Análise estrutural de pórticos planos com vínculos rígidos e elásticos: aplicações do método da rigidez direta em elementos de concreto armado

Abstract

The structural analysis of reinforced concrete buildings seeks to evaluate, using tools grounded in solid mechanics, the strength of the structures, being indispensable for ensuring their stability and safety. The aim is always to achieve the best modeling of the structure in comparison to real constructions. In plane frames, for example, the beam and column elements that constitute it are analyzed, as well as the connection between these elements. The standard that establishes criteria for such structures is NBR 6118-2023, where it is possible to find, among other things, the safety factors, acceptable deformation limits, and the stiffness that should be considered in the supports when analyzing isolated elements. In the present work, the software FTOOL and TQS were used, in addition to manual calculations, to analyze the distortions between spatial and plane frame models of a four-story reinforced concrete building, using the Direct Stiffness Method, both in complete frames and in isolated horizontal elements (beams) belonging to the structure. Hypotheses and corrections are tested regarding beamcolumn connections and the stiffness of the columns to axial deformation. After a comparative evaluation of the results, the difference in the moments considered for structural calculation was verified, and how this possibly affects the safety and longevity of the structure, as well as the possible difference in the sizing of the elements relative to the internal force diagrams acting on the structure in each case, observing whether elements with the same sizing can be adopted in all approaches, or whether the impacts of normative conventions interfere both with safety and the amount of material. The comparative analysis between the models highlighted that the lack of adjustments reflecting the construction reality significantly compromises the safety and durability of structures, potentially leading to errors that exceed the margins established by NBR 6118:2023. Although software like TQS already incorporates these corrections, the engineer must master the concepts to apply them consciously, even when using simpler tools. Normative approximations, such as the flexibility of continuous beams, help reduce errors but still generate significant distortions that can affect the design and lead to structural pathologies. Therefore, it is recommended that students and professionals apply manual corrections, such as the use of MULAXI and spring supports, even in software like FTOOL, in order to achieve results that are more consistent with the actual behavior of the structure.