Search Results (1,721)

Water-retaining roller-compacted concrete (RCC) dams suffer severe deterioration under coupled moisture ingress and freeze–thaw (F-T) cycles. To elucidate the damage mechanisms, this study employed industrial X-ray computed tomography (CT) synchronized with uniaxial compression and acoustic emission (AE) monitoring. The cross-scale damage evolution of RCC was investigated under dry, water-saturated, 25, and 50 F-T cycle conditions. The results indicate the following: (1) Macroscopically, F-T damage causes linear peak stress attenuation, shifting the failure mode from brittle axial splitting to ductile oblique shear. (2) Mesoscopically, frost-heaving stress expands native mesopores (500–2500 μm), increasing their volume fraction from 8.45% to 14.86% and remodeling isolated voids into a 3D interconnected defect network. (3) Microscopically, GMM-based AE clustering reveals a fracture transition. Driven by moisture lubrication and defect propagation, global shear cracks surpass the 50% threshold at 25 cycles (53.5%), reaching 68.6% at 50 cycles. (4) For cross-scale mapping, calibrating the AE b-value via Aki’s method decouples pore-water signal attenuation. Its pre-peak characteristic (an initial decrease followed by a rebound) accurately maps microcracks unstably coalescing along interconnected pores to form macroscopic shear planes. This cross-scale mechanism provides a scientific paradigm for condition monitoring of massive concrete in cold regions. Full article

Holes in the flanges of steel beams and girders are commonly required for bolted connections and can influence both flexural strength and rotational ductility. Although flange-hole effects have been investigated previously, the experimental basis of several traditional provisions was developed using older steels with relatively low yield-to-ultimate strength ratios. Current design specifications differ considerably in their treatment of open and fastener-filled flange holes. In particular, the relationship between flange-area reduction, flexural resistance, rotational ductility, and net-section fracture in modern structural steels remains insufficiently quantified. This study addresses these issues through tests of twenty-five full-scale W200 × 42 beams fabricated from ASTM A992 steel with a measured (F_y/F_u) ratio of approximately 0.77. The test program included solid beams, beams with open holes in the tension flange, beams with open holes in both flanges, and beams with fastener-filled holes in both flanges. The results demonstrate that flange-area reduction affected rotational ductility more severely than flexural strength. For the most severe tension-flange reduction investigated (A_fn/A_fg = 0.52), the maximum moment decreased by 16.8% relative to the solid beams’average maximum moment, whereas the total rotation capacity (R_y) decreased by 77.2%. The experimental capacities were also compared with predictions from AISC-LRFD, AASHTO-LRFD, CAN/CSA-S16, and AS 4100. Based on the observed strength and failure behavior, a design framework considering gross-section flexural resistance and modified net-section fracture resistance as competing limit states is proposed. Across the investigated specimens, the ratio of measured maximum moment to the proposed design moment (M_m/M_dp) ranged from 1.21 to 1.47, indicating conservative predictions within the experimental range considered. Full article

Finely dispersed Al–Ca–Ti composite alloys with a set of remarkable properties can be considered as new promising structural materials. For wider use of these alloys, data on their fatigue behavior are needed. In this work the comparative study of the low-cycle fatigue strength of hot-rolled Al–xCa–0.2Ti alloys with different eutectic fractions determined by different calcium contents was conducted. The fatigue tests were carried out according to a single-plane bending scheme using a dynamic mechanical analyzer. A symmetrical loading cycle (asymmetry coefficient R = −1) with a constant stress amplitude was used. The maximum number of cycles was 20,000. It was found that increasing the eutectic fraction from 40% to 80% led to a 75% increase in the fatigue limit—from 80 to 140 MPa—which directly correlated with the alloy’s yield strength. The fatigue crack propagation occurred with the formation of a scaly fracture surface, whereas final static rupture was associated with a ductile dimple fracture. The microstructural mechanisms of alloy fatigue failure were discussed. It was found that increasing the total length of the eutectic particles/aluminum matrix interphase boundaries changed the failure mechanism to a more brittle one. Full article

