Abstract:The reliability of the brick column underpinning joints is one of the important factors to ensure the safety of building monolithic moving. In order to study the mechanical performance of the brick column underpinning joints in the process of moving, this paper takes a protected building as an example and uses the ABAQUS finite element software to establish the finite element model of the brick column underpinning joints. Through the simulation analysis，the stress and deformation performance of high performance ferrocement laminate（HPFL） reinforced and unreinforced underpinning joints are investigated. Meanwhile， the comparison with field monitoring data are also carried out. The results show that HPFL reinforcement method can effectively improve the bearing capacity and deformation capacity of the brick columns underpinning joints，and the ability of effective resistance under various adverse effects in the process of translation is also proved. The method is safe and reliable. The simulation results are in good agreement with the field monitoring results ，which proves the feasibility of the simulation method.

Abstract:In order to study the mechanical properties of steel fiber reinforced concrete（SFRC），a new constitutive model of SFRC is established in this paper based on the smeared crack model of the plain concrete and considering the bonding effect between fiber and concrete. In this model，the reinforcement of the steel fiber is considered in two cases. Before the cracking，the steel fiber and concrete matrix are fully bonded，which meets the two-phase composite law. When the concrete crack initiates and propagates，the contribution of the concrete and the steel fiber is considered separately. And the strengthening effect of fiber on the concrete cracked plane is considered through the bond-slip model during the process of fiber partially debonded and fully debonded from the concrete matrix. Through Fortran programming，the proposed constitutive model is introduced into ABAQUS software by using the subroutine Umat，and the finite element model is established to simulate the tensile tests and 4-points flexural tests of SFRC. Though the comparison of numerical simulation results and available experimental data，the accuracy of the constitutive model is verified. Meanwhile，the mechanical properties of SFRC including tensile strength，residual strength，flexural strength，and toughness are analyzed in detail.

Abstract:In order to improve the stress lag problem when using orthogonal steel strips to strengthen brick masonry walls，it is proposed to apply pre-tension stress to horizontal steel strips. Five specimens were tested under low reversed cyclic loading. The failure process of the specimen was described，and the hysteretic curve，skeleton curve，bearing capacity，stiffness and ductility were also analyzed. The results show that strengthening brick masonry wall by pre-stressed steel strips can improve its seismic performance; increasing the steel strips’ pre-stress level within the appropriate range can further improve the bearing capacity of the specimen，and has little effect on the lateral stiffness corresponding to its cracking point，but the ductility decreases slightly; increasing the Vertical load level of the wall can improve both the bearing capacity and lateral stiffness of the specimen，but the ductility also decreases slightly; and increasing the aspect ratio of the wall to 1，the strengthening effect is relatively worse. Furthermore，based on the analysis of the strain development of steel strips，it can be found that pre-stress application can effectively improve the utilization ratio of the material. Finally，the recommended value of pre-stress and calculating formula of shear capacity were proposed.

Abstract:Based on the finite element software ANSYS/LS-DYNA，the numerical models of prestressed concrete T-beams，explosives and fragments are established，and the dynamic response and damage of the beams when subjected to shock wave-fracture composite effects are explored. The effectiveness of the model is verified by test results. The similarities and differences of damage and displacement responses of T-beams under the action of shock wave and fragment group and their combined effects are analyzed. Using parametric analysis methods，the effects of tensile control stress，longitudinal reinforcement ratio，non-encrusted area stirrup reinforcement ratio，concrete compressive strength，explosive proportional distance，and burst position on the damage effect of T-beam were studied. The results show that with the increase of tensile control stress，longitudinal reinforcement ratio and non-densified zone reinforcement ratio，the anti-explosion performance of T-beams appears nonlinear; the compressive strength of concrete has no obvious effect in enhancing the anti-blast performance of T-beams; when the proportional distance is the same，the damage effect of the explosive on the beam is more prominent than the distance from the center of the explosion to the beam surface. The greater the quality of the explosive is，the more serious the damage of the T-beam is; the peak value of the displacement of the mid-span bridge across the upper point increases approximately uniformly from the side close to the blast center to the side away from the blast center; the smaller the distance between the blast center and the center point is，the greater the dynamic response of the beam's mid-bottom surface displacement is.

