Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 57 11.3 Bases, base plates and foundations 11.3.1 General The following terminology for the components at the foundation is used in this document:  Base - the combined arrangement of base plate, holding down bolts, and concrete foundation. The terms nominally pinned and nominally rigid are usually applied to the performance of the base, in relation to its stiffness.  Base plate - the steel plate at the base of the column, connected to the column by fillet welds.  Holding down bolts - bolts through the base plate that are anchored into the concrete foundation.  Foundation - the concrete footing required to resist compression, uplift, and, where necessary, over-turning moments.  Anchor plates - plates or angles used to anchor the holding down bolts into the foundation. They should be of such a size as to provide an adequate factor of safety against bearing failure of the concrete. In the majority of cases, a nominally pinned base is provided, because of the difficulty and expense of providing a nominally rigid base which is moment resisting. Not only is the steel base connection significantly more expensive, the foundation must also resist the moment, which increases costs significantly. Where crane girders are supported by the column, moment resisting bases may be required to reduce deflections to acceptable limits. Typical base plate/foundation details are shown in Figure 11.3 to Figure 11.5. In a nominally pinned base for larger columns, the bolts can be located entirely within the column profile (Figure 11.3(a)). For smaller columns (less than approximately 400 mm), the base plate is made larger so that the bolts can be moved outside the flanges (Figure 11.3(b)). A nominally rigid, moment resisting base is achieved by providing a bigger lever arm for the bolts and a stiffer base plate by increasing the plate thickness as shown in Figure 11.4. Additional gusset plates may be required for heavy moment connections, as illustrated in Figure 11.5.