Civil Engineering Reference
In-Depth Information
there would be two vertical and two horizontal components of support reaction but
only three independent equations of statical equilibrium.
In some instances beams are supported in such a way that both translation and rotation
are prevented. In Fig. 1.13(a) the steel I-beam is connected through brackets to the
flanges of a steel column and therefore cannot rotate or move in any direction; the
idealized form of this support is shown in Fig. 1.13(b) and is called a
fixed, built-in
or
encastré support
. A beam that is supported by a pinned support and a roller support as
shown in Fig. 1.14(a) is called a
simply supported beam
; note that the supports will not
necessarily be positioned at the ends of a beam. A beam supported by combinations
of more than two pinned and roller supports (Fig. 1.14(b)) is known as a
continuous
beam
. A beam that is built-in at one end and free at the other (Fig. 1.15(a)) is a
can-
tilever beam
while a beam that is built-in at both ends (Fig. 1.15(b)) is a
fixed, built-in
or
encastré
beam.
When loads are applied to a structure, reactions are produced in the supports and in
many structural analysis problems the first step is to calculate their values. It is impor-
tant, therefore, to identify correctly the type of reaction associated with a particular
Beam
Steel
Rubber
Foundation
F
IGURE
1.12
Idealization of a
sliding or roller
support
(a)
(b)
Beam
Column
F
IGURE
1.13
Idealization of a
built-in support
Bracket
(a)
(b)