Abstract:Based on the CR full nonlinear calculation model and the Timoshenko beam theory，and considering the beam element shear effect，the beam-column theory（stability function format） is adopted to establish a fine and efficient plane beam element analysis theory，which considers the axial force，bending moment，shear and their coupling effect of the element. The beam-column theory and the CR coordinate method are used to improve the fast solving method for the geometric nonlinear problem of plane beam element under the high precision target. On the basis of the two order beam-column theory，the concrete form of the angular displacement equation for the shear effect is derived，and the exact stability function expression of the stiffness coefficient is obtained. The power series of the above stability function is transformed and the corresponding truncation criterion is put forward on the premise of ensuring the numerical accuracy and the stability of the calculation process. Subsequently，the formula for calculating the node force of the element considering the effect of shear deformation on the bowstring effect is derived，and the program is compiled and compared with classic examples. Moreover，it is analyzed with the actual engineering. The results show that，for the general multi-span continuous beam structure，the calculation results of the classical calculation can be obtained by the calculation theory proposed in this paper. For the class of large displacement，such as the elbow rigid frame structure，the full process deformation curve of the load-displacement considering the shear effect can be obtained by this theory，and the first and two critical points of leap buckling are also consistent with the classical literature. For the long-span cable-stayed bridge with different main girder sections，reasonable overall deformation characteristics can be obtained by using this theory，and the efficiency of analysis can also be significantly improved.

Abstract:In order to accurately calculate the deflection of steel-concrete composite girders under long-term loads，considering the shear deformation of composite girder，slip effect at the steel-concrete interface and shrinkage and creep of the concrete slab，the equilibrium differential equations for calculating the deflections of steel-concrete composite girder are derived by using the energy variational method. By introducing the boundary conditions on the simply supported and continuous composite girders under uniformly distributed load，the deflection calculation formulas can be obtained. The reliability of the calculation formulas is verified by comparing the experimental results and the results of finite element analyses. The results show that maximum deflection of two-span continuous composite girder considering shear deformation and interlayer slip increases by 37.4% when compared with the results from primary beam theory，and the deflection increases by 58% after considering the shrinkage and creep of concrete. The calculated maximum deflection of simply supported composite girder after considering the shrinkage and creep of concrete is 1.55 times larger than that of the primary beam theory. It can be seen that shrinkage and creep can have a significant influence on the girder's deflection. The research results can provide a theoretical basis for the deflection calculation of steel-concrete composite girders under the long-term loads.

Abstract:In order to study the shear capacity of reinforced concrete corbels，and evaluate the accuracy and safety of the design method of Chinese and abroad code，based on the collected test data of 209 corbels，the shear capacity formulas of ACI 318-19，EC2，CSA A23.3-04 as well as the main strut-and-tie models were evaluated. It was found that the calculation results of abroad code are too conservative，while the softened strut-and-tie model（SSTM） can better predict the shear capacity of corbel. On this basis，a series of reinforced concrete corbels were designed according to the Chinese code with various parameters including shear span，concrete strength，reinforcement strength，etc. By comparing the designed shear capacity with the calculation results of the softened strut-and-tie model，the accuracy and safety of Chinese code under different design parameters were analyzed. Then，the simplified formula of the modification factor of the corbel bearing capacity was proposed. Based on the collected test data，the simplified formula was proved to be accurate. Design suggestions were proposed for the corbels under shear load，which can be used as a reference for the design of reinforced concrete corbels.

Abstract:The elastic-plastic characteristics of the structure will lead to large dispersion of the residual displacements，which makes it difficult to predict the residual displacements accurately under strong earthquake excitations. In order to accurately evaluate and predict the residual displacements of the structure and realize the refined aseismic design，it is necessary to investigate the dispersion of the residual displacement of structures. In the light of this，based on a large number of classified ground motions，different normalized parameters are used to define the residual displacement ratio in this paper. The residual displacement ratios spectra of single degree of freedom（SDOF） systems are constructed by means of nonlinear response time-history analyses. The results are statistically organized to evaluate the influence of the following parameters: elastic-plastic characteristic parameters（ductility factor and strength reduction factor） and site condition. A simplified expression is presented to estimate the variation coefficient spectra of residual displacement ratios. It is concluded that the correlation between residual displacements and inelastic spectral displacements is better than that between residual displacements and elastic spectral displacements. The dispersion of the residual displacements is less affected by the site conditions. The variation coefficient spectra of residual displacement ratios increase with the increase of elastic-plastic characteristic parameters. It is suggested to select the inelastic spectral displacement as the normalized parameter，which can reduce the dispersion of the residual displacement ratios.

