Search Results (40)

Progressive collapse has become a critical concern in resilient structural design due to accidental impacts, abnormal loading scenarios, and sudden localized damage events that may lead to the sudden loss of structural elements under extreme or unforeseen actions. In this context, UFC 4-023-03 provides design approaches for improving collapse resistance, including the Alternate Path Method, Enhanced Local Resistance Method, and Tie Forces Method. This study focuses on the Tie Forces Method, which is based on mechanical interconnection but remains relatively underexamined in the literature. A six-story reinforced concrete office building was evaluated to determine the required tie reinforcement area for progressive collapse resistance according to UFC 4-023-03. Ten national building codes were considered, with office live loads ranging from approximately 2.0 to 4.8 kN/m². In this study, the selected national codes are not compared in terms of their complete progressive collapse provisions. Instead, UFC 4-023-03 is adopted as the main Tie Forces Method calculation framework, while national-code-based live load values and reinforcement properties are used as input parameters. Peripheral, longitudinal, transverse, and vertical ties were comparatively assessed. The largest percentage reduction was observed for the peripheral transverse tie reinforcement at the first floor, where the Eurocode-based input set produced a required tie reinforcement area approximately 21.7% lower than that obtained from the Russian input set. In contrast, Canadian provisions govern the highest demand at the ground floor, while South Korean provisions produce the highest demand at upper floors. Overall, the findings highlight the influence of national live load provisions and reinforcement properties on tie force requirements. Full article

The effective length factor method cannot account for variations in axial forces between columns and the mutual assistance among columns, resulting in overestimation of the critical load of columns that receive assistance and underestimation of that of columns that provide assistance. Moreover, this method is not readily applicable to bent frames and frame structures with multi-story tie beams. The phenomenon of critical load redistribution among columns under non-uniform loading conditions is revealed in this paper, and its underlying mechanical mechanism is elucidated. Based on this, a two-stage loading procedure for critical load redistribution analysis is proposed, in which the instability process of irregular structures is divided into two stages: independent loading of individual columns and combined loading of the assembly. By superimposing the critical load of columns in regular structures with the remaining load capacity, a formula for evaluating the overall stability critical capacity of bent and frame structures is established. The proposed method effectively accounts for the restraint provided by tie beams between columns, eliminating the need for iterative solutions of transcendental equations or the construction of complex total potential energy equations, thereby significantly simplifying the computational process. Comparative analyses of numerical examples demonstrate that the proposed method achieves high accuracy and enables quantitative assessment of mutual assistance between columns. It provides a conceptually clear, computationally efficient, and reliable practical tool for the stability design of bent and frame structures under complex loading conditions. Full article

Background/Objectives: High-altitude pulmonary edema (HAPE) remains a serious condition with limited preventive options. This study evaluated the prophylactic protective effects of nebulized human umbilical cord mesenchymal stem cell-derived extracellular vesicles (hUC-MSC-EVs) in a rat model of hypobaric hypoxia-induced lung injury and explored potential mechanistic clues, with a focus on oxidative stress and TEK/Tie2 signaling. Methods: Rats were exposed to hypobaric hypoxia (47 kPa; 9.7% O₂) for 72 h and received prophylactic nebulized hUC-MSC-EVs (300 μg/rat). Lung injury was evaluated by histopathology, wet-to-dry ratio, and bronchoalveolar lavage fluid (BALF) protein concentration. Invasive pulmonary function indices were measured using a forced oscillation system. BALF cytokines (TNF-α, IL-6, and IL-10), reactive oxygen species (ROS), and TEK/Tie2 expression in lung tissue were assessed. In addition, transcriptome sequencing (RNA-seq) was performed to characterize global transcriptional changes. N-acetylcysteine (NAC), a classical antioxidant, was included as an auxiliary mechanistic intervention to assess the association of ROS with TEK/Tie2 changes. Results: Compared with hypoxia controls, prophylactic nebulized hUC-MSC-EVs reduced histopathological injury, pulmonary edema, and barrier leakage, and improved pulmonary function indices. hUC-MSC-EV intervention also attenuated inflammatory responses in BALF, with decreased TNF-α and IL-6 and increased IL-10. Hypobaric hypoxia increased ROS accumulation and decreased TEK/Tie2 expression, whereas nebulized hUC-MSC-EVs reduced ROS and partially preserved TEK/Tie2 expression. NAC pretreatment similarly reduced ROS and was accompanied by Tie2 preservation. Conclusions: Prophylactic nebulized hUC-MSC-EVs mitigated hypobaric hypoxia-induced lung injury, accompanied by reduced oxidative stress, improved vascular barrier integrity, and preservation of TEK/Tie2 expression. These findings support nebulized hUC-MSC-EVs as a potential lung-targeted prophylactic strategy for hypobaric hypoxia-induced lung injury and suggest that ROS imbalance may be associated with Tie2 preservation. Full article