Four full-scale exterior beam-to-column connections comprising H-section beams and square hollow-section (SHS) columns were tested under low-cycle reversed loading to investigate two engineering-oriented T-stub section configurations and the effects of the presence or absence of triangular stiffeners. Failure modes, moment–rotation response, stiffness degradation, energy dissipation, and cumulative damage were evaluated, together with nonlinear finite element simulations and a modified Park–Ang damage assessment. All specimens progressed from bolt-hole slip through plastic deformation to localized fracture. In the unstiffened connections, damage concentrated near the T-stub flange-to-web junction; stiffeners redistributed critical demand toward the stiffener welds, adjacent T-stub webs, and SHS column walls. The maximum differences in initial rotational stiffness relative to J1A were 15.69% and 15.07% in the positive and negative loading directions, indicating that the elastic-stage response reflected the combined deformability of the T-stub, blind-bolt assembly, and column wall. The maximum increases in yield moment, peak-resistance moment, and ductility coefficient were 20.59%, 43.71%, and 45.91%, respectively. Complete-history energy dissipation varied non-monotonically across the tested configurations. The finite element model reproduced the global and local responses, while the damage-index results showed overall correspondence with the observed failure progression. The findings emphasize stiffness compatibility and rational distribution of plastic demand rather than maximum local stiffness. Full article

The use of manufactured sand (MS) as a substitute for natural sand or quartz sand in the production of ultra-high-performance manufactured sand concrete (UHPMC) represents a critical approach to alleviating the shortage of high-quality aggregates and promoting low-carbon development. However, after steel fibers and steel rebars are introduced into this material system, the synergistic working mechanism and damage evolution characteristics of the resulting ultra-high-performance manufactured sand-reinforced concrete (UHPMRC) beams under flexural loading remain largely unexplored. Acoustic emission (AE) technology, owing to its high sensitivity to the initiation and propagation of microcracks, enables real-time dynamic monitoring of UHPMRC beams throughout the entire process from the elastic stage to fracture failure, thereby providing an effective means to reveal the internal performance degradation law. Accordingly, this study conducted simultaneous AE monitoring on small-scale reinforced beams under four-point bending and investigated the effects of MS replacement ratios (0%, 50%, 100%) and steel fiber contents (1.0%, 1.5%, 2.0%). Results show that UHPMRC beams with 100% MS replacement and 1.5% steel fiber content achieve optimal performance. Compared to 0% MS specimens, those with 100% MS exhibit superior early stiffness, ductility, and flexural capacity due to the combined effects of steel fibers and MS. Beams with 2% steel fiber content experienced fiber clustering, reducing bridging capability and promoting earlier cracking relative to those with 1.5% fibers. AE energy parameters accurately identified cracking and characterized crack propagation in UHPMRC beams. Increasing MS content raised the proportion of shear cracks while reducing tensile cracks. The highest shear signal proportion occurred at 1.0% steel fiber content. These findings provide a valuable reference for the design of sustainable high-performance reinforced-concrete structures using manufactured sand. Full article

To address the insufficient load-bearing capacity and overall stiffness of timber truss roofs in brick–timber and earth–timber structures in rural areas, as well as the requirements for preserving traditional architectural characteristics, a steel–timber composite roof system was proposed. The system was developed through rational integration of timber and steel components to enhance the overall mechanical performance of the structure. At the joint level, flexural performance tests were conducted on cramp-iron joint, gusset–plate joint, and steel–timber joint. The moment–rotation relationships, failure modes, and ductility characteristics of the three joint types were systematically investigated. Based on the experimental results, a trilinear moment–rotation model was established. Furthermore, a finite element model of the roof structure was established using SAP2000 (26.2.0), and the stress distribution and load–displacement responses under horizontal static loading were analyzed through numerical simulation. The influence of different joint configurations on the mechanical performance of the roof structure was evaluated from an overall structural perspective. The results demonstrated that the peak bending moment of the steel–timber joint was increased by approximately 163.50% and 3.74% compared with those of the cramp-iron joint and gusset–plate joint, respectively. The ductility coefficient was enhanced by approximately 9.33% and 62.91%, respectively. In the finite element model of the roof structure, the peak load of the roof system with the steel–timber joint was increased by approximately 114.96% and 9.54%, while the corresponding displacement capacity was improved by approximately 76.62% and 43.41%, compared with the other two roof systems, respectively. Future studies will focus on further evaluating the seismic performance of steel–timber composite roof systems through cyclic loading experiments, dynamic response analysis, and full-scale structural validation, thereby providing a more comprehensive understanding of their long-term applicability in earthquake-prone rural buildings. Full article

