Abstract:With the identification of ground photos taken by unmanned aerial vehicles （UAV） in urban areas， information on ground buildings can be quickly obtained. And the geomorphic conditions in the survey area can be effectively obtained and parameterized. The category of the near ground wind field in this area can be determined by establishing the corresponding relationship between the ground roughness Z0 and the growrd roughness index α. At the same time， the wind field and wind profile in the area were measured by the anemometers carried by UAV， and the near ground wind field category in the area was obtained through analysis. The near ground wind field categories obtained by the two methods are compared. The results show that the site categories determined by the two methods are consistent， and the relative error is within 5%. The research realizes the judgment of wind field category related to the target building according to the actual landform， and the method proposed in the paper has broad applicability. The research results can provide new ideas for the wind resistance design of buildings in urban areas.

Abstract:Aiming at the miss of bridge drawings and extensive structural modeling works that need to be done in bridge seismic analysis， this paper presents a bridge finite element reverse modeling technology based on UAV oblique photography technology. The parametric bridge FE modeling process was first introduced. Then the oblique photography technology based on motion recovery structure and the multi-view stereo matching algorithm was introduced. Combined with UAV multi-view sequence images， a three-dimensional real-scene model of the target bridge was constructed. The non-uniform rational B-spline algorithm was introduced to extract the complex bridge surface and obtain the geometric data of the bridge. The internal structural parameters of bridges， which cannot be observed by UAV， were obtained through network big data， bridge design specifications， design standard atlas， and field measurement， and then the FE models of bridges can be reconstructed. A three-dimensional scene model of Baxizhou Bridge in Changsha City is established， and the model error is less than 2%. The Midas FE model of the target bridge was reconstructed based on the actual scene model and the bridge’s internal parameters obtained by big data and expert prior information. The modal frequency error of the Midas model was less than 2%， and the calibration coefficient of the static load test was 0.57~0.79. The research results show that the bridge FE model established by UAV oblique photography is reliable and accurate， which can facilitate bridge health monitoring and seismic analysis， and has scientific and engineering value.

Abstract:Based on the wind tunnel test of the single-span transmission line aeroelastic model， the characteristics of displacement spectrum， aerodynamic force spectrum， aerodynamic damping， and gust response factor for single and 4-bundled conductors are investigated， and the effects of wind speed， conductor bundled number and intensity turbulence are discussed. The results show that the multi-modes are significantly involved in the wind-induced vibration of the conductor， and the modal frequency increases nonlinearly with the increase of wind speed while the frequency increases more obviously at high turbulence. The response spectrum energy for the conductor increases with the intensity of turbulence and bundled number， and a multi-bundled conductor and high turbulence can shift the vibration energy of the conductor to a lower frequency. The background component of conductor aerodynamic force increases overall with the increase of wind speed and intensity turbulence and decreases with the increase of bundled number. The trend of aerodynamic damping ratio with increasing wind speed and intensity turbulence is not obvious. The conductor aerodynamic damping ratio of the first-order mode is about 5~9 times that of the no-wind state， and about twice that of the second-order mode. The gust coefficient of displacement is significantly lower than that of drag， and the two kinds of gust coefficients increase overall with the increasing turbulence.

