Abstract:Aiming at the problem that hot-casting sockets are easy to fail at elevated temperatures due to the low melt point of Zn-Cu alloy （approximately 460 ℃±10 ℃）， high-temperature tensile tests were carried out on the hot-cast anchor sockets of prestressing twisted wire strands to obtain the failure modes and tensile capacity of specimens at elevated temperatures. The ultimate tensile capacity calculation formulas of the hot-cast anchor sockets of twisted wire strands and critical temperature under various load ratios were proposed， which can be used for the fire resistance capacity verification and fire protection layer thickness design of the hot-cast anchor sockets. Test results show that the failure mode is the rupture of the strand when the temperature is lower than 200 ℃， while the failure mode is the pull-out of the strand from the socket when the temperature is greater than 200 ℃. When the temperature is in 150~440 ℃ range， the load capacity of the anchorage decreases as the temperature increases. The load capacity at the anchorage temperature of 287 ℃， 340 ℃， 392 ℃ and 425 ℃ is 77.3%， 39%， 35.2% and 10.5% of that at ambient temperature， respectively.

Abstract:Taking Yanji Yangtze River Bridge （YJB） as the engineering background， firstly， the seismic performance of YJB is analyzed using the dynamic nonlinear time history method. Moreover， the effects of installing the eddy current-friction combined damper （EC-FCD） and viscous damper （VD） on the seismic performance of the long-span suspension bridge are studied. Furthermore， the parameter sensitivity analysis of the friction force， damping coefficient and damping index of the EC-FCD is carried out， respectively. Finally， from the perspective of energy dissipation， the characteristics of the EC-FCD on the large-span suspension bridge under earthquake are analyzed. The results show that under the E2 earthquakes， the resistance bending moment of key sections of the pylons is greater than the demand bending moment， and the longitudinal displacement of the stiffened girder end is relatively large under the longitudinal and vertical earthquakes. The longitudinal displacement of the stiffened girder end can be effectively reduced by installing longitudinal dampers at the interaction of pylon and girder. Moreover， increasing friction and damping coefficient， as well as decreasing damping index can improve the control effect of longitudinal displacement at the stiffened girder end. However， changing these parameters has little effect on the seismic response of the key sections of the pylons. When the damping coefficient is large， eddy current damping dominates the energy dissipation of the EC-FCD. Compared with the VD， the EC-FCD has a better control effect on the longitudinal displacements of the stiffened girder ends.

Abstract:To study the bending hysteresis performance of aluminum alloy gusset joints and compare them with static performance， four full-scale specimens were tested and subjected to hysteresis and monotonic loading， and the entire experimental loading process was numerically simulated using the general finite element software package ABAQUS. The failure mode， bending moment-rotation angle relationship， and energy dissipation capacity of aluminum alloy gusset joints were studied. Adopting the symmetrical loading method， the joint area is a pure bending segment. The research results indicate that the aluminum alloy gusset joint is a typical semi-rigid joint， and its destructive process can be divided into elastic stage， bolt slip stage， bolt and screw hole extrusion stage， and failure stage. The relationship curve of bending moment and rotation angle is obtained. The failure mode of the joint is the fracture of the member end section， and the crack begins to expand from the outermost row of screw holes at the end of the member. The joint has no obvious warning before failure and it’s a typical brittle failure， with no decreasing load. The skeleton curve of joint is similar to the monotonic loading curve， but due to the accumulated damage of the joint during the hysteresis loading process， the ductility is lower than that of monotonic loading. Increasing the number of bolts can improve the energy consumption performance of the joint and make the hysteresis loop fuller.

