The design of tensile, compression, and bending members was separately treated in Chapters 9, 10, and 11, respectively. In actual structures, the axial and the bending forces generally act together, specifically the compression due to gravity loads and the bending due to lateral loads. An interaction formula is the simplest way for such cases wherein the sum of the ratios of factored design load to limiting axial strength and factored design moment to limiting moment strength should not exceed 1.