Steel Buildings in Europe

Part 2: Concept Design 2 - 25 3.4 Preliminary Design 3.4.1 Main frames Although efficient portal frame analysis and design will use bespoke software, preliminary design is simple. In most circumstances, a reasonable estimate of the maximum bending moments will be obtained by considering only the vertical loads. Combinations of actions including wind actions must be validated in the final design, and may be important for preliminary design if the wind actions are onerous (e.g. near the sea, or if the portal frame is tall). Based on the vertical load alone, charts that provide initial sizes are given in Section 8. As an alternative to the sizes given in Section 8, the bending moment at the eaves and apex can be calculated based on an elastic analysis. L S M I I I I f h M W WL 32 E C R R C 2 A / m Figure 3.11 Details of a pinned base portal frame For the pinned base frame shown in Figure 3.11, the bending moment at the eaves, M E and at the apex M A can be calculated as follows:   N M wL m 16 3 5 2 E   and E 2 A 8 M wL m M    where: N = B + mC C = 1 + 2 m B = 2( k + 1) + m m = 1 +   = h f s h I k I C R 