Increase In Load-bearing Capacity Research Articles

Study of the tensile mechanical properties and failure mechanisms of CFRP screwed joints

Removable joint technology is commonly used in composite laminates for various load-bearing structures. However, existing research primarily focuses on bolted joints, there is relatively limited research on screwed joints in composite materials. This study investigates the influence of connected layer thickness and hole diameter on the tensile behavior of threaded joints in carbon fiber-reinforced polymer (CFRP) laminates. After fabricating different CFRP screwed joint specimens, tensile tests were conducted. The digital image correlation (DIC) technique captured the deformation process. The experiment results indicate a significant increase in load-bearing capacity with the increase in diameter. For instance, joints with an 8 mm diameter exhibited a load-bearing capacity of 10.82 kN. The increase in the connected layer thickness correspondingly enhanced the load-bearing capacity of the joint. The joint with a thickness of 7 mm had the highest load-bearing capacity of 8.83 kN. Besides, with the increase in the thickness of the connected layer, the failure mode transitioned from shear failure in the connected layer to screw pull-out. The tilt angle of the screw during the pull-out process also decreases with the increase in the connected layer thickness. Strain and out-of-plane displacement measurements under ultimate load conditions verify these observations.

I-section steel columns strengthened by wire arc additive manufacturing - concept and experiments

Wire arc additive manufacturing (WAAM) is a method of metal 3D printing which, when strategically combined with traditional methods of manufacture, has the potential to make a significant impact on the construction sector. To illustrate this potential, an experimental investigation into the flexural buckling response of 15 hot-rolled I-section columns, strengthened by WAAM, has been undertaken and is presented herein. The WAAM material was added at the flange tips and distributed non-uniformly along the member length. Complementary tensile coupon tests on the I-section and WAAM steel material were also carried out. 3D laser scanning was employed to determine the geometry and global geometric imperfections of all specimens, while digital image correlation measurements were taken to provide a detailed insight into the surface deformation characteristics of the specimens during testing. The WAAM stiffeners provided three mechanisms of strengthening: (1) increased cross-sectional area and second moment of area, (2) enhanced local buckling capacity and (3) a more favourable residual stress pattern. Disproportionately high increases in axial capacity of between 17% and 54% for relatively modest increases of mass between 2% and 26% (of the weight of the strengthened I-section column) were achieved, demonstrating, for the first time, the substantial benefits in terms of enhanced structural efficiency and material savings, that can be realised by the combination of WAAM with traditional manufacturing methods. In the best case, the efficiency of the WAAM material (in terms of increase in load-bearing capacity per unit mass) was almost eight times that of the bare steel section. The described hybrid manufacturing concept can be employed to improve the performance and reduce the environmental impact of structures and could be a game changer in both new construction and the rehabilitation of existing infrastructure.

Multi-objective optimization of multifunctional composite laminates for improved microwave absorbing and load bearing capacity

The thin structure that possesses both excellent stealth and load-bearing capabilities has a high demand in the military. This article proposes a multifunctional composite laminates, along with its optimization strategy. The novel structure comprises several layers of Glass Fiber Reinforced Plastics and each layer has a fixed thickness. The matrix of each layer is made of polymer dispersed with graphene oxide of varying volume fractions, which facilitates the transmission, absorption, and reflection of microwave. The multi-objective optimization strategy of composite laminates is conducted by considering the ply orientation and volume fraction of graphene oxide as design variables, and the bending stiffness and microwave absorbing bandwidth of the overall structure as design objectives, meanwhile the JAYA, a metaheuristic algorithm is employed as the optimizer. The results demonstrate that the optimization algorithm can efficiently adjust the structure to an optimal state. Furthermore, compared with the original structure, the optimized structure has a 190% increase in load-bearing capacity and a 30.3% increase in microwave absorbing performance. This method can be used for rapid design of aircraft stealth skins.

