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This experimental study investigates the effectiveness of retrofitting fiber-reinforced concrete (FRC) beams using nano-graphene oxide (GO) and carbon fiber-reinforced polymer (CFRP) sheets. The primary goal is to evaluate the combined effect of GO and CFRP sheets on the mechanical performance of FRC beams. The experimental program involved preparing and testing multiple concrete beam specimens, with some retrofitted using GO and CFRP sheets. The principal results indicate that the integration of GO significantly enhances the compressive and tensile strength of concrete. Additionally, the application of CFRP sheets markedly improves the flexural strength and ductility of the beams. The retrofitted specimens exhibited higher load-bearing capacity and greater deformation before failure compared to control specimens. The significant conclusions drawn from this study are that the combined use of GO and CFRP sheets provides a synergistic effect, improving the overall mechanical performance of FRC beams. However, failure modes such as debonding and delamination of CFRP sheets highlight the need for optimization in bonding techniques and materials. The primary research outcomes demonstrate that retrofitting FRC beams with GO and CFRP sheets is a promising approach for enhancing the structural performance. This study underscores the potential of advanced materials in structural retrofitting and provides insights for future research to address observed failure modes and further improve the retrofitting techniques. [ABSTRACT FROM AUTHOR]

[Objective] The transverse joints within the panels of prefabricated diaphragm walls are the weak points in the entire wall structure. Therefore, it is necessary to study the stiffness and strength characteristics of these joints. [Method] In conjunction with prefabricated diaphragm walls commonly used in foundation pit engineering, a new type of transverse welded joints for prefabricated diaphragm walls is introduced. The force and deformation behavior of this new joint under bending moment actions are studied using numerical simulation methods. [Result & Conclusion] Under bending moment actions, the tensile stress in the concrete at the end of the angle steel on joint tensile side is the highest, while the compressive stress in the concrete at this position on joint compressive side is the highest. The failure of the joint begins with cracks of the concrete on tensile side. The deflection curve of the component shows no significant mutation at the joint, indicating good deformation performance of the joint, which effectively prevents water leakage. The stress in the angle steel, weld, and rebar on joint tensile side is greater than that on the compressive side. After cracks appear in the concrete on the tensile side, the stress in the angle steel, weld, and rebar of the prefabricated component remains at a low level. [ABSTRACT FROM AUTHOR]

This research investigates the flexural performance of slabs reinforced with high-strength steel-strand mesh (HSSM) and engineered cementitious composites (ECCs). By employing finite element analysis (FEA) and theoretical modeling, this study aims to deepen the understanding of how these materials behave under bending stresses. A finite element model was developed to simulate the nonlinear behavior of ECCs during bending, considering critical elements such as tensile and compressive damage, as well as bond–slip interactions between the steel strands and the ECCs. Furthermore, a theoretical model was created to predict the load-bearing capacity of HSSM-reinforced ECC slabs, incorporating variables like reinforcement ratios, slab dimensions, and material characteristics. The findings reveal that increasing the reinforcement ratio substantially enhances both flexural stiffness and load-bearing capacity while reducing deflection. Comparisons between the FEA results, the theoretical forecasts, and the experimental observations show close alignment, validating the proposed models. This work provides important insights for optimizing the design of HSSM-reinforced ECC slabs, highlighting their potential improvements in structural systems that demand high flexural performance. [ABSTRACT FROM AUTHOR]

Understanding the advantages of combining traditional construction methods and 3D concrete printing is the gateway to the general structural applicability of three-dimensional concrete printing (3DCP) technology. To further this objective, in this study, 3D-printed concrete is used as permanent formwork for the manufacture of reinforced concrete beams. Different treatment methods for the interfaces between the printed formwork and the cast core concrete, including embedding of shear connectors, entraining of micro-cables, and inclusion of ribs in the 3D printing of the formwork, are explored to improve the integral mechanical capacities of so-called 3D-printed and cast-in-place composite beams. Specifically, flexural behaviors are studied experimentally through observation of damage and failure processes via visualization with the digital image correlation (DIC) method. The mesoscale architecture at the interface between 3D-printed permanent formwork and cast-in-place concrete is investigated through computed tomography (CT) scanning to infer the cooperative bonding mechanisms of different bonding treatment methods. The stress-transfer mechanism is thus elucidated. The applicability of 3D-printed concrete as permanent formwork is validated in view of a 14.3% increase in the bending capacity from a composite beam with bottom ribs compared to that of a completely cast counterpart. From the experiments, incorporation of shear connectors contributes most to the bonding performance of the formwork--concrete interfaces. Meanwhile, interfacial bonding can be enhanced by increasing the roughness of the 3D-printed formwork, interlocking of the formwork with the inner aggregated concrete, or improving the consistency of the elastic and shear moduli of the formwork and cast concrete. In particular, the appropriate thickness of both the formwork and the aggregated concrete as a cover to yield the optimal integrated bending capacity of composite beams is derived from the current study. [ABSTRACT FROM AUTHOR]

