models. Thirdly, an advanced ductile fracture prediction framework is proposed to simulate the complete tensile behavior of structural steels. Based on the proposed framework and object-oriented programming technique, the complete tensile behavior can be accurately and conveniently predicted by employing the proposed WA model, proposed ductile fracture model and developed user defined material subroutine. The verified WA method and ductile fracture model would contribute to predicting the failure of structural steel members, connections, welds and structures. It is meaningful to prevent casualties and property losses resulting from the subsequent structural progressive collapse. [ABSTRACT FROM AUTHOR]

Traditional support structures cannot meet the complex conditions of different excavation depths and areas in underground transportation hubs. On the basis of fully considering the spatial position relationship of foundation pit groups, this article proposes a multilevel retaining system that meets the requirements of multilevel foundation pit excavation. The evolution law of the support structure during the excavation process of the inner pit was explored using on-site monitoring and numerical simulation methods. The results indicate that the excavation of the inner pit reduces the passive earth pressure, and the deformation of the outer support structure can be effectively suppressed by setting a retaining structure or a bottom slab in the bench zone. The excavation of the inner pit causes significant vertical deformation of the support structure adjacent to the foundation pit, while the impact on the structure far away from the foundation pit is relatively small. According to the contact force chain and soil pressure between the two rows of support structure, the soil in this area is divided into a "relaxation zone" and a "compression zone." The evolution mechanism of earth pressure in the case of mutual-effect failure between two rows of piles is revealed. This paper addresses the deformation properties of multilevel support structures as well as the mechanism of earth pressure evolution between structures. [ABSTRACT FROM AUTHOR]

To investigate flow uniformity within individual unit cells in internal manifold-type solid oxide fuel cell stacks with respect to electrical capacity and stack height variations, numerical analyses using computational fluid dynamics techniques were conducted on SOFC stack models with capacities of 1 kWe, 2 kWe, and 3 kWe. The results of these calculations reveal that while the inlet flow rate increases with an increase in the number of unit cells, the flow rate supplied to each unit cell remains largely consistent, resulting in a nearly uniform pressure drop in the core region. Nonetheless, the flow rate in the pipe and manifold regions increases proportionally to the inlet flow rate for 1 kWe, 2 kWe, and 3 kWe models, leading to a corresponding increase in pressure drop. Furthermore, the patterns of mass flow rate and pressure drop within unit cells are comparable. Particularly, the pressure drop within unit cell channels is primarily influenced by the pressure distributions in the outlet manifold regions. In summary, as the stack height increases, the uniformity of pressure and flow rate distributions among unit cells decreases. This effect is more pronounced in the cathode with a higher flow rate than the anode, and it has implications for achieving uniform flow rates while minimizing flow rates in individual unit cells. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effectiveness of grout and the mechanism of force transfer in socket connections. In doing so, it proposes a new transfer mode called integral transfer mode (ITM), as opposed to the conventional separate transfer mode (STM). The proposed ITM suggests that, in a reinforced concrete socket connection, if there is a strong bond between the column, grouting material, and receiving member, the socket connection will function as an integral structure, deforming together as a whole rather than as separate components. Consequently, the grouting material does not need to provide a significant lateral bearing force, and the interface shear stresses become the key focus in designing a socket connection. To explore this concept, quasi-static tests and numerical analyses using solid elements were conducted on three half-scale specimens with varying grout strengths. The results demonstrated that the performance of specimens with normal-strength grout was comparable to that of the specimen with high-strength grout. And the proposed ITM was better than STM at predicting failure modes, force–displacement relationships, the stress states of reinforcements, and grout stresses. [ABSTRACT FROM AUTHOR]