High-strength steel has attracted increasing attention in civil engineering because of its high strength-to-weight ratio and potential for material-efficient design. This narrative review, supported by a structured literature search, summarizes recent advances in the material behaviour, durability and structural performance of high-strength steel. The discussion covers constitutive behaviour, fatigue and fracture, corrosion degradation, high-temperature and post-fire properties, residual stresses, structural members and connections. Existing studies show that increasing steel strength is commonly accompanied by reduced ductility and strain-hardening capacity, while local buckling, residual stress, welding-induced heterogeneity, fatigue damage, corrosion and thermal degradation remain important design concerns. The accuracy of current design provisions varies with steel grade, product form, section geometry, failure mode and exposure condition, and direct extension from conventional steels is not always appropriate. Future research should emphasize coupled degradation mechanisms, consistent material characterization, broader experimental validation and design models with clearly defined applicability limits. Full article

This study investigates the time-dependent seismic fragility of reinforced concrete (RC) bridge piers exposed to the harsh saline–alkali environments of Northwest China. A comprehensive analytical framework was developed by integrating quasi-static cyclic tests, nonlinear finite element modeling, and incremental dynamic analysis (IDA). Four pier specimens were subjected to accelerated corrosion in a composite sulfate–chloride solution for up to 90 days. Experimental results reveal a critical threshold: once the actual mass loss of the longitudinal reinforcement reaches approximately 12.05% (corresponding to a stirrup mass loss of approximately 21.45%), the severe loss of core confinement triggers a fundamental failure mode transition from ductile flexural yielding to brittle flexural-shear failure. Traditional displacement-based parameters are fundamentally inadequate for capturing this brittle shift; therefore, the Krätzig hysteretic energy dissipation index was adopted to rigorously quantify structural damage. Subsequently, a time-dependent Probabilistic Seismic Demand Model (PSDM) was constructed, explicitly incorporating the experimentally calibrated reinforcement degradation laws. The fragility analysis demonstrates a distinct biphasic degradation mechanism: while short-term sulfate attack temporarily enhances initial stiffness via a “pore-filling effect,” prolonged composite exposure drastically amplifies seismic vulnerability. Notably, under a severe earthquake intensity of 1.0 g (PGA), the exceedance probability for Severe Damage reaches 50.24% after 90 days of exposure, representing a 2.7-fold increase compared to the uncorroded baseline This research provides a robust, energy-based quantitative methodology for the lifecycle seismic evaluation and maintenance of transport infrastructure in aggressive composite environments. Full article

Cost is one of the decisive factors when selecting a fibre type for structural strengthening. This study therefore tested the hypothesis that a low-cost fibre can still provide a substantial improvement in the mechanical performance of strengthened timber beams. Four-point bending tests were carried out on 25 pine beams, comprising an unstrengthened reference series and four series strengthened with glass fibre reinforced polymer (GFRP) sheets, each series consisting of five specimens. The beams had nominal dimensions of 80 mm × 80 mm × 1600 mm. The reinforcement was bonded exclusively to the external surfaces, with a focus on the tension zone. Two variables were examined: the number of sheet layers and the extent of coverage of the timber surface. The reinforcement ratio ranged from 0.38% to 1.15%. The response of the beams was assessed in terms of load-bearing capacity, stiffness, ductility, and failure mode. Bonding three layers of sheet to the bottom face of the beams increased the load-bearing capacity by up to 58.20%. The effect on stiffness was less pronounced, with a maximum increase of 20%, which is attributable to the relatively low elastic modulus of the sheets. However, the ductility of the beams increased significantly (up to 126.14%, based on energy considerations), a result that can be directly attributed to the composite’s high adhesion and high elongation at rupture. The transformed cross-section method and finite element simulations were used to predict the behaviour of the strengthened elements, and both showed good agreement with the test results within the elastic range. It is concluded that GFRP sheets are a rational strengthening solution, although satisfactory effectiveness was obtained only at higher reinforcement ratios; at least two layers are recommended for the configurations tested. The effect of the strengthening configuration on the load-bearing capacity, on the deflection at maximum load and on the ductility was statistically significant, whereas its effect on the bending stiffness was not. Full article

