Influência dos redutores de rigidez na análise da estabilidade global em edificações de dois a quatro pavimentos

Abstract

The γz coefficient is a widely used stability parameter inthe analysis of global stability. However, its application is limited in buildings with more than 4 floors. Due to its ease of application, it is frequently employed in research exploring the global stability of tall and slender structures. Its application is restricted due to item 15.7.3 of NBR 6118 (2023), where rigidity reducers are applied as an approximate means to consider the physical nonlinearity of reinforced concrete. Therefore, Bueno (2014) and Moreira e Martins (2018) proposed different methodologies for rigidity reduction factors applicable to buildings with less than 4 floors. Additionally, the current edition of ACI 318 (2019) presents simplified equations for determining the effective stiffness of structural elements, without height limitations in application, considering axial load, eccentricity, reinforcement ratio, and characteristic compressive strength of concrete. Thus, this study explored the impact of the γz coefficient on second-order effects in buildings with 2 to 4 floors, using different approaches to reduce the stiffness of the analyzed structural models. Through the TQS software, four distinct types of buildings were simulated, varying the number of floors from 2 to 4. The analysis began by considering the γz coefficient as a method for estimating second-order effects adjusting stiffness reducers based on previous studies such as Bueno (2014), Moreira e Martins (2018), and recongnized standards like ACI 318 (2019) and NBR 6118 (2023). For result validation, the P – Δ process was used as a more refined method for estimating efforts, in conjunction with the Physical Geometric Nonlinear Portal (PNLFG). The comparison between methods aimed to identify how stiffness variation impacts the assessment of the global stability of the γz coefficient. During the analysis of the results, satisfactory performance of the γz coefficient as a method for estimating second-order effects was observed in buildings with less than four floors. In the studied models, it was found that, when applying the γz coefficient, the stiffness reduction factors from the studies of Bueno (2014) provided a better estimate for buildings with 2 floors: As for the 3 floors models, the factors derived from the research of Moreira e Martins (2018) exhibited a better approximation compared to the validation models. Keywords: Global instability. γz. P – Δ. Effective stiffness. Nonlinear analysis.