This paper investigates flexural behavior and analytical approach for predicting the load and deflection at critical performance points of reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) sheets. A finite element model is developed to simulate the interaction between the RC beam and the CFRP sheets, capturing key aspects such as failure modes, ultimate load, and mechanical behavior across the three phases of failure. The analysis reveals that increasing the prestress level significantly enhances the performance, delaying the initiation of cracking, steel yielding, and increasing the ultimate load capacity. Two distinct failure modes are identified, i.e., concrete crushing in the compressive zone and composite plate peeling. An analytical approach is then proposed to estimate the load corresponding to initial cracking, steel yielding, and ultimate failure. Comparison between the experimental, numerical and analytical results shows that the proposed method accurately predicts the flexural capacity of RC beams strengthened with prestressed CFRP sheets. [ABSTRACT FROM AUTHOR]

Backfilling mine goafs can significantly advance the mining industry; however, few researchers have used geopolymers reinforced with polypropylene fibers as filling materials. In this study, the flexural properties of fiber-reinforced green composite cementitious matrix–cemented tailings were examined, and the evolution mechanism of the internal structural properties of the prepared composite materials was determined. For this purpose, three-point bending tests, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction were performed on composite samples with different blending ratios, and discrete-element numerical simulations were conducted using PFC3D particle flow simulation software. The obtained results revealed that the flexural strength and fracture properties of the studied samples increased with increasing NaOH content, decreased with increasing water-to-solid ratio, and first increased and then decreased with increasing fiber content. At a fiber content of 0.6%, the reinforcement effect reached a local optimum. The higher the NaOH content, the more efficiently fly ash and slag formed polymerization products in an alkaline environment, which contained tailing sand aggregate particles, increasing the compactness of the composite structure. The fibers in the composite material were distributed both as a single inlay and as a three-dimensional network structure to form an effective wrapping and supporting system, which further improved the flexural performance of the sample. The PFC3D simulation data were consistent with the results of three-point bending tests, illustrating the sample degradation process. The findings of this work can provide a theoretical basis for the development of fiber-reinforced green sand filling materials for mine replenishment. [ABSTRACT FROM AUTHOR]

Copyright of New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

［Objective］The transverse joints within the panels of prefabricated diaphragm walls are the weak points in the entire wall structure. Therefore, it is necessary to study the stiffness and strength characteristics of these joints. ［Method］In conjunction with prefabricated diaphragm walls commonly used in foundation pit engineering, a new type of transverse welded joints for prefabricated diaphragm walls is introduced. The force and deformation behavior of this new joint under bending moment actions are studied using numerical simulation methods. ［Result & Conclusion］Under bending moment actions, the tensile stress in the concrete at the end of the angle steel on joint tensile side is the highest, while the compressive stress in the concrete at this position on joint compressive side is the highest. The failure of the joint begins with cracks of the concrete on tensile side. The deflection curve of the component shows no significant mutation at the joint, indicating good deformation performance of the joint, which effectively prevents water leakage. The stress in the angle steel, weld, and rebar on joint tensile side is greater than that on the compressive side. After cracks appear in the concrete on the tensile side, the stress in the angle steel, weld, and rebar of the prefabricated component remains at a low level.

Abstract The performance of joint connections in composite slabs is crucial for ensuring their bidirectional load-bearing capacity and overall structural integrity. To effectively address the challenge of protruding rebar in precast components, a new structural form of a tightly connected hollow concrete composite slab without protruding rebar on the slab side is proposed. To investigate the mechanical performance and failure modes of this slab-side tight-joint connected hollow concrete composite slab, bending performance tests under monotonic load were conducted on three tightly connected hollow composite slabs and one seamless hollow composite slab. The analysis focused on the failure modes, crack distribution, bending capacity, and bending stiffness of additional steel bars at the joints of the slabs. The results indicate that, under normal operating conditions, the flexural performance development of concrete hollow composite slabs with tightly connected slab sides is generally consistent with that of the non-spliced cast hollow composite slab. Under ultimate conditions, tearing or brittle fracture failure at the joint interface is likely to occur in the composite slabs, leading to a reduction in flexural bearing capacity. With an increase in joints, the bending capacity of the hollow composite slab decreases by 17.1%, Conversely, when joints are positioned away from the most stressed section, the flexural stiffness of the section increases by 13.5%. A comparison of experimental data and theoretical calculations indicates that the additional rebar at the joints effectively contributes to the lateral load transfer in the hollow composite slab, achieving bidirectional load-bearing capacity. This further validates that the design of the single-joint, tight-joint connected hollow concrete composite slab without protruding rebar meets the requirements for bidirectional load-bearing performance.

