Abstract:Aiming at the phenomenon of local circumferential corrosion of concrete-filled steel tubular columns caused by splash zone in the marine environment， this paper uses the mechanical reduction method to simulate the local circumferential corrosion of steel tube wall thickness and carries out seven eccentric compression tests of concrete-filled square steel tubular columns， reveals the influence of corrosion rate and eccentricity on its eccentric compression bearing capacity， and expands the analysis of corrosion rate through numerical simulation. Finally， the reduction coefficient of eccentric compression bearing capacity based on the weakening rate is proposed， which is brought into the Chinese and American codes to calculate the eccentric compression bearing capacity. The results show that the local circumferential variable thickness of steel tubes seriously weakens the eccentric bearing capacity and lateral deflection capacity of concrete-filled square steel tubular columns. The larger loading eccentricity also reduces its eccentric bearing capacity but increases its lateral deflection capacity. After introducing the reduction factor of eccentric compression bearing capacity， the eccentric compression bearing capacity calculated according to China and the US codes is in good agreement with the experimental values. Compared with the Chinese code， the calculated method in American code is more conservative in calculating eccentric bearing capacity.

Abstract:To explore the axial compressive stress-strain relationship of Ultra-High Performance Seawater Sea-sand Concrete （UHPSSC） and study the influence of steel fiber volume content on the axial compressive mechanical properties and axial compressive complete stress-strain curve of UHPSSC， the complete stress-strain curve of UHPSSC was obtained through the compression tests with the Instron 1346 universal material ， and the Pycharm curve fitting program was used to fit and modify the existing concrete complete stress-strain curve model. The results show that the higher the steel fiber content， the smaller the damage degree of UHPSSC under axial compression， and the compressive strength and peak strain also increase. The rising section of the UHPSSC stress-strain curve fitted by the existing model is similar to the test curve， and the gap between the falling section and the later stage is large. By modifying the shape parameters of the descending section， a modified model more suitable for describing the complete stress-strain curve of UHPSSC was obtained， and the applicable scope of the modified model was verified.

Abstract:Axial compression tests of 17 CFRP-PE-stainless steel-reinforced concrete （CPSSRC） short columns and 8 counterparts were carried out to investigate the influences of the stainless steel type， hoop spacing， CFRP thickness， and PE thickness on the failure mode， load versus strain curve， ultimate strain， ultimate strength and ductility of the CPSSRC short column. The experimental results showed that the PE cushion between CFRP and concrete improved the ductility of the CPSSRC column and reduced its ultimate strength. Increasing the CFRP thickness improved the ultimate strength and ultimate strain of the CPSSRC short column， but increased the brittleness. Reducing hoop spacing or increasing steel strength improved the ultimate strength， peak strain， and ductility of the column. A finite element （FE） model was established. The FE analysis showed that increasing the thickness-to-diameter ratio of the PE cushion significantly improved the deformation capacity and ductility of the CPSSRC short column and reduced the effect of CFRP on its ultimate strength. Increasing the hoop ratio， stainless steel strength， CFRP tensile strength， and CFRP thickness improved the ultimate strain and ultimate strength of the CPSSRC short column. Increasing the concrete strength improved the ultimate strength of the CPSSRC short column but reduced its ultimate strain. Finally， a ductile design method， ultimate strength model， and ultimate strain model for the CPSSRC short column were proposed.

Abstract:This study examines the transverse bridge stresses of the link slab for the disaster such as the structural crack in the simply-supported steel-concrete composite bridge. The link slab's deflection and stress distribution functions are determined using linear elastic theory and the partial differential equation of the plate. A nonlinear finite element model is also established based on actual bridge load testing. The theoretical solution， finite element solution， and real bridge load test results are compared to validate the theoretical solution and finite element. The study shows that the upper face of the link slab at the end of the steel girder experiences the maximum tensile stress in the direction of the transverse and longitudinal bridge. The paper also explores the impact of the link slab area size on the peak stress in the transversal bridge direction. Results reveal that smaller longitudinal beam spacing and longer longitudinal beam end length increase the maximum transversal tensile stress of the link slab， causing the link slab to develop cracks before reaching the design load. Therefore， for a jointless bridge with a small longitudinal girder spacing and a long girder end length， only calculating the mechanical performance in the longitudinal bridge direction yields dangerous calculation results. It is advisable to consider the transverse bridge direction stress according to the method in this paper.

