The Tian’e Longtan Bridge, currently under construction and boasting the world’s largest span arch at 600 m, employs a concrete-filled steel tube (CFST) as its primary structural component, forming the stiffness skeleton upon which an outer reinforced concrete arch ring is constructed. As the internal defects of CFST, once encased by outer concrete, cannot be remedied, it becomes imperative to prevent long-term debonding of the core concrete. In recent years, expansion agents have been extensively utilized in CFST arch bridge engineering to compensate for early autogenous and thermal shrinkage. However, a comprehensive comprehension of the creep behavior of core concrete expansion under extended steel tube confinement remains elusive. To address this concern, the radial expansion process of the core concrete can be segmented into two stages: debonding and restriction. We derive a long-term deformation model for the radial expansion of core concrete during the restriction stage, based on elastic mechanics and linear creep mechanics. We represent the expansion process of these two stages uniformly using piecewise functions. Subsequently, in conjunction with the ongoing construction of the Tian’e Longtan Bridge, we measure the core concrete’s behavior in full-size CFST specimens (Φ0.92 m × 12 m × 0.01 m) both with and without expansion agents for up to 114 d. This validates the practicality of the creep model and enables us to determine its relevant parameters. Our results reveal that a debonding gap of 0.142 m occurred before the initial setting of the core concrete. The core concrete underwent a radial expansion of 290.1 × 10−6, with 158.3 × 10−6 being used to address early debonding, and the remaining 131.8 × 10−6 generating self-stress on the steel tube. The creep model indicates that radial creep of the core concrete persisted for approximately six months under the hoop limitation of the steel tube, resulting in a residual expansion deformation of 26.4 × 10−6 and a residual self-stress of 0.119 MPa. Additionally, axial deformation results of CFST without expansion agents demonstrated a decreasing constraining force of the steel tube on the core concrete from the outer to the inner sections, attributable to local core concrete yield. Conversely, the inclusion of an expansion agent altered the stress state of the core concrete, maintaining consistent constraining forces within the same section. As a result, we derive an axial long-term expansion model for the core concrete under steel tube restriction. Finally, the introduction of laboratory specimen deformations enhances the practicality of our model, with results demonstrating strong alignment between measured data and the model. The experimental findings and theoretical models developed provide critical support for quantifying the expansion behavior of CaO and MgO-based compound expansive agents in the vault of CFST arch bridges.
This study focuses on a reasonable lateral isolation system for a typical long-span single-tower cable-stayed bridge with a significantly asymmetric span arrangement that is particularly suitable for mountainous areas. Based on the Jinsha River Bridge, the significant structural asymmetry and its effects on structural seismic responses were analyzed. The significantly asymmetric characteristics could result in complex dynamic behavior in seismic conditions and the lateral seismic responses of the structure are governed by multiple modes. A multilinear model composed of an ideal elastoplastic element and a multilinear elastic element was used to simulate different hysteresis, and a parametric analysis was conducted to investigate the appropriate damping hysteresis for the lateral seismic isolation of such a bridge. It shows that the inverted S-shaped hysteresis has relatively smaller secant stiffness and could help to balance the great difference in the lateral stiffness of the tower/piers. Thus, the inverted S-shaped hysteresis could lead to more efficient damping effects and less base shear forces of the tower/piers. A correlation between the reasonable yield forces of the dampers in the lateral isolation system, determined through an influence matrix-based method, and the shear forces of the corresponding bearings in the lateral fixed system was also observed. Moreover, the influence of geological conditions including different terrain and site conditions on the reasonable lateral isolation system was further investigated. It suggests to use dampers at all tower/pier locations when the side span crosses a steep valley slope, while a lateral isolation system without using dampers at the auxiliary piers could be employed when the side span crosses a gentle valley slope. Soft sites require larger damper yield forces and cause greater seismic responses compared to hard sites.
In this study, the optimal weight designs of steel truss towers are determined, considering the notch effect. Thus, the impact of discontinuities in the cross-sections of steel elements on the total weight of the structure is revealed. For this purpose, the optimal weight designs of different truss towers analyzed by other researchers in previous years are reexamined using Particle Swarm Optimization and Firefly Algorithm. The main program where finite element analyses and optimization algorithms are encoded has been developed in MATLAB. Displacement, stress, geometric, and section height constraints are used in optimization methods. The effectiveness of these methods has been demonstrated by comparing both the results in the literature and with each other under un-notched conditions. Subsequently, considering the notch effect on the tension bar with the highest stress capacity in each structure, the impact of stress concentration on the minimum weight sizing of the structure is investigated using these proven methods. When the analysis results of both cases are examined, it is observed that the optimum weights of all structures under the notch effect have slightly increased. The stress concentration around the notch severely raises the nominal stress in the cross-section. In this case, the cross-section becomes insufficient due to the overcapacity, requiring larger profiles. The structure’s weight shows an increasing trend depending on the number of notched elements and the severity of stress concentration. Additionally, SAP2000 software is utilized for numerical simulations of the structures under identical conditions, enhancing the research content and providing further support for the comprehensive design optimization analyses. Consequently, minimizing the adverse effects of notches through careful material selection, proper manufacturing and assembly techniques, and regular maintenance is essential. The effects of notches should be considered in structural analysis and design, with measures taken to mitigate these effects when necessary.
