In designing structural members, designers
should use whichever is larger of the following:
1. Loadings specified in the local or state
building code.
2. Probable maximum loads, based not only
on current site conditions and original usage of proposed building spaces but
also on possible future events.
Loads that are of uncertain magnitude and
that may be treated as statistical variables should be selected in accordance
with a specific probability that the chosen magnitudes will not be exceeded
during the life of the building or in accordance with the corresponding mean
recurrence interval.
The mean recurrence interval generally used
for ordinary permanent buildings is 50 years. The interval, however, may be set
at 25 years for structures with no occupants or offering negligible risk to
life, or at 100 years for permanent buildings with a high degree of sensitivity
to the loads and an unusually high degree of hazard to life and property in case
of failure.
In the absence of a local or state building
code, designers can be guided by loads specified in a national model building
code or by the following data:
Loads applied to structural members may
consist of the following, alone or in combination: dead, live, impact, earth
pressure, hydrostatic pressure, snow, ice, rain, wind, or earthquake loads;
constraining forces, such as those resulting from restriction of thermal,
shrinkage, or moisture-change movements; or forces caused by displacements or
deformations of members, such as those caused by creep, plastic flow,
differential settlement, or sideways (drift).
