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Garage Cable Guardrails (was 200# Load on Cable Guardrail)
- To: seaint(--nospam--at)seaint.org
- Subject: Garage Cable Guardrails (was 200# Load on Cable Guardrail)
- From: "Jake Watson" <jwatson(--nospam--at)utahisp.com>
- Date: Fri, 25 Jul 2003 11:45:03 -0600
to another question. How many people still design parking garages with
cable guardrails? If so, how do you justify the impact loading?
There is a big difference between 200# and and the impact
Salt Lake City, UT
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.
haven't, but the interpretation by the City is correctly applied as far as
the 4" sphere test goes since it is a guardrail. We have seen the
requirement before and have usually opted to provide a midspan (i.e. between
the columns) vertical support to reduce the length over which the cable
spans vertically. This support is in no way able to take car impact
loads so the horizontal span remains the column clear spacing +/-. We
usually provide the support as the cables have a tendency to relax reducing
the preload and allowing larger deflections to become
That said, if your cables are at 4"oc then they are 3 1/2" clr.
If my math is correct, you need a 270lb load or so for a 1/2" deflection
assuming 20" wide columns at 15'oc and a total cable length of 120', a
4000lb preload and 270ksi uncoated PT strand. So you could make the argument
that they meet the test. Note that the elongation calc is sensitive to
preload and total cable length, i.e. less preload or more length reduces the
vertical load required to deflect the cable 1/2". You could also
do an empirical test on an existing structure if the City will buy into that
We have been asked by the city to provide a
letter stating that the cable guardrail system in a parking garage can
support a 200# load and still not allow a 4" sphere to pass through.
According to the UBC, the 200# load requirement is applicable to
"handrails" not "guardrails". Cable guardrail systems are fairly
common here in Texas. Typically, these cables are spaced at 4" on
center with a 4000# prestress force in the cable. The supports are
at 15'-0" on center. You cannot reasonably maintain a maximum clear
distance of 4" when a 200# load (placed anywhere) is
applied to the cable.
Has anyone else been asked to provide
such a letter?
All comments and suggestions are