Elasto-plastic Nonlinear Dynamic Analysis Of Flexible Frame Structure With The Consideration Of Yield Strengthening

As the increasing popularity of high-strength steel in structures,there are more and more flexible frame structures with slender members.Due to the yield strengthening characteristics of high-strength steel,the section still has a certain degree of stiffness after yielding,and the bending moment can continue to increase.The plastic corner of the yield section and the redistribution of internal forces in the structure will be different from that of an ideal elasto-plastic material,and the nonlinear characteristics of the structure will also change.The strain strengthening effect of high-strength steel after yielding appears to be more important to the structural performance.Therefore,it is unreasonable to still adopt the ideal elasto-plastic constitutive model for high-strength steel frame structures with obvious yield-strengthening characteristics.At the same time,the structure is affected by the geometric-material dual nonlinearity under the action of wind,wave,earthquake and other dynamic loads.The large deformation and large rotation response are more significant,and the dynamic effect and the geometric-material dual nonlinearity are coupled with each other.How to better track the force balance path and dynamic response of the flexible frame structure under the influence of the geometry-material dual nonlinearity are very important.For this reason,this paper adopts the idea of rigid body criterion to analyze the geometric-material dual nonlinear coupling problem of flexible frame structure under large displacement and large rotation.Combining the concentrated plastic hinge model and the bilinear bending moment-angle relationship of the section considering the yield strengthening effect,the geometric nonlinear behavior of the structure is assigned to the rigid body criterion for processing,and the yield strengthening effect of the structure is considered through the change of the stiffness of the plastic hinge spring.Established an elasto-plastic nonlinear analysis method for frame structures considering the yield strengthening characteristics of steel.Based on the aforementioned elasto-plastic nonlinear static analysis method,combined with the direct integration method,the time step in the dynamic analysis is regarded as the load increment step similar to the static analysis,and the element nodal force is calculated using the rigid body criterion.An elasto-plastic nonlinear dynamic analysis method suitable for flexible frame structures is introduced,and the elasto-plastic nonlinear static analysis method based on the rigid body criterion is introduced into the dynamic analysis.In this paper,the bilinear elasto-plastic plane beam element and its nonlinear analysis method are used to perform nonlinear static analysis on the one-way pushover test of the flexible frame and explore the influence of member size and loading ratio on the horizontal bearing capacity.The plastic plane beam element is a further step from ideal elastoplastic to bilinear elasto-plastic,which can effectively describe the yield strengthening of the high-strength steel frame section.The elasto-plastic nonlinear dynamic analysis method is used to analyze the dynamic time-history response of the flexible frame under earthquake action.It is verified that the method in this paper can effectively analyze the strong dynamic nonlinear behavior of the flexible frame structure under large displacement and large rotation,and the stability is good.And take into account the calculation accuracy and efficiency.At the same time,the elastoplastic spatial beam element model is used to analyze the stability of the long-span steel grid dome structure,and the effect of initial defects on the stability of the structure is studied.Applicability in linear analysis.