Abstract
A mechanical model was developed to evaluate the reliability of very slender columns subject to creep, employing the nonlinear moment-curvature relationship. Second-order effects were considered by the finite difference method. Numerical tests were carried out on 432 columns with a slenderness index between 100 and 200. The general nonlinear method was adopted to determine the design load, applying the displacement of the stress-strain diagram for consideration of creep. The reliability index was calculated using the Monte Carlo method and the First Order Reliability Method. Among the results obtained, it was observed that it is important to review the safety criterion of the Brazilian Standard NBR 6118 about the very slender columns (90 < λ ≤ 200) by performing the calibration of the additional coefficient γn1. In addition, it was observed that an increase in the reinforcement ratio commonly produces a reduction in the reliability index; an increase in the first-order relative eccentricity promotes a decrease in reliability, among other evaluated factors.
Highlights
Considering that Brazil presents a favorable condition about the absence of seismic activity and other natural phenomena, it is possible to construct slender buildings
The numerical tests showed that the general nonlinear method proves to be efficient for determining the ultimate load in very slender columns
The variation in the concrete strength did not significantly affect the value of the reliability index, but this aspect needs to be better evaluated because only fck = 30 MPa and fck = 60 MPa were considered in numerical tests, within the range of 20 to 90 MPa allowed by the Brazilian Standard NBR 6118 (ABNT, 2014);
Summary
Considering that Brazil presents a favorable condition about the absence of seismic activity and other natural phenomena, it is possible to construct slender buildings. In this way, more slender columns are observed, in which the second-order effects become quite significant. The Brazilian Standard NBR 6118 (ABNT, 2014) admits the design of columns with a slenderness index (λ) up to 200. Creep effects should be considered in columns with λ > 90 and only the general method can be used for elements with λ > 140, with an additional coefficient γn being required for 140 < λ ≤ 200. Several requirements related to very slender columns need to be analyzed to guarantee the reliability of this type of structural element
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