Abstract:Aiming at the issue of low efficiency in the random analysis and calculation of train-track-soil coupled system due to the random characteristics of track irregularity，the pseudo-excitation method（PEM） is used to reduce the computing cost of large samples. Considering the sparsity of equivalent stiffness matrix of train-track-soil coupling system，the large-scale sparse matrix was stored in Compressed Sparse Row（CSR） format. The symmetric positive definite equation of equivalent static equilibrium is solved by the preconditioned conjugate gradient（PCG） method，and the parallel program is developed by the MATLAB-CUDA（Compute Unified Device Architecture） hybrid platform. The numerical example shows that the efficiency of solving equivalent static equilibrium equation based on MATLAB-CUDA hybrid platform is 86.13 times that of the multi-point synchronization algorithm，which greatly reduces the total calculation time of the random vibration analysis，and the memory usage is small and it is easy to implement on a personal computer. When using PCG method to solve the large sparse linear equations of vehicle-track-foundation soil coupling system，it is suggested to take the acceleration as the control index of convergence accuracy of iteration. By choosing the appropriate convergence accuracy of iteration，the balance of calculation accuracy and efficiency is achieved.

Abstract:In this study，a three-dimensional finite element analysis method was used to simulate tunnel excavation nearby a perpendicularly crossing existing tunnel，in order to investigate the effects of construction sequences on cross-cutting tunnels. The hypoplastic constitutive model of sand and soil is adopted and the soil small-strain stiffness is considered in the numerical analysis，so as to study the effect of construction sequences on cross-cutting tunnels as well as the stress transfer mechanism of the soil near the existing tunnel. The results show that the existence of the existing tunnel reduces the maximum settlement by 14% when compared with the condition without the existing tunnel; when the new tunnel is above the existing tunnel，the settlement is larger，but the impact range is smaller. When the tunnel face approaches the centerline of the existing tunnel，the stress of the existing tunnel is transferred from the vault to the abutment；when the tunnel face is between 3D behind and 6D in front of the centerline of the existing tunnel，the effect of stress relief on the existing tunnel is significant; when the new tunnel is under the existing tunnel，the deformation and bending moment of the existing tunnel are greater. In the construction of vertical cross tunnels，the impact of the construction sequence on the ground settlement and the existing tunnel should be considered comprehensively.

Abstract:Based on the principle of drillability，the concept，significance and key issues of boreability of strata by shield construction are combed. The displacement method，the strength method and the energy method are put forward to express the boreability，and the representative indexes of three methods are preliminarily selected as: penetration，field penetration index and specific energy. Combined with a shield tunnel project，the time history analysis on the change rule of construction parameters and boreability index of shield tunneling is carried out，and four main working stages of tunneling are put forward. Based on the different working stages of single ring driving，statistical data of three kinds of stratum and the results of relevant literature，the correlation between the boreability indexes is analyzed. There is a good unity among penetration，field penetration index and specific energy，which can be used to express the boreability of the stratum. Supplemented by the special stratum in the project，the feasibility of the response feedback between boreability and shield machine-geotechnical state is analyzed. At last，the study on the problem of boreability is considered. It is suggested that the study on the classification of strata should focus on the statistical work between the main physical mechanical parameters and the boreability index of the geotechnical，and accelerate the development of traditional geological exploration to drilling methods based boreability.