Abstract:To address the fatigue cracking issue and the resultant maintaining difficulties of orthotropic steel bridge decks （OSDs）， which are common in long-span steel bridges， the research group at Hunan University proposed a new UHPC-based strengthening structure and with this strengthening technique， the fatigue cracks in OSDs can be exempt from repairing. Based on a long-span in-service suspension bridge as the research subject， this paper introduces the application background of the new strengthening technique， and presents a series of in-site experimental tests that were performed to reveal the response of the OSD under three states， i.e.， with original the asphalt overlay， with no overlay， and with a UHPC strengthening layer. The fatigue performance of four typical fatigue-prone details in the OSD was systematically revealed based on the test results， including the stress distribution as well as the stress reduction after strengthening. At the same time， a local finite-element （FE） model was established for the bridge and the load cases considered in the experimental tests were simulated in the FE model. It was found that the stress response surfaces of the fatigue-prone details are basically consistent with the corresponding test results， and the maximum difference is about 10%. The research results show that for each fatigue-prone detail， the stresses exhibit no significant differences under two states， i.e.， with the original asphalt overlay and without overlay， indicating that the original asphalt overlay deteriorated seriously and could not effectively improve the mechanical state of the OSD. The stresses of the fatigue-prone detail were reduced by 41%~85% when the OSD was strengthened by a thin UHPC layer. For the fatigue-prone detail of the U rib-to-deck plate welded connection， the stresses were reduced by 85%， while for the fatigue-prone details at the upper cutouts and at the intersections between the U rib and diaphragm， the stresses reductions were revealed as 44% and 41%， respectively. This confirms that the thin UHPC layer could significantly improve the local bending stiffness of the OSD and consequently reduce the stresses caused by vehicle loads. Moreover， the response lines were obtained for different fatigue-prone details in the OSD and it was found that the response lines differ significantly for different fatigue-prone details. For the fatigue-prone detail near the upper cutout， the transverse response scope of the compressive stress is small， while the transverse response scope for the tensile stress is larger. Furthermore， the longitudinal response scope for the fatigue prone detail near the upper cutout is also short. For the intersections between the U rib and diaphragm， the stress is maintained at a high level even though the distance between the vehicle load and the fatigue-prone detail exceeds the spacing of 3 successive diaphragms or cross beams.

Abstract:To address the problem of the reduced efficiency of prestress introduction in the supporting area due to the wrinkle effect of corrugated steel webs restrained by concrete lining， a new lining with chute-stud connection encasement is proposed. In order to explore the influence of new lining on the wrinkle effect and shear performance of corrugated steel webs， I-steel beam specimens with pure corrugated webs and new lining composite corrugated webs are designed. A numerical simulation scheme is established through the sensitivity analysis of the constitutive relationship， welding residual stress， and geometric initial defect amplitude. The numerical simulation results are compared with the experimental results in the literature to verify the rationality of the simulation scheme. Then， the axial stiffness， strain distribution， buckling mode， and shear strength of the newly lined composite corrugated web and the pure corrugated web are compared. The results show that the numerical simulation scheme can accurately simulate the buckling mode， ultimate bearing capacity， and strain distribution of the structure. After the new lining is installed， the axial stiffness of the beam structure with composite corrugated webs is basically unchanged. The distribution of the normal strain and the shear strain of the pure corrugated web and the newly lined composite corrugated web is basically the same， and the normal strain obeys the quasi plane section assumption， and the shear strain uniformly distributes along the height of the web. The buckling modes of the front and rear webs of the new liner are both interactive buckling modes. After the new lining is installed， the ultimate bearing capacity of the structure is increased by about 23%， and the vertical deflection at failure is increased by about 71%. The new lining improves the out-of-plane stiffness of the web and restricts the development speed of out-of-plane displacement in the early stage. In the late stage of loading， the existence of the new lining limits the development degree of out-of-plane displacement.

Abstract:To realize reasonable evaluation of the seismic behavior of in-service reinforced concrete （RC） shear walls under a frost action environment， using the relative dynamic elastic modulus as the freeze-thaw damage coefficient and combining with the modified Petersen model， a non-uniform freeze-thaw damage model is constructed. With the existing formula by accurately verified， the shear hysteretic model of intact RC shear walls is established. Then， by analyzing the variation trend of shear strain and shear force of the frozen-thawed damaged RC shear wall affected by parameters， the shear hysteretic model of frost-damaged RC shear wall is established by multi-parameter regression analysis. Based on the existing material data， the bond strength model of uneven freeze-thaw damage is established. At the same time， combined with the existing bond-slip model， the slip model of uneven frozen longitudinal reinforcement is established through theoretical derivation. Combined with the established non-uniform freeze-thaw damage model， freeze-thaw shear hysteretic model， and freeze-thaw non-uniform bond strength slip model， a numerical model of freeze-thaw damaged shear wall components is proposed. Finally， the accuracy of the proposed numerical model is verified by using the quasi-static measured data of 8 freeze-thaw damaged RC shear walls with different parameters. The results show that the numerical model established in this paper can accurately simulate the load-deformation relationship of freeze-thaw damaged RC shear walls under low-cycle cyclic loading， and can be used to evaluate the seismic performance of RC shear walls under freeze-thaw environment.