A robust analytical model of Eccentric Braced Frames (EBFs), as a well-known seismic resistance system, helps to comprehensive earthquake-induced risk assessment of buildings in different performance levels. Recently, the modeling parameters have been introduced to simulate the hysteretic behavior of shear links in EBFs with specific Coefficient of Variation associated with each parameter to consider the uncertainties. The main purpose of this paper is to assess the effect of these uncertainties in the seismic response of EBFs by combining different sources of aleatory and epistemic uncertainties while making a balance between the required computational effort and the accuracy of the responses. This assessment is carried out in multiple performance levels using Endurance Time (ET) method as an efficient Nonlinear Time History Analysis. To demonstrate the method, a 4-story EBF that considers behavioral parameters has been considered. First, a sensitivity analysis using One-Variable-At-a-Time procedure and the ET method has been utilized to sort the parameters with regard to their importance in seismic responses in two intensity levels. A sampling-based reliability method is first used to propagate the modeling uncertainties into the fragility curves of the structure. Radial Basis Function Networks are then utilized to estimate the structural responses, which makes it feasible to propagate the uncertainties with an affordable computational effort. The Design of Experiments technique is implemented to acquire the training data, reducing the required data. The results show that the mathematical relationships defined by Artificial Neural Networks and using the ET method can estimate the median Intensity Measures and shifts in dispersions with acceptable accuracy.
Coarse-grained soils are fundamental to major infrastructures like embankments, roads, and bridges. Understanding their deformation characteristics is essential for ensuring structural stability. Traditional methods, such as triaxial compression tests and numerical simulations, face challenges like high costs, time consumption, and limited generalizability across different soils and conditions. To address these limitations, this study employs deep learning to predict the volumetric strain of coarse-grained soils as axial strain changes, aiming to obtain the axial strain (
The excavated soil in the chamber of an earth pressure balance (EPB) shield is typically required to achieve a plastic flow state during tunneling to ensure a stable excavation face and the smooth discharge of soil. When EPB shield tunneling takes place in composite strata with gravelly sand above and moderately weathered argillaceous siltstone with high clay mineral content below, the changing sand–rock ratio on the excavation face leads to a greater risk of water spewing and clogging on the cutterhead, posing enormous challenges to soil conditioning. In the study reported here, we used foam and bentonite slurry as conditioning materials for mixed soil. A series of laboratory tests were performed on the conditioned soil with different sand–rock ratios and water contents to determine the optimal injection ratios of conditioning materials. A miniature EPB shield model test involving soil pressure balance, conditioning material injection, and tunneling control was conducted to simulate the continuous excavation process from full-face sand to full-face rock stratum. The model and field test results of thrust, torque, and soil pressure in the soil chamber and screw conveyor validate the effectiveness of the proposed soil conditioning schemes for composite strata with different sand–rock ratios. The test results indicate that the volume ratio 4:1 of foam to bentonite slurry achieves better performance of the conditioned gravelly sand at a lower total injection ratio (TIR < 10%). The bentonite slurry has a significant improvement effect on the flow plasticity of crushed moderately weathered argillaceous siltstone. The influence of bentonite slurry on the slump value of conditioned soil is greater than that of foam. Based on the optimal injection ratios of conditioning materials for full-face sand (ϕ = ∞) and full-face rock (ϕ = 0), the injection ratios for composite strata were obtained by weighted summation according to the area ratio of different strata on the tunnel face. This research provides valuable insights into soil conditioning and parameter determination methods for EPB shield tunneling in composite strata.
The infrastructure in the urban core area is becoming increasingly dense, leading to restrictions on intensive development; however, there is a lack of adequate research on the structural mechanics of quasi-rectangular pipe jacking tunnels. This paper presents an experimental investigation that was conducted to analyze the impact of ground surcharge on the structural behavior of a quasi-rectangular tunnel located at Jing’an Temple station of Shanghai Rail Transit Line 14. The experimental setup included a scaled-down model of a quasi-rectangular tunnel, which was considered to be typical of underground structures. A series of tests were carried out by applying varying surcharge loads and eccentricities on the ground surface located above the tunnel. The tunnel structure’s response was monitored and analyzed through the use of earth pressure gauges, displacement sensors, and strain gauges. The experimental results revealed that ground surcharge on existing tunnels is mainly influenced by eccentricity and depth, with distinct effects at zero eccentricity and increasing eccentricity. Shallow tunnel burial depths intensify the impact of ground surcharge on the tunnel structure.