Abstract:It is difficult to consider the prediction of ground settlement under the coupling effect of multiple factors for the finite element method and formation loss rate. Based on the multi-factor and nonlinear fitting ability of back-propagation neural network（BPNN） and random forest（RF），these two machine learning algorithms are adopted to predict the tunneling-induced ground settlement. The optimum hyper-parameters of the two machine learning algorithms are determined by particle swarm optimization（PSO），and k-fold cross validation method is used to improve the robustness of the prediction method. The prediction results indicate that the prediction error of BP neural network is larger and it’s hard for BP neural network to predict the large settlement. The random forest algorithm can accurately predict the maximum settlement and longitudinal ground settlement curve.

Abstract:According to the corrosion ions in the groundwater and soil of the platforms along Lanzhou metro，four kinds of compound salt solutions containing SO2-4，Cl-，and Mg2+ were prepared. The reinforced concrete specimens were placed in the compound salt solution，and nondestructive testing was conducted every 90 days by an electrochemical workstation and ultrasonic sound velocity detector. A durability life prediction model of reinforced concrete was established by using a non-monotone Wiener stochastic degradation process. When the relative dynamic modulus of elasticity reached 0.4，it was regarded as the failure condition of concrete，and when the crack width reached 0.2 mm，the corrosion current density was used as the failure threshold of reinforcement in concrete. The results show that，under the coupled salt solution environment，the polarization curve moves towards the direction of increasing corrosion current density and negative potential. The ac impedance spectrum shows a double capacitive reactance arc. At the initial moment，the low-frequency impedance arc radius is large，the slope is high，and the corrosion cycle increases. The low-frequency impedance arc radius gradually decreases and shrinks to the real part of the impedance，and the impedance spectrum gradually shifts to the left. When corrosive ions enter the concrete，cementitious materials are consumed，and expansion products are produced. When the crack width reaches 0.2 mm，the failure threshold of the corrosion current density is 7.637 5 μA/cm2. The life of steel bars is less than that of concrete through Wiener random process. The life of steel bars is about 7 200 days，2 900 days，4 500 days，and 2 000 days，respectively，in A，B，C，and D solutions，while the life of concrete in the solutions is about 10 000 days，6 500 days，5 500 days，and 5 000 days，respectively. Moreover，the life of steel bars is more sensitive to chloride，while the life of concrete is more sensitive to sulfate.

Abstract:The joints in the precast segmental ultra-high performance concrete（UHPC） bridge are quite critical for the mechanical performance of this type of bridge，especially for its shear performance. Based on the Plastic Damage Model in ABAQUS，the nonlinear finite element model（FEM） was built to investigate the direct shear behavior of the UHPC dry joints with big shear keys，and this FEM was corrected and verified by the experimental data from available literature. On the basis of the verified FEM，the direct shear behavior and the failure mechanism of the UHPC dry joint with big shear keys were investigated. Two failure modes of the UHPC joint，slip failure and direct shear failure，were found in this paper. Furthermore，a parameter analysis was conducted to the big shear key in the UHPC dry joint，where the considered parameters included the depth，inclination and lateral compressive stress. According to the modeling results，the reasonable big shear key is suggested to have the height to shear height ratio of 0.15~0.25 and the inclination angle smaller than 37°. Finally，based on the Mohr’s stress circle theory and FEM results，a formula for predicting the direct shear capacity of UHPC dry joints was established. It was proved that the formula had promising availabilities by test data.

Abstract:Considering the initial configuration and support stiffness of cable-stayed bridge，the multi-cable-stayed shallow-arch model with vertical elastic constraints is established. Firstly，based on the classical dynamics equations of the cable and shallow arch，the theory of in-plane free vibration of the model is deduced by dividing the shallow arch into several segments at the cable-arch coupling points. Then，the double-cable-stayed shallow-arch model is taken as an example and its in-plane eigenvalue problem is solved by separation-of-variable method. At the same time，taking the double-cable-shallow arch model as an example，the corresponding finite element model is established. The frequencies and mode shapes calculated by the present method are compared with those obtained by finite element method，which verifies the correctness of the method and model in this paper. Finally，a systematic parametric analysis on the dynamics properties of the model is conducted. It is shown that the vertical stiffness has a significant effect on the dynamics properties of the system.