This study evaluates the resistance of existing reinforced concrete buildings to progressive collapse using the Tie-Force Method specified in UFC 4-023-03. Five multi-storey residential reinforced concrete buildings in different regions are analysed. In situ rebar scanning and Schmidt hammer tests revealed existing reinforcement layouts and concrete strengths (14–26 MPa). From the measured geometries, material properties and design loads, the required peripheral, longitudinal–transverse and vertical tie forces are calculated and converted into equivalent reinforcement areas. The results show that none of the investigated buildings satisfies all tie-force requirements with its current detailing. In particular, approximately 40% of the total Ø12 reinforcement required for the most critical peripheral ties in the other functional areas is concentrated in a single building. For longitudinal and transverse ties within the slab plane, additional Ø12 bars are required, especially along the most unfavourable grid lines in large-span panels. Vertical tie demands are modest and can generally be met with about 1–7 Ø16 bars in the selected columns. The findings indicate that, in the investigated sample, tie-force deficiencies appear to be governed more by design era and structural layout than by geographic location, and that strengthening slab-plane ties is critical for improving progressive-collapse resistance in the investigated buildings. In typical existing RC frame buildings, tie-force inadequacy is governed primarily by slab-plane ties rather than by vertical ties and the variation in required tie reinforcement across buildings is controlled more by design era and plan-geometry/floor-load characteristics than by geographic location. Full article

Research on the configuration and mechanical performance of arch-column-tie beam joints, which combine features of arch-tie beam joints and tubular joints, remains limited, particularly for long-span structures subjected to heavy loads at high building stories. This study focuses on a joint in an engineering structure comprising a circular arch beam, a square-section inclined column, and a tie beam, where both the arch and the inclined column are concrete-filled steel tube (CFST) members. A novel joint configuration was proposed, then a refined finite element model was established. The joint’s mechanical mechanism and failure mode under axial compression in the arch beam were investigated, considering two conditions: the presence of prestressed high-strength rods and the failure of the rods. Subsequently, a parametric study was conducted to investigate the influence of variations in the web thickness of the tie beam, the steel tube wall thickness of the arched beam, the steel tube wall thickness of the supporting inclined column, and the strength grades of steel and concrete on the bearing capacity behavior and failure modes. Numerical simulation results indicate that the joint remains elastic under the design load for both conditions, meeting the design requirements. The joint reaches its ultimate capacity when extensive yielding occurs in the tie beam along the junction region with the circular arch beam, as well as in the steel tube of the arch beam. At this stage, the steel plates and concrete within the joint zone remain elastic, ensuring reliable load transfer. The maximum computed load of the model with prestressed rods was 2.28 times the design load. The absence of prestressed rods could lead to a significant increase in the high-stress area within the web of the tie beam, decreasing the joint’s stiffness by 12.4% at yielding, but have a limited effect on its maximum bearing capacity. Gradually increasing the wall thickness of the arch beam’s steel tube shifts the failure mode from arch-beam-dominated yielding to tie-beam-dominated yielding along the junction region. Increasing the steel strength grade is more efficient in enhancing the bearing capacity than increasing the concrete strength grade. Finally, a design methodology for the joint zone was established based on three aspects: local stress transfer at the bottom of the arch beam, force equilibrium between the arch beam and the tie beam, and the biaxial compression state of the concrete in the joint zone. Furthermore, the construction process and mechanical analysis methods for various construction stages were proposed. Full article

