In order to investigate the fire resistance of post-earthquake steel beams insulated with lightweight and high ductile fire-resistive engineered cementitious composites （FR-ECC）, reversed cyclic loading tests and fire tests were conducted on the steel beams. The finite element method was used to analyze the temperature field distribution and displacement change response of the steel beams subjected to fire tests under constant load conditions. The validity of the finite element models was verified by comparing with the test results, and extended parametric analyses of steel beams protected with FR-ECC materials were carried out. The research results show that the established ABAQUS finite element analysis model can effectively simulate the heat transfer process and displacement response of steel beams protected with fireproof coatings subjected to fire tests under constant load conditions. Through extended parameter analysis, it can be concluded that the higher the load ratio, the lower the fire-resistance limit temperature and the shorter the fire-resistance limit time; As the thermal conductivity of FR-ECC decreases, the heating process of the steel beam slows down, and the ultimate fire-resistance time becomes longer. Changes in thermal conductivity have the greatest impact on the steel beam in the undamaged state of the fireproofing.

To support China's dual carbon goals, this study explores the use of recycled glass aggregates as a sustainable alternative in concrete. Traditional mix design methods are often inadequate for capturing the nonlinear effects introduced by glass aggregates and involve high trial costs. Based on 331 experimental mix designs, five machine learning models （ANN, SVR, DT, RF, XGBoost） were developed to predict the 28-day compressive strength of concrete, aiming to enhance prediction efficiency and design efficiency. Results show that XGBoost and RF achieved the highest accuracy on training and testing sets （R²=99.3% and 88.5%）, while ANN and RF demonstrated the best generalization on three newly developed concrete materials （R²=92.2% and 93.4%）. SHAP analysis was further adopted to interpret feature contributions, confirming the models' interpretability and robustness. This study highlights the practical potential of machine learning in supporting the efficient design of eco-friendly concrete materials.

Ultra-High-Performance Concrete （UHPC）, a cementitious composite material with high strength, ductility and durability, is now widely used for wet joints of overlapping rebar connections in prefabricated structure. Effective bonding and anchoring of the steel bars in early-age UHPC is an important guarantee for rapid assembly construction. In this paper, pull-out tests were conducted on rebars in UHPC specimens at 3-day age, considering the effects of development length on the bond-anchorage behavior. The results show that： （1） two failure patterns appeared in the tests, namely, the rebar pullout failure without yielding and the rebar pullout failure with yielding; （2） for the anchorage design of rebar in 3-day age post-cast UHPC joints, a cover thickness greater than 2.5 times the diameter of the rebar is recommended; （3） for the HRB400 rebar in UHPC at 3-day age, the critical yield development length is 6 times the diameter of the rebar, which effectively reduces the development length compared with that of normal strength concrete; （4） the calculation formula for the development length in the Code for Design of Concrete Structures （GB 50010—2010） is reliable and relatively safe, but it is recommended to relax code limit conditions of tensile strength for UHPC.

With the recent development of the Hengsha Xinzhou Park, the demand for wharf construction has risen steadily, while the complex engineering-geological conditions pose challenges to pile design and construction. This paper characterizes the site's geology by analyzing the stratigraphic profile and mechanical parameters of the seabed soils. Based on the geotechnical investigation data, the engineering-geological conditions for pile foundations were evaluated. The results indicate that soft and liquefiable soil layers may adversely affect the stability of piles, necessitating appropriate engineering countermeasures. Using a simplified scour-resistance test apparatus, scour tests were carried out on the seabed soils. The findings reveal that sandy silt and clayey silt have relatively poor resistance to scour; therefore, scour countermeasures are required. The studies will provide essential technical support for the development of the Hengsha Xinzhou Park and the regional economy.

This paper addresses the limitations of materials used in viscoelastic dampers for high-rise buildings and develops a new type of viscoelastic damper with styrene-hydrocarbon copolymer thermoplastic elastomer as the core energy-dissipating material. Cyclic loading tests were conducted on two specimens of the novel damper. The test results demonstrate that the damper utilizing this material offers advantages such as large deformation capacity, low temperature sensitivity, and strong energy dissipation capability, providing full and stable hysteretic curves under various temperatures. Based on these findings, a structural design methodology for the new damper is proposed. A practical super high-rise building is adopted as a case study to complete the damper layout, and time-history analysis is performed to verify the effectiveness of the proposed method. This study provides a reference for the engineering application of the new viscoelastic damper in seismic and wind-resistant design of high-rise buildings.

For the key issue of one-pass full-section excavation construction of an underground ventilation station with multiple bifurcations, this study takes the Suzhou International Rapid Logistics Corridor Phase II Project—Yangtze River Road South Extension Project as the engineering background. Given the structural complexity of the underground caverns in the ventilation station, the structural unit containing the main cavern is selected, and a three-dimensional numerical model is established. The model is used to analyze the spatial structural response, deformation characteristics, and surrounding rock evolution of the underground cavern group, with emphasis on the cross-section and large-span connection sections of the ventilation station. The analysis verifies the feasibility of the proposed construction method and can provide valuable references for the design and construction of similar underground projects under comparable conditions.

