Advanced Materials Research Vols. 243-249

Abstract: Influenced by a variety of factors, such as driving skill, traffic composition, signal control, traffic management, and traffic environment and so on, the traffic flow characteristic parameter statistics embodies multi-state characteristic which is incapable to describe precisely by using a single distribution model. In order to fit the headway characteristic parameter of multi-state traffic flow, based on the denseness of mixture Gamma distribution, the data could be fitted more accurately with the method of expectation maximization algorithm and by means of controlling the number of branches under the condition of precision beyond 95%. Take actual survey data as the example, this paper compares the fitting errors of negative exponential distribution, Erlang distribution and mixture Gamma distribution and the result shows that the fitting result based on mixture Gamma distribution is closer to actual case.

Abstract: Traffic volume forecast of urban river-crossing channel is the basis and premise of construction of urban river-crossing channel. By analyzing characteristics of traffic volume of urban river-crossing, a method of traffic volume forecast of urban river-crossing channel was put forward. Firstly, components of traffic volume of urban river-crossing channel were analyzed. Secondly, the OD matrix was divided into urban internal transportation and interurban transportation. Two different forecast methods were adopted, and results of the two parts calculated by different methods were added to work out the total traffic volume of urban river-crossing channel. Thirdly, the total traffic volume was allocated to several river-crossing channels by calculation, and the traffic volume of each river-crossing channel was gained. The method proposed in this paper was proved to be effective by the example calculation of river-crossing channel of Fu Ma Yangtze River Bridge in Wan Zhou district of Chong Qing.

Abstract: The present rear-end collision accident proportion on the road increases day after day, car collision avoidance system is more and more paid attention. Analysising the existing car collision avoidance system, we propose a car anti-collision algorithm based on safe distance model in this paper. This method takes the influence factors of safety distance for main parameters which fully considers the speed change and the acceleration change of the car 1 and the car 2. It may realize real-time information acquisition and warning judgment according to the state of car 2, the car could automatic braking if necessary. VB simulation shows that the algorithm can effectively avoid collision, also automatically maintain the distance between vehicles, and lay a foundation for further research on the unmanned car.

Abstract: In order to analyze the characteristic of cyclist throw distances and head injuries in car to electric-bicycle side impact accidents, this paper presents an approach to reconstruct the car to electric-bicycle side impact accident using PC-Crash. The distribution characteristic of cyclist head impact points with the hood and windshield is analyzed and the relationships between the vehicle impact velocities and the cyclist’s head injuries are described. In addition, based on several factors including road friction coefficient, vehicle load and braking deceleration, we analyzed the relationships between the vehicle impact velocities and the cyclist throw distances. The results show that 50km/h can be regarded approximately as the threshold of impact velocity to cause the cyclist’s head injuries, meanwhile, the cyclist throw distance is less influenced by the road friction coefficient and vehicle load, and the cyclist throw distance might be larger under lower impact velocities and smaller deceleration conditions.

Abstract: Based on the comparative analysis on the low-noise road surface, noise reduction green belts, noise barriers and other noise reduction methods, the sound barrier is put forward as an important method for reducing the city road traffic noise. The noise reduction effects for different heights and different distances of the sound barrier are tested and analyzed through noise and vibration test and analysis system, the following conclusions can be drawn. At the same heights from the ground, the father the test points away from the noise barrier, the higher the sound pressure level will be; At the same distances from the sound barrier, the nearer the test points from the ground, the smaller the sound pressure level will be; All of the sound pressure level curves have basically the same variation trend and the main noise frequency band is from 160 to 1600Hz; In the high frequency range which is greater than 1600Hz, the sound pressure level decrease significantly, indicating that the sound barrier has better noise reduction effect for high frequency range. The results provide the basis for the design of the sound barriers.

Abstract: In this paper, the mechanism of typical temperature crack is systemically analyzed and the main cause for crack is discussed. Some efficient methods such as surface heat preservation, low temperature placing, interior heat gradient control, cooling height control, selection of water cooling mode have been discussed in depth. In additional, temperature monitoring, feed-back simulation instantaneous and crack risk early-warning are also considered as indispensable component for the temperature control and crack prevention work. At last, a series of temperature control and crack prevention new methods for super-high arch dam are suggested to ensure the safety of the dam under construction.

Abstract: The river ice is a commonly natural phenomenon in the cold region. And serious ice situation can cause the ice-flood disaster. So the impact assessment on ice situation is an important factor which need considering in development and utilization of water resources. Based on the backwater calculation of ice jam in ice-flood period, and take the reach near Dazhunzeng Second-line Yellow River Railway Bridge for example, the backwater calculations of ice jam are carried on for the conditions before and after the construction of Dazhunzeng Second-line Yellow River Railway Bridge, and the conclsions are drawn that: (1) the construction of Dazhunzeng Second-line Yellow River Railway Bridge has less influence on the ice-flood control during freezing period; (2) after the construction of Dazhunzeng Second-line Yellow River Railway Bridge, during river-ice breakup the bridge section is combined affected by the old and new bridge, as a result the backwater height before the ice dam of bridge section is about 7.59m, and the ice surface elevation of the bridge section is up to 981.80m; (3) According to the current operation mode of Wanjiazhai Reservoir, the construction of Dazhunzeng Second-line Yellow River Railway Bridge will not have bad impact on the operation of Wanjiazhai Reservoir.

Abstract: The strength and stress-strain relationship of saturate concrete is investigated in this paper. The influence of moisture to concrete strength is assumed to be related to cement surface energy reduction by water. The initial elastic modulus of concrete is obtained by considering the deformation of both pore and microcracks in concrete. The stress-strain relationship is achieved with damage mechanics by comparing the damage evolution rules between dry and saturated concrete under external loading. The comparison between experiments and the results by the model proposed in this paper indicates a favorable agreement.

Abstract: The temperature stress due to temperature changes is often more than the concrete tensile strength during construction period and operation period in massive concrete structures in hydraulic engineering, so the analysis of temperature stress, temperature control and measures to prevent the cracks become very important. The solution of large sparse linear equations is essential to finite element simulation in simulation analysis of temperature field. However, the traditional direct method will cost too much memory and calculation time, and the nodes is limited. The symmetric successive over relaxation (SSOR)-preconditioned conjugate gradient (PCG) method is a very efficient iterative method for solving large sparse linear equations. Construction process simulation and temperature filed calculation during construction period about Caohe river landing rectangle aqueduct of Beijing-Shijiazhuang emergency water supply engineering of middle-route of south-to-north water transfer project are carried out by FEM code using SSOR-PCG method, then the calculation result and monitoring value are compared. The comparison result shows that temperature field during construction can be accurately simulated by simulation calculation, which is helpful for guiding construction and choosing construction scheme, and worthy to popularize to other similar projects.

Abstract: Based on numerical simulation of the seepage field of earth rockfill cofferdam using nonlinear Finite Element Method under the action of flood during construction period, the stability of the cofferdam slope with nonlinear shear strength is studied. The effectiveness and applicability of the method introduced in the paper is certified through computation in the study on the practical project. The paper provides an effective analysis method for the study on the stability of dam slope of earth rockfill cofferdam.