Search Results (1,148)

This study presents an experimental characterization and numerical assessment of Cu–Al–Be (CAB) shape memory alloys (SMAs) for potential applications in U-shaped flexural plate (UFP) seismic dampers. Six alloy compositions were evaluated through monotonic tensile tests, ASTM F2516 superelastic protocols, and increasing-amplitude cyclic loading to identify the material exhibiting stable superelastic behavior at room temperature. Among the tested materials, alloy CAB4.76-A showed the most favorable response, with high transformation stress, stable pseudoelastic behavior, and strain recovery exceeding 95% for strains up to 2.5%. A phenomenological finite element model based on the Auricchio constitutive formulation was calibrated using experimental data within the validated strain range (ε ≤ 0.025), showing good agreement in stiffness and stress prediction. The calibrated model was subsequently applied to simulate the response of a UFP device under orthogonal cyclic loading. The results indicate a strong dependence on loading orientation due to coupled bending–torsion effects, with the 90° direction exhibiting significantly higher strength and energy dissipation capacity. Comparison with analytical formulations originally developed for steel UFPs showed that these expressions provide approximate estimates when applied to SMA-based devices. The results suggest that Cu–Al–Be alloys are a promising alternative for UFP applications, while highlighting the importance of loading orientation and the need for future experimental validation at a device scale. Full article

Localized failures of structural components can lead to serious social, economic, and environmental consequences, such as the collapse of an entire structure or part of it. Therefore, it is important to thoroughly investigate and justify the acceptance criteria for these components, taking into account their performance in extreme conditions. However, the scientific literature lacks a systematic analysis of how various factors can affect the resistance of structures and influence acceptance criteria under extreme conditions. Therefore, this study investigates the typical substructures of reinforced concrete frame buildings in areas that are potentially prone to local collapse. To assess their resistance and structural robustness, an analytical model has been developed. The results of 22 tests on typical substructures of monolithic and precast frames, reported in various research studies, were used to validate this model. Further, this analytical model was used to conduct a parametric study on the impact of various factors on the performance of substructures under extreme conditions. These factors included the depth-to-span ratio of the beam, the strength of the bond between the steel reinforcement and the concrete, the stiffness of the horizontal bracing within the substructure, and the proportion of the effective depth to the total depth of the beam section. It has been found that the ultimate rotation angle in the plastic hinge of beams increases as the ratio of the beam’s cross-sectional depth to the span increases. An increase in the bond strength between the reinforcement and concrete leads to a decrease in the ultimate rotation angles in the plastic hinge at the flexural and arch stages of resistance and, in some cases, to reinforcement rupture without transitioning to the catenary stage of resistance. A decrease in the ratio of the effective depth of the beam section to its overall depth leads to an increase in the load-bearing capacity at the catenary stage of 19%. Full article

This study experimentally investigated the structural behavior of reinforced concrete beams with circular openings created by core drilling in the midspan and shear span regions under fixed-ended boundary conditions. A total of 21 full-scale beams with shear span-to-effective depth ratios (a/d) of 1.25, 1.75, and 2.25 were tested under a four-point bending setup. After concrete hardening, 100, 200, and 300 mm diameter openings were introduced by core drilling. The results showed that the effect of opening location on load-carrying capacity varied with the a/d ratio. In the a/d = 1.25 and 1.75 series, openings in the shear span caused more pronounced reductions, whereas in the a/d = 2.25 series, midspan openings became more influential. Increasing the opening diameter reduced both load-carrying capacity and energy dissipation capacity, and this reduction varied with opening location and a/d ratio. Openings in the shear span led to shear failure in the a/d = 1.25 and 1.75 series, whereas flexural effects became more pronounced in the a/d = 2.25 series. Nevertheless, 300 mm openings caused shear failure even in beams expected to exhibit more flexure-dominated behavior. Full article

