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RE: Vehicle Barriers Rule (was RE: Guard Rail)

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David,

I know this is a continuation of the Guard Rail thread, but I tell from the
Guard Rail thread if you are considering the 17,000 lbs from the 120 mph or
some other load.  I don't recall IBC specifying this load.  Perhaps I missed
it.

I recently was reading the PCI Parking Structures Design manual (pg 2-21).
In there they state the guard rail load is an ultimate 10,000 lbs value.
If you are using wood and 10,000 lbs I would think you could make a valid
assumption of increased allowable stress.

Rich


-----Original Message-----
From: David Merrick, SE [mailto:MRKGP(--nospam--at)winfirst.com] 
Sent: Wednesday, July 30, 2008 2:29 PM
To: SEAINT
Subject: Vehicle Barriers Rule (was RE: Guard Rail)

Wind and Earthquake scoot over and make room for the crashing car event with
a higher probability and design load!

A barrier is required to catch the vehicle load 18" above the ground. Curbs
don't do that. Street curbs are not a vehicle barrier to protect a building
occupants and sidewalk pedestrians. 

The vehicle design force is higher than that of most shear walls for a small
2 story commercial wood building. It looks like the car threat is a big
deal. 

Impact loads are first increased (doubled) then added to the live load "L"
for the applicable load combinations. 

The vehicle barrier live load is not treated, in the code, as an impact
load. It appears to be only a live load. It is a live load that lasts less
than 10 minutes, not an impact, and is the Live Load "L" in the load
combinations.

Live load increase of allowable stress factor are only allowed for wood and
for soil capacities in table 1804.2.

Clearly the code does not treat the vehicle crash as an impact load but the
wood load category of "ten minutes" is not ruled out and so the wood allowed
stress increase of 1.6 might be allowed. 

IF the vehicle barrier load was WRONGLY considered as an impact load then
the load should then be doubled (as for impact loads of ASCE 7-05 sec 4.7)
Additionally: if the wood is pressure treated then the stress increase
factor is not 2.0 but limited to 1.6 (ASD)

I had asked about a factor of 1.33. This is for a pole (bollard)
cantilevered in soil IBC 1805.7.2.1 which references the soil table 1804.2.
The note "d" permits a 1/3 increase for ASD wind or seismic. I see that the
vehicle load is not wind or seismic and so not allowed for the vehicle
barrier. 

Is there a reference to allow a soil strength increase factor for a vehicle
barrier?

David Merrick, SE
Sacramento


References:

NDS 2005 table 2.3.2 note 2. (limits stress increase factor to 1.6 or less
for pressure treated)

ASCE 7-05  sec 4.4.3 "...Vehicle Barrier...6000 lb ... 1 ft 6 inch..." This
is part of Ch4 "Live Loads" but not part of 4.7 "Impact Loads". Vehicle
barrier loads are then not to be increased or doubled prior to being applied
to the load combinations.

ASCE 7-05  sec 4.7 States that all live loads ie vehicle barriers are
"assumed to include adequate allowance for ordinary impact conditions."

ASCE 7-05  sec 4.7 "Impact Loads"... increased by 100 percent..."


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