NONLINEAR ANALYSIS OF REINFORCED CONCRETE FRAMES (JOINT FLEXIBILITY)

The parameters that influence the nonlinear behavior of R/C frames including geometry, material and joint, are discussed. The geometric nonlinearity as represented by the member stability, the deformed connectivity of the structure and the axial shortening of the member due to changes in geometry, is modeled. Nonlinear constitutive relations of R/C sections are formulated. The nonlinear moment-rotation relation of the beam-column connection is modeled. The nonlinear behavior of R/C frames is investigated using the models presented in this study. The effect of geometric and material nonlinearities and joint flexibility on the behavior and analysis of frames is discussed.; It was determined that material nonlinearity plays the major role in controlling the behavior of frames. The implementation of geometric nonlinearity in the analysis is also essential to accurately predict the load-deformation relation of the structure. Joint flexibility coupled with geometric nonlinearity gives a very good prediction of the load-deformation relationship of ductile frames under vertical loads, and an upper bound on the strength of ductile and stiff frames under combined vertical and lateral loading condition. However, the assumption of rigid joint is reasonable to accurately predict the behavior of a reinforced concrete frame if the analysis accounted for the geometric and material nonlinearities.