Scientific paper ID 2778 : 2026/1

This paper investigates in detail the influence of second order effects, also known as geometric nonlinearities and commonly represented through the p Δ effect, on the horizontal load carrying capacity of reinforced concrete columns. These effects arise from the interaction between axial forces and lateral displacements, leading to additional moments that can significantly reduce the resistance of slender structural elements. Understanding their impact is essential for the reliable assessment and design of columns subjected to combined vertical and horizontal actions, particularly in bridge engineering where such conditions are frequent. To evaluate the magnitude of these nonlinear phenomena, a series of nonlinear static analyses were conducted using two independent finite element based software products - ETABS and SOLVIA. The initial investigation is focused on a column with a height of 6 m, representing an element with relatively low slenderness. Capacity curves were generated for models with and without consideration of second order effects, allowing a direct comparison of the resulting horizontal resistance. For this configuration, the observed differences were minimal, indicating that geometric nonlinearities have limited influence when the column’s slenderness ratio is small and lateral displacements remain small to moderate. To further explore the sensitivity of column behavior to slenderness, an additional model with a height of 16 m was analyzed using ETABS. In this case, the increased height led to significantly larger lateral displacements under horizontal loading, amplifying the p Δ effect. The comparison between the two modeling approaches revealed a reduction of approximately 10% in the base shear capacity when second order effects were d. This result highlights the substantial role geometric nonlinearities can play in tall or slender columns, where even moderate axial loads can magnify lateral deformations and reduce overall stability. The findings presented in this study provide valuable insight for structural and bridge design engineers, emphasizing the importance of correctly accounting for second order effects in the analysis of slender reinforced concrete columns. The results demonstrate when such nonlinearities can be safely neglected and when they become critical for ensuring accurate capacity estimation and structural safety.