Structural Reinforcement Research Articles

Shear contribution of beams of different sizes strengthened in shear with anchored CFRP strips

Carbon-fibre-reinforced polymer (CFRP) materials can be used as structural reinforcement in engineering projects, but its effectiveness is jeopardised by debonding of the CFRP. Anchoring of the CFRP is thus crucial for efficient shear strengthening. The effect of anchoring on the shear resistance of nine CFRP U-wrapped concrete beams with varying shear span-to-depth (SSD) ratios (1.0, 1.5 and 2.0) and depths of 300–900 mm was investigated in this work. Nine unanchored beams and nine plain (without CFRP wrapping) concrete beams were also included in the comparison, considering the influence of the beam effective depth and the SSD ratio, with reference to prior research. An evaluation of the shear contribution of the CFRP wrapping was conducted, particularly for cases involving large dimensions and diverse SSD ratios. The anchoring effect was found to be most pronounced in small-scale beams with a large SSD ratio, demonstrating an improvement of over 60% compared with the CFRP shear-strengthened beam without anchoring. In contrast to beams without CFRP wrapping, the shear performance was enhanced by approximately 90%. Additionally, formulas for calculating the shear capacity from different national specifications were analysed and compared. A new calculation method for CFRP shear resistance was established and its accuracy was verified.

Secondary flexural behaviour of reinforced concrete beams strengthened with special-shaped rivet bonded steel plates and prestressed CFRP bars

Special-shaped rivet and glued steel plate reinforcement is an innovative structural reinforcement technology. A riveted glued steel plate primarily relies on the rivet to transfer shear. Prestressed carbon fibre-reinforced polymer (CFRP) reinforcement is a new technique for strengthening concrete structures. These studies focus on the ‘primary load’, overestimate the ultimate flexural load of the components by neglecting the ‘secondary load’ of the components in real engineering. In this study, the flexural properties of concrete beams strengthened using special-shaped rivet steel plates and CFRP prestressed bars were studied theoretically and experimentally. The cracking load, ultimate load capacity, and strain of the steel plate, steel bar and CFRP bars were recorded during the tests. In addition, the failure mode of the beams was observed, and the effect of secondary stress on the flexural capacity of the beams was analysed. The failure load of the beams strengthened by CFRP prestressed tendons increased by 67.8% and 46.1% for beams with primary and active secondary loads, respectively. The failure load of the special-shaped rivet and glued steel plate strengthened beam increased by 115.7% and 160.5%, for beams with primary and active secondary loads, respectively. Both methods have a strong guiding significance for engineering practice.

Cost-effective topology optimization of masonry structure reinforcements by a linear static analysis-based GA framework

The paper presents a novel optimization framework aimed at the minimization of seismic retrofitting-related costs for existing unreinforced masonry building structures. The framework provides topology optimization of reinforcements (reinforced plasters) to implement in masonry walls for the accomplishment of seismic safety checks under the reference seismic load combinations. Optimization is carried out by a genetic algorithm (GA) developed in MATLAB®, which controls a 3D finite element equivalent frame model of the masonry structure developed in OpenSees. The GA routine iterates the reinforcement configurations employing specific genetic operators. The feasibility of each candidate retrofitting solution is assessed by performing in-plane shear and flexural safety checks of masonry walls. The framework is finally tested with a case study masonry structure supposed to be made of average-quality or poor-quality masonry. Results will show that the proposed framework can effectively provide the minimization of seismic retrofitting costs for existing masonry structures, giving as output the optimal configuration of the reinforcements within the structural layout.

Fatigue enhancement of welded thin-walled tubular joints made of lean duplex steel

