Welded Box Sections for Two-Way Bending Square or rectangular · Q355B · Internal diaphragms · Full-penetration corners A box section is a closed rectangle made from four plates. Its virtue is symmetry: the section modulus is nearly the same about both axes, so it carries bending in any direction without a weak side. That is why it appears where the load direction is uncertain, where a beam spans two ways, or where a column takes moment and axial force at once. Where a Box