Abstract:In order to investigate the seismic behavior of diagonal-reinforced coupling beams with a small span-depth ratio， the equivalence of the two reinforcement arrangements （individual diagonal reinforcement and full diagonal reinforcement） is verified. Six RC diagonal-reinforced coupling beams were tested under cyclic loading considering the effect of variable parameters such as span-depth ratio and layout of reinforcement. Test device adopts double wall-column loading， so that the coupling beam can realize equal double curvature bending. The test results show that the failure mode changed from bending failure to shear failure with the decrease of span-depth ratio， and ultimate rotation decreased from 4.89% to 1.98%. Two types of diagonal reinforcement coupling beams have close mechanical performance. The limit of shear compression ratio in national code JGJ 3 is reasonable. Based on a database analysis of diagonal-reinforced coupling beams， a new shear capacity formula is obtained. The new calculation formula is more accurate than that in current standard， and reflects the force mechanism better.

Abstract:To improve the progressive collapse resistance of RC frame structures， one of the often-used methods is to increase the reinforcement amounts of longitudinal reinforcement in girders. However， this method may lead to the adverse failure mode of “strong beam-weak column” under earthquakes. In view of this， an alternative method that has the advantage of improving the progressive collapse resistance of the RC frame structures without affecting their seismic performance is proposed in this study， which uses kinked steel plates locally debonding and embedded in the RC girders. First， low-cycle reciprocating tests were conducted on RC beams using kinked steel plates with different height-to-length ratio （ratio of the height hkp to the length lkp of a kinked steel plate）. Test results identify that the RC beam with an appropriate height-length ratio of 3/40 has similar behavior to the conventional RC beam in terms of bearing capacity， stiffness degradation characteristics， energy dissipation capacity and deformation mode. Furthermore， parametric analysis was carried out using numerical simulation， revealing appropriate height-length ratios ranging from 1/8 to 1/16. Finally， pushover and pushdown analyses of the designed RC frame structure were conducted. The results show that the employment of kinked steel plates with an appropriate height-to-length ratio （taking 1/10 in case study） exhibits little effect on seismic performance of structures， but largely improves their progressive collapse resistance.

Abstract:The Horizontal Seismic Decrease Coefficient （HSDC） is an important parameter in seismic isolated design. This paper investigates the influencing factors of HSDC theoretically in the Two-Degree-of-Freedom equivalent vibration system， in which the stiffness ratio of superstructure to isolation layer （SRSI） is regarded as a basic variable. The equivalent converting coefficient of the superstructure was calculated by mode-shapes analysis. The internal force and HSDC were both derived and expressed in SRSI， and then the influencing factors of HSDC were analyzed. The limits of SRSI， required for the seismic isolation structure to meet the requirements of HSDC， were calculated according to the design codes. The fixed curve of HSDC was found and defined as the Datum Curve， as well as the concept of Datum Points in HSDC was further proposed for design. The results show that： HSDC is determined by SRSI and the damping ratio of the isolation layer， and furthermore， HSDC decreases with the increase of SRSI and the damping ratio of the isolation layer； the HSDC is lower than 0.5 or 0.4 when SRSI is greater than 4.5 or 8， respectively； the HSDC’s expression gives accurate estimates when comparing with 5 example projects. The results are arranged into tables for reference.

Abstract:In order to solve the structural dynamic response caused by nonzero initial condition and external load in the discrete frequency domain， a new frequency domain algorithm is constructed. The discrete Fourier transform （DFT） of Diarc δ function and its first derivative is derived based on the Fourier transform （FT） and finite difference formula. With this new algorithm， the numerical divergence of dynamic response caused by nonzero initial displacement in the traditional frequency domain algorithm is effectively overcome. Three numerical examples are used to further study the performance of this algorithm. They are a linear system of single degree of freedom （SDOF）， a 4 000-DOF truss structure， and a cantilever beam with concentrated mass at the top， respectively. These structures all have nonzero initial displacement and initial velocity. The numerical results show that the improved frequency domain algorithm provides consistent results with the traditional numerical method， and has higher accuracy and efficiency， which is suitable for solving the dynamic response of various linear vibration problems.