AbstractIn this study, the out-of-plane performance of ultra-high performance concrete (UHPC) thin panels reinforced with basalt fiber reinforced polymer (BFRP) bars was investigated. Eight panels were tested under four-point load, with the investigating parameters including panel thickness, reinforcement ratio, and the presence of steel fibers. The failure mode, crack pattern, load vs. mid-span displacement, and reinforcement strain relationships were studied. Test results revealed that panels with a higher thickness (70 mm) exhibited 178.6% higher initial stiffness, 34.5% higher cracking loads, and 88.7% higher peak loads compared to those with a lower thickness (50 mm). The effects of a larger reinforcement ratio and the presence of steel fibers became more pronounced after concrete cracking, leading to 21.2% and 22.1% higher post-cracking stiffness, respectively. Adding steel fibers helped control the development of diagonal cracks and shifted the panel failure mode from shear to flexural failure. Based on the comparison of test results with design codes, the expressions in CAN/CSA-S806-12 were recommended for predicting the load-carrying capacity of the specimens. Furthermore, a two-dimensional finite element (FE) model was developed to reproduce the test results, which validates the adopted CDP model for UHPC and the bond-slip behaviors between UHPC and BFRP bars. [ABSTRACT FROM AUTHOR]

In the face of the huge consumption of fresh water and river sand by the concrete industry and the poor flexural performance of plain concrete, it is theoretically feasible and environmentally friendly to use bamboo fiber as a replacement to reinforce concrete mixed with seawater and sea sand. In this research, taking the volume fraction (0.6%, 1.2%, and 2.4%), aspect ratio (10, 20, and 30) and diameter (1.0, 1.5, and 2.0 mm) of bamboo fibers as parameters, 15 groups of bamboo fiber‐reinforced concrete (BFRC) prisms and one control group of plain seawater sea sand concrete prisms were subjected to four‐point bending test, followed by analyzing the crack pattern, ultimate load, mid‐span deflection and strain. Under the condition of 1.2% volume fraction, 20 aspect ratio, 1.5 mm diameter, and 30 mm length, the maximum increase rate of flexural strength in this research was obtained, and then it was compared with that of flexural strength of concrete prisms reinforced by various natural fibers. In addition, relevant fitting equations and theoretical calculation formulas were derived, laying a foundation for the subsequent research and application of BFRC. [ABSTRACT FROM AUTHOR]

This work examines the performance of reinforced concrete (RC) beams strengthened using bonded steel wire rope (SWR) at various prestressing levels. The strengthening approach has, however, been applied to the flexural strengthening of RC T-beams in the negative moment region, in order to determine its advantages. For this purpose, four RC T-beams were fabricated and tested under monotonic four-point bending: one control beam (S00), one beam strengthened with non-prestressed SWR (S20), and two beams strengthened with SWR (prestressed at 10% and 20% of their ultimate tensile strength: S21 and S22). The results indicate that the strengthened beams exhibit higher load-carrying capacities. Specifically, the cracking load, yield load, and ultimate load of S20, S21, and S22 increase by 10%–30%, 30%–50%, and 50%–90%, respectively, compared to S00. Additionally, there is an improvement in stiffness and energy absorption capacity. However, these strategies may have a dual effect on the specimens, resulting in a reduction in their ductility index. Finally, the tested beams were replicated using a three-dimensional finite element model, which has proved effective in predicting the behavior of such structures and, therefore, was found to be appropriate for use in future studies. [ABSTRACT FROM AUTHOR]

In order to study the difference of bearing capacity between polypropylene fiber reinforced engineered cementitious composite ( PP-ECC) bridge pier and ordinary concrete bridge pier under compressive-bending load, the flexural performance of six PP-ECC bridge piers and two ordinary concrete bridge piers were studied by quasi-static test. Combined with the failure process of PP-ECC bridge pier, the characteristic points of compressive-bending failure of PP-ECC bridge pier were determined. Then, based on the simplified constitutive model of PP-ECC material, the theoretical cracking, yield and ultimate load formulas of PP-ECC bridge pier were derived. The characteristic parameters of the simplified PP-ECC constitutive model were determined by uniaxial tensile and uniaxial compression tests of PP-ECC materials. The calculation results were verified by the experimental results, and the differences of flexural bearing capacity and maximum deformation of piers under different axial compression ratios and PP-ECC zone heights were compared. The results show that after PP-ECC bridge pier is cracked, PP-ECC in the tensile zone still work, and cooperates with the tensile steel bar to participate in the section force. When PP-ECC bridge pier reaches the ultimate load, the crack develops steadily, and there is no large area of concrete spalling in the protective layer of ordinary concrete pier. The maximum deformation of PP-ECC bridge piers under ultimate load are larger than that of ordinary concrete piers, and the increase of axial compression ratio will reduce the deformation capacity of piers. Increasing the height of PP-ECC zone at a higher axial compression ratio, the flexural capacity of the pier increases by 8. 8%. When using the simplified constitutive model to calculate the flexural bearing capacity of PP-ECC bridge pier feature points, the calculation accuracy reaches 0. 86 - 1. 13, and the variance analysis value is small, which has good calculation accuracy. [ABSTRACT FROM AUTHOR]

