Análise dos efeitos globais de segunda ordem de torção em edifícios de lajes lisas de concreto armado

Abstract

The use of flat slabs, i.e. with a direct connection between the slab and the column, has been a structural solution increasingly adopted in construction projects in Brazil. The choice of this type of structure is due to the simplification of some construction processes, such as the cutting and execution of forms, shoring and concreting. In ad-dition, the absence of beams provides greater architectural freedom, since these ele-ments do not condition the position of walls or partitions. In addition, there is no need to drill holes in beams for pipes, avoiding rework and pathologies. As a result, the use of flat slabs increases the speed of construction and the final quality of the building. However, global stability is a critical point in the design of this type of building, since there are no bracing frames, and the equilibrium of the structure is conditioned to the rigidity of the slabs and columns alone. The Brazilian standard NBR 6118:2023 speci-fies methods for assessing global stability, and consequently second-order global ef-fects, only for translational displacements. In addition to the lack of normative recom-mendations for the consideration of torsional effects in buildings, there are few studies exploring the subject. Therefore, this work analyzes the torsional instability coefficient 𝛾�𝜃�, proposed by Franco (2003), in ten computer models developed with the TQS soft-ware, simulating 10-storey buildings. Five different geometries were tested, with two models for each configuration, one with a traditional structural typology, with slabs, beams and columns, and the other with flat slabs, in order to compare the difference in the behavior of the 𝛾�𝜃� parameter in the two versions of each version analyzed. The results show that buildings with flat slabs suffer an increase in the torsional instability coefficient, i.e. second-order global effects are more prevalent in this type of structure. In addition, a certain constancy in the 𝛾�𝜃� values was observed in both the beam and flat slab models, indicating that the presence of a rigid core in the building is a prepon-derant factor for global stability, due to its high rigidity.