Civil Engineering Reference
In-Depth Information
CONTINUUM STRUCTURES
Examples of these are folded plate roofs, shells, floor slabs, etc. An arch dam is a
three-dimensional continuum structure as are domed roofs, aircraft fuselages and
wings. Generally, continuum structures require computer-based methods of analysis.
1.4 S
UPPORT
S
YSTEMS
The loads applied to a structure are transferred to its foundations by its supports.
In practice supports may be rather complicated in which case they are simplified, or
idealized
, into a form that is much easier to analyse. For example, the support shown
in Fig. 1.11(a) allows the beam to rotate but prevents translation both horizontally and
vertically. For the purpose of analysis it is represented by the idealized form shown in
Fig. 1.11(b); this type of support is called a
pinned support.
A beam that is supported at one end by a pinned support would not necessarily be
supported in the sameway at the other. One support of this type is sufficient tomaintain
the horizontal equilibrium of a beam and it may be advantageous to allow horizontal
movement of the other end so that, for example, expansion and contraction caused
by temperature variations do not cause additional stresses. Such a support may take
the form of a composite steel and rubber bearing as shown in Fig. 1.12(a) or consist
of a roller sandwiched between steel plates. In an idealized form, this type of support
is represented as shown in Fig. 1.12(b) and is called a
roller support
. It is assumed
that such a support allows horizontal movement and rotation but prevents movement
vertically, up or down.
It is worth noting that a horizontal beam on two pinned supports would be statically
indeterminate for other than purely vertical loads since, as we shall see in Section 2.5,
Beam
Support
Pin or
hinge
Bolt
Foundation
F
IGURE
1.11
Idealization of a
pinned support
(a)
(b)