Abstract:Passive battered piles are mostly applied in the supporting engineering of the excavation foundation pit but are rarely used in the anti-skid engineering of filling bodies ， and the engineering character is not yet clear. To analyze the mechanical deformation characteristics of passive battered piles under lateral surcharge， based on the strain wedge model （SW model） and combined with the Boussinesq solution， this paper establishes the deflection differential equation of passive battered piles under lateral surcharge， derives the finite difference solution of the corresponding internal force and lateral displacement of the piles， and then verifies the effectiveness of this method by comparing the results of field tests and indoor model tests. The results show that under the same surcharge， the top lateral displacement and the bending moment of the straight pile are the largest， followed by the positive battered pile， and the negative battered pile is the smallest. The top lateral displacement and the bending moment of the positive and negative battered pile decrease with the inclination angle increase. Under lateral surcharge， the battered pile undergoes “translating and rotating”. Within the range of conventional pile body inclination angle （≤20°）， the pile at the foot of the slope set as a negatively battered pile with a larger inclination angle towards the center of the pile load can achieve a better engineering effect.

Abstract:To study the dynamic response law of large diameter variable cross-section single pile in liquefaction sites under different ground motion intensities， shaking table tests were conducted. Employing the 5010 wave and subjecting the system to ground motion strengths ranging from 0.10g to 0.45g， this study examined the evolution of sand pore pressure ratio， horizontal displacement at the top of the piles， bending moment along the pile body， as well as the time history response of pile acceleration and foundation damage. The test results show that the pore pressure ratio of saturated sand increases obviously with the increase of ground motion strength. The pore pressure ratio of saturated sand increases obviously with the increase of ground motion intensity. When the ground motion intensity is ≥0.30g， the stable value of the pore pressure ratio of saturated sand is near 0.9， and the sand is completely liquefied. Under the action of 0.45g ground motion， the acceleration of pile body， the horizontal displacement of pile top and the bending moment of pile body all reach the maximum. The peak acceleration at different positions along the pile body lags behind that of the input seismic wave， and the acceleration response of the pile top and variable cross-section is weaker than that of the pile tip. The maximum bending moment of the pile appears at the boundary between the liquefied soil layer and the non-liquefied soil layer， and the bending moment at variable cross-section is smaller than that at the soil layer interface. When the ground motion strength reaches 0.30g， the damage of a large diameter variable cross-section single pile occurs. Therefore， in the seismic design of the single pile foundation of a large diameter variable cross-section bridge under a liquefaction site， the bending capacity at the boundary of the saturated sand layer and variable section should be considered to ensure that the strength of the single pile meets the anti-seismic requirements.

Abstract:Tunnel excavation can easily cause settlement and deformation of the surface of the overlying surface， which will further cause the stress and deformation response of the existing pipeline. Based on this， a simplified method for calculating the deformation of the overlying pipeline due to shield excavation is proposed. Firstly， the Loganathan formula is selected to solve the additional stress along the pipeline induced by tunneling underlying， and the pipeline is further simplified into an infinitely long beam resting on the Pasternak foundation. The influence of the lateral displacement of the infinite distal soil on the existing pipeline is introduced. Then， the mechanical equilibrium method is used to obtain the control equation of the vertical force and deformation of the pipeline. The finite difference method is selected to obtain the numerical analytical solution of the pipeline deformation and internal force analysis. The case analysis shows that， compared with the degradation analysis of this method， the calculation results are closer to the measured data of an actual project in the existing literature， which verifies the reliability of this method. Further parameter studies show that increasing the vertical clearance between the tunnel and the pipeline causes a nonlinear reduction in the stress and deformation of the pipeline. Increasing the volume loss rate results in a linear increase in the deformation and inner force of the pipeline. Increasing the pipeline bending stiffness reduces the pipeline deformation but greatly increases the pipeline bending moment.

