Abstract:In order to develop a theoretical model that can fully consider the coordinated deformation characteristics between the components of pile-supported embankments, a double equal settlement plane model for embankment-pile-soil coordinated deformation is proposed based on the deformation mechanism of the pile-supported embankments with the flexible pile. Firstly, the model introduces an equal settlement plane at a certain depth below the pile-toe base on the deformation characteristics of the pile-supported embankment and the equal settlement plane in the embankment. Secondly, considering the deficiencies of the existing soil-column model, a new soil-column model that can consider the influence of the relative displacement on the coefficient of friction between the inner and outer soil columns is proposed. The stresses at equal settlement plane are affected by the coordinated deformation between the embankment, pile and soil, thus affecting the overall settlement of the embankment and the pile-soil stress ratio. Finally, the calculation results of the proposed method and the composite modulus method are compared with the measured values. The results demonstrate that the calculation errors of the settlement are 9.6% and 19.4%, respectively. The relative error of the pile-soil stress ratio calculated by the proposed model is 9.91%, which verifies the rationality of the proposed model.

Abstract:Considering the nonlinear characteristic of soil materials, the nonlinear strength criterion and the associated flow rule were used to construct the curved failure mechanism and kinematically admissible velocity field of the strip plate anchor buried near a slope. The curved failure mode and upper bound solution of the uplift bearing capacity were derived based on the upper bound theorem of the limit analysis. Then, with the aid of DIC technology, a series of uplift load tests were conducted in laboratory for scaled strip plate anchor models, which were buried in the horizontal ground or at different distances from a sand slope with various slope angles, and the uplift bearing capacity and the failure mode of the anchors with different slope angles and different edge-distance ratios were obtained. The comparison results show that the error of the uplift bearing capacity from the laboratory tests and theoretical solutions is within 13%, and the failure mode is basically consistent, which verifies the rationality of the theoretical solution. Finally, the critical edge-distance ratio of the uplift strip anchor plates was examined. The analysis results show that the critical edge-distance ratio of the anchor increases with increase of the embedding depth and the initial cohesion, while decreases with the increase of the uniaxial tensile strength.

Abstract:A general constitutive theoretical framework of saturated pore-fracture media need be formulated to guide constitutive modeling. Firstly，based on the mixture theory and nested way，the energy balance equation of saturated pore-fracture media is obtained. Secondly，according to the thermodynamic work conjugation behaviors，the strain and stress state variables of the constitutive equation for saturated pore-fracture media are determined. Thirdly, based on the assumption of local equilibrium of thermodynamics, the general free energy potential constitutive equations are obtained for saturated pore-fracture media. Finally，deriving from the general free energy potential constitutive equations，an isotropic linear elastic equation is obtained taking into account the coupling of pore and fracture skeleton deformations. When the pore and fracture skeleton deformations are uncoupled, the equation is degenerated into Khalili’s linear elastic equation. The researches show that，the solid phase strain can be decomposed into the sum of fracture skeleton strain, pore skeleton strain and volumetric strain of solid material in the case of small strain；When the mixture homogenous response principle is valid and the fluid material constitutive model is the same as the single fluid one, the fracture skeleton strain，pore skeleton strain，volumetric strain of solid material，volumetric strain of fluid material in fractures and volumetric strain of fluid material in pores uniquely determine the effective stress of fractured media, effective stress of pore media，real pressure of solid material，fracture pressure and pore pressure，respectively. A linear elastic constitutive relation can be achieved when the free energy function is a quadratic function of state variables.