Designing reinforcements for concrete towers in extra-dosed cable-stayed bridges is challenging due to the passage of filament pipes, particularly in the D-region, where strain distribution is nonlinear under mechanical loading. The strut-and-tie model (STM) is a widely used approach for designing these regions; however, its development in the presence of filament pipe passages requires further refinement. This study introduces a functional STM based on topology optimization to represent stress flow beneath filament pipe passages. The method retains structural elements essential for force transmission while eliminating less significant ones, thereby establishing optimal load paths. Using ANSYS software, the effects of varying the radius of curvature of the cable saddle on stress distribution induced by filament pipes were analyzed. Results indicate that the curvature radius strongly influences internal forces in STM members: as the radius increases, both stress and internal forces decrease within the tower, clarifying the evolution of force distribution with changing curvature. These findings provide a functional framework for STM applications and are expected to serve as a reference for the comprehensive structural design of concrete towers in extra-dosed cable-stayed bridges. Full article

Anchored sheet-pile walls (ASPWs) are widely used as earth-retaining structures in engineering practice. The difficulty in analyzing sheet piles arises because the loading on the wall is a function of the deformation of the soil and the sheet-pile configuration. This paper discusses the predictions of different theoretical solutions for ASPWs, and it briefly presents and discusses four main theories of ASPWs: the two distribution theories, the finite element method, and Rowe’s theory. The effect of different influencing factors on the behavior and design of ASPWs is also examined. The above theoretical solutions are evaluated experimentally through measurements of strains, deflections, tie-rod force, and tie-rod yield on a small-scale sheet-pile model tested in a sandbox. The four theories provide an acceptable analytical solution for the ASPW problem under the given conditions. However, no theory fully predicts the behavior of ASPWs over the entire range of the different design parameters: soil conditions, sheet-pile flexibility, dredge depth, anchor location, and anchor yield. This paper proposes simple charts and tables for SPW design based on extrapolation between distribution theories while accounting for sheet pile flexibility and other influencing parameters. Illustrating examples for the proposed design procedure are provided. Full article

Long-span prestressed structures present distinct challenges during tensioning. Their considerable length inherently induces significant tendon friction, resulting in substantial prestress loss. Additionally, prestressing operations within buildings will induce initial stresses that affect adjacent structural members. However, research on the design and construction of ultra-long-span prestressed systems with composite materials in building structures remains limited. To investigate prestress effects in long-span building structures, this study examines prestress loss and tension timing for the 94.34 m arch tie girder in Shenzhen Museum. This project marks the first application of the bonded post-tensioning method to an ultra-long composite structural member. The analysis of the prestress loss is conducted by considering the friction, relaxation of steel tendon, creep, and shrinkage. An innovative finite element method, integrating creep and shrinkage effects for composite members, is developed in ANSYS. Four tensioning schemes are compared using nonlinear staged-construction simulation in NIDA software. The results demonstrate that the presented analytical method can effectively quantify the prestress loss. Early-stage prestressing effects can be minimized by optimizing the force transmission paths through construction joints. These findings provide practical and theoretical guidance for designing and constructing similar long-span structures. Full article

The purpose of this paper is to study the shear performance of reinforced concrete corbels under a synergistic change in the main stirrup inclination angle to explore the synergistic mechanism of the main reinforcement and the stirrup inclination angle, and to evaluate the applicability of existing design specifications. The shear performance test was carried out by designing RC corbel specimens with an inclination angle of the main reinforcement and stirrup. The test results show that a 15° inclination scheme significantly improves the shear performance: the yield load is increased by 28.3%, the ultimate load is increased by 23.6%, the strain of the main reinforcement of the 15° specimen is reduced by 51.3%, the stirrup shows a delayed yield (the yield load is increased by 11.6%) and lower strain level (250 kN is reduced by 23.7%), and the oblique reinforcement optimizes the internal force transfer path and delays the reinforcement yield. A CDP finite element model was established for verification, and the failure mode and crack propagation process of the corbel were accurately reproduced. The prediction error of ultimate load was less than 2.27%. Based on the test data, the existing standard method is tested and a modified formula of the triangular truss model based on the horizontal inclination angle of the tie rod is proposed. The prediction ratio of the bearing capacity is highly consistent with the test value. A function correlation model between the inclination angle of the steel bar and the bearing capacity is constructed, which provides a quantitative theoretical tool for the optimal design of RC corbel inclination parameters. Full article