Abstract:The force balance wind tunnel testing method was employed to obtain the shape coefficients of lattice tubular towers in the subcritical regime. Then， the variation characteristic of the shape coefficients of the tower versus the solidity ratio is analyzed. The Reynolds number reduction coefficient of the lattice tubular tower from the subcritical regime to the supercritical regime is fitted based on the data of the codes. Finally， the shape coefficients of the lattice tubular tower obtained from the wind tunnel tests are compared with those regulated in the codes. Experimental results show that the shape coefficient of the cross-arm is larger than that of the tower body under the same solidity ratio， because the rod of cross-arm has a higher slenderness ratio and the equivalent spacing between front and back surfaces is larger. In the subcritical regime， the shape coefficient of the tower body is close to that specified in the JEC-TR-00007—2015、DL/T 5551—2018 、GB 50009—2012 codes， whereas the shape coefficient of the cross-arm is larger than that specified in the codes. The shape coefficients of the lattice tubular tower regulated in various countries’ codes decrease with the increase of the solidity ratio in the subcritical and supercritical regimes. Then， the reduction coefficient of Reynolds number is obtained as 0.63+0.72 ? using the least square fitting method. In the supercritical regime， the shape coefficients of the tower body are close to that specified in the DL/T 5551—2018 and GB 50009—2012 codes， and the shape coefficients of the cross-arm are close to that specified in the IEC 60826—2017 and ASCE MOP 74—2020 codes.

Abstract:Structural health monitoring is an effective means to ensure the safe operation and maintenance of bridges and optimize the life cycle cost of bridges. Persistent Scatterer Interferometric Synthetic Aperture Radar （PS-InSAR） technology based on spaceborne synthetic aperture radar can realize long-term structural health monitoring of bridges with low cost， light weight and sustainability. In this paper， a high-speed railway steel arch bridge in China is taken as the research object， and 59 C-band Sentinel-1 radar satellite images from 2017 to 2018 are selected. The PS-InSAR technology is used to process the images to obtain the line of sight （LOS） displacement of the bridge， and the longitudinal displacement of the bearing is calculated according to the spatial geometric relationship of SAR imaging. The results show that the spatial and temporal characteristics of the longitudinal displacement of the bearing are consistent with the actual bridge structure， which verifies the feasibility of PS-InSAR technology to observe the displacement of the bridge structure. A linear correlation model between the longitudinal displacement of the bearing and the temperature is established and compared with the measured results of the structural health monitoring system. The two are in good agreement， and the relative error is close to 10 %， which verifies the reliability of PS-InSAR measurement of the bridge structure displacement. The displacement of the bridge bearing under the action of temperature is simulated by finite element method， and compared with the PS-InSAR displacement time series. The two trends are basically the same， and the LOS displacement error is within ［-10，10］ mm， which verifies the accuracy of PS-InSAR measurement of bridge structure displacement.

Abstract:To investigate the different effects of different ionic emulsifiers on the stability of emulsified asphalt， based on molecular dynamics simulation， the double-layer model structure of “asphalt-emulsifier-water-emulsifier-asphalt” was constructed by using Materials Studio software， and emulsified asphalt systems containing different ionic emulsifier molecules were simulated to compare the effect of anionic （SDS）/cationic （CTAC） emulsifiers on the stability of emulsified asphalt. The changes in the relative concentration distribution， interfacial film thickness， interfacial formation energy， and electrostatic potential （ESP） of the asphalt emulsions were compared with the addition of different emulsifier molecules in order to analyze the stability of the emulsified asphalt. The results show that the SDS emulsifier increases the thickness of the interfacial layer between asphalt and water， reduces the interfacial tension between the two phases， and improves the stability of the emulsified asphalt， compared with the CTAC emulsifier. From the perspective of electrostatic potential analysis， compared with CTAC emulsifier， SDS emulsifier molecule has a larger maximum electrostatic potential of the alkane chain， and it is more likely to bond with atoms with negative electrostatic potential. Therefore， the overall stability of emulsified asphalt with an SDS emulsifier is better than that of emulsified asphalt with a CTAC emulsifier.