In the present work, the fatigue strength and enhancement techniques of welded thin-walled (wall thickness of t = 2 mm) square hollow section (SHS) joints made of lean duplex stainless steel (grade EN 1.4162) are experimentally and numerically studied. Experimental fatigue tests were carried out on gas metal arc-welded tubular X-joints subjected to fully reversed (applied stress ratio of R = −1) constant amplitude in-plane bending moment. Geometrical improvement techniques were investigated by applying fully penetrating fillet welds and using structural reinforcements. The applications of high-frequency mechanical impact (HFMI) treatment were examined in the context of further enhancing the fatigue strength of the geometrically improved joints. In addition to the experimental work carried out in this study, the fatigue test data of welded thin-walled SHS and rectangular hollow section (RHS) joints were extracted from literature. Structural stress concentration factors were numerically and analytically obtained to validate the fatigue assessment model for welded thin-walled tubular joints using the structural hot-spot stress method. In addition, the effective notch stress (ENS) concept with the reference radius of rref = 0.05 mm was implemented. Compared to the joints in the as-welded state, fatigue strength improvements of 1.53–2.7 were found in the geometrically improved joints. On the other hand, the HFMI treatment did not lead to an additional increase in the fatigue strength capacity of the studied AW joints. The CIDECT guidelines for the structural hot-spot stress method were found conservative for thin-walled joints (t < 3 mm) and could be recommended for fatigue design.

Research on Single-Event Burnout Reinforcement Structure of SiC MOSFET.

In this paper, the single-event burnout (SEB) and reinforcement structure of 1200 V SiC MOSFET (SG-SBD-MOSFET) with split gate and Schottky barrier diode (SBD) embedded were studied. The device structure was established using Sentaurus TCAD, and the transient current changes of single-event effect (SEE), SEB threshold voltage, as well as the regularity of electric field peak distribution transfer were studied when heavy ions were incident from different regions of the device. Based on SEE analysis of the new structural device, two reinforcement structure designs for SEB resistance were studied, namely the expansion of the P+ body contact area and the design of a multi-layer N-type interval buffer layer. Firstly, two reinforcement schemes for SEB were analyzed separately, and then comprehensive design and analysis were carried out. The results showed that the SEB threshold voltage of heavy ions incident from the N+ source region was increased by 16% when using the P+ body contact area extension alone; when the device is reinforced with a multi-layer N-type interval buffer layer alone, the SEB threshold voltage increases by 29%; the comprehensive use of the P+ body contact area expansion and a multi-layer N-type interval buffer layer reinforcement increased the SEB threshold voltage by 33%. Overall, the breakdown voltage of the reinforced device decreased from 1632.935 V to 1403.135 V, which can be seen as reducing the remaining redundant voltage to 17%. The device's performance was not significantly affected.

Robust profiled carbon rovings made of multiple yarns for textile reinforcements in concrete and asphalt matrix

The load-bearing behavior and the performance of composites depends largely on the bond between the individual components. Conventional grid-like textile reinforcement structures with thin and smooth yarn structures transmit forces primarily by an adhesive bond with the surrounding matrix. A sufficient load transmission is not possible. Thick, pultruded rebars made of fiber-reinforced plastics can be profiled by subtractive (e.g. milling) or additive (e.g. wrapping) techniques in order to create a rip-like structure and increased shear bond. Yet the discontinuous fiber course results in material inefficiency. A newly developed profiling technique allows a tetrahedral profiling of the complete roving structure, yet considering its anisotropic properties. In the article, we present this approach, and the first results from single yarn tensile and pull-out tests of single, double and triple plied profiled rovings in concrete and asphalt matrix. Thus, the highest bond is achieved in the brittle concrete matrix. Plied rovings with strong tetrahedral profiles show up to 600% higher bond stress compared with rovings with circular profiles, while maintaining high tensile properties. However, splitting-induced failure of the reinforced test specimens occurs, making plied profiled rovings favorable for high concrete cover and less brittle matrixes; for example, asphalt. The reinforced asphalt specimens show at −10°C similar bond properties, but at 30°C the bond decreases by 80%. In summary, the study shows that bond properties of profiled rovings are superior to conventional circular rovings, and promise a high material efficiency for use in concrete and asphalt reinforcements.

A review of the application of FRP materials in Asia-Pacific region

FRP (Fiber Reinforced Polymers) materials are being increasingly used in various engineering fields due to their high specific strength, designability and durability. Having been rapidly developing in recent years, the Asia-Pacific region is also equipped with a continuously expanding demand for the research and application of FRP materials. This paper summarizes the application of FRP materials in the Asia-Pacific region through literature and case analysis. Some of the current issues existing in the procedure of FPR materials application are discussed, and predictions on the development and application prospects of this kind of materials in the Asia-Pacific region are also briefly suggested. It is found that FRP materials have been widely utilized in various fields including concrete structures reinforcement, bridge engineering construction and new energy facilities in the Asia-Pacific region, where is equipped with a relatively broad and promising market. Meanwhile, the shortcomings relevant to this kind of materials in several aspects, such as expensive unit prices and imperfect technical specification systems, also restricted the application of FRP materials in this region.

