Integration And Application Of Explicit Integration Method And Triangular Shell Element With Opensees

Research on the performance of engineering structures in extreme disasters and the seismic collapse resistance of engineering structures has become critical issue in recent years.Implicit method encounters numerical difficulties in convergence when solving these extreme problems with high non-linearity,Therefore,explicit method is better to solve these problems because explicit method can avoid iteration.OpenSees,as an open source finite element software,has been widely used because it is versatile and extensible.However,only basic central difference method is integrated in OpenSees.This method cannot ensure the equations uncoupled,which will limit the application of explicit method.Aimed at above demands,an explicit method based on leap-frog method and central difference method is established and corresponding damping models are discussed.In addition,a new triangular flat shell element is proposed in order to improve the capacity of OpenSees in shell element.Finally,all the functions are integrated in OpenSees and validated through numerical examples.The main research works of this study are as follows:(1)An explicit integration method and corresponding damping model for explicit method are discussed.An explicit integration method based on leap-frog method and central difference method and its corrected format is developed.The influence of Rayleigh damping model on the stability of explicit method is discussed.Furthermore,several damping models suitable for explicit method are proposed.Finally,the performance of the explicit method and damping models is validated through some numerical tests.Results show that this explicit method can achieve good accuracy.Compared with implicit method,this explicit method has lower numerical damping and no convergence problem.(2)A three-node triangular flat shell element is proposed.Membrane element GT9 and plate element DKT are selected to create the new flat shell element DKGT.Its geometric nonlinear formula NLDKGT is also developed.The performance of new shell element is validated through numerical examples.Analysis results show that the new triangular shell element has good accuracy,and can totally avoids shear locking.In addition,the new triangular shell element shows high performance in convergence when encountering warping,which makes it a powerful tool to simulate buckling compared with other shell elements in OpenSees.(3)The abovementioned explicit method,damping model and shell element are integrated in OpenSees.The procedure of integration work and the method to realize these function modules are introduced in detail.(4)Seismic analysis and collapse simulation of several typical large structures are conducted using explicit method.Results show that the explicit method proposed in this study has wide applicability and high accuracy,which make it a useful tool in research on the dynamic response of engineering structures in extreme disasters.