Abstract:This paper proposes an innovative dual-function damper based on the elastoplastic torsional deformation of steel tubes. The damper adopts a V-shaped polyline design， enabling the components to achieve elastoplastic torsional deformation under external loads， thereby providing both load-bearing and energy-dissipation capabilities. Theoretical analyses were conducted to derive fundamental mechanical parameters， including the initial stiffness， yield load， and yield displacement of the damper. A dual-torsion tube three-fold V-shaped brace， referred to as the double-torsional-tube V-shaped brace （DTTB）， was designed and utilized as a diagonal brace for frame structures. Under quasi-static low-cycle loading conditions， experimental and simulation results revealed that the damper exhibited full hysteresis loops and strong energy dissipation capacity. The equivalent viscous damping coefficient reached 0.38 at the design displacement of 50 mm， meeting the performance level of similar buckling-restrained brace （BRB）. The stiffness degradation and energy dissipation characteristics of the specimens were found to be similar to those of BRBs， validating the feasibility of the proposed damper as a dual-function energy-dissipative brace. The simulation results were highly consistent with experimental observations， verifying the accuracy of the theoretical model. By optimizing the initial angle of the support bar to 25°， the axial tension-compression imbalance coefficient was reduced to 1.2， meeting the requirements of relevant standards and further verifying the engineering feasibility of the design. Finally， the issue of excessive axial tension-compression imbalance caused by geometric nonlinearity was analyzed in detail， providing theoretical insights for enhancing future design schemes.

Abstract:During the swivel construction process of cable-stayed bridges， the bottom of the pylon is not fully solidified， causing a risk of overturning and collapse under wind loads. However， existing anti-overturning safety assessments mostly rely on the safety factor method， and there is limited research based on reliability. Taking a single-pylon cable-stayed bridge in Wuxi City during its swivel construction process as the research subject， the limit state equation and the design expression using partial factors for wind-induced overturning of pylons during the swivel construction process were formulated. According to static aerodynamic force coefficients obtained by virtual wind tunnel testing， the aerostatic response and buffeting response of the bridge were calculated using finite element methods， and then the internal force at the bottom of the pylon under all wind direction angles was obtained. The Monte Carlo method was employed to acquire the anti-overturning reliability index of the pylon， and results showed a minimum reliability index under the wind in the direction perpendicular to the bridge. A sensitivity analysis was conducted， revealing that the structural self-weight and wind speed have the greatest impact on the calculation results. Based on the target reliability index， the partial factors of structural self-weight and wind load in the anti-overturning calculation of the pylon were calculated using the checking point method （JC method）， serving as a reference for the swivel construction design of bridges.

Abstract:To address the response of adjacent piles caused by foundation pit excavation， this study first adopts the image source method to deduce the calculation expression for the soil free displacement field around a foundation pit from the deformation curve of the retaining wall using non-uniform soil convergence mode. Subsequently， through incorporating the layering property of soil ground and introducing the Vlasov foundation model， the differential equation governing the response of adjacent piles induced by foundation pit excavation is established using the two-stage approach， and then its theoretical solution and calculation method are developed based on the finite difference method. Finally， two typical case studies are performed and discussed to verify the reliability of the developed theoretical solution， and the influences of elastic modulus of layered soils and the non-uniform convergence coefficient on the response of adjacent piles are calculated and discussed. The results indicate that the change of soil parameters in the soil layer at the bottom of the foundation pit has the most significant impact on the response of adjacent piles. At the interface of layered ground， the shearing force of adjacent piles has a turning point， while the corresponding foundation reaction shows an abrupt change. With the increase of the non-equal soil convergence coefficient， both the horizontal displacement of adjacent piles and foundation reaction gradually increase at the upper part while decreasing at the lower part. In addition， the influence at the upper part is more remarkable than that at the lower part， while the influence on the shear force and bending moment of adjacent piles show opposite patterns.