To simulate the fracture behavior of members during structural collapse, this paper proposes a member fracture simulation algorithm that integrates the plastic hinge model with a ductile fracture damage model within the member discrete element method (MDEM) framework. The coupling is achieved by computing stresses at the four most unfavorable edge points of the contact section and using the minimum fracture strain as the section-level failure criterion. The algorithm is validated against a cantilever beam fracture example, yielding results in good agreement with reference data under two yield stress conditions. The fracture algorithm is then embedded as a self-contained module into an adaptively coupled DEM/FEM algorithm and applied to simulate the shaking table collapse test of a single-layer spherical reticulated shell. The simulation predicts structural collapse at a peak ground acceleration (PGA) of 2268 gal—consistent with the experimental value—with 126 members fractured at collapse onset, and reproduces the observed fracture sequence in which first-ring diagonal members near the supports fail progressively from the bottom upward. The proposed framework provides a computationally robust and practically deployable tool for collapse analysis of large-span reticulated structures, with direct implications for progressive-collapse prevention in seismic design and post-event structural forensic investigation of collapse mechanisms. Full article

The structure comprising precast prestressed concrete components (SCOPE joint) is widely used in prefabricated buildings. For this type of joint, insufficient anchorage of U-shaped reinforcing bars can lead to premature core failure. To address this, finite element models of SCOPE joints are developed in ABAQUS for parametric and mechanical analysis of U-shaped bars, and an improved joint with steel-strand-embedded anchorage is proposed. Comparisons of seismic performance and frame performance are conducted. The results indicate that in the conventional SCOPE joint, the strain of the U-shaped reinforcing bars concentrates within 100–150 mm outside the column, and the anchorage effect of the vertical segments is not mobilized; the yield penetration phenomenon further aggravates bond failure. In the improved joint, steel strands are anchored into the core and lapped in opposite directions, leading to a superior failure mechanism and plastic hinge formation sequence, enhanced capacity and ductility, and better conforming to the strong-joint–weak-component principle. This research offers a theoretical basis and detailing reference for seismic optimization of the SCOPE system. Full article

Welded reinforcement cages (WRCs), which connect longitudinal reinforcement and stirrups through welding, have attracted increasing attention for industrialized construction of reinforced concrete (RC) structures. However, the welding process may introduce heat-affected zones, residual stresses, and local metallurgical changes in reinforcing bars, raising concerns regarding the potential influence of welded longitudinal-bar-to-stirrup connections on the seismic performance of RC bridge piers. This study experimentally investigates this issue through quasi-static cyclic tests on two large-scale RC bridge pier specimens with identical reinforcement layouts but different reinforcement connection methods. One specimen adopted conventional tied connections between longitudinal reinforcement and stirrups, whereas the other employed welded connections. The seismic responses of the specimens were evaluated in terms of failure mode, hysteretic behavior, skeleton curve, strength, ductility, stiffness degradation, energy dissipation, residual displacement, and strain development. The results showed that both specimens exhibited flexure-dominated failure with similar crack propagation and concrete-cover spalling characteristics. The differences in yield and peak strengths were within 5%, and the cumulative energy dissipation differed by only 2.1%, indicating comparable global seismic performance. The welded specimen exhibited a slightly larger ultimate displacement (12.8%) and ductility coefficient (9.4%), while the stiffness degradation characteristics remained nearly identical. Although several weld spots detached during the post-peak loading stage, no fracture or necking of the longitudinal reinforcement was observed, suggesting that the adopted welding procedure did not adversely affect the cyclic deformation behavior of the reinforcement. Within the scope of the tested specimens, the results demonstrate that welded longitudinal-bar-to-stirrup connections can maintain the seismic performance of RC bridge piers and provide experimental evidence for the potential application of WRCs in industrialized bridge construction. Further studies involving additional specimens and broader design parameters are required to validate the general applicability of these findings. Full article

To systematically investigate the effects of C-shaped and rectangular steel frames on the seismic performance of assembled composite shear walls, this paper, based on the validation of existing pseudo-static test results, employs ABAQUS software to establish refined finite element models, and carries out parametric analyses on C-shaped steel-frame composite shear walls (CSCSWs) and rectangular steel-frame composite shear walls (RSCSWs). With shear-span ratio, axial-load ratio, boundary frame steel plate thickness, and concrete strength grade as variables, a total of 28 numerical models are designed to systematically examine the influence laws of each parameter on bearing capacity, ductility, energy dissipation capacity, and failure modes, and to reveal the performance differences in the confinement mechanisms of the two cross-sectional types. The results indicate that: as the shear-span ratio decreases from 3.0 to 1.0, the bearing capacity increases by up to 171%, but the ductility drops by up to 43%, and the failure mode shifts from flexure-dominated to shear-dominated; increasing the steel plate thickness can simultaneously enhance bearing capacity and ductility, with the peak load increasing by up to 52% and cumulative energy dissipation by over 110%, the mechanism being the synergistic enhancement of the flexural contribution of the boundary frame and the passive confinement effect on the core concrete; increasing the axial-load ratio can improve bearing capacity by about 24%, but significantly impairs ductility and energy dissipation capacity, and it is recommended that the design axial-load ratio be controlled between 0.26 and 0.43; the concrete strength grade has a limited effect on bearing capacity, and as the strength increases, brittle characteristics emerge, leading to a ductility decrease of about 12%; therefore, provided that the strength requirements are met, enhancing the concrete strength grade should not be taken as the primary technical approach for improving the seismic performance of such structures. Comparing the two cross-sectional types, the rectangular cross-section, by providing more uniform and effective lateral confinement, exhibits superior bearing capacity, ductility, and energy dissipation to the C-shaped cross-section across the entire parameter domain, and its performance advantages are more pronounced under conditions of high axial-load ratio and large shear-span ratio. Full article