Abstract:To reveal the deformation and failure characteristics of the metro shield tunnel overpassing buried fault， a self-designed loading test device for faulting simulation was used to carry out a 1∶ 25 geometric scale cross-fault shield tunnel model test. The mechanical response law and deformation failure characteristics of the shield tunnel under normal faulting were analyzed. The test results show that under 2 cm normal faulting， the longitudinal differential deformation of the tunnel shows a nonlinear increasing trend. The opening of the circumferential joint is mainly located at the vault of the footwall tunnel. The arch bottom of the hanging wall tunnel and the peak opening of the circumferential joints have exceeded the waterproof limit of the joints. The diameter convergence deformation of the segment lining at the junction of the fault extension line and the tunnel occurs severely. The stress state of the outer side of the arch waist of the tunnel lining is tensioned， while the outer side of the vault and the arch waist are compressed. The contact pressure between the tunnel and the stratum is greatly affected by the faulting， and there are surrounding rock compression and loosening zones. However， the peak value of contact pressure is relatively limited. Tensile fracture of the circumferential joint， longitudinal cracking of the segment， and joint deformation are the main deformation and failure characteristics of the shield tunnel. The probability of oblique shear failure and local crushing failure is low. Based on the longitudinal deformation and failure characteristics of shield tunnels， the joints deformation and the tensile fracture of the circumferential joint should be taken as the main control indexes to define the structural failure of cross-fault shield tunnels. Based on the deformation and failure characteristics of segmental lining， suggestions on structural design and countermeasures of cross-fault shield tunnel are proposed.

Abstract:Due to the complexity of seismic coupling between vehicles and highway bridges， current research on the mechanism of vehicle-bridge interaction under seismic action is relatively scarce， leading to diverse specifications about whether live load should be taken into account in national seismic bridge design codes. Existing studies have shown that vehicles possibly would produce beneficial effect on bridge seismic responses in one circumstance but adverse effects in another. The simulation of contact behaviors between vehicle and bridge is simplified in this study. On this basis， the mechanism of vehicle-bridge interaction is analyzed thoroughly by employing the energy method. Analysis results demonstrate that the impact of vehicle-bridge interaction on horizontal energy input to the bridge is negligible.However the interaction can reduce the total energy input to the bridge in the vertical direction， therefore reducing the vertical seismic responses of the bridge， while input energy to the vehicle’s vertical direction comes mainly from the bridge’s vibration. On the other hand， the smaller the vehicle mass， the greater the horizontal input energy to the vehicle caused by bridge vibration.

Abstract:Health monitoring plays an important role in guaranteeing the structural safety of a cable-stayed bridge throughout its life. However， the use of sensor data for health monitoring of cable-stayed bridges has some limitations. Combining the Benchmark model to monitor bridge structures can compare and evaluate different health monitoring methods criteria in a given state， which is valuable for bridge design， operation and management. This paper proposes a modified Benchmark model for health monitoring technology of cable-stayed bridges. Firstly， a simplified finite element model of the spine-beam model is established using Matlab software to conduct the dynamic analysis and model modification of the structure. In addition， a detailed finite element model is established as a simplified supplementary model and modal correction model. Then， an orthogonal test design is used to perform a significance analysis on the dynamic characteristic parameters of the cable-stayed bridge for the parameters to be modified in the modeling process， and the sensitive parameters are clarified. Finally， the model parameters are modified based on the genetic algorithm， and the dynamic adaptive technique and the method of parallel selection are proposed to optimize the structure of the genetic algorithm， which interferes with the genetic selection process and gives higher dispersion to the initial population. Compared with the GA function， the method with the improved genetic algorithm has higher computational efficiency and smaller error for model parameters.

Abstract:Through the wind tunnel test by section models with a scale ratio of 1/6 for the 1V and 2V flat single-axis tracking photovoltaic， the influences of inclination angles （-60° to 60°）， damping level， and gap between photovoltaic modules on the wind vibration characteristics of the structure are investigated. Results indicate that 1V exhibits obvious torsional flutter at inclination angles from -30° to 30°， while 2V exhibits such flutter at ±10°， ±20°， and ±30°； when the absolute value of inclination angles is increased for the two types of photovoltaic， the critical dimensionless wind speed of structural flutter first decreases and then increases； the maximum difference exceeds 3.87 times （1V） and 2.45 times （2V）， and under identical operating conditions， the negative inclination angles perform better than the positive inclination angles on the flutter； it is recommended to set 0° as the wind protection angle of the structure； when the damping ratio is increased， both 1V and 2V's flutter performance improve， although 1V's improvement in flutter performance is less sensitive to damping than 2V's. The gaps between photovoltaic modules have virtually no effect on the flutter performance of the structure.