Microbial induced calcium carbonate precipitation (MICP) offers a sustainable technique to improve geologic properties of soils in engineering structures. The applications encompass improved soil strength, scour mitigation, fracture sealing, and in situ contaminant immobilization. Previous studies have presented fundamental processes and implementation in lab- and field-scale. Most of these studies were examined in saturated conditions despite many MICP applications including those in coastal and riverside areas which will likely take place under unsaturated conditions. The study herein investigated the effect of soil water retention curve (SWRC) parameters and attachment coefficient (Kat) on CaCO3 precipitation in sand. Using numerical analyses, a continuum model was developed in which unsaturated flow and transport were coupled with biological and chemical reactions in variably saturated conditions. Predictive modeling results compare mass percentage of calcium carbonate resulting from MICP at degrees of soil water saturations of 20%, 40%, 80%, and 100% in sandy soil media. The results indicate the bacteria attachment coefficient increases by a factor of 3 as the degree of saturation is decreased from 100% to 20%, as the higher suctions at lower saturation levels improve bacteria fixation. The drying branch of SWRC versus wetting front yields higher CaCO3 for identical MICP treatment. Numerical results show the trend in hydraulic conductivity with increasing cementation level. [ABSTRACT FROM AUTHOR]

Traditional and alternative joining techniques have been used for many years at the connection points of structural bearing systems. Especially, glued doweled and screwed type mechanical connections are widely used in wooden structures and furniture constructions. Although there are many studies related to the strength of dowel and screw joints, limited papers describe the practical use of self-threaded dowels (STDs) in the joints. In this study, thread geometry effect of the STDs in particleboard (PB) was investigated by determining the mounting force and withdrawal strength values. For this purpose, STDs including three different thread width (0,2 - 0,3 - 0,4 mm) and two different thread length (1 - 2 mm) were designed, produced and tested under static compressive and tensile forces. All STDs were produced with polylactic acid (PLA) by using Layer Plastic Deposition (LPD) method in 3D printing technology. Uniaxial compression tests were performed in order to determine the minimum mounting force while the tension tests were performed for determining the maximum withdrawal force required to put the STDs into the hole and pull out them, respectively. Numerical analysis (FEM) were used to analyze the contact pressures and stresses of the STD joints. Abaqus v6.13-1 software was utilized for the numerical analyses. In addition, multiple regression analysis was carried out to predict the mounting force and withdrawal strength of the STDs. Results showed that the predictive expressions developed provided reasonable estimates for mounting force and withdrawal strength of STDs. According to the statistical analyses; thread width, thread length and their interaction have significantly affected both mounting force and withdrawal strength of STDs. At the end of the experimental and numerical tests, STDs with 0,2 mm width and 2 mm length threads gave the lowest mounting force values, stresses and contact forces. However, the highest withdrawal strength values were obtained from the STDs with 0,3 mm width and 1 mm length threads. According to the results of the study, the optimum STD was the one with 0,3 mm thread width and 2 mm thread length. In conclusion, the STDs can be utilized as an alternative fastener to the conventional glued dowel type joints in PB. However, corner joints constructed of different kinds of wood-based composites and connected with the STDs should be investigated in the future studies.

This paper reviews latest developments of substructures for offshore wind turbines focusing on investigations and applications of hybrid foundations. Model tests and numerical analyses were used to simulate the loading of hybrid piles in sand. The results of pile-soil interaction were investigated to confirm the changes in soil stiffness around the hybrid monopile head. The mechanism and factors affecting the change in lateral stiffness of the hybrid foundation were explained by analysing p–y curves for M+H loading conditions in sand. Based on this research, a new shape of p–y curves for hybrid monopiles was established and a method for determining key parameters was proposed. The effectiveness of new p–y curves was verified by comparing back-calculated results with those from numerical simulations. The conducted tests confirmed that the hybrid monopile displacement is 30–50% smaller when compared to a standard monopile with similar dimensions. The gained experiences can be useful for designers and researchers to enhance the design of foundations for offshore wind turbines.