Engineered bamboo composites (EBCs) are increasingly considered as sustainable alternatives to tropical hardwoods in structural applications. In jacking systems, performance is primarily governed by compression perpendicular-to-grain (bearing), although improper use may introduce flexural demands. This study evaluates the bearing and flexural behavior of Dragonwood, a commercial parallel strand bamboo (PSB), in comparison to Ekki (Lophira alata) through 120 full-scale tests. Dragonwood exhibited higher mean bearing capacity than Ekki, with yield stresses exceeding those of Ekki by over 60%, indicating strong potential for bearing-dominated applications such as in jacking. However, face-bonded specimens showed sensitivity to glue-line orientation, resulting in flexural strength reductions of up to 42% and undesirable shear failures. Increasing adhesive content and pressing pressure in the manufacturing process did not eliminate this behavior. Single-lift specimens removed the glue-line and showed improved failure behavior in flexure, although with reduced strength. The results demonstrate that manufacturing strategy heavily influences PSB performance. While single-lift Dragonwood products show the most potential, further testing under bearing is required before its suitability for jacking applications can be fully established. Full article

Fiber-reinforced polymer (FRP) composites provide an effective strengthening solution for timber members because of their high tensile capacity, low self-weight, corrosion resistance, and practical applicability in rehabilitation works. Although FRP strengthening of timber beams has been widely investigated, most available experimental evidence concerns softwood and glued-laminated systems, whereas comparatively limited data are available for dense tropical hardwoods used in marine and waterfront infrastructure. This study investigates the flexural behavior of Azobé (Lophira alata) hardwood beams strengthened with externally bonded carbon-fiber-reinforced polymer (CFRP) and glass-fiber-reinforced polymer (GFRP) laminates. The main contribution of this work is the application of externally bonded FRP strengthening to Azobé timber members intended for marina pontoon and related waterfront applications, where structural upgrading may be required to accommodate increased service loads. Mechanical characterization of the timber was first conducted through compression and tensile tests. Subsequently, nine beams were tested under three-point bending, including three un-strengthened reference beams, three GFRP-strengthened beams, and three CFRP-strengthened beams. The average ultimate load increased from 26.92 kN for the reference beams to 35.59 kN and 39.85 kN for the GFRP- and CFRP-strengthened beams, respectively. Statistical indicators, including standard deviation, coefficient of variation, standard error, confidence intervals, and two-sample t-tests, were included to account for the limited number of specimens and the natural variability of timber. CFRP exhibited the highest mean response within the present test series; however, the difference between the CFRP- and GFRP-strengthened beams is interpreted as an indicative experimental trend rather than a general statistical conclusion. No visible premature de-bonding was observed, and the strengthened specimens failed mainly by FRP rupture, suggesting bond engagement under the tested configuration. Nevertheless, bond behavior was not directly quantified using strain, slip, or interfacial measurements. The experimental results were also compared with analytical predictions based on the Italian guideline CNR-DT 201/2005 and with a simplified section-level interpretation. Overall, the findings indicate that externally bonded FRP laminates can provide a practical upgrading solution for existing Azobé timber members in marina pontoon and waterfront structures, while larger experimental series and direct bond/strain measurements are required for broader validation. Full article

This paper presents a preliminary numerical investigation on the mechanical behavior under eccentric compression of T-shaped steel tube-steel reinforced concrete columns. A refined finite element (FE) model was developed in ABAQUS 2021 and validated against published axial compression test results. The effects of three key parameters (eccentricity, outer steel tube thickness, and built-in steel skeleton size) on the bearing capacity, failure mode, stiffness degradation, and stress distribution of the studied members were systematically analyzed via finite element analysis, followed by comparative calculations and an applicability analysis of the calculation of eccentric compression bearing capacity. All eccentric compression results presented herein were obtained through numerical simulation and have not been directly verified by physical tests. The results show that the ultimate bearing capacity decreases by more than 57% as the eccentricity increases from 0 mm to 75 mm, with the failure mode transitioning from axial compression failure to flexural failure. Within the studied parameter range, the 4 mm-thick outer steel tube exhibits superior comprehensive performance, including bearing capacity, stiffness, and ductility. Increasing the built-in steel skeleton size effectively enhances the flexural stiffness and ductility, and delays stiffness degradation. The existing code-specified formula demonstrates good accuracy (relative error < 6%) for e ≤ 50 mm but yields significant errors for e = 75 mm. An empirical expression for the equivalent eccentricity influence coefficient α is proposed, which reduces the overall average error from 4.89% to 2.26% within the parameter scope of this study. Full article

