Search Results (2,705)

This study investigates the flexural behavior, load-carrying capacity, and crack propagation of concrete beams reinforced with hybrid glass-fiber-reinforced polymer (GFRP) and steel bars. To evaluate the structural performance, concrete beam specimens with cross-sectional dimensions of 150 mm × 300 mm and a total length of 2050 mm were fabricated using a design concrete compressive strength of 35 MPa and tested under flexural loading. Each tested specimen featured a distinct hybrid reinforcement configuration to investigate the influence of bar arrangement on the mechanical behavior. Flexural cracks were systematically monitored using a crack-width comparator gauge at specific loading stages, accounting for key milestones such as ultimate load capacity and sudden load drops. The experimental findings were complemented by an analytical model to validate the performance parameters and predict the ultimate capacity. The results demonstrate that the specific configuration and arrangement of hybrid reinforcement significantly influence the post-cracking stiffness and crack growth. Specifically, the hybrid configuration effectively balances the ductile response of steel with the brittle behavior of GFRP, achieving significant control over serviceability crack widths and an enhanced ultimate load-carrying capacity. Experimental results indicated that for elements exhibiting identical axial stiffness, the reinforcement layering configuration provided a 66% improvement in the deformability factor alongside a 10% enhancement in the load-carrying capacity. It is recommended that the steel tension reinforcement be positioned in the inner layer at a spacing of about two times the GFRP bar diameter to mitigate corrosion risks. Additionally, it was established that the theoretical load capacity accounted for 70% to 86% of the experimental load capacity. Full article

Prefabricated steel–concrete composite bridge decks are widely used in the construction of long-span bridges due to their excellent mechanical performance and rapid construction speed. However, the joints in these decks are prone to tensile failure under negative bending moments, which limits the overall mechanical behavior of the structure. To improve the flexural–tensile performance of joints in prefabricated steel–concrete composite bridge decks under negative bending moments, a novel prefabricated steel grid–hybrid fiber concrete (PSG-HFC) composite bridge deck with closed-loop steel bar joints is proposed. Basic unit specimens of the composite bridge deck with closed-loop steel bar joints were designed and fabricated. Both physical and numerical experiments, including finite element modeling and model refinement, were conducted to clarify the mechanical response and failure mode of closed-loop steel bar joints under negative bending moments and to identify their rational structural parameters. Theoretical formula for calculating the flexural capacity of the closed-loop steel bar joints based on the strut-and-tie model theory was derived and verified. The results indicate that the failure mode of the novel PSG-HFC composite bridge deck under negative bending moments is typical plastic failure, with the ultimate failure mode being flexural–tensile failure at the joint section. The loading process includes elastic, elastoplastic, and plastic stages. From the perspectives of improving flexural capacity and fully utilizing high-strength materials, the rational structural parameters for the closed-loop steel bar joints are as follows: lap length of closed-loop steel bars of 230~250 mm, spacing of closed-loop steel bars of 130~150 mm, and bending radius of closed-loop steel bars of 70~90 mm. The maximum deviation between the theoretical formula results and the experimental and finite element numerical simulation results is 8.21%, indicating that the proposed formula is suitable for calculating and analyzing the flexural capacity of the joints in this novel composite bridge deck. This study reveals that the proposed closed-loop steel bar joint enables a ductile flexural–tensile failure mode in PSG-HFC composite deck under negative bending moments, and provides a validated theoretical formula for advancing the understanding of joint design in fiber-reinforced concrete structures. Full article

Reinforced concrete beams with a fiber-reinforced polymer (FRP) plate bonded to their soffit, known as FRP-plated RC beams, commonly fail due to premature debonding of the FRP plate, limiting the utilization of the FRP strength. Inclined U-jacketing has been demonstrated to be effective as the end anchorage for mitigating debonding failures. The mechanism by which the inclined U-jacketing mitigates debonding failure remains unclear, and no design approach has been developed. Therefore, the present study has been conducted to investigate the mitigating effects of the key parameters of the inclined U-jacket through a series of four-point bending tests and systematic modeling. The test results indicate that both the inclination angle and the chamfer radius significantly affected the bond behavior of inclined U-jacket-to-concrete joints. Compared with the 45° configuration, reducing the inclination angle to 30° increased the peak load and peak displacement by 85.4% and 81.6%, respectively. In contrast, the effect of U-jacket side height became negligible once an effective bonded height had been reached, as increasing the side height from 75 mm to 120 mm changed the peak load by only 2.17%. In addition, a pre-peak parameter identification framework based on a power-function-type cohesive element constitutive relationship was proposed and validated. By analyzing the power-function parameters, namely the coefficient a and exponent b, the influences of U-jacket geometric variables on interfacial mechanical behavior were quantitatively characterized. The proposed approach provides experimentally verifiable parameterization to support the optimized design of inclined U-jacket anchorage systems. Full article

