Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 7 Most load combinations will be asymmetric because they include either equivalent horizontal forces (EHF; see Section 3.2) or wind loads. A typical loading diagram and bending moment diagram are shown in Figure 3.2. Both the wind and the EHF can act in either direction, meaning the hinge positions on each side of the frame must be restrained. 1 1 1 Position of plastic hinges Figure 3.2 Bending moment diagram resulting from plastic analysis of a symmetrical portal frame under asymmetric loading A typical bending moment diagram resulting from an elastic analysis of a frame with pinned bases is shown in Figure 3.3. In this case, the maximum moment (at the eaves) is higher than that calculated from a plastic analysis. Both the column and haunch have to be designed for these larger bending moments. The haunch may be lengthened to around 15% of the span, to accommodate the higher bending moment. Figure 3.3 Bending moment diagram resulting from the elastic analysis of a symmetrical portal frame under symmetrical loading (haunch at 10% of span is denoted by solid line; that for 15% of span is denoted by a dotted line)