In this study, we propose the use of a fiber-reinforced plastic grid with polymer-cement-mortar (FRP Grid-PCM) to reinforce segment joints in tunnel shield linings. These joints play a crucial role in determining bearing capacity but are vulnerable to deterioration during operation. To investigate how to enhance the flexural performance of longitudinal shield lining joints, we built eccentric short column specimens by bolting two half-corbel columns together and tested them in the laboratory. The test program comprised two control specimens and three strengthened specimens with FRP grid applied on one side, away from the axial load. The tests varied two main parameters: loading eccentricity and the number of FRP grid layers. We conducted a detailed analysis of the failure process, bearing capacity, and bending stiffness of longitudinal joints under different conditions. Furthermore, we developed an analytical model to predict the flexural bearing capacity of longitudinal joints upgraded with the FRP Grid-PCM method and validated it through experimental results. The research demonstrates that the FRP grid effectively reduces joint opening and rotation angles while enhancing the bearing capacity of the short column, particularly with concurrent increases in loading eccentricity and the number of FRP grid layers. Overall, our findings offer a novel alternative for improving the flexural performance of longitudinal joints in shield tunnels. [ABSTRACT FROM AUTHOR]

The performance of joint connections in composite slabs is crucial for ensuring their bidirectional load-bearing capacity and overall structural integrity. To effectively address the challenge of protruding rebar in precast components, a new structural form of a tightly connected hollow concrete composite slab without protruding rebar on the slab side is proposed. To investigate the mechanical performance and failure modes of this slab-side tight-joint connected hollow concrete composite slab, bending performance tests under monotonic load were conducted on three tightly connected hollow composite slabs and one seamless hollow composite slab. The analysis focused on the failure modes, crack distribution, bending capacity, and bending stiffness of additional steel bars at the joints of the slabs. The results indicate that, under normal operating conditions, the flexural performance development of concrete hollow composite slabs with tightly connected slab sides is generally consistent with that of the non-spliced cast hollow composite slab. Under ultimate conditions, tearing or brittle fracture failure at the joint interface is likely to occur in the composite slabs, leading to a reduction in flexural bearing capacity. With an increase in joints, the bending capacity of the hollow composite slab decreases by 17.1%, Conversely, when joints are positioned away from the most stressed section, the flexural stiffness of the section increases by 13.5%. A comparison of experimental data and theoretical calculations indicates that the additional rebar at the joints effectively contributes to the lateral load transfer in the hollow composite slab, achieving bidirectional load-bearing capacity. This further validates that the design of the single-joint, tight-joint connected hollow concrete composite slab without protruding rebar meets the requirements for bidirectional load-bearing performance. [ABSTRACT FROM AUTHOR]

Concrete cracking is one of the important factors affecting the safety and durability of composite bridge structures. While the existing crack width calculation methods cannot accurately predict the crack width of ultrahigh-performance concrete (UHPC), this paper aims to investigate flexural crack performance (e.g., failure mode, crack width, and crack spacing) of an innovative composite deck structure comprising an I-steel beam and glass fiber‒reinforced polymer (GFRP) strips‒UHPC composite deck. Three GFRP‒UHPC composite slabs and two steel‒GFRP strips‒UHPC composite beams are designed to explore the cracking behaviors in transverse and longitudinal directions, respectively. The effects of reinforcement ratio and the steel fiber content on flexural cracking behavior are analyzed. The results showed that increasing the reinforcement ratio restricts the formation and growth of cracks and reduces the crack width and average crack spacing in the UHPC plate. However, the impact of steel fiber content is small. The steel‒GFRP strips‒UHPC composite beams fail owing to the yield of the I-steel beam and longitudinal reinforcement bar in the UHPC plate, while the GFRP‒UHPC composite slabs collapse as a result of the yield of reinforcement bar in the UHPC plate. Based on the existing test results, the formulas are proposed to estimate the reinforcement stresses and the maximum crack width in the steel‒GFRP strips‒UHPC composite deck structure, and the findings have indicated good agreement with the measured ones. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper describes the use of joints with bent bars and postcast ultrahigh‐performance concrete (UHPC) joints to enable formwork‐free and support‐free construction of composite slabs. To investigate their flexural performance, static loading tests on three full‐scale simply‐supported slabs and one monolithic slab were carried out. Flexural capacity, stiffness, and crack development were recorded, resulting on flexural failure experienced by all specimens. Main cracks of composite specimens developed along the UHPC–normal concrete interface, and cracks on both sides of the UHPC joint developed evenly, similar with that of the monolithic specimen. Besides, composite slabs and a monolithic slab showed similar flexural capacity. UHPC joint was not cracked when failure occurred, and bottom bars were anchored and connected in the UHPC joint, proving that the flexural anchorage method is feasible. The average strain of the composite specimen across the UHPC joint was still consistent with the assumption of plain section, and there was an approximate linear relationship between the expansion width of the joint at the bottom of the slab and the maximum crack width at bottom bars. Moreover, middle bars contributed to the flexural capacity and stiffness of composite specimens, while horse stool reinforcement may effectively prevent the interface shear failure on the composite interface. Based on test results, the formula to control cracking of UHPC is given in this paper. The design methods on flexural capacity, stiffness, and expansion width of composite slabs are also presented and discussed. [ABSTRACT FROM AUTHOR]

