Civil Engineering Reference
In-Depth Information
force
(4.8)
where
V
[kN/m] is the vertical load on the element,
h
[m] is the storey height and
ยต
[m]
is the misalignment.
The value of the total horizontal force due to misalignment depends on the number
of elements on one floor level
(n
h
)
and the number of elements above each other, i.e.
the number of storeys
(n)
. The value of the resulting total horizontal load is not
proportional to the number of vertical elements, since misalignment can occur in both
directions and some of the resulting horizontal forces may cancel each other out. This
can be approximately taken into account by introducing the probability factor 0.5
(n
h
n)
0.5
,
which leads to the formula for the total horizontal force as
(4.9)
This horizontal force represents the uniformly distributed horizontal load
p
m
[kN/m
2
]:
(4.10)
The vertical load
V
[kN/m] in the above formula is the average vertical load of the
vertical load bearing elements on a floor level.
4.1.4
Comparisons
The three types of horizontal load are quite different in nature. The magnitude of the
wind load is in direct proportion to the size of the building and, for cross-wall system
buildings, this leads to quite different wind loads in the two directions that are normally
considered for the structural analysis since the wider the building, the greater the wind
load (
Fig. 4.2/a
). Accidentally, this may go in parallel with a stronger bracing system
since a wider building normally has more bracing elements.
The situation is different with the seismic load. Its magnitude is primarily determined
by which seismic zone the building is in and the value is proportional to the mass of the
building. It follows that the seismic load does not depend on the size of the area of the
facade and it is of similar magnitude in every direction [cf. formula (4.5)] (
Fig. 4.2/b
)
.
This fact should be borne in mind in seismic design when in many cases an 'ordinary'