Openings are often used in cast-in-situ concrete hollow floors and the current direct design method does not consider the influence of the openings. In this paper, 270 case studies on 3x3 span box filler hollow floors with openings were analyzed using software ABAQUS. The effects of four parameters on the moment distributions of the hollow floors were investigated, i.e., the opening position, opening area ratio, slab span ratio and the beam-slab relative flexural stiffness ratio. The obtained results included the moment distribution coefficients for control sections of the floor strips, as well as the moment distribution coefficients for column strips. These results were also compared with the coefficients recommended by the code. It was found that the opening in the hollow floor weakened the section stiffness at the opening position, reduced the moment distribution coefficients of the section, and consequently increased the moment distribution coefficients of other sections. In the presence of an opening, the recommended values in the code are appropriate for the moment distribution coefficients for control sections of both the interior and end span. However, the moment distribution coefficients for the column strips in the code are not applicable and it is recommended to adopt the moment distribution coefficients proposed in this paper for the column strips,which account for openings.

Pore size distribution （PSD） significantly affects the water-retention and seepage characteristics of unsaturated soils. By assuming that the PSD of soil follows a fractal law and that soil volume deformation affects the PSD via changes in the fractal dimension, a fractal-based equation describing the evolution of PSD during soil volume deformation is proposed. This equation combines intrinsic constraints between the pore size ratio and the fractal dimension. Consequently, models for the unsaturated soil water retention curve （SWRC） and the relative hydraulic conductivity curve （RHCC） that consider the evolution of PSD are derived. The model parameters can be calibrated using water retention curve data from soil samples with two different initial porosities, enabling prediction of the SWRC and RHCC under various deformation states. Finally, the proposed model is validated against seven sets of experimental data, demonstrating that the hydraulic model based on fractal theory effectively describes the impact of volume deformation on the water retention and seepage characteristics of unsaturated soils.

In the design of general non-prestressed reinforced concrete structural components, the ultimate limit state calculation of bearing capacity and the crack width check are the two main calculation tasks according to the standards. Due to the influence of crack width control verification, the reinforcement in some components often cannot reach the design value of material tensile strength used in the calculation of bearing capacity limit state. Therefore, it is necessary to consider the influence of both factors when selecting and configuring reinforcement materials. In this article, based on different strength grades of steel bars and different types of fiber-reinforced polymer bars, formulas for calculating the utilization ratio of reinforcement strength for crack width control under various loads such as dead load, live load, and hydrostatic pressure are derived according to the relevant design codes’ formulas for bearing capacity limit state and crack width control verification. Corresponding numerical solution methods are provided, which enable a macroscopic understanding of the utilization of material strength in crack control situations. Finally, a program is developed to plot the calculation results into graphs, summarizing the patterns of the results and providing guidance for structural design optimization and material selection considerations.

The frame-damping-framed-tube structure is a new structural system in which the “damping-framed-tube” is used to approximate the core tube, with the frame bearing all vertical loads. This paper investigates the feasibility of applying this new structural system in the development of upper cover of urban rail transit. Elastic analysis under frequently occurred earthquake and elastoplastic time history analysis under rarely occurred earthquake were carried out. Analysis results show that the elastic and elastoplastic inter-story drift of the well-designed upper cover frame-damping-framed-tube structure of urban rail transit can meet the requirements of design standards. Under rarely occurred earthquake, the damping walls yield adequately and dissipate energy, with an additional damping ratio of whole structure up to 1.82% and that of upper cover structure up to 3.45%, showing excellent energy dissipation and seismic mitigation effects. Compared with conventional frame-core tube structures, the elimination of the core tube reduces the dead load of the upper cover structure, improves the load distribution in the transfer level, and benefits the design of the structure below the platform. It indicated that the new structure is suitable for the development of upper cover of urban rail transit. This paper also discusses the influence of the structure below the platform on the performance of frame-damping-framed-tube structure. Compared to being embedded on the ground, the seismic response of high floors of the upper cover frame-damping-framed-tube structure is amplified due to the whipping effect. Therefore, it is necessary to appropriately increase the stiffness and bearing capacity of the damping walls on the high floors to fully utilize their energy dissipation capacity.

