Análise comparativa dos métodos estático e dinâmico simplificado da NBR 6123 para ação do vento em edificações de variadas alturas

Abstract

Wind action constitutes one of the most critical loads in the design of concrete structures, especially given the increasing verticalization and slenderness of urban buildings. With the recent update of the Brazilian standard, ABNT NBR 6123:2023, after 35 years of validity of the previous version, investigations into the impacts of the new safety prescriptions become necessary. This work aims to perform a comparative analysis between the Static Method and the Dynamic Method (1988 and 2023 versions), evaluating the implications on the design of buildings with heights of 25, 50, 100, and 120 meters. For the application of the Simplified Dynamic Method of the new standard, a computational tool was developed and validated in a spreadsheet to automate the reading of charts for the determination of the dynamic factor (ξ). The structures were modeled in commercial software (TQS), adopting an iterative analysis process for the verification of the Ultimate Limit States (ULS) and Serviceability Limit States (SLS). The results revealed that all analyzed buildings presented a fundamental period greater than 1.0 second, falling outside the safe application range of the Static Method. For smaller buildings (25 and 50m), the structural design required higher stiffness than that purely for gravitational loads; however, the geometric dimensions of the elements remained constant for all analyzed wind methods. In these cases, the impact of the ABNT NBR 6123:2023 Dynamic Method was restricted to an increase in the reinforcement ratio. Conversely, for the 100 and 120-meter buildings, characterized by higher natural periods of vibration, significant geometric divergence was observed between the methods. The 120-meter model required, according to the new standard's Dynamic Method, a robust increase in the column cross-sections compared to the other methods, evidencing that ABNT NBR 6123:2023 imposes a significant increase in the stiffness of the analyzed structures.