Abstract
Abstract The χT parameter, a simplified method recently presented, allows to estimate the global second-order effects on reinforced concrete frames using the natural period of vibration. This parameter was developed based on the fact that both natural period of vibration and global second-order effects depend essentially on the stiffness and mass matrices of the structure, being thus related. In this paper, numerical analyses are conducted on nine models with different patterns of irregularity in terms of geometry in plan and stiffness. The main purpose of these analyses is to evaluate the applicability of the χT parameter in asymmetric structures as well as that can present torsional modes as the fundamental mode of vibration. In addition, different hypotheses are tested in order to verify the influence of the different modes of vibration in the structural sensitivity to global second-order effects. Results of the simplified analyses were compared to the final bending moment values obtained through a nonlinear numerical analysis considering the P-Δ effect. It is observed that the parameter χT is a promising indicator for a simplified estimation of the global second-order effects for concrete frames, especially when higher modes of vibration are taken account in the analysis.
Highlights
In the latest years, computational advancement and improvement of the material technology lead to the design of slender buildings more susceptible to global second order effects
This paper presented the applications and limitations of a simplified parameter, based on the natural period of vibration, used to evaluate the global second-order effects on irregular reinforced concrete structures
The obtained results have demonstrated that the χT parameter is a promising estimator for the global second-order effects, even in irregular reinforced concrete structures
Summary
Computational advancement and improvement of the material technology lead to the design of slender buildings more susceptible to global second order effects. An option for the second-order analysis is to adapt the stiffness matrix (K) to include second-order effects [4]. Direct and simplified methods are preferred to the second-order analysis. These methods adopt approximations and simplifications to describe the structural behavior; their efficiency relies on the selection of the most important variables and its influence on the structural behavior. The fictitious elements simulate the geometric stiffness matrix, which includes second-order effects while equilibrium is verified. The second-order forces are obtained through linear analysis and, are vastly used by steel structural design engineers. Global second-order effects can be neglected for the latter
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