Abstract:In order to explore the seismic performance of Concrete-Filled Double Steel Plate Composite Shear Wall after fire, the temperature field model and mechanical model were established and verified. Based on the same modeling method, a full-scale model of shear wall before and after fire was established to analyze the influences of different parameters on the seismic performance of shear wall. The results show that:(1) Before fire, increasing the axial compression ratio and shear span ratio can improve the flexural bearing capacity and deformation capacity of the wall. Increasing the reinforcement ratio of the wall can improve the flexural bearing capacity, but has little effect on the deformation capacity; (2) With the increase of fire time, the initial stiffness and shear capacity of the wall decrease. The larger axial compression ratio, the greater the impact of fire time; (3) After a long time fire, the failure mode of the wall with a large height-thickness ratio and a large axial compression ratio changes into the failure mode that the whole wall rapidly loses stability towards the fire side and the seismic performance deteriorates sharply; (4) For the wall with bending failure, fire increases the deformation capacity of the wall, whereas the overall instability of the wall caused by fire will weaken the deformation capacity of the wall for the wall with compression-flexure failure.

Abstract:In order to strengthen the seismic performance of double steel concrete combined shear wall, the number of the type steel (m=2,4,6), type steel size (I), type steel strength (Q235, Q345) (f_p), steel plate strength (Q235, Q345) (f_s), axial pressure ratio (n=0.4,0.5,0.7) were utilized as the main parameters. Nine double steel concrete combined shear walls were designed and its finite element model was established using ABAQUS software and validated with similar double steel concrete combined shear walls. The numerical results were compared with the test results o verify the rationality of the finite element model. Based on the verification results, the parameter analysis of 9 double steel concrete combined shear walls were conducted to study the main parameters affecting the seismic performance of reinforced double steel concrete. The results show that the bottom strengthening test piece has been improved in the load-carrying capacity, ductility, plastic degeneration capacity, stiffness degradation and energy consumption capacity. When the axial pressure ratios are 0.4 and 0.5, the ductility is close, whereas the ductility decreases when the axial pressure ratio reaches 0.7; When the axial pressure ratio is 0.5, the load-carrying capacity gradually increases with the increase of the number of the type steel. Increasing the strengths of the steel plate and type steel can significantly increase the ductility, initial stiffness and energy consumption and improve the seismic performance.

Abstract:For the purpose of studying the effect of the thermal-fluid-solid coupling on the fatigue life of T-pipe, the evolution of the pressure and velocity fields in the flow domain of the pipe was studied based on ANSYS finite element software, and the results were correlated according to the correlation theory and the Pearson correlation coefficient. The results show that the variation of the pressure and velocity in the flow field area has very little relationship with the temperature difference of the main branch pipe, and is closely related to the velocity difference of the main branch pipe. The variation of stresses in the pipe under complex stresses in the flow field and different initial stresses is obtained through the fluid-solid coupling analysis, and it is found that the maximum equivalent stresses in the pipe occur near the T-joint and the fixed end. On the basis of the Pearson correlation coefficient, the maximum equivalent stresses of the pipe and the fatigue life at the danger point were found to be significantly related to the temperature difference between the main branch pipe.

Abstract:Corrosion has a certain effect on the mechanical properties of pipe steel. In this paper, tensile tests were carried out on pipeline steels with different degrees of corrosion, and the relationship between the mechanical properties and corrosion loss of pipeline steels with different degrees of corrosion was studied. Based on the test results, a numerical analysis model was established to analyze the stress state at the corrosion pit. Under the action of axial tension, the fracture position of the pipeline steel with corrosion defects occurs at the corrosion pit with the largest aspect ratio. The results show that the yield strength and elastic modulus of pipe steel with surface corrosion defects have a low correlation with corrosion loss degree, but the yield load and equivalent elastic modulus decrease obviously with the increase of corrosion degree. The maximum depth to width ratio of the corrosion pit is the main factor affecting the stress concentration factor at the corrosion pit. The research results can be used to evaluate and predict the mechanical properties of pipelines in service, and provide an analysis basis for the prevention of pipeline leakage and life cycle.

