Portal Frames ~ these can be defined as two dimensional rigid
frames which have the basic characteristic of a rigid joint between
the column and the beam. The main objective of this form of design
is to reduce the bending moment in the beam thus allowing the
frame to act as one structural unit. The transfer of stresses from
the beam to the column can result in a rotational movement at
the foundation which can be overcome by the introduction of a pin
or hinge joint. The pin or hinge will allow free rotation to take
place at the point of fixity whilst transmitting both load and shear
from one member to another. In practice a true `pivot' is not
always required but there must be enough movement to ensure
that the rigidity at the point of connection is low enough to
overcome the tendency of rotational movement.
Portal Frames