Abstract:Pressure-cast-in-situ pile with spray-expanded frustum （PPSF） is a new type of pile developed by the authors， which has been widely used in practice due to its advantages of high bearing capacity and small deformation. To study the uplift bearing behavior of the PPSF， static load tests on the PPSF were carried out， and a three-dimensional finite element numerical calculation model for the uplift behavior of the PPSF was established. The reliability of the numerical calculation results was verified by using the static load test results of the PPSF. Based on the finite element numerical calculation results， the influence of factors， such as location， length-diameter ratio， diameter and frustum angle of expanded body with double-frustum， on the uplift bearing behavior of the PPSF was analyzed， and the failure mode of the PPSF and the interaction mechanism between expanded body with double-frustum and surrounding soils were clarified. The present research results can provide a reference for the establishment of deformation and bearing capacity calculation methods for the PPSF.

Abstract:To evaluate the suitability of gravelly sulfate soil as high embankment fill in arid regions with seasonally frozen ground， this study systematically investigated the effects of salt content， moisture content， and fine soil content on the water-salt migration and deformation characteristics of the gravelly sulfate soil through constant-temperature tests and freeze-thaw cycle tests under various conditions. The test results indicate that the increases in salt content （0.5%～0.9%）， moisture content （3.07%～5.07%）， and fine soil content （0.3%～5%） led to reductions in the soil’s freezing temperature by 61.9%， 20.9%， and 4.96%， respectively. The freezing temperatures of the tested soil samples ranged from -1.15 to -0.67 ℃. With the increase of soluble salt content， the freezing temperature gradually decreased， which could promote the migration of water and salt to the cold end. When the salt content of the sample was the same， increasing the fine soil content from 0.3% to 5% resulted in a 62.8% increase in maximum deformation. Higher fine soil content and salt content were found to facilitate a shift in deformation behavior from settlement to heave. The total deformation of the sample with 3% fine soil content was small， and the distribution of water and salt was close to the initial value， indicating relatively stable. It is suggested that the fine soil content controlled by the gravel sulfate soil high fill embankment in this area should not exceed 3%.

Abstract:In response to the limitations of random crack development and poor fracturing effect of circular boreholes in static fracturing of rocks， quadrilateral holes with the potential of stress concentration and directional fracturing were proposed as boreholes. The static fracturing mechanism based on quadrilateral holes was studied， and the fracture effect of the specimen was quantitatively analyzed according to the sharp angle stress and energy utilization efficiency. Meanwhile， the dynamic fracture process was monitored by digital image correlation technology. On this basis， PFC2D was employed to investigate the influence of borehole angle and double-hole spacing on the fracturing effect. The results indicate that the crack propagation direction of the quadrilateral hole is controllable， and fracture occurs along the extension line of its acute angle bisector. According to the displacement cloud map of the sample during the surface crack propagation process， its fracture process can be divided into three stages： initial stage， development and propagation stage， and connection stage. The stress concentration effect of boreholes is related to their shape and sharp angle. The stress growth rate reaches its maximum value when the sharp angle of the trapezoid is 30°， indicating the best stress concentration effect. The borehole shape has a relatively small impact on energy utilization efficiency. In contrast， the energy utilization efficiency of trapezoidal holes is slightly higher than that of diamond holes， with a difference of less than 5%. Furthermore， the change in the sharp angle of the borehole has a significant impact on energy utilization efficiency. When the sharp angle decreases from 60° to 30°， the energy utilization efficiency of diamond holes is increased by 19.63 percentage points， and that of trapezoidal holes is increased by 17.63 percentage points. In the single-hole simulation test， both diamond and trapezoidal holes have the maximum crack width and the best overall fracture effect at a sharp angle of 60°. In the double-hole joint fracturing simulation test， the optimal fracture effect is achieved when the spacing between the double diamond and trapezoidal holes is one-third of the length of the specimen.

Abstract:A strengthening method using a thin layer composed of longitudinally expanded steel mesh （ESM） and high-performance mortar is proposed to meet the principles of “minimal intervention” and “material compatibility” in the strengthening of concrete components for historical buildings. An experimental study was conducted on reinforced concrete columns with a designated concrete strength of C20. These columns was strengthened using the afore-mentioned method under small eccentric compression loading. The test results show that an increase in the number of steel mesh layers and the thickness of the strengthening mortar can significantly improve the bearing capacity and the ductility of the specimens. The cracks that appeared in the strengthening mortar when the specimen failed were mainly concentrated on the compression surface， the corners of the compression zone， and the two sides near the compression zone. This indicates that the strengthening layer has a significant confinement effect on the concrete in the compression zone. Considering the improvement effect of ESM and high-performance mortar on the compressive strength of constrained concrete， a limit state analysis was conducted on the strengthened columns under small eccentric compression， and the calculated values of their ultimate capacity were in good agreement with the experimental ones.