ELASTIC-PLASTIC DEFORMATION OF STEEL-CONCRETE BEAMS WITH LOCAL CRUMPLING DURING THREE-POINT BENDING

The study presents the results of experimental modeling of elastoplastic deformation of bent massive concrete filled steel tube beams under three-point bending. It has been shown that local deformations and local crushing in such structures have a significant impact on their behavior. The applicability of the theory of bending of a hollow steel beam according to the Bernoulli model is analyzed. A comparison has been made of the bearing capacity and stress-strain state of hollow steel tubes (according to the Bernoulli model and the results of experiments) and concrete filled steel tube beams, and the contribution of the concrete core to the bending resistance during elastoplastic deformation has been quantitatively assessed. The actual load-bearing capacity of a hollow pipe during three-point bending does not exceed 50% of the calculated theoretically determined one, which indicates the impossibility of using the classical bending model when designing systems of this kind. In this case, the concrete filled steel tube beam not only ensures the full functioning of the metal during the deformation process, preventing its disruption, but also provides some increase in load-bearing capacity due to the inclusion of a compressed zone in the concrete work. The increase in the load-bearing capacity of a beam due to the introduction of a concrete core can reach 70%. Despite their significant weight, bendable tube-concrete rods can be recommended in conditions of a complex stress-strain state, in which, in addition to transverse bending loads, significant longitudinal forces arise, as well as local force factors that contribute to the occurrence of local crushing deformations, since, unlike a thin-walled hollow tube, concrete the core significantly prevents these effects. Based on the results of the study, the potential effectiveness of flexible tube-concrete elements for a number of structures was proven.

Improvement of the calculation of ice crossings

Background: In winter, ice crossings open in the north of the Far Eastern region. In most cases, they are organized due to the lack of capital bridges. Ice crossings are used to deliver goods and passengers to remote settlements where the road network is poorly developed and the navigation period is limited, because to get to settlements it is necessary to cross reservoirs. Ice crossings remain the only way to connect such settlements with cities with a large population. The most reliable way to increase the load-bearing capacity is to freeze the floating bridge of the articulated circuit into the ice cover. The advantage of such crossings is low sensitivity to climatic conditions and the nature of the water flow, small rolls and sediment. Currently, these crossings are used at cross-border crossings of the Far East, but there are no calculation methods.
 Aim: Development of a methodology that would improve the calculation of ice crossings, taking into account the reinforcement in the form of metal pontoon structures consisting of articulated ferries on two supports.
 Materials and Methods: The article provides a calculation model. Design scheme: a metal structure frozen in ice lying on water is a rigid stamp on a plate lying on the elastic base of the crossing. To confirm the accepted calculation model, an experiment of a real crossing in the form of static tests was carried out.
 Results: The article presents the results of determining the crossing deflections according to the accepted calculation model and after the experiment. The carrying capacity of the reinforced ferry was also calculated by months.
 Conclusion: This study will help to carry out calculations of combined crossings for a significant increase in load-bearing capacity.

Seismic behavior and restoring force model of precast beam-column connections with locally reactive powder concrete

In this study, an innovative approach to enhance the seismic performance of prefabricated concrete frame beam-column joints, incorporating high-strength steel bars and reactive powder concrete (RPC), was developed. The research involved the construction of four prefabricated joints and one cast-in-place node, subjecting them to low-cycle reverse load tests. The findings indicate that the inclusion of high-strength steel bars in the node core area led to a notable increase in load-bearing capacity, ranging from 9.5 % to 9.7 %. Moreover, when RPC and high-strength steel bars were simultaneously used in the node core area, the load-bearing capacity improved even further, with an increase of 19.1 %–20.8 %. Additionally, RPC was found to enhance crack resistance in columns and beams, reducing the severity of node failures. Comparing specimens with different spacing of hoops in the core area, it was observed that RPC not only ensured the seismic performance of the nodes but also addressed the issue of excessive hoop density in the core area. Through experimental data, a restoring force model for prefabricated RPC/RC composite frame beam-column joints was established using theoretical analysis. This model exhibited strong agreement with experimental results and effectively depicted the stress distribution within the proposed joints at various stages.