The presence of karst formations significantly impacts the load-bearing capacity of pile foundations in karst geological environments, posing a challenge to their design. This study investigated the bearing characteristics of karst pile foundations using the physical model test and numerical analysis. First, the influence of cave height and span on the bearing capacity of pile foundations is examined using model tests. The results demonstrate that the height of karst caves greatly affects the bearing capacity of karst pile foundations. Subsequently, numerical analysis further explores the bearing characteristics of these foundations. It reveals that as the top load on pile increases, an arch-shaped tensile damage zone forms at the top of karst cave and gradually expands. The rock failure in this area leads to a decrease in adhesion between rock strata and pile foundation, consequently reducing its load-bearing capacity. Finally, experimental results are compared with numerical results to validate consistency and mutual verifiability between physical model tests and numerical analyses. The outcomes of the research provide valuable insights for designing rock-socketed pile foundations in similar karst areas.

Numerical analysis of a U-type solid oxide fuel cell stack was performed using computational fluid dynamics to investigate the effects of stack capacities and fuel/air utilization rates on the internal flow uniformity. The results indicated that increasing the fuel/air utilization rate improved the gas flow uniformity within the stack for the same stack capacity. The uniformity in the anode fluid domain was better than that in the cathode fluid domain. Furthermore, the flow uniformity within the stack was associated with the percentage of pressure drop in the core region of the stack. The larger the percentage of pressure drop in the core region, the more uniform the flow inside the stack. Additionally, under a fuel utilization rate of 75%, the computational results exhibited excessively high fuel utilization rates in the top cell of a 3 kWe stack, indicating a potential risk of fuel depletion during actual stack operation.

To improve the construction performance and seismic resilience of precast reinforced-concrete frame structures, an innovative self-centering precast steel–concrete hybrid frame has been proposed and subjected to cyclic loading tests. In this paper, a comprehensive numerical analysis was conducted to further investigate the frame’s hysteretic behavior. Initially, a numerical model was developed using the finite element software OpenSees. Numerical analyses of two frame specimens were conducted, demonstrating good agreement between the numerical and experimental hysteretic characteristics, thus validating the model’s accuracy. Subsequently, based on the numerical simulations, a quantitative comparison of hysteretic performance between a novel frame and a traditional reinforced-concrete frame of the same scale was performed. While the proposed frame exhibited slightly lower initial stiffness and energy dissipation capacity than the traditional frame, it outperformed in terms of load-carrying capacity and self-centering ability. Finally, parametric analyses were carried out to assess the influence of various design parameters on the hysteretic performance, including friction force in the web frictions devices, initial post-tensioned force of the prefabricated steel–concrete hybrid beams, the steel arm length, and the column longitudinal reinforcement ratio. The results showed that increases in these four parameters improved the load-carrying capacity and initial stiffness of the proposed frame. Additionally, an increase in the friction force, steel arm length, or column longitudinal reinforcement ratio enhanced the frame’s energy dissipation capacity, while an increase in the initial post-tensioned force or a decrease in the friction force enhanced the frame’s self-centering capacity.

This study is based on a finite element analysis of a heat storage material (HSM). Before starting the analysis, heat storage model, heat storage insulation material, heat transfer fluid (HTF) and HSM have been determined. The heat storage model was designed in the CATIA V5 program in accordance with the literature data, and the material of the heat storage vessel was determined as stainless steel (AISI–304) due to its high melting point. Basalt glass, which is a type of basaltic rock, was chosen as the HSM. In this study, the average temperature of basalt glass was around 901.5 K, and heat storage was carried out with basalt glass at this average temperature. Air was chosen as an HTF because it is suitable for storage at the high temperatures. The heat insulation material was determined as ceramic fiber because it is suitable for storing heat at high temperatures. After all, the heat storage components were designed and determined in the CATIA V5 program, and the Ansys software was used for the analysis. After the analysis was performed for 6000 s in Ansys Fluent, it was observed that approximately 13.57 kWh heat was stored. In this study, we observed that basalt glass can be used as an alternative material for HSM at high temperatures for concentrated solar power technologies. The obtained results were comparatively evaluated with the previous studies, and it was concluded that the system was compatible and applicable. [ABSTRACT FROM AUTHOR]

