Search Results (766)

The development of lightweight, high-strength structural systems is a persistent pursuit in modern civil engineering. This paper presents an experimental study on a novel hybrid beam concept in which a sawn timber core is fully bonded with an externally applied Carbon Fiber-Reinforced Polymer (CFRP) laminate, fabricated through a controlled hand lay-up process. The design seeks to exploit the complementary characteristics of the two materials: timber provides compressive resistance and serves as a permanent formwork, while the CFRP carries tensile stresses with high efficiency. Fourteen hybrid beams, with variations in the number of longitudinal CFRP layers (one, two or, three), the presence or absence of longitudinal CFRP layers bonded along the top and bottom surfaces, and the presence or absence of circumferential wrapping in the pure bending region, were tested under four-point bending alongside two solid timber control beams. The results demonstrate that circumferential wrapping is a critical design detail. Wrapped beams consistently failed by tensile rupture of the CFRP—the intended failure mode—and exhibited ultimate moments 15–20% higher than their unwrapped counterparts. Beams with two longitudinal CFRP layers offered the most favorable balance between strength enhancement and material efficiency; adding a third layer shifted the failure mode to crushing of the timber core, indicating a core-limited condition. All hybrid beams showed pronounced linear-elastic behavior up to sudden brittle failure, with performance variability attributable to the inherent inhomogeneity of wood and the sensitivity of the hand lay-up process. The study provides quantitative data and mechanistic insights that support the design and application of bonded CFRP–timber hybrid beams as efficient structural members. Full article

Accurate simulation of reinforced concrete (RC) members under cyclic loading requires hysteresis models that capture degradation and pinching, yet inverse identification of such models remains challenging because the internal-state evolution is strongly coupled and sensitive to incremental consistency. This study develops a physics-constrained, model-based framework to identify the full twelve-parameter Bouc–Wen–Baber–Noori (BWBN) model directly from cyclic force–displacement records and to deploy the calibrated parameters in OpenSees. Parameter estimation is posed as a bound-constrained nonlinear least-squares problem, where each objective evaluation advances the BWBN internal variables through a discrete incremental constitutive update and accumulates the energy-driven deterioration measure using a consistent trapezoidal work integration. Validation on nine RC column tests covering flexural, flexural–shear, and shear failures shows good agreement between simulated and experimental hysteresis loops, with R² ranging from 0.956 to 0.986 and RMSE ranging from 0.06 to 0.09 over the full records. Unlike simpler hysteresis models that omit degradation and pinching, the calibrated BWBN model reproduces mode-dependent deterioration and reloading pinching, and the identified parameters can be used directly in OpenSees for subsequent nonlinear simulations. Full article

The performance of polymer nanocomposites is governed primarily by the structure and properties of the matrix–filler interphase. This study presents a quantitative Raman spectroscopy analysis of interphase evolution in epoxy nanocomposites reinforced with two-dimensional WS₂, whose surface chemistry was systematically tuned via grafting of aminoacetic acid (AA) at concentrations of 2.5, 5.0, and 7.5 wt.%. By tracking peak shifts, linewidths, intensity ratios, and integrated areas of the characteristic WS₂ phonon modes (2LA(M) + E₂g¹, A₁g, and defect-related bands), we establish a non-linear, concentration-dependent interfacial response. Minor spectral variations at 2.5 wt.% AA indicate limited interfacial interaction. At 5.0 wt.% AA, suppression of the A₁g mode and significant band broadening reflect increased structural disorder. At 7.5 wt.% AA, coordinated red shifts (~−1.8 cm⁻¹) and the appearance of an additional band near 432.8 cm⁻¹ suggest the development of a strain-mediated interfacial state. Overall, increasing AA concentration leads to a non-linear evolution of the WS₂–epoxy interface, as reflected in peak positions, linewidths and intensity ratios. These Raman-derived descriptors correlate directly with enhanced mechanical properties (flexural and tensile strength) and thermal stability (Vicat softening point) of the composites. The results demonstrate that effective interfacial coupling requires a critical surface coverage and that Raman spectroscopy serves as a powerful tool for non-destructively probing and optimizing interphase architecture in TMD/polymer systems. Full article

