Search Results (222)

Geopolymer mortars were produced from construction and demolition waste using a binary binder of recycled brick powder/recycled concrete powder (RBP/RCP = 70/30 wt%), activated with a hybrid alkaline solution (NaOH/Na₂SiO₃/KOH) and reinforced with sisal fibres at 0–2 wt%. Mechanical performance (compression and three-point bending) and microstructure–phase evolution (XRD, FTIR, SEM-EDS) were assessed after low-temperature curing. Sisal addition delivered a strength–toughness trade-off with a reproducible optimum at ~1.0–1.5 wt%; at 2.0 wt%, fibre clustering and connected porosity reduced the effective load-bearing section, penalising flexure more than compression. Microstructural evidence indicates coexistence and co-crosslinking of N-A-S-H and C-(A)-S-H gels—enabled by Ca from RCP—leading to matrix densification and improved fibre–matrix anchorage. Fractographic features (tortuous crack paths, bridging, and extensive pull-out at ~1.5 wt%) are consistent with an extended post-peak response and higher fracture work without compromising early-age strength. This study achieves the following: (i) it identifies a practical reinforcement window for sisal in RBP/RCP geopolymers, (ii) it links gel chemistry and interfacial phenomena to macroscopic behaviour, and (iii) it distils processing guidelines (gradual addition, workability control, gentle deaeration, and constant A/S) that support reproducibility. These outcomes provide a replicable, low-embodied-CO₂ route to fibre-reinforced geopolymer mortars derived from CDW for non-structural and semi-structural applications where flexural performance and post-peak behaviour are critical. Full article

Designing long-span cable-stayed bridges in high seismic hazard zones presents significant challenges due to their flexible structural systems, the influence of multi-support excitation, and the need to control large displacements while limiting seismic demands on critical components. These difficulties are further amplified in regions with complex geology and for bridges required to maintain high levels of post-earthquake serviceability. This study develops a low-damage seismic design approach for long-span cable-stayed bridges and demonstrates its application in the New Panama Canal Bridge. Probabilistic seismic hazard assessment and site response analyses are performed to generate spatially varying ground motions at the pylons and side piers. The pylons adopt a reinforced concrete configuration with embedded steel stiffeners for anchorage, forming a composite zone capable of efficiently transferring concentrated stay-cable forces. The lightweight main girder consists of a lattice-type steel framework connected to a high-strength reinforced concrete deck slab, providing both rigidity and structural efficiency. A coordinated girder–pylon restraint system—comprising vertical bearings, fuse-type restrainers, and viscous dampers—ensures controlled stiffness and effective energy dissipation. Nonlinear seismic analyses show that displacements of the girder remain well controlled under the Safety Evaluation Earthquake, and the dampers and bearings exhibit stable hysteretic behaviours. Cable tensions remain within 500–850 MPa, meeting minimal-damage performance criteria. Overall, the results demonstrate that low-damage seismic performance targets are achievable and that the proposed design approach enhances structural control and seismic resilience in long-span cable-stayed bridges. Full article

This study proposes a high-strength bottom-bar interlocking and anchorage precast beam–column joint (HSRU-PBCJ), which utilizes high-strength longitudinal reinforcement combined with U-shaped anchorage at the beam bottom. Low-cycle reversed loading tests were conducted on two precast specimens and one cast-in-place specimen to evaluate their seismic performance. Based on these results, parametric analyses were conducted through numerical simulations to investigate the effects of axial compression ratio, concrete strength, beam-end longitudinal reinforcement strength, and beam-end longitudinal reinforcement ratio on the seismic performance. The results indicate that the proposed joint exhibits stable and full hysteresis loops, cumulative energy dissipation comparable to that of the cast-in-place joint, and a 23.94–26.39% increase in equivalent viscous damping after yielding, achieving a displacement ductility coefficient of 4.14, which confirms its substantially improved seismic performance. The parametric study shows that maintaining a moderate axial compression ratio (≤0.6) enhances both load-bearing capacity and energy dissipation, whereas excessive values result in strength reduction. Increasing the beam-end longitudinal reinforcement strength significantly improves load-bearing capacity but may reduce energy dissipation. In addition, improving concrete strength and appropriately increasing the reinforcement ratio can further enhance both load-bearing capacity and energy dissipation, although a balance between seismic performance and economic considerations is recommended. Full article