Abstract:To evaluate the seismic performance of Q690D steel box-section frame columns， based on a low-cycle horizontal reciprocating loading test on three welded box-section steel columns， the finite element modeling method verified by the test results was used to establish 30 FE models with different width-to-thickness ratios under four seismic grades. The seismic performance was analyzed from the aspects of the hysteretic response， skeleton curve， ductility coefficient， and the development of cross-section plasticity. The results show that the ductility coefficient of the Q690D steel box-section frame column is small， which is between 1.68 and 2.55. When the axial compression ratio is large， the ultimate inter-story drift angle is less than 0.02， which does not meet the required limit value of 1/50 of elastic-plastic drift angle in GB 50011―2010 Code for Seismic Design of Buildings. So， it is recommended that the limit value of the axial compression ratio should not exceed 0.5 in seismic design for high-strength steel structures. The plastic development coefficient and component ductility decrease with the increase of width-to-thickness ratio and axial compression ratio. It is unreasonable that the seismic code only uses the width-to-thickness ratio as the only factor to distinguish the seismic grade， and the influence of the axial compression ratio on seismic performance needs to be considered.

Abstract:The preparation of composite cementitious materials from tailings is an important way to realize the utilization of tailings industrialization resources and reduce carbon emissions in the construction industry. This paper focuses on the activation mechanism and hydration characteristics of gold ore tailings under different activation methods. High-temperature activation， mechanical activation， and chemical-high temperature-mechanical composite activation were used to enhance gold tailings activity， and the influence of activation methods on gold tailings activity was analyzed. The water consumption and standard consistency setting time were measured to analyze the effect of different gold tailings content on the physical properties of composite cementing materials. The activation mechanism and hydration characteristics of gold tailings were revealed by XRD analysis， SEM analysis， and pozzolans property test. The results show that the activation effect is as follows： chemical-high temperature-mechanical composite activation>high temperature-mechanical composite activation>mechanical activation> thermal activation. Under the chemical-high temperature-mechanical composite activation， the compressive strength ratio of the gold tailings mortar test block in 28 days was 74.98% and 58.25% higher than that of the original gold tailings. The crystallinity of the main mineral phases of gold tailings tends to decrease after high-temperature activation or mechanical activation， but the activity of pozzolanic ash is low. The presence of CaO is helpful for further reducing crystallinity， and the alkaline environment provided in the hydration reaction process can obtain active SiO2 and Al2O3， and accelerate the reaction of Ca（OH）2 with active SiO2 and Al2O3. The content of C—S—H gel and aluminate hydrate increases， the structure is denser， and the compressive strength is improved.

Abstract:The technology of recycled aggregate concrete （RAC） is an effective way to realize the resource utilization of construction waste. By collecting the data on the chloride ion corrosion test and carbonation test of RAC， variables related to materials and test environments were set as input parameters. The electric flux and carbonation depth were used to quantify the RAC’s resistance to chloride ion corrosion and carbonation， respectively. The machine learning methods were used to construct the prediction models of durability for RAC. On this basis， taking strength， durability， and cost as the optimization goals， the optimal design method of the RAC mixture was proposed by combining the NSGA-Ⅱ algorithm and the technique of order preference similarity to the ideal solution. Results show that the gradient boosting tree model can predict the RAC’s resistance to chloride ion corrosion better than other models， and the Gaussian process regression model has the best performance in predicting the RAC’s resistance to carbonation. A low-cost RAC mixture that meets the requirements of durability and mechanical properties was obtained with the proposed mixture optimization design method， which can be used to guide the construction mix design.