Abstract:The π-shaped section is widely used in bridge construction because of its simple structure and good mechanical performance， but it is easy to generate vortex-induced vibration（VIV） because of its poor wind resistance. Therefore， in this paper， a bridge with π-shaped section with a side box type is taken as the research object， and the same step vibration and pressure measurement test is carried out by using a π-shaped section rigid section model with an aspect ratio of 10∶1. Moreover， the vorticity vibration performance of π-shaped section and the vibration suppression mechanism of the deflator are studied by comparing and verifying the method of computational fluid dynamics. The experimental results show that significant VIV occurs at wind attack angles of 0° and ±3°. The vertical bending and torsional VIV can be suppressed by adding a guide plate with specific form and size parameters on both sides of the section. Among them， the inverted L-shaped baffle has a significant aerodynamic optimization effect， which can effectively eliminate the VIV amplitude， while the horizontal baffle has a limited vibration suppression effect. Compared with the vertical curved VIV， the torsional VIV is more sensitive to the size of the horizontal baffle. By comparing the numerical simulation results with the surface aerodynamic pressure distribution， the inverted L-shaped baffle can optimize the aerodynamic profile of the section， weaken the scale and energy of vortex loss on the upper and lower surfaces of the section， and reduce the periodic aerodynamic force on the section， thus effectively suppressing the VIV of the section.

Abstract:Wind tunnel testing is employed to study the wind pressure distribution and wind load on low-elevation enclosed skybridges. The characteristics of shape coefficients and non-Gaussian distributions on the four surfaces of the skybridges are analyzed. The overall shape coefficients of the skybridges concerning wind azimuths and skybridge length are investigated. Then， the windward overall shape coefficients and skewed wind loading distribution factors of low-elevation enclosed skybridges are provided. The peak wind pressure coefficients under all azimuths based on extreme value analysis are given. Finally， recommended values for the wind-resistant design of skybridges are suggested. Results show that the shape coefficients in the leeward side of a low-elevation enclosed skybridge range from -1.04 to -0.86， which are much larger than -0.6 in magnitude specified for the square tall building in the load code. As a result， the overall shape coefficient of the enclosed skybridge is 1.61， which is larger than the 1.4 specified for the square-high building in the load code. In the windward direction， the overall shape coefficient in the middle section is larger than that in the other section. The overall shape coefficient in the windward direction is larger than that in the other azimuths. The longer the skybridge length， the larger the overall shape coefficient. In the windward direction， the pressures on the windward surface present a Gaussian distribution， whereas those on the other three surfaces present a non-Gaussian distribution. The windward overall shape coefficients and skewed wind loading distribution factor are used as references for the main load-resistant design of the enclosed skybridges.

Abstract:Compared with the traditional streamlined box girder， the typical Π-shaped open section is prone to vortex-induced vibration （VIV） because of its high section bluff configuration. In this research， the simultaneous vibration and pressure vibration of wind tunnel tests and computational fluid dynamics （CFD） are used for studying the characteristics of the pressure distribution along the surface of the typical open section and the nonlinear phenomena such as different aerodynamic components and hysteresis characteristics. First， the initial characteristics of the local pressure in different periods in the VIV lock-on region are analyzed. Secondly， the CFD dynamic grid method is used to realize the fluid-solid coupling analysis of the section. On this basis， the different frequency components of the aerodynamic forces in the VIV process are decomposed by the Hilbert vibration decomposition （HVD） method. The research results show that the average surface pressure on the leading edge of the opening section is in the negative pressure zone， where the airflow is separated. At the extreme point of the VIV， the pulsating pressure changes most violently in the area of 0.1