To evaluate the stability of fiber-reinforced cemented foamed backfill (FCFB) in complex underground mining environments, this study investigates the synergistic effects of fiber content and modified coal gangue (MCG) under acidic and high-temperature conditions. Through a systematic analysis of hydration processes, compressive strength, and deformation characteristics, the research identifies critical mechanisms for optimizing backfill performance. Calcination of MCG at 700 °C enhances gelling activity via amorphous phase formation, while modified aluminum dross (MAD) treated at 950 °C develops dense α-Al₂O₃ and spinel phases, significantly improving chemical stability. In acidic environments, the suppression of calcium silicate hydrate (C-S-H) is offset by the development of Al³⁺-driven C-A-S-H gels. These gels adopt a tobermorite-like structure, substantially increasing acid resistance. Mechanical testing reveals that while 1% fiber reinforcement promotes nucleation and densification, a 2% concentration hinders hydration. Compressive strength at 28 days shows constrained growth due to pore inhibition, and failure modes transition from multi-crack parallel failure (3-day) to single-crack tensile-shear failure. Under acidic conditions, strain concentration in the upper sample highlights a competitive mechanism between Al³⁺ migration and fiber anchorage. Ultimately, the coordinated regulation of MCG/MAD and fiber content provides a robust solution for roof support in challenging thermo-chemical mining environments. Full article

Based on ongoing experimental research, the present manuscript presents the effect of the slippage of a steel reinforcing bar due to corrosion on the chord rotation and deformation of corroded Reinforced Concrete members. The experimental results recorded that the increase in the corrosion level of the steel led to bond strength loss and relative slip between the steel and concrete, which was increased from 1.5 mm in non-corroded conditions to 3.5 mm even at low corrosion levels, up to a 5% steel mass loss. This slippage of corroded reinforcing bars from the anchorage leads to a proportional increase in terms of chord rotation due to pull out resulting in an additional increase in the displacement of the column’s top. In conclusion, the present study highlights the great importance of the contribution of the resulting slippage of a steel reinforcing bar due to corrosion in the calculation of the limit chord rotation (column–beam), a term which is of major importance in the assessment of the structural integrity of old RC structures, which was introduced as an adequacy requirement by both Eurocode 8-3 and the Greek Code of Structural Interventions (KAN.EPE). Full article

Grouted sleeves are commonly used to connect prefabricated structural components, but construction defects can easily occur after installation, posing potential risks to the structure. This study conducts comparative uniaxial tensile tests on 39 grouted-sleeve specimens in 13 groups—including standard specimens, defective specimens, and specimens repaired with supplementary grouting. The strain distribution patterns under different grouting lengths and loading levels are analyzed to investigate the load-transfer mechanism between reinforcement bars and grouted sleeves, as well as the influence of various supplementary grouting amounts and material strengths on the mechanical performance of defective sleeves. In the uniaxial tensile test of grouted sleeves, with grout strengths of 85 MPa and 100 MPa and HRB400-grade steel bars, when the grouted anchorage length was 4 d, insufficient anchorage length resulted in low bond strength between the grout and the steel bar, leading to bond–slip failure. When the grouted anchorage length reached 6 d, steel bar fracture occurred inside the sleeve. When the total anchorage length formed by two grouting sessions reached 8 d, specimen slippage decreased, showing a trend where the strain growth rate of the sleeve gradually decreased from the grouted end to the anchored end, while the strain growth rate of the steel bar gradually increased. The longer the total anchorage length in the sleeve after grout repair, the stronger its anti-slip capability. The bearing capacity and failure mode of the specimens depend on the strength of the steel bars connected to the grouted sleeves and the strength of the threaded connection ends at the top. Experimental results show that the anchorage length and strength of high-strength grout materials have a significant reinforcing effect on defective sleeves. The ultimate bearing capacity of specimens with anchorage length of 6 d or more is basically the same as that of steel bars. Specimens with a total anchorage length of 8 d show approximately 10~20% less slippage than those with 6 d. The safe anchorage length for HRB400-grade steel bars in sleeve-grouted connections is 8 d, even though the bearing capacity of grouted sleeves with a 6 d anchorage length already meets the requirements. Bond strength analysis confirms that the critical anchorage length is 4.49 d. When the grouted anchorage length exceeds the critical length, the failure mode of the specimen is steel bar fracture. When the grouted anchorage length is less than the critical length, the failure mode is steel bar slippage. This conclusion aligns closely with experimental results. In engineering practice, the critical anchorage length can be used to predict the failure mode of grouted sleeve specimens. Based on experimental research and theoretical analysis, it is clear that using grout repair to reinforce defective grouted sleeve joints with a safe anchorage length of 8 d is a secure and straightforward strengthening method. Full article

