Investigation of moment-curvature and effective section stiffness of reinforced concrete columns

In determining the seismic performance of reinforced concrete (RC) structures in national and international seismic code, it is desired to use effective section stiffness of the cracked section in RC structural elements during the design phase. Although the effective stiffness of the cracked section is not constant, it depends on parameters such as the dimension of the cross-section, concrete strength and axial force acting on the section. In this study, RC column models with different axial load levels, concrete strength, longitudinal and transverse reinforcement ratios were designed to investigate effective stiffness. Analytically investigated parameters were calculated from TBEC (2018), ACI318 (2014), ASCE/SEI41 (2017), Eurocode 2 (2004) and Eurocode8 (2004, 2005) regulations and moment-curvature relationships. From the numerical analysis results, it is obtained that the axial load level, concrete strength, longitudinal and transverse reinforcement ratios have an influence on the effective stiffness factor of RC column sections. The calculated effective stiffness for RC columns increases with increasing transverse reinforcement ratio, longitudinal reinforcement ratio and concrete strength. Due to the increase of axial force, effective stiffness values of concrete have increased.