The utilization of recycled materials in concrete technology has gained significant attention in recent years, promoting sustainability and resource conservation. This paper investigates the behavior of lightweight self-compacting concrete (LWSCC) with recycled tire steel fibers (RTSFs). The effects of RTSFs on the flowability of the composite material and its density were assessed. The mechanical properties of the developed material were examined and beam tests were performed, aiming to assess its feasibility for structural applications. The compressive and tensile strengths were determined to evaluate the mechanical properties of the developed concrete mixtures. The beam tests were conducted to assess the flexural behavior of the beam specimens. Three different steel fiber contents of 0, 0.5, and 1% volumetric fractions of concrete were used in this study. The test results indicate that incorporating the fibers did not negatively impact the flowability and density of the LWSCC mixtures. In addition, the use of RTSFs enhanced the tensile strength of the developed concrete mixtures, where fibrous concrete showed increases in the splitting tensile strength in the range of 38 to 76% over that of non-fibrous concrete. On the other hand, the compressive strength of the mixtures was not affected. The test beams with RTSFs exhibited improved flexural performance in terms of delaying and controlling cracking, enhancing ultimate load, and increasing ductility. Compared with the control non-fibrous beam, the increases in the cracking load, ultimate load, and ductility index were up to 63.8, 9.3, and 16%, respectively. The test results of the beams were compared with theoretical predictions, and good agreement was found. [ABSTRACT FROM AUTHOR]

To explore the mechanical properties of reinforced concrete beams reinforced by steel plates of various shapes, reinforced concrete beams reinforced with steel plates and corrugated steel plates were tested via a two-point loading test. Based on tests, further investigations investigated the deflection of the sample under different loads and the influence of corrugated steel plate properties (thickness, wave height, strength) on the flexural capacity of the reinforced beam, culminating in the development of corresponding numerical models. The findings indicate that the corrugated steel plate has the best reinforcing effect. In contrast to reinforcement utilizing steel plates containing an equivalent quantity of steel material, the corrugated steel plate augments the space within the reinforced beam and the lower shaft region, enhancing the efficiency of the upper compressive steel reinforcement and concrete in bearing loads, bolstering overall load-bearing potential, and exhibiting superior resistance to deformation. To maintain the ductility of the specimen, interface failure must be prevented. Too high wave height will affect the coordination of wave thickness and strength and inhibit the improvement of flexural performance. Therefore, reinforcement design should prioritize wave height determination.

Fibre alignment and 3D concrete printing have become increasingly popular in research and industry while these technologies face a lack of deep integration. Aligning steel fibres in concrete is different from in mortar systems due to the interference originated from coarse aggregate. This paper reports the results of an experimental programme investigating manufacturing reinforced concrete by placing concrete and aligned steel fibres in multi-layer in replicating the 3D printing. The X-ray CT scan was deployed to characterise the fibre distribution by digitally colouring the fibre orientation deviation and calculating the fibre orientation efficiency which reached 0.77 in this study. 4-point bending tests were performed on beam specimens of the multi-layer aligned steel fibre reinforced concrete to assess the flexural performance. Alignment of the steel fibres resulted in 56 % increase of the ultimate load resistance compared to that being two-dimensionally distributed. A model for estimating the tensile strength of multi-layer aligned steel fibre reinforced concrete was developed with consideration of the layer proximity to the neutral axis of the beam. Change of the concrete composition was observed to yield influences on the interface bond performance between the fibre layer and concrete and the influences were quantified by correlating experimental data. This study revealed that the space characteristics of the fibre distribution in multi-layer required concrete mix constituent of good rheology to develop adequate bond performance for further additive manufacturing without formwork.

The aim of this study is to evaluate numerically the effects of carbon fiber-reinforced polymer (CFRP) sheets strengthening on the flexural performance of high-strength concrete (HSC) beam using ABAQUS 3D finite element (FE) modeling software. The developed FE models were verified against the experimental results found in literature. The FE models can accurately estimate the performance of CFRP-strengthened high-strength reinforced concrete (RC) beams. Subsequent parametric analysis was performed to assess the performance of CFRP-strengthened concrete beams considering various parameters including compressive strength of concrete, CFRP width, thickness, length, number of CFRP layers, and CFRP strengthening schemes. Based on the results of FE analysis. It was demonstrated that using HSC significantly enhances the performance of CFRP-strengthened RC beams. It was also confirmed that width, thickness, and layer number of CFRP sheets improve the flexural behavior of CFRP-strengthened HSC beams by increasing the ultimate loads and strain-hardening behavior of the specimens. The strengthening schemes contribute to delaying or inhabiting the debonding especially when the CFRP sheets are added along the bottom of the beams. It was demonstrated that using CFRP sheets U-wrapping contributes to the prevention or delay of debonding and increases the capability of resisting the stress imposed on the concrete. Therefore, installing the CFRP sheets at the bottom face of beam below the tensile reinforcement enhances the performance of CFRP-strengthened HSC beams.