The integration of mechanics-based analysis and materials design procedures has become central to the development of multi-material structures with tailored mechanical and dynamic performance. In this study, the dynamic and flexural behaviour of multi-material FDM sandwich beams composed of PETG face sheets and an ABS core is experimentally investigated. Seven different infill patterns Grid, Line, Wavy, Honeycomb, Gyroid, Cubic, and Triangle were implemented in the core layer to assess their influence on damping and natural frequency behaviour. Experimental modal analysis was performed using impact testing to identify the first three vibration modes. Natural frequencies were extracted from Frequency Response Functions (FRFs), and modal damping ratios were determined using the half-power bandwidth method. The reliability of the damping results was evaluated through statistical analysis. Additionally, quasi-static three-point bending tests were conducted to assess flexural strength and load-carrying capacity. The results demonstrate that infill topology has a significant impact on both dynamic and mechanical responses. In particular, geometrically complex infill patterns exhibit enhanced stiffness, higher natural frequencies, and improved damping performance. Among the investigated designs, the Triangle infill exhibited the highest natural frequency values across the first three vibration modes (f₁ ≈ 24.910 Hz, f₂ ≈ 162.609 Hz, f ≈ 466.595 Hz), indicating its superior stiffness characteristics. In terms of damping behaviour, the Cubic infill showed the highest loss factor in the first vibration mode (0.0426), while the Line and Gyroid patterns exhibited the highest damping in the second (0.0439) and third modes (0.0354), respectively. Moreover, the force–displacement results revealed that the Triangle infill exhibited the highest load-bearing capacity, further confirming its superior structural stiffness among the investigated designs (SEA = 110.83 J/kg). These findings highlight the potential of multi-material FDM for designing polymer-based sandwich structures with tailored vibration and energy dissipation characteristics. Full article

This study investigates the seismic behavior of reinforced concrete (RC) columns with hollow rectangular cross-sections through experimental testing and analytical evaluation. A series of hollow-sectioned column specimens with different shear span ratios and failure modes were tested under cyclic lateral loading to examine their flexural and shear performance. The results demonstrated that flexure-dominated columns exhibited stable load-deformation responses and sustained seismic performance, even with the reduced shear span ratio. The experimental results also showed that the presence of the hollow cross-section had minimal influence on flexural strength and bar strain distribution. The shear strength of RC columns with hollow cross-sections tended to be underestimated by the conventional equation; however, improved accuracy was achieved by applying an equivalent cross-sectional area in the calculation. A nonlinear finite element analysis successfully reproduced the flexural load-deformation response of the specimens. While some discrepancies were observed in the shear-dominated cases, the analytical model provided conservative estimates under positive loading. These findings provide new insights into the seismic design of RC columns with hollow cross-sections, highlighting their potential applicability in building structures when flexural and shear behaviors are properly considered. Full article

