The Müller-Breslau principle provides a quick method and is of great
value for establishing the general shape of the influence line for building
frames. Once the influence-line shape is known, one can immediately
specify the location of the live loads so as to create the greatest influence
of the function (reaction, shear, or moment) in the frame. For example,
the shape of the influence line for the positive moment at the center I of
girder FG of the frame in Fig. 10–23a is shown by the dashed lines.Thus,
uniform loads would be placed only on girders AB, CD, and FG in order
to create the largest positive moment at I.With the frame loaded in this
manner, Fig. 10–23b, an indeterminate analysis of the frame could then
be performed to determine the critical moment at I.