Civil Engineering Reference
In-Depth Information
P
L
h
p
h
e
(
h
e
-
h
p
)/2
M
e
M
e
H
e
H
e
b
t
R
e
R
e
FIGURE 5.28
End post forces from through truss portal action.
shown in Figure 5.28. In this case, the vertical load,
R
e
, and horizontal shear,
H
e
, are
P
L
((h
e
+
h
p
)/
2
)
R
e
=
,
(5.38)
b
t
P
L
2
,
H
e
=
(5.39)
and the end post bending moment,
M
e
, due to the force,
P
L
, is estimated as
P
L
((h
e
−
h
p
)/
2
)
M
e
=
.
(5.40)
2
The end portal bracing member forces can then be determined from free body equi-
librium equations for one leg of the portal. The end portal bracing member forces for
various portal configurations are shown in Examples 5.11 through 5.14. Example 5.15
outlines the analysis of a typical railway through truss span end portal.
Example 5.11
The axial forces in lattice portal frame members (
Figure E5.11)
are
⎛
⎝
⎞
⎠
h
p
+
P
L
(h
e
+
h
p
)/
2
b
p
±
P
A
=
,
2
b
t
h
p
3
h
e
+
4
h
p
,
−
P
L
8
h
p
h
p
P
B
=
+
2
h
e
+
.
h
p
+
3
P
L
8
h
p
P
C
=
2