This study investigates hybrid fiber-reinforced polymer (FRP)–steel-reinforced concrete (RC) beams by using three-dimensional finite element models. The research systematically analyzes the influence of key parameters, including FRP type, FRP bar ratio (ρ_f), the ratio of FRP to total reinforcement (ρ_f/ρ_t), and concrete strength. The load–deflection response of the hybrid RC beams is analyzed in detail. The results show that the investigated parameters have a relatively limited influence on the cracking moment, but significantly affect both the yield and ultimate moments. When ρ_f/ρ_t increases from 0 to 0.75, the yield moment decreases by up to 44.34%. When ρ_f increases from 0.55% to 0.88%, the yield moment increases by 50.63%. Meanwhile, increasing the concrete strength significantly enhances the ultimate moment, with a maximum increase of 38.46%. In addition, an energy ductility index is adopted to quantitatively evaluate the structural ductility. The results indicate that the energy ductility index is consistently lower than the conventional ductility index. Finally, to improve the accuracy of theoretical predictions, a semi-empirical simplified formula is proposed for estimating the FRP bar stress at the ultimate state of hybrid beams. The verification results show that the proposed prediction method agrees well with the experimental data, demonstrating that the simplified formula has good applicability and reliability within the parameter range investigated in this study. Full article

Basalt fiber (BF) is an effective reinforcement for improving concrete’s mechanical properties and crack resistance due to its high tensile strength and bridging ability. To investigate the influence of fiber length combinations on the mechanical performance of concrete, basalt fiber-reinforced concrete (BFRC) specimens were prepared using single and hybrid blending methods. Compressive and splitting tensile tests, scanning electron microscopy, and numerical simulations were conducted to evaluate the effects of fiber content and length hybridization, and analyze the possible reinforcement mechanisms. Results showed that for single-blended BFRC with 18 mm BF, both compressive and tensile strengths peaked at a 0.2% dosage, then declined. Conversely, the strengths of hybrid BFRC continuously increased with fiber content, reaching 33.00 MPa and 2.38 MPa at a 0.3% dosage, significantly outperforming the single-length fiber systems. Microstructural observations and numerical analyses suggested that fibers with different lengths contributed to complementary reinforcement effects during the loading process. The improved performance was attributed to the combined effects of crack bridging and stress redistribution provided by fibers with different lengths. Full article

The enhancement of reinforced concrete (RC) beams using externally bonded carbon fiber-reinforced polymer (CFRP) systems and shape memory alloy (SMA) systems has been growing in recent years, but its comparison is not generalizable unless it is based on an equal basis of stiffness. In this paper, an equivalent axial stiffness approach is applied to study the effect of CFRP and SMA plates on RC beams. The following four beam configurations were considered: Unstrengthened control beam, beam strengthened with a 5 mm SMA plate, beam strengthened with a 5 mm CFRP plate, and beam strengthened with an 18.96 mm SMA plate, which was chosen to provide similar axial stiffness as the 5 mm CFRP plate. The finite element model was created using ANSYS and compared with experimental results from the literature, and was further validated with a mesh sensitivity study. The test results indicated that all strengthening systems had a better flexural response than the control beam, but with varying degrees of improvement depending heavily on the amount of stiffness provided by the strengthening material. The control beam showed the first signs of cracking and had the lowest resistance. The moderate improvement was seen in the 5 mm SMA plate, which increased the load corresponding to the first crack to 50.2 kN from 41.7 kN. The 5 mm CFRP beam and the stiffness-equivalent SMA 18.96 mm beam, on the other hand, were able to significantly improve the first-crack load to 77.6 kN and 82.97 kN, respectively. In terms of flexural strengthening performance, stiffness equivalence takes into account the first-crack load of the performance of the SMA beam, which shows that SMA can provide flexural strengthening performance comparable to, and even higher than, that of the CFRP system in terms of crack-initiation resistance. The overall performance of the strengthened beams was also found to be better than the control beam in terms of the post-cracking stiffness and moment—curvature relationships. These results indicate that a stiffness-equivalent framework is more rational than comparing the two strengthening systems directly in terms of thickness, and in this way, the ability to compare the advantages and disadvantages of the two systems. The conclusions, however, should be understood based on the assumptions of the numerical model, such as the perfect bond assumption at the interface and the use of a simplified monotonic material model used for SMA. Additional studies should be conducted that incorporate debonding, cyclic loading, temperature, and field size verification. Full article