Abstract:In order to explore the anti-cracking and anti-scouring characteristics of XYY biopolymer modified clay, several cracking and scouring tests were carried out. The test results show that under dry conditions, with the addition of biopolymer, the anti-cracking characteristics of the sample are significantly improved. The addition of biopolymer enhances the tensile strength of the soil, which is greater than the tensile stress of the sample due to drying and dehydration. With the increase of the biopolymer content, the sample changes from cracking to dehydration and shrinkage, the residual moisture content of the sample increases with the increase of the content of biopolymer. The addition of XYY biopolymer enhances the water retention of the soil. After scouring, plain soil samples develops obvious erosion damage traces, and the scouring rate is 49.56%, while the structure of biopolymer improved soil is still relatively complete. When the content of biopolymer reaches 2.0%, the scouring rate of the sample is only 0.81%, indicating that the clay improved by biopolymer has a good anti scouring effect. At the same time, the micro mechanism analysis shows that the XYY biopolymer can effectively fill voids between clay particles, make the clay structure more compact, and effectively improve the anti-cracking and anti-scouring characteristics of clay.

Abstract:Based on the close packing theory, the MAA model and Fuller maximum density theory were used to select the optimal gradation of aggregate. The orthogonal test method was used to determine the optimal mix ratio of epoxy concrete, and the mechanical properties evaluation and microscopic analysis were carried out. The results show that the close packing porosity of aggregate is significantly reduced after gradation optimization, and the most closely packed porosity is only 22.23%. The bone-binder ratio has a significant influence on the splitting tensile strength of epoxy concrete, and cement is suitable for incorporation into epoxy concrete as a filler. The cube compressive strength of epoxy concrete increases slightly with the increase of age, and is closely related to the curing degree of epoxy resin. When the epoxy resin is completely cured, the cube compressive strength basically does not change with the age. The mechanical properties of epoxy concrete after gradation optimization are improved, the cube compressive strength is increased. Through SEM microscopic test analysis, it is found that the internal harmful defects of epoxy concrete after gradation optimization are significantly reduced, the system is dense and uniform, and the internal bonding force becomes stronger.

Abstract:The two-dimensional mixed random aggregate model of rubber concrete is established, and the meso mechanical properties of rubber concrete are analyzed by base force element method based on the complementary energy principle. The stress-strain curve, failure process diagram and maximum principal stress and strain cloud diagram are obtained. The failure process of rubber concrete is simulated, the compression failure mechanism of rubber concrete is analyzed, and the influence of different particle sizes and contents of rubber particles on the compressive strength of rubber concrete is explored. The results show that the compressive strength decreases obviously with the increase of the rubber content. At the same dosage, the compressive strength can be slightly improved by using rubber particles with a large particle size. The damage first occurs in the area with dense rubber particles, so the rubber particles should be dispersed evenly as far as possible when configuring rubber concrete. The model can reasonably simulate the failure process of rubber concrete under uniaxial compression, and provides a new method for analyzing and predicting the micromechanical properties of rubber concrete.

Abstract:In order to study the stability of rock slope with serrated discontinuity, by combining with the empirical formula of shear strength of serrated discontinuity and considering the influences of structural plane parameters, anchoring effect, seismic action and groundwater depth, the safety factor calculation formula of anti-sliding stability of the slope with anchor structural plane was derived in this paper based on the improved pseudo-dynamic method, and the influential factors of rock slope stability were analyzed. The results show that the shear strength of the serrated structural plane has a linear relationship with the fluctuation Angle and increases with the increase of the fluctuation angle. With the increase of the seismic coefficient, slip plane dip angle, water level depth, slope dip angle and soil weight, the slope stability decreases and increases with the increase of the internal friction angle. The larger the anchoring force, the greater the shear strength of rock mass, and the anti-sliding stability of slope is improved. However, the increase of the anchoring angle has a negative effect on the stability of slope.