Effect of BFRP ties on the axial performance of RC columns reinforced with BFRP and GFRP rebars

The adoption of fiber-reinforced polymer (FRP) bars in lieu of traditional steel reinforcement for concrete structures has gained prominence. Nevertheless, prevailing international standards have not incorporated provisions to assess the significant contribution of FRP materials to the axial capacity and deformability of compression members. This study investigates the impact of Basalt (BFRP) ties on the axial performance of full-scale concrete columns reinforced with BFRP and Glass (GFRP) rebars, alongside traditional steel longitudinal rebars. Ten columns were subjected to concentric loading, with parameters including the type of longitudinal rebars (BFRP, GFRP, and steel), spacing of BFRP ties (180 mm, 120 mm, and 60 mm), and diameter of steel rebars (16 mm and 20 mm). Varied steel rebar diameters aimed to discern the influence of axial stiffness on column behavior. Results indicate an 18 % to 26 % higher axial load capacity in steel-reinforced concrete (RC) columns compared to FRP-RC columns. Both types of FRP rebars contributed approximately 12 % to the axial capacity. Reducing BFRP tie spacing from 180 mm to 60 mm significantly increased deformability by up to 250 % in FRP-RC columns and ductility by up to 14 % in steel-RC columns. The study highlights conservative predictions in existing design equations (ACI 440.11–22 and CSA S806-12) for the axial load capacity of BFRP and GFRP RC columns, underestimating by 14 % to 20 %, as they neglect the contribution of FRP rebars. Utilizing a concrete crushing strain of 3,000 µε and 3,500 µε as the ultimate FRP compressive strain produced predictions closest to the experimental axial load capacity.

Axial compression performance of underwater columns reinforced with stainless steel tube-FRP grids

Stainless steel tubes have excellent plasticity and ductility, and FRP grids have favorable advantages for application in specific structural reinforcements. For systems including underwater construction without drainage, underwater columns reinforced with stainless steel tube-FRP grids are proposed using nondispersive mortar (NDM) as the reinforcement layer to best leverage the material properties of all elements. This paper carried out axial compression tests on 18 underwater columns reinforced with stainless steel tube-FRP grids (SS-FGWCs), 6 columns reinforced with stainless steel tube-FRP grids on land (SS-FGLCs), 3 underwater columns reinforced with stainless steel tubes (SSWCs), and 3 unreinforced concrete columns. The research parameters include the number of FRP grid layers, the types of FRP grids, and the reinforcement layer mortar pouring environments. The test results showed that FRP grids can be combined with stainless steel tubes (SSs) and nondispersive mortar (NDM) to reinforce concrete columns in underwater construction without drainage. In addition, compared with those of the SSWC specimens, after the BFRP grid and CFRP grid were built in, the ultimate stresses of the specimens increased by 13.4% ∼ 20.8% and 19.5% ∼ 25.4%, respectively, and the ultimate strains increased by 6.8% ∼ 31.7% and 21.8% ∼ 59.1%, respectively. Compared to BFRP grids, CFRP grids provide better reinforcement of the underwater columns. Existing prediction models were evaluated for ultimate stress calculations, the calculation methods for the ultimate stress and ultimate strain applicable to the SS-FGWCs and SS-FGLCs were revised, and a calculation model for the FRP grid failure point was proposed. Finally, a corresponding full stress–strain curve model was established.

