Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 17 h 0.75 h Figure 3.9 Dummy member to model nominally rigid column base Note that the reaction at the pinned end of the dummy member will affect the reaction at the column base. This must be corrected by taking the base reaction equal to the axial force in the column, which equals the sum of the reactions at the base and the pinned end of the dummy member. 3.4.1 Pinned and rocker bases Where a true pin or rocker is used, as illustrated in Figure 3.10, the rotational stiffness is zero. The use of such bases is rarely justified in practice. Where they are adopted, careful consideration needs to be given to the transfer of shear into the foundation, and temporary stability of the column during erection. Figure 3.10 Examples of zero stiffness column bases 3.4.2 Nominally rigid column bases If a column is rigidly connected to a suitable foundation, the following recommendations should be adopted: Elastic global analysis: For Ultimate Limit State calculations the stiffness of the base can be taken as equal to the stiffness of the column. For Serviceability Limit State calculations the base can be treated as rigid to determine deflections under serviceability loads.