To address the engineering challenges of frequent flexural deformation and instability of composite roadway roofs and the difficulty in accurately controlling the support strength range during deep coal mining, this study takes the soft–hard interbedded composite roof of the working face in the West No. 1 Mining Area of Shuangyang Coal Mine in Shuangyashan as the engineering background. Typical fine sandstone (hard rock) and tuff (soft rock) from the on-site roof were selected to prepare layered composite specimens, and indoor four-point bending tests were conducted. Combined with theoretical calculations, strain monitoring, and acoustic emission (AE) real-time localization technology, the regulatory mechanisms of three key factors—lithological combination, loading rate, and span—on the flexural mechanical properties, deformation and failure modes, and fracture evolution laws of layered composite rock masses were systematically investigated. The research results show the following: (1) The flexural performance of layered composite rock masses is dominated by the interlayer interface effect. Their flexural strength is 46.7% and 41.1% lower than that of single hard rock and soft rock specimens, respectively, and the competitive mechanism between interface slip and delamination fracture is the core inducement of strength deterioration. (2) The strength and deformation characteristics of layered composite rock masses exhibit a significant loading rate effect. When the loading rate increases from 0.002 mm/s to 0.02 mm/s, the flexural strength decreases by 51.8% and the mid-span deformation deflection reduces by 50.1%. High loading rates will exacerbate the deformation mismatch between soft and hard rock layers, trigger premature failure of interface bonding, and inhibit the full development of structural plastic deformation. (3) Increasing the span significantly optimizes the flexural bearing performance of layered composite rock masses. When the span increases from 170 mm to 190 mm, the flexural strength increases by 65.7% and the mid-span deformation deflection synchronously increases by 65.7%. A large span can extend the flexural deformation path, promote the coordinated deformation of rock layers, and suppress local stress concentration. (4) The flexural failure of layered composite rock masses is dominated by Mode II shear cracks, while single-lithology specimens are mainly dominated by Mode I tensile cracks. Loading rate and span significantly change the crack propagation mode and energy release law. This study establishes a calculation method for the equivalent flexural stiffness of layered composite rock masses and reveals the mesoscopic mechanism of flexural failure of heterogeneous layered rock masses. The research results can provide a theoretical basis and experimental support for the optimization of support schemes and the prevention and control of roof collapse hazards for composite roofs of deep coal mine roadways. Full article

A novel corrugated steel-reinforced concrete pipe that enhances electromagnetic shielding performance compared to the conventional reinforced concrete power pipes is developed and presented in this paper. In order to investigate the pipe’s behaviour under jacking and service conditions, the critical axial compression and flexural moment distributions were represented by two separate flat segments of a circular pipe cross-section, respectively. A total of six column specimens were designed for axial compression testing, while another four beam specimens were prepared for four-point bending tests to examine the bending behaviour. Prior to testing, all specimens were subjected to standard curing, and the material properties of steel and concrete were determined via standard tests. The load versus deformation curves of column specimens, the moment versus deflection curves of beam specimens, and the corresponding failure modes were obtained from the tested specimens. It was revealed that the load-carrying capacities of the corrugated steel-reinforced concrete cross-sections were comparable to those of the conventional reinforced concrete counterparts. Advanced finite element (FE) models incorporating the mechanical properties of encased corrugated steel plates (CSPs) and the damage development of concrete were developed and were validated against the experimental failure modes and load-carrying capacities. Based on both experimental and numerical results, the load-carrying capacity of corrugated steel-reinforced concrete cross-sections was evaluated by referring to Chinese standard GB/T 11836 and American standard ASTM C76. The experimental and numerical finding can pave the way for further research and applications of this novel type of corrugated steel-reinforced concrete pipe. Full article

To investigate how lateral impact influences the residual axial resistance capacity of cross-shaped steel-reinforced concrete (CSRC) columns, the residual axial resistance test was carried out following impact test. A finite element model (FEM) was developed to simulate axial and lateral impact loading, and its accuracy was confirmed through comparison with test results. The analysis shows that the numerical model can simulate the impact force, deflection, deformation mode and residual axial resistance of the column with adequate accuracy. With the verified finite element models, the residual axial resistance (N_r) of CSRC columns under six different parameters was further analyzed. Results demonstrate that the column primarily undergoes flexural deformation under impact, whereas shear effects are localized at the impact zone. A higher structural steel ratio (α) and yield strength of the cross-shaped steel (q) contribute to improved N_r and reduced mid-span displacement (Δ_max). With the increase in compressive strength of concrete (c) and axial compression ratio (n), the N_r increases to a certain level and then decreases, and the Δ_max decreases first and then increases in a similar manner. The change in slenderness ratio (γ) in a small range can improve the N_r of the column, and the significant increase in γ results in instability and failure. In particular, when the slenderness ratio increases from 8 to 12, the residual bearing capacity of the column decreases by 19.4%. This study proposes a residual bearing capacity-prediction formula based on seven key influencing parameters, which shows high accuracy (R² = 0.93). A damage evaluation index based on flexural bearing capacity (D_dag) is introduced, and the structural state is accordingly classified into four damage levels. Compared with conventional numerical simulations that typically require more than 3 h of computation time, the proposed method can rapidly complete the damage assessment of columns within 5 min, providing an efficient approach for structural safety evaluation and response strategies. Full article