Residual strength and structural performance of reinforced concrete (RC) structures subjected to rebar corrosion need to be precisely evaluated for an efficient rehabilitation process. However, the performance of deteriorated structures cannot be specified by using design methods since the damaged conditions are different in each type of structures due to corrosion degree, corrosion position, environmental condition. This study first presents an experimental investigation on the flexural performance of RC beam subjected to rebar corrosion. To complement the test data, an analytical corrosion model developed by the authors, which is based on Rigid Body Spring Method (RBSM), was employed. The results obtained from both analytical model and experiment confirmed that the corroded beam appeared to obtain a significantly lower bending stiffness and lower flexural capacity than those of the sound beam. The developed corrosion model can be able to capture the load-displacement curve of experimental results with good agreement.

Additive manufacturing (AM), particularly fused filament fabrication (FFF), has gained significant attention for its design flexibility and cost-effectiveness. This study focuses on optimizing FFF parameters that employ response surface methodology (RSM) to enhance the flexural performance of polyethylene terephthalate glycol (PETG) parts. Three essential parameters—layer height, print speed, and nozzle temperature—were varied, and their effects on flexural strength, flexural modulus, flexural toughness for ultimate strength, flexural toughness at 5% strain, and strain at ultimate strength were evaluated. Based on a Box–Behnken design, the experiments revealed significant effects of these parameters on the mechanical responses. The analysis of variance (ANOVA) indicates that layer height predominantly affects flexural modulus and toughness, while nozzle temperature significantly impacts flexural strength. The RSM models exhibited high accuracy, with R2 values exceeding 99%. Optimal parameter combinations yield remarkable improvements: flexural strength reached 39.55 MPa, flexural modulus peaked at 1344.60 MPa, flexural toughness for ultimate strength reached 218.22 J/mm3, flexural toughness at 5% strain reached 381.47 J/mm3, and strain at ultimate strength reached 3.50%. Validation experiments confirm the effectiveness of the optimization, with errors below 3.17%. [ABSTRACT FROM AUTHOR]

The use of seawater sea sand concrete (SSSC) and fiber-reinforced polymer (FRP) has broad application prospect in island and coastal areas. However, the elastic modulus of FRP reinforcement is obviously lower than that of ordinary steel reinforcement, and the properties of SSSC are different from that of ordinary concrete, which results in a limit in the bearing capacity and stiffness of structures. In order to improve the flexural performance of FRP-reinforced SSSC beams, a novel SSSC beam with built-in glass FRP (GFRP) tubes was proposed in this study. Referring to many large-scale beam experiments, one specimen was used for one situation to illustrate the study considering costs and feasibility. Firstly, flexural performance tests of SSSC beams with GFRP tubes were conducted. Then, the effects of the GFRP tubes' height, the strength grades of concrete inside and outside the GFRP tubes, and the GFRP reinforcement ratio on the flexural behaviors of the beams were investigated. In addition, the concept of capacity reserve was proposed to assess the ductility of the beams, and the interaction between the concrete outside the GFRP tube, the GFRP tube and concrete inside the tube was discussed. Finally, the formulas for the normal section bearing capacity of beams with built-in GFRP tubes were derived and verified. Compared to the beam without GFRP tubes, under the same conditions, the ultimate bearing capacities of the SSSC beam with 80 mm, 100, and 200 mm height GFRP tubes were increased by 17.67 kN, 24.52 kN, and 144.42 kN, respectively. [ABSTRACT FROM AUTHOR]

In this study, the flexural and cracking performance of ultra-high performance concrete (UHPC) beams reinforced with high-strength steel reinforcement (HSSR) is investigated. Four beam specimens, including two UHPC beams and two normal-strength concrete (NSC) beams with different HSSR ratios were tested under flexure. The effect of concrete type and HSSR ratio on the flexural behaviour was evaluated. The failure mode, load-deflection response, stiffness, ductility and strain of the concrete and HSSR were discussed. Test results show that UHPC coupled with HSSR achieved better flexural performance and the ability to limit the development of the crack. The flexural capacity, deflection and stiffness for the UHPC beams were increased but the ductility was decreased as the HSSR ratio increased. The flexural behaviors of UHPC beams were predicted by section analysis. The flexural performance of HSSR-UHPC beams should consider the contribution of steel fibre to the tensile strength. Considering the influence of steel fibre, an equation was proposed to predict the average crack spacing. UHPC beams showed excellent agreement with the experimental results. The maximum crack width of 630 MPa reinforced UHPC beams was calculated by NF P 18-710 in accordance with the test results. [ABSTRACT FROM AUTHOR]

