Application Of Contactalgorithm In The Pile Soil Structure Interaction (PSSI)

For a long time, the earthquake response analysis method for conventional seismicdesign was based on the rigid foundation assumption, and the upper structure andfoundation were considered separately as independent structural units so as to carry outthe hydrostatic equilibrium calculations and analyses. A great quantity of theoreticalresearches and experiments show that when an earthquake occurs, there is dynamicinteraction among upper structure, groundwork and foundation, and this interaction willhave great impacts on the seismic response of the upper structure. Now a majority ofresearchers and engineers have been aware that it is necessary to consider the dynamicinteraction among the superstructure, groundwork and foundation in the seismic design.In the paper, the background of the subject was described, the history and current statusof researches on the dynamic interaction among the superstructure, groundwork andfoundation were summarized, and some major problems remaining in the field werediscussed. The earthquake damages caused by the dynamic interaction among thesuperstructure, groundwork and foundation were illustrated and the related researchmethods and their applicable fields were summarized. A general description of thecontact problem was given. The basic equations of contact finite element and the definiteconditions required for contact boundary were given. The contact finite elementequations were derived according to the virtual work equations for contact problems.Based on the form of contact potential energy of penalty function and the contact surfacediscretization, the finite element equations by means of the penalty function method werederived. The finite element software ABAQUS was briefly introduced; the details ofestablishing this model, such as the selections of material parameters and units,determination of damping factor, boundary processing, the simulation of pile-soil contactboundary and measures for controlling the solution process, etc., were described. A3-Dnonlinear finite element model of a pile-soil-structure system was built via ABAQUS;under two orthogonal horizontal seismic excitations, the peak responses of absoluteacceleration, story drift, moments at beam ends as well as the internal forces of differentcolumns and shear walls were analyzed. The conclusions obtained from the paper are asfollows: for the high-rise frame shear wall structure considering the pile-soil-structureinteraction, the use of seismic design method specified in the Code for Seismic Design ofBuildings is safe for most floors. However, the seismic response of structural members ofsome floors may be amplified, so the seismic design method is unsafe for these areas. Under the excitation of bi-directional horizontal earthquake, the influences of fieldnonlinearity on the seismic response of the two directions are different, so a largerreduction factor shall be used. The reduction factor for the structural response at differentstages is different, and the changes in the reduction factor are not linear along thestructural height. Therefore, the constant or linear reduction factor specified in the Codefor Seismic Design of Buildings is unreasonable. In addition, the influences ofpile-soil-structure interaction on members at different locations are different, so differentreduction factors shall be used in the seismic design.