The utilization of cement is one of the primary sources of carbon emissions in concrete, driving the search for sustainable alternative materials. Although extensive research has been conducted on the use of agricultural waste as supplementary cementitious materials (SCMs), the effects of coconut shell ash (CSA) and coir fiber (CF) on concrete properties have not been extensively investigated. This study systematically investigates the influence of CSA as a SCM (0–20%) and CF as a reinforcement material (0–0.32%) on the workability, density, compressive strength, flexural strength, splitting tensile strength, and failure modes of concrete, complemented by microstructural mechanism analysis. The cement and CSA were characterized using XRF, XRD, and SEM. The results indicate that the incorporation of both CSA and CF reduces the workability and density of concrete. For concrete with CSA only, the compressive strength decreases by up to 24.7% when the replacement level reaches 20%. However, concrete with 10% CSA still maintains 87.2% of the strength of ordinary concrete, which satisfies the C40 requirement. In contrast, CF incorporation alone improves the mechanical properties, with compressive strength, flexural strength, and splitting tensile strength reaching peak increases of 6.4%, 13.9%, and 7.5%, respectively, when the CF content is 0.24%. Incorporating 0.16% CF into 10% CSA concrete mitigates the strength reduction caused by CSA, achieving compressive, flexural, and splitting tensile strengths of 47.99 MPa, 5.63 MPa, and 3.99 MPa, respectively (95.7%, 98.3%, and 96.4% of the strengths of ordinary concrete). Microstructural analysis reveals that CSA deteriorates the interfacial transition zone (ITZ), while CF compensates for partial strength loss through the bridging effect, although its reinforcement efficiency is influenced by fiber dispersion and ITZ quality. This study provides a theoretical foundation and technical reference for the utilization of coconut shell waste in sustainable concrete. Full article

To enhance the mechanical properties of bamboo-reinforced concrete slabs, 1%, 1.5%, and 2% of steel fibers (SF) were added to C30 bamboo-reinforced concrete slabs to produce two test groups, each containing 12 slabs. One group was tested under static loads, and the other under impact loads. In each group, the slab thickness was set to 50 mm, 65 mm, and 80 mm, and the steel fiber dosages were 0%, 1%, 1.5%, and 2%. While existing studies on bamboo-reinforced concrete slabs (BRCS) have primarily focused on static flexural behavior, and research on steel fiber-reinforced concrete (SFRC) has mainly addressed fiber network effects in plain or steel-reinforced matrices, the synergistic mechanism between bamboo and SF in steel fiber-reinforced bamboo-reinforced concrete slabs (SFRBCS) under dynamic impact loading remains unexplored. This study innovatively combines bamboo’s elastic energy absorption with SF’s plastic energy dissipation. Static load and drop hammer impact tests were carried out in each group to study the mechanical properties of SFRBCS under static and dynamic loads. The test results show that: under static load, adding SF transforms the failure mode of the slab from brittle shear failure to ductile bending failure, increases the ultimate load, and delays the development of the main crack. Under the action of impact loads, bamboo absorbs impact energy through elastic deformation, while SF dissipates energy through plastic deformation. The combined effect of the two significantly slows down the development speed of cracks. The slab with 80 mm thick and 2% SF dosage exhibits excellent impact ductility. Based on theoretical analysis and tests, the corresponding correction coefficients are introduced to establish the bearing capacity calculation model of SFRBCS under uniformly distributed loads, considering the synergistic effect of the mechanical properties of bamboo and the reinforcing effect of SF. The combination of 1.5% SF dosage and 80 mm slab thickness can effectively enhance the material utilization rate (defined as the ratio of the increment in ultimate bearing capacity to the increment in steel fiber dosage). Test and calculation models provide a theoretical basis for the design and application of SFRBCS, which is applicable to engineering fields such as low-rise buildings and temporary structures. Full article

