ETL 1110-2-534
30 Sep 94
the railing. The maximum bending moment M in
Mapplied
P
h
Pf
the post will occur at its point of attachment to the
platform, at a distance h from the top railing. In
or as
continuous, multispan railing installations (most
common), the horizontal load applied to the top rail
Mapplied
P
(h
h1)
Pf
at any one post is distributed, in part, to the adjoin-
ing posts on either side. Therefore, in many
instances, the loading carried by each post is actu-
for a concentrated load with a reinforcing insert of
ally considerably less due to load sharing among
height h1 at the post base (refer to Figure A-1). If
adjacent posts. Load distribution is determined by
end posts differ from intermediate posts in strength,
stiffness of the rail relative to stiffness of the posts
the load-distribution pattern becomes indeterminate
and by the total number of spans in the run. For a
and end posts should then be designed to carry
straight run of railing, the load-proportion factor Pf
100 percent of the concentrated load. Intermediate
may be determined from the graph in Figure A-2,
posts may then be designed to the "center loaded"
based on the stiffness ratio R, which is determined
condition. For single span railings (i.e., only two
as:
end posts) or where the top rail is completely flexi-
ble (such as a cable), the posts are assumed to carry
kRail
the entire applied loading.
R
kPost
(3) Uniform rail loading is assumed to apply
over the full length of the railing. Therefore, no
where
load distribution occurs among posts. The load
carried by a single post is thus equal to the load per
ERail
IRail
unit length w multiplied by the post spacing, or
kRail
L
span. End posts carry only half as much rail load
but, for practical reasons, are generally made of the
same pipe size as that required for the intermediate
EPost
IPost
posts. The maximum applied moment for this load
kPost
case is thus:
h
Mapplied
w
l
h
and
k = stiffness
(4) For all loadings, the applied bending stress
fapplied is calculated as:
Mapplied
I = moment of inertia
fapplied
S
L = length
where S = section modules. Applied bending stress
The formula used in developing this graph assumes
can be compared to the allowable bending stress
that all posts are of identical material and section.
fallow as discussed in paragraph A-2c above. The
If one or both ends of the rail are free-standing, the
applied stress should always be less than the allow-
"end-loaded" condition must be assumed. If both
able stress.
ends of the run are braced laterally by a change in
direction or attachment to a firm structure, the "cen-
g. Rail analysis. A concentrated load applied
ter-loaded" proportion factor may be used. The
to a rail exerts its greatest bending moment when
stiffness ratio is plotted on the graph to obtain the
applied at mid-span. The moment is determined by
load proportion factor. This factor is then multi-
the load P, and the length of the span L, and is
plied by the total load to determine the applied
calculated as:
moment on a single post as:
A-5
Previous Page