Thermoplastic injection molding is a widely used process for producing complex three-dimensional plastic parts with tight dimensional tolerances. A key determinant of part quality is the switchover point—the transition from velocity-controlled filling to pressure-controlled packing. This transition affects critical product attributes, such as d imensional accuracy, weight consistency, and surface finish. Precise control of the switchover point enhances process stability, robustness, and adaptability. This review consolidates recent advancements in switchover methods and adaptive control techniques. Improvements in traditional methods include the use of pressure gradient detection to mitigate viscosity variations and adaptive control to refine stroke- and time-dependent switchovers. In addition, deformation-based strategies detect the mold-opening force associated with cavity pressure through clamping force, mold separation, or tie-bar elongation. The integration of machine learning and feature extraction techniques enables the real-time adjustment of the switchover point by mapping relationships between process parameters and quality criteria. In addition, ultrasonic sensors provide non-invasive melt front detection, reducing the risk of mold damage. Real-time simulations, updated through nozzle pressure feedback, complement these methods to achieve precise switchover timing. This review also identifies persistent challenges, such as sensitivity to material properties, machine wear, and environmental conditions, and it explores future directions for improving the accuracy and adaptability of switchover control in modern injection molding processes. Full article

The diagnosis of post-stressed anchor rods is essential for maintaining the service and ensuring the safety of Electricité de France (EDF) structures. These rods are critical for the mechanical strength of structures and electromechanical components. Currently, the standard method for estimating the effective tension of post-stressed tie rods with a free length involves measuring the residual force using a hydraulic jack. However, this method can be costly, impact the structure’s operation, and pose risks to employees. Until now, there has been no reliable on-field approach to estimating residual tension using a lightweight setup. This research introduces a nondestructive method using multimodal ultrasonic guided waves to evaluate the residual tension of anchor rods with a few centimeters free at one end. The methodology was developed through both laboratory experiments and simulations. This new method allows for the extraction of dispersion curves for the first three modes, bending, torsional, and longitudinal, using time–frequency analysis and enables the estimation of the steel bar’s properties. Future work will focus on applying this methodology in the field. Full article

In order to promote the development of bridge assembly technology and accelerate the application of rectangular steel-tube–concrete composite truss bridges, this study focuses on the Yellow River Diversion Jiqing Main Canal Bridge as the engineering example and conducts a numerical analysis of a rectangular steel-tube–concrete composite truss bridge. Based on the results of the analysis, structural optimization is achieved in three dimensions—structural design, construction methods, and force analysis—leading to the establishment of key design parameters for through-type ultra-high-performance rectangular steel-tube–concrete composite truss bridges. The results show that filling the hollow sections with ultra-high-strength concrete can significantly enhance the load-bearing capacity. Additionally, employing prestressed concrete components addresses the bending and tensile load capacity challenges of composite structures, thus maximizing the material strength advantages. The proposed preliminary design scheme incorporates prestressed PBL-reinforced tie rods filled with ultra-high-performance concrete with optimal design parameters, such as high span ratios, wide span ratios, and ideal segment lengths, are suggested to ensure that the strength, stiffness, and stability comply with relevant standards. While ensuring that the structure meets safety, applicability, and durability criteria, the preliminary design scheme reduces steel usage by 23.5%, concrete usage by 11.6%, and overall costs by 17.29% compared to the original design. The proposed design demonstrates distinct advantages over the original in terms of mechanical performance, construction efficiency, economic viability, and durability, highlighting its promising application potential. Full article