Abstract:To improve the energy dissipation capacity and construction benefit of prefabricated shear walls， a new type of prefabricated shear wall structure with the function of friction shear resistance and energy dissipation was proposed， and the seismic performance tests were carried out. To make up for the insufficient quantity of specimens and accurately determine the design requirements of the optimal slip load， based on the seismic performance test results of the proposed structure， this paper discussed the establishment method of the corresponding high-precision finite element model. The multi-parameter analysis of structural seismic performance was carried on. At last， based on the finite element analysis results and the working principle of the new prefabricated shear wall， the optimal slip load was determined. The results show that the proposed new prefabricated shear wall has good hysteretic energy dissipation capacity. Bolt preload， steel friction coefficient and total bolt distance have significant effect on the seismic performance of the structure， and they can be used as the main design parameters of the structure. Vertical load， steel plate thickness and steel elastic modulus have little effects and can be ignored. When the slip load is set as the yield load of the wall， the energy dissipation value of the structure model reaches the peak， and the energy dissipation coefficient begins to decrease significantly. Therefore， the yield load of the wall can be determined as the optimal slip load of the structure.

Abstract:To evaluate the load-carrying capacity of concrete frame structures under dynamic loads in case of sudden column failure， this paper is based on the multi-stage repeated collapse dynamic tests of mid-column removal in reinforced concrete （RC） and fully assembled precast concrete （PC1 exposed corbel dowel rob nodes） concrete frame substructures carried out by the research team， the accuracy of the sub-structural detailed finite element model established by the ABAQUS software was verified by fitting the displacement response curves under primary collapse load conditions， and the damage resistance of the frame structure to progressive collapse was quantified and evaluated using the column removal method. Since the research team tests were multiple repetitive collapse tests， it was not possible to obtain the load-carrying capacity in one collapse for the RC and PC1 （exposed corbel dowel rob nodes） specimens， and dynamic load tests were not conducted for the fully assembled precast concrete （PC2 hidden corbel dowel rob nodes）. The final damage loads of the RC， PC1 and PC2 frame structures were predicted using the trial algorithm based on the accurate calibration model， and the failure modes and damage conditions of the three structures were compared and analyzed. During the failure， the RC beam-column was severely damaged， the reinforcement at the beam end was pulled off， the concrete at the connection area of the fully assembled precast concrete beam end was crushed， and the dowel rob was sheared off. The collapse resistance of the reinforced concrete specimen was significantly higher than that of the fully assembled precast concrete specimen， and it was also found that the collapse resistance load-carrying capacity of the fully assembled precast concrete structure can be improved by strengthening the steel angle cleat of the assembled structure.

Abstract:The external prestressed tendon is regarded as a constant strain member consolidated and connected with the beam at the anchorages and the deviators，respectively. Based on the geometric relationship of the external prestressed tendon and beam body at the anchorages and the deviators， the tangent stiffness matrix and resistance of the tendon end in the structural coordinate system are derived by the co-rotational （CR） method. Combined with the conventional CR plane beam element， a geometric nonlinear finite element model is established and the program is compiled. The geometric nonlinear analysis of the example in two cases is carried out and compared with results obtained by ABAQUS. The results show that the beam-ends horizontal displacement， the middle-span vertical displacement and the axial force of the external tendon calculated by the two methods are in good agreement， for both prestress application state and load application state. For the axial force of the external tendon， the proposed method can better reflect the mechanical performance of the external tendon as a constant strain member， which can be used for the nonlinear finite element analysis of the externally prestressed structure.

Abstract:The traditional Kiewitt reticulated single layer shell mesh was optimized by the method based on the Spring Force between nodes and the Laplacian Smoothing method， and two new spherical mesh forms are obtained. Firstly， the calculation principle and process of the two algorithms are introduced： the method based on the force between the nodes assumes the member as a spring， and moves the node in the direction of the unbalanced force， so as to obtain a grid （SF mesh） with a more uniform length of the member. At the same time， a smoother mesh （LS mesh） can be obtained by using the Laplacian smoothing method. Then， the Kiewitt mesh， SF mesh， and LS mesh were compared. In terms of geometric indices， the average length of the member， the change rate of member length and the shape coefficient of the mesh triangle of the three kinds of reticulated shells were compared. In terms of mechanical properties， the elastic strain energy and nonlinear stability bearing capacity of three kinds of reticulated shells under different load modes are compared. The numerical analysis results show that the SF mesh has better geometric indices than the LS mesh. In most cases， the SF mesh and LS have lower strain energy； and the stability ultimate bearing capacity of the three meshes is relatively close. On the whole， the SF mesh has the best overall mechanical properties； the LS mesh has the best mesh fluency； SF mesh and LS mesh are both better than the traditional Kiewitt reticulated shell.

