What type of columns requires a minimum of four thickness measurements?

Tube (HSS) and pipe columns require a minimum of four thickness measurements due to their cylindrical shape and manufacturing processes. Unlike square or rectangular columns that have flat surfaces making it easier to take single measurements at key points, cylindrical columns can have variations in thickness due to fabrication inconsistencies or changes in the material composition. Taking multiple measurements at different points around the circumference ensures that any discrepancies are identified and accounted for, which is crucial for structural integrity and compliance with design specifications. This thorough approach helps ensure the columns perform as intended under load, as uneven wall thickness can lead to weaknesses or failure.