Search Results (173)

Reinforced concrete (RC) deep beams constructed with low-strength concrete are susceptible to sudden splitting failures in the strut region due to shear–compression stresses. To mitigate this vulnerability, various strengthening techniques, including steel plates, fiber-reinforced polymer sheets, and cementitious composites, have been explored to confine the strut area. This study investigates the structural performance of RC deep beams with low-strength concrete, strengthened externally using an Engineered Cementitious Composite (ECC) layer. To ensure effective confinement and uniform shear distribution, shear reinforcement was provided at equal intervals with configurations of zero, one, and two vertical shear reinforcements. Four-point bending tests revealed that the ECC layer significantly enhanced the shear capacity, increasing load-carrying capacity by 51.6%, 54.7%, and 46.7% for beams with zero, one, and two shear reinforcements, respectively. Failure analysis through non-linear finite element modeling corroborated experimental observations, confirming shear–compression failure characterized by damage in the concrete struts. The strut-and-tie method, modified to incorporate the tensile strength of ECC and shear reinforcement actual stress values taken from the FE analysis, was used to predict the shear capacity. The predicted values were within 10% of the experimental results, underscoring the reliability of the analytical approach. Overall, this study demonstrates the effectiveness of ECC in improving shear performance and mitigating strut failure in RC deep beams made with low-strength concrete. Full article

The effectiveness of an innovative retrofit scheme using near-surface-mounted (NSM) X-shaped CFRP ropes for the strengthening of substandard RC beam–column joints was investigated experimentally. Three large-scale beam–column joint subassemblages were constructed with poor reinforcement details. One specimen was subjected to cyclic lateral loading, exhibited shear failure of the joint region and was used as the control specimen. The other specimens were retrofitted and subsequently subjected to the same history of incremental lateral displacement amplitudes with the control subassemblage. The retrofitting was characterized by low labor demands and included wrapping of NSM CFPR-ropes in the two diagonal directions on both lateral sides of the joint as shear reinforcement. Single or double wrapping of the joint was performed, while weights were suspended to prevent the loose placement of the ropes in the grooves. A significant improvement in the seismic performance of the retrofitted specimens was observed with respect to the control specimen, regarding strength and ductility. The proposed innovative scheme effectively prevented shear failure of the joint by shifting the damage in the beam, and the retrofitted specimens showed a more dissipating hysteresis behavior without significant loss of lateral strength and axial load-bearing capacity. The cumulative energy dissipation capacity of the strengthened specimens increased by 105.38% and 122.23% with respect to the control specimen. Full article

Particulate matter (PM) originating from road dust is an increasing concern in urban air quality, particularly as non-exhaust emissions from tire–pavement interactions gain prominence. Existing models often focus on meteorological and traffic-related variables while oversimplifying pavement surface characteristics, limiting their applicability across diverse spatial and traffic conditions. This study investigates the influence of concrete pavement macrotexture—specifically the Mean Texture Depth (MTD) and surface wavelength—on PM₁₀ resuspension. Field data were collected using a vehicle-mounted DustTrak 8530 sensor following the TRAKER protocol, enabling real-time monitoring near the tire–pavement interface. A multivariable linear regression model was used to evaluate the effects of MTD, wavelength, and the interaction between silt loading (sL) and PM₁₀ content, achieving a high adjusted R² of 0.765. The surface wavelength and sL–PM₁₀ interaction were statistically significant (p < 0.01). The PM₁₀ concentrations increased with the MTD up to a threshold of approximately 1.4 mm, after which the trend plateaued. A short wavelength (<4 mm) resulted in 30–50% higher PM₁₀ emissions compared to a longer wavelength (>30 mm), likely due to enhanced air-pumping effects caused by more frequent aggregate contact. Among pavement types, Transverse Tining (T.Tining) exhibited the highest emissions due to its high MTD and short wavelength, whereas Exposed Aggregate Concrete Pavement (EACP) and the Next-Generation Concrete Surface (NGCS) showed lower emissions with a moderate MTD (1.0–1.4 mm) and longer wavelength. Mechanistically, a low MTD means there is a lack of sufficient voids for dust retention but generates less turbulence, producing moderate emissions. In contrast, a high MTD combined with a very short wavelength intensifies tire contact and localized air pumping, increasing emissions. Therefore, an intermediate MTD and moderate wavelength configuration appears optimal, balancing dust retention with minimized turbulence. These findings offer a texture-informed framework for integrating pavement surface characteristics into PM emission models, supporting sustainable and emission-conscious pavement design. Full article

