Buildings 

. 
Thus far we have discussed primarily how structures like beams,... 
columns, and bridges support downward acting loads applied in 
the same plane as the structure. That is, basically parallel
to the 
two dimensions of height and span. Buildings, however, can 
experience significant sideways, or lateral, loads also due to 
twodimensional loading 

winds blowing against the exposed walls, snowdrifts, earthquakes,
etc. This is in addition to 
vertical acting external and internal loads such as snow, and loads
borne by the floors above 
ground.
In the following section you will see how structural engineers stabilize
buildings, 
spaceframes, and towers to withstand forces in threedimensions. 
. 
Three
dimensional stability 
. 
Building
designs vary widely to serve many different purposes. In simplest
terms, a building 
can be
considered to be a threedimensional boxlike framework designed to
envelop an 
interior
space. Attached to this framework is a floor upon which rests the
people, animals, 
and
equipment being housed; a roof that shelters the interior from rain, snow,
and wind; 
and
walls that support the roof and supply shelter. The skeletal
framework is created by 
joining
beams and columns end to end at right angles to each other like the edges
of a cube. 
When the
sides of this box are viewed faceon the inherent instability of each of
the square 
shaped
faces is selfevident. Recall the previous discussion of stable
polygons. 
. 


Fig. 194  Instability of the 

square faces of a cube 

◄ 4 < 2 ( 4 )  3 

therefore unstable 

(visualization model) 




. 
There
are four basic ways to stabilize the structural members framing the faces
of a cube. 
. 




a) single cross brace 
b) double cross brace 
c) diaphragm 
d) rigid joints 
. 
Fig. 195  Four basic ways of stabilizing the faces of a cube
(visualization models) 

. 
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Page 117
 Building stability  Buildings 