Abstract:Cast steel tubular joints have the advantages of excellent integrity and low stress concentration levels， making them widely used in spatial structures. However， current design codes do not provide verification formulas for such joints， which forces engineers to rely on finite element analysis for safety validation. This often leads them to search for reasonable design schemes through a trial-and-error approach. To improve the design efficiency and quality， this paper first proposes a novel shape optimization method， which develops the parametric modeling of joints based on subdivision surface， realizes the automatic finite element analysis of joints through secondary development in ABAQUS， and adjusts the shape of the joints with the genetic algorithm. Secondly， the objective function of the shape optimization problem under multiple load cases is constructed using four objective merging methods， namely linear weighted method， compromise programming method， ε-constraint method， and minimax method， respectively， and the shape optimization problem under multiple load cases is transformed into a single-objective optimization problem. Finally， the above methods are applied to a cast steel tubular joint in a cylinder shell， and the results demonstrated that the proposed method can reduce the peak Mises stress of the joint by 44%~60%， effectively reducing the stress level of the joints without increasing the joint volume significantly. At the same time， among the objective merging methods， the maximum minimization method can balance different load cases most effectively and exhibit similar peak Mises stress under different load cases， making the most use of the material.

Abstract:Partially Encased Composite （PEC） columns offer the advantages of good stability and high precast degree. Adding steel fibers into the concrete mix can effectively restrain the development of concrete cracks. In this paper， eight steel fiber-reinforced PEC column specimens with corrugated web were designed and tested， with the anchorage length and steel fiber content as variables. The bond-slip behavior at the interface was studied. The results show that the steel fiber-reinforced concrete specimens are broken through the interface cracks in the load decreasing section， and the failure mode of the specimens is the natural bonding force failure at the interface. The interface bond performance is the best when the steel fiber content is constant and the anchoring length is 650 mm. Adding steel fiber into the concrete can improve the bond properties. With the increase of steel fiber content， the initial slip load and initial strength increase， and the ultimate load first decreases and then increases. When the steel fiber content is 1.5%， the ultimate strength reaches the minimum value and the residual strength reaches the maximum value. The strain of the flange of the steel plate is approximately exponential with the anchorage length in the load rising section， and the strain of the corrugated web is wavy. A calculation formula of the specimen’s characteristic bond strength was obtained by linear regression fitting. Comparing the calculated value with the test value， it was found that the error was small， which could provide a reference for the bearing capacity design and application of the corrugated web steel fiber PEC column.

Abstract:Screw groove piles， a new type of precast pile， are economically and environmentally friendly， and they can improve the load-bearing performance of the pile through a unique screw groove structure. Through model tests and finite element calculation， the difference in load transfer characteristics between screw groove piles and equal section piles is analyzed， and the concept of material utilization is introduced to explore the bearing characteristics of piles with different screw groove parameters. The results demonstrate that the vertical settlement curve of the screw groove pile exhibits a gradual trend， with an ultimate bearing capacity 1.85 times higher than that of the equal section pile， and its material utilization rate is 2.85 times higher. The screw groove structure increases the pile-soil interaction surface， thereby increasing the skin friction resistance of the pile. The screw groove surface end resistance and pile tip resistance form a multipoint vertical bearing mode. Increasing the inner diameter of the screw groove piles increases the load-carrying capacity by 337.2%， but the material utilization ratio is decreased by 133.8%. The existence of optimal screw groove spacing enables efficient material utilization， while a groove thickness-to-inner diameter ratio greater than 1 leads to reduced resource utilization efficiency. The bearing capacity of screw piles can increase significantly with the increase of screw groove width； however， their material utilization initially increases and then decreases.