Abstract:Aiming at the problem of pipeline settlement and stress caused by urban shield tunnel construction underneath an existing gas pipeline， indoor model tests and finite element numerical simulations are carried out with an under-construction highway in Henan Province as the engineering background. Considering the effects of different discontinuous pipe joint spacing， joint stiffness and pipe-tunnel spacing， the effects of tunnel excavation on settlement， bending moment and pipe-soil contact stresses of discontinuous pipes under pipe-tunnel orthogonal conditions are investigated. The research results show that： a settlement concentration zone exists in loess shield orthogonal down through the pipeline， and in the range of the zone， the size of the pipeline joints and pipe section relative stiffness ratio of the pipeline average settlement growth rate has a greater impact on the pipeline average settlement growth rate， where the relative stiffness ratio is decreased from 1.30 to 0.21， and the average settlement growth rate of the discontinuous pipeline is increased by 1.5 times； relative stiffness ratio of the relative size of the discontinuous pipeline settlement and the bending moment played a decisive role； by defining the integrated stiffness ratio of the discontinuous pipeline， it reveals the maximum settlement change rule of the discontinuous pipeline and the relative change rule of the maximum positive and negative bending moments of the pipeline under different integrated stiffness ratios， in which the integrated stiffness ratio and the maximum settlement of the pipeline obey the 3rd polynomial fitting function， and the maximum positive bending moment of the pipeline obeys the 4th polynomial fitting function along with the change in the maximum negative bending moment value； the changes in the pipe-soil contact stresses of the pipeline are presented with a “bimodal type”. Numerical simulation shows that the maximum settlement of the pipeline decreases with the increase of the spacing between the tubes and tunnels， the turning point occurs at the ratio of the spacing between the tubes and tunnels and at the diameter of the tunnel excavation of one.

Abstract:Scours at the foundations of hydraulic structures have gradually become the major cause of structural damage. The traditional numerical simulation is based on the Euler mesh method， which is not easier to converge or accompanied by large deformation of grids and eventually results in the loss of solution efficiency and accuracy. This paper numerically simulated the scour process of riverbed by utilizing the Smooth Particle Hydrodynamics（SPH）based on the Lagrange coordinate. It treated the sediment phase as a non-Newtonian phase and divided it into three states： sediment， bed load， and suspended load. To accurately describe the effect of liquid-sediment interaction， the Drucker-Prager and Shields stress model was introduced in the numerical model as the criteria for the transformation judgment between three states of sediment， including assigning different rheological properties for sediment particles in different states. In this study， a modification scouring algorithm based on the two-phase flow was proposed， and the sediment scouring calculation module was built and accelerated by GPU. Finally， a numerical flume model was designed for comparison with the Louvain dam-break experiment as well as a similar numerical model. The conclusions are drawn： the current numerical model proposed could more accurately reflect the overall trend of scour development； the RMSE of the free surface profile of the water and sediment-liquid interface were within a reasonable range at the specified moment； the result of numerical model was in good agreement with the experimental data.

Abstract:Based on the classic plasticity theory， the criterion of seepage stability of unsaturated soil is established by the concept of instability modulus （HIN）. Aiming at the post-failure mode of unsaturated soil slopes （i.e. limited frictional slips and rapid flow slides）， by introducing the elastoplastic suction-dependent constitutive model， the expression of HIN identifying different failure modes of the slope is given. Taking the loose volcanic ash soil with potential liquefaction ability for example， the calibration procedure of theoretical model parameters is introduced. On this basis， the failure mode and its corresponding instability water content of volcanic ash slopes were predicted， thus validating the correctness and rationality of the theoretical model from flume tests. It is worth mentioning that based on the infinite slope model and the theory of instability modulus， the expression of the safety factor of the slope under different instability modes could be derived. Lastly， through parameter analysis， the influence of model parameters on the failure mode of the slope under different boundary conditions is investigated. This study can further clarify the inherent mechanism of different failure modes of unsaturated soil slopes under rainfall conditions， as well as provide theoretical guidance for the evaluation and design of seepage slope stability.

Abstract:Existing simplified calculation methods for critical load of pile piers in bridge structures exhibit significant errors in most cases， limiting their applicability. Based on calibration using field load tests on pile foundations in soft soil regions， a finite element method based on eigenvalue buckling analysis was employed to calculate the critical load of typical pile piers and compared with the results obtained from existing simplified calculation methods. The study identified the applicability range of the existing simplified calculation methods and found that they are not suitable for calculating pile piers in soft soil regions. Using a large dataset of finite element eigenvalue buckling analysis results for pile piers， the random forest algorithm was applied to analyze the calculation results， yielding a random forest model capable of calculating the length of pile piers and determining the importance index of various influencing parameters. Finally， based on the form of commonly used simplified calculation formulas and incorporating the important parameters identified by the random forest algorithm， a simplified calculation method for determining the critical load of pile piers in deeply soft soil regions was proposed through regression analysis.