Steel-structured fully indoor substations are the preferred solution for urban green substations, offering advantages such as land conservation and stable operation. However, once a fully indoor substation suffers earthquake, it will lead to enormous economic losses. Additionally, traditional seismic design overlooks the structure-equipment interaction, resulting in designs that tend to be unsafe. In this study, the coupling model and the main structure model were established respectively for a 110 kV steel-structured fully indoor substation. The coupled model accounts for the structure-equipment interaction, while the main structure model treats equipment as floor loads. Subsequently, dynamic characteristic analysis （to obtain key parameters such as natural vibration frequencies and mode shapes） and time-history analysis were conducted on the two types of models. Finally, the Incremental Dynamic Analysis （IDA） method was adopted： by adjusting the peak ground acceleration （PGA） of seismic waves, the response indices of the main structure and equipment under different seismic intensities were quantified, so as to comprehensively evaluate the seismic vulnerability of both. The results show that： （1） The acceleration amplification effect of the 2nd-floor GIS （Gas Insulated Switchgear） equipment bushings is significant （with an average value of 4.2 and a maximum value of 5.1）, which is much greater than that of the 2nd-floor slab, making the bushings prone to damage due to excessive acceleration during earthquakes; （2） The structure-equipment interaction exerts a notable impact： the maximum difference in amplification factors between the coupled model and the main structure model is 20%, and the maximum difference in inter-story drift angles is 15%; （3） Under the action of some seismic waves, the torsional displacement ratio of the coupled model exceeds 1.2, so torsion reduction measures need to be implemented; （4） Under the same seismic intensity, the failure probability of electrical equipment is far higher than that of the main structure. For instance, when PGA=1.0g, the equipment damage probability reaches 60%, while the main structure barely collapses.

Concrete-filled circular steel tubes （CFCSTs） are widely used in high-rise and long-span structures for their superior bearing capacity, ductility, and construction efficiency. However, the axial compressive capacity calculation provisions for CFCST short columns differ between Chinese and foreign codes. Therefore, it is essential to evaluate the calculation accuracy of the axial compressive bearing capacity formulas for CFCST short columns in various national codes. To this end, the two research methods （“hoop theory” and “unified theory”） were reviewed, and the differences in axial compression capacity using the two theories were compared. The calculation provisions of the axial compressive capacity for CFCST short columns in Chinese and foreign codes were introduced in detail, and the similarities and differences in the formulas were briefly analyzed. Based on a large amount of concrete material test data and 378 CFCST short column axial compression test results, conversion relationships for various concrete material indexes were established to unify the axial compression test results, and the calculation accuracy of each code formula was further analyzed. The results show that the axial compressive bearing capacity ratios using “hoop theory” and “unified theory” increase and then decrease as the confinement index increases, and the ratios are related to the core concrete compressive strength confinement improvement factor. The calculation accuracy of the “hoop theory” and “unified theory” formulas in “Technical code for concrete-filled steel tubular structures” （GB 50936—2014） is comparable, and the calculated values are closer to the average values, with the lowest safety margin. The calculation accuracy of “Recommendations for design and construction of concrete filled steel tubular structures” （AIJ—2008） is second, and the calculation accuracy of “Design of composite steel and concrete structures-Part 1.1： General rules and rules for buildings” （EN 1994-1-1： 2004） is lower than that of AIJ—2008, but higher than that of “Specification for structural steel buildings” （AISC 360‒22）.

Based on the problems found in the post-evaluation process of the square steel pipe adding elevator structure and comparing the advantages and disadvantages of different systems, the technical feasibility of adopting H-shaped steel adding elevator structure is discussed. By analyzing the overall index of the model with different entry forms, floors, ground roughness categories and other multi-factors and multi-levels, the optimal member cross section of H-shaped steel structure under different conditions is obtained. The safety of the connection joints is verified by bearing capacity calculation and finite element analysis. Special analysis is carried out on key issues such as structural performance of adding elevator structure under rare earthquake and calculation method of stiffness of the bottom floor of half-floor entry. An implementation project is used to evaluate the economy of H-shaped adding elevator structure. The analysis results show that： the H-shaped adding elevator structure has the advantages of simple connection, easy inspection and maintenance, high degree of assembly, and convenient on-site construction; the reasonably designed H-shaped adding elevator structure can meet the design requirements of the current code, and the deformation of the components and the level of stresses are low; it is more reasonable to use the shear-bending stiffness statistical stiffness ratio of the bottom floor of the half-floor entry structure with the consideration of the stiffness of the beams in the interstorey; reasonably constructed bolted-welded or fully bolted column connections and beam-column connection joints can meet bearing requirements; H-shaped adding elevator structure has a slight economic advantage over square steel tube structure. The research results of this paper can be used as the technical reserve for the preparation of design guidelines.

A combined base-isolation system incorporating isolation bearings and additional dampers can effectively mitigate seismic forces and control the deformation response of the isolation layer to a certain extent. However, under multi-level seismic excitations, combined isolation systems employing conventional viscous dampers generate excessively high damping forces, which compromise the isolation effectiveness. To address this issue, a viscous damper with overload protection （VD-OP） and its corresponding combined isolation system are proposed in this study. The design, fabrication, and experimental testing of the VD-OP were conducted, and a mechanical model describing its nonlinear damping and overload protection characteristics was established based on experimental data calibration. The effectiveness of the VD-OP combined isolation system and its advantages in multi-level vibration control were verified. The results indicate that the proposed VD-OP system exhibits a velocity-dependent nonlinear damping mechanism and force-limiting capability, effectively preventing excessive damping forces induced by high-level seismic excitations, enhancing isolation efficiency, and controlling the acceleration response of the isolated structure. The performance-based design approach proposed in this study provides practical guidance for the implementation of VD-OP systems and offers a reference for the seismic mitigation design of structures in high-intensity seismic regions.

