In this dissertation, a numerical method for predicting the inelastic and nonlinear behavior of reinforced concrete frames was developed, using a layered finite element method.
When stress is beyond elastic limit or cracking occurs in a member under axial force and biaxial bending, curvature about each principal axis can be affected by axial force and bending moments about both major and minor principal axes. These coupling effects are important to accurate evaluation for reinforced concrete members under axial force and biaxial bending. Thus, these coupling effects were considered in the proposed numerical method.
The analytical results are found to be highly sensitive to the chosen element size. This problem is overcome by modifying the stress-strain curve of concrete for each layer of the element, in which curvature localizes, based on curvature localization length.
Reinforced concrete members are internally statically indeterminate. Thus, creep and shrinkage cause a continuous change in the stress in concrete and steel. In general, reinforcement reduces creep and shrinkage deformations. In this study, a simple method for calculating creep and shrinkage equivalent forces was proposed, considering this restraint effect of reinforcement.
There have been many experimental studies on reinforced concrete members but they have mostly limited to members under uniaxial bending. There have been but a few tests of members under axial force and biaxial bending. However, only the behavior until ultimate load was measured in their tests. The post-peak behavior is important for ductility and energy absorption capacity. Thus, for the present study, a series of tests was also carried out for 18 tied reinforced concrete columns under various loading conditions. The test results were compared with those of numerical analysis and ACI's moment magnifier method. Data from other investigators were also used for further evidence of the reliability of the proposed numerical method.