Abstract:To investigate the lateral response of a pile under the combined action of lateral harmonic load H（t） and vertical load V at the top of the pile， based on the Pasternak foundation and Euler beam theory， a lateral vibration analysis model of pile-soil interaction is established. The improved finite beam element method is used to solve the comprehensive stiffness matrix equation considering the P-Δ effect and soil shear effect， and the corresponding analytical solution is obtained by combining the pile-soil continuous boundary conditions. The rationality of the proposed method is verified by comparing its predictions with the results of existing analytical solutions， finite element solutions， and model tests. Finally， the main factors affecting the internal forces and deformations of the pile are analyzed. The results show that： 1） Compared with the Pasternak foundation model， the traditional Winkler foundation ignores the shear effect of the foundation soil， which exaggerates the actual force of the pile so that the calculated lateral displacement and bending moment of the pile are larger than the results obtained by the Pasternak foundation. Additionally， as the pile-soil elastic modulus ratio （Ep/Es） decreases， the difference in maximum lateral displacement and bending moment between the two foundation models becomes increasingly pronounced； 2） As the vertical load on the pile head increases， the lateral displacement and bending moment of the pile are significantly affected by the P-Δ effect. When the characteristic parameter λ of the vertical load on the pile head increases from 0 to 2， the maximum lateral displacement and bending moment of the pile increase by 40.85% and 78.57%， respectively； 3） Compared with the infinite pile （L>20dp ）， the dynamic response of the lateral displacement and bending moment of the finite pile is more affected by the slenderness ratio L/dp； The maximum lateral displacement and bending moment of the pile increase with the increase of the amplitude of the horizontal harmonic load H0， and decrease with the increase of the dimensionless frequency a0.

Abstract:To accurately describe the constitutive relationship of the corroded steel under cyclic loading， the mechanical properties and degradation rules of the corroded steel were obtained through the monostatic tensile and cyclic loading tests on 16 groups of corroded Q355 steel specimens subjected to artificially accelerated corrosion. The influence of corrosion on the hysteretic properties of steel specimens was analyzed， and a cyclic constitutive model of corroded steel was established based on Giuffre-Menegotto-Pinto （GMP） model. The results show that the yield strength， ultimate strength and corresponding yield strain， ultimate strain and other mechanical properties of steel show a linear degradation trend with the increase of corrosion degree； corrosion weakens the energy consumption capacity of steel， making it difficult to ensure the safety of the structure under reciprocating loads； the cyclic constitutive model of corroded steel is in good agreement with the test results， which can provide support for the seismic performance evaluation of steel members and structures in corrosive environments.

Abstract:Based on the analysis of the physical properties of granite residual soil， microbial induced carbonate precipitation experiments are conducted on granite residual soil with different perfusion times in the designed laboratory test device， using a mixture cement of bacillus pasteurii with calcium chloride and urea colloidal solution under different concentration. Experiments are conducted on cemented specimens of different treatment conditions for the Unconfined Compression Strength （UCS） experiment， calcium carbonate precipitation experiment and disintegration experiment. In this paper， X-Ray Diffraction （XRD） and Scanning Electron Microscopy （SEM） are also used to analyze the microstructure besides. Based on the above experiments， the effect of cement concentration and perfusion times on the strength characteristics of cemented granite residual soil is investigated. The results show that the cementing effect of the specimens is best when the concentration of the cementing solution is 1. 0 mol/L within the range of the experiment parameters and the perfusion times are the same. When the concentration of the cementing solution is the same， the more perfusion times， the better the cementing effect of the specimens. The disintegration of the cemented specimens is greatly reduced， and the disintegration coefficients are less than 30%. In addition， the calcite crystals produced by biocement appear as distinct clusters， which fill and cement between the soil agglomerates. This is distinct from the microbial cementing properties of sandy soils， but the cemented process and mechanism of both are similar.

