In general, load control method is used in finite element method for nonlinear structural analysis. Using this method, however, we can not realize the behavior of the reinforced concrete structure which has softening part after peak load. In this paper a computer program for displacement control method was developed, in which one displacement of the structure is increased and applied loads and another displacements are obtained.
In a frame, the relationships of moment-curvature and axial force-axial strain of column are continuously changed for a difference of axial force and moment respectively. So, the relationships of moment-curvature assumed appopriately that were linearized as elasto-softening model for compressive failure part and as elasto-plastic-softening for tensile part. And since the results of nonlinear structural analysis considering the strain-softening depended on the element size beyond elastic zone, the relationship of moment-curvature was modified for each element by using the concept of fracture energy approach.
Using these relationships of moment-curvature and axial force-axial strain, reinforced concrete structures were analyzed by displacement control method until the failure state. On the whole, this analytical program accurately predicted the load-displacement behavior of reinforced concrete frames.