Traditional and alternative joining techniques have been used for many years at the connection points of structural bearing systems. Especially, glued doweled and screwed type mechanical connections are widely used in wooden structures and furniture constructions. Although there are many studies related to the strength of dowel and screw joints, limited papers describe the practical use of self-threaded dowels (STDs) in the joints. In this study, thread geometry effect of the STDs in particleboard (PB) was investigated by determining the mounting force and withdrawal strength values. For this purpose, STDs including three different thread width (0,2 - 0,3 - 0,4 mm) and two different thread length (1 - 2 mm) were designed, produced and tested under static compressive and tensile forces. All STDs were produced with polylactic acid (PLA) by using Layer Plastic Deposition (LPD) method in 3D printing technology. Uniaxial compression tests were performed in order to determine the minimum mounting force while the tension tests were performed for determining the maximum withdrawal force required to put the STDs into the hole and pull out them, respectively. Numerical analysis (FEM) were used to analyze the contact pressures and stresses of the STD joints. Abaqus v6.13-1 software was utilized for the numerical analyses. In addition, multiple regression analysis was carried out to predict the mounting force and withdrawal strength of the STDs. Results showed that the predictive expressions developed provided reasonable estimates for mounting force and withdrawal strength of STDs. According to the statistical analyses; thread width, thread length and their interaction have significantly affected both mounting force and withdrawal strength of STDs. At the end of the experimental and numerical tests, STDs with 0,2 mm width and 2 mm length threads gave the lowest mounting force values, stresses and contact forces. However, the highest withdrawal strength values were obtained from the STDs with 0,3 mm width and 1 mm length threads. According to the results of the study, the optimum STD was the one with 0,3 mm thread width and 2 mm thread length. In conclusion, the STDs can be utilized as an alternative fastener to the conventional glued dowel type joints in PB. However, corner joints constructed of different kinds of wood-based composites and connected with the STDs should be investigated in the future studies. [ABSTRACT FROM AUTHOR]

This paper reviews latest developments of substructures for offshore wind turbines focusing on investigations and applications of hybrid foundations. Model tests and numerical analyses were used to simulate the loading of hybrid piles in sand. The results of pile-soil interaction were investigated to confirm the changes in soil stiffness around the hybrid monopile head. The mechanism and factors affecting the change in lateral stiffness of the hybrid foundation were explained by analysing p-y curves for M+H loading conditions in sand. Based on this research, a new shape of p-y curves for hybrid monopiles was established and a method for determining key parameters was proposed. The effectiveness of new p-y curves was verified by comparing back-calculated results with those from numerical simulations. The conducted tests confirmed that the hybrid monopile displacement is 30-50% smaller when compared to a standard monopile with similar dimensions. The gained experiences can be useful for designers and researchers to enhance the design of foundations for offshore wind turbines. [ABSTRACT FROM AUTHOR]

Abstract Slabs with cast-in-place steel formwork are composite structural elements composed of concrete and steel. The horizontal shear failure mode is the most common in composite slabs based on numerous experimental studies. This failure mode consists of loss of adherence and mechanical contact at the interface of the composite system and often occurs before the system reaches its full bending capacity. Thus, the design of this constructive system is determined by the value of the longitudinal shear strength, which can be computed by the semi-empirical so-called traditional m-k method based on the four-point bending test proposed by several standards. One of the most known factors to influence the longitudinal shear strength is the geometry of embossments present in the steel work. Calibrated computational simulation using the finite element method can be an alternative way to simulate this type of test. The present work modified and adapted a methodology explicitly including the geometry of embossments in the analysis in order to use materials and products with characteristics available to structural engineers in Brazil and used this methodology to derive m-k coefficients. This is being made with the objective of numerically simulating the effect of relevant parameters for determining the longitudinal shear strength at the concrete-steel interface of composite slabs. Force versus slip, force versus displacement graphs were obtained and the m-k coefficient values found were compared with those of other authors in the literature. The simulations presented values consistent with the literature and in relation to the rupture mode by longitudinal shear, the numerical simulations performed presented ultimate strengths with goodness-of-fit measured by the conventional coefficient of determination, reaching a good value for the semi-empirical relation using the results of the finite element data.