Abstract:To investigate the uniaxial tensile mechanical properties of high-early-strength high ductility concrete （HES-HDC） at different PE fiber diameters and volume fractions， 17 groups of thin-plate specimens were designed and loaded under uniaxial tensile tests. The effects of PE fiber diameters （22 μm and 25 μm） and fiber volume fractions （1.00%， 1.25%， and 1.50%） on stress-strain curve， tensile strength， and strain of HES-HDC specimens at different curing ages （2 h， 24 h， 7 d， 28 d and 56 d） were investigated. A tensile toughness evaluation method suitable for the characteristics of HDC was proposed based on the test results. The results show that the HES-HDC stress-strain curve exhibits strain-hardening characteristics under uniaxial tensile loading， and the failure process is carried out with multiple cracks. The tensile strength and strain of HES-HDC at 2 h reach over 3.29 MPa and 0.88%， respectively， and the tensile strain at 28 d could remain more than 1.28%. When the fiber volume fraction is 1.00%， small-diameter fiber is beneficial to the tensile strain of specimens， while large-diameter fiber is beneficial to the tensile strength of specimens. Considering the tensile strength and strain of specimens with large-diameter fiber， the optimal fiber volume fraction is 1.25%. The proposed tensile toughness evaluation method can evaluate the tensile toughness of HDC during its whole loading process. In addition， the tensile toughness index of HES-HDC decreased with the increase of curing age， while the tensile strength coefficient increased. The tensile toughness of specimens with small-diameter fiber is higher than that of specimens with large-diameter fiber. The tensile toughness of specimens is the highest when the fiber volume fraction is 1.25%.

Abstract:Simply supported reinforced concrete （RC） beams without web reinforcement under asymmetric concentrated load have two different shear span-depth ratios， while the relationship between the shear capacity and the shear action of each shear span is uncertain. An experimental study on the shear behavior of 6 simply supported RC beams without web reinforcement under asymmetric concentrated load and 4 specimens subjected to symmetric concentrated load was carried out. The failure patterns， load-midspan displacement curves and the strains of longitudinal tensile reinforcement were obtained. Moreover， the applicability of the corresponding formula in the Chinese code for design of concrete structures （GB 50010—2010）， the modified compression field theory， the strain-based shear strength model and Zsutty’s formula were analyzed. The results indicate that when the small shear span-depth ratio of simply supported RC beams without web reinforcement is always 1.0 and the large shear span-depth ratios are from 2.0 to 4.0， the shear failure occurs in the larger shear span. When the larger shear span-depth ratio increases from 3.0 to 3.5， the ultimate load capacity of the beam is controlled by the smaller shear span changed from being controlled by the larger shear span. The locations of shear failure in simply supported RC beams without web reinforcement under asymmetric concentrated load predicted by GB 50010—2010 are opposite to the experimental results， while Zsutty’s formula provides a less biased prediction.

Abstract:To investigate the flexural behaviors of RC slabs strengthened with textile-reinforced highly ductile concrete （TR-HDC）， the four-point bending test was carried out on one reference slab， one slab strengthened with highly ductile concrete （HDC）， one slab strengthened with textile reinforced mortar （TRM） and three slabs strengthened with TR-HDC. The effects of adding with or without PVA fibers and the mumber of layers of textile on the failure modes， load-deflection curves， flexural capacity， ductility factor， and strain analysis were studied. The test results showed that for the RC slabs strengthened with textile-reinforced highly ductile concrete， the cracking width and space of strengthened slabs were reduced apparently， which showed the characteristic of thin and dense. The flexural capacity of RC slabs strengthened with TR-HDC was greatly improved. The maximum increases in the cracking， yield and peak loads were 104%， 89% and 127%， respectively. The rupture of the textile in the TR-HDC strengthening layer reduced the ductility of the slabs. Therefore， the textile rupture should be avoided as much as possible in the practical project. Based on the plane section assumption， the formulas for calculating the flexural capacity and deflection of RC slabs strengthened with TR-HDC were proposed. The calculated results were in good agreement with the test results. It can provide the theoretical basis for practical application.

Abstract:The influence of steel fiber spacing （2， 4， 6， 8， 10 and 12 mm） on the pullout performance of steel fiber in ultra-high performance concrete（UHPC） matrix was studied by the double steel fiber pullout test. Six sets of double fiber specimens and one set of single fiber specimens embedded with 0.2 mm copper-plated straight round steel fibers were fabricated. Based on the parameters of the pullout load-slip curve， average bond strength， and maximum pullout stress， and combined with scanning electron microscope （SEM）， the micro-appearance of steel fibers after pulled out， the micro-morphology of UHPC matrix tunnel and the failure part were observed. The influence of steel fiber spacing on the pullout performance between UHPC matrix and steel fibers was analyzed. The steel fiber pullout test results showed certain discreteness； the maximum pullout load of double fibers pullout test was less than twice that of the corresponding single fiber pullout test. The steel fiber and UHPC matrix tunnel had different degrees of damage. The scratches on the surface of steel fiber and the holes in the matrix tunnel of double fiber specimen were more serious than those of the single fiber specimen， while the inner wall of the single fiber specimen was relatively complete.