Abstract:The bearing capacity of pre-bored grouted planted (PGP) pile under compression and tension is investigated based on a group of field compression and tension tests. The load-displacement curves of two test piles are compared and analyzed, and the effective stress method is adopted to estimate the shaft capacity of the test piles. The test results show that: the ultimate shaft resistance of PGP pile under tension is smaller than the ultimate shaft resistance of PGP pile under compression, due to the different stress conditions of the soil around the pile and the Poisson's ratio of pile shaft; the pile head displacement needed to fully mobilize the shaft resistance of test pile under tension is larger than the displacement needed to fully mobilize the shaft resistance of test pile under compression; a ultimate depth (or ultimate vertical effective stress) exists when the effective stress method is adopted to calculate the ultimate skin friction of the soil layers, and the value of the vertical effective stress corresponding to the ultimate depth should be adopted in the calculation of ultimate skin friction in effective stress method.

Abstract:In order to study the working characteristics of cap-pile method on the extremely soft foundation in mud flat, this paper carries out the field test and finite element analysis. According to the measured ground surface settlements and earth pressures, the two-dimensional plane strain model is established. Furthermore, excess pore water pressures, earth pressures, and settlements of foundation soil in different periods are examined. The results show that the differential settlements between piles and surrounding soils increase with the increasing filling height. The differential settlements lead to the occurrences of soil arching effect and tensioned membrane effect, which increase the axial force of the pile as well as the load sharing ratio of the pile and the pore water pressures of the soil at the pile bottom. After the completion of the construction, the excess pore water pressures dissipated and the foundation soil gradually consolidated. The differential settlements between piles and soils increase and then tend to be stable. The pile load sharing ratio gradually stabilized at about 80%. The geogrid has low tension and limited ability to transmit loads. Since the shallow foundation soil has negative frictional resistance to the pile, the axial force of the pile increases with the growing depth in shallow area and then decreases as the depth increases. Finally, the cap-pile method can effectively control the horizontal displacement of foundation soil.

Abstract:Based on the Biot dynamic consolidation equation and the Kelvin model, the vertical vibration characteristics of the incompletely bonded pipe pile in saturated soil are investigated by considering the three dimensional effect of soil and the relative slip between the soil plug and pipe pile. Firstly, by introducing the potential functions and combining with the initial conditions and boundary conditions of the pile surrounding soil and soil plug, the vertical vibration solutions of the pile surrounding soil and soil plug are obtained by the Laplace transform method, Helmholtz decomposition method and separation variable method, respectively. Then, combining with the coupling conditions of pile-soil system, the complex stiffness, the frequency domain solution of the velocity and the semi-analytical solution of the velocity in the time domain of pipe pile top are obtained. Next, the degenerate solutions of this paper are compared with the corresponding existing solution to verify the rationality of the solution of this paper. Similarly, a parametric sensitivity analysis of the Kelvin model is conducted to preliminarily obtain the suitable values of the parameters of Kelvin model. Finally, the influence of the length of pipe pile, the permeability coefficient, porosity, shear modulus and viscous damping coefficient of soil plug on the vertical vibration characteristics of the incompletely bonded pipe pile in saturated soil are studied. The results show that, the shorter length of pipe pile leads to more obvious influence of the degree of bond between the soil plug and pipe pile on the vertical vibration characteristics of pipe pile in the saturated soil. The porosity and viscous damping coefficient of the soil plug have obvious influence on the vertical vibration characteristics of incompletely bonded pipe pile in saturated soil, and the influence of shear modulus and permeability coefficient of soil plug are too small to be neglected.

