MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 4

1.2.1 Loading Conditions
One of the considerations in the design of a project is the type of loading the
structure will be subjected to during its design life. The two basic types of
loads are static and dynamic. Each type affects the material differently, and
frequently the interactions between the load types are important. Civil engi-
neers encounter both when designing a structure.
Static loading implies a sustained loading of the structure over a period
of time. Generally, static loads are slowly applied such that no shock or vi-
bration is generated in the structure. Once applied, the static load may re-
main in place or be removed slowly. Loads that remain in place for an
extended period of time are called sustained (dead) loads. In civil engineer-
ing, much of the load the materials must carry is due to the weight of the
structure and equipment in the structure.
Loads that generate a shock or vibration in the structure are dynamic
loads. Dynamic loads can be classified as periodic, random, or transient, as
shown in Figure 1.1 (Richart et al. 1970). A periodic load, such as a har-
monic or sinusoidal load, repeats itself with time. For example, rotating
equipment in a building can produce a vibratory load. In a random load, the

Time

(a)

Time

(b)

Time

FIGURE 1.1 Types of
dynamic loads: (a) periodic,
(b) random, and (c) transient.

(c)