Apparent defects in underwater concrete structures are significantly challenged by complex environmental factors including water turbidity, variable lighting conditions, and flow velocity. These interferences lead to difficulties in defect localization and low recognition accuracy during underwater inspections. To address these limitations, this study proposes an intelligent recognition framework based on deep learning. The methodology integrates three key components： generation of a multi-scenario defect database replicating complex underwater environments; application of small-sample expansion and image enhancement algorithms for robust preprocessing; implementation of the YOLOv5 target detection algorithm for multi-category defect identification and localization. Experimental results demonstrate that the proposed approach achieves a mean average precision （mAP） of 83% and a recognition precision exceeding 83%. This framework effectively mitigates accuracy degradation caused by underwater environmental complexities and limited sample sizes, providing a reliable technical solution for automated structural health monitoring of submerged infrastructure.

Yichun West Railway Station is the highest-latitude high-speed railway station in China and the first prefabricated canopy station constructed in permafrost regions under severe cold climate. The structural performance of prefabricated canopies is significantly affected by soil frost heave. In this study, a finite element model of the canopy structure is developed to simulate the impact of frost heave on pile foundations. Parameters such as freeze-thaw cycle duration, deformation magnitude, and freeze-thaw position are analyzed. The research reveals the influence patterns of frost heave on the structural behavior of prefabricated canopies, offering a basis for ensuring their safe application in severely cold regions.

The fatigue properties of LY100, LY160, and LY225 low-yield-strength steels were investigated. The effects of strain rate on the fatigue life, crack initiation, and propagation cycles of these steels were examined, along with an analysis of the fracture mechanism. Cyclic loading tests were conducted in accordance with the relevant specifications for metal energy dissipators. The results indicate that the low-yield-strength steels exhibit superior fatigue performance. As the steel grade increases, the fatigue life shows a slight improvement. Variations in strain rate do not significantly affect the fatigue life of the material. The fatigue fracture of low-yield-strength steels is characterized as ductile fracture. The fracture process involves the propagation of multiple micro-cracks into macroscopic cracks, followed by instantaneous rupture. The studied steels meet the requirements for metal energy dissipators and demonstrate good fatigue performance.

To enhance the stability and flood control capacity of aged earthen embankments, a coating material prepared from polylactic acid （PLA） binder, water, and sand was selected and laid on the slopes and crests of the embankments. Tests were conducted on simulated embankments, where photographic equipment combined with an image measurement and analysis system was employed to compare the blocking effect between untreated earthen embankments and those coated with the material during overtopping breaching. The results revealed that applying the PLA coating altered the breaching pattern and delayed the breaching process, with a 5cm-thick coating completely preventing breaching. This study provides a reference for the ecological reinforcement of aging embankments.

Four types of novel lightning rod flange joints were designed, and cyclic loading tests were conducted to investigate their hysteretic performance under horizontal repeated loads. The failure modes, stress development and distribution patterns of the flange joints were examined. The load-displacement hysteretic curves, skeleton curves, stiffness degradation, energy dissipation capacity, and ductility coefficients of the four flange joint types were compared. The results show that the rigid flange joints （S1, S2, and S3） exhibited local buckling on the compression side and steel tube tearing on the tension side at the bottom of the specimens, while the flexible flange joint （S4） failed due to fracture of the weld between the upper steel tube and the flange plate. The rigid flange joints with a ring plate or a core tube demonstrated better ductility than the conventional rigid flange joint. Reducing the stiffeners and bolts in the flange joint （as in specimens S2 and S4） led to decreases in initial stiffness and energy dissipation capacity, whereas adding a core tube effectively improved the hysteretic performance.

A computational fluid dynamics （CFD） method is employed to analyze the influence of longitudinal spacing on the flow field around a photovoltaic array and the resulting wind load on the panels. The validity of the numerical simulation is confirmed through comparison with wind tunnel test results. The findings indicate that longitudinal spacing significantly affects the wake flow field behind the first row, causing the wind load on the second row to be the most sensitive to changes in spacing. Moreover, it is observed that the second row can experience considerable torque when the longitudinal spacing is small. In contrast, the wind load on the third to the eighth rows is only marginally influenced by the longitudinal spacing and generally decreases as the spacing is reduced.

With the increasing span of building structures, traditional precast concrete floor slabs are no longer suitable. Therefore, a new type of prestressed concrete prefabricated bottom plate integrated with a long-span steel pipe truss is proposed. In this study, static load tests were carried out on three large-span prestressed concrete prefabricated floor slabs with steel pipe trusses of different widths （each spanning 8,400 mm）. The cracking patterns, deformation behavior, load-deflection curves, concrete strain, as well as strains in the steel tubes and web members were obtained. Based on the experimental results, the influence of various parameters on the mechanical properties of the prefabricated bottom plate was further investigated through numerical simulation. The test results indicate that cracks initially occur above the top support of the slab and subsequently develop at the bottom mid-span of each span. The cracking load of the prefabricated bottom plate decreases as the plate width increases. Specifically, the cracking load of the specimen with a plate width of 4,200 mm decreases by 20.61% compared to that of the 2,100 mm-wide specimen. The arrangement of supports alters the mechanical performance of the prefabricated bottom plate and effectively restrains the overall deformation of the specimen. Moreover, the number of supports, the diameter of the steel pipe, and the truss span are found to have a significant influence on the bearing capacity of the prefabricated bottom plate, while the truss height has a relatively minor effect.