Reinforced concrete (RC) beams are crucial load-bearing members in multistory buildings. Due to architectural modifications, increased service loads, or construction deficiencies, these members often require flexural strengthening to restore or enhance their performance. The use of prefabricated reinforced ultra-high-performance fiber-reinforced concrete (UHPFRC) plates has recently emerged as a promising strengthening technique. When attached to the tension, compression, or both faces of RC beams, these plates provide noteworthy structural benefits. This study presents a detailed investigation—using nonlinear calibrated finite element (FE) models—into the flexural strengthening of RC beams using reinforced UHPFRC plates. A total of 18 large-scale RC beams were explored, including two control specimens and 16 strengthened beams. The control specimens comprised one beam with a tensile steel ratio close to the minimum code thresholds and another with a conventional reinforcement ratio typical of standard design. The strengthening schemes were developed to enhance the flexural capacity of the first control beam to a level comparable to the ideal reference specimen. A simplified analytical tool was developed to estimate the peak load of control and strengthened specimens for the design of upgrading schemes. The parametric study in the FE matrix examined the effects of reinforcement type within the UHPFRC plates (steel or glass fiber-reinforced-polymer (GFRP) bars), plate location (tension side, compression side, or both), bonding method (adhesive, mechanical, or combined), and end anchorage condition (with or without fiber-reinforced polymer (FRP) U-wraps). The beams’ behavior was evaluated in terms of load-deflection response, stiffness, and failure mode. The results demonstrated that combined adhesive–mechanical bonding with compression-side UHPFRC plates provided the most efficient and reliable strengthening technique. Full article

This study investigates the blast-protective performance of RC slab strengthened on the blast face with various concrete protective layers under contact-detonation loading. The research focuses on analyzing shock wave propagation characteristics, peak pressures at measurement points, energy absorption capacities of the protective layers, the development of damage, and the governing failure mechanisms of the RC slab. The protective layers used for structural reinforcement include Steel Fiber-Reinforced Cellular Concrete (SFR-CC), Asphalt Concrete (AC), Rubberized Concrete (RBC), and Foamed Concrete (FC). Among these, the maximum support rotation angle of the structure strengthened with the SFR-CC concrete layer (T-1) is 0.20°, indicating significantly less damage and deformation compared to other protective schemes. Based on the damage coefficient calculated from the remaining sectional moment of inertia of the protected RC slabs, the destruction grades of the structures at different concrete protective schemes were classified. Among these, the SFR-CC layer exhibits the most effective attenuation of shock wave peak pressure. Additionally, the maximum support rotation angle of the structure strengthened with the SFR-CC concrete layer is 0.20°, indicating significantly less damage and deformation compared to other protective schemes. Damage grades were assigned according to a coefficient derived from the residual sectional moment of inertia of the protected RC slabs. The SFR-CC configuration (T-1) gives the lowest damage index, 0.178, approximately 64.5% below that of the NC scheme, and is classified as slight damage. In contrast to the severe damage sustained by the protected RC slabs strengthened with the NC concrete scheme, those strengthened with the AC, RBC, and FC protective layer schemes exhibit only a moderate damage grade. Empirical formulas predicting the damage index of protected structures under the combined effects of varying blast charges and concrete layer thicknesses were further developed for rapid damage assessment. Full article

Externally bonded fiber-reinforced polymer (EB-FRP) systems have been extensively investigated for tension strengthening concrete structures. Interpretation of the available evidence remains challenging because experimental methods, specimen scales, material systems, anchorage configurations, and reporting practices vary substantially across the literature. This systematic review synthesized 174 peer-reviewed studies published between 1994 and 2026, comprising 3908 experimental test results and 42 analytical formulations addressing unanchored and anchored EB-FRP systems. Review findings showed that bond performance in unanchored systems is governed primarily by FRP stiffness, bond geometry, concrete properties, adhesive behavior, surface preparation, and environmental exposure. These parameters influence bond capacity, debonding strain, effective bond length, and failure mode. Anchored configurations consistently enhanced force transfer, delayed premature debonding, and improved load-carrying capacity relative to unanchored systems. Unanchored systems dominated the available evidence base with 3162 test results, whereas only 96 multi-anchor system tests were identified, highlighting limited understanding of anchor interaction and load redistribution mechanisms. CFRP represented the dominant material system, while substantially fewer studies investigated GFRP, BFRP, and AFRP systems. Existing strength models generally captured specific failure mechanisms within their calibration ranges but demonstrated limited transferability across different geometries, loading conditions, anchorage configurations, and environmental conditions. Limited evidence remains available for scale transfer, durability degradation, anchor strip interaction, and multi-anchor load sharing under field-representative conditions. Future research should focus on standardized benchmarking procedures, large-scale validation programs, durability-informed design approaches, experimentally validated numerical modeling, and unified design provisions for EB-FRP strengthening systems. Full article

