摘要: The viscosity change rules of cement pastes, cement fly-ash pastes and cement silica fume pastes with different water to powder ratios were studied by using paste penetration test.Paste adhesive capacity to aggregate and paste leakage condition were analyzed based on mixture mixing test and vibration compaction test, and the design method of no-fines porous concrete composition at vibration compaction condition was provided.Analysis result indicates that in the mixing process of mixture, the amount of paste adhered to aggregate increases firstly and then decreases with the increase of paste penetration value, and paste adhesive ability is great when penetration value is 20-40 mm.Penetration value is further narrowed to 20-25 mm to avoid paste leakage and specimen damage at vibration compaction condition.No-fines porous concrete with 21.8% void ratio is designed by using the method, pore distribution in specimens is uniform, and 28 d compressive strength and flexural strength can reach 22.8 MPa and 3.4 MPa respectively.更多>
摘要: The deformation feature of middle wall for tunnel during construction was analyzed, the inner relationship between the deformation and the horizontal load was studied, and a new calculation method of horizontal surrounding rock pressure for tunnel was proposed.In the method, the analysis theory of structural mechanics was adopted to establish the relationship, in which the pressure was obtained by utilizing the monitoring deformations of middle wall.The pressure of V grade surrounding rock of shallow-buried soil tunnel in Tianhengshan is 110 kPa gained by the new method, and its range is 88-145 kPa gained by the Xie Jia-xiao method.When the friction angle of surrounding rock is 45° taken by the Xie Jia-xiao method, the pressure is 115 kPa and is close to the value computed by the new method, and their difference is 5 kPa, which proves that the new method is feasible.更多>
摘要: The absolute ratio of mean power reclaimed in the semi-active control mode divided by the value consumed in the active control mode was proposed as the evaluating index of energy availability for active suspension without external energy supply(ASWEES).The performance and energy availability of ASWEES were analyzed based on optimized PID and LQG controllers, which were designed for a quarter-heavy-vehicle ASWEES.When the damping ratio was 0.1, PID control parameters were optimized by using the genetic algorithm with suspension quadratic performance index taken as the objective function.It is pointed that the suspension quadratic performance index of ASWEES based on optimized PID control is 3.32% bigger than the index based on LQG control, and their energy availability indexes are 17.15 and 226.33 respectively.The result indicates that the performance of ASWEES based on LQG control is weakly better, two ASWEESs meet the demand of energy availability, and the energy availability of ASWEES based on LQG control is strongly better.更多>
摘要: From the points of macroscopic factors such as economic development level, population number, vehicle ownership and road condition, the regularities of traffic accidents at home and abroad were analyzed.The relations among per capita GDP and vehicle ownership per 1 000 population, mortality per 10 000 vehicles, mortality per 100 000 population were studied.Based on macroscopic econometrics and Cobb-Douglas function, the panel data model of traffic accident was set up by using the historical data in seven countries.Fixed effect model and random effect model were used to estimate parameters respectively, Hausman test was carried out, and the macroscopic econometrics models of traffic accidents for the seven countries were set up.Calculation result shows that among the parameters of traffic accidents, mortality per 100 000 population is negative correlation with per capita GDP and per capita road length, mortality per 100 000 population is positive correlation with vehicle ownership per 1 000 population.Through Hausman test, chi-square distribution value is 3.91 when freedom is 3, the probability is 0.02 and less than the confidence level which is 0.05.Compared with the random effect model, all the confidence levels of variables for fixed effect model are less than 0.05, and the goodness of fit is better.So the fixed effect model is effective.更多>