In response to the load-bearing characteristics of rigid and flexible flange joints in single steel tube lightning rods and based on an analysis of a collapse accident, this study proposes four new types of flange joints. These designs incorporate a core pipe to enhance the joint's bending stiffness. The static load performance and patterns of stress distribution of the new joints and a traditional rigid flange joint were analyzed using ABAQUS finite element software. The results showed that the new flange joints exhibited bearing capacity and flexural stiffness comparable to those of the traditional rigid joint. Moreover, the new designs demonstrated a significant improvement in mitigating stress concentration. This enhancement is beneficial for improving the fatigue performance of the lightning rod flange joints.

With rational application, energy dissipation technology can help structures meet stiffness requirements under seismic conditions, and demonstrates high applicability to high-rise buildings in high-intensity zones. The weak connection scheme using lead-rubber bearings not only satisfies the normal serviceability requirements under minor earthquakes and wind loads, but also controls the structural joint width within the allowable range during major seismic events, while avoiding the adverse effects associated with a rigid connection scheme. Taking two high-rise connected buildings as an example, this paper investigates the design of energy dissipation technology and high-rise connections. First, in response to the limited size of the core tube, viscous damping walls are installed in suitable locations to fulfill stiffness demands, and the stories where viscous damping walls perform most effectively are identified through calculation and analysis. Second, based on the features of high-rise connections, a weak connection scheme is selected after comprehensive comparison, utilizing lead-rubber bearings at the connection points. Finally, reliable anti-collision and anti-fall measures are designed, and the seismic performance objectives of the structure are established, providing a reference for similar projects.

Currently, the main connection methods between square steel tubes include welding, flange connection, sleeve connection, and splicing connector connection. Based on the existing research results of various connection joints, this article proposes a new type of fully bolted column-column splicing joint that uses angle steel as the splicing connector. Firstly, monotonic loading tests were carried out on two column-column joint specimens with different splicing lengths and bolt arrangement forms under combined compression-bending-shear loading conditions, and the influence of the length of the connecting member and the arrangement form of the bolts on the ultimate bearing capacity and stiffness of the joint was analyzed. Finite element analysis software was used to simulate the monotonic loading tests, and the numerical simulation results were compared with the test results to verify the accuracy of the numerical model and obtain the mechanical performance of the two types of joints under monotonic loading. The research results show that the failure process of the specimen using the fully bolted column-column splicing joint with square steel tubes can be divided into three stages, namely, elastic stage, elastic-plastic stage, and failure stage. The longer the splicing member of the joint, the higher the ultimate bearing capacity and stiffness of the specimen. However, the stiffness of specimens using connecting joint is smaller than that of general column components without joint.

In this paper, the fire resistance of high-strength fire-resistant steel bending members is studied by finite element numerical simulation in ABAQUS. Based on the existing test results, the finite element model established by the thermo-mechanical method is verified, and the effects of load ratio, slenderness ratio and steel strength grade on the fire performance of high-strength fire-resistant steel bending members are further analyzed. The results show that the load ratio has a great influence on the fire resistance of the members, while the slenderness ratio and steel strength grade have little influence on the critical temperature of the members. The fire resistance of the bending members gradually decreases with the increase of the load ratio. Finally, the stability parameters for high-strength fire-resistant steel bending members at elevated temperature are proposed by modifying the existing specifications, which are validated by the test results and finite element simulation.

Corrosion of steel structures exhibits high uncertainty, while the Monte Carlo method has been widely used to address stochastic problems. Therefore, the combination of Monte Carlo and finite element methods has become an effective approach for studying steel structure corrosion. This paper presents a numerical investigation on the yield and ultimate bearing capacities of corroded high-strength weathering steel H-beams in the large deformation stage. The influence of random corrosion was considered by introducing random cuboid pits on intact steel beams. The parameters considered include volume loss rate, pit depth, and beam span-to-depth ratio. These parameters were orthogonally combined to generate 540 random pitting models, and bending capacity analyses were conducted to determine their yield and ultimate bearing capacities. The results indicate that under the same corrosion level, different pit depths and span-to-depth ratios lead to variations in the bearing capacity reduction factors of the steel beams. The reductions in both yield and ultimate bearing capacities exhibit an approximately linear negative correlation with the corrosion rate. Furthermore, a comparison between the bending capacities of beams with random corrosion and those with uniform corrosion revealed that the uniform corrosion model significantly overestimates the bending capacity of corroded steel beams, with the overestimation becoming more pronounced as the corrosion rate increases.

