Search Results (171)

The main objective of this research is to investigate the impact of the tendon profile layout on the shear strength of unbonded post-tensioned prestressed concrete bridge I-girders. This study involves an experimental investigation where ten unbonded post-tensioned bridge girders are cast and subjected to four-point loads. The focus of the investigation is on the effect of different tendon profile layouts, including trapezoidal, parabolic, and harped shapes. The experimental results reveal that the shear behavior of the specimens progresses through three distinct stages: the elastic stage, the elastic–plastic stage, and the plastic stage, with all specimens ultimately failing due to shear. The results show that tendon profiles with higher eccentricity at the end of the beams (80 mm above the neutral axis) had the highest ultimate load capacity for each tendon profile shape, coupled with the largest deflection. Conversely, profiles with lower eccentricity (80 mm below the neutral axis) demonstrated the lower ultimate load capacity for each tendon profile shape and minimal deflection. Among the various tendon profile layouts that were tested, the specimen with the harped tendon profile (GF-1 HA) showed the highest ultimate load capacity, with an increasing rate of 17.52% in ultimate load and a 45.55% increase in ultimate deflection compared to the control beam (GF-1 ST) with a straight tendon profile. On the other hand, the harped tendon profile specimen (GF-1 HA) exhibited the lowest deflection among the various tendon profile shapes with an increasing rate of 5.7% in ultimate load deflection in comparison with the control beam (GF-1 ST) with a straight tendon profile. These improvements in stiffness, load capacity, and deflection are attributed to enhanced resistance, particularly at the supports. Consequently, the optimized tendon layouts offer an increase in the overall structural efficiency, leading to potential cost savings in bridge girder production. Full article

Strain monitoring during the service life of a nuclear containment structure is an effective means to evaluate whether the structure is operating safely. Due to the failure of embedded strain sensors, surface-mounted strain sensors should be installed on the outer wall of the structure. However, whether the data from these substitute sensors can reasonably reflect the internal deformation behavior requires further investigation. To ensure the feasibility of the added strain sensors, a refined 3D model of a Chinese Pressurized Reactor (CPR1000) nuclear containment structure was developed in ANSYS 19.1 to study the internal and external deformation laws during a containment test (CTT). Solid reinforcement and cooling methods were employed to simulate prestressed cables and pre-tension application. The influence of ordinary steel bars in concrete was modeled using the smeared model, while interactions between the steel liner and concrete were simulated through coupled nodes. The model’s validity was verified against embedded strain sensor data recorded during a CTT. Furthermore, concrete and prestressed material parameters were refined through a sensitivity analysis. Finally, the variation law between the internal and external deformation of the containment structure was investigated under typical CTT loading conditions. Strain values in the wall thickness direction exhibited an essentially linear relationship. Near the equipment hatch, however, the strain distribution pattern was significantly influenced by the spatial arrangement of prestressed cables. Refined FEM and sensor systems are vital containment monitoring tools. Critically, surface-mounted strain sensors offer a feasible approach for inferring internal stress states and deformation behavior. This study provides theoretical support and a technical foundation for the safe assessment and maintenance of nuclear containment structures during operational service. Full article

Ensuring the stability of monolithic concrete slabs during construction represents a crucial safety challenge in monolithic reinforced concrete buildings. Theoretical models and structural analyses often assume ideal conditions of supporting props. However, significant deviations occur in practice due to variations in technical condition and installation methods. This study investigates the magnitude of prestressing forces generated in adjustable telescopic steel props depending on manual tightening and hammer blows. Experimental measurements were conducted on different types of props compliant with EN 1065, including both new and worn specimens, to simulate real on-site conditions. The influence of worker body weight was also analyzed. The results confirmed that the technical condition of the prop is the decisive factor affecting the level of prestress. Props in poor condition achieved substantially lower and inconsistent prestressing forces, while new props subjected to five hammer blows reached maximum values up to 13.16 kN. This difference can significantly influence static calculations for slab construction. Contrary to expectations, the influence of worker body weight was not statistically significant; instead, the dominant role was played by installation technique and the accuracy of hammer blows. The findings contribute to the optimization of safety guidelines and the improvement of calculation models for temporary support systems in monolithic construction. Full article