This paper presents the lateral pile-soil response occurring in coral and silica sand foundations through comparative numerical studies. In this study, the Hypoplastic constitutive model was implemented into Abaqus software to simulate the stress–strain relationship of coral sand and silica sand with the same particle gradation. The validation of numerical model was verified by centrifuge test results. Afterward, forty-eight numerical analyses were employed to assess the influence of pile diameter, embedment length, loading eccentricity, and relative density on the lateral response of piles in two kinds of sands. The load–displacement response, pile deflection, bending moment, and p-y curves were compared and analyzed in detail. The results showed that, with the increase in displacement level and relative density, the load responses of piles in coral sand gradually became greater than that in silica sand, the p-y curves in coral sand were also significantly higher than that in silica sand, and the bending moment and deflection profile of pile in silica sand were larger than that in coral sand. The difference in pile response between the two kinds of sands became more significant as the density and load level increased. Finally, a multi-parameter modified p-y model for coral sand was proposed, and its applicability and rationality were validated. [ABSTRACT FROM AUTHOR]

Microbial induced calcium carbonate precipitation (MICP) offers a robust technique to improve strength and stiffness properties of subsurface soils supporting infrastructures. Several unknown factors, including the MICP reactive transport parameters, however, limit the ability to predict spatial distribution of calcium carbonate (CaCO3) precipitation within a subsurface area and with depth. As it was shown that calcium carbonate distribution is highly affected by biomass profiles in subdomains, five bacteria attachment models (constant-rate, power-law, exponential, gamma distribution, and " cstr based on colloid attachment theory") were calibrated here using data from both small- and large-scale testing programs. Out of the five models, colloid attachment theory with modified velocity and straining terms was shown to be the most promising approach in yielding the most fitted CaCO3 distribution compared with the experimental data. A new parameter, cstr , was incorporated to modify straining and the constraint peak value of biomass attachment due to straining at distances larger than a 0.14×sample size. Using the results from the numerical simulations, relationships were developed for velocity and straining coefficients of "the cstr based on colloid attachment theory" (hereafter "colloid attachment cstr ") as a function of bacteria size, soil particle size, sample size, volume of injected bacteria, and soil pore volume. [ABSTRACT FROM AUTHOR]

Geotechnical Seismic Isolation (GSI) is an innovative technique for protecting structures in earthquake-prone areas. The main idea is to improve the foundation soil so that seismic energy is partially dissipated within GSI before being transmitted to the structure. Among other materials proposed for foundation soil improvement, gravel-rubber mixtures (GRMs), with rubber grains manufactured from end-of-life tires, have attracted significant research interest thanks to their good mechanical properties. GRMs also represent a modern recycling system to reduce the stockpile of scrap tires worldwide. The present study investigated numerically the effect of a GRM layer located underneath the shallow foundations of a real structure. The structure is a typical reinforced concrete building in southern Italy. A Finite Element Modelling (FEM) was carried out to evaluate the overall static and dynamic behaviour of the soil-GRMs-structure system. Three FEM models were performed with and without the GRM layer, varying the GRM layer thickness and the seismic inputs. The comparisons among the models allow us to assess the performance of the GRM underneath the foundations as a new eco-sustainable solution for the seismic isolation of structures. [ABSTRACT FROM AUTHOR]

In this paper, we propose an efficient numerical method for the two-dimensional (2D) linearly elastic clamped plate model. Specifically, we choose the linear Lagrange element to discretize the first two components in the vector displacement space, as well as the Morley element to discretize the third component. Moreover, the existence of discrete solution, uniqueness and a-priori error estimate is analysed. Finally, numerical experiments are presented to verify theoretical results. [ABSTRACT FROM AUTHOR]

