Statics: Bending

Profiles of girders

(a)                                             (b)                                              (c)
Fig. 4-5: A series of girders supporting windows at airport terminals

Large curtain or window walls are often seen at airport terminals. Fig. 4-5 shows three such walls. These large window walls are supported by a series of plane girders. The wind loads applied on the window walls are transmitted to the girders and through the girders to their supports.

The girders act like vertical simply supported "beams". The bending moments in the "beams" induced by wind loads are maxima at or close to their centres and minima at their ends. If the wind load is uniformly distributed, the diagrams of bending moments along the "beams" will be parabolas. Thus it is reasonable to design the girders to have their largest depths at their centres and their smallest depths at their ends with the profiles of the girders being parabolas. The girders shown in Fig. 4-5c reflect this and appear more elegant than those shown in Figs. 4-5a and 4-5b.