To investigate the synergistic mechanism of the interface between recycled aggregate concrete （RAC） and normal concrete （NC） and promote its engineering application in composite structures, this study explores the shear resistance and failure mechanisms of the RAC-NC interface through direct shear tests and numerical simulations. Bonded RAC-NC interface specimens were designed and fabricated, and direct shear tests were conducted to analyze the interfacial shear capacity and failure modes. A numerical model was established using ABAQUS finite element software and validated against experimental results. The results indicate that the interfacial shear capacity significantly decreases with an increase in the replacement ratio of recycled coarse aggregates. When the replacement ratios of recycled coarse aggregates were 25%, 50%, 75%, and 100%, the interfacial shear capacity decreased by 9.9%, 15.0%, 20.8%, and 26.4%, respectively, compared to normal concrete. The finite element model effectively simulated the peak shear load during failure, with errors between simulated and experimental results within 10%. This study reveals key factors influencing the shear performance of the RAC-NC interface and provides a theoretical basis for the design and reinforcement of recycled concrete composite structures.

Ultra-High Performance Concrete （UHPC） is a high-performance cementitious composite material characterized by ultra-high compressive strength, superior toughness, enhanced ductility, and excellent durability. However, a systematic and standardized framework for UHPC mix design remains lacking. In both engineering applications and scientific research, mix proportioning still heavily relies on empirical approaches.To address this gap, this study compiled a comprehensive database consisting of 300 mix designs and corresponding experimental material properties from a thorough review of the existing UHPC literature. The database incorporates seven key influencing factors： cement content, fly ash content, silica fume content, quartz sand content, superplasticizer dosage, steel fiber content, and water content, along with their experimentally measured compressive strengths.Based on this dataset, several machine learning algorithms—including Random Forest （RF）, Extreme Learning Machine （ELM）, Support Vector Regression （SVR）, and Backpropagation Neural Networks （BPNN）—were employed to develop predictive models for the compressive strength of UHPC. Furthermore, a machine learning-driven mix design methodology was proposed to achieve targeted compressive strength.The results demonstrate that all adopted machine learning models can provide reasonably accurate preliminary predictions of compressive strength based on the constituent proportions, with the coefficient of determination （R²） of the training set exceeding 0.8, indicating satisfactory predictive performance. The proposed method effectively generates UHPC mix proportions that meet specified strength requirements, offering a data-driven alternative to conventional empirical design.

In order to study the safety of the precast concrete composite structure, which was suitable for the single-column double-span underground metro station, low-reversed cyclic loading tests were conducted on large-scale models of the bottom joint of outer wall which was the key part of the structure. The results showed that the failure patterns of the composite specimens were similar to that of cast-in-place （CIP） specimen, all of which were compressive bending failure at the bottom of the wall and the upper edge of the haunching, and both the composite specimens with single-skin wall and double-skin wall had good structural integrity. The P-δ hysteresis loops of the composite specimens and the CIP specimen were generally full, showing a stable hysteresis response, and the bearing capacity of all the specimens can meet the design requirements. The ductility coefficients of the two composite specimens were both 3.1, which were about 3.3% higher than that of the CIP specimen. The energy dissipation capacity and stiffness degradation of the composite specimens were similar to those of the CIP specimen in general. On the basis, the influence of different designed details on the seismic performance of the bottom joint was further analyzed through the finite element analysis. The results showed that the bearing capacities of the composite specimens were close to that of the CIP specimen when the connecting steel bars of the composite walls were designed according to the principle of equivalent bearing capacity of the bottom sections.

In the connection of prefabricated concrete structures and the reinforcement of existing structures, the shear behavior of the interface between new and old concrete directly governs structural safety and integrity. Current methods for predicting shear capacity often rely on simplified roughness classifications or single-parameter analyses, which fail to fully account for the coupled effects of multiple factors. To address this, a multi-parameter prediction model based on a BP neural network is proposed in this study, which comprehensively considers factors such as the strength of old and new concrete, surface treatment methods, roughness magnitude, normal stress, interface reinforcement ratio, and loading mode. The model was trained and validated using 270 sets of experimental data. The results demonstrate that the model exhibits high predictive accuracy and reliability, providing an effective tool for evaluating the shear capacity of concrete laminated surfaces in practical engineering applications.

As most existing coal silos adopt a joint-silo structure, the uneven distribution of coal stored in the silo during actual operation causes the foundation to withstand eccentric loading for extended periods. This leads to uneven settlement, which severely affects the overall stability of the superstructure. Based on the reinforcement scheme for the rectification project of a heavy-duty coal mixing silo, this paper analyzes the distribution of static pile loads and the characteristics of foundation settlement and deformation at various construction stages, and monitors the static pile loads and foundation settlement during the construction process. The results indicate that： （1）Stress concentration occurs in the region of maximum foundation settlement, where the static piles require greater bearing capacity during the stop-sinking phase. As the foundation gradually returns to a level position during the corrective stage, the loads on the static piles in different areas tend to become uniform; （2） The deformation curve of the coal mixing silo foundation exhibits a wave-like pattern with changes in coal storage volume： settlement increases with rising coal storage and recovers as coal storage decreases, but irreversible deformation occurs under long-term cyclic loading; （3） When excavating guide pits, care should be taken to avoid excessive stress relief in foundation areas with originally good bearing conditions, which may lead to additional settlement; （4） After the static piles are installed, they quickly assume load-bearing function. The pile load varies noticeably with changes in coal storage volume, and the fluctuation range of the foundation deformation curve is significantly reduced. The practice in this project demonstrates that the static pile replacement technique is well-suited for foundation reinforcement in heavy-duty coal silos. It can promptly provide bearing capacity, rapidly enhance the foundation's load-bearing capability, and meet the design requirements for settlement control.