Abstract:To study the shear performance of segmental prefabricated continuous composite box girder with corrugated steel webs， two scaled test beams were made， including segmental continuous box girder with variable section corrugated steel webs and monolithic continuous box girder with variable section corrugated steel webs in the same size. Through static tests and numerical analyses， the distribution of shear stress and shear ratio of corrugated steel webs are obtained. The results show that the shear stress of the corrugated steel webs of the segmental and monolithic beams at 1/4 of the mid-span is evenly distributed along the beam height， and the shear stress value of the segmental beams is greater than that of the monolithic beams. The calculation formula of shear stress of segmental assembly box girder with variable section corrugated steel webs is derived， and the effect of construction technology on shear stress is considered. The shear ratio of corrugated steel webs of two test beams is less affected by the load and maintains a constant ratio. The shear ratio of the steel web of the two test beams at the position of the middle support is about 50%， and increases along the longitudinal direction of the test beam to both sides. At the position of 1/4 of the middle span， the shear ratio of the steel web of the segment-assembled beam reaches more than 85%， and the shear ratio of the steel web of the whole beam is about 75%. The shear ratio of the two testing beams at the corresponding position of the side span is not much different. The shear strength calculation formula of the AASHTO joint applicable to segmental concrete box girder multiplied by 0.9 can be applied to the calculation of the shear bearing capacity of the joint section. The error between the above formula value and the experimental value as well as with the finite element result is about 5 %. It can better predict the shear strength of steel-concrete composite structure adhesive joints.

Abstract:With the rapid development of urban transportation， its construction requirements are increasingly high， urban bridges are mainly ramp bridges， ramps and other non-regular bridges. In order to obtain the damage mechanism and hysteresis characteristics of the fabricated pier under the combined seismic action of compression-bending- shearing-torsion， the quasi-static test for three types of bridge piers including prefabricated piers with grouting sleeves（GS）， prefabricated piers with grouting sleeve and concrete-filled steel tube（GSS） and cast-in-place reinforced concrete （RC） pier subjected to combined loads was carried out. Combining the shearing-torsion correlation curve in the existing code for design of concrete structures， the shearing and torsion load capacity of the fabricated pier under the combined load was analyzed and compared with the test results. The results show that the GS specimen and RC specimen are dominated by compression bending and torsion damage， while the GSS specimen with inserted steel tube shear keys undergo plastic hinge uplift and exhibit shear torsion damage. GS and RC specimens have better bending energy dissipation capacity， while GSS specimen with the steel tube shear key has a larger bending capacity. The assembled pier joints resulted in weaker integrity， and the torsional load capacity of the GS and GSS specimens were less than that of the RC specimen. The shear torsion correlation of each specimen under combined load is close to the quarter-circle theoretical curve in the specification. The research results can provide a reference for the seismic performance analysis of fabricated piers with grouting sleeves under the combined action of compression-bending-shearing-torsion.

Abstract:This research took the breathing microenvironment as the object to conduct an analysis on personal exposure risk in the human breathing process under the effect of the limited space air stability by means of a full-scale experiment and numerical simulation. The results showed that the personal exposure level mainly depended on the breathing activity during the pollutants initial releasing period. As the pollutants went further， the influence of limited space air stability and ventilation on personal exposure became important and presented a characteristic of time independence. In the stable condition， due to the lock-up effect of the stratified environment， the transport of the exhaled pollutants tended to remain in the initial inertia force direction， and not easy to spread； The unstable condition was more likely to disturb the ability of the initial inertia force transport direction and to accelerate the diffusion of pollutants， thus greatly reducing the personal exposure in the breathing microenvironment. This study has theoretical and practical significance in controlling the transport of pollutants， preventing the spread of disease， and ensuring occupant health.