Experimental study on the flexural behavior of bonded prestressed concrete beams strengthened with CFRP sheets

This paper presents an experimental study on the flexural behavior of bonded prestressed concrete (PC) beams strenthening using CFRP sheet. Two (PC) beams were fabricated, with overall dimensions of 150 × 200 × 2700 mm. One specimen served as an unstrengthened control, while the other was strengthened using CFRP sheets to enhance flexural performance. The specimens were simply supported and subjected to a four-point bending test until failure, allowing assessment of their flexural behavior. The results show that the CFRP-strengthened PC beams exhibited a 24% increase in load-bearing capacity compared to the control specimen. The stiffness of the strengthened beams was also significantly enhanced, leading to a reduction in deflection. Based on the obtained results, it is evident that the application of CFRP sheets for strengthening PC beams is a viable solution.

Characterization of differential distribution patterns between mitofusin isoforms and their interaction in developing skeletal muscles of rat.

Skeletal muscle during postnatal development undergoes several structural and biochemical modifications. It is proposed that these changes are closely intertwined with the increase in load-bearing capacity of the muscle (i.e., myofibrils) and molecular machinery to support the energy demand (i.e., mitochondria). Concomitant establishment of the sarcoplasmic reticulum (SR) and mitochondrial network seems to be a major developmental adjustment of skeletal muscle leading to adult phenotype. Here, we have studied oxidativeness, vascularization, and the changes in mitofusins (Mfn) 1-Mfn 2 expression and interaction in the due course of muscle development. Towardthis, we used a series of histochemical techniques to compare neonatal and adult limb muscles (Gastrocnemius and Quadriceps) of Wistar rat (Rattus norvegicus). Additionally, we probed the proximity between Mfn 1 and Mfn 2 using a highly sensitive antibody-based proximity ligation assay indicating the change in mitochondrial fusion pattern or mitochondria-SR interaction. The results show that neonatal fibers bear a uniform distribution of mitochondria while a differential pattern of distribution is seen in adults. The distribution of the blood vessels is also quite distinct in adult muscles with a well-formed capillary network but in neonates, only central blood vessels are seen. Interestingly, our Mfn 1-Mfn 2 interaction data show that this interaction is uniformly distributed throughout the neonatal fibers, while it becomes peripherally localized in fibers of adult muscles. This peripheralization of Mfn 1-Mfn 2 interaction must be an important event of muscle development and might be critical to cater to the metabolic needs of adult muscle.

Tooth root stress reduction of plastic gears with biological inspired shape optimization

The geometry of plastic gears used today is usually based on conventional steel gears, which are bound to the restrictions of the machining production of gears. The injection molding process provides more design freedom. This paper presents an approach to reduce the tooth root stress of plastic gears using a biologically inspired shape optimization method called CAO (Computer-Aided Optimization). CAO imitates the biological growth behavior from nature, such as bones or trees, which adapt to the load. It strengthens more heavily loaded areas of the surface and weakens less heavily loaded areas, resulting in an increase in load-bearing capacity. The simulation method is based on finite element analysis and considers the complex material behavior of short fiber reinforced plastics as well as the inhomogeneous fiber orientation. Object of the study are polymer gears made of polyamide 46 with and without short fiber reinforcement. By using the method presented here, it is possible to reduce the tooth root stress by up to 24% compared to a trochoidal tooth root with maximum rounding.

Performance of Novel U-Connector in CFS Truss-to-Column Bolted Connection under Axial Force

This paper presents an experimental and numerical investigation of the tensile and compressive behaviour of a novel U-connector in the cold-formed steel (CFS) truss-to-column connection. Tensile tests were performed on 12 specimens representing the tension chords of the trusses in the connection. The results were used to validate a finite element model. The validated model was then subjected to both compressive and tensile loads, which revealed low stiffness in both the compressive and tensile components of the proposed connection. An optimisation of the geometry by using one long nut instead of two nuts was carried out to improve the behaviour and stiffness of the connection. The optimised results were compared with both experimental and numerical data, and conclusions were drawn regarding the effectiveness of the components in the proposed connection. The use of long-nut optimisation in the tension and compression components of the proposed connection shows a significant increase in load-bearing capacity, which makes it very promising for future applications in CFS truss-to-column connections. However, further validation through experimental testing is required to confirm the effectiveness and reliability of the connection in full-scale structures.