To simultaneously address the deterioration of mechanical properties in lightweight aggregate concrete (LAC) and the insufficient deformation control capacity of hybrid fiber-reinforced polymer (BFRP) bars, an experimental study on the flexural behavior of hybrid fiber-reinforced BFRP-LAC beams was conducted. A total of eight beams with dimensions of 120 mm × 200 mm × 2000 mm were fabricated. The effects of hybrid fibers and BFRP reinforcement ratio on the flexural performance were investigated. Four-point bending tests were performed to analyze the failure modes, load–deformation responses, crack development patterns, and sectional strain distributions. The results indicate that two failure modes were experimentally observed in the BFRP-reinforced hybrid fiber LAC beams, namely concrete crushing and BFRP bar rupture, whereas balanced failure was considered a theoretical failure condition. The failure mode was strongly dependent on the reinforcement ratio. At a low reinforcement ratio ($\rho$ = 0.68%), tensile failure governed by BFRP bar rupture occurred. At a moderate reinforcement ratio ($\rho$ = 1.02%), a relatively ductile concrete-crushing failure was observed. When the reinforcement ratio increased to 1.56% and 1.81%, brittle concrete-crushing failure dominated. The incorporation of hybrid fibers improved the ductility and optimized the failure process. Both the hybrid fiber content and the BFRP reinforcement ratio significantly influenced the load-carrying capacity and deformation behavior of the beams. Increasing the fiber content enhanced the cracking load and ultimate load, delayed crack propagation, and reduced crack width, whereas increasing the reinforcement ratio was more effective in improving the ultimate capacity. The load–deflection curves exhibited a typical two-stage response without a yielding plateau. The bridging effect of hybrid fibers effectively mitigated stiffness degradation and improved crack control performance. Moreover, the plane section assumption was validated for hybrid fiber-reinforced BFRP-LAC beams. This study provides a technical basis for enhancing the performance of LAC and promoting the application of BFRP bars in structural engineering. Full article

To mitigate the shortage of natural river sand in northwest desert regions, utilize local desert sand resources, and address structural performance under harsh winter conditions, this study investigates the flexural behavior of freeze–thaw conditioned desert sand concrete beams (DSCBs) through rapid freeze–thaw and flexural testing. The investigated variables included desert sand replacement ratios (0%, 20%, 40%, 60%) and freeze–thaw cycles (0, 25, 50, 75). Failure modes, load–concrete strain curves, load–deflection relationships, and load–longitudinal reinforcement strain were analyzed. The results indicate that the crack development and failure modes of DSCBs are similar to those of normal concrete beams, and the plane-section assumption remains valid after freeze–thaw cycles. After 75 freeze–thaw cycles, specimens with the same replacement ratio exhibited the poorest mechanical properties—compared to unfrozen specimens, the ultimate capacity decreased by up to 17.5%, reinforcement strain increased by up to 31.9%, and failure deflection decreased by up to 62.0%. Under all freeze–thaw conditions, the 20% replacement ratio yielded the best performance, with ultimate capacity up to 5.3% higher, reinforcement strain up to 18.2% lower, and failure deflection up to 37.5% higher than those of ordinary concrete beams. Finally, correction factors for desert sand replacement ratio and freeze–thaw cycles were introduced to establish predictive equations for cracking moment and ultimate flexural capacity. The predictions are in good agreement with experimental results, providing a theoretical basis for engineering applications. Full article