The structural performance improvement of concrete members is by far a crucial theoretical issue for engineers, and the development of modern smart and composite materials makes it possible to gradually enhance the durability design of the concrete structure. In this study, six beams of the same size and reinforcement ratio, the proposed composite beam (SMA-GFRP-ECC) and five comparative beams (RC, R-ECC, SS-ECC, GFRP-ECC, SMA-ECC), were designed and tested under low-cycle unidirectional cyclic loading and unloading conditions. The energy dissipation capacity, displacement ductility, residual deformation, and self-repairing performance of each concrete beam were evaluated. Afterward, a concise calculation model for the studied composite beam is deduced and developed based on the existing relevant constitutive models and concrete assumptions. The test results indicate that compared with RC beams, the composite reinforced ECC beams show obvious multi-cracking and smaller crack width during the loading process and have good bending ductility. The innovative SMA-GFRP-ECC beam is capable of a high bearing capacity, ductility, and damage self-repairing. The new proposed beam has more than 80% of the maximum crack width recovery capacity during unloading. Hence, the proposed SMA-GFRP-ECC beam is a rather good first attempt of strengthened beams, combining the advantages of SMA, GFRP, and ECC. [ABSTRACT FROM AUTHOR]

Reinforcing seawater sea-sand concrete (SSC) with basalt fiberreinforced polymer (BFRP) bars can adequately resolve chloride corrosion issues. However, the multiple-element ions in seawater and sea sand can increase the concrete alkalinity and accelerate the degradation of BFRP bars. This study aims to enhance the durability performance of BFRP-SSC beams by regulating concrete alkalinity. A low-alkalinity SSC (L-SSC) is designed by incorporating a high-volume content of fly ash and silica fume. A total of 16 BFRP-SSC beams were designed based on the current standards and prepared using normal SSC (N-SSC) and L-SSC. The beam flexural performances before and after long-term exposure are characterized through the four-point bending test. The test results indicate that exposure in the simulated marine environment can reduce the load-bearing capacity and change the failure mode of BFRP beams with N-SSC. After exposure at 55°C for 4 months, the load-bearing capacity of the BFRP-SSC beams was reduced by 70.0%. Moreover, a slight enhancement of load-bearing capacity and ductility of the BFRP-L-SSC beams was observed due to the enhanced interface performance with further concrete curing. Furthermore, the long-term performance of the sand-coated BFRP bars is better than that of the BFRP bars with deep thread. The load-bearing capacity of the BFRP-L-SSC beams increased by approximately 20% after 4 months of accelerated aging due to concrete strength growth, and the BFRP-L-SSC beams maintained the concrete crushing failure mode after exposure. Finally, a loadbearing capacity calculation model for the BFRP-SSC beams is proposed based on the experimental investigation, and its prediction accuracy is higher than that of the current standards. This study can serve as a valuable reference for applying BFRP-SSC structures in the marine environment. [ABSTRACT FROM AUTHOR]

To improve the flexural performance of damaged reinforced concrete T-beams, a method of filling ultra-high performance concrete (UHPC) in the damaged area was adopted. Experimental studies were conducted on two UHPC-reinforced concrete T-beams with different lengths of damaged areas and one undamaged concrete T-beam as a reference. Crack distribution, failure modes, cracking loads, flexural capacities, and strain variation of the specimens were analyzed. Subsequently, a nonlinear finite element (FE) model of the UHPC-reinforced Tbeam was developed using ABAQUS, and the FE model results were compared with the experimental results to validate the accuracy of the FE simulation method. The results indicated that the two UHPC-reinforced T-beams exhibited a similar flexural failure process to the undamaged T-beam. The longitudinal tensile strain distribution at the mid-span section showed that the composite section formed by the filling of UHPC in the damaged region still adhered the assumption of the planar section. Owing to the excellent bond performance between UHPC and the existing concrete, the main cracks of the UHPCreinforced T-beams appeared in the chiseled area, and the crack widths of the UHPC-reinforced T-beams under the same load were smaller than those of the reference T-beam. Overall, the reinforcing method of filling UHPC in the damaged region can restore or even enhance the flexural performance of the damaged reinforced concrete T-beams. [ABSTRACT FROM AUTHOR]

Flexural performance of joints is critical for prefabricated structures. This study presents a novel channel steel-bolt (CB) joint for prefabricated subway stations. Full-scale tests are carried out to investigate the flexural behavior of the CB joint under the design loads of the test-case station. In addition, a three dimensional (3D) finite element (FE) model of the CB joint is established, incorporating viscous contact to simulate the bonding and detachment behaviors of the interface between channel steel and concrete. Based on the 3D FE model, the study examines the flexural bearing mechanism and influencing factors for the flexural performance of the CB joint. The results indicate that the flexural behavior of the CB joint exhibits significant nonlinear characteristics, which can be divided into four stages. To illustrate the piecewise linearity of the bending moment-rotational angle curve, a four-stage simplified model is proposed, which is easily applicable in engineering practice. The study reveals that axial force can enhance the flexural capacity of the CB joint, while the preload of the bolt has a negligible effect. The flexural capacity of the CB joint is approximate twice the value of the designed bending moment, demonstrating that the joint is suitable for the test-case station. [ABSTRACT FROM AUTHOR]