The use of miniscrews as Temporary Skeletal Anchorage Devices (TSAD) in orthodontics has allowed clinicians to perform challenging tooth movements by dissipating undesired forces into the bone structure; thus, avoiding unwanted movement of the adjacent teeth. It is essential for miniscrews to be highly resistant to fracture during clinical use. While many studies have analysed torsional loads, none have measured the changes in flexural and bending strength of miniscrews before and after an ageing process. This study aims to analyse the resistance to orthogonal forces of miniscrews with different diameters, focusing on both new and aged materials, the latter subjected to thermocycling and autoclaving laboratory processes to simulate a 3- and a 6-month exposure to the oral environment. A total of 105 pristine miniscrews have been tested; specimens were divided into seven groups based on the different endosseous body diameters. Each group was further subdivided into three subgroups, according to the simulated ageing of the miniscrews (intact, 3 months of ageing and 6 months of ageing, respectively). An Instron Universal Testing Machine has been used to measure deflection at 0.1 mm and 0.2 mm, as well as maximum load at fracture. The results evidenced that miniscrews respond differently to cutting forces; in particular, the resistance to orthogonal loads increases as the diameter of the miniscrews increases. Linear regression analysis revealed a significant influence between all the dependent variables—maximum load, 0.1 mm deflection load, and 0.2 mm deflection load—and the independent variables, such as diameter and thermocycling (p < 0.05). Both new and aged miniscrews are suitable for orthodontic and orthopaedic loads; moreover, ageing up to 6 months does not seem to significantly decrease the resistance to shear forces for the same diameter. Linear regression analysis of the miniscrews subjected to experimental ageing showed a slight but significant decrease in resistance to orthogonal loading. Full article

This study presents an experimental investigation into the seismic performance of seismically deficient reinforced concrete (RC) bridge columns retrofitted with passive and active confinement systems. Four single-cantilever RC columns, representing 1/3-scale bridge piers, were constructed with poor transverse reinforcement detailing to simulate seismic deficiency. One column was left un-strengthened for baseline comparison, while the remaining three were retrofitted using: (1) a CFRP jacket, (2) welded Fe-SMA plates, and (3) bolted Fe-SMA plates. All columns were subjected to quasi-static lateral cyclic push-only loading reaching extreme drift levels exceeding 16% and high loading rates up to 6 mm/s. The study specifically explores the confinement effectiveness of CFRP and thermally activated Fe-SMA plates, comparing their contributions to lateral strength, ductility, energy dissipation, failure mode, and damage suppression. The results show that while the as-built column failed at 3.65% drift due to brittle flexural-shear failure, all retrofitted columns demonstrated significantly enhanced ductility, drift capacity, and post-peak behaviour. The CFRP and Fe-SMA jackets effectively delayed damage initiation, minimized core degradation, and improved energy dissipation. The bolted Fe-SMA system exhibited the highest and full restoration of lateral strength, while the welded system achieved the greatest increase in cumulative energy dissipation of around 40%. This research highlights the practical advantages and seismic effectiveness of Fe-SMA and CFRP confinement systems under extreme drift levels. However, future work should explore full-scale column applications, refine anchorage techniques for improved composite interaction, and investigate long-term durability under cyclic environmental conditions. Full article