The connection between a prefabricated reinforced concrete column and a pocket foundation is a case treated from a general perspective in the European Standard named EN 1992-1-1 (EC2), and when the structural engineer deals with the dimensioning or verification of the connection, he must tackle several unknowns. The present work aims to fill in the missing information by presenting detailed calculation models based on the strut-and-tie method for four widely used pocket foundations: a pedestal pocket foundation with smooth, rough or keyed internal walls and a pad foundation with a pocket possessing keyed internal walls. In establishing the strut-and-tie models and writing the equation for the internal forces, we consider several standards (EC2, NBR 9062 and DIN 1045-1), good practices (from Austria, England, Germany and Romania) and numerous experimental and numerical investigations. Additionally, detailed design prescriptions applicable to seismic areas are given. This manuscript covers a wide range of design and technology aspects necessary for designing and building columns connected with pocket foundations, information for which is shown only in fragmented form or partially in other publications. Afterward, as a case study, a pocket foundation is designed in all four variations, with the structural design particularities, similitudes and differences being pointed out. Finally, to conclude, we mention the advantages and disadvantages of pocket foundations with respect to the type of internal wall surface used. Quantifiable data based on the case study undertaken are available. Full article

Due to the complexity of the actual geotechnical environment, the backfill compaction design theory and calculation method are not reflected in the current specification. Therefore, in order to investigate the effect of the hydraulic compactor on the foundation structure during the treatment of the backfill of an independent foundation under a column, the Menard formula was modified. At the same time, relying on an independent foundation project under a column in Jinan, the dynamic model of compactor tamping backfilling soil was established. The applicability of the calculation formula is verified by simulating the single-point multiple tamping on the backfill directly above the foundation tie beam, and the influence law of two factors, the thickness of the backfill and the tamping energy, on the force of the foundation tie beam is elucidated. The results show that after reaching the optimum number of tamping, the cumulative soil settlement and the effective reinforcement depth of tamping show a stable trend, and their simulation results are in good agreement with the analytical solution, which provides a supplement to the relevant safety standards. At this critical point, the force on the tie beams peaked and showed up and down fluctuations under the subsequent ramming action. The tamping action of the compactor has a significant effect on the structural forces within the effective reinforcement range, and there is a negative correlation between the magnitude of the structural forces and the thickness of the backfill. According to the numerical calculation results to choose the best construction programme, the on-site monitoring shows that under 42 KJ tamping energy and 1.5 m single backfilling thickness, the tie beam reinforcement stress reaches 18.5~55.5% of the specification warning value, which meets the safety standard. The research results of this paper can provide important guidance for the hydraulic tamping treatment of an independent foundation backfill project. Full article

This paper aims to investigate the effects of soil penetration resistance, tillage depth, and operating speeds on the deformation and fatigue of the subsoiling shovel based on the real-time measurement of tractor-operating conditions data. Various types of sensors, such as force, displacement, and angle, were integrated. The software and hardware architectures of the monitoring system were designed to develop a field operation condition parameter monitoring system, which can measure the tractor’s traction force of the lower tie-bar, the real-time speed, the latitude and longitude, tillage depth, and the strain of the subsoiling shovel and other condition parameters in real-time. The time domain extrapolation method was used to process the measured data to obtain the load spectrum. The linear damage accumulation theory was used to calculate the load damage of the subsoiling shovel. The magnitude of the damage value was used to characterize the severity of the operation. The signal acquisition test and typical parameter test were conducted for the monitoring system, and the test results showed that the reliability and accuracy of the monitoring system met the requirements. The subsoiling operation test of the system was carried out, which mainly included two kinds of soil penetration resistances (1750 kPa and 2750 kPa), three kinds of tillage depth (250 mm, 300 mm, and 350 mm), and three kinds of operation speed (4 km/h low speed, 6 km/h medium speed, and 8 km/h high speed), totaling 18 kinds of test conditions. Eventually, the effects of changes in working condition parameters of the subsoiling operation on the overall damage of subsoiling shovels and the differences in damage occurring between the front and rear rows of subsoiling shovels under the same test conditions were analyzed. The test results show that under the same soil penetration resistance, the overall damage sustained by the subsoiling shovels increases regardless of the increase in the tillage depth or operating speed. In particular, the increase in the tillage depth increased the severity of subsoiling shovel damage by 19.73%, which was higher than the 17.48% increase due to soil penetration resistance and the 13.07% increase due to the operating speed. It should be noted that the front subsoiling shovels consistently sustained more damage than the rear, and the difference was able to reach 16.86%. This paper may provide useful information for subsoiling operations, i.e., the operational efficiency and the damage level of subsoiling shovels should be considered. Full article