Three-Dimensional Non-Linear Analyses of Special Reinforced Concrete Moment Frames

The design of special reinforced concrete moment frames (SMFs) requires the consideration of both strength and stiffness. SMFs are proportioned and detailed to allow for extensive inelastic deformations, but most frames are designed using elastic (or modified elastic) two-dimensional models. Two concepts not included in design are the increased lateral stiffness of axially loaded compressive columns (and by contrast, the loss of stiffness of columns in tension) and the increased displacement of leeward columns due to concrete beam elongations. In this paper, shear-force distribution between columns and corresponding beam elongations will be presented using three-dimensional non-linear finite element analyses (3DFEAs). Analyses include load-to- displacement results and associated changes in beam stiffnesses from the 3D-FEA and compare those results to two-dimensional finite element analyses.