Abstract
abstract: Current practices in structural engineering demand ever-increasing knowledge and expertise concerning stability of structures from professionals in this field. This paper implements standardized procedures for geometrically nonlinear analysis of steel and reinforced concrete structures, with the objective of comparing methodologies with one another and with a geometrically exact finite element analysis performed with Ansys 14.0. The following methods are presented in this research: Load Amplification Method, from NBR 8800:2008; the γ z coefficient method, from NBR 6118:2014; the P-Delta iterative method and the α c r coefficient method, prescribed in EN 1993-1-1:2005. A bibliographic review focused on standardized approximate methods and models for consideration of material and geometric nonlinearities is presented. Numerical examples are included, from which information is gathered to ensure a valid comparison between methodologies. In summary, the presented methods show a good correlation of results when applied within their respective recommended applicability limits, of which, Eurocode 3 seems to present the major applicability range. The treated approximate methods show to be more suitable for regular framed structures subjected to regular load distributions.
Highlights
1.1 Initial considerationsIn recent decades, structural engineering and civil construction underwent significant technological advancements, which resulted in the reduction of weight and overall improvement of structural systems, in turn allowing the construction of buildings with heights previously deemed impossible
This paper presents four approximate methods: the Load Amplification Method (MAES, in Portuguese), originally presented in ANSI/AISC 360-16 [10], and subsequently adopted by NBR 8800:2008 [11] for the structural design of steel buildings; the γ z coefficient prescribed in NBR 6118:2014 [9] and used for the classification of the structure and as a design factor for the horizontal loads; the equivalent lateral force method, adopted by NBR 8800:1986 [12], which adds fictitious lateral loads to the horizontal loads; and the method prescribed in the European standard EN 1993-1-1:2005 [13] for the design of steel structures, that uses the αcr coefficient to classify a structure according to its sensitivity to second order effects
Concerning the analysis of displacements, the exact analysis performed with Ansys presents the most conservative results, followed by γZ coefficient and the Eurocode method, known for overestimating horizontal loads
Summary
1.1 Initial considerationsIn recent decades, structural engineering and civil construction underwent significant technological advancements, which resulted in the reduction of weight and overall improvement of structural systems, in turn allowing the construction of buildings with heights previously deemed impossible. A first order analysis is characterized by determining the equilibrium equations of structures in their undeformed condition In this type of analysis, structures are assumed to undergo small displacements that bear no effect on the developed internal forces. In a second order geometric analysis (or nonlinear), the equilibrium equations refer to the structure in the deformed configuration, resulting in a system of nonlinear equations. This approach is required when the applied loads interact with the resulting displacements inducing significant additional internal forces [1].
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