Nonlinear Analysis Of Frame Structure Based On Opensees And Research On Reducing Factor Of Member Stiffness

The second order effect is a common mechanical phenomenon in the structure,and it is a structural analysis problem.In the structural analysis,the second order effect on internal force and deformation cannot be ignored.The second-order effect refers to the additional effect of the load in the post-deformed structure or the axial force in the deflected member in addition to the first-order effect.From the research results of the second-order effect and the design specifications of each country,the current approach is elastic second-order analysis method considering member reduction stiffness.The method considers the nonlinearity of the material under the actual force condition by the stiffness reduction of the component.The geometric nonlinear characteristic is considered by the elastic second order analysis of the structure.This method is also adopted in Chinese 2010 version of "Code for Design of Concrete Structure".The analysis shows that when the reasonable component comprehensive stiffness reduction factor is selected,the calculation accuracy and efficiency of the method are sufficient to meet the needs of engineering design.From 1997 to 2004,Professor Bai Shaoliang led the team(the author's mentor is one of the participants)to study this issue,and put forward the stiffness reduction factor scheme of the frame structure member which has been adopted by our concrete specification.But limited to the conditions and technical means at the time,the proposed stiffness reduction factor needs to be re-examined.In this paper,based on the practical engineering RC frame structure nonlinear simulation and stiffness reduction factor analysis,the following research work is completed:1 The effectiveness of the nonlinear program OpenSees for the simulation of concrete structure test is verified by the simulation analysis of the cantilever column and the single-layer single-span frame test by adding the zero-length cross-section element considering the bar bond slip at the end of the component.2 The non-linear analysis of the RC frame structure,which is based on the actual engineering,is completed,and the shortcomings of the existing American norm and the Chinese standard are proposed.3 Adopt “piecewise approximation method” to solve the equivalent stiffness of the component,put forward and verified the proposal,the component stiffness reduction factor values of the proposed scheme can better reflect the real deformation and internal force of structure.The relevant research results can be used to guide the actual engineering design,and provide reference and basis for the revision of relevant provisions and follow-up research work.