The exploration of oil and gas resources is shifting toward ultra-deep and extra-deep reservoirs, including in the Tarim Basin, where various types of carbonate rocks are buried. Owing to the extreme burial depths, the mechanical behavior of these rocks under extra-deep conditions differs significantly from that of shallow formations, making it essential to understand their mechanical responses. This study investigated the mechanical properties and failure modes of carbonate rocks, specifically dolomite, argillaceous limestone, and pure limestone. Samples from extra-deep formations were initially analyzed for mineral composition and microstructure, after which uniaxial and triaxial compression tests were conducted to evaluate strength, static elastic modulus, and axial strain at peak stress. The results indicate that dolomite exhibits the highest mechanical strength and stiffness among the three lithologies. Under conditions of a high confining pressure of 100 MPa and a temperature of 160 °C, its elastic modulus and triaxial compressive strength are 65.4 GPa and 611.2 MPa, respectively, compared with 52.8 GPa and 444.2 MPa for limestone. Strength increases with confining pressure for all lithologies, with dolomite showing the most pronounced strengthening response. Although elevated temperature reduces rock strength, its effect is weaker than that of confining pressure. The failure mode is strongly controlled by confining pressure. At low confining pressures, failure is dominated by localized shear bands and brittle fracturing, whereas increasing confining pressure promotes a transition toward quasi-brittle deformation or ductile plastic flow. Dolomite predominantly maintains a quasi-brittle failure mode, argillaceous limestone exhibits a clear brittle-to-ductile transition, and pure limestone shows the greatest tendency to develop ductile plastic flow under high confining pressure conditions. The results further demonstrate that mineral composition and microstructural characteristics play critical roles in controlling the deformation and failure mechanisms of carbonate rocks. High-calcite pure limestone can exhibit ductile-like deformation behavior due to cataclastic processes, allowing significant strain without localization failure. These insights enhance understanding of carbonate rock behavior under extra-deep formations, informing practical applications in geology science. Full article

This study investigates the shear behavior and failure mechanisms of innovative hybrid structural beams fabricated by filling pultruded glass fiber-reinforced polymer (GFRP) box sections with waste rubber-reinforced concrete (RuC). Environmentally friendly concrete was produced by replacing natural aggregate with recycled tire-rubber fibers at proportions of 0%, 5%, 10%, and 15%. Twelve hybrid beam specimens were tested to evaluate the synergistic effects of rubber content and stirrup spacings of 16, 20, and 27 cm on shear capacity, ductility, and crack propagation. The experimental results revealed that the reference specimen (S16-0%) exhibited the maximum shear capacity of 154.41 kN and a brittle failure mode, while an increase in rubber content to 15%, combined with wider stirrup spacing, significantly reduced this capacity to a minimum of 96.89 kN (S27-15%). However, the 5% rubber replacement ratio achieved an optimal performance balance by preserving sufficient load-carrying capacity while enhancing flexural deformation and ductility, particularly in specimens with 16 cm stirrup spacing. Damage analysis demonstrated that longitudinal splitting cracks initiated in the mid-span tension zone at the bottom of the pultruded profiles, with final localized damage concentrated at the geometric corners of the box section. Crucially, the outer pultruded GFRP profiles provided substantial structural confinement, effectively mitigating the strength loss associated with high rubber incorporation and controlling the progression of sudden brittle failure. These findings highlight that combining pultruded GFRP profiles and optimized RuC offers a structurally viable and sustainable solution for modern infrastructure applications. Full article