Dynamic Nonlinear Characteristics Analysis Of Pier-piles System Under Transient Load

Owing to its high bearing capacity and small settlement, pile foundations are widely used in various kind of foundation engineering such as in high-rise building structures, large-scale factory building, nuclear power station, water resources and hydropower Engineering, railway and bridge engineering, harbour and offshore production platform as well as structures with large dynamic machine. In most practical filed and academic institution, calculating parameters and dynamic character, which make critical consequence of the interaction in piles-soil system under dynamic loads and earthquake, are the focus because of the extensive application and complication of piles-soil system. In actual engineering project, dynamic response of piles-soil system under the transient load which cause by collision, mechanical vibration as well as acceleration and deceleration of vehicle driving is a fundamental problem.With intent to analyse the dynamic response of pier-piles-soil system under transient load, this passage builds simplified model which is based on dynamic Winkler Model in the software of ANSYS and acquire the analytical solution by using mathematical method. The main research content is as follows:(1)With the overview and summarization of some interrelated reference about the dynamic interaction of piles-soil system, a comparison of different theory and research methods on model is represented.(2)To solve the dynamic equilibrium equation, acquire the analytical solution and dynamic response, analyse the dynamic interaction mechanism of piles and soils, theories like structural dynamics, mechanics of materials, Laplace Transform and Transfer Function are used in this passage.(3)Based on the analytical solution of single pile and introducing the attenuation function, the pile-soil-pile dynamic interaction factor is deduced by analyzing the character of lateral dynamic response between pile and pile under transient load. According to the dynamic interaction factor and principle of superposition, analytical solution and lateral response of pile groups subjected to lateral transient load at the pile head is studied.(4)In practical project, though the existence of pile cap and pier leads a major influence to the vertical dynamic response of pile groups system, considering the mass of it contributes to a more accurate solution of the pier-cap-piles system which subjected to lateral transient load. Taking a single pile of pile groups as example, theoretical derivation about dynamic response of pile groups is deduced with the assumption of rigid constraint at the pile head while the mass of cap and pier as well as the boundary conditions are taking into account.(5)In the past, research on the model and the dynamic interaction of pile-soil system was generally based on the analytical solution. Different scholars and engineers who have different algorithm program, are taking previous research results as the exact solution to compare the results of their own. However, it is not conducive to the simplicity and universality of application. Therefore, based on the analytical solution which is deduced above, this passage builds the simplified model of the pier-piles-soil system by utilizing general finite element model software ANSYS to analyse the dynamic response characteristics which caused by transient load of this system. On one side, in order to find out the difference of dynamic response characteristics in different type of load, three time dependent loading cases are considered, namely, step load, cosine load and triangular load. On the other side, with the purpose of analyzing the distinctions of dynamic response that caused by parameters, two different impedance function are applied on the simplified model, one called the Gazetas Impedance, the other called Dongjia Liu Impedance.(6)In order to verify the dynamic response results obtained from the simplified model, a finite element analysis model, which considers the contact nonlinear characteristic between piles and soil and the radiation damping of soil on far field, is built by utilizing the finite element model software ANSYS. Besides, some influence factors of the pier-piles-soil system which is subjected to lateral transient are taked into account, such as the distribution of soil layers, the boundary conditions and the rigidity of soil. With comparison and analysis, some constructive conclusions are summarized.