In order to achieve the strategic goal of manufacturing power in our country and the urgent need of developing new industrial clusters in big cities, the original urban incremental development model is difficult to continue. Because of the serious shortage of new industrial land, the“industry upstairs” mode has emerged and become the preferred mode of high-quality industrial development in big cities in recent years. In view of the higher design requirements of “industry upstairs” compared with conventional industrial buildings, this paper takes a high-rise “industry upstairs” project in Shenzhen as an example, under the condition that the other basic design parameters are consistent, to analyse the differences of structural calculation indexes between concrete and steel structure systems. In addition, the influences of design parameters including industrial load, column span and story height on the overall material consumption are investigated. Meanwhile,considering the construction period difference, the cost of different structural systems is compared, which can provide reference for similar “industrial upstairs” projects.

Precast concrete small box girders are extensively adopted in China owing to their lightweight, high construction efficiency, and cost-effectiveness. However, strength variations between wet joints and box girder concrete may trigger differential shrinkage and creep during construction, potentially causing early cracking. Consequently, selecting appropriate materials for repair and pre-maintenance is paramount. This study investigates the mechanical properties of three cementitious crystalline waterproofing materials （Oriental Yuhong PCC-501, Kaiton T1, and Cybers Concentrate）, one interface agent （Huanyu Xiupu-SP）, and two high-strength mortars （Huanyu Xiupu SJ40F and Sikadur 31CFN）. All experiments were conducted in strict compliance with relevant standards, encompassing tests for wet surface bonding strength, compressive strength, and flexural strength. Furthermore, twelve brushing schemes with varying application sequences were designed for bridge implementation, with the optimal construction order determined through field analysis. The results demonstrate that among the cementitious materials, Oriental Yuhong exhibits the highest wet substrate bonding strength, while Kaiton achieves superior impermeability. The interface agent attains a 14-day tensile bond strength exceeding the minimum standard requirement. Among high-strength mortar materials, Sikadur 31CFN demonstrates optimal performance in flexural, compressive, and tensile strength. The optimal brushing sequence entails the sequential application of cementitious crystalline waterproofing materials, interface agents, and high-strength mortars. However, further research is necessary to identify the most effective material combinations.

The leakage issue at assembly joints of prefabricated pipe galleries poses a serious threat to their safety and stability, making efficient and accurate leakage detection a pressing need. This paper proposes a leakage location detection method for assembly splicing nodes in prefabricated pipe galleries based on cyclic frequency characteristics. First, ultrasonic technology is employed to collect pulse reflection signals from the nodes and determine their positions. Second, the cyclic spectral density of the node pulse reflection signal is established, from which the cyclic frequency characteristics are extracted. The principal component analysis method is introduced to reduce the dimensionality of the features, thereby improving feature accuracy. Finally, the quantum swordfish algorithm is used to optimize the LSTM network, and the reduced cyclic frequency characteristics are input into the optimized network to achieve leakage location detection at the assembly joints of the prefabricated pipe gallery. Experimental results demonstrate that the proposed method achieves high accuracy in feature extraction, leakage detection, and node localization.

To assess stirrup stress in reinforced concrete beams under concentrated loads, ATENA software was employed to perform nonlinear finite element analysis of shear behavior in test beams. This study compiled shear test data from 158 reinforced concrete beams with stirrups subjected to concentrated loads （shear-span ratio ≥2.5）. Using a validated finite element model, we calculated the stress in stirrups intersected by the critical diagonal crack at the ultimate limit state of bearing capacity. Results demonstrate that the 45° truss model substantially underestimates stirrup shear resistance in ultimate limit state conditions. We recommend revising GB/T 50010—2010 （Code for Design of Concrete Structures） to adopt a stirrup effectiveness coefficient of 1.25 in the shear capacity design formula for reinforced concrete beams, along with corresponding adjustments to the concrete contribution term.