Abstract:The traditional fiber element does not consider the constraint of the fixed end， which leads to the reduction of numerical simulation accuracy of reinforced concrete （RC） columns. The impact of the fixed end constraint on the damage pattern of RC columns and the simulation accuracy of the fiber unit was analyzed. 45 RC columns with a high shear span ratio in the literature were selected and the solid element models were established for numerical simulation. The results show that the modeling method is reasonable and reliable. The restraint mechanism of the fixed end and the influence of the restraint effect of the fixed end on the bearing capacity and ductility of RC columns were then explained. The control section position and its load-carrying capacity calculation method were defined， and the corresponding relation between the numerical integration point position and the control section position， and between the weight coefficient and the equivalent plastic hinge length was clarified. Finally， the formula for calculating the control section position and the equivalent plastic hinge length considering the influence of the fixed end constraint was proposed， and a fiber element simulation method considering the influence of the fixed end constraints was built. Through the numerical simulation analysis of 45 RC test columns in the literature， it is shown that the proposed method can reasonably consider the influence of fixed end constraints and has good applicability.

Abstract:The elevated temperature tests on four relatively large-scale reinforced reactive powder concrete （RPC） beams and a reinforced normal concrete （NC） beam were performed under constant bending load， followed by bending test after exposure to high temperature， in order to evaluate the fire resistance of reinforced RPC beams. The cross-sectional temperature filed and deflection development at the mid-span position were measured under elevated temperature. The influence of the control temperature and the wrapped mortar layer on the flexural performance were also analyzed through the bending test on the specimens after high temperature. The results show that the explosive spall phenomenon of reinforced RPC beams can be effectively avoided by adding 2% steel fiber and 0.3% Polypropylene fiber （volume dosage） into RPC mixture. Control temperature has important effect on the deflection development of RPC beam under high temperature and its residual flexural performance after the elevated temperature test. After RPC beams were subjected to high temperature of 600℃ and 800℃， their residual flexural carrying capacities was decreased by 13% and 24%， respectively. Wrapping mortar layer on the surface of RPC beam can effectively reduce the high temperature damage and improve the residual bending properties after high temperature. Compared with the reinforced NC beam， the reinforced RPC beam exhibits relatively higher mechanical stability and safety after a high temperature test. Based on the equivalent temperature of cross section， calculation formulas are proposed for predicting the flexural mechanical performance of RPC beam after exposure to high temperatures.

Abstract:The shear performance of geopolymer concrete was studied by direct shear test. Sixteen test cases were set up， including three cases with ordinary concrete strength for benchmarking. The test results show that the shear strength of geopolymer concrete increases significantly with the increase of concrete strength and shear reinforcement ratio， and decreases with the increase of the shear plane height. The shear plane width has insignificant influence on the shear strength. The modes of shear crack growth and shear failure of the geopolymer concrete are consistent with those of the ordinary concrete while its ultimate shear strength is slightly higher than that of the ordinary concrete. The mean ratio of the experimental shear strength to the theoretical value by Loov and Patnaik is 1.21， with the Loov and Patnaik value being the closest to the experimental value compared with other theoretical values.

Abstract:In order to study the electrochemical characteristics of reinforced concrete with different mineral admixtures after carbonization， the electrochemical workstation was used to conduct non-destructive testing regularly， and the changes of the microstructure of reinforced concrete during the carbonation cycle were analyzed by electrochemical parameters such as polarization curve and AC impedance graph. Kramers-kronig conversion was used to verify the AC impedance data， and an appropriate equivalent circuit was selected to perform electrochemical parameter fitting. Chi-square test was used to verify the fitting degree of parameters. The results show that the equivalent circuit R（QR）（QR） can effectively fit the electrochemical impedance spectrum of reinforced concrete in carbonized environment， and the chi-square value of equivalent circuit fitting is recommended to be less than 10-4 orders of magnitude. In the carbonization corrosion environment， with the increase of carbonization period， the resistance value of concrete shows a trend of fluctuation increase， and the resistance of steel shows a trend of fluctuation decrease. Polarization curve with the increase of carbon cycle entirely moves to the corrosion current density and negative potential direction， at 49 d， the reinforcement corrosion degree was from big to small order as the mixed system， single doped system， the benchmark system， three mixed system， and single with double mixing system concrete is nearly at medium corrosion state， while benchmarking and three concrete mixing system is still in the low state of corrosion. Under different gel systems， the single and double doped reinforced concrete is more sensitive to carbonation corrosion environment， while the triple doped reinforced concrete has the best carbonation resistance.