Abstract:To study the tensile mechanical properties of basalt textile reinforced highly ductile concrete （TR-HDC）， 36 sets of TR-HDC dog-bone tensile specimens were designed and manufactured. The effects of the textile reinforcing ratio， PVA short fiber content， matrix type and mesh spacing （5mm， 10mm） on the tensile mechanical properties of TR-HDC were studied through uniaxial tensile tests. The research results showed that with the increase of the textile reinforcing ratio， the tensile strength of the TR-HDC specimens were significantly improved， and the multi-cracking characteristics were obvious. The adding of PVA short fiber effectively improved the interface property between textile and matrix， which prevented the stripping of base， reducing the slip between textile and matrix. Thus， the strength utilization rate of textile were improved. As the mesh spacing increased， the PVA short fiber can easily pass through the mesh and fully contact with the fiber bundle. This effect increased mechanical anchorage between textile and matrix， thus contributing to the improvement the strength utilization rate of the textile. The change of fly ash admixture in the matrix had little effect on the tensile strength of TR-HDC specimens， while the specimens with more fly ash content showed larger strain and smaller crack spacing. Based on regression analysis of the test results， the simplified TR-HDC uniaxial tensile strength calculation model is proposed by considering the coupling effect of PVA short fiber content and textile reinforcing ratio.

Abstract:To study the dynamic response characteristics of large-diameter variable cross-section pile group foundations under different types of seismic waves in soft soil site conditions， the shaking table test was carried out based on the solid project of Xiang-An Bridge. The synthetic 5010 and 1004， Kobe， and El-Centro waves with a ground motion intensity of 0.15g were selected in the test. The dynamic response characteristics of the pile group foundation， such as the seismic settlement of soil around the pile， acceleration of the pile body， horizontal displacement of the pile top， and bending moment of the pile body， are studied experimentally. The test results show that under the action of the earthquake， the soft soil layer has seismic subsidence， and the amount of seismic subsidence is in the range of 0.16 ~ 0.22 cm， which is related to the spectral characteristics of the input seismic wave. The acceleration time history response curve of the pile end is more “dense”， and the soft soil has an amplification effect on the acceleration. The peak acceleration of the input seismic wave appears earlier than the pile end， the pile top， and the variable section. The acceleration of the pile and the horizontal displacement of the pile top reach the maximum under the action of the 1004 wave and Kobe wave， respectively. Under the 5010 and 1004 waves， the pile top produces permanent lateral displacement. Under the Kobe wave， the peak bending moment of the pile is the largest， and the peak bending moment appears the latest. Therefore， in the seismic design of pile group foundations， different seismic wave types can be selected for different pile foundation characteristics.

Abstract:The quartet structure generation set （QSGS）， as well as improved QSGS， were used to equivalently reconstruct the three-dimension（3D） isotropy and anisotropy pore structure of the real soil. Combined with the lattice Boltzmann method （LBM）， the numerical simulation of the seepage field employing the MATLAB automatic program was carried out to explore the influence of different pore parameters and model anisotropy on seepage characteristics. The results showed that when the mesh size of the 3D model was 100×100×100， the maximum increase of pore connectivity rate nc reached 19.23 %. The fluid preferred to form the main seepage channel in the position with good connectivity and large pore throat diameter， and there was a “finger-in” effect. The closer the fluid was to the axis of the channel， the greater the flow velocity was. The calculated permeability k of 3D reconstructed soil increased with the increase of model porosity n and decreased with the decrease of soil particle size. When the distribution probability Pc was 0~0.05， the permeability k decreased significantly， and the reduction was 42.86%. The seepage velocity at the outlet boundary of the reconstructed model considering anisotropy fluctuated greatly and irregularly. The streamline distribution streamline sparse and interlaced， with no prominent main seepage channel. This study can better reveal the flow law of fluid in the 3D pore structure and provide some references for the research methods of 3D soil reconstruction and meso-seepage simulation.

Abstract:To address the limitations of the Ubiquitous-Joint model which does not consider the effects of joint length， joint spacing， and joint stiffness， the parameters of the Ubiquitous-Joint model in FLAC3D were calibrated using triaxial compression numerical tests and parameter calibration criteria. The distinctions of modeling results between the Ubiquitous-Joint model and the 3DEC model including the deformation， the plasticity zone， and the maximum principle stress were compared and analyzed by an example of circular tunnel excavation. Based on the Xinhua Mountain Tunnel project with typical layered rock mass， the deformation and failure mode were analyzed with the calibrated Subiquitous model and discrete element method after the tunnel was excavated and primary support finished. Finally， the deformation and plastic zone of surrounding rock influenced by bedding angle was discussed， which further verified the applicability of the calibrated Subiquitous model in engineering. The results confirm that the calibrated Subiquitous model is capable to well describe the anisotropic behavior of layered rock， which can be applied to similar engineering projects.

