Master's Dissertation
DOI
https://doi.org/10.11606/D.18.2020.tde-03092020-120633
Document
Author
Full name
Mariane Filiagi Pastore
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2020
Supervisor
Committee
Almeida Filho, Fernando Menezes de
Trautwein, Leandro Mouta
Title in Portuguese
Análise de pilares esbeltos de concreto armado de seção retangular submetidos à flexão composta oblíqua
Keywords in Portuguese
Flexão composta oblíqua
Método Geral
Pilares esbeltos
Abstract in Portuguese
Title in English
Analysis of slender reinforced concrete columns of rectangular crosssection subjected to combined biaxial bending and axial load
Keywords in English
Approximate methods
Combined biaxial bending and axial load
General Nonlinear Method
Slender columns
Abstract in English
In the design of slender reinforced concrete (RC) columns, it is essential to check their stability. In situations where second-order effects cannot be neglected, column analysis can be carried out using approximate methods or the General Nonlinear Method. The objective of this work was to analyse the behaviour of slender reinforced concrete columns (90 ≤ λ ≤max 140) of rectangular cross-section subjected to combined axial loads and biaxial bending according to four different calculation methods presented in the Brazilian design code for concrete structures named ABNT NBR 6118: 2014. These four methods were compared with a total of 9,720 simulations which considered the following parameters: cross-section geometric ratio (1:1; 3:1 and 5:1), slenderness index (90;115 and 140), reinforcement ratio (2%; 3% and 4%), relative axial load (0,3;0,4;0,5; 0,6), relative bending moment, proportion between bending moments of the base and top (-1;-0,5;0;0,5;1), biaxial bending angle with respect to the horizontal axis (30º; 45º and 60º) and creep coefficient (0 and 2). The columns were processed using the software SecTrans and an automation routine was implemented in the program to obtain all results. Results showed that the comparison of the approximate methods and the General Method was mainly influenced by the slenderness index, the relative axial load, the relative bending moment and the cross-section geometric ratio (width/height). In the Method Coupled to diagrams, the dimensionless stiffness κ must meet a certain minimum dimensionless stiffness kmin in order to the calculations be valid. Although ABNT NBR 6118: 2014 allows to neglect the creep effect for columns with slenderness ratio less than or equal to 90, it was observed the importance of considering creep for all levels of slenderness studied including λ = 90. Finally, the approximate methods resulted in higher values of final design bending moments than the General Method for all valid situations, however in most cases they led to exaggerated values, being supposedly economically unavaible. This finding may make impractical the use of approximate methods in these situations when calculation routines that consider the General Method are readily available with theoretically more accurate results.