Robustness Evaluation of Substitute Frame Model for Determination of Force Actions in Columns of RC Moment Frames

Nowadays, extensive nonlinear dynamic analysis is widely used in different fields of research and design of structural and earthquake engineering. It has been applied in performance-based design, resilience-based design, and also other probabilistic fields and optimization. This extensive analysis imposes a high computational cost on the researcher. However, using simplified models is an appropriate approach. The Substitute Frame is a simplified model for steel and RC moment frames, which on the one hand predicts the displacement responses of the frame with very good accuracy and on the other hand, reduces the analysis time by several times. Despite numerous evaluations of the substitute frame model in nonlinear dynamic analyses, incremental dynamic analyses, and fragility analyses, the model's accuracy has not yet been investigated for predicting moment frames' force responses. In performance-based engineering, force-control actions should be designed to prevent the undesirable failure mechanism. Hence, in this study, first, the force response of the columns was predicted using the substitute frame model, and then its accuracy was evaluated comparing to the original frame response. The results of evaluations showed that the substitute frame predicts the columns bending moments, shear forces, and axial forces of the original frame with more than 90% accuracy.