Page 29 - mechanics

Chapter – 5 Equilibrium of rigid body & Reactions of supports

diagram that includes all the external forces applied to the
body. A new type of external forces that we are now familiar
with is the reaction of support. We now illustrate some 2D
reactions which are divided into three categories as follow:
1) One force reactions. This category includes supports and
connections causing a reaction of one force in a known line of
action. Some of these supports, like cables and smooth surface,
have also a known sense of direction.
2) Two-components force reactions. This category includes
supports and connections causing a reaction of one force in an
unknown line of action. Thus, the reaction force is resolved
into two components in x and y directions.
3) Two-components force and a couple reactions. These
reactions are caused by fixed supports which involve three
unknowns, consisting usually of the two components of the
force and the couple moment.

Table 5.1 illustrates the reactions for some common 2D
supports. When the sense of an unknown force or couple
moment is not known it is arbitrarily assumed. If the result sign
is negative, the reaction is directed in the opposite direction.

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