Abstract:Based on the equivalent heat transfer coefficient method and orthogonal experiments，a method for evaluating the thermal performance of various envelopes in existing buildings is proposed. The heat transfer coefficients of the external wall，external window，roof，and external door are integrated into an index（comprehensive equivalent heat transfer coefficient）. It is only necessary to measure indoor and outdoor temperature sequences of the existing buildings and geometrical dimensions of envelopes. The comprehensive equivalent heat transfer coefficient can be calculated，and the equivalent heat transfer coefficient of various envelopes can be obtained by orthogonal experiments and regression analysis. By comparing the equivalent heat transfer coefficients of various envelopes with heat transfer coefficient limits in standards，the thermal performance can be evaluated. To verify the feasibility of the method，a small experimental building located in Changsha is taken as an example. The equivalent heat transfer coefficients of the external wall，external window，roof and external door are1.62 W/(m2·K），2.84 W/(m2·K），1.25 W/（m2·K） and 3.14 W/（m2·K），respectively. Comparing equivalent heat transfer coefficients with actual heat transfer coefficients，the values are in good agreement，which proves that the method is feasible in engineering applications.

Abstract:The tensile and shear properties of basalt fiber reinforced polymer（BFRP） and glass fiber reinforced polymer（GFRP） tendons after thermal aging were tested by the universal testing machine，and the effects of elevated temperatures on the mechanical properties and failure mode of BFRP and GFRP tendons were studied. Furthermore，the tensile strengths of BFRP and GFRP tendons after treatment under various elevated temperatures were statistically analyzed by Weibull model，and the thermal degradation mechanism of BFRP and GFRP tendon was quantitatively analyzed by a thermo-gravimetric analyzer. The results show that the color and morphologies of BFRP and GFRP tendons change obviously with the elevated temperatures. The tensile strength，ultimate strain，toughness and shear strength of BFRP and GFRP tendons slightly increase firstly and then decrease with the temperature，while the elastic modulus does not change significantly. Compared with the GFRP tendon，the BFRP tendon treated under the same temperatures exhibits lower tensile properties but better shear performances. The pyrolysis characteristics of BFRP and GFRP tendons properly explain the degradation mechanism of their mechanical properties after elevated temperatures.

Abstract:The four-point bending test of 5 groups of recycled aggregate substitute rates and 4 groups of steel fiber reinforced recycled aggregate concrete prism specimens were conducted to study the effects of recycled aggregate substitution rate and steel fiber content on the flexural strength and the scale effect of recycled concrete. The test results show that there is scale effect in the flexural strength of each kind of prism specimens. With the increase of the substitution rate of recycled aggregate, the scale effect of the flexural strength of recycled concrete increases first and then decreases. The scale effect of the flexural strength of the specimen with a substitution rate of 75% is about 1.32 times and 1.09 times that of the specimens with a substitution rate of 0 and 100%, respectively. The content of steel fiber has a certain effect on the scale effect of the flexural strength of recycled concrete. When the steel fiber content ranges from 0% to 0.75%, the larger the content of steel fiber, the more pronounced the scale effect is. The scale effect of specimens with steel fiber content of 0, 0.25% and 0.5% is about 79%, 85% and 94% of the specimen with steel fiber content of 0.75%, respectively. When the steel fiber content is over 0.75%，the variation on the scale effect of flexural strength with different steel fiber contents is limited. The scale effect of the specimen with steel fiber content 0.75% is about 99% of the specimen with fiber content of 1%. A calculation formula for the scale effect law of the flexural strength of recycled concrete is proposed，which can be used to analyze the flexural strength of recycled concrete.

Abstract:In this paper，an efficient optimization algorithm based on subset simulation is proposed for solving the resource leveling problem of construction projects with multiple resources. In the resource leveling problem，if the decision variables are chosen to be the scheduled starting time for the involved activities，the logical relationship between the activities may be violated during the implementation of the optimization algorithm. In order to avoid this problem，the interval rate variables are introduced to substitute the scheduled starting time in modeling the resource leveling problem of construction projects with multiple resources so as to simplify the procedures of the proposed optimization algorithm based on subset simulation. As shown in the illustrative example，compared with the widely used genetic algorithm，the proposed optimization algorithm can obtain higher improvement in the stability of achieving the optimal solution.