A non-uniform lattice design method for lightweight structures in 3D printing

Lightweight design is an essential topic in aerospace, automotive and other fields. In automobile manufacturing, the engine connecting rod is one of the main components; its lightweight design has a high reference value. And 3D printing provides a feasible solution for designing and manufacturing lightweight structures. Unlike the traditional geometrically homogeneous point design, this study offers a non-homogeneous point design method based on the spatial stress state of additively manufactured components. After numerical simulation of quasi-static stresses on a model of an engine connecting rod, finite element grid cells with different stress values are replaced by lattice cells with different specific stiffnesses at similar local stress levels. The overall specific stiffness of the structure is further improved by continuing the optimized design with the corresponding gradient-type reinforcement of the non-uniform lattice structure. The basic idea of this design is to perform non-uniform adaptive filling of solid parts under localized loading by employing different types of unit cells. Stereolithography 3D printing technology prepares the engine lattice structural parts for quasi-static compression comparison experiments and fracture analysis after failure. The conclusions show that the engine connecting rod members with non-homogeneous lattice have more excellent overall mechanical properties than homogeneous lattice members. This work demonstrates the feasibility of such design methods for 3D printing lightweight structures and optimization.

4D printing of fiber-reinforced auxetic structures: the building blocks: A review

Abstract Four-dimensional (4D) printing has recently received much attention in the field of smart materials. It concerns using additive manufacturing to obtain geometries that can change shape under the effect of different stimuli. Such a technique enables the fabrication of 3D printed parts with the additional functionality of scalable, programmable, and controllable part shapes over time. &amp;#xD;This review provides a comprehensive examination of advances in the field of 4D printing, emphasizing the integration of fiber reinforcement and auxetic structures as crucial building blocks. &amp;#xD;The incorporation of fibers enhances structural integrity, while auxetic design principles contribute unique mechanical properties, such as negative Poisson's ratio and great potential for energy absorption due to their specific deformation mechanisms. Therefore, they present potential applications in aerospace, drones, and robotics.&amp;#xD;The objective of this review article is first to describe the distinctive properties of shape memory polymers (SMPs), auxetic structures, and composite (fiber-reinforced) materials. A review of applications that use combinations of such materials is also presented when appropriate. The goal is to get a grip on the delicate balance between the different properties achievable in each case. The paper concludes by describing recent advances in 4D printing of fiber-reinforced auxetic structures.&amp;#xD;

LOAD-BEARING CAPACITY, BOND BEHAVIOR, ENVIRONMENTAL IMPACT AND APPLICATION OF BFRP-REINFORCEMENT IN CONCRETE

Because of its high tensile strength, high durability and comparatively low environmental impact reinforcement made of BFRP should be investigated on its usability as structural reinforcement. Further, there is the ability to increase the life span of concrete members due to the use of BFRP-reinforcement, what can also lower the environmental impact. Due to the fact that reinforcement products made of BFRP are not generally regulated normatively in Germany, there are many characteristics that have to be investigated experimentally At the Kiel UAS experimental and numerical investigations on the flexural and shear capacity and the bond and cracking behavior of BFRP-reinforced concrete members were carried out. Based on this, specific applications where developed. As examples a BFRP-reinforced bridge cap made of RC-concrete and a ground plate with BFRP-reinforcement can be named. In conclusion we can say that the benefit of using BFRP-reinforcement depends on the application. Especially in corrosive milieu BFRP-reinforcement can be a useful alternative to steel-reinforcement.

LOAD-BEARING CAPACITY, BOND BEHAVIOR, ENVIRONMENTAL IMPACT AND APPLICATION OF BFRP-REINFORCEMENT IN CONCRETE

Because of its high tensile strength, high durability and comparatively low environmental impact reinforcement made of BFRP should be investigated on its usability as structural reinforcement. Further, there is the ability to increase the life span of concrete members due to the use of BFRP-reinforcement, what can also lower the environmental impact. Due to the fact that reinforcement products made of BFRP are not generally regulated normatively in Germany, there are many characteristics that have to be investigated experimentally At the Kiel UAS experimental and numerical investigations on the flexural and shear capacity and the bond and cracking behavior of BFRP-reinforced concrete members were carried out. Based on this, specific applications where developed. As examples a BFRP-reinforced bridge cap made of RC-concrete and a ground plate with BFRP-reinforcement can be named. In conclusion we can say that the benefit of using BFRP-reinforcement depends on the application. Especially in corrosive milieu BFRP-reinforcement can be a useful alternative to steel-reinforcement.