Abstract:To solve the optimization problem of control algorithm parameters， damper parameters， and layout location in the semi-active control systems with magnetorheological （MR） dampers， an improved adaptive niche genetic algorithm is proposed. The proposed genetic algorithm is improved in selection strategy， crossover and mutation operation， and adaptive adjustment of crossover probability and mutation probability. Two different niche technologies， the pre-selection mechanism and sharing mechanism， are used in the improved genetic algorithm. The results of a numerical example show that the optimization result of the improved adaptive niche genetic algorithm （GA-Ⅰ） and an improved simple genetic algorithm （GA-Ⅱ） is generally consistent， indicating the correctness of the former algorithm. Moreover， the GA-Ⅰ consumes an average of 32.7% less computation time to obtain the optimal solution for the first time than the GA-Ⅱ， which means that the former algorithm converges faster than the latter. In addition， optimization results of 30 times indicate that the GA-Ⅰ has stronger stability than the GA-Ⅱ. The semi-active control system with MR dampers optimized by the GA-Ⅰ achieves effective vibration suppression. The maximum values of inter-story drift angles and floor absolute accelerations of the semi-actively controlled structure under El Centro， Chi-Chi and man-made waves are decreased by 64.1%， 54.7%， and 55.9% on average compared to those without control， respectively. The numerical example demonstrates the effectiveness of the GA?Ⅰ， and the integrated optimization of the semi-active control system with MR dampers is realized.

Abstract:To address the vibration problem of the airport ground transportation center （GTC） induced by low-to-medium speed maglev train， a coupled vibration model of maglev train-guideway girder and a finite element model of guideway girder-GTC-soil are established， and then the two-step method is used to analyze the response characteristics， propagation laws， and vibration levels of the vibration problem. The maglev train is modeled using multi-body dynamics， and the guideway girder is modeled using finite element method. The coupled vibration model is formed by linear magnet-rail relationship between the two components， and the correctness of the model is verified by field measurement results. Based on the established coupled vibration model， the time history curves of the fastener force between the H-shaped rail sleeper and the rail support platform are obtained. The fastener force is applied to the guideway girder-GTC-soil model， and the dynamic response of typical observation points of GTC is obtained by transient analysis. The results show that when the vibration induced by maglev train propagates along the height direction， the vibration responses of structural columns and floors decrease first and then increase with the increase of height. When the vibration propagates along the horizontal direction， the vibration response decreases rapidly with the increase of distance. There is an obvious frequency doubling phenomenon in the vibration response of GTC， that is， there is an obvious peak value in the power spectral density curve of the vibration response at the frequency doubling of the main frequency of the fastener force. When the vehicle speed is 60 km/h， the main frequency of the vehicle excitation is close to the first-order vertical natural frequency of the guideway girder. At this time， the maximum vibration level of the 1/3 octave of the observation point is greater than other vehicle speeds. When the maglev train passes through the GTC at 60~120 km/h， the maximum Z vibration level of each floor does not exceed the standard limit， indicating that the airport GTC has good overall stiffness.

Abstract:The strain rate effect of timber should be taken into account in the detailed analysis of timber structure during earthquakes. In order to investigate the impact of seismic strain rate on the mechanical properties of timber under uniaxial compression， two types of timber， Larix and Pinus Sylvestris， were selected， and perpendicular-to-grain and parallel-to-grain specimens were designed for each type. The stress-strain relationship， failure mode， elastic modulus， and compressive strength of the timber were investigated through uniaxial compression tests under seismic strain rates of 10-3 s-1， 10-2 s-1， 10-1 s-1， as well as a quasi-static strain rate of 10-4 s-1. The results indicated a noticeable seismic strain rate effect on the compressive strength and elastic modulus of timber under uniaxial compression. As the seismic strain rate increased， the compressive strength of timber exhibited a more significant increase. The uniaxial compression constitutive model was established， taking into account the seismic strain rate effect. Additionally， a corresponding UMAT subroutine was programmed and integrated into the ABAQUS finite element software. The numerical simulation of timber under uniaxial compression was performed. The results exhibited a strong agreement with the experimental findings， thereby validating the accuracy of both the constitutive model and UMAT subroutine. The research findings can offer constitutive support for seismic analysis of timber structures.

