Nonlinear Performance Analysis Of RC Frame Structures Using Discrete Element Method

Research on nonlinear response and collapse damage of structure under earthquake is an important subject in structural engineering disciplinary and one of the research hotspots currently. Although scholars have already put forward several numerical analysis methods, these methods are still difficult to perfectly deal with the entire process simulation on the structure from elastic to plastic, from small deformation to large deformation and even to collapse.Discrete element method (DEM) as a non-continuous numerical analysis method, does not require the displacement of coordination between elements, and applies to solving the issues in structural collapse such as non-continuous displacement field, large displacement, large rotation. The discrete element method was firstly developed in geotechnical engineering, and has gradually applied in structural nonlinear seismic response and collapse mechanism analysis. However, the previous model based on DEM which are of undefined physical meaning in constitutive relation and oversize number of elements, so that these model are difficult for large complex collapse damage analysis. Furthermore, the accuracy of structural nonlinear behavior simulation before structural collapse using DEM also requires to be further studied.This paper focuses on the nonlinear performance analysis of RC frame structure using DEM, the specific work as follows:1. Summarize the research status of numerical analysis method such as DEM in structural nonlinear and collapse analysis. And make an improvement in the segment-multi-spring model (SMSM) which was built based on DEM. Add a torsion spring in SMSM spring group to satisfy the requirements of member multi-direction loading and torsion performance.2. Numerical simulation of two RC column specimens under low cyclic load has been carried out and compared with experimental test and FEM analysis. The result indicates that SMSM is able to accurately simulate the axial force-bending coupling effect of RC members, and finely describe the history of mechanical behavior on the cross section of RC members. This model can accurately simulate the nonlinear hysteretic performance of RC beam-column members under complex loading.3. Numerical simulation of RC plane frame specimens under low cyclic load has been carried, and the results show good agreement with the experimental test. Therefore, the structural analysis model established is reasonable. The SMS-Collapse program can truly and correctly descript the structural reaction in this paper, and can be applied to the whole structural nonlinear analysis with high accuracy.4. The secondary development with the RC frame structure nonlinear response and collapsed simulation program named as SMS-Collapse has been carried out. Improve the pre-processing module using FORTRAN language, the improvement includes adding the INPUT text output module and custom material subroutine interface module. The program's versatility and scalability is greatly improved. Thus, users can directly modify the model parameters in INPUT text and call existing uniaxial material constitutive model.5. Improve the structural static algorithm in DEM by quasi-static loading method to minimize the inertia effects on the analyzed result when a structure is statically loaded. The quasi-static loading methods deal with nonlinear problems without iterative solution. Compared with previous iterative algorithm, this method greatly reduces the computational complexity on the premise of high calculation accuracy.