To investigate the influence of various types of cavities—including single and multiple cavities in strata—on ground surface settlement induced by tunnel construction, a specific section of Nanchang Metro Line 3 was selected as the research object. Using ABAQUS software, a three-dimensional numerical model incorporating cavity defects was established by simulating cavities through the “element kill” technique at corresponding positions. The simulation results indicate that the presence of cavities alters the deformation pattern of the stratum, leading to corresponding shifts in the ground surface settlement trough as the cavity location changes. In the case of a single cavity, the increase in ground surface settlement is significantly influenced by the net distance between the cavity and the tunnel, as well as the size and position of the cavity. When the cavity diameter exceeds 2 m or the net distance is less than 3 m, the maximum ground surface settlement increases by approximately 1.3 and 1.5 times, respectively. If the cavity is situated outside the tunnel arch bottom or arch shoulder, the maximum settlement rises by 0.63 and 1.42 times, respectively. The shape of the cavity has a relatively minor effect on settlement, with the maximum increase ranging between 0.55 and 0.95 times. For multiple cavities, ground surface settlement increases notably in strata with double or triple cavities, and the influence zone broadens, mainly extending from 5 m to 15 m from the tunnel centerline. These findings provide a useful reference for tunneling in complex cavity-containing strata.

In response to the high requirements for frame column connection joints in prefabricated steel structure substations located in high-seismic-intensity areas, this paper designs a new type of fully bolted column-column splicing joint using angle steel as the splicing component. Low-cycle cyclic loading tests were conducted on two column-column joint specimens with different splicing lengths under combined compression-bending-shear conditions, and the load-deformation hysteretic curves of the joints were obtained. Subsequently, the skeleton curves were extracted and compared with the completed monotonic loading test curves, revealing the strength degradation phenomenon of the joints under cyclic loading. Finite element analysis software was used to perform numerical simulation of the cyclic loading tests. The numerical analysis results were compared with the experimental results to verify the accuracy of the numerical model. Finally, the displacement ductility coefficient and equivalent viscous damping coefficient were adopted to evaluate the hysteretic performance of the joints. The results show that compared with the previous monotonic loading test results, the ductility of the joints decreases under cyclic loading （Specimen J-6-22 decreases by 32%, Specimen J-6-13 decreases by 16%）, while the reduction in bearing capacity is small （Specimen J-6-22 decreases by 7%, Specimen J-6-13 decreases by 4%）, and the joints still maintain good bearing capacity.

To address the need for lightweight tuned seismic retrofitting of existing reinforced concrete （RC） frame structures, this study proposes a performance-based seismic retrofitting design method utilizing a series-parallel-Ⅱ inerter system. A dynamic model of an RC frame structure equipped with the series-parallel-Ⅱ inerter system is established. By defining dimensionless parameters including the inertance ratio, damping ratio, and stiffness ratio, the structural displacement transfer function is derived. Based on the principle that the transfer function reaches local peaks at fixed points, optimal design formulas for the inerter system parameters are deduced. A performance-based retrofitting design framework for existing RC frame structures is subsequently proposed. Taking a five-story school building in Shanghai as an engineering example, the retrofitted structure exhibits only a 1% shift in its fundamental natural period, indicating that the tuned design of the inerter system preserves the original dynamic characteristics. Elastoplastic time-history analysis shows that the maximum inter-story drift ratios of the structure in the X- and Y-directions under rare earthquakes were reduced from 1/111 and 1/130 to 1/303 and 1/280, respectively, corresponding to reductions exceeding 57%. These results satisfy the performance objective of minor damage under rare earthquakes, validating the effectiveness of the proposed method in enhancing seismic performance while maintaining the inherent dynamic properties of existing structures.

Considering the poor ductility of steel frame joints with concrete floors and the susceptibility to weld damage at the beam lower flanges, this paper proposes a new type of composite joint. The joint employs a mono-symmetrical steel beam section that weakens only the lower flanges by increasing their width while reducing the width of the upper flanges. This design mitigates the upward shift of the neutral axis of the composite beam section induced by the concrete floor, thereby reducing the risk of brittle fracture in the welds of the lower flanges. Using the finite element software ABAQUS, the effects of several parameters on the hysteretic behavior of the composite joint were investigated, including the distance from the weakening start point of the lower flange to the beam-column interface, the weakening length, and the weakening depth. By comparing hysteresis curves, skeleton curves, stiffness and strength degradation curves, and energy dissipation capacity, recommended value ranges for the weakening start distance, weakening length, and weakening depth are provided.

Under the long-term combined effects of load and environmental exposure, steel structures are susceptible to corrosion, leading to a reduction in load-bearing capacity and compromising structural safety. For the domestically produced Q355 H-beam, bending tests were conducted on corroded specimens. Combined with changes in the geometric characteristics of the corroded cross-sections obtained via structured light scanning, the degradation law of the bending performance of the corroded H-beam was revealed. The characteristic load values of the steel beams exhibited a linear relationship with either the average or maximum degree of cross-sectional corrosion. The corrosion extent of the flanges and web changed synchronously with the overall cross-sectional corrosion degree. Accordingly, a simplified method for calculating the geometric characteristics of corroded steel beams was proposed. Predictions of the yield load and ultimate load based on the actual cross-sectional shape, the uniform corrosion cross-section, and the flange contribution method were compared. The average prediction error for the yield load using the three methods remained within 5%. The simplified approach considering only the flange area for calculating the flexural capacity showed good agreement with the experimental results.