This study investigates the axial–flexural behavior of steel fiber–reinforced concrete (SFRC) columns under combined constant axial load and monotonic lateral loading. Nine column specimens with different axial load ratios (0.0, 0.10, and 0.20) and steel fiber contents (0.0%, 0.5%, and 1.0%) were tested under monotonic loading to evaluate their failure modes, load–deflection behavior, ductility, and energy absorption capacity. In addition, a sectional P–M interaction analysis was performed to examine the influence of steel fiber inclusion on flexural strength under different axial compression levels. The interaction diagrams indicated that steel fibers expanded the flexural strength envelope, with a more pronounced enhancement in the low-axial-load region. The test results revealed that increasing the axial load ratio enhanced the specimens’ peak load capacity but reduced their ductility, leading to a brittle failure mode. Conversely, the incorporation of steel fiber improved the crack distribution, delayed crack propagation, and enhanced both ductility and energy absorption, particularly under moderate axial load conditions. The failure modes were characterized generally by flexural cracking and localized crushing in the compression zone, with the specimens that contained steel fiber exhibiting a more gradual post-peak load response than the specimens without steel fiber. The energy absorption capacity, quantified as the area under the load–deflection curve, was maximized when the axial load ratio of 0.10 was used in tandem with steel fiber reinforcement, indicating an optimal balance between strength and ductility. Overall, steel fiber inclusion improved deformation capacity and energy absorption under monotonic loading, particularly at low-to-moderate axial load ratios. Full article

Conventional Fiber-Reinforced Polymer (FRP) materials may exhibit certain performance uncertainties in harsh environments, limiting their reliability for structural strengthening. To address this, Basalt Fiber-Reinforced Polymer (BFRP) plates fabricated with silicate-modified epoxy resin are proposed for the flexural strengthening of reinforced concrete (RC) beams. The research aims to evaluate their short-term strengthening performance and establish a reliable calculation method for flexural capacity. Four-point bending tests were conducted to investigate the effects of BFRP plate thickness and end anchorage configuration on failure modes, flexural capacity, and ductility. Finite element simulations incorporating interfacial bond–slip behavior reproduced typical debonding failures, followed by a comprehensive parametric analysis. Based on the experimental and numerical results, a modified BFRP plate strain formula at debonding was proposed to establish a calculation method for the flexural capacity of BFRP-strengthened beams governed by debonding failure. The results indicate that beams without end anchorage were prone to interfacial debonding, where increasing the plate thickness from 0.5 mm to 2 mm raised the flexural capacity gain from 4.5% to 15% but intensified the ductility reduction from 42.9% to 64.9%. Conversely, applying mechanical anchorage improved the ductility index by over 20% compared to unanchored counterparts. The adopted FRP–concrete bond–slip constitutive model accurately characterizes interfacial debonding behavior, and the proposed flexural capacity model demonstrates high accuracy with overall deviations within 5%. It can be concluded that the novel BFRP plates exhibit strengthening behavior comparable to existing FRP systems. Effective end anchorage further enhances flexural capacity and prevents brittle failure. The proposed debonding strain formula for the novel BFRP system offers a reliable basis for capturing the critical onset of interfacial failure. Building upon this, the developed flexural capacity model provides a reliable theoretical basis for the design and assessment of RC beams strengthened with the novel BFRP plates. Full article