Quantitative analysis of deformation performance for skew slab based on deformation energy decomposition method of triangular prism element

In order to propose a simpler and more effective method to quantitatively analyze the macroscopic basic deformation properties such as tension, bending and shear of the skew slabs, and provide theoretical basis and technical support for targeted design and reinforcement. Based on mathematical orthogonality, mechanical equilibrium and physical parameters, this paper proposes a deformation energy decomposition method suitable for 3D 6-node arbitrary triangular prism elements. By applying this method to the finite element model discretized by triangular prism element, the quantitative information of 6 kinds of rigid body displacement and 12 kinds of deformation energy of skew slab can be obtained. The quantitative and visual analysis of the basic deformation performance of the skew slab is carried out by using the method in this paper. Then the targeted structural design and reinforcement design of the skew slab can be guided according to the principle of matching design with deformation. Compared with the existing deformation decomposition methods based on square elements, which are only applicable to 2D or quasi-3D regular structures, the deformation energy decomposition method based on arbitrary triangular prism elements in this paper can be used to analyze the deformation performance of 3D irregular structures. The influence of skew angle and span-width ratio on the deformation performance of skew slab is analyzed by deformation energy decomposition method. The results show that when the skew angle is greater than 25°, the proportion of ductile deformation energy such as tension and bending of skew slab decreases rapidly. In this case, the shear design of the skew slab should be focused on. When the angle is greater than 45°, the span-width ratio should be appropriately reduced to improve the ductility of the skew slab, and the torsion design needs to be focused on.

Numerical analysis of the working performance of ring combination reinforced retaining wall

In this study, a new combined reinforcement structure suitable for reinforced soil-retaining walls is proposed. FLAC 3D finite element software was used to establish three-dimensional numerical models of reinforced soil retaining walls with different forms of reinforcement, and the effects of reinforced rings on the mechanical and deformation characteristics of retaining walls, as well as the mechanism of the reinforced rings working with horizontal geogrids, were investigated. The test results verified the superiority of the ring combination-reinforced structure in bearing and deformation under the same loading conditions. Moreover, the ring combination-reinforced soil retaining wall exhibited a stronger ability to resist deformation than the horizontal-reinforced soil retaining wall.

Study on the Mechanical Properties of a Carbon-Fiber/Glass-Fiber Hybrid Foam Sandwich Structure.

Considering the different structural strength requirements of different parts of fiberglass yachts, carbon fiber/glass fiber hybrid reinforcement can be applied to the skins of sandwich panels in special areas. This paper designs and prepares 12 foam sandwich panel samples composed of pure carbon fiber, a carbon fiber/glass fiber hybrid, pure glass fiber skin, and PVC and SAN foam sandwich, with reference to the layup structure of the outer panel of a fiberglass yacht. Through a comparative analysis of low-speed impact experiments, edge compression experiments, and short beam three-point bending experiments, we seek the optimal carbon fiber/glass fiber hybrid layup design scheme for local structures to guide production. The results show that a reasonable hybrid carbon fiber layup in fiberglass skin can effectively reduce the low-speed impact damage of the sandwich structure, reduce edge compression damage, and improve the bending and compression resistance of sandwich structure. The impact resistance, compression resistance, and shear resistance of the SAN sandwich structure are stronger than the PVC sandwich structure. The carbon fiber/glass fiber hybrid SAN foam sandwich structure can be used for the local structural reinforcement of special parts such as the bow, side, and main deck of fiberglass yachts.

A novel investigation of co-processing porous geopolymer using glass fibres recycled from waste turbine blades

Abstract This work investigates the possibility of using recycled glass fibre (rGF) to co-process porous geopolymer. A new procedure was developed to incorporate rGF into geopolymer preparation and the content of rGF in porous geopolymer was varied to investigate its effect on thermal and mechanical properties. The rGF was co-processed through mixing with a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution to supplement raw materials required to make geopolymer but also provide fibres as potential structure reinforcement. Due to the enriched silica content obtained from rGF and leftover fibres, a nearly 80 % strength increase (from 0.092 MPa to 0.165 MPa) was obtained without compromising its low thermal conductivity. This opens up a potential route to re-using rGF in the development of improved porous geopolymer for thermal insulation applications.