With the increasing popularity of wearable devices, typically employed in fitness and health monitoring, there is an evident need to extend their autonomy and replace the conventional power sources with environmentally friendly alternatives. Piezoelectric energy harvesting systems, optimized for collecting kinetic energy from random human motion and transduce it into electrical energy, represent a viable option for powering autonomous wearables. Since established analytical methods are unable to model the behaviour of piezoelectric harvesters with complex optimized geometries, suitable numerical models need to be employed for their design. This implies the need of a thorough study focused on the mechanical engineering design optimization purposes of how the finite element type and mesh density affect the uncoupled modal and coupled transient responses of a new class of optimised design configurations of the studied devices. [ABSTRACT FROM AUTHOR]

The paper focuses on the detailed analysis of the dynamic characterisation of polyurethane to evaluate the effects of polyurethane injections into soil with the aim of geotechnical seismic isolation. To determine the dynamic properties, resonant column (RC) tests were performed at the University Kore of Enna (Italy) on specimens of pure polyurethane with different values of density and subjected to different mean confining pressures. The results obtained by means of RC tests, in terms of shear modulus G and the damping ratio D as a function of shear strain γc, allowed to develop an analytical formulation for G-γc and D-γc curves, taking into account the linear relationship with density, of both the maximum value of shear modulus Gmax and the minimum value of damping ratio Dmin. The analytical formulation derived from the experimental results is applied for ground response seismic analyses of cohesive soils injected with polyurethane, using a finite element code. The numerical results show that the polyurethane injections reduce the value of maximum acceleration on the ground surface and the reduction varies with the thickness of the soil modified by polyurethane injections. [ABSTRACT FROM AUTHOR]

Vibrations are an issue of increasing importance in current footbridge design practice. More sophisticated footbridges with increasing spans and more effective construction materials result in lightweight structures and a high ratio of live load to dead load. As a result of this trend, many footbridges have become more susceptible to vibrations when subjected to dynamic loads. The most common dynamic loads on footbridges, other than wind loading, are pedestrian-induced footfall forces due to the movement of people. This paper concerns the experimental and numerical dynamic characterization of a newly built steel and wooden cable-stayed footbridge. The footbridge was dynamically tested in situ under ambient vibration, and the results allowed the real dynamic behavior of the footbridge to be captured. The dynamic response under pedestrian dynamic loads was also investigated and compared with the limitations provided by the main international codes and guidelines for footbridge serviceability assessment. A numerical model of the footbridge was also developed and updated based on the experimental outcomes. Then, the calibrated model was used to numerically assess the footbridge's serviceability following the guideline prescriptions for pedestrian load simulation, and the design accuracy was also validated. This paper aims to increase the state-of-the-art knowledge about footbridge dynamic testing so as to support the design of new and futuristic structures as well as prove the effectiveness of using the requirements of codes and guidelines for footbridge serviceability assessment by adopting a calibrated numerical model. [ABSTRACT FROM AUTHOR]

Laser cladding is a directed energy deposition process and can lead to high residual stresses, which can compromise the quality of the specimen. As a result, it is crucial to accurately predict and investigate the residual stress distribution in cladded parts and understand the formation mechanisms. In this study, a thermo-mechanical metallurgical simulation model of the laser cladding process was developed for three different deposition sequences for a thin wall hexagon with inner junctions to investigate the formation of residual stress and distortion. The study was performed for single and multilayer scenarios. Two types of computational techniques, the detailed transient approach and the imposed thermal cycle approach, were performed and comparisons conducted. Consistent results were observed when comparing the resultant stress patterns for the single layer; subsequently, the imposed thermal cycle method was applied for the five-layer models. A preheat scenario is explored. This reduced the computational cost significantly, but the stress patterns were not similar. This indicates that building up worn regions at the top of a thin-walled component, such as a roll die, needs to be investigated further as unique issues have been highlighted. The differences between the implemented computational techniques are described as well as the advantages and disadvantages of each. Knowledge obtained from these case studies provides a foundation for efficient and rapid optimization of laser cladding processes, with the aim of minimizing residual stress in both simple and complex laser cladding structures. [ABSTRACT FROM AUTHOR]

