|
is
hung are called spandrels. The web of a spandrel girder is |
 |
|
often wider than that of an interior girder to help it resist
bending |
|
despite the fact that its tributary area may be less. It has
to bear |
|
the weight of the curtain wall cladding which is often comprised |
|
of
windows and thin panels that cannot tolerate bending induced |
|
stresses. Also spandrels are subjected to lateral forces such
as |
|
wind. Perimeter columns often have larger cross-sections than |
|
interior columns
for the same reasons. Since the skeletal frame |
click image to enlarge |
|
is carrying the
entire load of the building, the columns must be |
Fig. 220 Exterior cladding |
|
spaced relatively
close together. |
(scale visualization model) |
|
|
. |
|
Long span
construction |
|
. |
|
Structures like aircraft hangers, coliseums, or atriums, that require
greater open areas |
|
between
columnar supports than standard wood or steel
structural members can span, are |
|
built
with long span construction technology. Many designs have been used
successfully |
|
depending on the area to be spanned, the anticipated roof loads, occupancy
use, etc. |
|
This lesson
will cover only bar joists, trusses, space frames, and folded shell
structures. |
|
. |
|
Bar joists |
 |
|
|
|
Bar joists are simply long floor or ceiling truss joists. They |
|
usually span from girder to girder, which themselves are |
|
supported by widely spaced columns or bearing walls.
|
|
Prefabricated bar joists are available that are designed for |
|
specific load requirements. |
Fig. 221 - Bar joist peaked roof |
|
|
. |
|
|
Trusses |
|
 |
|
|
Standard truss designs, like those shown previously for |
|
bridges, can also be used to provide a clear span inside |
|
buildings since they require no intermediate supports. A |
|
triangulated truss has a higher H/S ratio than a truss joist. |
|
Fig. 222 - Hanger with |
Also, it is fabricated from structural steel shapes like T- |
|
long span truss roof |
shapes and angles rather than small
diameter rods. The |
|
|
design of the truss depends on the
anticipated loads, the |
|
|
amount
of open floor space required, and the overall shape of the building.
If the truss |
|
must
bear a downward acting roof load, a design that is efficient in supporting
a load |
|
applied
to the top chord, like the Howe, Pratt, and Warren deck truss designs, is
standard. |
|
. |
|
Back
to Knowhere |
|
 |
Page 131
- Building stability - Long-span construction |
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|
