the railing. The maximum bending moment *M *in

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

(*h*

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 *h*1 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 *P*f

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

the entire applied loading.

(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

unit length *w *multiplied by the post spacing, or

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

posts. The maximum applied moment for this load

case is thus:

and

(4) For all loadings, the applied bending stress

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.

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-

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

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