Pre-sizing and Optimal Cross-Section Selection of Steel Gravity-Load Columns in Multi-story Concentrically Braced Frames

Pre-sizing plays a key role in structural conceptual design, gaining renewed relevance in the current context of integration between Artificial Intelligence (AI) and computational tools, as it allows first-attempt dimensions to be defined in the early stages of the design process. Within the framework of the General Theory of Structural Conceptual Design developed by the authors, this paper focuses on gravity-load steel columns in multi-story buildings with concentrically braced frames. A critical review of the literature shows that the available rules for column pre-sizing are often highly aggregated and only partially account for the main parameters governing axial demand and buckling resistance. The study first discusses the selection of a target cross-section family among European hot-rolled steel sections, identifying the HEB series as a suitable reference for gravity-load columns. A parametric procedure is then developed to correlate the column size with the number of supported stories and the steel grade. The results are expressed through growth laws and reorganized into a semi-empirical tri-linear model. Finally, the equivalent number of stories is introduced to extend the results to systems with different grid dimensions and design loads.