This study investigates the effects of polypropylene fibre content on the workability and compressive strength of recycled aggregate concrete (RAC), as well as the flexural behaviour of RAC beams. The results indicate that recycled aggregates adversely affect the mechanical properties of concrete and reduce the crack resistance, stiffness retention, and crack-control capacity of concrete beams. Although polypropylene fibres reduce mixture workability, they improve the mechanical properties of recycled concrete and enhance the flexural behaviour of recycled concrete beams. The contribution of polypropylene fibres is mainly reflected in improved crack control and post-peak behaviour, whereas their effect on ultimate load-bearing capacity remains relatively limited. In addition, the improvement provided by the fibres does not increase proportionally with fibre dosage. A moderate fibre content can effectively balance load-bearing capacity, deformation capacity, and crack control, whereas excessive fibre addition may weaken the reinforcement effect because of poor fibre dispersion and reduced matrix uniformity. These findings provide useful guidance for evaluating the flexural performance and potential engineering applications of fibre-reinforced recycled aggregate concrete beams. Full article

Steel–concrete composite beams are widely used in bridge infrastructure but are vulnerable to deterioration due to uniform and pitting corrosion, particularly at the lower flange. This study investigates the flexural behavior of corroded steel–normal strength concrete (NSC) composite beams and evaluates rehabilitation using ultra-high-performance concrete (UHPC) slab replacement, with and without additional steel plate strengthening. A comprehensive finite element analysis was conducted considering three beam spans (5, 7, and 9 m), two corrosion types, and three corrosion levels. The results indicate that both corrosion types significantly reduce flexural capacity due to cross-sectional loss, with pitting corrosion causing greater strength reduction than uniform corrosion at the same weight loss because of stress concentration effects. Replacing the NSC slab with a UHPC slab effectively restores and often enhances load-carrying capacity beyond that of intact beams while reducing dead load, demonstrating the superiority of the proposed rehabilitation approach. The combined use of UHPC slab replacement and welded steel plate strengthening provides the greatest improvement, revealing a strong synergistic effect. A case study of a corroded steel bridge in Pennsylvania confirms the practical applicability of the method, showing that UHPC-based rehabilitation increases the load rating from below unity to above unity. These findings highlight UHPC as an efficient and sustainable solution for extending the service life of aging steel bridges. Full article

Using industrial by-product lithium slag (LS) as a raw material for ultra-high performance concrete (UHPC) is an important way to achieve low-carbon prefabricated structures. However, existing studies lack a constitutive model for LS-UHPC and its application in prefabricated beam connection nodes. To fill this gap, this paper first established a tensile-compressive constitutive model for LS-UHPC through mechanical tests; then it was embedded into the finite element model to simulate the bending performance of the connection nodes of the post-cast LS-UHPC prefabricated beams and verified by the test results. Finally, parameter analysis is carried out. The results show that moderately increasing the diameter of longitudinal reinforcement can significantly improve the flexural bearing capacity of the connection node, but when the diameter exceeds 18 mm and HRB500 high-strength steel bars are used, the node exhibits over-reinforced failure characteristics; increasing the strength grade of ordinary concrete has a limited effect on the improvement of flexural bearing capacity (<5%). This study clarified the mechanical constitutive relationship of LS-UHPC, revealed the failure mechanism and bearing capacity evolution law of its prefabricated connection nodes under parameter changes, and provided a theoretical basis and design suggestions for the application of low-carbon lithium slag UHPC in prefabricated assembly structures. Full article

Research on the long-term durability of concrete has continued due to its widespread application in construction. Freeze–thaw cycles significantly impact concrete durability, particularly in regions with harsh climates. While most studies focus on the material properties of concrete, limited research has addressed the performance degradation of reinforced concrete structures. This study investigates the freeze–thaw resistance of RC beams made with 35 MPa concrete, with particular emphasis on the influence of air content on flexural performance. RC beams were exposed to freeze–thaw cycles using the air freeze–thaw method and the ASTM C666/C666M-15 water freeze–thaw method. Their flexural behavior was evaluated through four-point bending tests. The results showed that low-air-content RC beams exhibited notable reductions in yield load and energy absorption capacity after freeze–thaw cycles, indicating decreased strength and ductility. Conversely, RC beams with appropriate or high air content exhibited minimal reductions, demonstrating superior freeze–thaw resistance. These findings underscore the importance of optimizing air content to enhance the durability of RC structures in harsh environmental conditions. Full article