Abstract:In view of the influence of groundwater on the safety and stability of rock slope, taking the left cutting slope with excavation depth of about 200 m of zhongyuntai mountain, Lianyungang as the research object, the groundwater distribution on the slope was studied and the seepage interception effect of fine aggregate concrete spray layer on the excavated slope was evaluated through calculation and analysis of groundwater monitoring data. The results show that the groundwater supply source of the slope is rainfall infiltration and the abandoned quarry at the south end of the slope is the main discharge area. There is a strong hydraulic connection between the four platforms where the osmometer is embedded. The aging damage of the fine aggregate concrete spraying layer in the area with high seepage flow is higher than that in other areas, but on the whole, the seepage interception effect of the fine aggregate concrete spraying layer is better.

Abstract:Temperature gradient action is an important reason for the cracking of concrete at arch foot in concrete-filled steel tube arch bridge during the service period. For Yaowan southeast highway bridge, the local model of arch foot was established by HohaiRCFE-S program, and the stress states of arch foot under four working conditions of uniform temperature rise, uniform temperature drop and superposition of sunshine and suddenly-decreased temperature respectively were analyzed. It was found that the sunshine and suddenly-decreased temperature significantly increased the tensile stress of concrete at arch foot and improved the risk of cracking. In order to control the cracking of arch foot, the limiting conditions of the concrete tensile stress aiming at crack width control were proposed. Five crack control measures were established respectively, such as increasing the thickness of surrounding concrete, adding shear nails, setting chord supports between arch ribs, placing the steel plate on the top surface of concrete and applying prestress near the top surface, and the stress comparison and crack control effect were analyzed. The results show that under the working conditions of uniform temperature rise + sunshine and uniform temperature drop + suddenly decreased temperature, only increasing the thickness of surrounding concrete or adding shear nails cannot meet the requirements of the tensile stress control. Setting chord supports or placing the steel plate has a poor crack control effect, and applying prestress can obviously reduce the tensile stress of concrete at arch foot; The two combination schemes of applying prestress + adding shear nail and adding prestress + increasing the thickness of surrounding concrete show a good crack control effect under four working conditions.

Abstract:In order to study the post-construction subsidence characteristics of open-cut and buried tunnels in the sand-stick-powder interbedded strata at the edge of the North China alluvial plain and the influence of the groundwater level on the tunnel subsidence, according to the 18 months settlement monitoring data during the construction and operation of the Jingxiong Railway Airport Tunnel 2, by combining with the geological conditions and groundwater level data, the subsidence characteristics and differences of the tunnel were comprehensively analyzed and the Asaoka, hyperbolic and three-point methods were used to predict the final settlement values. The results show that the settlement curves of sand-silt-clay interbedded strata with higher groundwater levels can be divided into three types:hyperbolic-like, U-shaped and oscillatory, and that the settlement values and settlement characteristics of the tunnel are positively correlated with the content of cohesive soil in the main compression layer. When the content of cohesive soil in the main compression layer exceeds 64%, the settlement curve is quasi hyperbolic. Groundwater level height and backfill depth are important factors affecting tunnel settlement, and groundwater buoyancy is the main force of tunnel lifting. The longer data accumulation time, the higher prediction accuracy of curve fitting method. After the 9 months of data accumulation after dead load, the error of final settlement predicted by Asaoka method and three-point method is less than 10%.