Abstract:The fatigue life of polypropylene fiber reinforced concrete （PFRC） under constant-amplitude fatigue uniaxial compression at multiple levels was investigated. A total of 180 specimens were made taking into consideration of two factors： tested with polypropylene fiber aspect ratios and volume fractions and aspect ratios taken into consideration， with an emphasis on the fatigue failure mode， fatigue deformation behavior， and a fatigue equation is established. The results showed that three failure modes of PFRC can be classified： splitting failure， wedge failure and shear failure. Meanwhile， the failure section of the specimen could can be divided into three zones： fatigue source zone， fatigue crack stable propagation zone and instantaneous fracture zone. In addition， the PFRC specimen with an aspect ratio of 280 and a volume fraction of 0.2% provides the highest fatigue strength among all the designed specimens， and its fatigue strength is increased by up to 33.83% when compared with plain concrete. Finally， a unified fatigue equation was developed in consideration of fiber parameter， which can concisely describe the relationship between stress level， fatigue life and fiber parameter at a certain failure probability. The research provides a reference for the future development of design specifications and analysis of PFRC structures under cycle dynamic loads.

Abstract:Based on the numerical simulation method， the influence of projecting slab length on flutter stability of steel truss girder suspension bridge is studied. The flutter stability of the initial design girder （projecting slab length L is 0.947 m） at different attack angles for the originally designed section of some suspension bridge steel truss girder was tested by wind tunnel test， and the results were compared with that of CFD to verify the reliability of the numerical method. Based on the study on the input energy value of aerodynamic force in a single period and the evolution of flow field under the same reduced wind speed， the influence of projecting slab length （0.0L， 0.5L， 1.0L， and 1.5L） on the flutter stability of steel truss girder is obtained. The results show that the influence of projecting slab length on the flutter stability of steel truss girder is not obvious at the positive attack angle， but the flutter stability of steel truss girder with a 1.5L projecting slab is significantly better than other conditions at 0° and negative attack angle. The change of pressure caused by the movement of the vortices on the upper surface and the change of the pressure on the windward side of the lower surface at 0°attack angle become the dominant factors of the aerodynamic force. The direction of the aerodynamic force is consistent with that of the steel truss girder， which promotes the divergence of torsional vibration. However， increasing the length of the projecting slab weakens the scale of the vortices on the upper surface， and forms a relatively stable pressure region at the projecting slab. There is no obvious vortex on the upper surface at negative attack angle steel truss， and the evolution of vortices on the lower surface and pressure change become the dominant factors of flutter divergence. Increasing the cantilever arm can weaken the scale and intensity of the vortex on the lower surface， and continuously form a stable negative pressure zone on the lower surface of the windward cantilever arm. The energy input of aerodynamic force is negative.

Abstract:The welding temperature fields and residual stress distribution of the Q345 I-girder with corrugated steel web were studied through numerical simulation and experimental methods. The thermoelastic-plastic three-dimensional finite element models of the I-girder with corrugated steel web were established by using the complete coupling method， and the welding temperature fields and stress fields were obtained. By defining multiple research paths in the finite element models， the distributions of longitudinal and transverse residual stresses of the I-girder with corrugated steel web under different welding paths were studied. In the welding process of the I-girder with corrugated steel web， the infrared temperature measurement method and resistance strain gauge method were used to study the welding temperatures and residual stresses. The results show that the numerical simulation results of welding residual stresses are in good agreement with the measured results， which verifies the correctness and feasibility of the numerical simulation method. During the welding process， the stable temperature of the heat source center is up to 140 1 ℃， and the temperature away from the heat source center decreases rapidly. When the distance from the heat source center is more than 25 cm， the temperature approaches room temperature. The maximum von Mises stress of the weld at the bending corner of the corrugated web is 395 MPa， which is much higher than the yield strength of the material. The longitudinal residual stresses on the web surface 0.5 cm away from the weld is up to 351 MPa， while the transverse residual stress on the web surface fluctuates in the form of parabola， with a maximum value of 48.5 MPa. The welding residual stresses on the I-girder with corrugated steel web are mainly longitudinal stresses， which are mainly distributed within 20 cm from the weld. The research results of this paper can provide a reference basis for the elimination of residual stresses of the I-girder with corrugated steel in practical engineering.

