Capacidade resistente de vigas mistas de aço e concreto com aberturas de base elíptica submetidas a momento fletor negativo

Abstract

The use of steel beams with sequential web openings offers advantages such as weight reduction, greater compatibility with building services, and the ability to span longer distances. When combined with concrete slabs through shear connectors, these beams form composite elements with enhanced load-bearing capacity and improved performance against vibrations and deflections. However, under negative bending moments, such systems may be susceptible to a stability failure mode known as lateral-distortional buckling (LDB). This study investigates the structural behavior of steel–concrete composite beams with sequential elliptical web openings under negative bending. A finite element model was developed in Abaqus and validated against experimental results from Salah (2009) and Tong et al. (2014). A parametric study was conducted with 360 models, considering variations in elliptical opening geometry, unbraced length, steel I-section dimensions, and moment distribution. Additionally, the predictive accuracy of current design codes, namely ABNT NBR 8800:2024 and prEN 1994-1 1:2024, was evaluated for estimating the ultimate moment under LDB, even though these standards were not originally developed for beams with elliptical openings. Different approaches were adopted to determine the elastic critical moment (Mcr). The results indicated that the moment distribution significantly influences the ultimate capacity, with the uniform moment scenario being the most critical. Longer unbraced lengths increased susceptibility to LDB, while thicker flanges and webs improved lateral stability, despite localized plastification and web-post buckling. The use of Mcr values from linear buckling analysis improved the accuracy of ultimate moment predictions, especially when combined with the specific reduction factor from EN 1993-1-1:2022. Although some non-conservative results were observed, this approach outperformed other methods. Among the design codes, ABNT NBR 8800:2024 showed better agreement with numerical predictions than prEN 1994-1-1:2024 when using the general-case formulation.