Column analysis is an integral part of finding the gravity and lateral load capacity of existing steel-frame buildings, and so partly determines the feasibility of alteration and reuse. Since 1923, the American Institute for Steel Construction has published a national steel specification for buildings in the United States; before then, calculated column capacities varied based on local building codes. Early column code formulas provided axial strength based only on the section properties and the unbraced length. Later formulas included the effect of combined axial load and moment through the use of interaction formulas, and the effect of column-end fixity and sidesway through the use of an effective-length factor, K. Columns designed before modern codes may differ substantially from modern designs. For a given existing column, the variable parameters are the unbraced length, the end-fixity conditions, and the applied axial load and moment. By varying these parameters and comparing results for different codes, it is possible to determine when the old designs are unconservative relative to current code, allowing for easier analysis of existing buildings.