ABSTRACT
The maximum bending moment in a pitched portal frame subject to a vertical uniformly distributed load will still nearly always occur at the junction between the column and the beam, more accurately described in this case as a sloping rafter. In most pitched portal frames encountered in practice, the maximum positive, or sagging, moment at the two positions near to the central hinge will be much less than the maximum negative moment at the column to rafter junction. One of the most subtle relationships between the principle of the three-hinged portal frame and the quality of an architectural space occurs in the structure of Wright's Administration Building of the Johnson Wax Corporation in Racine, Wisconsin, USA, completed in 1939. Buildings in which portal frames are openly expressed usually convey a sense of structural harmony as well as of spatial order. Different structural forms may at first sight be perceived as expressions of separate, unconnected modes of physical behaviour.