Abstract:Aiming at the key problems such as excavation，deformation and rupture of surrounding rock, and mechanism of support structure in the experimental study of deep composite stratum TBM tunnel, based on the new method of transparent rock mass test, a composite stratum was developed to meet the test requirements. Also, the tunnel boring machine (TBM) simulation experiment device and the TBM segment production device were developed. On this basis, digital photographic measurement technology was used to compare and analyze the deformation and fracture of surrounding rock with and without support, and it revealed the deformation and rupture mechanism of the surrounding rock with and without support. Combined with the deformation and fracture of the surrounding rock, the characteristics of the thrust structure were reversed. The research results show that: 1) Under the premise of axial loading and surrounding constraints, the deformation and fracture mechanism of the surrounding rock on TBM tunnel in the deep composite stratum is shear-slip type (without support) and expansion type layer deformation type (with support). 2) The supporting structure can restrain the development of deformation around the tunnel, greatly reducing the deformation of the surrounding rock, cutting down the degree of fragmentation of the surrounding rock and increasing the bearing capacity of the surrounding rock by about 2 times. Also, the stress state of the surrounding rock is changed from local tensile shear to overall vertical compression, which reduces the stress concentration and makes the shallow surrounding rock form a certain bearing capacity. Moreover, the bottom drum is effectively suppressed, thus protecting the stability and safety of the tunnel. 3) Stress concentration occurs at the corners of the two walls in the TBM tunnel. In the actual project, measures such as backfilling grouting with bean gravel and local grouting reinforcement can be used to improve the stability of the weak link.

Abstract:Microbially induced carbonate precipitation (MICP) has become a research hot spot due to its environmental friendliness in recent years. This paper introduces the mechanism of MICP, and expounds the influence of bacteria, nucleation microdots and Extracellular Polymeric Substances (EPS) on the reaction of MICP. Similarly, the relevant theoretical models involved in this technology are summarized, including the model of solution transmission and distribution, the model of urea hydrolysis rate and the model of pore. In addition, through summarizing the relevant literature, it is found that, based on MICP better fluidity and cemented precipitation, MICP can play a good improvement effect in broadly application fields, such as sand solidification, foundation improvement, anti-seepage plugging, concrete repair. Finally, the current research problems and future research directions of MICP are discussed and prospected based on the current research results.

Abstract:Aiming at the flutter stability of the main girder section at high attack angles, this paper studies the flutter stability of a thin plate and a streamlined box girder section at different attack angles（0°，±3°，±5°，±8°）by numerical simulation method. Two-dimensional fluid-structure interaction（FSI） method combined with Newmark-β method is developed based on ANSYS FLUENT user-defined function（UDFs） and dynamic mesh technology. Meanwhile, the numerical simulation results are compared with the wind tunnel test data. The results show that the critical flutter wind speeds of the thin plate section and the streamlined box girder section obtained from numerical simulation method are in good agreement with those from wind tunnel tests, which verifies the accuracy of the two-dimensional FSI analysis method for bridge deck section. The flutter critical wind speed of the thin plate section decreases significantly with the increase of attack angle. The flutter critical wind speed of the streamlined box girder section decreases with the increase of attack angle in the range of positive attack angles, and increases firstly and then decreases with the increasing of absolute values of attack angles in the range of negative attack angles. When the attack angle is large enough, the thin plate section and the streamlined deck section all characterize bluff body, and therefore the incoming flow passes around the leading edge of the section separates and generates large vortices along the upper and lower edges of the section, which leads to a decrease of the critical flutter wind speeds of the bridge girder section.

Abstract:In order to clarify the buffeting performance of the joint system composed of free-standing steel pylon and tower crane as well as the effect of tower crane on the buffeting response of steel pylon, wind tunnel tests of aeroelastic model of the joint system and free-standing pylon are designed and carried out. Modal parameters and buffeting performance under different wind speeds and wind yaw angles of the two systems are obtained. The effects of wind speed and wind yaw angle on the two systems are summaried and compared, and the vibration responses of the joint system between tower crane and steel pylon in both longitudinal direction and lateral direction are compared in the end. The results show that the mean value of wind-induced buffeting displacement of steel pylon and tower crane can be approximately treated as a quadratic function of wind speed, while the standard deviation of displacement oscillates back and forth with the increase of wind speeds, and the existence of tower crane can decrease the mean value and standard deviation of wind-induced buffeting displacement of steel pylon significantly. Wind yaw angle has obvious effects on the wind-induced response of steel pylon and tower crane. The vibration response of the tower crane is much larger than that of pylon in longitudinal direction of bridge, but it is a little smaller in lateral direction due to the local vibration of tower crane.