Abstract:Plate stiffener is the most basic form of open stiffener， and its local instability is the main failure mode. In order to study the local stability of plate stiffener， two groups of Q420 open flat plate stiffened panel specimens with different thicknesses and heights were designed for axial compression tests， and the corresponding finite element model was established. The simplified calculation formulas for the local stability of the plate stiffener and trilateral simply supported plate were obtained. The experimental and analytical results show that： when the width-to-thickness ratio of plate stiffener is less than 16， the simultaneous buckling failure of plate stiffener and stiffened plate occurs， on the contrary， the local buckling failure of plate stiffener occurs； With the increase of the width-to-thickness ratio of plate stiffener， the ultimate average stress decreases gradually， and the instability deformation of the specimen becomes more obvious.When the relative width-to-thickness ratio exceeds 1.08， the fitted cubic polynomial fitting curve of the plate stiffener in the member is higher than that of other code curves； When the relative width-to-thickness ratio exceeds 1.32， the fitted cubic polynomial fitting curve of trilateral simply supported plate is higher than that of Euler curve， and it is higher than the curves in Chinese steel bridge code and Japanese code in the whole range of relative width-to-thickness ratio. The fitting formula of plate stiffener in the member can accurately calculate the bearing capacity of the actual specimen， and the fitting formula of a trilateral simply supported plate is safer. It is recommended to use the fitting formula of a trilateral simply supported plate for design.

Abstract:As wind-sensitive structures， the standing seam roof system （SSRS） will be damaged to different degrees or even fail under wind load with different strength grades. To reduce the wind-induced damage， an analysis method of wind fragility is proposed for SSRS based on the multistage performance levels. A mechanical model of the SSRS is established to analyze the failure patterns and the whole process of wind-induced damage； The relative displacement of the large rib nodes of the roof panels is used as the quantitative indicator， and the three-stage performance level and quantitative model of the SSRS is divided and derived； Then， combined with the wind fragility analysis method of probabilistic reliability， the wind fragility analysis is carried out on the SSRS in a typical project. The analysis results show that the fragility curves obtained by the proposed method can well predict the damage state of the SSRS. The wind speed ranges corresponding to light damage， moderate damage， severe damage and wind-uplifted failure are 0~14.9 m/s， 20~26.8 m/s， 30~46.9 m/s and more than 46.9 m/s， respectively， which can be used as a reference for the engineering design and practice of the SSRS.

Abstract:A constitutive relation model under off-axis transverse compression is proposed for ancient wood， which has few parameters， simple physical meaning and easy access to parameters. The constitutive relation model introduces the Sun-Chen constitutive relation model in the field of unidirectional fiber composites， and combines the off-axis transverse compression characteristics of ancient wood to reflect the cumulative damage of ancient wood by a simple method， so as to accurately describe the mechanical response of ancient wood under off-axis transverse compression. Taking the replacement parts of the Forbidden City as samples， seven groups of 70 specimens are made. The corresponding stress-strain curve is obtained through the transverse compression test of specimens. The model parameters are solved by using the test results with off-axis angles of 0°， 45° and 90°， respectively， and the determination coefficient of the main curve is 0.94. Using this model， the yield strength and stress-strain curves with off-axis angles of 15°， 30°， 60° and 75°， respectively， are obtained. The comparison between the model calculation and testing results shows that using a small number of test results， the constitutive relationship model proposed in this paper can accurately calculate the transverse compressive yield strength and stress-strain curve of ancient wood with multiple off-axis angles. The constitutive relationship model can describe the characteristics of Dougong material compression damage， and it is also helpful in the protection of ancient wooden structures.

