] [Thread] [Date] [Author]

[ad026(--nospam--at)hwcn.org (Paul Ransom)]

> From: "Schwan, Martin K." <SchwanMK(--nospam--at)ci.anchorage.ak.us>

> I have required guards to be designed for a 200 lb concentrated load applied
> in any direction along the top rail and a 50 lb load applied to the
> intermediate supports and openings.  This is consistent with section
> 1607.7.1.1 aand 1607.7.1.2 of the 2000 IBC.   The 1997 UBC table 16-B
> category 9 and footnotes 8 and 9 apply to guardrails (no mention of 200 lbs)
> and require 50, 20, or 25 lb depending on occupant load and or components.
> Category 11 and footnote 11 appy to handrail and you'll see the 200 lb
> loading requirement.  Our inspectors will apply the lean test to the cable
> rail systems...They take their 4" sphere and lean into the openings...if it
> pushes thru they'll tell you to tighten the turn buckle...hopefully you
> won't get one of our big inspectors.

In my opinion, the application of the 4" sphere test in combination with
the 200# force is inappropriate (consider the purpose for each), despite
the fact that it may be required as proper design by the authority. One
is a strength requirement and the other is a service requirement. In
neither case do the codes/standards specify the reflected condition
(e.g. deflection under 200# force or required force to create 4"
opening). However, reasonable efforts to force the 4" sphere through a
flexible barrier (e.g. wire rope) is, in my opinion, appropriate. A
defined force would ensure that all tests were made equally, maintenance
could be consistently qualified and one could design suitably.

I wouldn't be surprised if the sphere was initially considered as a
design guiding concept which was adopted as a simple physical field test
device with limited consideration of engineering principles.

So, the issue of implementation requirements by authorities should be
addressed, most suitably by added commentary to the codes/standards. Is
there a committee member reading this and taking notes?

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

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