Calculation of stiffness in slender reinforced columns and arches in concrete bridges: A parametric study on stiffness calculation for isolated columns according to Eurocode

Abstract

For slender compressed reinforced concrete members such as bridge columns and arches, high stiffness is essential to limit deformations and ensure stability. How ever, increasing stiffness can generate significant restraint forces within the struc ture. Previous Norconsult projects on strengthening old bridges in Jämtland showed that the nominal stiffness values prescribed by EC2 are insufficient. Like wise, Norconsult’s design of the Bukkestein Bridges demonstrated that when the superstructure deforms due to temperature changes and concrete shrinkage, it develops high forces that subject the substructure to loads beyond the intended design forces. This thesis presents a parametric study of slender reinforced-concrete columns using nonlinear analysis in accordance with EC2’s general method. The proposed calculation approach is validated by finite-element simulations in DIANA. With the revised version of EC2 set to be adopted in the coming years, this study also evaluates its new provisions. The updated code replaces the nominal stiff ness concept with an effective stiffness calculation that accounts for reinforcement yielding in the cross section and introduces a simplified global analysis method for column stiffness. Both revised-code approaches yield stiffness estimates compara ble to those from the nonlinear analysis. The parametric study examines how axial load, reinforcement ratio, and concrete strength influence stiffness and overall performance of slender columns. Results show that stiffness increases with higher axial force and reinforcement content. Analyses across various concrete-strength percentiles demonstrate that equivalent stiffness often exceeds nominal values making it possible to increase stiffness in capacity calculations by at least 29 %. The analysis shows that a reduction factor of approximately 0.45 can be applied to single, isolated columns, whereas columns with adjacent structural elements require a uniform reduction factor of 0.85 for all cases considered. By incorporating these factors into calculations, restraint forces can be mitigated, resulting in more efficient structures