Abstract:This study aims to comprehensively improve the mechanical properties， permeability and durability of the pervious concrete with recycled aggregate through optimization of cementitious matrix and adding recycled fine aggregate with different content. Firstly， the simplex-centroid design method was used to optimize the ternary cementing system composed of cement （C）， fly ash （FA） and silica fume （SF）， and the high-performance cementitious matrix is obtained. Then， the effects of high-performance cementitious matrix and recycled aggregate content （0%， 30% and 50%） on mechanical properties and durability of pervious concrete were analyzed. The experimental results show that the compressive strength and freeze-thaw durability of pervious concrete with recycled aggregate can be significantly improved by using high-performance cementitious materials， and it can also meet the permeability requirements. When the recycled aggregate content is 0%， 30% and 50%， the 28 d compressive strength is increased by 72.4%， 100% and 44.2%， respectively； the mass loss of 50 freeze-thaw cycles was 1.5%， 2.2% and 2.5%， respectively. In addition， it is found that the failure mode of pervious concrete with recycled aggregate is related to the performance of cementitious material and the content of recycled aggregate， which can provide a reference for the design and application of pervious concrete with recycled aggregate.

Abstract:The water damage of asphalt pavement shortens the service life of pavement， and it can be effectively improved by improving the cohesion of asphalt and the adhesion between asphalt and aggregate. In this paper， 3-aminopropyl trethoxysilane （KH550） was used to modify montmorillonite （NH2-MMT） so as to enhance the cohesion of styrene-butadiene-styrene block copolymer （SBS） modified asphalt. The granite （Gr） aggregate （NH2-GR） was modified by amino-silane KH550 to improve the adhesion between asphalt and aggregate. The montmorillonite and Gr aggregates were characterized by X-ray diffraction （XRD）， scanning electron microscopy （SEM） and X-ray photoelectron spectroscopy （XPS）. The adhesion work of NH2-MMT/SBS modified asphalt to NH2-GR aggregate is increased by 19%， and the peeling work is decreased by 24% by simultaneously increasing the cohesion of asphalt and the adhesion between asphalt and aggregate. Compared with base asphalt， the cohesion work of SBS modified asphalt， NaMMT/SBS modified asphalt and NH2-MMT/SBS modified asphalt is increased by 15%， 22% and 28%， respectively. Compared with base asphalt and Gr aggregate， the cohesion work of NaMMT/SBS modified asphalt and NH2-MMT/SBS modified asphalt is increased by 6% and 12%， respectively. Photoelectric colorimetry was used to test the adhesion between asphalt and aggregate. Compared with base asphalt/Gr aggregate， the UV absorption peak value of NH2-MMT-SBS modified asphalt /Gr aggregate is increased from 0.483 to 0.499. The UV absorption peak value of NH2-MMT-SBS modified asphalt/NH2-GR aggregate increases from 0.474 to 0.557. The results show that the simultaneous modification of cohesive force and adhesive force can effectively improve the water damage resistance of asphalt， and the effect of modified aggregate is more obvious.

Abstract:Aiming at the problems of poor identification accuracy in small sample size asphalt pavement damage classification recognition， five common types of pavement damage were selected. The shallow depth convolutional neural network model based on VGG is designed as an automatic classification method of asphalt pavement damage image. Firstly， the collected image samples are made into data sets for model training. Moreover， three different batch sizes and two different network layers are set up for training， and the most suitable size for the network model is selected so as to obtain the shallow VGG. The processed road image is directly used as the input of the model for training， verification and testing of the model. Finally， the test result was compared with SVM and the current mainstream deep convolutional neural network. The results show that the classification accuracy of the training set， verification set and a test set of shallow VGG is close， the classification and recognition accuracy rate of pavement damage image is more than 98%， which shows the good ability of recognition of shallow VGG. Compared with SVM and the current mainstream deep convolutional neural network， shallow VGG network model takes less time and has strong generalization ability， and can capture more global information. It can be seen that the shallow VGG model has significant advantages in the classification and recognition of small-scale images， it is more robust and the results are more accurate compared with other methods.