Experimental study on using steel wires via the NSM method to improve the behaviour of masonry panels

The use of masonry materials in load-bearing walls has a history of centuries. Many efforts have been made to overcome their poor structural strength; one such solution is the near-surface mounted method. In the present study, steel wires 2.5 mm in diameter were used as reinforcement in the near-surface mounted method to strengthen masonry walls. Compared to rival materials, steel wires enjoy such advantages as small dimensions, eliminating buckling damage, lower cost, and ease of installation. The objective of the study was to determine the feasibility of using wires in the near-surface mounted method and to identify the best wire arrangement. For the purposes of, eight masonry wall panels of 920 × 920 × 100 mm were constructed to investigate the effects of different steel wire arrangements on such panel properties as strength, load-bearing capacity, and wall pseudo-ductility. The results showed that steel wires placed along the wall in the diagonal direction had the best effects on improving the performance of the masonry wall panels. Experimental results confirmed the desirable effects of the steel wire in the near-surface mounted method. This is evidenced by a 21-fold increase in Load-bearing capacity, a 52-fold increase in energy dissipation, and a 17-time rise in shear modulus as a result of using the wires. The near-surface mounted method is an appropriate method to reduce damage to residential masonry buildings and to safeguard historical and cultural heritage monuments.

Fibre-Reinforced Polymers and Steel for the Reinforcement of Wooden Elements-Experimental and Numerical Analysis.

These elements are innovative and of interest to many researchers for the reinforcement of wooden elements. For the reinforced beam elements, the effect of the reinforcement factor, FRP and steel elastic modulus or FRP and steel arrangement of the reinforcement on the performance of the flexural elements was determined, followed by reading the load-displacement diagram of the reinforced beam elements. The finite element model was then developed and verified with the experimental results, which was mainly related to the fact that the general theory took into account the typical tensile failure mode, which can be used to predict the flexural strength of reinforced timber beams. From the tests, it was determined that reinforced timber beam elements had relatively ductile flexural strengths up to brittle tension for unreinforced elements. As for the reinforcements of FRP, the highest increase in load-bearing capacity was for carbon mats at 52.47%, with a reinforcement grade of 0.43%, while the lowest was for glass mats at 16.62% with a reinforcement grade of 0.22%. Basalt bars achieved the highest stiffness, followed by glass mats. Taking into account all the reinforcements used, the highest stiffness was demonstrated by the tests of the effectiveness of the reinforcement using 3 mm thick steel plates. For this configuration with a reinforcement percentage of 10%, this increase in load capacity was 79.48% and stiffness was 31.08%. The difference between the experimental and numerical results was within 3.62-27.36%, respectively.

Analytical Solutions for Radial Consolidation of Soft Ground Improved by Composite Piles Considering Time and Depth-Dependent Well Resistance

Composed of a stiffer core with gravel shell, composite pile is a new pile technology with a variety of shapes and sizes to improve soft soils. Compared with piles with single materials, composite ground improved by composite piles avoids some drawbacks with slow consolidation and limited increase in load bearing capacity. After converting unit cells with noncircular composite piles into cylindrical ones using an annular conversion method, based on an equal strain assumption and the hypothesis that water volumes flowing into and out of the gravel shell are equal, an analytical model is proposed to investigate consolidation characteristics of soft ground improved by composite piles. Furthermore, the hypothesis that the discharge capacity of the composite pile is exponentially decreased with time owing to clogging, and linearly varied with depth is employed in the derivation. In addition, detailed solutions subjected to an instantly applied load are obtained using a Bessel function, and the degeneration of this answer is calculated to verify its accuracy. Then, some comparisons between this method and previous studies including mathematical methods and a case are made to verify the feasibility and applicability of the presented solution. Finally, a parametric study is conducted to find detailed effects of time-dependent clogging and depth-dependent well resistance on consolidation. The results show that consolidation rate is proportional to B1, while it is negatively correlated with B2, α3, and H.