A building can be subject to multiple accidental loads during its service life. Partially precast concrete (PC) beams are primary force-bearing members. When subjected to an impact load, their impact resistance considerably affects the overall safety of the structure. In this study, we performed numerical analyses of the dynamic response of PC beams subjected to impact loading. The related parameters, including the element type, material model, contact type, and hourglass control, were discussed in detail. The simulation and test results were compared. The model's validity is verified from four aspects: energy conversion, failure form, impact-force time history curve, and midspan-displacement time history curve. Based on these findings, the effects of the concrete strength, longitudinal reinforcement ratio, and stirrup ratio on the impact resistance of the components were evaluated. Furthermore, the differences in the equivalent plastic strain cloud diagram, impact-force time history curve, and midspan-displacement time history curve under different parameters were compared. The results show that an increase in the strength of the post-pouring concrete can reduce local damage to PC beams, and improving the overall strength of concrete can reduce overall damage of PC beams. In addition, an increase in the longitudinal reinforcement ratio can ease the failure of the normal cross-section of PC beams, and an increase in the stirrup ratio can effectively inhibit the generation and development of oblique cracks. Then, by fitting the parameters, we established simplified formulas for calculating the peak and residual values of the midspan displacement. According to the formulas, when the external impact mass and height are known, the component's damage degree can then be predicted, which provides a basis for the design of fabricated structures. [ABSTRACT FROM AUTHOR]

Insulating glasses (IGs) are composed by glass plates entrapping a cavity filled with a gas sealed by perimeter spacers. This composition pretends to guarantee higher energy efficiency and airborne sound insulation in buildings. The structural performances achieved by these IGs is not normally considered in detail. In fact, in codes there is no specific mechanical model for structural IGs under different loadings and boundary conditions, namely to estimate the vertical deflections when applied horizontally. For this, here a specific model, by combining some existing approaches, was proposed for two or four side supported IG under distributed/linear loadings. The main goal is to quantify if an IG follows a monolith or layered behaviour. Several analytical and numerical analyses using a finite element method (FEM) have been carried out. Then, the results have been validated against experimental laboratory measurements. Two specific IGs with different sizes have been used as case studies. Results show that FEM analyses of IGs are in close agreement with experimental measurements, whereas analytical code models are not as accurate as the numerical approach, in particular for two side supported IGs under linear loadings. Also, the effects of the gas and the interactions between superior and bottom glasses for a large IG are more relevant than for a small IG.

Recently, the soil-vegetation-atmosphere (SVA) interaction is becoming a topic of intense scientific research within the geotechnical community, because it was recognized to potentially induce significant pore pressure variations in slopes, at both shallow and larger depths, being then responsible for weather-induced landsliding. The processes within such interaction are of different nature, and result in a chemo-thermo-hydro-mechanical transient boundary condition at the ground level, causing exchanges of liquid, gas and energy within the soil cover layer (from ground level to 3-4 metres depths). Hence, both the soil cover material and its thermo-hydro-mechanical constitutive properties, as well as the vegetation properties, become of key relevance within such processes. In this study, with reference to a full scale in-situ test where deep-rooted crop spices were seeded and farmed, the hydraulic properties of rooted clayey soil were investigated in the laboratory as well as in-situ in terms of both saturated permeability and retention properties. As for the saturated permeability, both laboratory and in-situ tests were conducted, the latter being also back-analysed. The retention states of the material were investigated by means of the filter paper technique in the laboratory and were of use for the numerical back-analyses of the Guelph-induced wetting process in the soil cover. The measurements show that roots within the vegetated zone determine both an increase of the permeability and a reduction of the retention properties of the composite material if compared to the soil in bare conditions.

