Impact of design parameters and stress-strain diagrams on the ultimate limit state of instability in reinforced concrete columns

Impacto dos parâmetros de dimensionamento e do diagrama tensão-deformação no estado limite último de instabilidade em pilares de concreto armado

Abstract

In high-rise buildings, high-strength concrete (HSC) columns are often used to reduce cross-sectional dimensions while supporting high loads. However, this design decision may result in structures that are more susceptible to deformation, raising concerns about their structural stability. Therefore, this paper aims to study the key design parameters such as concrete strength, column slenderness, eccentricity, longitudinal reinforcement ratio, and creep effects that may lead the columns to the ultimate limit state of instability. Besides, this work studies the use of various stress-strain diagrams to represent the concrete behavior according to standards and codes. Consequently, it was noted that columns with a lower ratio of eccentricity to the effective length, higher slenderness, and lower longitudinal reinforcement are more prone to reaching the ultimate limit state of instability. The use of different stress-strain diagrams had a marginal impact on determining the ultimate limit state, but accounting for the creep effect was essential for accurate results. Assessing the ultimate bearing capacity using various stress-strain diagrams yielded different outcomes, highlighting the significance of choosing one in accordance with safety standards. The new stress-strain diagram proposed by Brazilian code decreased the ultimate load capacity of most analyzed columns and reduced the number of columns experiencing failure due to instability.

Keywords:
column; instability; slenderness; reinforced concrete; stress-strain diagram; NBR 6118:2023