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NCHRP report 350

NCHRP report 350

NCHRP report 350

(OP)
I am designing an extended curb that will anchor a test level 3 traffic rail per the NCHRP 350 spec and need an impact force.  I know how to calculate impact forces, but the report only designates weight, initial speed, and impact angle.  I need change in velocity (lateral) for the calculation.  The report does give limiting occupant speed and decel (g's) and I am thiking of using those.  Any thoughts or sugguestions?

RE: NCHRP report 350

Check the AASHTO specs for guardrails...it gives you what you're looking for.

RE: NCHRP report 350

Gerald,

AASHTO requires a design (unfactored) impact load of 400 kips for structures adjacent to a roadway that are not protected by an independent barrier.

Or you could assume a final velocity of zero and use F*deltaT = m*deltaV (impulse relation from high school physics). The smaller the deltaT, the higher the F.

Jeff
 

RE: NCHRP report 350

(OP)
Thanks for the input.  I havent found the reference in my google searches on AASHTO guard rail specs.  400 kips for a TL3 design seems very high.  The TL3 is a 2000kg pick-up traveling 100 km/hr with a 25 degree impact angle. For a complete stop, yes the loads are very high, but for a glancing blow, veloctiy change is much smaller, but what is it? The 12 m/sec occupant limitation yields 106 kips, which seems more reasonable.

RE: NCHRP report 350

Gerald01,

If I recall correctly, the 400 kips was for a tractor-trailer impact or a train impact.

But when the contract doesn't specify the requirements (as a recent letting project did), I bid it high to cover my butt. Didn't win the job, but I'm not eating the cost of missing it from the design-build item.

Jeff
 

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