Abstract:To study the influence of circumferential joint leakage， taking Shanghai Metro Line 1 as the engineering background and based on the finite element analysis， this paper establishes a three-dimensional shield tunnel joint leakage model and the iterative relationship between the joint permeability coefficient and curvature radius of the longitudinal settlement curve to realize the dynamic evolution of the joint permeability coefficient based on the joint opening size. The results of the dynamic evolution of the joint permeability coefficient were compared with the results of the constant permeability coefficient. The results show that the assumption of an unchanged permeability coefficient significantly underestimates the harmful degree of tunnel leakage and the dynamic evolution model of permeability coefficient should be adopted for research. After the leakage of the circumferential joint occurs， the ground emerges a settlement funnel， which results in the tunnel’s uneven settlement in the longitudinal direction. Therefore， the joint opens， and the lining flattened deforms. The principle of "early detection and early treatment" should be emphasized in dealing with the problem of tunnel leakage. The treatment work should be completed within 0.2 years after the occurrence of leakage at the latest.

Abstract:To analyze the influence of shield tunneling reception on the additional stress of work shaft enclosure structure， taking a shield work shaft as the supporting engineering， a calculation method for additional stress of work shaft enclosure structure caused by bulkhead additive thrust of shield cutter head， friction force between shield shell and soil， synchronous grouting pressure and soil loss was proposed by establishing mechanical model of work shaft enclosure structure in the shield tunneling reception period， based on Mindlin stress solution of elasticity mechanics and Sagaseta formula. The main influencing factors of the additional stress of the work shaft enclosure structure were calculated and analyzed， and the mechanical behavior of the work shaft enclosure structure during receiving period was studied by numerical simulation. The principle of the shield tunneling proximity control was formed based on engineering examples. The results show that： 1） the influence range of additional stress of work shaft enclosure structure increases with the increase of shield tunnel diameter and mainly occurs in the 1.5 times of shield diameter. The depth of the shield machine has an important influence on the maximum value of additional stress. 2） The total additional stresses are mainly caused by frontal additional thrust and friction between shield shell and soil， accounting for about 1/3 and 2/3， respectively. The additional stresses caused by synchronous grouting and soil loss are negligible when compared with the first two. 3） The theoretical calculation and numerical simulation results of total additional stress are basically the same， which verifies the reasonableness of the calculation method. At the same time， the numerical simulation shows that the bending moment and deformation of the enclosure structure of the working well during the receiving period of shield tunneling increase by about one time， which should be paid attention to in the receiving construction of shield tunneling. 4） Based on the calculation and analysis results of the additional stress of the work shaft enclosure structure caused by the excavation speed， the principle of “low speed” reception is adopted in the key receiving interval of the project （10-0 rings）， which ensures the safe receiving of shield and provides a reference for similar projects.

Abstract:Aiming at the problem that the unreasonable design of the traditional Heated Kang leads to uneven surface temperature， worse thermal comfort， and low thermal efficiency， a heterogeneous design method for traditional Heated Kang was proposed in this study. Meanwhile， in order to better reveal the design principle of this new Heated Kang and analyze its thermal equilibrium and thermal comfort， the influence of the vertical hole rate （VHR——the proportion of the vertical hole area to the overall area of Heated Kang）， the thickness of the heat storage layer， the temperature of the inlet flue gas， and inlet and outlet positions of Heated Kang on the thermal uniformity and thermal comfort were investigated by CFD. The results showed that the combination with the vertical hole rate of 83%， the thickness of the heat storage layer of 80-50-20 mm （80 mm in Zone Ⅰ， 50mm in Zone Ⅱ， and 20 mm in Zone Ⅲ）， the inlet flue gas temperature of 275℃， the inlet and outlet positions in the form of turn-around is optimum ones. A uniform Kang surface temperature can be obtained with a standard deviation of 5.6 ℃ and a higher average temperature of 36.4 ℃. Additionally， the surface heat balance of the Heated Kang is significantly improved by 50% by adopting the heterogeneous design method of the internal structure. The design of the turn-around not only makes the temperature of the Kang surface more uniform but also increases the temperature of the Kang tail by 9.1℃. This work provides a new idea for the energy-saving design and improvement of thermal efficiency of traditional Heating Kang and has important reference value for the further research and development of Heating Kang.