A building may be subjected to a variety of accidental loads during its service life. Partially precast concrete (PC) beams are a primary structural component. Their impact resistance can have a substantial impact on the overall safety of a structure when it is subjected to an impact load. In this study, numerical analyses were performed on the dynamic response of PC beams strengthened with bonded steel plates subjected to impact loading. The model was verified from four aspects: energy conversion, failure form, impact force–time history curve, and midspan displacement–time history curve. The dynamic response eigenvalues of the peak impact force, peak midspan displacement, and residual midspan displacement were compared between the numerical simulations and experimental tests. The relative inaccuracy of the peak impact force ranged from 9.51% to 14.0%, with an average value of 11.9%. The average relative error for the midspan displacement was −0.09%, with the greatest relative errors varying between −0.64% and 0.3%. The residual value errors of the midspan displacement ranged from −0.95% to 2.38%, with an average relative error of 0.94%. On this basis, the effects of the impact mass, impact height, width, and length of the bonded steel plate on the impact resistance of the components were evaluated. Furthermore, the differences in the equivalent plastic strain contours, impact force–time history curves, and midspan displacement–time history curves under different parameters were compared. The results demonstrated that the failure modes and flexural deformations of the test beams were influenced by the impact mass and impact height. The increase in the length and width of the steel plate had no effect on the impact force response, but the peak and residual values of the midspan displacement decreased, which could significantly increase the impact resistance of the beams. Lastly, the impact mass m, the impact height h, the thickness t of the bonded steel plate, the length of the bonded steel plate hs, and the width of the bonded steel plate bs were all taken into account in the fitting formula. These five parameters were used to predict the peak impact force response, the peak value of the midspan displacement, and the residual value of the midspan displacement. The results demonstrated that the fitting formula had small errors and could accurately reflect the dynamic responses of the PC beams strengthened with bonded steel plates under impact loading. [ABSTRACT FROM AUTHOR]

Owing to the new rules of the German National Annex to EN 1998‐1, the relevance of the seismic action has increased, materialising in extended seismic areas and higher spectral accelerations. This may lead to seismic loading being decisive on the design of steel and composite frames. However, the demand is lower in Germany than in other seismic areas. Consequently, these challenges are addressed in an ongoing German national research project, by developing joints with dissipative connections, classified as semi‐rigid and partial‐strength, for steel and composite frames that could allow for the use of behaviour factors in the range of 1.5 to 3. The development started with typical connections from the German catalogue, designed to withstand static loads in the elastic range, followed by performance and detailing improvements. Developments (e.g., increase in sagging/hogging bending: 125 %/18 % of steel joints and 70 %/40 % of partially composite joints) resulted from pre‐test finite element analyses (FEA) on joints and frame models. Improvements to joint detailing were made according to the provisions of the newest draft of Eurocode 8. The optimised joints were integrated in frame specimens, which are currently being tested under monotonic and cyclic loads at RWTH‐Aachen University. This article introduces the developed joint solutions, describes the experimental and numerical programs and presents the monotonic response of frame specimens based on the results of FEA, as well as the main conclusions. [ABSTRACT FROM AUTHOR]

Several constitutive models had been developed by other researchers to cover the main features of mechanical behaviour of natural overconsolidated clays, such as the nonlinear stress–strain response at small and large strains, and the recent stress history effect. Kinematic hardening models include these features to facilitate realistic predictions of soil–structure interaction. This paper presents the further development of a kinematic hardening model BRICK that includes anisotropy and the influence of soil structure on the mechanical behaviour of a natural clay. High quality laboratory tests were used to calibrate the input parameters of the model in a single element configuration, and a documented boundary value problem of tunnel excavation was used to validate the model in finite element calculations. A comprehensive comparative study between the predictions of different kinematic hardening models, using two different software packages, was carried out. It was observed that the SA_BRICK model is in fair agreement with the observed data and gives improved predictions in comparison to other kinematic hardening models, particularly in terms of narrowness of the settlement trough above the tunnel. Advanced predictions of ground deformations caused by tunnel excavations can be effectively used to mitigate possible damage of existing structures affected by tunnelling in an urban environment. [ABSTRACT FROM AUTHOR]