Fiber-reinforced polymers (FRPs) are being increasingly used to replace rebars as reinforcements for concrete. This study evaluated the seismic behavior of concrete walls reinforced with grid-type carbon FRP (CFRP; carbon grid) through quasi-static cyclic tests and compared the results with that of the reinforced concrete (RC) wall. The experimental variables were the ratio of the carbon-grid anchorage length in the foundation to the wall length and the axial force ratio. Based on the results of the quasi-static cyclic tests, the ratio of the equivalent stiffness at the crushing of the compression-edge cover concrete to the initial stiffness of the carbon-grid-reinforced concrete specimens was 0.14 on average. This indicates that the specimens reached their maximum load due to the crushing of the compression-edge cover concrete after a significant reduction in stiffness due to cracking. The skeleton curve for the carbon-grid-reinforced concrete specimens was found to be bilinear, with reduced stiffness due to cracking and failure due to the crushing of the compression-edge cover concrete, making it definable and predictable. Additionally, in specimens with a high axial force or small ratio of the anchorage length in the foundation to the wall length, some of the longitudinal CFRP strands fractured at the same time as they reached the failure load. Moreover, the load at the crushing of the compression-edge cover concrete of the carbon-grid-reinforced concrete specimen increased by 1.10 times with the increase in the axial force ratio and decreased by 0.96 times with the decrease in the ratio of the anchorage length in the foundation to the wall length. It was found to be 0.73–0.80 times the flexural strength based on the assumption of plane sections remaining plane. In comparison with RC specimen, the cumulative absorbed energy of the carbon-grid-reinforced concrete specimen began to decrease after a story drift ratio of 1%, and the cumulative absorbed energy up to the target story drift ratio of 3.0% was found to be 0.60–0.62 times that of the RC specimen. Full article

A precast concrete sandwich panel (PCSP), consisting of inner and outer wythes, an insulation layer, and connectors, relies heavily on the shear behavior of these connectors, which governs the structural performance of the entire system. Owing to their low thermal conductivity, excellent durability, and high strength, fiber-reinforced polymer (FRP) connectors offer strong potential for widespread application. This study introduces a novel cross-shaped FRP rod connector designed to provide improved anchorage performance, bidirectional shear resistance, and ease of installation. However, concern remains about the specific influence of embedment depth, outer-wythe thickness, and insulation-layer thickness on its shear performance. Moreover, no calculation model for shear capacity or shear–slip model has been established considering the shear-bending interaction within the connector. To evaluate its shear behavior, six groups of push-out tests were conducted, with key parameters including embedment depth, outer-wythe thickness, and insulation-layer thickness. The specimens exhibited two primary failure modes: connector fracture and concrete anchorage failure. The measured shear capacity per connector ranged from 5.63 kN to 14.19 kN, increasing with longer embedment depths, decreasing with increasing insulation thickness, and showing no clear dependence on outer-wythe thickness. Guided by test results and the Hashin failure criterion for composite materials, analytical formulas to estimate the shear capacity of FRP connectors were developed. The mean ratio of calculated to experimental values is 0.97, with a standard deviation of 0.06, indicating good agreement between the predicted and measured shear capacities. Furthermore, a theoretical shear–slip model was established. The correlation coefficients between the experimental and calculated load–slip curves for all specimens are greater than 0.98, indicating a high consistency in curve shape and variation trend. Full article

The SBPDN (Steel Bar Prestressed Deformed Normal relaxation) bar, which has ultra-high yield strength yet much lower bond resistance than conventional deformed bars, has been recently proposed to be used as the longitudinal rebar instead of a normal-strength deformed bar to simply realize strong earthquake-resilient concrete components. To facilitate and promote the application of concrete components reinforced with SBPDN rebars to the structures located in earthquake-prone regions, it is indispensable to develop reliable and effective anchoring means and clarify the bond strength of SBPDN bars embedded in concrete and/or grout mortar. This paper presents experimental information on the pull-out tests of fifteen SBPDN bars embedded in grout mortar, along with a discussion on the effective anchorage details and the bond strength of SBPDN bars. The tested SBPDN bars have a nominal diameter of 22.2 mm, the maximum diameter currently available on the market. All SBPDN bars were embedded in high-strength grout mortar with a targeted compressive strength of 60 MPa. The primary experimental variables included the end anchorage details, the diameter of sheath ducts, and the embedded length of the bars. Test results demonstrated that either screwing two nuts and a washer at the end of SBPDN bars or providing a rolling-threaded end region was effective in preventing them from premature slip from grout mortar. If the embedment length was 20 times the bar diameter or longer, the proposed two anchorages could ensure the SBPDN bar to fully develop its specific yielding strength as high as 1275 MPa. In addition, it has also been experimentally revealed that the bond strength of SBPDN bars embedded in grout mortar was much lower than that of conventional deformed bars and varied between 2.84 MPa and 3.98 MPa. Full article