Abstract:This paper proposes a method to control structural vibrations by arranging obstacles to divert the bidirectional crowd flow. A modified social force model that takes into account pedestrian self-stopping and deceleration avoidance is used to simulate the bidirectional crowd movement. Each pedestrian is regarded as an MSD model to establish a coupled system of human-structure interaction and vibration control equations， and calculate the vibration response of the structure. A laboratory footbridge is used as an example to investigate the effect of obstacle placement on pedestrian walking characteristics and structural vibration， and to explain the damping mechanism from an energy perspective. The results show that the structural vibration caused by the bidirectional crowd density exceeding 0.6 pedestrians per square meter leads to pedestrians’ discomfort， and after arranging four obstacles on the pedestrian bridge， the vibration reduction rate reaches 12.4% and 13.1% for the two directions with one pedestrian and two pedestrians， respectively， and the energy input to the structure is significantly reduced. The reduction rates of mass kinetic energy， viscous damping energy， and elastic strain energy output of the structure reached 38.46%， 67.48%， and 50.68%， respectively. The research can provide ideas for vibration reduction methods for large-span pedestrian bridges.

Abstract:Composite box girder with corrugated steel webs has small torsional stiffness and is easy to produce warping deformation. To reasonably calculate the shear stress of single-box multi-cell composite box girders with corrugated steel webs under restrained torsion， the shear flow was decomposed， and constants that can reflect the shear flow transfer mechanism of each cell box wall were introduced based on the shear flow transfer path， longitudinal equilibrium of differential bodies and warping displacement continuity. The practical formulas for section geometrical property and shear stress considering the folding effect of corrugated steel web were deduced. The governing differential equation for analyzing restrained torsion was established based on Reissner’s principle， and an analytical solution was obtained by employing the initial parameter method. The torsional shear stress of the simply supported box girder under an eccentric loading was calculated by the present analytical method and ANSYS finite element method. The shear stress increment coefficient reflecting the effect of torsional shear stress on total shear stress and the shear stress coefficient reflecting the contribution degree of the warping shear stress to the total shear stress were introduced. The influences of girder width and cell number on the shear stress were analyzed. The results show that the present analytical solution agrees well with ANSYS finite element solution. The increase in girder width and cell number can reduce torsional shear stress. The shear stress increment coefficient of the outside web under restrained torsion reaches 1.69， and the total shear stress distribution between webs shows obviously uneven. The influence of warping shear stress on torsional shear stress can’t be ignored. The effect of torsional shear stress on principal tensile stress in the top and bottom concrete slab should be considered in the design to avoid oblique cracks.

Abstract:Hospital outpatient rooms are characterized by high pedestrian flow， high viral load， poor patient immunity， and frequent close contact between doctors and patients， making them a high-risk site for the transmission of respiratory infections. In this study， we first described the behavioral characteristics of patients and doctors during outpatient visits and assessed the risk of cross-infection through questionnaires and on-site research in outpatient rooms of two third-class hospitals in Changsha， followed by experimental tests and CFD simulations to reveal the dispersion pattern of exhaled flow from patients， and finally explored the effectiveness of current prevention and control measures. The results of the questionnaire and on-site research showed that there were many loopholes in prevention and control in outpatient rooms， i.e. windows and air conditioning were not always open， ventilation was poor， there were no purifiers in the room， disinfectant was used less frequently， and there were high-risk behaviors such as removing masks and physical contact. The research found that one doctor in the outpatient room treated up to 70 patients a day， the average length of a patient's visit was around 6~13 minutes， the number of people inside the room could reach up to 6~8， and was often accompanied by people walking around， which tended to accelerate the spread of exhaled flow， so it was necessary to strictly limit the number of people entering the room. Experimental tests and simulations showed significant differences between the trajectories and peak concentrations of exhaled flow from different people， demonstrating the complex nature of human sources. Exhalation patterns have a small effect on peak concentrations throughout， but breathing and speaking can result in high concentrations being maintained in front of the face for long periods. Wearing a mask significantly reduces the horizontal dispersion of pollutants， but causes an increase in dispersion distance in the vertical direction. The results of this study are expected to provide basic information for proposing and improving prevention and control measures in outpatient rooms.

