Research On Inland River Ice Mechanical Property And Ice Impact Force On Bridge Pier

Ice hazard usually occurs in all rivers north to 30°N in China, and especially the spring ice flood in the rivers in the region north to 35°N and in Qinghai-Tibetan Plateau. Drift ice in spring is a great threat to the bridge in the extremely cold area of China. Great kinetic energy is generated by large ice sheet driven by water flow, which causes large collision force on piers and abutments in river way, and which has more serious influence on pier damage, pier stability and bridge structure vibration, and which has severe threat to safe operation of bridge structure. However, the collision force between floating ice and pier is influenced by many factors, such as river ice strength, ice failure mode, ice flow velocity and direction, wind speed, water velocity, pier forms, and ice-breaking body forms, etc.,which makes the collision force calculation become more complicated. At present, ice load formula of China is empirical and short of enough experimental and theoretical bases. The existing "general code for design of highway bridges and culverts" (JTG D60-2004) provides the empirical calculation method for ice load based on the norm of the former Soviet Union "design standard for railway and road bridges and culverts" (SNiP 2.05.03-84).The characteristic values of ice compressive strength are taken from the local ice compressive strength of ice temperature at 0℃, and the influence of ice temperature on ice strength are considered by temperature coefficient in the norm. The influence of ice strain rate on ice strength isn't taken into account in the norm.The determination method of ice compressive strength characteristic value has problems. Therefore, in order to reduce the damage to the existing or under construction bridges caused by drift ice, and ensure the safe operation of the bridges, which has great theoretical and practical significance to carry out the research on the physical and mechanical property of river ice and the collision force between river ice and pier in Heilongjiang Province which is the coldest region in China.According to ice conditions character and ice zoning of Heilongjiang Province, the typical test river reach inⅠ,Ⅱ, andⅢregions of Heilongjiang Province are selected to carry out the floating ice temperature field experiments, river ice uniaxial compressive strength experiments and bending strength experiments. And then, the calculation method of characteristic values of river ice strength inⅠ,Ⅱ, andⅢregions of Heilongjiang Province is proposed. Based on the results of river ice physical and mechanical property experiments and the collision force experiments between river ice and pier, the computer simulation analysis model of collision force between river ice and pier is established, by the explicit dynamical analysis software package LS-DYNA. The main works are as follows:(1)River ice temperature field tests are carried out at four typical test rivers inⅠ,Ⅱ, andⅢ regions of Heilongjiang Province in drift ice epoch. The distribution laws of floating ice temperature along ice thickness are discussed, and river ice temperature of drift ice epoch is determined by adopting the method of weighted mean. The mathematical models of air temperature, water temperature and ice temperature in drift ice epoch are established by adopting 1stOpt mathematical optimization analysis tools software package, and using Quasi-Newton method and the general global optimization method.(2) River ice unaxial compressive strength experiments are carried under eight kinds of ice temperature and five kinds of strain rates, and river ice bending strength experiments are also carried under eight kinds of ice temperature and four strain rates at five typical test rivers inⅡandⅢregions of Heilongjiang Province. The influences of ice temperature and strain rate on river ice compressive strength and bending strength are analyzed, and the mathematical models of ice temperature and ice strength are established. The mathematical models of ice temperature, strain rate and river ice strength are set up by adopting 1stOpt software package using Quasi-Newton method and the general global optimization method. According to the experiment datum of river ice unaxial compressive strength experiments and bending strength experiments inⅡandⅢregions of Heilongjiang Province, river ice compression elastic modulus and bending elastic modulus are determined under different ice temperature and strain rate, and the relationship among ice temperature, strain rate as well as the elastic modulus is researched, and the corresponding mathematical models are established.(3) The calculation method of characteristic values of river ice strength under the influence of ice temperature and strain rate is put forward based on floating ice temperature field tests and river ice unaxial compressive strength experiments. The characteristic values of river ice strength are worked out, and the advices are given accordingly.(4) The computer simulation analysis model of collision force between drift ice and pier is studied by the explicit dynamical analysis software package LS-DYNA, using the measured river ice stress-strain constitutive relationship, nonlinear finite element theory and contact-impact theory.Effects of element type selection, coupled modes between different elements, contact method and arithmetic, ice sheet near field size, mesh density of ice sheet near field, mesh density of main beam and pier on ice collision force are studied. And the calculation results on ice collision force are compared with the measured ones.A new method for the characteristic values determination of river ice strength and the collision force analysis between drift ice and pier has been provided by the results, and it is very important in theory and practice for bridge structure design in cold region.