To address early-age cracking in concrete walls of hydraulic structures such as ship locks, basalt fibers (BFs) were incorporated as a reinforcement strategy. The effects of varying BF dosages and lengths on the workability, mechanical strength, and crack resistance of concrete were systematically evaluated. Furthermore, the internal microstructure was examined using scanning electron microscopy (SEM), and the durability performance, including impermeability, freeze–thaw resistance, and abrasion resistance, was assessed. The results indicate that workability decreased with increasing fiber content and length. The highest mechanical performance among tested mixes was achieved with 0.1% BF of 9 mm length, increasing 7-day and 28-day compressive strength by 17.47% and 22.59%, respectively, compared to plain concrete. The greatest crack resistance was observed with 0.2% BF of 18 mm length, delaying cracking by 150% and reducing crack width by 85%. Durability tests showed that a 0.2%-18 mm BF mix reduced water permeability depth by 47.37% and a 0.3% BF content optimized abrasion resistance. Freeze–thaw cycles indicated that a 0.3% fiber content effectively maintained the relative dynamic elastic modulus. SEM analysis revealed that BFs act as micro-bridges within the matrix, optimizing pore structure, inhibiting micro-crack propagation, and enhancing concrete density. This study evaluates BF-reinforced concrete and provides a practical reference for improving crack resistance and long-term durability in ship lock structures. Full article

The rate of change of the normalized Cumulative Counts of the acoustic hits, recorded while marble specimens are compressed uniaxially, and is analyzed in the Natural Time Domain. The analysis reveals the systematic presence of a characteristic plateau that could potentially serve as a precursor to fracture. Starting initially well below unity, the specific parameter increases towards a limit equal to one and is stabilized around this value with minor fluctuations. The starting “instant” of this plateau is linearly related to the loading rate applied. This “instant” and the respective load level are in very good agreement with the abrupt change of the average rate of generation of acoustic signals. These findings are juxtaposed to the respective ones drawn by analyzing data from previously published experimental protocols involving marble specimens of varying geometries subjected to various loading schemes and are found highly consistent with each other. The same holds true for the agreement between the data of the present study and recently published ones dealing with both plain and fiber-reinforced concrete beams. This consistency suggests that the conclusions drawn exhibit a kind of universality, highlighting the potential of this plateau’s onset to serve as a reliable index for Structural Health Monitoring purposes. Full article

To investigate the impact resistance of hybrid fiber-reinforced recycled aggregate concrete (RAC) under dry–wet cycles and sulfate attack, hybrid fiber-reinforced recycled aggregate concrete (RAC) was prepared. Dynamic impact compression experiments were conducted using an SHPB test device with a 50 mm diameter. The microstructure of recycled aggregate concrete (RAC) within dry–wet cycles and sulfate attack was examined using SEM. The results indicate that the dynamic compressive strength first rises and then declines with the rise in dry–wet cycles, and increases with the increase in the average strain rate. When the number of dry–wet cycles reaches 16, the dynamic compressive strength reaches its peak, with the B4S6 group achieving a maximum dynamic compressive strength of 59.02 MPa. The dynamic elastic modulus follows a good quadratic parabolic function distribution with respect to the number of dry–wet cycles. Both the incident energy and dissipated energy density initially rise and then reduce with increasing dry–wet cycles. The energy values of RAC with different fiber types follow the order: B4S6 > S6 > B4 > RAC. Under impact loading, the strain rate–strain time history curve of recycled aggregate concrete (RAC) exhibits the change of “increase–decrease–stable–decrease”. With increasing dry–wet cycles, the degree of fragmentation of recycled aggregate concrete (RAC) first increases and then decreases, the fractal dimension first decreases and then increases, and the average particle size first increases and then decreases. SEM results and microscopic reaction mechanisms reveal that in the early stage of dry–wet cycles, sulfate ions generate ettringite and gypsum within the recycled aggregate concrete (RAC), which fill internal cracks and pores, making the concrete denser and enhancing its mechanical properties. Towards the end of the dry–wet cycle, the amount of expansive ettringite and gypsum inside the recycled aggregate concrete (RAC) increases, leading to a sharp increase in pore wall stress, which induces new microcracks in the specimens, manifesting as a decline in mechanical properties at the macroscopic level. Full article