Abstract:To study the horizontal bearing characteristics of bridge pile foundations in the developed karst area with steep slope， the effects of slope changes on the ultimate bearing capacity of pile foundations， pile bending moment， and soil resistance on the pile side under the action of horizontal load on the pile foundations are investigated by using the centrifugal model test with the highway project as the basis， when the pile foundation thread through the karst cave and is located in the steep slope areas. The results show that the horizontal ultimate bearing capacity of the pile foundation decreases with the increasing foundation slope. For slopes less than 30°， the horizontal ultimate bearing capacity of the pile foundation is reduced by less than 10%， whereas for slopes greater than 30°， the horizontal ultimate bearing capacity of the pile foundation and the horizontal displacement of the pile top are significantly affected. The pile bending moment first increases gradually and then decreases gradually to zero along the direction of burial depth， and the decay rate is maximum in the embedded rock layer. The maximum value of the bending moment appears in the range of 2.5 to 5 times the pile diameter from the top of the pile. As the slope increases， the maximum value of the pile bending moment gradually increases and the position of the maximum bending moment gradually moves downwards. The soil resistance on the pile side increases and then decreases to zero along the depth of the pile foundation. The maximum soil resistance appears within 2.5 to 5 times the pile diameter from the pile top. With the increase of load， the depth of the maximum soil resistance of the pile side gradually moves down. The soil resistance on the pile side under different foundation slopes shows the small pattern in front of the pile and the large one behind the pile， and the difference in soil resistance is concentrated in the range of 2.5 to 5 times the pile diameter from the pile top.

Abstract:Soft rock within embankments is prone to continuous particle breakage， migration， and rearrangement due to rain infiltration and traffic loads， leading to uneven subsidence. subsidence deformation is a key indicator of embankment stability and safety， making accurate prediction essential for preventing road defects and instability. However， traditional single prediction models often lack generalizability and are not suitable for varying conditions in embankment engineering. This study collected and analyzed subsidence data from 18 soft rock embankments in highways and railways， which exhibited distinct subsidence patterns， including wave-like， broken line， and parabolic trends. Based on these data， using the Stacked Generalization （SG） ensemble algorithm， an SG fusion model predicting soft rock embankment subsidence was developed combining the prediction models from three different fields. The model avoided the hyperparameter tuning process， allowing for direct application in engineering practices. Besides， a Blocked K-Fold training strategy was employed to improve robustness. In comparison with traditional models， under conditions of limited monitoring data， the SG fusion model demonstrated significantly lower error rates and higher prediction accuracy across various projects. The findings suggest that the SG model is more applicable and robust for predicting soft rock embankment subsidence. This research provides theoretical and technical support for evaluating the service performance and post-construction maintenance of soft rock embankments.

Abstract:The Loess Plateau region is prone to frequent strong earthquakes， which often trigger large-scale， intensive loess landslides. Shallow buried bias loess tunnels are highly susceptible to significant seismic damage due to factors such as thin overburden and unsupported slope faces， which result in pronounced seismic amplification effects. The seismic damage characteristics and mechanisms of shallow buried bias large section loess tunnels were systematically investigated through large-scale shaking table model tests. The results indicate that the presence of tunnel cavities significantly influences the distribution characteristics of acceleration amplification factors on the slope face， with the main affected region being between 0.25H and 0.80H. The horizontal acceleration amplification factor within the slope increases nonlinearly with elevation， with weaker amplification effects below approximately 2/3 of the slope height and significantly stronger amplification effects above approximately 2/3 of the slope height. Under horizontal seismic loading， the tunnel lining experiences extensive tensile and compressive through-cracks along the conjugate 45° directions from the right arch waist to the left wall foot， and from the left arch waist to the right wall foot， resulting in severe seismic damage. Under the condition of small-angle bias， continuous slip surfaces extend from the slope crest to the tunnel’s deep-buried side wall foot， with local continuous sliding and localized collapse occurring at the slope surface and crest. The dynamic amplification effect of the tunnel cavities is the primary cause of the formation of local slip surfaces at the slope surface， while the combined shear force from the seismic inertia force and gravitational force of the rock-soil body is the fundamental cause of the inward deformation of the tunnel lining on the deep-buried side and outward deformation on the shallow side. The findings of this study provide valuable insights into the seismic design of shallow buried bias loess tunnels.