Traditional internal support systems for deep foundation pits often suffer from issues such as insufficient stiffness, excessive displacement, and large support areas. To address these problems, the authors developed a novel spatial steel joist internal support system. Based on a large-scale field model test, this study investigates the bearing characteristics of the proposed system in deep foundation pits. A stiffness formulation for the novel support system was analytically derived and experimentally validated through a calibrated finite element model. After validation with test results, the effects of different vertical prestressing forces on the structure were analyzed. The results indicate that the proposed system provides significant support in deep foundation pits. The application of both horizontal and vertical prestressing increases the internal forces within the support structure while reducing overall displacement. The numerical predictions of horizontal displacement, bending moment, and the axial force distribution of the main support, as well as their development trends, align well with the model test results. Moreover, increasing the prestressing force of the steel tie rods effectively controls the deformation of the vertical arch support and enhances the stability of the spatial structure. The derived stiffness formula shows a small error compared with the finite element results, demonstrating its high accuracy. Furthermore, the diagonal support increases the stiffness of the lower chord bar support by 28.24%. Full article

Metro foundation pits are important components of urban infrastructure projects. Dewatering and excavation are essential stages in foundation pit construction; however, this process can significantly induce groundwater drawdown, as well as diaphragm wall deformation and surface settlement. Based on a subway station foundation pit project, in this study, we employ three-dimensional numerical software to simulate the process of dewatering and excavation. A refined model is used to investigate groundwater seepage, the deformation of the retaining structure, and surface settlement under spatial effects. The finite element model accounts for stratified excavation and applied prestress conditions for the support system within the foundation pit. Its accuracy is validated through a comparison and analysis with measured data from the actual foundation pit. The results indicate that foundation pit excavation leads to significant groundwater drawdown around the pit and the formation of a characteristic “funnel-shaped” drawdown curve. Moreover, extending the diaphragm wall length contributes to maintaining a higher external groundwater level surrounding the foundation pit. The horizontal displacement of the diaphragm wall increases progressively during dewatering and excavation, and the bending moment of the diaphragm wall exhibits a trend consistent with its horizontal displacement. Surface settlement decreases as the length of the diaphragm wall increases. Full article

Urban rail transit networks’ rapid expansions have led to increasing intersections between existing and new lines, particularly in dense urban areas where new stations must underpass existing infrastructure at zero distance. Deformation controls during construction are critical for maintaining the operational safety of existing stations, especially in soft soil conditions where construction-induced settlement poses significant risks to structural integrity. This study systematically investigates the influence mechanisms of different construction schemes on base plate deformation when an open-top UBIT (underground bundle composite pipe integrated by transverse pre-stressing) underpasses existing stations. Through precise numerical simulation using PLAXIS 3D, the research comparatively analyzed the effects of 12 pipe jacking sequences, 3 pre-stress levels (1116 MPa, 1395 MPa, 1674 MPa), and 3 soil chamber excavation schemes, revealing the mechanisms between the deformation evolution and soil unloading effects. The continuous jacking strategy of adjacent pipes forms an efficient support structure, limiting maximum settlement to 5.2 mm. Medium pre-stress level (1395 MPa) produces a balanced deformation pattern that optimizes structural performance, while excavating side chambers before the central chamber effectively utilizes soil unloading effects, achieving controlled settlement distribution with maximum values of −7.2 mm. The optimal construction combination demonstrates effective deformation control, ensuring the operational safety of existing station structures. These findings enable safer and more efficient urban underpassing construction. Full article

Addressing the stability control challenges of roadways with composite roofs in the No. 34 coal seam of Donghai Mine under high-strength mining conditions, this study employed integrated methodologies including laboratory experiments, numerical modeling, and field trials. It investigated the mechanical response characteristics of the composite roof and developed a synergistic control system, validated through industrial application. Key findings indicate significant differences in mechanical behavior and failure mechanisms between individual rock specimens and composite rock masses. A theoretical “elastic-plastic-fractured” zoning model for the composite roof was established based on the theory of surrounding rock deterioration, elucidating the mechanical mechanism where the cohesive strength of hard rock governs the load-bearing capacity of the outer shell, while the cohesive strength of soft rock controls plastic flow. The influence of in situ stress and support resistance on the evolution of the surrounding rock zone radii was quantitatively determined. The FLAC^3D strain-softening model accurately simulated the post-peak behavior of the surrounding rock. Analysis demonstrated specific inherent patterns in the magnitude, ratio, and orientation of principal stresses within the composite roof under mining influence. A high differential stress zone (σ₁/σ₃ = 6–7) formed within 20 m of the working face, accompanied by a deflection of the maximum principal stress direction by 53, triggering the expansion of a butterfly-shaped plastic zone. Based on these insights, we proposed and implemented a synergistic control system integrating high-pressure grouting, pre-stressed cables, and energy-absorbing bolts. Field tests demonstrated significant improvements: roof-to-floor convergence reduced by 48.4%, rib-to-rib convergence decreased by 39.3%, microseismic events declined by 61%, and the self-stabilization period of the surrounding rock shortened by 11%. Consequently, this research establishes a holistic “theoretical modeling-evolution diagnosis-synergistic control” solution chain, providing a validated theoretical foundation and engineering paradigm for composite roof support design. Full article