Basalt-fiber-reinforced recycled aggregate concrete (BFRAC) produced with 100% recycled coarse aggregate is still constrained by the inferior quality of recycled aggregate and the difficulty of optimizing fiber reinforcement parameters. This study investigated the effects of basalt fiber length configuration and dosage on the mechanical performance and pore structure of recycled aggregate concrete incorporating recycled coarse aggregate subjected to two-step pretreatment with nano-silica and cement slurry. Four fiber length configurations, namely 6, 12, and 24 mm and a mixed-length system, were evaluated at volume fractions of 0.1, 0.2, and 0.3%. The reinforcing effect was assessed through compressive strength, splitting tensile strength, scanning electron microscopy, mercury intrusion porosimetry, and statistical analysis. The pretreatment improved recycled aggregate quality, reducing water absorption from 4.97% to 3.11% and crushing index from 20.5% to 13.4%. Basalt fiber incorporation generally enhanced mechanical performance, although the response depended on fiber length and dosage. At 28 days, BF24V1 achieved the highest compressive strength, whereas BFmixV1 exhibited the best overall performance by combining high compressive strength with the highest splitting tensile strength. Relative to the average performance of the corresponding single-length mixtures at the same dosage, the mixed-length system showed a positive synergistic effect. Microstructural observations indicated that this behavior was associated with more effective crack bridging and refinement of the pore-size distribution. The results demonstrate that a low-dosage mixed-length basalt fiber system provides an effective route for upgrading pretreated waste-derived aggregate into higher-performance recycled aggregate concrete. Full article

The present study investigates the development of non-autoclaved aerated concrete (NAAC) incorporating rice husk ash (RHA)-derived amorphous silica, polypropylene microfibers, and a polycarboxylate-based superplasticizer to improve mechanical performance and durability while maintaining low density and thermal conductivity. Experimental investigations included density, compressive strength, thermal conductivity, water absorption, X-ray diffraction (XRD), microstructural observations, and TG–DTA analysis. The developed compositions containing 5–7% RHA and 0.10–0.20% polypropylene microfibers achieved compressive strength values of 4.5–4.8 MPa at densities of 520–560 kg/m³, which are comparable to or higher than values commonly reported for non-autoclaved aerated concrete of similar density. Thermal conductivity decreased to 0.12–0.13 W/(m·K), while water absorption was reduced to 15–18%. XRD, microstructural, and TG–DTA analyses suggested enhanced hydration reactions and improved development of the cementitious matrix due to pozzolanic interaction between amorphous silica and calcium hydroxide. The incorporation of polypropylene microfibers was associated with improved structural homogeneity of the developed NAAC compositions, whereas the superplasticizer enhanced mixture homogeneity and pore stability. The results suggest that the combined use of agricultural waste-derived silica and fiber reinforcement provides an effective approach for producing sustainable and energy-efficient NAAC without autoclave curing. Full article

To investigate the dynamic impact performance of carbon fiber reinforced polymer (CFRP)-confined recycled concrete, this study designed four series comprising 80 specimens with parameters including strain rate, recycled coarse aggregate replacement ratio, and number of CFRP confinement layers. Split Hopkinson Pressure Bar (SHPB) impact tests were conducted to analyze the dynamic failure mode, stress–strain responses under dynamic loading, and variation in compressive strength of the CFRP-confined concrete specimens. Additionally, a modified Weibull statistical model and fractal theory were employed to analyze the dispersion characteristics of dynamic compressive strength. The results show that the dynamic compressive strength exhibits clear strain-rate sensitivity. The presence of CFRP confinement does not alter the fundamental shape of the stress–strain curves under different strain rates. The proposed modified Weibull statistical model accurately predicts the distribution of dynamic compressive strength at varying strain rates, with an average prediction error of 3.4% and a maximum error of 5.3%. Fractal dimension can quantitatively characterize the evolution trend and degree of crack-induced damage. Within the strain rate range of 52.85–138.42 s⁻¹, the fractal dimension of unconfined ordinary concrete specimens increases from 1.647 to 2.138; for unconfined recycled concrete, it increases from 1.612 to 2.158. The fractal dimension for CFRP-confined ordinary concrete specimens increases from 1.524 to 1.938, and for CFRP-confined recycled concrete specimens, from 1.503 to 2.019. The fractal dimension increases with the increase of strain rate, reflecting a typical strain rate effect. Full article