Innovative FRP-Reinforced Self-Bearing Arches

The architectural beauty of curved structures is recognized worldwide. Owing to their balanced form, vaults, domes, and arches were largely adopted over the last centuries. Currently, the erection of new curved masonry structures is dramatically reduced. However, strengthening existing arches is often required to prevent their collapse under static or seismic force. Present limitations regarding such constructions include the antiquated and expensive erection technique employed for curved members. Moreover, the assembly of provisional supporting structures (scaffolding) is generally time- and cost-consuming. Accordingly, the following research provides an innovative construction method that focuses on overcoming the drawbacks of the scaffolding-based approach. A fast lift-up technique was developed to reduce the time and costs of traditional construction techniques. Specifically, the required number of blocks that constitute the arch in this study was aligned side by side on the floor and then connected using a bonded strip of composite material (i.e., FRP—fiber-reinforced polymer). The middle block was then lifted. Thus, each corresponding block could be rotated around the contact point with the adjacent block. When all blocks left the floor, an arch shape was achieved. To validate the proposed method in terms of mechanical performance, an experiment was conducted, as reported herein. A traditional masonry arch built using scaffolding was tested for comparison, and two types of reinforced arches were tested until failure. The first was traditionally built and then reinforced, whereas the second was built using the proposed innovative technique. The specimens were instrumented and tested under a centered or eccentric vertical point load. In all cases, the composite application prevented failure of the hinged joints, as is typical of unreinforced arches, resulting in significantly increased loadbearing capacity, which registered scatters of |11|% and |28|% for the centered and eccentric loads, respectively, when comparing the traditional reinforced arch with the innovative solution.

Numerical Analysis of the Pile-Grout System in Soft Clay under Vertical and Lateral Load

In this paper, a numerical investigation of the effects of grout parameters on the load response of concrete pile-grout systems in soft clay is presented. The study examines the influence of grout diameter and depth on the load bearing capacity of the pile under vertical and lateral loads. The research findings indicate that grouting can enhance the load bearing capacity of a single pile system by up to 27% under vertical loads and up to 51% under lateral loads, depending on the diameter and depth of the grout used. This is due to the grout's ability to fill voids in the soil and improve the soil-pile interface, resulting in better soil-pile interaction. Additionally, the study demonstrates that increasing the diameter and depth of grout leads to a larger treated soil area and subsequently an increase in load bearing capacity. Furthermore, the research indicates a linear relationship between the amount of grout material utilized and the increase in the load bearing capacity of the pile. The study concludes that grouting is an effective method for improving the pile performance systems, particularly in soft soil conditions. The results of the research are consistent with prior studies on the use of grout material to enhance the load-carrying capacity of pile systems.

Experiments on Increased Loadbearing Capacity of Confined FRP Reinforced Beams

Fibre Reinforced Polymers (FRP) have been in use in aerospace engineering since the 1940s in military aircraft. Later as manufacturing technology developed it became available to other sectors. The use of FRPs in concrete construction can offers a variety of advantages over steel reinforcement. For the technology to be employable on a wider scale related research needs to address certain disadvantages and other properties of FRP rebars. One area that needs further discussion is the brittle failure of FRP reinforced concrete elements. There are several methods proposed aiming to modify the behaviour of elements in bending, among them is the utilization of concrete crushing failure and confinement to achieve a more ductile failure.

Experimental studies on stocky masonry pillars strengthened with steel cords and PBO fibres

This paper presents a study of stocky masonry pillars strengthened by stainless steel cords and PBO fibres in bed joints. Ten physical models were used in experimental testing, of which 3 served as reference specimens and the remaining seven were confined in bed joints using different techniques. The pillars were constructed with lime mortar with parameters similar to those used in historical structures. To assure conditions similar to the real objects steel cords and PBO fibres were placed in grooves, which were made in the pillars after the mortar had set. The main failure mechanisms, ultimate load-bearing capacity and longitudinal and transverse deformations were determined through the experimental testing. In addition, the longitudinal stiffness and the stresses at which cracking appears were determined on the basis of observations and analysis of experimental results. The strengthening effectiveness was also determined in relation to the increase in load-bearing capacity, stiffness and cracking stresses. The methods used for strengthening stocky pillars in bed joints increase their load-bearing capacity, stiffness and counteract cracking without any significant impact on the visual appearance of the pillars, which is especially important in the strengthening of historic structures.