Abstract:In order to study the influence of hail disaster on the stability of soil slope， a set of hail falling device was designed independently and the model slope was loaded with self-made ice balls. Three groups of tests were carried out in this paper. The earth pressure was obtained through a high-sensitivity dynamic earth pressure monitoring system， and the impact force was fitted. Particle Image Velocimetry （PIV） was used to monitor the velocity vector change when the puck impinged on the slope， and the normal and tangential restitution coefficients were calculated. At the same time， the displacement change law during the loading process was monitored. The moisture content of slope was monitored by a moisture content monitoring system， and the rule of the water migrating before and after the test was analyzed. The experimental results show that when the loading density and loading times are large， the impact causes shallow sliding of the slope， and the ice puck on the top surface of the slope can redistribute and form accumulation， gradually melt， and form seepage downward. The impact load is formed instantaneously after loading， and it can be fitted as a decaying half-sine waveform. The normal recovery coefficient is small， and the tangential recovery coefficient is large. The puck tends to move along the slope during impact. The water content sensor responds sequentially from top to bottom， the melt water seepage velocity at the rear end of the slope is faster than that at the front end， and water mainly affects the slope top platform. The middle layer of the slope top platform has the fastest water migration speed. The static earth pressure is directly related to the load on the slope top and the seepage of the ice ball melting. The overall deformation of the slope is small， and the maximum deformation is located at the corner of the top of the slope. The experimental results reflect three aspects of the influence of hail falling on slope stability： impact， stacking and infiltration， which can provide a reference and basis for slope safety warning under the condition of extreme snow and ice disaster.

Abstract:In order to explore the evolution law of mechanical property indexes of cement-soil and establish the evolution equation corresponding to each mechanical property index， this paper first analysed the testing data for the mechanical property indexes， such as the shear strength indexes （cohesion c and internal friction angle φ） and modulus （inclduing elastic modulus E， secant modulus E50 and deformation modulus E0） of clay cement-soil in the existing literature； Then， the original sample data of each mechanical property index with cement ratio of 10%~25% and age of 3~90 d was obtained； Next， the mean value and confidence interval with 95% confidence level of the above mechanical property indexes at different ages were estimated based on Bayesian Bootstrap method； Finally， based on the improved interval regression analysis method proposed in this paper， the hyperbolic function equations of the mean value， the upper and lower limits of the confidence interval with 95% confidence level of the above mechanical property indexes were obtained， and the recommended values of the parameters in each evolution equation were given， respectively. The research results can provide a reliable basis for parameter selection in the design and calculation of cement-soil related projects.

Abstract:The pre-stressed high-stress concrete （PHC） nodular pile can promote the bearing capacity owing to the nodules along the pile shaft. Nevertheless， the PHC nodular pile installation process will induce more severe disturbance to the surrounding soil， which reduces its bearing capacity. To analyze and study the bearing capacity of PHC nodular piles embedded in soft soil， the finite element software ABAQUS was adopted to simulate the load-displacement response of PHC nodular piles under compression based on the field tests. The test and simulation results show that： the soil around the nodular pile was largely disturbed during the PHC nodular pile installation process， and the strength of the soil around the PHC nodular pile was only 1/2 of the strength of intact soil after the nodular pile was installed for 40 days， and the ultimate bearing capacity of PHC nodular pile was much higher than the ultimate bearing capacity of PHC pipe pile when the strength of soil around the pile was fully recovered. The nodule size shows larger effect on the lateral resistance of nodule piles， and the increase of nodular diameter in some range can significantly increase the ultimate compressive capacity of PHC nodule piles， and there is an optimal nodular diameter， which results in the highest compressive bearing capacity per unit volume concrete of PHC nodular pile.

Abstract:The coincidence among meteorological parameters in the traditional design day of air-conditioning system design is not considered sufficiently， resulting in the design cooling load of air-conditioning system being far from the actual peak cooling load. In order to select the reasonable coincident design day for air-conditioning system design load， a method based on the meteorological daily ordinal number is proposed to select a coincident design day for air-conditioning system. In this method， the concept of meteorological daily ordinal number is first defined. Then， the dynamic cooling load of room is calculated using historically measured meteorological data and dynamic cooling load calculation mode， and a general daily ordinal number set is selected according to indoor thermal environment risk level. At last， a multi-dimensional and multi-parameter clustering analysis method is proposed to select a representative coincident design day from the general daily ordinal number set. This method is applied to select the coincident design day of Hong Kong and Changsha from their long-term measured meteorological data. A case study shows that the number of coincident design days determined by this method is few， which suits engineering design application. Comparison with the traditional design day shows that the coincident design day determined by this method has better accuracy in calculating design cooling load and can well meet the requirements of engineering design accuracy.