Abstract:Based on the wind speed samples collected by the ultrasonic anemometers atop Shanghai World Financial Center during Typhoon Rumbia, the fluctuating wind characteristics parameters, such as the mean wind characteristics, turbulence intensity, gust factor, peak factor, turbulence integral scale, and power spectral density are analyzed in detail. It is found that the variation trends of the mean wind speed in 3 seconds, 10 minutes and 1 hour within an hour are consistent with each other. Turbulence intensity decreases first and then stabilizes with the augment of mean wind speed. The mean values of longitudinal and lateral turbulence intensity are 0.135 and 0.132, respectively. The gust factor increases linearly with the increase of turbulence intensity. The turbulence integral scale shows no obvious variable trend with the increase of the mean wind speed. The measured wind speed spectra agree well with the Von -Karman spectra.

Abstract:In order to figure out the different temporal and spectral characteristics between two earthquakes with close hypocenter and short time interval in the same seismic sequence, two main shocks，MW 6.4 and MW 7.1 among the 2019 Ridgecrest earthquakes at California USA in July are selected. The attenuation trend of ground motions parameters with the change of epicentral distance for these two earthquakes is compared with Yu's model. The difference of three key elements of ground motions between these two earthquakes，including peak ground acceleration, response spectrum and duration，are analyzed. The potential seismic damage to structures is discussed by the response spectrum analysis of the selected two severest ground motions. The Hilbert-Huang transform（HHT） is adopted to obtain the HHT spectrum of ground motions for identifying the energy distribution in temporal and spectral domains. It shows that the attenuation trend of most of data agrees with Yu’s model. The response spectra of the two earthquake events are similar. The instantaneous frequency corresponding to the largest energy of HHT spectrum is close to peak-trough frequency corresponding to the time series cycle with peak ground acceleration. Structures may be severely damaged subjected to two earthquakes occurred successively.

Abstract:The parametric vibration of cables in the pretensioned folded line type 3D-trussed arch was studied and the finite element model of pretensioned arch structure was established to investigate the possibility of parametric vibration of cable by utilizing ANSYS. The nonlinear time-history analysis method was adopted to study the dynamic response of the structures under different frequency harmonic load and seismic waves and to investigate the mechanism of parametric vibration of cable arch structure. The influence of parameters, such as the prestress and excitation amplitude, were investigated. The results indicated that the cable parametric vibration appeared when the ratio of the excitation frequency to the natural frequency of cable was 2.05 ∶ 1，the amplitude of cable increased by about 63 times and the response of some key nodes and members in the structure increased; the cable had a relatively large response when the frequency of the seismic wave concentrated on the frequency range in which the cable had a parametric vibration. The effect of cable parametric vibration on the structure response was necessary to be considered for ensuring the safety of the structure under earthquakes.

Abstract:A method for identifying the backbone curve parameters of the modified Ibarra-Medina-Krawinkler （IMK） model by using quasi-static test data of reinforced concrete columns and thus improving the simulation accuracy of reinforced concrete frame structures is proposed in this paper. In this method, a robust unscented Kalman filtering algorithm based on singular value decomposition（robust SVD-UKF algorithm） is introduced to suppress the influence of gross error of the observation on the parameter identification, and the particle swarm optimization algorithm is adopted to automatically optimize the initial covariance matrix, the process and measurement noise matrices. The identification of backbone curve parameters of the modified IMK model is realized using MATLAB，in which the symmetric and asymmetric hysteresis behavior of the columns in the positive and negative direction is considered. The effectiveness of the proposed method is verified by model backbone curve parameter identification based on the measured hysteretic curves of reinforced concrete columns and its application in the nonlinear simulation of frame structures.