Feasibility Study of UHPC Reinforced Masonry Structure

With the increase of service life of masonry structure and the damage of masonry structure caused by external environment, the structure will be difficult to meet the design requirements. It is necessary to repair and reinforce the existing structure or replace the original structure with a new type of composite structure. ultra-high performance concrete (UHPC) is a kind of high strength, high ductility, high durability material, which has the advantages of almost impermeability, almost no carbonization, and almost zero chloride ion penetration and sulfate penetration. UHPC has been widely used in the field of concrete structure reinforcement, whether the masonry structure can be better strengthened has become the research content of this paper. Basic mechanics of UHPC materials at home and abroad By systematically combing and summarizing the research progress of performance and reinforcement design, the feasibility of UHPC reinforced masonry structure is obtained.

Chloride binding by layered double hydroxides (LDH/AFm phases) and alkali-activated slag pastes: an experimental study by RILEM TC 283-CAM

Chloride binding by the hydrate phases of cementitious materials influences the rate of chloride ingress into these materials and, thus, the time at which chloride reaches the steel reinforcement in concrete structures. Chloride binding isotherms of individual hydrate phases would be required to model chloride ingress but are only scarcely available and partly conflicting. The present study by RILEM TC 283-CAM ‘Chloride transport in alkali-activated materials’ significantly extends the available database and resolves some of the apparent contradictions by determining the chloride binding isotherms of layered double hydroxides (LDH), including AFm phases (monosulfate, strätlingite, hydrotalcite, and meixnerite), and of alkali-activated slags (AAS) produced with four different activators (Na2SiO3, Na2O·1.87SiO2, Na2CO3, and Na2SO4), in NaOH/NaCl solutions at various liquid/solid ratios. Selected solids after chloride binding were analysed by X-ray diffraction, and thermodynamic modelling was applied to simulate the phase changes occurring during chloride binding by the AFm phases. The results of the present study show that the chloride binding isotherms of LDH/AFm phases depend strongly on the liquid/solid ratio during the experiments. This is attributed to kinetic restrictions, which are, however, currently poorly understood. Chloride binding by AAS pastes is only moderately influenced by the employed activator. A steep increase of the chloride binding by AAS occurs at free chloride concentrations above approx. 1.0 M, which is possibly related to chloride binding by the C–(N–)A–S–H gel in the AAS.

Evaluation of sulfuric acid effect on bending strength of steel used in concrete reinforcement in sanitation structures

Most sanitation structures in the world are constructed using concrete which is reinforced by the steel, this type of concrete is called Reinforced Cement Concrete (RCC). The RCC structure is believed to be relatively resistant to corrosion which the sanitation structures are prone to due to the aggressive environment in which they are subjected to. This belief has been compromised since the reinforced concrete used in the sanitation structures such as the concrete sewer pipes has become susceptible to Microbiologically Induced Deterioration (MID). This MID leads to degradation and compromised strength and service life of the RCC. In the reinforced concrete structure, the backbone of this structure is the reinforcing steel which when its strength is compromised by the MID, the whole structure is compromised. The present research therefore aimed at evaluating the effects of sulfuric acid, resulting from the MID process, on the bending strength of steel metal used for reinforcing concrete in sanitation structures. Reinforced concrete specimens were developed using different types of cement and different concrete cover. The three different types of cement were, Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC) and Limestone Calcined Clay Cement (LC3), while concrete covers of 15mm and 25mm were applied. They were then subjected to a harsh environment (a sample of sewage) suitable for corrosion just like in their actual operational environment. To determine the effects of sulfuric acid resulting from MID on the steel metal, the steel metal was tested using a Universal Testing Machine (UTM). The bending strengths before and after being subjected to an aggressive environment were determined. The testing of the specimens was done at an interval of 14 days for a period of three (3) months. According to the results, for a concrete cover of 25mm, LC3 showed a minimum percentage reduction in strength compared to PPC and OPC. It had the lowest percentage reduction in strength after 84 days which was 5.25%, OPC 7.20%, and PPC 7.24%. In conclusion, there was a strength reduction for all specimens tested. LC3 showed good resistance to the effects of MID compared to PPC and OPC. In terms of concrete cover, 25mm showed good resistance to MID compared to 15mm concrete cover.