Abstract:The construction process of shallow buried large span and small clear distance tunnel is complex and the construction progress is slow. The step method of micro-pile locking foot was proposed for the construction of shallow buried large-span and small clear distance tunnels, and the mechanical action mechanism of the step method of micro-pile locking foot was analyzed. The micro pile model can be better applied to the mechanical analysis of the strong lock foot, effectively play the support potential of the foot lock, and expand the application scope of the bench method. The step method of micro-pile locking foot can achieve the construction effect equivalent to CD method. The results of theoretical analysis and engineering field monitoring measurement were further compared and analyzed, which showed that the practical application effect of step method of micro-pile locking foot was good. The results can provide a new idea for the construction of shallow buried large span and small clear distance tunnels.

Abstract:In order to accurately grasp the current situation of agricultural non-point source pollution in Handan of Haihe River Basin, this paper used the output coefficient method, equal standard pollution load method, and ArcGIS technology and system clustering method to estimate and analyze the pollution of counties of Handan city. In 2019, the chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) and ammonia nitrogen (NH₃-N) of pollutants in Handan city were 58396t, 6046t, 1348t and 4669t respectively, and the COD pollutants were the largest. The equivalent pollution load evaluation showed that TN and TP were the main pollutants, and the load ratios were 29.67% and 33.08%, respectively. Livestock and poultry breeding source and fertilizer loss source were the main pollution sources, and the load ratios were 41.97% and 38.72%, respectively. The fertilizer loss pollution was the main contributor to TP while the livestock and poultry breeding pollution was the main contributor to NH₃-N, and the contribution rates of each pollution source to COD and TN were relatively average. The agricultural non-point source pollution in Handan city was divided into six pollution types, the strict supervision area was determined, and the corresponding treatment measures were put forward so as to provide a reference and guidance for comprehensive treatment in the future.

Abstract:For the two types of landfill sites including the industrial solid waste and domestic waste in Hebei Plain area, the electric identification characteristics of pollutants/landfill were determined by the combination method of "High density resistivity method + Induced polarization (IP) sounding + time spectrum IP parameters", and the spatial distribution of the contaminants delineated was consistent with the results of the borehole verification. The results show that the high density resistivity method has the advantages of high efficiency, strong anti-interference ability, and more prominent shallow information, which provides an important reference for rapid identification of the target area. The characteristics of time-spectrum IP parameters are more stable than the traditional P parameters in the identification and delineation of pollutants. The combined method is verified and supplemented in the detection of leakage pollution of industrial solid waste landfill and domestic waste landfill, and has achieved good identification effect.

Abstract:Based on the orthogonal experimental design, TiCN films were deposited by magnetron sputtering on the surface of aluminum alloy. The effects of the magnetron sputtering process parameters (titanium target power, carbon target power, nitrogen to argon ratio) on the hardness and corrosion resistance of Al-Cu-Mg-Ag alloy were investigated by using salt spray corrosion, electrochemical corrosion and hardness test. The mechanism was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the effects of magnetron sputtering parameters on the hardness of the alloy film, the maximum corrosion depth of salt spray, the corrosion current density and the adhesion of membrane and substrate of the film are in the following order:N₂/Ar > C target power > Ti target power; C target power > N₂/Ar > Ti target power; C target power > N₂/Ar > Ti target power; and Ti target power > C target power=N₂/Ar. When the power of C target is 200 W, the power of Ti target is 100 W, and the nitrogen to argon ratio is 1:40, TiCN films with excellent corrosion resistance, hardness and adhesion of membrane and substrate can be obtained.

Abstract:In order to better evaluate the vehicle handling stability performance, this paper simplified the vehicle into a three-degree-of-freedom model containing lateral, transverse and lateral sway. A joint simulation model was built on Carsim and Simulink, and the simulation test was conducted based on double shift and serpentine test conditions. According to the evaluation guidelines in QC/T480-1999, the model simulation results and the real vehicle test results were comprehensively evaluated and scored, and a comparative analysis between them was conducted. The results show that the evaluation scores of the simulation results of the three-degree-of-freedom model are very close to those of the real vehicle test results, which can better represent the handling stability of the real vehicle and provide some references for the subsequent evaluation of the vehicle handling stability.