Abstract:To investigate the distribution patterns of the temperature field， residual stress field， and deformation field in welded joints of steel bridges， a 3D finite element model of a butt weld in a 16 mm-thick bridge steel plate was established using finite element software. The accuracy of the model was verified through the blind-hole method experimental data. Based on this validated model， the distribution characteristics of the temperature field， residual stress field， and deformation field in the welded components were further analyzed. Additionally， an initial crack was introduced into the weldment to explore the impact of initial defects and welding residual stress on the fatigue life of the weld. The study results indicate that along the direction perpendicular to the weld seam， the longitudinal residual stress exhibits a tensile-compressive distribution. Within the 60 mm heat-affected zone near the weld， tensile stress is predominant， with a peak value of 415 MPa， exceeding the yield strength of the material. As the distance from the heat-affected zone increases， the longitudinal tensile residual stress transitions to compressive stress. The transverse residual stress reaches its peak value of 205 MPa at the weld toe. Under unconstrained conditions， the welding-induced deformation presents as typical out-of-plane angular distortion， with deformation at each measurement point increasing linearly with distance from the weld seam center. The maximum deformation occurs at the outer edge of the weldment， measuring 14.58 mm. Even small residual stresses， regardless of their state， influence fatigue life. Residual tensile-compressive stresses of 3% and 8% result in a decrease of 16.7% and an increase of 68.4% in fatigue life， respectively. Residual tensile stress leads to a reduction in fatigue life as stress increases， but the rate of reduction gradually diminishes. When the tensile/compressive stress values are comparable， compressive stress has a far greater impact on fatigue life than tensile stress. During the prefabrication of actual components， methods such as pre-deformation should be employed to control the deformation of the weldment， while post-weld surface treatment techniques should be used to manage residual tensile stress， thereby improving material fatigue life and extending the service life of the structure.

Abstract:Based on the concept of effective working width， the bridge deck is simplified as a multi-span continuous beam. The constraints of the main beam on the bridge deck are equivalent to anti-bending springs. When the stress mechanics of the deck between two main girders is analyzed， this deck is equivalent to a single-span beam. The anti-bending capacities from side spans are also simplified into anti-bending springs. A series of comprehensive equivalent stiffness parameters from the anti-torsion of the main girders and the anti-bending of the side spans are derived recursively. The variations of comprehensive equivalent stiffness parameters against the stiffness ratio of the anti-torsion stiffness from the main girder to the anti-bending transverse stiffness from the bridge deck are studied. The formulae of slopes and moments at endpoint and middle-span point are formulated for the deck constrained by the main girders and side spans under distributing load， concentrated load and partially distributed load， which provides a simplified theory for transverse bending moment calculation of multi-span continuous bridge decks. A background bridge consisting of prestressed-concrete I-type girders and reinforced-concrete bridge decks is studied. The transverse bending moment distributions and transverse bending moment modification factors of different-span bridge decks under model self-weight and automobile section distributing loads are analyzed， and the effect of beam height， deck thickness， beam number and load on transverse bending moment modification factors is investigated. The results demonstrate that： the analytical transverse bending moment from the present theoretical formulae agrees with the finite element， and the equivalent single-span beam method is feasible to simplify the multi-span continuous deck. The maximum result of the transverse bending moment modification factors is 0.666 7 at the supporting point， which is less than the value of 0.7 specified by the Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts （JTG 3362—2018）. When t/h<1/4 （the ratio of the bridge deck thickness t to the main girder height h）， the maximum value of the transverse bending moment modification factors is 0.670 3， which is larger than the value 0.5 specified by JTG 3362—2018. The calculating results based on the specification JTG 3362—2018 are unsafe for the design practice. When t/h>1/4， the maximum value of the transverse bending moment modification factors is 0.679 4， which is less than the value of 0.7 specified by JTG 3362—2018. To ensure the design of the bridge deck safe， further investigation into the transverse bending moment prescribed in JTG 3362—2018 is recommended.