Steel portal frames are widely used in industrial buildings due to their high strength-to-weight ratio and rapid erection capability. However, many existing structures exhibit insufficient load-carrying capacity under current design requirements. This study investigates the use of external post-tensioning (PT) cables and rigid wedge anchorages to enhance the overall performance of steel portal frames. Two stages of numerical analysis were performed: (i) two-dimensional parametric studies to identify the most efficient configuration and (ii) three-dimensional verification under combined gravity, wind, and seismic loading conditions. Results show that the proposed PT system significantly increases the load-carrying capacity of both beams and columns, reduces bending demands, and improves global stability without major geometric modification. The strengthening method is safe, reversible, and offers a practical alternative to conventional welded or plated retrofit techniques. Full article

Background/Objective: To outline strategies for the safe clinical use of orthodontic temporary anchorage devices (TADs) by analyzing papers that examine associated risks, complications, and approaches for their prevention and resolution. Methods: The research protocol used PubMed, Medline, and Scopus up to May 2024, focusing on controlled and randomized clinical trials aligned with the review objective. Fourteen studies were included; bias risk was assessed, key data extracted, and a descriptive analysis performed. Study quality and evidence strength were also evaluated. Results: TADs optimize anchorage control without relying on patient compliance. However, they carry risks and complications. TAD contact with the periodontal ligament or root without pulp involvement requires removal for spontaneous healing. If pulp is involved, the TAD should be removed and endodontic therapy performed. If anatomical structures are violated, TAD should be removed. If transient, spontaneous recovery occurs, but sometimes pharmacological treatment may be needed. A 2 mm gap between the TAD and surrounding structures can prevent damage. In the maxillary sinus, a less than 2 mm perforation of the Schneiderian membrane recovers spontaneously; wider perforations require TAD removal. Good oral hygiene and TAD abutments prevent soft tissue inflammation, which resolves with 0.2% chlorhexidine for 14 days. Unwanted forces can cause TAD fractures, requiring removal. Minor TAD mobility due to loss of primary stability can be maintained; significant instability requires repositioning. Conclusions: The use of TADs requires meticulous planning, radiological guidance, and monitoring to minimize risks and manage complications. With proper care, TADs improve orthodontic outcomes and patient satisfaction. Full article

Tree stability under wind loading is a critical concern for risk management in urban and natural environments. Despite advances in assessment methods, discrepancies persist between theoretical predictions and real-world tree behaviour. This study presents results from an extensive field investigation conducted at the University of Dundee Botanic Gardens to evaluate tree uprooting stability through non-destructive static, dynamic, and uprooting tests. This paper focusses on the programme of non-destructive and uprooting tests conducted across twenty-one trees of a variety of coniferous and deciduous species. Regarding the non-destructive tests, multiple tests were carried out on the same trees, varying both the pulling direction and the pulling height. Geotechnical properties, including shear strength, water content, soil water retention behaviour, and granulometry, were characterized to assess their role in root anchorage. These characteristics were seen to be at least as important as species. The results revealed that the maximum overturning moment (M_L) occurred between a 1.6 and 2.9° inclination during uprooting for the partially saturated ground conditions at the time of testing, irrespective of species or biometric parameters. The findings contribute to refining tree stability assessments, offering practical insights for arboriculture and urban planning. Full article

In deep coal mines characterized by high temperature, high humidity, high-salinity water, and elevated ground stress, stress corrosion cracking (SCC) of bolts is widespread, causing frequent instability of roadway surrounding rock and hindering long-term stability. This study systematically examines the failure characteristics of anchorage materials in highly corrosive roadways and clarifies the effects of deep-mine temperature and humidity on material corrosion. Long-term corrosion tests on bolts reveal changes in mechanical properties and macroscopic morphology and elucidate the intrinsic mechanisms of SCC. The results show that with the increase in corrosion time, the yield strength, ultimate load and elongation of the anchor rod decrease by up to 11.8%, 13.6%, and 7.08%, respectively. Under high stress, localized corrosion pits form on bolt surfaces, rupturing the oxide film and initiating rapid anodic dissolution and cathodic hydrogen evolution. Interaction between corroded surfaces and microcracks produced by internal impurities leads to progressive damage accumulation and ultimate fracture of the bolts. These findings provide guidance for corrosion protection of coal mine roadway support materials and for improving the long-term performance of roadway supports. Full article