The work presents and examines a fiber anchoring system of NSM CFRP strips proposed for strengthening RC beams. The study included 11 beams: 3 unstrengthened beams, 3 beams strengthened with NSM CFRP strip without anchorage, and 5 beams strengthened with NSM CFRP strips with additional anchorage in two variants (the fiber anchor wrapped around the CFRP strip end and fan-folded on the beam surface; the fiber anchor connected with a 20 cm overlap to the strip). All beams were loaded until failure with two concentrated forces (four-point loading test). The measurements were carried out using digital image correlation (DIC). The obtained ultimate load values reached an average of 43.5 kN for unstrengthened beams, while for strengthened beams, they ranged between 56.6 kN and 60.2 kN. The strengthening efficiency was comparable for all beams regardless of the anchorage used and ranged from 29% to 37%. All strengthened beams failed due to strip debonding. The obtained results did not allow confirmation of the effectiveness of the proposed anchoring system. Detailed analysis showed that the lack of anchoring effectiveness was related to the debonding initiating factor, i.e., vertical crack opening displacement, which has not been described in proper detail by the researchers. Full article

The interference of metal working surfaces on the electric field can lead to performance variations between the flush mounting and non-flush mounting of capacitive proximity sensors in industrial applications. Traditional active shielding circuit designs are complex, while grounding shields not only reduce the sensor sensitivity but are also unsuitable for grounded sensors. To address this issue, this paper proposes an innovative near-ground (NG) shielding structure. This structure effectively concentrates the electric field between the sensing electrode and ground by adding a common ground electrode around the sensing electrode, thereby reducing the electrical coupling between the metal working surface and the sensing electrode and achieving the desired shielding effect. Through finite element analysis and experimental verification, this study performed an in-depth investigation of the capacitance difference $C_d$ and the rate of change of capacitance with the target distance of sensors under the two mounting methods. The proposed structure achieved a performance comparable with active shielding (17 fF $C_d$) while operating passively, which addressed a critical cost–adaptability trade-off in industrial CPS designs. The results show that although the performance of the NG shielding was slightly inferior to active shielding, it was significantly better than traditional grounding shielding, and its structure was simple and low cost, showing great potential in practical applications. Full article

In this paper, a systematical study on the influence of strengthening parameters on the flexural performance of RC beams using the NSM application was carried out. Experimental results consist of two reference beams and 25 beams divided into two groups using NSM systems with various embedded bars and strengthening configurations were presented. Additionally, theoretical analysis was conducted to enrich the research on the parameters affecting the strength and failure mode of the beams. The accuracy of the theoretical formulas has been verified through experimental results, and the average value of the ratio between the theoretical and experimental values is approximately 0.9. Results indicated that NSM technology is an effective approach for strengthening RC structures. Compared with the control specimens, the maximum load-bearing capacity of the beams with the NSM system experiences a remarkable enhancement of nearly 140%. The flexural behavior of the beams strengthened by the NSM system are closely related to the material properties (steel bar, NSM bars, concrete, and filler), location of the cutoff points, external confinement, and prestress level. The NSM bars characterized by high strength and high elasticity prove to be far more advantageous in enhancing the strength of the strengthened specimens. The research findings can provide theoretical support for the practical engineering applications of the NSM technology in strengthening reinforced concrete structures. Full article

Ground-based ground-penetrating radar (GPR) has been applied successfully for decades in archaeological geophysics. However, there are sometimes severe problems arising in cases of rough terrain, permission to enter a site, or due to vegetation. Other issues may also make it impossible to use conventional ground-based GPR. Therefore, mounting the GPR antenna below a drone could be a potential alternative. Successful applications of drone-based GPR have already been reported, e.g., in the fields of geological mapping, glaciology, and UXO-detection. However, it is not clear whether faint archaeological remains can also be mapped using this approach. In the survey discussed below, we tested such a drone-based GPR setup at an archaeological site in Bavaria, where well-preserved Roman foundations at a shallow depth are known from previous geophysical surveys with magnetics and ground-based GPR. The aim was to evaluate the possibilities and problems arising with this new approach through a comparison with the afore-mentioned data, obtained in previous ground-based surveys of this site. The results show that under certain circumstances, the archaeological remains can be resolved while using a drone. However, the remains are much harder to detect with a lower degree of resolution and survey setup and acquisition time play a crucial role for a successful survey. Especially relevant are two factors: First, the correct choice of profile orientation, as there are strong reflections caused by near-surface features (like field boundaries) due to decoupling the antenna from the ground. Second, a very dry soil is mandatory, as otherwise too much signal is lost at the air-ground-interface. Considering these factors, drone-based GPR represents a valuable tool for modern archaeological geophysics. Full article