Asynchronous-pouring construction (APC) technology employs a suspended hanging basket directly supported by corrugated steel webs (CSWs) with high shear strength, significantly enhancing construction efficiency. To further elucidate the characteristics of APC and promote its application in prestressed concrete (PC) composite box girder bridges with CSWs, this study analyzes the sustainable development of APC from two aspects, including environmental impact and economic performance. Finite element models of APC and traditional balanced cantilever construction (TBCC) were established for the case bridge with a main span of 105 m. The stress distribution and deflection of the main girder in the cantilever construction state are compared with field measurements, and the variations in stress and deflection in typical sections during construction are analyzed. Additionally, a simplified theoretical method is proposed for calculating stress and deflection in PC composite girder bridges during the cantilever construction stage using APC. Results demonstrate that APC demonstrates significant advantages in reducing economic costs and minimizing long-term environmental impacts. Furthermore, this method ensures acceptable stress and deflection throughout construction. The proposed simplified formula for CSW deflection in the maximum segment agrees well with both measured data and finite element results, providing a valuable reference for deflection calculation in APC applications. Full article

In order to make the anchor bolt support prestress field fully diffuse in the composite rock stratum, improve the overall bearing capacity of surrounding rock, and give full play to the role of active support of the anchor bolt, a self-made 1:1-scale composite rock stratum similarity simulation test bed was used to compare and analyze the distribution of the anchor bolt support prestress field using different anchoring surrounding rock lithology and anchorage lengths, and the principle for optimum selection of anchoring parameters of composite rock stratum was proposed based on the test results. Considered from the point of view of stress diffusion, the effect of prestress diffusion of end anchorage bolts is better than that of lengthening anchorage; at the same time, the anchorage section should be preferentially arranged in hard rock, and the area of anchorage section near the free section should avoid the structural plane of surrounding rock. In conclusion, an industrial test was carried out under the conditions of a deep composite roof of the 2# coal seam in Qinyuan Mining Area, which determined a reasonable anchoring method and position of the composite roof under different conditions and achieved good results. Full article

Rainfall can easily cause local sliding and collapse of carbonaceous mudstone deep road cut slopes. In order to study the strength characteristics of carbonaceous mudstone under different water environments, large-scale horizontal push shear tests were conducted on carbonaceous mudstone rock masses in their natural state and after immersion in saturated water. The push shear force–displacement relationship curve and fracture surface shape characteristics of carbonaceous mudstone samples were analyzed, and the shear strength index of carbonaceous mudstone was obtained, and numerical simulations on the stability and support effect of carbonaceous mudstone slopes were conducted. The research results indicate that carbonaceous mudstone can exhibit good structural properties and typical strain softening characteristics under natural conditions. The fracture surface, shear strength, and shear deformation process of carbonaceous mudstone samples will undergo significant changes after being soaked in saturated water. The average cohesion decreases by 33% compared to the natural state, and the internal friction angle decreases by 15%. The numerical simulation results also fully verify the attenuation of mechanical properties of carbonaceous mudstone after immersion, as well as the effectiveness of prestressed anchor cables and frame beams in supporting carbonaceous mudstone slopes. The research results provide an effective method for understanding the shear performance of carbonaceous mudstone and practical guidance for evaluating the stability and reinforcement design of carbonaceous mudstone slopes. Full article

Shear lag stresses increase significantly in cracked concrete box girders; however, most existing models assume intact sections and are, therefore, unsuitable for rapid field diagnosis. This study integrates a stepped stiffness model with deflection influence lines to accurately capture the mechanical response of damaged, simply supported box girders. Regions containing flexural cracks are assigned a reduced bending stiffness ${EI}^{\prime }$, whereas intact zones retain the original stiffness $EI$. A closed-form stiffness-reduction coefficient $\phi ={EI}^{\prime }/EI$ is obtained from crack geometry and, independently, from the second derivative of the deflection influence line. Embedding $\phi$ in a variational shear lag formulation yields explicit expressions for flange displacement and normal stress without numerical iteration. This approach is validated by finite element simulations of a plexiglass scale model with four preset damage levels and by a load test on a 30 m prestressed concrete box girder bridge. Field measurements show that midspan stiffness decreased to 81% of the as-built value; the proposed method reproduces this value with a deviation of 3%. Predicted upper-flange stresses differ from measured values by 5.7–13.6% and from finite element results by less than 10% for damage ratios up to 40%. The second derivative of the influence line difference exhibits a distinct peak at the cracked region, accurately localizing the damage. Compared with classical formulas, the proposed model (i) is fully closed-form, (ii) links global deflection data to local shear lag stresses, and (iii) delivers conservative estimates suitable for routine bridge assessment. Full article

