Rice Lake Z6 Single-Ended Beam, SS Welded-seal, IP67, OIML C3 - Manual (Page 52)

48 Load Cell and Weigh Module Handbook
Figure 22-3.
Because of the many variables in vessel design and site
conditions, it is impossible to deal comprehensively with the
calculation of wind and seismic forces in this text. However,
the following subsections deal with these forces in general
terms and point out the information necessary for a complete
analysis. Refer to the Uniform Building Code (UBC) for further
details.
While the effects of both wind and seismic forces should be
considered, it is acceptable to consider these forces in
isolation.
22.2 Wind Forces
Consideration must be given to the effects of wind loading
when a weigh vessel is installed outdoors. This is particularly
important for tall slender vessels, vessels installed in exposed
locations (for example, facing a large body of water), or those
installed in a high wind-speed location. In analyzing the effects
of wind loading, it must be assumed that the wind may blow
at a vessel in any horizontal direction.
Figure 22-4 illustrates the effect of wind blowing at a vertical
cylindrical vessel. Note that not only is there a force exerted
against the windward side of the vessel, but there is also a
suction force on the leeward side. These forces are additive,
and tend to tip the vessel in the direction of the wind. At right
angles to the wind direction are suction forces pulling on each
side due to the increased speed of the wind at these points.
Since these are equal and opposite in direction, they have no
net effect on the stability of the vessel.
To perform a complete wind force analysis, the following
information is necessary:
• Vessel: The vessel’s dead and live weights, number
of supports, and overall dimensions such as height,
length of legs, diameter, etc.
• Minimum basic wind speed: This may be taken from
F i g u r e 2 2 - 5 , w h i c h i s a m a p o f t h e U S A
superimposed with wind speed contours. This map
is based on a 50-year mean recurrence interval
w h i c h h a s t r a d i t i o n a l l y b e e n a c c e p t e d a s a
reasonable risk. If local records indicate higher
50-year wind speeds, then the higher values should
be used. This map does not consider the effects of
tornadoes.
• Exposure: The exposure conditions at the site must
be known. Built up or rough terrain can cause a
substantial reduction in wind speed. The United
Building Code (UBC) defines 3 exposure categories:
Exposure B: has terrain with buildings, forest or
surface irregularities 20 feet or more in height
covering at least 20% of the area extending one
mile or more from the site.
Exposure C: has terrain which is flat and generally
open, extending one half mile or more from the site
in any full quadrant.
Exposure D: represents the most severe exposure in
areas with basic wind speeds of 80 mph or greater
and has terrain which is flat and unobstructed facing
large bodies of water over one mile or more in width
relative to any quadrant of the vessel site. Exposure
D extends inland from the shoreline 1/4 mile or 10
times the vessel height, whichever is greater.
• Importance Factor: An importance factor of 1.15 is
used for essential facilities which must be safe and
usable for emergency purposes after a windstorm in
order to preserve the health and safety of the general
public. Such facilities include medical facilities having
surgery or emergency treatment areas, fire and
police stations. A factor of 1.0 is used for all other
facilities.
With this information, the wind forces can be calculated in
accordance with methods described in the UBC. This
information may be used to verify the stability of the vessel using
standard mounts, or to design additional restraints if deemed
necessary.
Figure 22-4.
Top view
of cylindrical vessel
.25D .35D
CG
.5D
= Diameter
= Center of Gravity
= 3 point support
= 4 point support
D
CG
Wind Direction