Strengthening lapped spliced reinforced concrete (RC) beams using tiny-diameter steel wires as near-surface-mounted (NSM) rods has not been carried out previously. Thus, the purpose of this work is to examine the behavior of RC beams with insufficient lap splices that are strengthened by NSM steel wires with different schemes to improve durability, efficiency, and effectiveness. At the middle of the beam, a splice length equal to 25 times the diameter of the rebar was used to join two tension bars. Many different schemes were implemented in strengthening the splice region, such as attaching longitudinal wires to the sides and/or bottom of the beam in different quantities with/without end anchorage, placing perpendicular and inclined U-shaped wires at the splice region in different quantities, and implementing a network of intersecting and opposite wires in two different directions. The effect of variables on the behavior of strengthened beams was studied. The findings proved that when the longitudinal wire reinforcement-to-lapped rebars area ratio was 9.4%, 18.7%, and 28%, the ultimate load of the beams was improved by 15.71%, 71.43%, and 104.57%, respectively. When the transverse U-shaped wire reinforcement ratio was 0.036, 0.051, 0.064, 0.075, and 0.150, the ultimate load of the beams was improved by 3.7%, 20%, 31.4%, 50%, and 80%, respectively, and the ultimate deflection was enhanced by 2%, 32%, 19%, 67%, and 62.4% compared to the unstrengthened beam. Full article

The aim of this experimental study was to develop and evaluate the effectiveness of a new strengthening system for reinforced concrete slabs employing external jackets consisting of ultra-high-performance fiber-reinforced-concrete (UHPFRC) and mechanical anchor systems. The issue of debonding between old and fresh concrete layers, as well as the efficiency of utilizing CFRP rods, is the primary challenge of applying the UHPFRC jackets with embedded CFRP rods. In this study, we propose a novel retrofitting technique for implementing a mechanical anchor system to improve the binding of fresh UHPFRC jackets with old RC slabs. An experimental test was conducted by subjecting three slabs to cyclic loads by utilizing a dynamic actuator: a reference slab, a retrofitted slab with an external UHPFRC layer, and a retrofitted slab with an external UHPFRC layer incorporating CFRP bars. Furthermore, finite element models (FEMs) were utilized to investigate the responses of the retrofitted slabs and compare the novel method with traditional strengthening techniques, including near-surface-mounted (NSM) CFRP rods, externally bonded CFRP strips, and epoxy-bonded UHPFRC jackets, as well as two models that were the same as the experimental strengthened slab specimens except for the fact that they did not have a mechanical anchor system. Additionally, analytical mechanistic models were employed to determine the flexural moment capacity of the RC slabs. The experimental findings demonstrated that the proposed strengthening strategy considerably prevented premature debonding and enhanced the maximum load of retrofitted RC slabs by over 82%. Also, the FEM and analytical results are significantly consistent with the experimental outcomes. In conclusion, the newly suggested strengthening technique is a reliable system for enhancing the efficacy of slabs, effectively preventing early debonding between existing and new components. Full article

Reinforced concrete (RC) walls are mainly used in RC structures to resist gravity and lateral forces. These structural elements may need to be upgraded to withstand additional forces and extend their life cycle. Therefore, it is crucial to provide effective strengthening techniques using low-cost sustainable materials under optimal conditions to rehabilitate RC walls. This study presents an experimental and numerical investigation of reinforced normal concrete (NC) walls strengthened with near-surface mounted (NSM) steel bars, confined with or without an externally bonded reinforced (EBR) galvanized steel sheets (GSSs). A total of six RC walls were constructed, loaded, and tested to failure. The examined parameters included the type of strengthening technique, materials used, and the position and configuration of the strengthening. Both EBR and NSM techniques were applied using GSSs and steel bars, respectively. The configurations were introduced in vertical and horizontal positions to resist gravity and lateral forces, respectively. The experiments revealed that these parameters significantly influenced the crack control, energy absorption, mode of collapse, and ultimate load capacity. Nonlinear three-dimensional finite element models were developed and verified against experimental results, achieving a validation accuracy of 95% on average. This was followed by a parametric study investigating the effect of confinement with or without vertical reinforcements. Both experimental and numerical results confirmed that the strengthening could increase the ultimate load capacity from 20% to 38%. Full article

This study presents a novel method for calculating the stress and bending moment in reinforced concrete (RC) beams strengthened with prestressed near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP), focusing specifically on separation failure at the end concrete cover. By characterizing the geometry of the failure body and integrating it with the concrete tooth model, a comprehensive theoretical framework has been developed. This framework utilizes sectional strain distribution characteristics to establish the bending moment–curvature relationship and the load–deflection curve during loading. Comparisons with experimental data confirm the accuracy and applicability of this analytical model. The results demonstrate that the model is capable of accurately predicting the load–deflection behavior of the strengthened beam. Additionally, this study underscores the substantial impact of the CFRP prestress level on the concrete cover separation failure, showing that optimizing prestress settings can effectively enhance the ductility and bearing capacity of the strengthened beam. Full article