Abstract:To address the issues of inadequate resource utilization， complex processes， and low economic added value associated with electrolytic manganese residue （EMR） solid waste， in order to effectively consume and utilize EMR， this study utilizes experimental methods， underpinned by preliminary theoretical analysis， to examine the impacts of basic raw material ratios （mass ratio of EMR to the combined mass of EMR and FA）， alkaline activator ratios （proportions of water glass， NaOH， and mixed water）， and the types and quantities of foaming and stabilizing agents on the performance of the targeted insulation material. The findings indicate that both the basic raw material ratio and the alkaline activator ratio profoundly affect the molar ratios of SiO2/Al2O3， SiO2/Na2O， and liquid/solid mass ratio， significantly influencing the mechanical properties of the samples. Optimal mechanical performance of the construction material samples is achieved with a basic raw material ratio of 0.7， a SiO2/Al2O3 molar ratio of 4.0， a SiO2/Na2O molar ratio of 2.5， and a liquid/solid mass ratio of 0.5， resulting in a compressive strength of 11.15 MPa and a density of 1 476 kg/m3. Furthermore， the type and quantity of foaming and stabilizing agents influence the sample properties significantly； optimal performance of the building insulation material samples occurs when using hydrogen peroxide as the foaming agent （4~6 g） and a laboratory-made stabilizing agent （2 g）， achieving a thermal conductivity of 0.104~0.131 W/（m·K）， compressive strength of 0.69~1.49 MPa， density of 433~533 kg/m3， and a cost of 1 294~1 722 CNY/m3. This study offers new perspectives on the extensive consumption and utilization of EMR， reducing building energy requirements while fulfilling insulation and thermal resistance needs， with considerable potential for engineering applications after further optimization.

Abstract:As a unique type of deployable structure， bistable composite material structures have extensive applications in various fields such as foldable wings， energy harvesters， and adaptive structures. When these bistable structures are employed in complex environments， the changes in material properties have a significant impact on their bistable characteristics. By combining theoretical and numerical investigations， this study examines the impact of material properties on the bistability of composite cylindrical shells. A theoretical model is developed for antisymmetrically laminated composite cylindrical shells， and analytical expressions for the strain energy of the shell during deformation are derived. Moreover， the effects of characteristic constants including longitudinal modulus of elasticity， transverse modulus of elasticity， shear modulus， and Poisson’s ratio on strain energy， principal curvatures， and torsional rates are analyzed for the shell structure. The results indicate that variations in the longitudinal and transverse modulus of elasticity of the material significantly affect the strain energy per unit area and the principal curvature of the second stable state in bistable cylindrical shells. Specifically， when the shear modulus G12 decreases from 10 GPa to 2 GPa， the strain energy per unit area is reduced by approximately 72.98%.The Poisson’s ratio has almost no impact on the performance of the second stable state.

Abstract:Ferrous extraction tailing of nickel slag （FETNS） is the secondary tailings of ferronickel slag （FNS） after ferrous extraction treatment. This paper tests the hydration heat of the FETNS-original portland cement composite binder system using isothermal conductive calorimetry and constructs a hydration kinetics model using the Krstulovic-Dabic model. Both macroscopic and microscopic methods are employed to investigate the basic properties， reaction products， and element leaching of the composite binder system. The results indicate that the hydration kinetics model can accurately reflect the impact of FETNS on the hydration reaction. The incorporation of FETNS reduces the reaction rates and extent of crystal nucleation and growth， phase interface reactions， and diffusion during the hydration process. The addition of FETNS decreases the leaching of reactive elements， delays the setting of the composite binder system， inhibits the formation of hydration reaction products， increases the content of harmful pores in the system’s internal structure， and significantly reduces the early compressive strength.

Abstract:Based on the strain-displacement relationship of the spatial curved beam theory， a galloping model for an iced single conductor with four degrees of freedom was established. The dynamic equation of the iced single conductor was constructed using the principle of virtual work. Element independence was verified through numerical calculations， and the impact of modal truncation on the galloping response was analyzed， verifying the accuracy of the model. In addition， the compound damping cable was used for the anti-galloping device of transmission lines， and a nonlinear vibration control finite element equation for an iced single conductor structure was established with a compound damping cable. The influence of relevant parameters on the galloping amplitude of the conductor was analyzed. The research results indicate that the galloping model of the iced single conductor can predict the galloping response of transmission lines. The compound damping cable can effectively suppress the galloping of a single conductor and achieve a damping rate of over 85%. The higher the installation height of the compound damping cable， the better the vibration reduction effect of the compound damping cable. However， at the same installation height， when the horizontal installation position is close to the mid-span of the conductor， the vibration reduction effect first increases and then decreases， indicating that there is an optimal installation position. Simultaneously increasing the stiffness of the primary cable and reducing the stiffness of the return spring can improve the vibration reduction effect of the compound damping cable. In addition， appropriately increasing the damping coefficient and the mass of the primary cable leads to better vibration reduction effect of the compound damping cable.