Abstract:Aiming at the problems of many meso parameters of PFC 3D， difficulty in analyzing the influence mechanism between macro and meso parameters， and insufficient interpretability of parameter calibration model， an improved BP algorithm is proposed employing the function with steepness factor， adaptive Nesterov momentum method and adaptive learning rate for lightweight analysis of meso parameters. The comparison with the traditional BP algorithm shows that this algorithm improves the stability and convergence speed of the traditional algorithm and can reasonably and accurately quantify the sensitivity between macro and meso parameters， screen out the key meso parameters and obtain a lightweight macro-meso parameter analysis model. Based on the lightweight model， the correlation and influence mechanism between macro and meso parameters are analyzed， and the influence law of single and multiple key meso parameters on macro parameters is studied. The research shows that the elastic modulus increases linearly with the increase of the equivalent modulus. The parallel bond stiffness ratio can inhibit the growth of elastic modulus， and the elastic modulus decreases greatly when the stiffness is relatively high. There is a linear relationship between Poisson's ratio and stiffness ratio， and the increase of friction coefficient causes the nonlinear decrease of Poisson's ratio. The strength parameters have an incentive effect on the peak strength. The combination of the parallel bond tensile and shear strength at a high level has the most significant impact on the increase in the peak strength. The internal friction angle mainly has an influence on the post-peak strength of the rock. The internal friction angle has a certain control effect on the particle sliding on both sides of the shear zone when the sample is loaded after the peak. The research results have reference values for PFC parameter calibration.

Abstract:Aiming at the disadvantage that manual detection of large-scale wind turbine structures is time-consuming， labor-intensive， and dangerous， an identifying method for dynamic characteristics of large-scale wind turbine structures based on the optical flow method and UAV is proposed. The vibration law of UAV hovering in space was first studied， and the space displacement compensation method of the UAV lens based on background fixed point and self-scale factors was proposed. Then the UAV was used to capture the vibration videos of the wind turbine structure in the edgewise and flap-wise direction， and the optical flow method was used to visually track the monitoring points to obtain its displacement response， which was compared with the traditional monitoring methods in time history domain and frequency domain. Finally， the global modal shapes of wind turbine structure were identified by segmented monitoring method and verified by shaking table test. The results show that the displacement compensation method of background fixed point and self-scale factors can effectively solve the influence of spatial displacement drift caused by vibration during UAV hovering. Combined with the segmented monitoring method， the computer vision monitoring system equipped on UAV can identify the mode shapes of large-scale wind turbine structures well， which can realize long-distance， non-contact， and low-cost structural health monitoring， and provide a basis for the state evaluation of large-scale structures such as wind turbines.

Abstract:Adjacent foundation pit engineering in dense urban areas is easy to cause deformation， structural cracking， and water leakage of shield tunnels with super-large diameters （>15m）. At present， the construction of super-large diameter shield tunnels is in the initial stage， the deformation response law of tunnels under the influence of foundation pits is unclear， and there is a lack of reasonable influence zoning. In this paper， a three-dimensional finite element model of the excavation of the side foundation pit of the super-large diameter tunnel is established by using finite element software. The structural deformation response mechanism of the super-large diameter tunnel is analyzed， and the influence laws of factors such as tunnel buried depth， tunnel-foundation pit spacing， and foundation pit excavation depth are discussed. It is found that "bulge belly" horizontal displacement and "spoon" vertical displacement towards the foundation pit are caused by the excavation of the foundation pit. Compared with the small-diameter shield tunnel， the large-diameter shield tunnel presents a weaker longitudinal deformation and more significant transverse deformation. The tunnel deformation decreases with the increase of tunnel-retaining wall distance， increases first， then decreases with the burial depth， and increases with the excavation depth. After normalization by the excavation depth， the maximum tunnel deformation and distance can be fitted well by an exponential function. A normalized influenced zone was proposed， which provides an important reference for the protection of the large-diameter shield tunnels in engineering practice.