Abstract:In order to study the influence of stirrup corrosion level on the failure modes, peak stress, peak strain, ultimate strain and shape of stress-strain curve of the confined concrete，15 reinforced concrete prism specimens are subjected to acid rain erosion in the acid environment modeled by artificial climate simulation technique followed by axial compression tests. Based on the Mander’s model and the existing research results, the calculation formulas for the peak stress，peak strain, ultimate strain and shape factor of the uncorroded specimens are determined. The factor calculation formulas for peak stress, peak strain, ultimate strain and shape factor of corroded specimens are developed by regression analysis of test data, respectively, and then the constitutive model of confined concrete by acid rain erosion is established. By comparing the simulation results with the experimental data, it can be found that all the peak stress, peak strain, ultimate strain and stress-strain curves shape of the specimens obtained by proposed method are in good agreement with the experimental data. Thus, the constitutive mode for confined concrete established in this paper can accurately reflect the mechanical performance of RC prism specimen by acid rain erosion, indicating its adaptiveness for estimating the residual bearing capacity and the seismic performance of RC structure under the acid rain environment.

Abstract:In this paper, the combination of experimental and theoretical analysis was used to study the effect of Textile Reinforced Concrete (TRC) confinement on the bond behavior between the deformed steel bars and concrete with different corrosion ratios through the pull-out experiment at electrochemical corrosion center. The experimental results showed that，without TRC confinement, the bond strength decreased with the increase of the corrosion ratio, especially after the rust crack was obvious. The TRC confinement had a good effect on the bond performance between the rust bar and the concrete, especially when the degree of corrosion was large. For the specimens with rust cracks, TRC confinement had a good effect on limiting cracking and increasing ultimate bond stress, and also had a significant effect on maintaining the bond stiffness. Finally, the rising section of the bond-slip constitutive relationship between the TRC-confined concrete and the corroded steel bar was established.

Abstract:Based on the existing pull-out tests on shear connectors, total five glued laminated bamboo (glubam)-concrete composite beams were tested under four-point bending loading to investigate the effect of connector type and numbers on the bending performance of composite beams. Three types of connector were selected in the current study including the screw connector，the notch connector and the pre-tightening notched connector. Test results show that all composite beams with different connectors exhibit high initial composite action and relatively stable composite action under the serviceability limit state. For the composite beams with screw connectors, the ultimate load carrying capacity is determined by the tensile strength of the glubam at the fingure joint. However, the ultimate load carrying capacity of the composite beams with notch connectors and the pre-tightening notched connectors mainly relied on the shear strength of the end connector. The semi-prefabricated composite beam with pre-tightening notched connectors shows the similar bending capacity when compared with the corresponding casting in-situ composite specimen, indicating a good prospect considering its high construction efficiency. The equivalent stiffness method predicted by Eurocode 5 overestimates the load carrying capacity of all specimens, and it is not suitable for glubam-concrete composite beams.

Abstract:Three-dimensional morphology scanning, monotonic tensile test, and fracture scanning of cold-formed steel with 10 years of service in the industrial environment were performed to investigate the effect of corrosion on the surface morphology and mechanical properties of cold-formed steel. The two-dimensional and three-dimensional surface topography, corrosion damage parameters, stress-strain curves, mechanical property indexes, and microscopic fracture topography of the corroded cold-formed steel were obtained. The variation rules of the corrosion damage parameters and mechanical property indexes were also analyzed. Finally, a constitutive model of the corroded cold-formed steel was established. The results indicate that the number of corrosion pits on the steel surface decreased, and the morphology of corrosion pits changed significantly with the increase in corrosion degree. The proportion of the uniform corrosion and maximum depth of the corrosion pits gradually increased, and the surface of the corroded steel became increasingly rougher. The elastic modulus, yield strength, ultimate strength, and elongation after fracture linearly decreased with an increase of the material loss rate. The yield platform also became shorter or even disappeared. Moreover, the macrofracture and microfracture morphologies changed obviously. The established constitutive model can accurately reflect the variable trend of the stress-strain curve of the corroded cold-formed steel.