Prestressed concrete structures, designed to enhance the compressive strength of concrete through internal pretension, are increasingly susceptible to serviceability issues caused by rising live loads, material degradation, and environmental impacts. Strengthening or retrofitting offers a practical and cost-effective alternative to full replacement. This study investigated the flexural strengthening of prestressed concrete T-beams in the negative moment region using near-surface mounted (NSM) carbon-fiber-reinforced polymer (CFRP) rods. Validation against experimental results from the literature demonstrated high accuracy, with an average numerical-to-experimental ultimate load ratio of 0.97 for reinforced concrete T-beams strengthened with NSM-CFRP rods, a negligible difference of 0.49% for prestressed concrete I-beams, and a minimal error of 1.30% for prestressed concrete slabs strengthened with CFRP laminates. Parametric studies examined the effects of CFRP rod embedment depths and initial prestressing levels. In certain cases, achieving the minimum embedment depth is not feasible due to design or construction constraints. The results showed that fully embedded CFRP rods increased the ultimate load by up to 14.02% for low prestressing levels and 16.36% for high levels, while half-embedded rods provided comparable improvements of 11.20% and 15.76%, respectively. These findings confirm the effectiveness of NSM-CFRP systems and highlight the potential of partial embedment as a practical solution in design-constrained scenarios. Full article

Spaceborne instruments have an irreplaceable role in detecting fundamental vegetation features that link physical properties to ecological theory, but their success depends on our understanding of the complex dynamics that control plant spectral properties—a scale-dependent challenge. We explored differences between the warmer and cooler areas of tree canopies with a ground-based experimental layout consisting of a spectrometer and a thermal camera mounted on a portable crane that enabled synergies between thermal and spectral reflectance measurements at the fine scale. Thermal images were used to characterise the thermal status of different parts of a dense circular cluster of containerised trees, and their spectral reflectance was measured. The sensitivity of the method was found to be unaffected by complex interactions. A statistically significant difference in both reflectance in the visible (VIS), near-infrared (NIR), and shortwave infrared (SWIR) bands and absorption features related to the chlorophyll, carotenoid, and water absorption bands was found between the warmer and cooler parts of the canopy. These differences were reflected in the Photochemical Reflectance Index with values decreasing as surface temperature increases and were related to higher carotenoid content and lower Leaf Area Index (LAI) values of the warmer canopy areas. With the increasingly improving resolution of data from airborne and spaceborne visible, near-infrared, and shortwave infrared (VSWIR) imaging spectrometers and thermal infrared (TIR) instruments, the results of this study indicate the potential of synergies between thermal and spectral measurements for the purpose of more accurately assessing the complex biochemical and biophysical characteristics of vegetation canopies. Full article

Pile splicing is generally considered in construction because of transportation limits, length requirements, construction means and methods, and strength capacity. A major challenge in the use of precast prestressed UHPC piles is the lack of efficient and effective splicing solutions. To address the problem, this study evaluated different pile splicing methods for UHPC H-piles and their constructability. The analysis and design for strength capacity and detailing presented here are based on relevant established guidelines and design codes for UHPC. This study assessed two pile splicing methods: epoxy-bonded dowels and near-surface mounted bars (NSMBs). The analysis demonstrated that the epoxy-bonded dowel method provides a moment capacity that is 127% of the pile moment capacity in the strong direction and 139% of the pile moment capacity in the weak direction. In comparison, the NSMB method achieved 121% in the strong direction and 106% in the weak direction. Both methods developed the established strength capacity requirements. The constructability of both pile splicing options was evaluated to provide practical guidelines for their preparation in preplanned and unplanned situations. The results reported are for 18-inch UHPC H-piles; however, the construction and analytical approach applies to other pile sizes as well. The pile splicing options developed are recommended for further experimental investigations. Full article

In this study, an analytical model was developed for the local bond degradation behavior between a near-surface mounted (NSM) fiber-reinforced polymer (FRP) and concrete under fatigue loading. A trilinear local bond stress–slip relationship was adopted to characterize the fundamental bond behavior at the FRP-epoxy-concrete interface at different stages of elastic, softening and debonding. A series of post-fatigue direct pull-out tests (DPTs) of NSM FRP-bonded concrete blocks was conducted to provide the local bond degradation laws for the analytical model. The bond region was discretized into finite elements to include the effect of bond degradation to different extents, and a closed-form solution was derived by virtue of appropriate boundary conditions in each fatigue cycle. The model is capable of predicting the FRP strain distribution, local bond stress distribution and relative slip development at a targeted number of fatigue cycles. The reliability of the analytical model was confirmed by experimental data, and its sensitivity to various parameters such as local bond strength, the residual bond strength ratio and Young’s modulus of FRP reinforcement was also assessed in this study. Full article