The function of the crane girders is to support the rails on which the
traveling cranes move. These are subjected to vertical loads from crane,
horizontal lateral loads due to surge of the crane, that is, the effect of
acceleration and braking of the loaded crab and swinging of the suspended load
in the transverse direction, and longitudinal force due to acceleration and braking
of the crane as a whole. In addition to the weight of the crane, impact and
horizontal surge must be considered. According to IS: 875, the values given in
Table 13-9 may be taken for the design of crane gantry girders and columns.
Both the horizontal forces, lateral and longitudinal, are assumed not to act
together with the vertical loads simultaneously. Only one of them is to be
considered acting with the vertical load at a time. Vertical load, of course,
includes the additional load due to impact.
The crane girder spans from column to column, usually having no lateral
support at intermediate points excepting when a walkway is formed at the top
level of the girder which restrains the girder from lateral bending. Thus under
normal circumstances, the crane girder must be designed as laterally
unsupported beam carrying vertical and horizontal load at the level of the top
flange. Apparently a girder with heavier and wider compression flange is
required. Figure 2.27 shows some typical sections adopted for crane girders