Abstract:Because of the characteristics of an ultra-long isolated structure in cold regions， such as long construction period， complex plane shape， large structure span， significant seasonal temperature difference， and multi-stage construction， a calculation method for the thermal shrinkage deformation of the isolation layer during the whole construction process of the ultra-long isolated structure is established. Combined with the site construction progress， scheme， and sequence， the construction process is simulated in detail using finite element software， and the size and evolution law of the thermal shrinkage deformation of the isolation layer during the construction process of the structure are analyzed. The simulated results are compared with the field measurement results. Finally， the influence rules of structure construction in stages， construction path， and post-pouring belt setting mode on the thermal shrinkage deformation of the isolation layer are discussed. The analysis results show that the simulation results of the thermal shrinkage deformation during the construction process agree well with the measured results. The thermal shrinkage deformation of the isolation layer generally changes periodically with the progress of construction and has the change in ambient temperature. When the ultravery-long isolation structure is constructed in multi-stage， there is mutual restraint between the structures in each stage， and the final thermal shrinkage deformation of the structure is due to the coordinated deformation of the structure in each stage. Reasonable construction path and structural unit division can effectively reduce the thermal shrinkage deformation of the isolation layer. Compared with the case without the post-pouring belt， the maximum thermal shrinkage deformation of the isolation layer only decreased by 6.3% when the reinforcement was connected at the post-pouring belt， while the maximum thermal shrinkage deformation of the isolation layer decreased by 36.3% when the steel reinforcements were fully overlapped at the post-pouring belt.

Abstract:To study the influence of water-to-binder ratio， rice husk ash， and cellulose fiber on the durability performance of concrete， nine orthogonal tests were conducted with three variables： rice husk ash content （0， 10%， and 20%）， cellulose fiber content （0.7 kg/m3， 1.1 kg/m3 and 1.6 kg/m3）， and water-to-binder ratio （0.37， 0.41 and 0.45）. The impact of these factors on chloride ion penetration resistance and freeze-thaw resistance of concrete was analyzed， and prediction models for mass loss rate and relative dynamic elastic modulus of rice husk ash and fiber concrete during freezing and thawing were established， separately. The results show that the degree of impact of each factor on chloride ion penetration resistance and freeze-thaw resistance of concrete is as follows in descending order： water-to-binder ratio > rice husk ash content > cellulose fiber content. The chloride ion penetration resistance and freeze-thaw resistance of concrete are significantly enhanced with increasing rice husk ash content， while it shows a trend of first enhancing and then weakening with increasing cellulose fiber content. The optimum performance is achieved at a water-to-binder ratio of 0.37. When the rice husk ash content is 20%， the concrete has the best chloride ion penetration resistance and the optimal freeze-thaw resistance. When the cellulose fiber content is 1.1 kg/m3， the concrete exhibits the best chloride ion penetration resistance and the strongest freeze-thaw resistance. Increasing the dosage of rice husk ash，and adding a suitable amount of cellulose fibers can improve the density of the concrete matrix， reduce microcracks， and enhance the durability performance of the concrete. The prediction model for the mass loss rate and relative dynamic modulus of elasticity of rice husk ash fiber concrete established is in good agreement with experimental results， and has a certain applicability. This can provide a theoretical basis and support for the preparation of green high-performance concrete.

Abstract:Ventilated mattresses are designed to remove polluted air from the bedroom microenvironment by using a ventilation port located near the feet， thereby achieving pollution control at the source. However， experimental research has found a risk of local discomfort due to cold drafts caused by its use. Therefore， this study explores the automatic control potential of the ventilated mattress coupled with a local heating device based on local skin temperature， which can meet different thermal microenvironment needs of users by adjusting the mattress and local heating device in real-time according to users’ feedback. A comparison was made between the skin temperature and thermal acceptability of ten body parts of 30 awake subjects lying on the ventilated mattress， including the forehead， right scapula， upper left chest， upper right arm， lower left arm， left hand， front right thigh， lower left leg， right instep， and left instep. The acceptability of the whole body， face， forehead， neck， chest， back， arm， hand， thigh， leg， and foot were also recorded. The results showed that local female skin temperature was generally lower than male， while their acceptability was higher. The Gaussian regression model can calculate optimal skin temperature range for each part. Combined with the thermal acceptability correlation matrix results of each part and the control potential of the ventilated mattress and local heating device， the skin temperatures of the foot， hand， and back were finally selected to realize personalized automatic control of the bedroom microenvironment. This study provides new ideas and suggestions for exploring the automatic control potential of the ventilated mattress based on local skin temperature and could provide a reference for the optimization and improvement of the bed microenvironment.