Earthquake Response Analysis For Engineering Structure Including Foundation Structure Interaction

In general,buildings own a relatively small volume,and locate on the flat landscape.When analyze the earthquake response of a structure,rigid foundation assumption was often adopted,and on the basis of uniform motion input,i.e.,ignoring foundation structure dynamic interaction.High dams built on high mountain and valley,which foundation surface located on bedrock surface excavation and part of slope,appeared 'U' or 'V' shape.In researching the catastrophic behavior of high dams subjected to extreme earthquakes,it is essential to investigate open and close,sliding for dam-foundation surface and adjacent monolith.If neglecting dam-foundation dynamic interaction,numerical simulation results would be seriously unreasonable.In recent years,super-large cooling towers under construction in thermal and nuclear power in China have now reached more than 200m high with 150m bottom diameters.Natural vibration characteristics of cooling tower shows that first ten modes,even first hundred modes belong to local mode shapes,and corresponding natural vibration frequency are much dense,that is different from traditional building structures.Based on characteristics mentioned above,it is easy to associate that cooling tower structure is highly sensitive to foundation structure dynamic interaction and traveling wave effect.As far as seismic research of high dams and cooling towers,foundation structure dynamic interaction effect is more evident,which is an inevitable key scientific issue.With respect to these two kinds of structure,taking actual engineering projects as research background,3D analysis models including foundation structure dynamic interaction with viscous-spring artificial boundary were performed.Equivalent nodal dynamic load formula were deduced on five artificial surfaces at the different position of the front,back,left,right and bottom of near field ground under S wave and P wave incident in vertical direction,SH wave and LOVE surface wave in horizontal direction,individually.General program ANSYS is used to perform comparative analysis research on earthquake response for RCC dam and cooling tower example considering foundation structure dynamic effect in many conditions.The major research contents and achievement are as follows:1.Taking an actual RCC gravity dam in Indonesia as example,3D finite element nonlinear disaster analysis of concrete gravity full dam under MCE condition was performed.Time history analysis for earthquake response was used for massless foundation with uniform motion input and viscous-spring artificial boundary motion input methods,separately,while considering geometric and contact nonlinearity.Open-close-contact-slide status were turned up between each joints on contact surfaces.From permanent displacements of crest nodal points,crack region area at dam foundation surface,open and sliding value of transverse joints,and the static sliding factor of safety for post-earthquake,it can be seen that the example dam has safety margin.Dynamic response results for viscous-spring boundary input model including radiation damping of infinite foundation were more conservative than that of massless foundation input model.2.Catastrophe form during the MCE action process of the whole structure system was obtained in condition of normal pool level and static forces as initial conditions for foundation-reservoir-gravity dam model.Afterwards,seismic safety evaluations for typical monolith of sliding and overturn were performed.3.Based on theory of elastic wave propagation,motion input formula of SH wave and LOVE surface wave transmitting in horizontal direction were deduced for the fisrt time,and programming by using APDL so as to realize in ANSYS software.Though SH and LOVE wave example in sine function,validated with analytical solution for accuracy of the new motion input approach.4.Influence laws of dynamic characteristics of cooling tower model with the different stiffness of foundation were analyzed.Applied engineering information of the cooling tower,FEM of the homogeneous elastic foundation and cushion cap-piles collaboration work were built.The results show that natural frequency distribution of cooling tower is very intensive.The fundamental modes were all local ones of the tower,while the whole mode appeared in lower-ranking.With the increasing of the foundation rigidity,the frequency values were also increasing,but amplitudes were limited.Dynamic characteristics of the model considering cushion cap-piles collaboration work was in accordance with foundation cooling tower FEM.5.Influence rules on seismic response of the cooling tower structure was discussed,considering traveling wave effect and FSI at the same time.In the condition of uniform motion input,tower present nodes in meridian and circumference direction had a little changes,presented horizontal translational as a whole.There is a little influence on dynamic response of the tower with the rigid changes of foundation.While under condition of SH wave and LOVE surface wave motion input,the fundamental vibration of local vibrations were motivated.When considering radiation damping effect,the peak values of acceleration at the bottom of the cooling tower reduce 20%?50%,but distributions of the circumference direction are the same,which are larger in motion input direction than in another horizontal direction.When considering traveling wave effect,phase differences were turned up for each node at bottom of the cooling tower.SH waves motion input in horizontal direction under the soil layer with the different shear wave,if the velocity of SH wave is low,the response will be small,traveling wave effect is obvious,on the contrary,if the velocity of SH wave is high,the response will be violent,close to the results of massless foundation model.As to the structure,radiation damping effect is more important than traveling wave effect.With the increasing of shear wave,absolute acceleration at the bottom of cooling tower is close to free field motion input,scattering effect of superstructure to the motion is decrease gradually.6.Under condition of uniform motion input with massless foundation model,with the increasing of foundation rigid,axial forces of X-columns change a little,while the moments in the circumference direction increase obviously.Using viscous-spring boundary model,including radiation damping effect,increasing inner force of tower in the circumference direction,and decreasing inner force of tower in the meridian direction.The maximum inner forces of X-columns also decreased 20%to 50%.After considering traveling wave effect of SH wave and LOVE surface wave,the maximum principal stress has increased.In condition of SH wave motion input,including SSI,the local vibration shapes were motivated,and with increasing of velocity of SH wave,inner force of X-columns increase obviously.It can be seen that radiation damping effect is very important and can not be ignored during the dynamic analysis.