This preliminary study explores the feasibility of using the flat-jack test to assess residual prestress in post-tensioned concrete elements. Experimental testing was conducted on three concrete slabs under controlled laboratory conditions, with known stress states induced by axial loading. Two flat-jack sizes and two gage lengths were considered, and a tailored calibration procedure was implemented to reflect expected field conditions. The test produced acceptable stress estimations, with accuracy influenced by both the gage length and the jack size. The results are discussed within the broader context of prestress assessment, including a comparison between the flat-jack test’s performance in concrete and masonry and its positioning relative to alternative methods. The experimental design, result presentation, and theoretical analysis in this study are intentionally simple and not yet sufficiently mature to support practical application. Nevertheless, the findings offer promising initial insights and practical inspiration for practitioners and researchers exploring alternative methods for residual stress assessment in prestressed concrete structures, underscoring the need for further research to refine the methodology and validate its broader applicability. Full article

For several years now, fruit-growers have increasingly often used pre-tensioned, pre-stressed concrete posts for supporting branches of fruit trees and suspending protective nets in order to limit damage to fruits caused by hail, wind, snow, heavy rainfall, insects and birds. Pre-tensioned, pre-stressed concrete posts most often have a trapezoidal cross-section, which is ideally suitable for mass production in a self-supporting non-dismantlable steel mould on a pre-stressing bed. Posts with 70 mm × 75 mm, 80 mm × 85 mm and 90 mm × 95 mm cross-sections are typically produced, whereas 100 mm × 120 mm and 130 mm × 140 mm posts are manufactured to order. Furthermore, it is proposed to produce hollow posts. Such posts are lighter than solid posts, but they require a more complicated production technology. This paper presents selected parts of a comparative computational–experimental analysis of solid and hollow posts. In the Building Structures Laboratory in the Building Structures Department at the Civil Engineering Faculty of the Wrocław University of Science and Technology, experimental tests of pre-stressed concrete orchard posts of 70 mm × 75 mm and 90 mm × 95 mm with solid and hollow cross-sections were carried out on a full scale. The theoretical analysis and research has shown that the resistance to bending, cracking resistance and rigidity of hollow posts (with their cross-sectional outline unchanged) will not significantly differ from those of the currently produced solid posts. At same time, material savings will be achieved. Therefore, the main task is to master the continuous moulding of hollow posts from dense plastic concrete with the simultaneous pulling out of the cores, producing longitudinal hollows in the posts. Full article

Shear failure in reinforced concrete (RC) beams is abrupt and brittle, occurs without warning, and leaves no opportunity for internal stress redistribution. Despite the critical need for accurate shear strength assessment, existing methods vary widely across regions, leading to inconsistencies in practice. This study presents a unified shear strength equation for non-prestressed rectangular RC beams without stirrups, developed for simplicity and broad applicability. The model requires only basic geometric and material properties and applies to both shear-slender and non-shear-slender beams. It was formulated using a data-driven approach that combines an extensive experimental database collected up to 2007 with advanced computational techniques, including Artificial Neural Networks, Generative Adversarial Networks, and Bayesian optimization. The proposed equation was evaluated against established shear provisions, such as ACI 318-25 and CSA A23.3-24, and benchmarked with an experimental database. The results show that the model improves prediction accuracy, reduces uncertainty, and provides a more consistent method for shear strength assessment. The robustness of the equation was further confirmed through additional experimental database gathered after 2007, demonstrating strong agreement with test results and lower prediction uncertainty than current code provisions. These findings support the potential adoption of the proposed equation in engineering practice. Full article

Bridges are critical nodes in transportation networks, and the evaluation of their service performance is of vital importance. Rapid assessment techniques based on the theory of influence lines have become a significant research topic. This study proposes a rapid testing method for the influence lines of beam-type bridges, with the synchronous monitoring of dynamic vehicle positions and a wireless network of multiple sensors. Field testing on a 30 m span T-beam bridge revealed that the measured vertical displacement during slow continuous driving corresponded with the static load test data within a deviation of ±6%, with the entire testing process completed in only 5 min, demonstrating efficiency and minimal traffic interference. Based on the measured influence lines, rapid bridge bearing capacity assessments and finite element model updating were researched. A case study of a simply supported T-beam bridge composed of prefabricated prestressed concrete showed that the calculated values using the proposed rapid assessment method deviated from traditional load test values between −5.68% and 4.69%, indicating a small error margin. After applying this method to the model updating of a (25 + 45 + 25) m continuous beam bridge on a highway, the inversion errors of the concrete elastic modulus and prestress were 1.40% and 1.20%, respectively, confirming the reliability of the precision. The rapid testing method for influence lines can be applied to bridge inspection, evaluation, and model updating. Full article