In this study, the flexural behavior of notched steel beams retrofitted with CFRP is investigated. Two series of tests, including W200 × 22 and W14” wide-flange notched beams rehabilitated with externally bonded (EB) CFRP are evaluated under static loading. The W200 × 22 beams were received directly from a factory, whereas the W14” wide-flange beams were extracted from the Original Champlain Bridge after roughly 60 years in service. The parameters considered include the CFRP elastic modulus, CFRP configuration, notch depth, anchorage system, and adhesive type. The effect of the CFRP elastic modulus on the rehabilitation technique is examined by using Normal Modulus (NM) and Ultra-High Modulus (UHM) CFRP with approximately the same tensile capacity. Failure modes, load–deflection behavior, strain distributions along the CFRPs, and Crack Mouth Opening Displacement (CMOD) are thoroughly discussed in this study. The results reveal that both UHM and NM CFRP significantly enhance the load-carrying capacity. However, specimens retrofitted with UHM CFRP exhibit a brittle behavior, whereas those strengthened with NM CFRP show a more ductile behavior. Full article

Delamination is a critical failure mode in composite laminates that degrades the structural performance and load-carrying capacity. This study investigates the improvement of Mode I and Mode II interlaminar fracture toughness of carbon fiber-reinforced polymer (CFRP) laminates through the interleaving of electrospun thermoplastic nanofiber mats. Nanofiber veils were inserted between carbon fiber plies to enhance resistance to delamination under tensile opening (Mode I) and in-plane shear (Mode II) loading. The effects of nanofiber interleaving were evaluated using double cantilever beam (DCB) tests for Mode I and end notch flexure (ENF) tests for Mode II. Both tests were conducted on a symmetric quasi-isotropic laminate [-45/45/90/0₅]_s containing a thick unidirectional 0° ply at the mid-plane. Thermally induced residual stresses resulting from mismatches in ply coefficients of thermal expansion and unsymmetric arm lay-ups were accounted for in the experimental determination of fracture toughness. These stresses, generated during cooling from the cure temperature, influence the effective strain energy release rate and were included in the fracture toughness calculations to ensure accurate toughness evaluation and consistency with numerical predictions. The results demonstrate improved delamination fracture toughness, highlighting the potential of nanofiber interleaving for aerospace and wind energy applications. Full article

Based on the dual requirements of building energy efficiency and construction industrialization, along with the development of high-strength, high thermal resistance (low thermal conductivity) foamed concrete (HLFC), this study proposes a new prefabricated high-strength foamed concrete thermal self-insulating shear wall system (called HFSW shear wall) suitable for multi-story buildings, which could address the core shortcomings of existing organic insulation materials in buildings, such as poor fire resistance and short life cycles. Concerning the research gap in the flexural performance of this wall type, this study conducted seismic tests on two full-scale wall models and systematically analyzed the fundamental performance parameters under quasi-static loading, including bending failure phenomena, load-bearing capacity, stiffness degradation, energy dissipation capacity, and ductility. The results show that HFSW walls with large shear span ratios generally exhibit typical bending failure characteristics. However, due to the relatively low material strength, extensive development of shear and flexural–shear cracks occurs, leading to minimal differences in typical seismic performance indicators compared to shear-dominated failure scenarios in traditional shear walls (indicating significant flexural–shear coupling effects). Finally, a finite element model was used to simulate the wall capacity under various parameters, including axial compression ratio, wall thickness, and longitudinal reinforcement in edge columns. Based on the validated and calibrated finite element results, and in accordance with the wall failure mode as well as the load transfer mechanism, a calculation model for the flexural strength of HFSW shear walls was established to guide design and engineering application, achieving a theoretical calculation accuracy of 0.97. The research findings provide meaningful guidance for the design and application of this wall system. Full article