Four-point bending tests were conducted on precast ultra-high-performance concrete (UHPC) segmental beams reinforced with unbonded prestressing tendons. A nonlinear finite element model was established and rigorously validated against the experimental data to simulate their flexural behavior. The experimental results show that compared with monolithic beams, the segmental beams experience a slight reduction in flexural capacity of 9.22% and 12.44% for the double-joint and triple-joint configurations, respectively. Nevertheless, the segmental beams possess greater ductility reserves; specifically, their average peak displacements increased from 9.83 mm for the monolithic beams to 11.60 mm and 14.78 mm for the double-joint and triple-joint beams, respectively, demonstrating substantially improved ductility. Based on the validated finite element model, extensive parametric analyses were performed. The numerical results indicate that concrete strength and steel strand reinforcement ratio significantly enhance the load-carrying capacity. Furthermore, shifting the joint positions away from the loading points increases the beam’s bending capacity, though this enhancement aggressively flattens out beyond a critical distance threshold of 0.25 L (L is the effective span). Finally, segmental beams with shear-resistant keyed joints exhibit higher overall stiffness and ultimate load-carrying capacity compared to those with plain flat joints. Full article

The adoption of sustainable construction materials in the building sector is increasing, driven by global net-zero targets, regulatory pressures, and growing demand for low-carbon and resource-efficient construction. In this context, this research investigates the feasibility of using bio-based fibre-reinforced epoxy resin composite laminates with recycled polyethylene terephthalate cores in structural insulated panels (SIPs) as an alternative to conventional SIP systems. Laminates were fabricated via a wet layup method using two epoxy resins and five fabric types, including flax, hemp, and recycled PET fabrics. Tensile and flexural testing revealed that hemp fabric paired with a fully bio-based epoxy provided the optimum combination of strength and elastic modulus. Small-scale SIP prototypes utilizing optimum laminate and rPET cores were tested for edgewise compression and flexure against expanded polystyrene (EPS) equivalents. The rPET SIPs demonstrated compressive and flexural capacities two to three times greater than the EPS panels. These findings demonstrate the potential of sustainable fabric-reinforced epoxy resin composite SIPs for specialized high-performance construction applications where enhanced structural capacity and sustainability are required. Although further work is needed to address cost, fire performance, and scalable manufacturing, the proposed system presents a promising alternative for next-generation sustainable building systems. Full article

Quasi-zero stiffness (QZS) isolators provide excellent vibration isolation performance at low frequency. This paper presents an innovative flexural–torsional buckling QZS isolator, which depends on its linear negative stiffness to provide a more stable dynamic response than other QZS isolators. First, the force and stiffness characteristics of the flexural–torsional buckling toggle under vertical load are simulated, and it is proposed that they can be fitted with a piecewise function and its derivative. Next, the cross-sectional dimensions, and height-to-span ratios are discussed to determine their contributions to the static characteristics. Then the dynamic model of the QZS isolator is established and analyzed by a harmonic balanced method and the solutions are validated by numerical analysis. Finally, the comparison with an ordinary QZS isolator shows that the advantages of the proposed isolator are the linear negative stiffness and a certain load-bearing capacity at equilibrium position rather than the zero capacity of common isolators. The static characteristics of the proposed QZS isolator indicate that the negative stiffness is significantly influenced by the cross-sectional width, with the slope k increasing by 8.6 times as the width increases from 1 cm to 1.5 cm. The proposed mechanism exhibits an approximately linear negative stiffness with a maximum static bearing capacity of about 1000 N at the equilibrium position, contrasting with the nonlinear, non-capable negative stiffness of the ordinary Euler buckled beam model. The dynamic characteristics demonstrate excellent performance, operating effectively with ultra-low transmissibility. This study provides an innovative negative stiffness mechanism and a corresponding isolator based on flexural–torsional buckling, offering a potential solution for a wide range of large-scale engineering vibration problems. Full article