ETL 1110-2-534
30 Sep 94
tolerances within which the section sizes can devi-
result, this is likely the most applicable loading for
ate from the nominal dimension. While these
most USACE facilities where large groups of peo-
allowable dimension variations may appear small
ple (such as guided tours) are generally not
and insignificant, they could conceivably affect the
expected. Other widely accepted building codes are
overall section properties, and thus the available
directed more toward the restraint of large groups
strength of an already marginal structural member.
of people at one time. They specify uniform load-
ings over the length of the rails, which are consid-
(4) Also note that since the analysis is being
ered to represent the force exerted by tightly
conducted on railing which may have been in ser-
grouped persons leaning on or pressed against the
vice for years, its possible deterioration must be
railing. Such loading requirements range from
considered. This can only be determined through
292 to 730 N/m (20 to 50 lb/ft), usually applied
careful field reconnaissance and measurements.
horizontally to the top rail. Some codes require
The railing can deteriorate from both the outside
also that railing in certain locations be designed to
where it is readily visible, or from the inside where
carry loads as high as 100 lb/ft applied vertically
it is not readily visible. Deteriorated railing can be
downward on the rails.
accounted for in the structural analysis by appropri-
ately reducing the available cross-section of the
(4) Because EM 385-1-1 governs all of the
member(s) or by reducing the allowable stresses.
Corps' safety requirements, the 890-N (200-lb) con-
centrated load criterion is the minimum that railings
(5) Reinforcing inserts are sometimes used at
on USACE facilities must meet. However, based
the base of the guardrail posts to shorten the length
on the above discussion and knowledge of specific
of the posts, thereby increasing the allowable loads
railing demands, the USACE engineer may deter-
on the railing. The presence of these items must be
mine that other loading criteria are more applicable
established for an analysis since it will significantly
to a particular situation. However, the engineer
affect the post's available load capacity.
must always meet the EM criteria as a minimum.
e.
Loadings.
f.
Post analysis.
(1) The following discussion and calculations
(1) The most critical loads for guardrails are
are applicable to free-standing, straight run railings
those which are applied horizontally since these
with uniform post spacing. Lateral bracing, curv-
produce the maximum bending moment on posts.
ing, or attachment to other structures may reduce
The maximum bending moment on a rail member,
bending stresses substantially, which may be taken
under a concentrated load, results when the load is
into account. A typical guardrail system is depicted
applied at the center of the rail span. Posts act as
in Figure A-1.
columns in resisting vertical loading on rails, and as
vertical cantilever beams in resisting horizontal
loading on either the rails or the posts themselves.
Usually it is the bending moment due to the canti-
lever beam action under horizontal loading that
produces the highest stress.
(2) EM-385-1-1 specifies that "the anchoring
of posts and framing of members for all guardrails
shall be of such construction that the completed
structure shall withstand a load of at least 890 N
(200 lb) applied in any direction at any point on the
toprail without failure and with a minimum of
deflection."
Figure A-1. Typical guardrail system
(3) This concentrated loading is the same as
that specified by the Federal Occupational Safety
(2) Concentrated rail loading P, as specified by
and Health Administration (OSHA) for railings in
the USACE, is assumed applied at any point along
places or areas where persons are employed. As a
A-4
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