A Simplified Plastic Zone Method for Frame Analysis

Abstract: A methodology for the geometric and material nonlinear analysis of plane steel frames suitable for implementation in a microcomputer or personal computer platform is presented. The proposed procedure takes into consideration both geometric and material nonlinearities in its formulation. Geometric nonlinearity in the form of member and frame instabilities is accounted for by the use of pseudo‐joint loads derived from the geometric stiffness matrix of the structure. Material nonlinearity in the form of cross‐sectional plastification and progressive member yielding is accounted for by the use of a cross‐sectional plastification model and the concept of effective member stiffness. Since both cross‐sectional plastification and spread of yield along member length are considered in the analysis, the proposed approach is regarded as a plastic zone model. Unlike conventional plastic zone models in which intensive computations are required to obtain solutions, the proposed model employs simplified procedures by which spread of plasticity in the structural frame is accounted for in an approximate manner. Despite its simplicity, the proposed model gives reasonably accurate results when compared with other more rigorous approaches. To verify the applicability of the approach in predicting inelastic frame behavior, the proposed method was used to analyze a variety of frame structures. The results, expressed in terms of load‐deflection responses, member forces, and moments, compared well with those obtained using other more elaborate inelastic analysis methods.