This study proposes the use of three-dimensional (3D) printed artificial aggregates as phase change material (PCM) carriers and investigates its effects on alkali-activated slag concrete. The artificial aggregates were manufactured using Fused Deposition Modeling (FDM) and Stereolithography (SLA) techniques and PCM was injected into the artificial aggregates. Natural aggregates were replaced with FDM or SLA-type artificial aggregates by 15% and 30% by volume and alkali activated slag concrete specimens were produced. The characteristics of artificial aggregates and their impact on mechanical, physical, and thermal properties of concretes are examined. The results showed that 3D-printed artificial aggregates ameliorated the abrasion resistance of concrete specimens. The concrete samples had a minimum strength of 32 MPa after 28 d, with 15SLA concrete achieving 42.5 MPa, which is comparable to the reference concrete. Thermal test results demonstrated that the PCM helps maintain the concrete surface temperature 3.7 °C higher than the reference mix when the ambient temperature drops below zero and notably slows down the temperature decrease. The concrete mixes without PCM showed ice formation on their surfaces when the ambient temperature dropped to −5 °C, while no ice formation was observed on samples incorporating PCM. Furthermore, the inclusion of PCM improved the freeze–thaw resistance of concretes.
3D printed concrete undergoes compressive deformation when printed fresh, often overlooked by traditional methods, impacting buildability prediction accuracy. In this paper, the buildability prediction model is modified by incorporating the Mohr–Coulomb damage criterion and focusing on the compressive deformation during the printing process. The prediction model combines the following key components: 1) the utilization of bilinear stress−time loading curves to simulate nonlinear stress−time loading curves during the actual printing process; 2) conducting uniaxial unconfined compression tests on cylindrical fresh specimens with different aspect ratios (ranging from 0.25 to 2) to extract the stress–strain response of the material; 3) the refinement of material parameters (including elastic modulus and plastic yield stress) and their variations with aspect ratio derived from the uniaxial unconfined tests. The material experimentation results indicate that the green strength exponentially decreases with increasing aspect ratio, while Young’s modulus exhibits a linear increase with the same parameter. Experimental comparisons were made during hollow drum printing tests using two different printing materials against the Mohr–Coulomb buildability prediction model. The results from these experiments demonstrate the improved accuracy of the new model in predicting failure heights (with relative error rates of 5.4% and 10.5%).
The increasing consumption of plastics, and the threat of environmental impact of their disposal, renders the management of their waste of interest. In the present study, an effort has been made to investigate the influence of waste polyvinyl chloride (PVC) and polypropylene (PP) of various origin in lime-based mortars, applied in the restoration of traditional structures. Nine mortar compositions (based on lime and natural pozzolan) were designed, manufactured and tested, in which natural aggregates were partially substituted by waste plastics (in proportions of 12.5% and 25% v/v of aggregates). According to the research results, shrinkage deformations were reduced in the short term in all modified compositions, porosity showed slight changes, while apparent specific gravity and capillary absorption index were decreased. Mechanical properties were enhanced in the case of the PVC and the lower PP flakes addition (12.5% v/v), while compressive strength was reduced around 5%–25% in the higher proportion (25% v/v). Generally, it could be asserted that the 12.5% v/v proportion of waste plastics offered benefit, and in particular PVC addition was beneficial in terms of physico-mechanical properties, rendering the exploitation of plastic waste in lime-based systems feasible.
With 200 km of new lines and 68 new stations, the Grand Paris Express (GPE) project is currently the biggest transport project under construction in Europe. Starting in 2010, the GPE project involves an ambitious schedule with major milestones planned between 2022 and 2030. To meet these deadlines as well as the associated cost, quality and safety goals, intensive construction technology is needed in this once-in-a-century megaproject, but this project also provides ideal opportunities to apply this technology. This paper offers a review of the new and innovative construction technologies used during the GPE project’s design and construction stages. Such a large project certainly presents a range of complexities and poses many technical, material, human and environmental challenges. Due to its high-risk nature, the risk management plan that applies throughout the whole GPE project, along with the contractual and insurance conditions, is introduced first. Then, an overview is provided of the design principles and construction methods selected to overcome the engineering challenges and reduce the technical risks, all of which are accompanied by monitoring methods and digital approaches. In addition, several new and innovative construction technologies adopted in this project are illustrated. The paper concludes with the project’s environmental protection.