Experimental Analysis of Surface Application of Fiber-Reinforced Polymer Composite on Shear Behavior of Masonry Walls Made of Autoclaved Concrete Blocks

This paper presents the results of an experimental study of the shear behavior of masonry walls made of aero autoclaved concrete (AAC) blocks strengthened by externally bonded fiber-reinforced polymer (FRP) composites. Fifteen small wall specimens were constructed and tested in a diagonal compression scheme. Two types of composite materials—carbon- and glass-reinforced polymers—were arranged in two configurations of vertical strips, adopted to the location of the unfilled head joints. The effect of the strengthening location and strengthening materials on changes in the strength and deformability parameters are discussed and the failure process of unstrengthened walls is also presented. The placement of the composite on unfilled head joints proved to be a better solution. Carbon-fiber-reinforced polymer (CFRP) strips provided a threefold increase in stiffness, a 48% increase in load-bearing capacity and a high level of ductility in the post-cracking phase. Glass-fiber-reinforced polymer (GFRP) strips offered a 56% increase in load-bearing capacity but did not change the stiffness of the masonry and provided relatively little ductility. Placing the composite between unfilled joints was only reasonable for CFRP composites, providing a 35% increase in load-bearing capacity but with negligible ductility of the masonry.

A 3D bi-material lattice concept for tailoring compressive properties

The current article explores 3D bi-material lattice concepts for tailoring compressive stress-strain response. The unit cells of the lattices consist of six stiff inclined struts that together form the edges of two stacked tetrahedra. The central plane (between the two tetrahedra) contains elastomeric elements that stretch when the lattice is compressed. The geometric configurations of the elastomers examined here include: (i) straight struts between each node pair within the central plane, (ii) multiple struts between each node pair, including one straight strut and one or more curved struts, and (iii) flat sheets, either uniform or graded in thickness, connected at the mid-plane nodes. Assessments of the concepts are made using analytical models, finite element simulations, and experiments on lattices fabricated by 3D printing. The experimental results affirm the understanding of mechanical response gleaned from the models and highlight the importance of joint design in attaining large straining capacity and strain reversibility. They also demonstrate a nearly twofold increase in load bearing capacity when straight struts are replaced by graded sheets. The work also raises the prospects for computational design optimization for maximum efficiency in material use.

Load-Bearing Capacities and Pseudo-Ductility of Carbon Fiber-Reinforced New Zealand Pine Timber Beams

Building construction contributes a significant portion to the global consumption of energy and greenhouse gas (GHG) emissions, and decarbonization has become one of the main targets. This has turned much attention to renewable materials, particularly timber construction. Wood is a natural composite, and it causes challenges in its natural state due to its mechanical properties and functionality, which has constrained its use in construction. Laminating wood sections into glue-laminated (glulam) and cross-laminated timber (CLT) components overcomes limitations in dimensions and inconsistencies in its properties. We went beyond these technologies and explored the potential of combining timber of the radiata pine species with synthetic fibers, aiming for hybrid natural–synthetic composite beams. This research illustrated various reinforcement mechanisms and analyzed their structural properties. The results from the experiments showed that carbon fiber-reinforced timber composites have up to 49% additional increase in load-bearing capacity compared to unreinforced beams. An identical amount of strain required less stress, and the composite portrayed a metal-like ductility property, a characteristic referred to as pseudo-ductility. It reduces the material consumption in beams through a more efficient use of materials, particularly around compression areas before tensile rupture. The resulting composites are sustainable yet structurally capable, contributing to the reduction in CO2 emissions in timber construction systems.