
37Structural Distress
Consider the following free body diagram of the static loading on the parapet wall
(Figure 2.23).
Summing forces we obtain
F
L
x
y
0
0
:
:
(2.73)
When the alumabeam falls and the coupling moment is produced, the static force F1
must remain the same and produce the failure of the parapet wall. So summing moments
about N,
ML FF
LF
F
N
=−++ =
=
0456531140
38 5170
226
21
2
2
:( .) () ()
(.)()
.
LL
(2.74)
e velocity at impact can be calculated through basic equations for the geometry of
Figure 2.24:
dgtt
d
g
v
d
t
=⇒==
== =
1
2
2
022
077
022
35
2
.
.
.
.
s
ft
s
ft
s
(2.75)
where
d is the distance to impact
t is the time to impact
v is the velocity at impact