The flexural performance of RC beams strengthened with a novel high-strength and high-toughness epoxy mortar thin layer was investigated through four-point flexural tests on two contrast beams and two strengthened beams. The effects of this strengthening method on the failure modes, crack distribution, load–deflection curves, and bearing capacity of the RC beams with two reinforcement ratios were studied. The experimental results revealed that the contrast beams exhibited the typical bending failure modes where the failure mode of the reinforced beam is the yielding of the tensile reinforcement of the original beam and then fracture damage of the new epoxy mortar-reinforced thin layer. No debonding phenomenon was observed between the reinforced thin layer and the original concrete, and no visible cracks appeared before the tensile failure occurred in the thin layer. The cracks in the reinforced beams developed slowly, increased in number, and decreased significantly in width and spacing. The stiffness of the strengthened beam increased significantly, while its deformation ductility coefficient noticeably decreased. Compared to the corresponding contrast beams, the cracking load for strengthened beams A1 and B1 increased by 14% and 23%, respectively; the yield load increased by 32% and 40%, respectively; and the peak load increased by 18% and 17%, respectively. Finally, a calculation method for the flexural bearing capacity of RC beams strengthened with the novel epoxy mortar thin layer based on the flat section assumption was proposed. The calculated values showed a good agreement with the experimental values (with errors at −11.73% and 4.14%, respectively), providing a valuable reference for further research and application related to this kind of reinforcement method. [ABSTRACT FROM AUTHOR]

To optimally use the excellent mechanical properties of ultrahigh performance concrete (UHPC), this study experimentally investigated the flexural behavior of 10 lightweight steel-UHPC composite beams constructed using thin UHPC slabs and ultrashort studs. The influences of stud spacing, slab thickness, stud aspect ratio (height-to-diameter ratio), and shear span ratio on moment capacities, postcracking and postyielding strength, and deflection increments were investigated, along with the observations of failure modes, crack patterns, strain distributions, slip/uplift behavior, and unloading response after failure. Experimental results indicated a 9% decrease in the moment capacity with a 22% larger ultimate deflection as the full shear connection degree decreased to 0.5. A decrease in the stud aspect ratio from 1.5 to 1.0 caused similar loads but 45% larger ultimate deflections due to the uplifting and splitting behavior of the composite beams. An increase in the thickness of the UHPC slabs from 35 to 55 mm increased the postyielding strength and deformability by relieving the local UHPC crushing failure. With only half and one-third the thickness of normal concrete slabs, the 35- and 55-mm-thick slabs provided an elastic flexural stiffness similar to and 26% higher than that of the composite sections, respectively, with higher ductility. The current design code accurately predicts the bearing capacity of ultrathin UHPC–steel composite beams. In future research, the coupling effects of both interfacial slip and uplift on the overall deflection of such composite systems should be investigated. [ABSTRACT FROM AUTHOR]

In recent years, the application of textile reinforced mortar (TRM) as an overlay has become an important method for repairing and strengthening old masonry structures. However, the quantitative analysis and design of TRM-strengthened reinforced concrete (RC) beams are still limited. To address this gap, a nonlinear finite element (FE) model is proposed in this study to simulate the flexural behavior of TRM-strengthened RC beams. The developed model is validated using experimental results and subsequently utilized for the design of TRM-strengthened RC beams. Various TRM design parameters, including the number of textile layers, textile longitudinal length, and textile mesh size, are parametrically investigated. The modelling results reveal that increasing the number of textile layers and longitudinal length while decreasing the textile mesh size can enhance the bending strength of TRM-strengthened RC beams. Furthermore, an analytical model is proposed to predict the flexural strength of TRM-strengthened RC beams, facilitating rapid strength estimation of TRM-strengthened RC beams. The predicted results demonstrate good agreement with the numerical simulation results. The established FE models can predict the bending performance of TRM-strengthened RC beams under different reinforcement conditions, and the simulation outcomes can provide valuable guidance for their design.

Fiberglass-reinforced ultraviolet cured-in-place pipe (UV–CIPP) composite material is one of the most trenchless materials for underground pipelines’ rehabilitation. In this paper, the bending resistance and damage evolution mechanism of glass fiber-reinforced UV-CIPP composites were investigated under the influence of glass fiber structure, the number of layers of glass fibers, the angle of fiber layups, and the thickness of the material by high-definition video, SEM and infrared thermal imaging. The results indicate that the damage evolution modes of UV-CIPP materials mainly include: (1) fiber pull-out and overall fiber bundle tensile failure caused by strong interfacial bonding, (2) fiber/matrix debonding and delamination, fiber fracture, and matrix cracking caused by weak interfacial bonding. Furthermore, among the seven different fiberglass structures of UV-CIPP materials, the [0°/90°] warp-knit axial/short-cut felt fiberglass fabric exhibit the best flexural performance, with a bending strength of 412 MPa and a bending modulus of 16.1 GPa for the 4 layers glass fiber fabric. Moreover, in the bending process of UV-CIPP materials, the surface temperature rises primarily due to fiber break, the temperature transition aligning with the stress transition. Finally, the energy release is mainly caused by the failure of the glass fibers, but the resin contributed comparatively little. This study provides a scientific reference for the structural design and optimization of UV-CIPP materials.