Comparison between Nonlinear Analysis and ACI Simplified Effective Stiffness Analysis Methods for Reinforced Concrete Frames Under Lateral Load

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The British University in Dubai (BUiD)
When reinforced concrete frames subjected to lateral load manifesting in inelastic damage in the form of cracks that diminish the structural element's stiffness. Evaluating this damage often employs non-linear analysis, yet simplified methods prescribed by international codes and numerous studies estimate the effective stiffness of these elements are used for elastic linear analysis. The accurate estimation of effective stiffness is crucial as it profoundly impacts the overall structural performance. This research endeavors to compare the non-linear performance of the structure with the linear performance using the assumptions proposed by ACI-318-19, permitting the use of 0.7EIg and 0.35EIg as effective stiffness values for columns and beams, respectively. To achieve this, 66 one-bay one-story frames are modelled and subjected to non-linear static analysis using ETABS software. The model parameters encompass compressive strength, reinforcement ratios, column height and axial load. The analysis presents load-deflection characteristics for the entire frame which used to calculate the effective stiffness. Results subjected to statistical analysis which indicate that increasing compressive strength augments structural stiffness, whereas heightened axial load and frame height notably diminish stiffness. Conversely, employing the non-linear analysis method result in higher effective stiffness than simplified method by mean value of 1.36, 1.44 and 1.57 for frames with compressive strength 40,80 and 120mpa respectively. Keywords: effective stiffness, static nonlinear analysis, simplified stiffness method
effective stiffness, static nonlinear analysis, simplified stiffness method